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Spectre Circuit Simulator User Guide

1. Fast models model fast 1x1 mos3 type n vto temp gt 27 C 0 8 0 77 ET wee EtG model fast_1x3 mos3 type n vto temp gt 27_C 0 9 0 78 bit we eee model fast 3x1 mos3 type n vto temp gt 27 C 0 95 05779 FL z etc model fast 3x3 mos3 type n vto temp gt 27 C 0 98 0 81 etc Typical models model typ 1x1 mos3 type n vto temp gt 27 C 0 90 0 75 MI irete model typ_1x3 mos3 type n vto temp gt 27_C 0 91 0 73 LA oe eEG model typ 3x1 mos3 type n vto temp gt 27 C 0 97 ORFE I4 sueta model typ 3x3 mos3 type n vto temp gt 27 C 0 99 0 84 LJ uw EEC Slow models model slow_1x1 mos3 type n vto temp gt 27_C 0 92 0 76 etc model slow_1x3 mos3 type n vto temp gt 27_C 0 93 0 74 etc model slow 3xl mos3 type n Ovto temp gt 27_C 0 98 0 78 J etc model slow 3x3 mos3 type n vto temp 27 C 0 98 Dag Ju etc The following file select models scs uses the structural if statement to select models based on parameters 1 and w Note that for MOS devices this could also be achieved by using auto model selection see spectre h mos3 but this example illustrates model binning and model selection based on the structural i statement which can be used to bin based on any combination of parameters not necessarily predefined device geometry models and for any device type that is not limited to M
2. L s 189 WAVE HO SL EO EIEN oos ars fossero ora rd Mea tai De Oe BP Hen DP reor da Oe CC RB 192 Specifying the Parameters You Want to Save lllllllslss 193 Specifying the Output Destination llle 194 Examples of the info Statement 22 45 22x 34 Su SER EREDALEN E EINER 194 Printing the Node Capacitance Table 0 0 cc eee eee 194 The options Statement 3 5 ue E t Aiea nants qoe d eters cece a tang Tce deo edet 198 options Statement Form at o4 trece ocd tae eh Esc ve nena ae E ees S 199 options Statement Examples vod eee ek eg ea lu here enka 199 Setting ToleraNC sS oor pts Ted nh op Si ae Ah oes Sawa Bb Rad Nese Woda he acs aider 199 Additional options Statement Settings You Might Need to Adjust 200 Ihe paramser Siaiement 5o utu br LEUR LCEDCECRADEDE las ye aber ee oeesed 200 THE SAVE Statement e puts rir ve qa an ere ns Sob b bien S ne Ge aw SU de E Rob rS EUR 201 Saving Signals for Individual Nodes and Components 201 Saving Gloups Ol Signals 293599 Poe dita UR o ert cea ee eee eis 207 ThesetStatement o poudre tn EE FE od i Cra P Por Ro EAE OP CDL RR 210 Tie Spell Statement ose wre eerta A ERE Qo Sed erat ean fva d ptc ol CQ re 211 The statistics Statement uu deseo T bct eee eee S IEEE bea et 211 8 Specifying Output Options ssusususuuususuuseueesuuueuueue 212 Oigrals ds OLEDHE seve co di serae Sub a d PORE Gebr wr o E EPOR SETA nce he TOT
3. 224 Defining Output File Formats 0 2 00 cece 225 ACCESSING Output Files Sordexesueertteerubtqes dee ee E E E Etre Nc Eee tee Gal eed 225 How the Spectre Simulator Creates Names for Output Directories and Files 226 Filenames for SPICE Input Files alist rendir DRE Cae ee n baat ees 228 Specifying Your Own Names for Directories 0 00 228 9 Running a Simulation 00 0 229 Starting Simulations 25 5 05 2 Fb 49 n Do Bees pecu arie 36 900 4989 D 48 cba A aad deoa ad BaD be 229 Specifying Simulation Options sad mm RE Y Y RR Rx ae ele eed qeu Reg 229 Determining Whether a Simulation Was Successful 230 Ghe cklng similgtiolo elatis serere 5 7 dete ee ee SR EX a ieee wee tote dog heat es 230 Interrupting a Simulation e cox stoi Be nt rte ee a d coq eau o ve ARN E DE ERU 2 231 Recovering from Transient Analysis Terminations lessen 231 Creating Recovery Files from the Command Line 232 Setting Recovery File Specifications for a Single Analysis 233 Restarting a Transient Analysis llllllllllleeleeA 233 Controlling Command Line Defaults 0 ee 233 Examining the Spectre Simulator Defaults 0 cee eee 234 Setting Your Own Defaults o x dee we eRe at Ee o ROO RO ake Pa od Te ow dide 234 References for Additional Information about Specific Defaults 235 Ov
4. If you do not specify the step size the sweep is linear when the ratio of the stop to the start values is less than 10 and logarithmic when this ratio is 10 or greater If you specify sweep limits and a values array the points for both are merged and sorted Examples of Parameter Sweep Requests This sweep statement uses braces to bound the child analyses statements swp Sweep param temp values 50 0 50 100 125 oppoint dc oppoint logfile This statement specifies a linear sweep of frequencies from 0 to 0 3 MHz with 100 steps Sparams sp stop 0 3MHz lin 100 The previous statement could be written like this and achieve the same result Sparams sp center 0 15MHz span 0 3MHz lin 100 This statement specifies a logarithmic sweep of frequencies from 1 kHz through 1 GHz with 10 steps per decade cmLoopGain ac start 1k stop 1G dec 10 This statement is identical to the previous one except that the number of steps is set to 55 cmLoopGain ac start 1k stop 1G log 55 This statement specifies a linear sweep of temperatures from 0 to 50 degrees in 1 degree steps The frequency for the analysis is 1 kHz XferVsTemp xf start 0 stop 50 step 1 probe Rload param temp freq 1kHz July 2002 160 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses This statement uses a vector to specify sweep values for device Vcc The values specified for the sweep are 0 2 6 7 8 and 10 SwpVccDC dc dev Vcc values 0 2 6 7 8 10
5. In the following example a parameterized model is declared within an inline subcircuit for a bipolar transistor The model parameters are the emitter width emitter length emitter area and the temperature delta t rise of the device above nominal Ninety nine instances of a 4x4 transistor are then placed and one instance of a transistor with area 50 is placed Each transistor gets an appropriately scaled model declare a subcircuit which instantiates a transistor with a parameterized model The parameters ar mitter width and length inline subckt bjtmod c be s parameters le lu we 2u area le we trise 0 model modl bjt type npn bf 100 letwe 2 area le 12 is 1e 12 le we area 1e 12 bjtmod c b e s modl trise trise inline component ends bjtmod some instances of this subck ql 23 1 0 bjtmod le 4u we 4u trise defaults to zero q2 23 2 0 bjtmod le 4u we 4u trise 2 q3 23 3 0 bjtmod le 4u we 4u q99 2 3 99 0 bjtmod le 4u we 4u q100 2 3 100 0 bjtmod le lu area 50e 12 Since each device instance now gets its own unique model this approach lends itself to statistical modeling of on chip mismatch distributions in which each device is taken to be slightly different than all the others on the same chip The value of bf is the same for the first 99 transistors For more details see Monte Carlo Analysis on page 161 Inline Subcircuits Containing Only Inline model Statement
6. Runt description a The lowest level of the hierarchy in the Results Browser now contains the names of the waveforms you can display 2 To display a waveform click on its name in the Results Browser with the right mouse button July 2002 37 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre For example if you click on out the following display appears in the Waveform Window ka waveform Window Active 2 Window Zoom Axes Curves Markers Annotation Edit Tools Help o vq out result OscResp tran l l ical Sau 9 u time s mouse L awviMouseSingleSele M R xcamCameraRas July 2002 38 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre If you zoom in on the right side of the waveform Zoom Zoom In and adjust the X axis Axes X Axis you see the following waveform Window Active 2 Window Zoom Axes Curves Markers Annotation Edit Tools Help out result OscResp tran WM 1i ILI time s You can add a more meaningful title with the Annotation Title command I ii Extracting Zero Crossing Points To extract zero crossing points of a waveform using the calculator 1 Make certain that the Evaluate Buffer button in the calculator is disabled July 2002 39 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre 5 6
7. Use realistic device models Make sure that all component parameters are reasonable particularly nonlinear device model parameters Increase the value of gmin with the opt ions statement Loosen tolerances particularly absolute tolerances such as iabstol on the options statement July 2002 275 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting B Simplify the nonlinear component models Try to avoid regions in the model that might cause convergence problems m When you have a solution write it to a nodeset file using the write parameter When you run the simulation again read the solution back in using the readns parameter in the dc statement W Ifthisis not the first analysis the solution from the previous analysis might be an inadequate solution estimate because it differs too much from the solution for the current analysis If this is so set restart yes M f you have an estimate of the solution use nodeset statements or a nodeset file to set as many nodes as possible W f using nodesets or initial conditions causes convergence difficulties try increasing rforce With the options statement B f you are simulating a bipolar analog circuit make sure the region parameters on all transistors and diodes are set correctly W If the analysis fails at an extreme temperature but succeeds at room temperature try adding a DC analysis that sweeps temperature Start at roo
8. xno215 15 14 no2 xno216 116 15 no2 xno217 90 16 no2 Next couple of lines sets variables for vdd and vss parameters vdd S1 23 3 parameters vss S1 20 0 vdd I1 vdd gnd vsource dc vdd S1 vss Il vss gnd vsource dc vss S1 Next line initializes nodes within ring ic 2 20 4 20 6 20 8 20 10 20 include q35d4h5 modsp section tt Analysis tempOption options temp 25 tt tran tran step 0 010n stop 35n Ss alter altergroup include q35d4h5 modsp section ss parameters vdd S1 23 0 alterTempTo100 alter param temp value 100 ss tran tran step 0 010n stop 35n Ff alter altergroup include q35d4h5 modsp section ff parameters vdd S1 23 3 alterTempTo0 alter param temp value 0 Ff tran tran step 0 010n stop 35n Ring Oscillator Spectre Deck for Three Input NOR Ring with No Fanouts nor3_ring sp This example uses Spectre syntax Ring oscillator spectre deck for 3 Input NOR ring with no fanouts simulator lang spectre global 0 gnd vdd vss aliasGnd gnd 0 vsource type dc dc 0 Spectre options SetOptionl options iabstol 1 00n audit full rforce 1 temp 25 MyAcctl info what inst extremes yes MyAcct2 info what models extremes yes MyAcct3 info what input extremes yes MyAcct5 info what terminals extremes yes MyAcct6 info what oppoint extremes yes Next section is the subckt for no3 subckt no3 nga ml vdd a 7 vdd p 1 0 35u w 3 60u ad 2 63p pd 8 66u as 0 38p
9. July 2002 262 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Selecting Limits for Parameter Value Warning Messages You can accept Cadence default soft limits that determine when you receive warning messages about parameter values or you can enter your own limits You can also control which parameters the Spectre simulator checks This section gives you instructions for all Accepting Cadence Range Limits Defaults The most convenient option for deciding which warning messages you receive is to accept Cadence Range Limits Defaults The Cadence defaults are located in your install dir tools dfII etc spectre range lmts and you can examine them to see if they meet your needs You can enter Cadence defaults with the SPECTRE DEFAULTS environment variable in your shell initialization file such as profile or cshrc The entry in your shell initialization file looks like the following setenv SPECTRE DEFAULTS param HOME tools dfII etc Spectre range lmts With this entry in the shell initialization file the Spectre simulator reads parameter limits from your install dir tools dfII etc spectre range lmts You can override a SPECTRE_DEFAULTS setting with the param option of the spectre command Specifying param as a command line argument overrides param in SPECTRE DEFAULTS and tells the Spectre simulator to read range limits fr
10. Monte Carlo Analysis The montecarlo analysis is a swept analysis with associated child analyses similar to the sweep analysis see spectre h sweep The Monte Carlo analysis refers to statistics blocks where statistical distributions and correlations of netlist parameters are specified Detailed information on statistics blocks is given in Specifying Parameter Distributions Usin Statistics Blocks on page 170 For each iteration of the Monte Carlo analysis new pseudorandom values are generated for the specified netlist parameters according to their specified distributions and the list of child analyses are then executed The Cadence design environment Monte Carlo option allows for scalar measurements to be linked with the Monte Carlo analysis Calculator expressions are specified that can be used to measure circuit output or performance values such as the slew rate of an operational amplifier During a Monte Carlo analysis these measurement statement results vary as the netlist parameters vary for each Monte Carlo iteration and are stored in a scalar data file for postprocessing By varying netlist parameters and evaluating these measurement statements the Monte Carlo analysis becomes a tool that allows you to examine and predict circuit performance variations that affect yield The statistics blocks allow you to specify batch to batch process and per instance mismatch variations for netlist parameters These statistically
11. The following table describes the circuit parameters you can change with the alter statement Parameter Description temp Ambient temperature tnom Default measurement temperature for component parameters scalem Component model scaling factor scale Component instance scaling factor Note If you change temp or t nom using an alter statement all expressions with temp or tnom are reevaluated The check Statement You can perform a check analysis at any point in a simulation to be sure that the values of component parameters are reasonable You can perform checks on input output or operating point parameters The Spectre simulator checks parameter values against parameter soft limits To use the check analysis you must also enter the param command line argument with the spect re command to specify a file that contains the soft limits The following example illustrates the syntax of the check statement It tells the Spectre simulator to check the parameter values for instance statements ParamChk check what inst n ParamChk is your unique name for this check statement n The keyword check is the component keyword for the statement n The what parameter tells the Spectre simulator which parameters to check The what parameter of the check statement gives you the following options Option Action none Disables parameter checking models Checks input parameters for all models only inst Checks input parameters for
12. statement There are additional i f statements in the statement1 and lt statement 2 gt fields if rseries 0 cl a b capacitor c c if gparallel 0 gpl a b resistor r 1 gparallel else r2 a x resistor r rseries c2 x b capacitor c c if gparallel 0 gp2 x b resistor r 1 gparallel In this example the Spectre simulator puts different instance statements into the simulation depending on the values of two parameters rseries and gparallel WB Ifbothrseries andgparallel are zero the Spectre simulator includes the instance statement for capacitor c 1 lf rseries is zero and gparallel is nonzero the Spectre simulator includes the instance statements for capacitor c1 and resistor gp1 B Ifrseries is nonzero and gparallel is zero the Spectre simulator includes the instance statements for resistor r2 and capacitor c2 July 2002 106 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features B Ifneither rseries nor gparallel is zero the Spectre simulator includes the instance statements for resistor r2 capacitor c2 and resistor gp2 Rules to Remember When you use the if statement B Ifthe statementi1 Or statement2 fields contain multiple statements place these fields within braces B Endthe statement1 and statement2 fields with newlines m Use a continuation character if you want to place a newline between the if and condition st
13. 0 665776 E 0 334223 0 s12 real imag s11 real imag 89151e 05 00010347 78302e 05 00020694 67453e 05 00031041 56604e 05 00041388 45756e 05 00051735 000113491 00062082 000132406 00072429 000151321 000827759 000170237 000931229 000189152 0010347 119 gendatal CO GX C OX G2 CO e CD o E OO COLoCO CY CO Oi OO CO S a a a S iE during analysis swp 22045e 16 334225 665775 334225 665775 334224 665775 334224 665775 334224 665775 334224 665776 334224 665776 334224 665776 334223 665776 334223 665776 00010347 89151e 05 00020694 78302e 05 00031041 67453e 05 00041388 56604e 05 00051735 45756e 05 0 00062082 Product Version 5 0 000113491 00072429 000132406 000827759 000151321 000931229 000170237 0010347 000189152 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features For polar formats the format is the same except that the appropriate polar format indication replaces the real imag indication of the previous example reference resistance port2 50 port1 50 format freq s11 mag rad s21 mag rad s12 mag rad s22 mag rad 0 0 1 0 mag s11 1 and phase s11 20 radians 0 0 mag s21 0 and phase s11 0 radians 0 0 mag s12 20 and phase s11 20 radians 1 0 mag s22 1 and phase s11 20 radians Reading the S Parameter Fi
14. 964230e 01 2 123240e 01 000000e 01 0 000000e 700 000000e 01 0 000000e 00 245710e 01 2 063540e 01 600000e 01 0 000000e 00 500000e 09 0 000000eE 00 284460e 01 6 244130e 01 449590e 02 7 277860e 02 1 84507e 00 1 226090e 00 w uaua NAOUN 7 709390e 01 2 551700e 01 5 000000e 01 0 000000e 00 5 000000e 01 0 000000e 00 7 982370e 01 2 450360e 01 6 325000e 01 0 000000e 00 7 199977e 01 0 000000e 00 When reading a file for HPMNS format the translator ignores anything before the line beginning with Variables Specify the S parameter variable in the variable definition section as described in the previous example which is between the Variables line and Values line Data entries must comply with the formats specified Use a comma to separate the real and imaginary numbers The index number is the first number of each frequency entry line starting from 0 and increasing monotonically The translator reads the frequency value from the second entry on each index line the frequency value must be given explicitly without a hidden scale factor The translator reads the S parameter data from the first line to the K 1 line after each index line for a k port file The impedance values of the ports pick up the data from the K 2 line to the K K 2 line and are read only at the first frequency point Each port impedance can be treated only as frequency independent The translator ignores the data between the K K 2 line and the next
15. FOURIER statement but is more accurate The Spectre simulator s Fourier analyzer has greater resolution for measuring small distortion products on a large sinusoidal signal Resolution is normally greater than 120 dB Furthermore the Spectre simulator s Fourier analyzer is not subject to aliasing a common error in Fourier analysis As a result the Spectre simulator can accurately compute the Fourier coefficients of highly discontinuous waveforms mH Better control of numerical error Many algorithms in the Spectre circuit simulator are superior to their SPICE counterparts in avoiding known sources of numerical error The Spectre circuit simulator improves the control of local truncation error in the transient analysis by controlling error in the voltage rather than the charge In addition the Spectre circuit simulator directly checks Kirchhoff s Current Law also known as Kirchhoff s Flow Law at each time step improves the charge conservation accuracy of the Spectre circuit simulator and eliminates the possibility of false convergence B Superior time step control algorithm July 2002 17 Product Version 5 0 Spectre Circuit Simulator User Guide Introducing the Spectre Circuit Simulator The Spectre circuit simulator provides an adaptive time step control algorithm that reliably follows rapid changes in the solution waveforms It does so without limiting assumptions about the type of circuit or the magnitude of the signals m
16. Select the waveform in the Results Browser by clicking the left mouse button over the name of the waveform Choose cross from the Special Functions menu in the calculator The Threshold Crossing form appears Type 0 inthe Threshold Value field type 0 in the Edge Number field and set Edge Type to either Click OK Enable the Evaluate Buffer button in the calculator This returns the list of zero crossing points time co ordinates of the waveform in the CIW Selecting New Colors for Waveforms To select a new color for a waveform 1 2 3 In the Waveform Window choose Curves Edit The Curves form appears In the Curves form select the curve name you want and the pen color Click OK Accessing Data from Multiple Directories There are two ways to access data from multiple directories If you are accessing data from multiple directories and each unique data directory path ends with a directory called psf use the awd command by itself and click OK in the Browse Project Hierarchy form In the Results Browser expand the hierarchy down to a data directory click the middle mouse button over the waveform name and select the Create ROF command from the middle mouse button menu Then expand this data tree to access the data To access a different data directory back up in the hierarchy in the Results Browser and then expand down to some other data directory Again select the Create ROF command for that part
17. Spectre Circuit Simulator User Guide Analyses m The start steps and omega parameters are not defined in the subcircuit calls They take the default values assigned in the subcircuit DC Analysis The DC analysis finds the DC operating point or DC transfer curves of the circuit To generate transfer curves specify a parameter and a sweep range The swept parameter can be circuit temperature a device instance parameter a device model parameter a netlist parameter or a subcircuit parameter for a particular subcircuit instance You can sweep the circuit temperature by giving the parameter name as param temp with no dev mod Or sub parameter You can sweep a top level netlist parameter by giving the parameter name with no dev mod Or sub parameter You can sweep a subcircuit parameter for a particular subcircuit instance by specifying the subcircuit instance name with the sub parameter and the subcircuit parameter name with the param parameter After the analysis has completed the modified parameter returns to its original value The syntax is as follows Name dc parameter value You can specify sweep limits by giving the end points or by providing the center value and the span of the sweep Steps can be linear or logarithmic and you can specify the number of steps or the size of each step You can give a step size parameter step lin log dec and determine whether the sweep is linear or logarithmic If you do not give a step s
18. Spectre Circuit Simulator User Guide Control Statements pwr To save power dissipated on a circuit subcircuit or device all To save all signals of the device n subcircuitName is the instance name of a subcircuit call Saving terminal currents for subcircuit calls is the same as saving terminal currents for other instance statements except that you must identify individual terminal currents you want to save by the terminal index Note To save all terminal currents for subcircuit calls you use a save statement or specify the subcktprobelvl parameter in an options statement The currents all option of the options statement saves currents only for devices Saving Subcircuit Signals To save a subcircuit signal with the save statement modify the main circuit syntax as follows Give a full path to the subcircuit name Start with the highest level subcircuit and identify the signals you want to save at the end of the path Separate each name with a period Examples of the save Statement The following table shows you examples of save statement syntax When you specify node names the Spectre simulator saves node voltages Currents are identified by the terminal node name or the index number Exception Currents through probes take the name of the probe save Statement Action save 7 Saves voltage for a node named 7 save Q4 currents Saves all terminal currents associated with component Q4 save Q4 static Saves resistive term
19. Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features sll real imag 0 00000000e 00 0 333333 0 0 666667 0 0 666667 0 0 666667 0 0 2393333 0 0 666667 0 0 666667 0 0 666667 0 0 333333 0 2 50000000e 07 0 549736 0 0181715 0 446126 0 0466097 0 450264 0 0181715 0 446126 0 0466097 0 546593 0 0556029 0 446126 0 0466097 0 450264 0 0181715 0 446126 0 0466097 0 549736 0 0181715 5 00000000e 07 0 546094 0 0359074 0 437504 0 0922889 0 453906 0 0359074 0 437504 0 0922889 0 533673 0 10951 0 437504 0 0922889 0 453906 0 0359074 0 437504 0 0922889 0 546094 0 0359074 An S parameter file for Spectre format must have a header The header must have a comment beginning with a semicolon as the first line must define the reference resistance of ports and the S parameter formats and can include any number of comment and blank lines When reading the file the translator ignores all the lines beginning with semicolons spaces commas and newlines in the header The translator reads the numbers immediately after on the lines after the reference resistance line as impedance data of the ports The format section is treated as the format definition of S parameter data entries You can enter the S parameters in any order but the frequency must be first and is separated from the S parameters with a colon Each S parameter can be expressed as real imag mag deg mag rad db deg
20. capacitor c 2 0115e 17 Io c2 nq vss capacitor c 6 287e 16 S Begin top level circuit definition xna3pll 1 90 na3pl xna3p12 21 na3pl xna3p13 32 na3pl xna3pl4 4 3 na3pl xna3p15 5 4 na3pl xna3pl6 6 5 na3pl xna3pl17 7 6 na3pl xna3p18 8 7 na3pl xna3p19 9 8 na3pl xna3p110 10 9 na3pl xna3p111 11 10 na3pl xna3p112 12 11 na3p1 xna3p113 13 12 na3pl xna3p114 14 13 na3p1 xna3p115 15 14 na3pl xna3p116 16 15 na3pl xna3pl17 90 16 na3p1 Next couple of lines sets variables for vdd and vss parameters vdd S1 23 3 parameters vss S1 20 0 vdd Il vdd gnd vsource dc vdd S1 vss Il vss gnd vsource dc vss S1 Next line initializes nodes within ring ic 220 420 6 20 8 20 1020 include q35d4h5 modsp section tt Transient analysis card tempOption options temp 25 typ tran tran step 0 010n stop 35n alter ss altergroup include q35d4h5 modsp section ss parameters vdd S1 23 0 July 2002 285 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits alterTempTol00 alter param temp value 100 ss_tran tran step 0 010n stop 35n myAlter2 altergroup include q35d4h5 modsp section ff parameters vdd_S1 3 3 alterTempTo0 alter param temp value 0 ff tran tran step 0 010n stop 35n Ring Oscillator Spectre Deck for Two Input NOR Ring with No Fanouts nor2 ring sp This example
21. Designer s Guide to SPICE amp Spectre Typographic and Syntax Conventions This list describes the syntax conventions used for the Spectre circuit simulator literal Nonitalic words indicate keywords that you must enter literally These keywords represent command function routine or option names filenames and paths and any other sort of type in commands argument Words in italics indicate user defined arguments for which you must substitute a name or a value The characters before the underscore _ in the word indicate the data types that this argument can take Names are case sensitive Vertical bars OR bars separate possible choices for a single argument They take precedence over any other character Brackets denote optional arguments When used with OR bars they enclose a list of choices You can choose one argument from the list 1 Kundert Kenneth S The Designer s Guide to SPICE amp Spectre Boston Kluwer Academic Publishers 1995 July 2002 14 Product Version 5 0 Spectre Circuit Simulator User Guide Preface Braces are used with OR bars and enclose a list of choices You must choose one argument from the list Three dots indicate that you can repeat the previous argument If you use them with brackets you can specify zero or more arguments If they are used without brackets you must specify at least one argument but you can specify more Important The language requires many
22. Formatting the model Statement You format the model statement as follows model name master parami valuel Xparam2 value2 The fields have the following values model The keyword model model is used for SPICE mode name The unique name you give to the model July 2002 68 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists lt master gt The master name of the component such as resistor bjt or tline This field can also contain the name of an AHDL module For more information about using the Spectre simulator with SpectreHDL see the SpectreHDL Reference manual lt parameteri valuel gt lt parameterN valueN gt This is an optional field you can repeat any number of times ina model statement Each parameter specification is a model parameter followed by an equal sign followed by the value of the parameter You can find a list of the available model parameters for each component in the parameter listings of Spectre online help spectre h Examples of model Statements The following examples give parameters for a t Line model named tuner and ab jt model named NPNbjt model tuner tline f 1MHz alphac 9 102m dcr 105m model NPNbjt bjt type npn bf 100 js 0 1fA Note The backslash is used as a continuation character in this lengthy mode1 statement model NPNbjt2 bjt type npn is 3 38e 17 bf 205 nf 0 978 vaf 22 N ikf 2 05e 2 ise 0 ne 1 5 br 62 nr 1 var
23. In general you use the ic parameter of individual components to specify initial conditions for those components and you use the ic statement to specify initial conditions for nodes You can specify initial conditions for inductors with either method Specifying cmi n for a transient analysis does not satisfy the condition that a node has a capacitive path to ground Note Do not confuse the ic parameter for individual components with the ic parameter of the transient analysis The latter lets you select from among different initial conditions specifications for a given transient analysis Specifying Initial Conditions for Components You can specify initial conditions in the instance statements of capacitors inductors and windings for magnetic cores The ic parameter specifies initial voltage values for capacitors July 2002 187 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements and current values for inductors and windings In the following example the initial condition voltage on capacitor Cap13 is set to two volts Cap13 11 9 capacitor c 10n ic 2 Specifying Initial Conditions for Nodes You use the ic statement to specify initial conditions for nodes or initial currents for inductors The nodes can be inside a subcircuit or internal nodes to a component The following is the format for the ic statement ic lt signalName value gt The format for specifying signals with the ic statement is similar
24. PWL takes a wave parameter that accepts time value pairs If the time value does not increase the Spectre simulator displays the following message Error found in spectre during initial setup vlO time is not strictly increasing in waveform Check the PWL component to fix this error Spectre Warning Messages Warning messages tell you about conditions that might cause invalid results Unlike error messages warnings do not stop a simulation When you receive a warning message you must decide whether the particular condition creates a problem for your simulation This section describes some common Spectre warning messages It also tells you how to modify parameters to correct conditions that might produce invalid simulation results The Spectre simulator often prints warnings and notices that are eventually determined to be uninteresting and there is a natural tendency after a while to ignore them We recommend that you carefully study them the first few times you simulate a particular circuit and whenever the simulator gives you unexpected results P N Junction Warning Messages Almost every semiconductor device includes at least one p n junction Normally these p n junctions are biased in a particular operating region Three types of warning messages are available for each p n junction one for exceeding a maximum current one for exceeding a melting current and one for exceeding a breakdown voltage Explosion Region Warnin
25. Q MOS levels 1 2 and 3 Q BSIM levels 1 and 2 m You can choose between the following substrate current models for the simulation Q The Toshiba model Q The BERT model To simulate the hot electron degradation of a circuit you need to run at least two transient analyses In the first analysis you establish baseline values for a new circuit To create this baseline you set the ci rcuitage parameter to zero ci rcuitage 0 circuitage 0 is also the default value if you leave this parameter unspecified For each subsequent transient analysis you reset the age of the circuit by changing the value of the circuitage parameter You specify circuitage values in years For example circuitage 4 0 specifies a circuit that is 4 years old Hot Electron Degradation Analysis To specify an analysis of hot electron degradation you need to provide appropriate parameter settings m You must be sure the degradation parameter is set to degradation yes for the instance statement of each component you want to analyze This parameter takes its default value from the setting in the model statement All MOS and BSIM components require model statements as well as instance statements B You must set all necessary parameters in the model statements of the components you want to analyze To determine which model parameters you must specify look at the parameter listings for each component in the Spectre online help spectre h Examine the fol
26. Q2 A RI nme T lee zu 35 gt 01 cc bl e npn P c3 b1 0 capacitor c 3nF B Rl b1 0 resistor r 10k Sample Netlist A netlist is an ASCII file that lists the components in a circuit the nodes that the components are connected to and parameter values You create the netlist in a text editor such as vi or July 2002 26 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre emacs or from one of the environments that support the Spectre simulator The Spectre simulator uses a netlist to simulate a circuit BIT ECP Oscillator lt Comment indicated by Indicates the file contains a Spectre netlist simulator lang spectre uh el oak 4 see the next section Place below first line Iee e 0 isource dc 1mA Q1 cc b1 e npn Q2 out b2 e npn L1 cc out inductor l 1uH C1 cc out capacitor c 1pf nstance statements C2 out bl capacitor c 272 pF 3 bl 0 capacitor c 3nF C4 b2 0 capacitor c 3nF R1 bl 0 resistor r 10k R2 b2 0 resistor r 10k ic bc 1 a amp Control statement sets initial conditions model npn bjt type npn bf 80 rb 100 vaf 50 Model statement cjs 2pf tf 0 3ns tr 6ns cje 3pf cjc 2pf OscResp tran stop 80us maxstep 10ns aq Analysis statement Elements of a Spectre Netlist This section briefly explains the components models anal
27. Use the Cadence analog circuit design environment Calculator expressions to measure the circuit performance You can use the analog design environment graphics tools to plot scalar performance data such as slew rates and bandwidths as a histogram or scattergram You can also display waveform data as cloud family plots For more information about the Monte Carlo analysis see Monte Carlo Analysis on page 161 For more information about using the Monte Carlo analysis with the analog design environment see the Advanced Analysis Tools User Guide B Hot electron degradation analysis Lets you control the age of the circuit when simulating hot electron degradation For more information about the hot electron degradation analysis see Special Analysis Hot Electron Degradation on page 175 Analysis Parameters You specify parameter values for analysis and control statements just as you specify those for component and model statements but many analysis parameters have no assigned default values You must assign values to these parameters if you want to use them To assign values to these parameters simply follow the parameter keyword with an equal sign and your selected value For example to set the points per decade dec value to 10 you enter dec 10 Note Some parameters require text strings usually filenames as values You must enclose these text strings in quotation marks to use them as parameter values When analysis p
28. circuit about a periodically varying operating point and accurately models frequency conversion effects For more information about the periodic transfer function analysis see SpectreRF Help m Other analyses ua Sensitivity analysis sens Determines the sensitivity of output variables to input design parameters The results are expressed as a ratio of the change in an output analysis variable to the change in an input design parameter The output for the sens command is sent to the rawfile or to an ASCII file For more information about sensitivity analysis see Sensitivity Analysis on page 147 Fourier analysis ourier Measures the Fourier coefficients of two different signals at a specified fundamental frequency without loading the circuit The algorithm used is based on the Fourier integral rather than the discrete Fourier transform and therefore is not subject to aliasing Even on broad band signals it computes a small number of Fourier coefficients accurately and efficiently Therefore this Fourier analysis is suitable on clocked sinusoids generated by sigma delta converters pulse width modulators digital to analog converters sample and holds and switched capacitor filters as well as on the traditional low distortion sinusoids produced by amplifiers or filters For more information about the Fourier analysis see Chapter 4 Analysis Statements of the Spectre Circuit Simulator Reference DC Match Analysis
29. dmEnableTestl alter dev Vtl param mag value 1 annotate no dmEnableTest2 alter dev Vt2 param mag value 1 annotate no dmLoopGain ac start lk stop 1G dec 10 dmDisableTestl alter dev Vtl param mag value 0 annotate no dmDisableTest2 alter dev Vt2 param mag value 0 annotate no common mode characteristics closed loop gain Av Vcm p power supply rejection ratio Vdd PSR Vdd p Vss PSR Vss p cmXferFunctions xf start 1lk stop 1G dec 10 probe Rocm cmNoise noise start 1k stop 1G dec 10 oprobe Rocm oportv 1 iprobe Vcm iportv 1 step response cmEnablePulse alter dev Vcm param type value pulse annotate no cmStepResponse tran stop 2us errpreset conservative cmDisablePulse alter dev Vcm param type value dc annotate no loop gain Tv tl nvg open loop gain av 2 cmout pvgtnvg cmEnableTestl alter dev Vtl param mag value 1 annotate no cmEnableTest2 alter dev Vt2 param mag value 1 annotate no cmLoopGain ac start 1k stop 1G dec 10 July 2002 110 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features cmDisableTestl alter dev Vtl param mag value 0 annotate no cmDisableTest2 alter dev Vt2 param mag value 0 annotate no The following file opamp ckt contains the differential amplifier opamp ckt Fully Differential CMOS Operational Amplifier This circuit requires t
30. for the design engineer to use The library then includes a symbol cell view for each inline subcircuit The design engineer then places a symbol cell view on a design which behaves just as if a primitive were being used The design engineer can then probe the device for terminal currents and operating point information Probing the Device The Spectre simulator allows the following list of items to be saved or probed for primitive devices including devices modeled as the inline components of inline subcircuits m All terminal currents save ml currents m Specific index terminal current save ml 1 1 drain B Specific named terminal current save ml s s source M Save all operating point information save ml oppoint m Save specific operating point information save ml vbe M Save all currents and operating point information save ml Note If the device is embedded in a regular subcircuit you have to know that the device is a subcircuit and find out the appropriate hierarchical name of the device in order to save or probe the device However with inline components you can use the subcircuit call name just as if the device were not in a subcircuit Operating point information for the inline component is reported with respect to the terminals of the inline component itself and not with respect to the enclosing subcircuit terminals This results in the following cautions July 2002 98 Product Version 5 0 Spectre Circuit Simu
31. h Setting Tolerances You need to set tolerances if the Spectre simulator s default settings do not suit your needs This section tells you how to make the needed adjustments If you need to examine default tolerances for any Spectre parameters you can find them in the Spectre online help spectre h Setting Tolerances with the options Statement The following opt ions statement parameters control error tolerances reltol One of the Spectre simulator s convergence criteria is that the difference between solutions in the last two iterations for a given time must be sufficiently small With reltol you set the maximum relative tolerance for values computed in the last two iterations The default for reltol is 0 001 July 2002 199 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements iabstol and vabstol July 2002 200 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Name paramset lt list of netlist parameters gt lt list of values foreach netlist parameter gt list of values foreach netlist parameter Here is an example of the paramset statement parameters pl 1 p2 2 p3 3 data paramset pl p2 p3 5 5 5 4 3 2 Combining the paramset statement with the sweep analysis allows you to sweep multiple parameters simultaneously for example power supply voltage and temperature The save Statement You can save signals for individ
32. npn Q2 out b2 e npn L1 vcc out inductor l 1uH Cl vec out capacitor c 1pf C2 out bl capacitor c 272 7pF C3 b1 0 capacitor c 3nF C4 b2 in capacitor c 3nF R1 bl 0 resistor r 10k R2 b2 in resistor r 10k ic bl 1 model npn bjt type npn bf 80 rb 100 vaf 50 N cjs 2pf tf 0 3ns tr 6ns cje 3pf cjc 2pf OscResp tran stop 80us maxstep 10ns method trap July 2002 48 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility This example shows several of the basic differences between SPICE and Spectre netlists Spectre netlists define the language context at the beginning of the netlist with the simulator lang spectre statement By default netlists are assumed to be in SPICE unless the simulator lang spectre statementis encountered or unless the netlist file ends in the extension scs The SPICE Reader will insert this line at the beginning of each SPICE to Spectre converted netlist In the SPICE language the component type is determined by the first letter of the component name which limits the component types to 26 The Spectre Netlist Language has unlimited component types since the component type is determined by the master name instead of the first letter of the component name An example of using the master name is the resistor field in the instance statements for R1 and R2 In many versions of SPICE the component name node numbers and other fields are limited to a maximum of 8 characters The Spe
33. or db rad You can use commas to separate the two parts of an S parameter Any number of frequency points can be presented They do not need to be equally spaced but the frequency index must be monotonic and the frequency data must be given explicitly with no hidden scale factors There is no limit to the number of ports S parameters use the syntax 13 15 when either port number is greater than 9 Output File Syntax Output file syntax is described in this section Some notes are given as follows time Shows the time when the output file is generated file Shows the input file name format Shows the complex number format definition resistance Showsthe input impedance value of ports or 50 if no input impedance is given July 2002 126 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features LIBRA Format A LIBRA output file has the following form Libra TM Ver 3 500 103 3 time Translated file file S format R resistance SCATTERING PARAMETERS Data section Data section shows the frequency and S parameter data in the format described in LIBRA Format on page 121 MHARM Format The output MHARM file complies with the format described in MHARM Format on page 123 HPMNS Format The general format for an HPMNS output file is as follows File Format Spectre format converted to MDS like format Some edit
34. statements If temp statements analysis statements or alter statements are not in the same file they might not get properly unfolded Here is an example of a Mos characterization deck written in SPICE M1 1 2 0 0 NCH VDR 10 2 July 2002 46 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility VG 2 0 1 JOP MODEL NCH NMOS LEVEL 49 TOX 1e 9 VTH0 0 5 VBOX 5 TEMP 25 75 100 INCLUDE dcAnalysis inc END where dcAnalysis inc iS DC VDR 0 5 0 1 VG 0 2 0 1 The netlist produced with spp convert does not include the sweep statement within the temperature sweep Mos characterization deck simulator lang spectre insensitive yes ml 1200 nch vdr 10 vsource dc 2 vg 2 0 vsource dc 1 model nch bsim3v3 type n tox le 9 vth020 5 vbox 5 include dcAnalysis inc swp tmpl sweep param temp values 25 75 100 SppSaveOptions options save allpub analysisOP1 dc oppoint logfile end You need to edit the netlist to insert the included analysis into the temperature sweep Mos characterization deck Simulator lang spectre insensitive yes ml 1200 nch vdr 10 vsource dc 2 vg 20 vsource dc 1 model nch bsim3v3 type n tox le 9 vth020 5 vbox 5 swe_tmpl sweep param temp values 25 75 100 SppSaveOptions options save allpub analysisOP1 dc oppoint logfile analysisDCswpl sweep param dc dev vg start 0 stop 2 step 0 1 analysisDCswp2 dc par
35. that you can specify if you want the absolute current values to depend on the device area For more information see Spectre Circuit Simulator Known Problems and Solutions Melting Current Warnings A separate model parameter imelt is used as a limit warning for the junction current This parameter can be set to the maximum current rating of the device When any component of the junction current exceeds imelt Spectre issues a warning and the results become inaccurate The junction current is linearized above the value of imelt to prevent arithmetic exception with the exponential term replaced by a linear equation at imelt Breakdown Region Warnings Messages like the following are breakdown region warnings D2 Breakdown voltage exceeded Q1 The collector substrate voltag xceeded breakdown voltage The warning message identifies the relevant component name D2 and Q1 and the affected junction The Spectre simulator issues breakdown region warnings only when you specify conditions for them For information on setting parameters to identify a breakdown region see Customizing Error and Warning Messages on page 262 Missing Diode Would Be Forward Biased Warning from spectre at time 501 778 ns during transient analysis tran to lu il q0 Missing collector substrate diode would be forward biased Notice from spectre at time 510 1688 ns during transient analysis tran to lu July 2002 258 Product Version 5 0 S
36. 0 Spectre Circuit Simulator User Guide Control Statements Parameter Setting Action Taken file C r info what File name when where file save all Saves all signals to output Other possible values are 1v1 allpub lvlpub selected and none nestlvl Specifies levels of subcircuits to report The default value is infinity xtremes yes Prints minimum and maximum values Other possible values are no and only title test Prints test as the title of the analysis in the output file Specifying the Parameters You Want to Save You specify parameters you want to save with the info statement what parameter You can give this parameter the following settings Setting Action none Lists no parameters inst Lists input parameters for instances of all components models Lists input parameters for models of all components input Lists input parameters for instances and models of all components output Lists effective and temperature dependent parameter values all Lists input and output parameter values oppoint Lists operating point parameters terminals The output is a node to terminal map nodes The output is a terminal to node map captab Prints node to node capacitance The info statement gives you some additional options You can use the save parameter of the info statement to specify groups of signals whose values you want to list For more information about save parameter options consult Saving Groups of Signals
37. 0 28449 64 6032 0 28449 64 6032 0 28449 64 6032 0 95696 17 1412 0 04424 145 522 0 28449 64 6032 0 04424 145 522 0 95696 17 1412 While reading the file the translator ignores all comment lines beginning with If a scale factor is presented on the line beginning with the translator ignores the f option If the scale factor is missing on the line the translator assumes the scale factor to be HZ unless you use the f option The scale factor can be HZ KHZ MHZ GHZ or THZ in uppercase or lowercase letters If an impedance value is given on this line it needs to follow the key character R and a space The complex number format needs to be specified on the line beginning with and can be RI MA or DB in uppercase letters RI The complex number is expressed in the form of real and imaginary MA The complex number is expressed in the form of magnitude and angle DB The complex number is expressed in the form of db magnitude and angle The data section needs to only include frequency and S parameter data The data entries at each frequency point are required to comply with the following formats Single port freq Sll mag S11 deg Two ports freq Sll mag Sll deg S21 mag S21 deg S12 mag S12 deg S22 mag S22 deg Three ports July 2002 122 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features freq S11 mag 12 mag 13 mag Fo
38. 0 6 Then for a given instance M1 1 2 3 4 ModelName w 3 1 1 5 the program searches all the models in the model group with the name ModelName and then picks the first model whose geometric range satisfies the selection criteria In the preceding example the auto model selector program chooses ModelName 2 July 2002 105 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features Conditional Instances You can specify different conditions that determine which components the Spectre simulator instantiates for a given simulation The determining conditions are computed from the values of parameters You specify these conditions with the structural if statement This statement lets you put if else statements in the netlist You can also use conditional instantiation with inline subcircuits For more information on using inline subcircuits see Scaling Physical Dimensions of Components on page 115 Formatting the if Statement You format the structural i statement as follows if condition statementi else statement2 statement The statementi and statement2 fields contain one or more instance statements or i f statements The else part of the statement is optional condition The condition fields are Boolean valued expressions where any nonzero value is taken as true An if Statement Example The following example illustrates the use of the i
39. 10 pb 0 605 js le 4 xj 0 65u ld20 5u wd 1 2u uo 206 bvj 14 model dnp diode is 3 1e 10 n 1 12 cjo 3 1e 8 pb 914 m 5 bvj 45 imax 1000 model dpn diode is 1 3e 10 n 1 05 cjo 9 8e 9 pb 605 m 5 bvj 45 imax 1000 endsection typical section slow MOSFETS and DIODES for process corner SLOW model nmos mos3 type n vto 1 48 gamma 1 90 phi 59 nsub 1e15 cgso 440p cgdo 440p cgbo 250p cj 440u tox 800e 10 pb 0 914 js le 4 xj 0 8u 1d20 38u wd 1 5u uo 2641 bvj 14 model pmos mos3 type p vto 1 42 gamma 0 58 phi 73 nsub 1 7e16 cgso 300p cgdo 300p cgbo 250p cj 120u tox 800e 10 pb 0 605 js le 4 xj 0 5u l1d 20 1u wd 1 5u uo 167 bvj 14 model dnp diode is 3 1e 10 n 1 12 cjo 3 1e 8 pb 914 m 5 bvj 45 imax 1000 model dpn diode is 1 3e 10 n 1 05 cjo 9 8e 9 pb 605 m 5 bvj 45 imax 1000 endsection slow endlibrary Process File This example of automatic model selection with the conditional i statement is more sophisticated than the previous example in Fully Differential CMOS Operational Amplifier on page 109 With this example you ask for an nmos transistor and the Spectre simulator automatically selects the appropriate model according to the process corner the circuit temperature and the device width and length The selection is done by the parameterized inline subcircuit and the conditional i statement The paramtest statements create warnings if the mod
40. 157 DC convergence problems correcting 274 dec parameter 160 defaults analyses 66 analysis parameters 133 C preprocessor CPP 233 Cadence range limits for warnings 263 checkpoint spectre command option 232 commandline 233 controlling destination and format of Spectre results 233 controlling system generated messages 233 creating checkpoints and initiating recovery 233 measurement units of parameters 116 name of the simulator 233 overriding in UNIX environment variables 235 percent codes 233 screen display 233 setting for environment with SPECTRE_DEFAULTS simulation environment 233 July 2002 spectre command 233 changing 234 examining 234 defining a library 73 degradation parameters for hot electron degradation simulation 177 178 Design Framework ll use of with Spectre 23 Designer s Guide to SPICE and Spectre 14 dev parameter 158 devices as pwr option 206 218 diagnosis mode use of 20 differential amplifier example of input file 109 direction associated reference 58 directory names generating 226 specifying yourown 228 displaying a waveform with awd 36 donominal parameter Monte Carlo analysis 167 double slash in Spectre syntax 59 dptran as homotopy parameter option 246 Dracula use of with Spectre 23 duoc parameter 177 178 duoe parameter 177 178 dvthc parameter 177 178 dvthe parameter 177 178 E e colon modifier 251 electrical current in Amperes 74 electri
41. 234 unload shared object 293 unusual parameter size warnings 259 usability features 19 user defined functions 89 V V 74 N predefined percent code 249 vabstol parameter 200 setting to correct accuracy problems 277 values parameter 160 variations parameter Monte Carlo analysis 166 vbcfwd parameter and determining operating regions for BUTS 271 vbefwd parameter and determining operating regions for BUTS 271 VCO definition of 21 vector parameter values 78 143 143 172 Product Version 5 0 Spectre Circuit Simulator User Guide vector values piecewice linear 72 Verilog coupling with Spectre 23 Verilog A 13 vertical bars in syntax 14 viewing output 32 W warning messages 19 about size of gmin 259 caused by invalid parameters in subcircuit calls 95 customizing 262 generating about transistor operating regions 270 options of spectre command 274 parameter is unusually large or small 259 P N junction warnings 257 requesting breakdown region warnings for transistors 269 responding to 31 selecting limits operating region warnings 270 parameter values 262 specifying conditions for in subcircuit calls 95 warnings melting current 258 waveform display 36 waveform storage format WSF 224 Waveform Window 36 Wb 74 what parameter of check statement 186 269 write parameter and creating state files 190 241 writefinal parameter and creating state files 190 241 WSF wavefo
42. 25 speed improvements 18 SPICE compatibility reasons for incompatibilities 55 scope 50 stress parameters 176 syntax 59 tutorial 24 usability features 19 Spectre and SPICE input languages reading 50 Spectre and SPICE input languages mixing 54 spectre command checkpoint option in transient analysis recovery 232 defaults 16 24 57 July 2002 changing 234 examining 233 error options 274 info options 274 introduction to 30 options format 225 raw 228 restarting transient analysis recover 233 specifying simulation options 229 starting a simulation 229 using to override environment defaults 235 using to specify output directory names 228 using to specify output file format 225 warning options 274 Spectre input mode combining with SPICE input mode 54 Spectre Netlist Language syntax rules 58 SPECTRE_DEFAULTS environment variable 234 263 overriding with param option of spectre command SpectreHDL definition 1 SpectreRF brief description 13 description of 21 a file 231 PICE 13 20 and Spectre input languages mixing 54 differences from Spectre 16 24 57 183 280 input language case sensitivity 59 case sensitivity of scale factors 82 combining with Spectre mode 54 reading 50 language title line 51 sptr command 121 sst2 output format 224 start parameter 159 starting a simulation 229 analyses from previous solutions 237 state files analysis efficiency with netlist example discussed 134
43. 3 alterTempTo0 alter param temp value 0 ff tran tran step 0 010n stop 35n Ring Oscillator Spectre Deck for Three Input NAND Ring with No Fanouts nand3 ring sp This example uses Spectre syntax Ring oscillator Spectre deck for 3 Input NAND ring with no fanouts simulator lang spectre global 0 gnd vdd vss aliasGnd gnd 0 vsource type dc dc 0 Simulator options to use SetOptionl options iabstol 1 00n audit full MyAcctl info what inst extremes yes MyAcct2 info what models extremes yes July 2002 284 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits MyAcct3 info what input extremes yes MyAcct5 info what terminals extremes yes MyAcct6 info what oppoint extremes yes Next section is the subckt for na3pl subckt na3pl nga ml nq a vdd vdd p 1 0 35u w 2 90u ad 1 10p pd 3 66u as 2 12p ps 7 26u m2 nq vdd vdd vdd p 1 0 35u w 2 90u ad 1 10p pd 3 66u as 1 10p ps 3 66u m3 nq vdd vdd vdd p 1 0 35u w 2 90u ad 2 12p pd 7 26u as 1 10p ps 3 66u m4 vss a 7 vss n 1 0 35u w 2 40u ad 1 75p pd 6 26u as 0 25p ps 2 61u m5 7 vdd 8 vss n 1 0 35u w 2 40u ad 0 25p pd 2 61u as 0 25p ps 2 61u m6 nq vdd 8 vss n 1 0 35u w 2 40u ad 1 75p pd 6 26u as 0 25p ps 2 61u cO 8 vdd capacitor c 1 341e 17 el vdd vss capacitor c 9 9445302e 16 nq vdd capacitor c 2 0719818e 15 a vss capacitor c 5 3760487e 16 vdd capacitor c 1 2446956e 15 nq capacitor c 7 308e 17 vdd
44. 5 0 isource dc 1m July 2002 103 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features dcop dc Binning Binning is the process of partitioning a device with different sizes into different models Before BSIM 3v3 it was very difficult to fit all the devices with a single model statement over very wide ranges of device sizes To improve fitting accuracy you might characterize devices into several models with each model valid only for a limited range of device sizes For example suppose you have a device with a length L from 0 25 um to 100 um anda width W from 0 25 um to 100 um You might want to divide your device as follows not drawn to scale A 100 um Mod1 Mod2 Mod3 10 um W Mod4 Mod5 Mod6 1 um Mod7 Mod8 25 um 25 um 1 um In this example nine models are used These devices are divided into bins For devices whose length lies between 1 um and 10 um and width lies between 10 um and 100 um Mod6 is used The process of generating these models is called binning The binning process is usually identical for all simulators because the equations for binning are always the same P PO Pl Leff Pw Weff Pp Leff Weff July 2002 104 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features There are two ways to do binning with the Spectre simulator m Auto model selection For more information on a
45. 50 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility Sources The SPICE Version 2G User s Guide vladimirescu8 1 is the reference for the SPICE2 input language The SPICE Reader accepts input formats from this document for all SPICE capabilities the Spectre simulator supports The SPICE Reader might not accept variations from SPICE 2G6 that are not in the user guide The SPICE3 Version 3e User s Manual B JohnsonXX is the reference for SPICE3 batch input language The SPICE Reader accepts input formats batch mode only from this document for all SPICE capabilities the Spectre simulator supports The SPICE BOOK vladimirescu81 is a general reference for SPICE2 3 based syntax s with common extensions Publicly available netlists provide references for many of the extensions to SPICE Compatibility Guidelines Mapping of SPICE must not adversely affect simulation results Where simulators follow different syntax rules support for each is attempted For example the TC property is an instance property in SPICE2 and model parameters TC1 TC2 in SPICE3 both are supported When a conflict exists between simulator syntax rules one method is selected and documented General Input Compatibility By default the SPICE Reader processes its input in the following manner Accepts the SPICE instance A Z and control dot cards as well as the Spectre native input language Reads in the first line a
46. 8 9 ml 4 2 3 3 nch w 20u 1 0 5u ad 0 3n as 0 3n pd 50u ps 50u m2 5 1 3 3 nch w 20u 1 0 5u ad 0 3n as 0 3n pd 50u ps 50u m3 4 4 8 8 pch w 20u 1 0 5u ad 0 3n as 0 3n pd 20u ps 20u m4 5 4 8 8 pch w 20u 1 0 5u ad 0 3n as 0 3n pd 20u ps 20u m5 3 7 9 9 nch w 20u 1 0 5u ad 0 3n as 0 3n pd 40u ps 40u m6 6 5 8 8 pch w 20u 1 0 5u ad 1 3n as 1 3n pd 350u ps 350u m7 6 7 9 9 nch w 20u 1 0 5u ad 2 3n as 2 3n pd 660u ps 660u m8 7 7 9 9 nch w 20u 1 0 5u ad 0 3n as 0 3n pd 40u ps 40u cc 5 6 4 4p ibias 8 7 8 8u ends opamp Original Open Loop Opamp openloop sp Allen amp Holmberg p 438 Original Open Loop OpAmp Configuration vinp 10 dc 0 ac 1 0 vdd 4 0 dc 5 0 vss 0 5 dc 5 0 vinm 2 0 dc 0 cl3 0 20p x11234 5 opamp Bring in opamp subcircuit include opamp cir Bring in models here model nch bsim3v3 model pch bsim3v3 type p Op simulator lang spectre tf 3 0 xf save lvlpub nestlvl 1 start 1 stop 1K dec 20 simulator lang spice dc vinp 0 005 0 005 100u print dc v 3 July 2002 289 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits ac dec 10 1 10MEG print ac vdb 3 vp 3 end LH Modified Open Loop Opamp openloop1 sp Allen amp Holmberg p 438 Modified Open Loop OpAmp Configuration vinp 10 dc 0 ac 1 0 vdd 4 0 dc 5 0 vss 0 5 dc 5 0 vinm 2 0 dc 0 cl3 0 20p x11234 5 opamp Bring in opamp subcircuit include opampl cir Bring in mo
47. B The master name of the component identifies the type of component B The parameter values associated with the component A typical Spectre instance statement looks like this Component name L R16 4 0 resistor r 100 Parameter value Node names m t Master name Note You can use balanced parentheses to distinguish the various parts of the instance statement although they are optional R1 1 2 resistor r 1 Q1 c b e s npn area 10 Gm 1 2 3 4 vccs gm 01 R7 x y rmod r 1k w 2u Component Names Unlike SPICE the first character of the component name has no special meaning You can use any character to start the component name For example July 2002 28 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre Load out o resistor r 50 Balun in o pout nout transformer Note You can find the exact format for any component in the parameter listings for that component in the Spectre online help Master Names The type of a component depends on the name of the master not on the first letter of the component name as in SPICE this feature gives you more flexibility in naming components The master can be a built in primitive a model a subcircuit or an AHDL component Parameter Values Real numbers can be specified using scientific notation or common engineering scale factors For example you can specify a 1 pF capacitor value
48. B The restart parameter If you set this parameter to rest art no in an analysis statement the Spectre simulator uses the DC solution of the previous analysis as an initial guess for the following analysis m The prevoppoint parameter If you set this parameter to prevoppoint yes in an analysis statement the Spectre simulator does not compute or recompute the operating point Instead it uses the operating point computed by the previous analysis Saving Time by Specifying State Information The Spectre simulator lets you provide state information the current or last known status or condition of a process transaction or setting to the DC and transient analyses You can specify two kinds of state information m Initial conditions The ic statement lets you specify values for the starting point of a transient analysis The values you can specify are voltages on nodes and capacitors and currents on inductors m Nodesets July 2002 237 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques Nodesets are estimates of the solution you provide for the DC or transient analyses Unlike initial conditions their values have no effect on the final results Nodesets usually act only as aids in speeding convergence but if a circuit has more than one solution as with a latch nodesets can bias the solution to the one closest to the nodeset values Setting Initial Conditions for All Transient Analyses You can s
49. Carlo run processes export statements that implicitly refer to the result of the child analyses These statements calculate scalar circuit output values for performance characteristics such as slew rate B Organizes the export data appropriately Scalar data such as bandwidth or slew rate is calculated from an export statement and saved to an ASCII file which can be used later for plotting a histogram or scattergram m After the Monte Carlo analysis is complete all parameters are returned to their original values July 2002 162 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Monte Carlo Analysis Parameters You use the following parameters for your Monte Carlo analysis Parameter Description numruns This is the number of Monte Carlo runs to perform not including the nominal run The default is 100 runs The Spectre simulator performs a loop running the specified child analyses numruns times or numruns 1 times if the donominal parameter is set to yes and evaluating any export statements numruns times seed This is the optional starting seed for the random number generator By always specifying the same seed you can reproduce a previous experiment If you do not specify a seed then each time that you run the analysis you get different results that is a different stream of pseudorandom numbers is generated If you do not specify a seed the Spectre simulator uses the Spectre process id PID as
50. Compatibility Note These statements must be in the Spectre context of a netlist If you need to place the Spectre input in continuation lines begin each line of a continuation with a Vbias vbb 0 1 2 spectre tc 0 001 options reltol 0 001 spectre diagnose yes Compatibility Limitations Conflicts between Spectre and Spice The Spectre simulator does not support all SPICE capabilities for example the isto and PZ analyses Slight modifications are often necessary to make input acceptable to both languages Superficial punctuation differences such as ignoring extra parentheses or equal signs fit this category For example the statement temp 125 whichislegal in SPICE cannot be mapped by the SPICE Reader Removing the extraneous punctuation solves the problem Compatibility is limited in the area of unsupported primitive devices in Spectre You are encouraged to use the extensive capabilities of Verilog A to model such devices Parameters that are to be passed into a subcircuit from an instance statement must be specified on the SPICE subcircuit line Allowing the instance to define a subcircuit parameter is not allowed in Spectre Incompatibilities remain for some rarely used SPICE2 features because the authors have concentrated their efforts on creating compatibility with commonly used features Conflicts between SPICE variations Node 00 is treated as a number that is zero in SPICE2 and
51. Condition Messages asecsben sve hz tal pee ee ene cee heh edi ae dt 262 July 2002 10 Product Version 5 0 Spectre Circuit Simulator User Guide Outp t Messages x xovs twa e et en e QR wt Eo ee ane Alem RR e d At 262 Customizing Error and Warning Messages selle 262 Selecting Limits for Parameter Value Warning Messages 263 Selecting Limits for Operating Region Warnings LL 270 Range Checking on Subcircuit Parameters 0 cece eee 271 Formatting the paramtest Component 0 0 ee 271 Controlling Program Generated Messages 00 cece eee 273 Specifying Log File Options 35 4 tac itti tee ah Se as eee ae ae ees wads 273 Correcting Convergence Problems 1 cece ae 274 Correcting DC Convergence Problems 0 ccs 274 Correcting Transient Analysis Convergence Problems 277 Correcting Accuracy Problems 2s dee e LEER estes esse CNN e eee es 277 Suggestions for Improving DC Analysis Accuracy lees 277 Suggestions for Improving Transient Analysis Accuracy LL 278 A Example CIE CDIES rore UpS or p ruber ERU re bte mus 279 Notes on the BSIM3v3 Model 3 ave Site reca uv does e rtr E 280 SPECIE Syntax sarai a e ed ee dr ee oe Mya rm ee e os e ta op i eds dA ed 280 SPICE BSIM 3v3 Model 1 uos Ee dant eee DA Read EU fridds 280 Spectre B
52. For example you can save the solution at the final point of a transient analysis and then continue the analysis in a later simulation by using the state file as the starting point for another transient analysis m You can use state files to create automatic updates of initial conditions and nodesets The following example demonstrates the usefulness of state files altTemp alter param temp value 0 Drift dc param temp start 0 stop 50 0 step 1 readns ua741 dc0 write ua741 dc0 XferVsTemp xf param temp start 0 stop 50 step 1 probe Rload freq 1kHz readns ua741 dc0 The first analysis computes the DC solution at T20C saves it to a file called ua741 dc0 and then sweeps the temperature to T 50C The transfer function analysis x resets the temperature to zero Because of the temperature change the DC solution must be recomputed Without the use of state files this computation might slow the simulation because the only available estimate of the DC solution would be that computed at T 50C the final point in the DC sweep However by using a state file to preserve the initial DC solution at T 0C you can enable the Spectre simulator to compute the new DC solution quickly The computation is fast because the Spectre simulator can use the DC solution computed at T 0C to estimate the new solution You can also make future simulations of this circuit start quickly by using the state file to estimate the DC solution Even if you have altered a ci
53. Spectre netlist instructions to display some status information For more information consult the Spectre online help about the sweep and steps options for the annotate parameter You can set the annotate parameter for most Spectre analyses Interrupting a Simulation If you want to stop the Spectre simulator while a simulation is running do one of the following m Send an INT signal with your interrupt character The interrupt character is usually Control c You can get information about the interrupt character for your system with the UNIX stt y utility m Send the INT signal with a kill 1 command When you use either of these commands the Spectre simulator prepares the incomplete output data file for reading by the postprocessor and then stops the simulation Caution Do not stop the Spectre simulator with a k111 9 command This command stops the simulation before the Spectre simulator can prepare the output files for reading by the postprocessor Recovering from Transient Analysis Terminations If a transient analysis ends before a successful conclusion you can recover the work that is completed and restart the analysis The Spectre simulator needs checkpoint files to perform this recovery This section tells you about the following ways to create checkpoint files m Automatically with defaults and options statement settings m From the command line during a simulation m For specific analyses with netlist instructions T
54. The nodes for this instance statement are the connections to the subcircuit and the master field in the subcircuit call contains the name of the subcircuit You can enter parameters in a subcircuit call to override the parameters in the subcircuit definition for that subcircuit call The following example shows a subcircuit call and its corresponding subcircuit definition cell is the name of the subcircuit being called Q1 is the unique name of the subcircuit call and o1 i1 andb2 are the connecting nodes to the subcircuit from the subcircuit call When you call the subcircuit the Spectre simulator substitutes these connecting node names in the subcircuit call for the connecting nodes in the subcircuit definition o1 is substituted for o i 1 is substituted for g1 and 52 is substituted for g2 The length of transmission line TL is changed to 500 um for this subcircuit call from its 355 um default value in the subcircuit definition Q1 ol il b2 cell length 500um d Subcircuit call PES gl g2 4 Substitutions parameters length 355um TL o gnd d gnd tline len length vel 0 36 Gt d g2 S nGaAs Ctgd d S capacitor c 0 033p Cgg g2 gnd capacitor c 3p Gb S gl gnd nGaAs Cbgd s gnd capacitor c 0 033p Ro d G resistor r 10k Co C gnd capacitor c 0 165p ends cell July 2002 94 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features Modifying Subcircuit Parameter Values The following exa
55. Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists contains the model parameter definitions Q1 is the name of the component and o1 i1 and b2 are the connecting nodes of the component Q1 o1 il b2 npn Note The model statement is described in Model Statements on page 68 You can specify additional parameters for an individual component in an instance statement that refers to a model statement You can find a list of available instance parameters and a list of available model parameters for a component in the Spectre online help for that component spect re h Basic Instance Statement Rules When you prepare netlists for the Spectre simulator remember these basic rules B You must give each instance statement a unique name B Ifthe master is a model you need to specify the model Identical Components or Subcircuits in Parallel If your circuit contains identical devices or subcircuits in parallel you can specify this condition easily with the multiplication factor m Specifying Identical Components in Parallel If you specify an m value in an instance statement it is as if m identical components are in parallel For example capacitances are multiplied by m and resistances are divided by m Remember the following rules when you use the multiplication factor m You can use m only as an instance parameter not as a model parameter m Them value need not be an integer The m value can be an
56. Viewing Your Output rotrert redo EE Dare OE Larne terea tage que Se had ap Ao ECHO ese 32 Starimg AWD quot eec Oba ea ar Ce tpm ee eed atia oh ale Aa t 32 July 2002 3 Product Version 5 0 Spectre Circuit Simulator User Guide Displaying a Waveform oieuni eid fe Retard dak E ELE ig ead ora iie eS ee Sete ys 36 Extracting Zero Crossing Points 2520 rasa era oec a LOC De ag a Ra a re DEO ee 39 Selecting New Colors for Waveforms csse 40 Accessing Data from Multiple Directories 0 0 0 0 eee 40 Learning More about AWD 25 45 2024 sod 2654 ee RR PRENNE ENSE EE as 41 3 SPICE Compatibility os 5 Et tr erre eer a 42 Reading SBIGE Netlists 3 5 5 9 9 103 30 each aon RC RC QUE RIS Mrd do APR Ve ARCA RR ak 42 R nning the SPICE Reader 5 pter REPE SAL Vota de URP AERE RSEN 42 Running the SPICE Reader from Analog Artist a aannaaien 43 Running the SPICE Reader from the Command Line 43 Using the SPICE Reader to Convert Netlists nnna 0 cece eee eee ee 45 Language Differences ss i922 402 bia erue ud Dec rau aed Ob OLEAN Raves dena Po don 48 Comparing the SPICE and Spectre Languages 0 0c eee eee eee 48 Reading SPICE and Spectre Files seller 50 S6oD6e ol tli Dot pallbllity sui oed uo RR CE EE E EAR es eee e dr S RU etos 50 OUNCES aaia a Sa EnS TAE Ai a duda dra ea FER ERE d AERIAL aa NNR eae 51 Compat
57. When you use the alter statement to modify a circuit parameter you leave both dev and mod unspecified n param mag identifies mag as the parameter you are modifying If you omit this parameter the Spectre simulator uses the first parameter listed for each component in the Spectre online help as the default n value 1 identifies 1 as the new value for the mag parameter If you leave value unspecified it is set to the default for the parameter Changing Parameter Values for Models To change a parameter value for model files with the altergroup statement you list the device model and circuit parameter statements as you would in the main netlist Within an alter group each model is first defaulted and then the model parameters are updated You cannot nest alter groups You cannot change from a model to a model group and vice versa The following example demonstrates altergroup statement syntax agl altergroup parameters pl 1 model myres resistor rl le3 af pl model mybsim bsim3v3 lmax pl lmin 3 5e 7 July 2002 184 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements The following example shows the full replacement of models using the altergroup statement ff 25 altergroup include models corner_ff For each model or device being altered the parameters are first defaulted and then set to the new values The parameter dependencies are updated and maintained You can include files into t
58. a parameter enclose the string in quotation marks In the following example the value for the parameter named file is the character string Spara data model sp_data nport file Spara data N Ports When you model N ports you must first create a file listing the S parameters Then you complete the modeling by using this file as input for an nport statement You can create the S parameter file listing in two different ways m You can run an sp analysis and create a listing of S parameter estimates automatically m If you already know the S parameter values you can create an S parameter listing manually with a text editor such as vi The S parameter data file describes the characteristics of a linear N port over a list of frequencies The format of the data file used by the Spectre simulator is flexible and self documenting The Spectre simulator native format describes N ports with an arbitrary number of ports specifies the reference resistance of each port mentions the frequency with no hidden scale factors and allows the S parameters to be given in several formats N Port Example This example demonstrates the use of the nport statement Two port test circuit global gnd simulator lang spectre Models July 2002 117 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features model sp_data nport file Spara data Components Port1 il gnd port num 1 TL1 ed gnd
59. a simulation with the alter statement The modifications apply to all analyses that follow the alter statement in your netlist until you request another parameter modification You also use the alter statement to change the following opt ions statement temperature parameters and scaling factors n temp n tnom n scale July 2002 183 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements n scalem You can use the altergroup statement to respecify device model and circuit parameter statements that you want to change for subsequent analyses You can also change subcircuits if you do not change the topology Changing Parameter Values for Components To change a parameter value for a component device or model you specify the device or model name the parameter name and the new parameter value in the alter statement You can modify only one parameter with each alter statement but you can put any number of alter statements in a netlist The following example demonstrates alter statement syntax SetMag alter dev Vtl param mag value 1 n SetMagis the unique netlist name for this alter statement Like many Spectre statements each alter statement must have a unique name n The keyword alter is the primitive name for the alter statement n dev Vt1 identifies vc 1 as the netlist name for the component statement you want to modify You identify an instance statement with dev and a model statement with mod
60. and then measures the flow of current When to Use Current Probes Sometimes it is preferable or necessary to use a current probe rather than a save statement You use a probe instead of a save statement under the following circumstances n Ifyou want increased flexibility for giving currents descriptive names With a current probe you can name the current anything you want With a save statement the name of the current must have a name suffix n Ifyou are saving measurements for current controlled components n l fyouare saving currents for an AC analysis n Ifyou are saving measurements for a current that passes between two parts of a circuit but not through a terminal July 2002 204 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements In the following example you insert a current probe to measure the current flowing between A and B Because there is no component between A and B there is no other way to measure this current except to insert a current probe that has an identical current to the one you want to measure Current probe inserted to measure current from A to B Probe Statement Example To specify a current probe place a statement with the following syntax in your netlist Name in out iprobe n Name is the unique netlist name for the current probe component The measured current also receives this nam
61. as a filter so that you do not save all process parameters to the file If you do not want to filter the list of process parameters do not specify this parameter This specifies the run that Monte Carlo begins with The default is 1 If irstrunis specified as a number n where n is greater than one the previous n 1 iterations are skipped The Monte Carlo analysis behaves as if the first n 1 iterations were run without performing the child analyses for those iterations The subsequent stream of random numbers generated for the remaining iterations is the same as if the first n 1 iterations were run By specifying the first iteration number you can reproduce a particular run or sequence of runs from a previous experiment for example to examine an earlier case in more detail Note To reproduce a run or sequence of runs you need to specify the same value for the seed parameter This parameter specifies the type of statistical variation to apply B process batch to batch variations only B mismatch per instance variations only B all both process and mismatch variations applied The default is process This assumes that you have specified the appropriate statistical distributions in the statistics block You cannot request that mismatch variations be applied unless you have specified mismatch statistics in the statistics block mismatch variations work only on components inside of subcircuits You cannot request that proces
62. be varied The Spectre simulator does however perform the requested sensitivity analysis for appropriate parameters The ana are the analyses for which sensitivities are calculated These can be analysis instance names for example opBegin and ac2 or analysis type names for example DC and AC Examples of the sens Command The following examples illustrate sens command format sens ql betadc 2 Out to vcc dc nbjtl rb for analDC This command computes DC sensitivities of the bet adc operating point parameter of transistor q1 and of nodes 2 and Out to the dc voltage level of voltage source vcc and to the model parameter rb of nb jt 1 The values are computed for DC analysis analDc The results are stored in the files analDC vcc dc and analDC nbjt1 rb sens 1 n2 7 to ql area nbjtl rb for analAC This command computes AC sensitivities of nodes 1 n2 and 7 to the area parameter of transistor q1 and to the model parameter rb of nb jt1 The values are computed for each frequency of the AC analysis analAc The results are stored in the files analAC ql area and analAC nbjtl rb July 2002 149 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses sens vbb p ql1 int c ql gm 7 to ql area nbjtl rb for analDCl This command computes DC sensitivities of the branch current vbb p the operating point parameter gm of transistor q1 the internal collector voltage gq1 int_c and the node 7 voltage to t
63. bulk diode d2 s b diodel r 10 source bulk diode ends mos d Here the operating point vds for the inline component is reported correctly because there are no extra nodes introduced by the inline subcircuit model However the reported ids for the inline device is not the same as the current flowing into terminal a because some of the current flows into the transistor and some through diode d1 Parameterized Models Inline subcircuits can be used in the same way as regular subcircuits to implement parameterized models When an inline subcircuit contains both a parameterized model and an inline device referencing that model you can create instances of the device and each instance automatically gets an appropriately scaled model assigned to it For example the instance parameters of an inline subcircuit can represent emitter width and length of a BJT device Within that subcircuit a model statement can be created that is parameterized for emitter width and length and scales accordingly When you instantiate the subcircuit you supply the values for the emitter width and length and the device is July 2002 99 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features instantiated with an appropriate geometrically scaled model Again the inline device does not get a hierarchical name and can be probed in the same manner as if it were a simple device and not actually embedded in a subcircuit
64. circuit simulator models and AHDL modules in Spectre netlists This chapter describes the powerful modeling capabilities of Spectre including m Instance Component or Analysis Parameters on page 77 Parameters Statement on page 82 Expressions on page 84 Subcircuits on page 90 Inline Subcircuits on page 96 Binning on page 104 Scaling Physical Dimensions of Components on page 115 N Ports on page 117 Instance Component or Analysis Parameters In this section you will learn about the types of component or analysis parameter values the Spectre circuit simulator accepts and how to specify them Types of Parameter Values Spectre component or analysis parameters can take the following types of values W Real or integer expression consisting of Q Literals Q Arithmetic or Boolean operators July 2002 77 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features Q Predefined circuit or subcircuit parameters Q Built in constants fixed values or mathematical functions software routines that calculate equations Q Real or integer constants The name of a component instance or model The name of a component parameter A character string must be surrounded by quotation marks A name from a predefined set of names available to specify the parameter value enumerated types Parameter Dimension Component or analysis parameters can be either scalar or vector If a
65. creating a completely new netlist you can use the include statement to insert your old files into the netlist at the location you want Note The Spectre simulator always assumes that the file being included is in SPICE language mode unless the extension of the filename is scs Formatting the include Statement You can use any of two formatting options for the include statement When you want to use C preprocessor CPP macro processing capabilities within your inserted file use the second format include These are the two format options include filename include filename The first option include is performed by the Spectre simulator itself The second option include is performed by the CPP You must use the include option when you have macro substitution in the inserted file Note CPP is not supported in Spectre Direct Rules for Using the include Statement Remember the following rules and guidelines when using the include statement B You must use the include format if you want the CPP to process the inserted file Also you must specify that the CPP be run using the command line option when you start the Spectre simulator m Regardless of which include format you use you can use the 1 command line option followed by a path to have the Spectre simulator look for the inserted files in a specified directory in addition to the current directory just as you would for the CPP include July 2002 70 P
66. default setting a11 five settings are possible for this parameter gmin stepping gmin source stepping source the pseudotransient method ptran and the damped pseudotransient method dpt ran You can also prevent the use of continuation methods by setting the homotopy parameter to none July 2002 246 Product Version 5 0 Spectre Circuit Simulator User Guide 11 Managing Files This chapter discusses the following topics B About Spectre Filename Specification on page 247 B Creating Filenames That Help You Manage Data on page 247 About Spectre Filename Specification Many analysis statements require a filename as a parameter value for the input or output of data It is often easier to keep track of output files if these filename parameter values are related to some other filename typically the input filename The Spectre circuit simulator s filename specification features help you manage your data by letting you systematically specify or modify filenames With the Spectre simulator you can easily identify data from multiple simulation runs or from single runs containing repeated similar analyses You can modify input filenames so that you can easily identify the output file from a specific simulation or analysis You can also construct output filenames in ways that prevent accidental overwriting of data Creating Filenames That Help You Manage Data The Spectre simulator helps you keep track of simulation data by let
67. eed wae wd 15 1 Introducing the Spectre Circuit Simulator 16 Improvements ovet SPICE 2244s d saves a Ehe RERERERXUEES ud tA pe eee ely 16 Improved Capacity 4 5 290i ei tuo E ep SebSpRELEPLSE ete tel eee DRE E ees 16 improved ACOU BO i6 ud caduto Dir deti ke ae Bone OE aay Die dd bed bd iud poh aoe aceon fe 17 Improved Speed EE 18 Improvec Heliabiliby 6x3 94109 VI eI DDR E ones E A orn Ae px oa he dts ea aa ed 18 Iimpr ved Models 1 22 20 12 3 309 9r cia Doa aa scr Po SEAE DR ata atia d Vie eae cart 19 Spectre Usability Features and Customer Service llllllsuun 19 Analog HDLS 15st huni aa diea ea Mta Mee ey Meet ie eade d buo ER pi t s Adae 20 RE Capabilti s petetichnieet ties tte tes het LLL MNRSQREEDeR Bt 21 Mixed Signal Simulation 4 5 2hatigestwdtawneud pas APRES eae aeet ee E RENE 23 ENVIFONMENIS 33 dens REGIGECIRRGCEUNR or aS bh cesta se retos uk CRUCE EUER E 23 2 Getting Started with Spectre sooeooosusuuuuuuu 24 Using the Example and Displaying Results llli 24 Sample Schematic 2 4 An erste ds e D e She orate d coke RUE LC i e ep tat teas 25 Sample Netlist 2243 05 tates EX Ey dy o ate bue ta eoe hb dae eee ed 26 Elements of a Spectre Netlist 2 0 0 0 0 2c eee eens 27 Instructions for a Spectre Simulation Run n aaas aaeeea 30 Following Simulation Progress x nx Re RESQUE RA RR E en RR E 31 ScreenmPHImOUED ers EAD EAS ICI uve dn Sided pele oe tet 31
68. either as c 1pf or c 1e 12 Depending on whether you are using the Spectre Netlist Language or SPICE you might need to use different scale factors for parameter values Only ANSI standard scale factors are used in Spectre netlists For more information about scale factors see Instance Statements on page 61 Control Statements The next section of the sample netlist contains a control statement which sets initial conditions Model Statements Some components allow you to specify parameters common to many instances using the model statement The only parameters you need to specify in the instance statement are those that are generally unique for a given instance of a component You need to provide the following for a model statement B The keyword model at the beginning of the statement m A unique name for the model reference by master names in instance statements B The master name of the model identifies the type of model B The parameter values associated with the model The following example is a model statement for a bjt The model name is npn and the component type name is bjt The backslash tells you that the statement continues on the July 2002 29 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre next line The backslash must be the last character in the line because it escapes the carriage return model npn bjt type npn bf 80 rb 100 vaf 50 cjs 2pf tf 0 3ns tr 6ns
69. help spectre h For example the July 2002 213 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options following is the instance definition of a microstrip line The terminal names are t 1 b1 t2 and b2 Name t1 bl t2 b2 msline parameter value q A terminal index The terminal index is a number that indicates where a terminal is in the instance definition You give the first terminal a terminal index of 1 the second a terminal index of 2 and so on In this example the terminal indexes are 7 for sink and 2 for Src Name sink src isource parameter value q Aname of an operating point parameter from the lists of parameters for each component in the Spectre online help q The name of a SpectreHDL Verilog A internal variable q Oneofthe following keywords currents To save all currents of the device static To save resistive currents of the device displacement To save capacitive currents of the device dynamic To save charge or flux of the device oppoint To save the operating points of the device probe To measure current of the device with a probe pwr To save power dissipated on a circuit subcircuit or device all To save all signals of the device n subcircuitName is the instance name of a subcircuit call Saving terminal currents for subcircuit calls is the same as saving terminal currents for other instance statements except that you must identify individual terminal currents yo
70. included files For all other design data Analog Artist produces netlists in the Spectre native syntax You can enable the use of the SPICE Reader by choosing the Setup Environment form and toggling the Use SPICE Netlist Reader spp button to Y Be sure that you do not have any relative paths specified for included files such as model files and that the Include Path field inthe Setup gt Simulation Files field is blank The SPICE Reader s inability to handle relative paths is documented in the Spectre Known Problems and Solutions Running the SPICE Reader from the Command Line When you run Spectre from the command line outside of the Artist Composer environment the SPICE Reader is disabled by default As described in Running the SPICE Reader on July 2002 43 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility page 42 you must use the spect respp command for the SPICE Reader to process the top level netlist spectrespp opamp sp This command calls Spectre with the spp and md1 command line options There are several command line options that can be used in conjunction with spect respp Specifying the design file The command line option design is used to identify the input file In the absence of any command line options the single argument after the spect respp command is assumed to be the input netlist Therefore the following commands are identical spectrespp opamp sp spectrespp desi
71. info what models where logfile extremes only For a complete description of the parameters available with the info statement consult the lists of analysis and control statement parameters in the Spectre online help spectre h Printing the Node Capacitance Table The Spectre simulator allows you to print node capacitance to an output file This can help you in identifying possible causes of circuit performance problems due to capacitive loading The capacitance between nodes x and y is defined as July 2002 194 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements oq xy ov where qx is the sum of all charges in the terminal connected to node x and v is the voltage at node y The total capacitance at node X is defined as dq x E on X where charge q and voltage v are at the same node x You may use the captab analysis to display the capacitance between the nodes in your circuit This is an option in the info statement Here is an example of the info settings you would set to perform a captab analysis Parameter Setting Action Taken what captab Performs captab analysis The default value is oppoint where logfile Prints the parameters to a logfile Other possible values are nowhere screen and file The value rawfileis not supported for node capacitance title captab Prints captab as the title of the analysis in the output file threshold 0 Specifies the threshold capacitance
72. mA 15 91 uA The 3 477 mA is the dc operating value of i vdd and 15 91 uA is the 3 sigma variation due to the device mismatches The device mp6 contributes the most to the output variation at 13 8 uA followed by m01 which contributes 6 99 uA The equivalent 3 sigma Vth variation of mp6 is 2 21 mV The relative 3 sigma beta current factor variation of mp6 is 0 35796 The equivalent 3 sigma gate voltage variation is 2 26 mV The relative 3 sigma Ids variation of mp6 is 1 7196 The output can also be written in psf and you can view the table using Analog Design Environment The following statement investigates the 3 sigma dc variation on output v n1 n2 The result of the analysis is printed in a psf file and the cpu statistics of the analysis are generated dcmm2 n1 n2 dcmatch mth 1e 3 where rawfile In the following example the output is the voltage drop across the 1st port of r3 dcmm3 dcmatch mth 1e 3 oprobe r3 portv 1 For the following statement the output of the analysis is printed to a file circuitName info what dcmm4 n3 0 dcmatch mth le 3 where file file C r info what You can use sweep parameters on the dcmatch analysis to perform sweeps of temperature parameters model instance subcircuit parameters etc In the following example the device parameter w of the device x1 mp2 is swept from 15um to 20um at each increment of 1pm demm6 n3 0 dcmatch mth 0 01 dev xl mp2 param w start 15e 6 stop 20e 6 step le
73. multiplication factor in 64 parameters 82 range checking for parameter values 271 saving groups of signals 208 220 saving individual signals 203 215 subckts as pwr option 206 218 suppressing messages 274 sweep limits setting 159 sweeping parameters See parameter sweeps 156 swept periodic steady state SPSS analysis brief description of 21 synopsis fourier 151 syntax conventions 58 system generated messages controlling 233 I t colon modifier 251 T predefined percent code 249 tdr analysis brief description of 130 Temp 74 temp parameter 90 158 in alter statement 186 244 tempeffects parameter 200 temperature changing with alter statement 186 244 in Celsius 74 terminal index subcircuit calls 203 214 use in save statement 202 214 terminal name use in save statement 202 213 Product Version 5 0 Spectre Circuit Simulator User Guide terminals as info statement parameter 193 223 terminal to node map 193 223 terminations of Spectre because of a Spectre error condition 230 by the operating system 230 manual 231 normal 230 recovering from transient analysis 231 with an error in an analysis 230 testing values of subcircuit parameters 271 time not increasing error message 257 time domain reflectometer tdr analysis brief description of 130 time step adjustment 144 time step control algorithm advantages of 17 timestep used minimum 26
74. n Parameters that control temperature n Parameters that select output data n Parameters that help solve convergence difficulties n Parameters that control error handling and annotation For a complete list of the parameters you can set with the opt ions statement consult the Spectre online help spectre h July 2002 198 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements options Statement Form at The options statement format is as follows Name options parameter value Name is a unique name you give to the opt ions statement The Spectre simulator uses this name to identify this statement in error or annotation messages options is the keyword options the primitive name for this control statement Parameter value is an options statement parameter followed by an equal sign and the value you choose for the parameter You can enter any number of parameter specifications with a single opt ions statement options Statement Example The following is a correctly formatted opt ions statement Examp options rawfmt psfbin audit brief temp 30 save lvlpub nestlvl 3 rawfile C r raw useprobes no The example sets the rawfmt audit temp save nestlvl rawfile and useprobes parameters for an opt ions statement named Examp The backslash at the end of the first line is a line continuation character Nonnumerical parameter values are chosen from the possible values listed in the Spectre online help spectre
75. not accurate below 0 C TooHot paramtest warnif temp gt 55 message The nmos model is not accurate above 55 C 724 Define inline subcircuit that implements automatic model selection this uses user supplied parameters 1 and w which represent devic geometry and the built in parameter temp to perform model binning based on both geometry and temperature inline subckt nmos dg s b parameters l lum w lum ls lum ld 1um Complain if subcircuit parameters are out of rang 124 TooShort paramtest warnif l lt lum message Channel length for nmos must be greater than lu TooThin paramtest warnif w lum message Channel width for nmos must be greater than lu ooNarrow paramtest warnif ls lt lum warnif ld lt lum message Stripe width for nmos must be greater than lu Model selection July 2002 113 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features include models scs include all model definitions include select_model scs section typical include code to auto choose models ends nmos Set the temperatur nmosSetTempTo27C alter param temp value 27 The following file models scs contains the models which depend on circuit temperature temp Each model parameter can take on one of two values depending on the value of parameter t emp
76. of transistors and diodes 276 replacing DC analysis with transient analysis to correct 276 restarts to correct 276 rforce parameter increasing with nodesets 276 step size 275 system messages helpful 274 temperature sweeps to correct 276 topcheck parameter enabling 275 transient analysis 277 unusual parameter values checking for 275 corners example 111 correlation coefficients correlation statements CPP C preprocessor defaults 233 using the include statement with 70 175 174 crigm parameter 177 criids parameter 177 criuo parameter 177 crivth parameter 177 cshrc file and environment defaults 234 Cadence range limits 263 current probes correcting convergence problems with 275 probe statement 205 217 saving individual currents with setting multiple 209 221 setting with the save statement 204 21 205 Product Version 5 0 Spectre Circuit Simulator User Guide 217 when to use 204 21 currents parameter example 209 221 formatting 209 221 not used in subcircuit calls 203 21 options statement 209 221 customer service contacting 19 256 customizing error and warning messages 262 percent codes 249 D D predefined percent code 249 damped pseudotransient method 245 data compression 146 dataDir command line option 32 DC analysis 138 brief description of 129 correcting accuracy problems 277 maxiters parameter and convergence problems 275 oppoint parameter 157 transfer curves
77. parameter P1 whose value is 5000 and you specify a standard deviation of 100 the actual distribution is produced such that log P N og 5000 100 m Uniform This distribution is specified using dist unif The uniform distribution for parameter x is generated according to July 2002 172 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses x unif mean N mean N such that the mean value is the nominal value of the parameter x and the parameter is varied about the mean with a range of N The standard deviation is not specified for the uniform distribution but its value can be calculated from the formula std N sqrt 3 The nominal value for the uniform distribution is the value of the parameter before the Monte Carlo analysis is run The uniform interval is specified using the parameter N For example specifying dist unif N 5 fora parameter whose value is 200 results is a uniform distribution in the range 200 N that is from 195 to 205 You can also specify percent yes in which case the range is 200 N that is from 190 to 210 Derived parameters that have their default values specified as expressions of other parameters cannot have distributions specified for them Only parameters that have numeric values specified in their declaration can be subjected to statistical variation Parameters that are specified as correlated must have had an appropriate variation specified for them in the statistics block For exa
78. power supplies have substantial amounts of signal latency If unchanged signal values for these circuits are repetitively written for each time point to a transient analysis output file this output file can become very large You can reduce the size of output files for such transient analyses with the Spectre simulator s data compression feature With data compression the Spectre simulator writes output data for a signal only when the value of that signal changes Using data compression is not always appropriate The Spectre simulator writes fewer signal values when you turn on data compression but it must write more data for every signal value it records For circuits with small amounts of signal latency data compression might actually increase the size of the output file You turn on data compression by adding the parameter compression yes to the transient analysis command line in a Spectre netlist DoTran z12 tran start 0 stop 003 step 0 00015 maxstep 6e 06 compression yes You cannot apply data compression to operating point parameters including terminal currents that are calculated internally rather than with current probes If you want data compression for terminal currents you must specify that these currents be calculated with current probes You can specify that all currents be calculated with current probes by placing useprobes yes in an options statement July 2002 146 Product Version 5 0 Spectre Circuit Simulator User Gu
79. problems The first strategy is to reduce the effect of discontinuities in nonlinear capacitors The second method is to eliminate discontinuous jumps in the solution Try the following suggestions if you have difficulty with transient analysis convergence m Use a complete set of parasitic capacitors on nonlinear devices to avoid jumps in the solution waveforms Specify nonzero source and drain areas on MOS models m Use the cmin parameter to install a small capacitor from every node in the circuit to ground This usually eliminates any jumps in the solution If you can identify a nonlinear capacitance that might have a discontinuity simplify the nonlinear capacitor model If you cannot actually simplify the model modifying it might help convergence B As alast resort relax the tolerance values for the lteratio or reltol parameters and widen transitions in the stimulus waveforms Correcting Accuracy Problems If you need greater accuracy from a Spectre simulation the most common solution is to tighten the reltol parameter of the options or set statements In addition be sure that the absolute tolerance parameters vabstol and iabstol are set to appropriate values If tightening xe1tol does not help or if it greatly slows the simulation try the additional suggestions in the following sections Suggestions for Improving DC Analysis Accuracy B Be sure there are no errors in the circuit Use the computed DC solution and the opera
80. setting the save parameter The nest 1v1 parameter controls how many levels are returned The set Statement Except for temperature parameters and scaling factors you use the set statement to modify any options statement parameters you set at the beginning of the netlist The new settings apply to all analyses that follow the set statement in the netlist You can change the initial settings for the state of the simulator by placing a set statement in the netlist The set statement is similar to the opt ions statement that sets the state of the simulator but it is queued with the analysis statements in the order you place them in the netlist You use the set statement to change previous options or set statement specifications The modifications apply to all analyses that follow the set statement in the netlist until you request another parameter modification The set and options statements have many identical parameters but the set statement cannot modify all options statement parameters The parameter listings in the Spectre online help tell you which parameters you can reset with the set statement The following example demonstrates the set statement syntax This example turns off several annotation parameters Quiet set narrate no error no info no n Quiet is the unique name you give to the set statement n The keyword set is the primitive name for the set statement n narrate error and info are the parameters you are changing Ju
81. stop 10M dec 10 readns C r dc25 please3 alter dev Vfb param mag value 0 annotate no XF XferVsFreq xf start 1 Hz stop 10M dec 10 probe Rload Transient StepResponse tran stop 250u please4 alter dev Vin param type value sin SineResponse tran stop 150u Multiple Analyses in a Subcircuit You might want to run complex sets of analyses many times during a simulation To simplify this process you can group the set of analyses into a subcircuit Because subcircuit definitions can contain analyses and control statements you can put the analyses inside a single subcircuit and perform the multiple analyses with one call to the subcircuit The Spectre simulator performs the analyses in the order you specify them in the subcircuit definition Generally you do not mix components and analyses in the same subcircuit definition For more information about formats for subcircuit definitions and subcircuit calls see Chapter 6 Analyses July 2002 136 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Example The following example illustrates how to create and call subcircuits that contain analyses Creating Analysis Subcircuits subckt sweepVcc parameters start 0 stop 10 Ib 0 omega 1G steps 100 setIbb alter dev Ibb param dc value Ib SwpVccDC dc start start stop stop dev Vcc lin steps 2SwpVccAC ac dev Vcc start start stop stop lin steps freq omega 6 283185 ends sweepVcc This examp
82. sweep July 2002 157 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses and an operating point the operating point information is generated for the last point in the sweep Setting Up Parameter Sweeps To specify a parameter sweep you must identify the component or circuit parameter you want to sweep and the sweep limits in an analysis statement A parameter you sweep can be circuit temperature a device instance parameter a device model parameter a netlist parameter or a subcircuit parameter for a particular subcircuit instance Within the sweep analysis only you specify child analyses statements These statements must be bound with braces The opening brace is required at the end of the line defining the sweep Specifying the Parameter You Want to Sweep You specify the components and parameters you want to sweep with the following parameters Parameter Description dev The name of an instance whose parameter value you want to sweep sub The name of the subcircuit instance whose parameter value you want to sweep mod The name of a model whose parameter value you want to sweep param The name of the component parameter you want to sweep freq For analyses that normally sweep frequency small signal analyses such as ac if you sweep some parameter other than frequency you must still specify a fixed frequency value for that analysis using the freq parameter paramset For the sweep analysis only allows
83. the DC sweep Drift dc param temp start 0 stop 50 0 step 1 readns ua741 dc write ua741 dc Drift dc param temp start 0 stop 50 0 step 1 readns ua741 dc writefinal ua741 dc July 2002 190 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Creating a State File Manually The syntax for creating a state file in a text editor is simple Each line contains a signal name and a signal value Anything after a pound sign is ignored as a comment The following is an example of a simple state file State file generated by Spectre from circuit file wilson during stepresponse at 5 39 38 PM jan 21 1992 1 588793510612534 2 1 17406247989272 3 14 9900516233357 pwr 15 VCC p 9 9483766642647e 06 Reading State Files To read a state file as an initial condition use the read transient analysis parameter To read a state file as a nodeset use the readns parameter This example reads the file int Cond as initial conditions DoTran z12 tran start 0 stop 0 003 step 0 00015 maxstep 6e 06 read intCond This second example reads the file soluEst as a nodeset DoTran_z12 tran start 0 stop 0 003 step 0 00015 maxstep 6e 06 readns soluEst Special Uses for State Files State files can be useful for the following reasons n You can save state files and use them in later simulations For example you can save the solution at the final point of a transient anal
84. the analog circuit design environment under the Cadence design framework II To see how the Spectre circuit simulator is run under the analog circuit design environment read the Cadence Analog Design Environment User Guide m Tlolearn more about specific parameters of components and analyses consult the Spectre online help spectre h orthe Spectre Circuit Simulator Reference manual B Tlolearn more about the equations used in the Spectre circuit simulator consult the Spectre Circuit Simulator Device Model Equations manual July 2002 13 Product Version 5 0 Spectre Circuit Simulator User Guide Preface B The Spectre circuit simulator also includes a waveform display tool Analog Waveform Display AWD to use to display simulation results For more information about AWD see the Analog Waveform User Guide B For more information about using the Spectre circuit simulator with SpectreHDL see the SpectreHDL Reference manual W For more information about using the Spectre circuit simulator with Verilog A see the Verilog A Language Reference manual B f you want to see how SpectreHF is run under the analog circuit design environment read SpectreRF Help m For more information about RF theory see SpectreRF Theory m For more information about how you work with the design framework II interface see Cadence Design Framework II Help B For more information about specific applications of Spectre analyses see The
85. time points If you use too few time points the polynomials deviate slightly from the true waveform between time points and all of the computed Fourier coefficients are slightly in error The algorithm that computes the Fourier integral does accept unevenly spaced time points but because it uses quadratic interpolation it is usually more accurate using time steps that are small and nearly evenly spaced This device is not supported within altergroup Instance Definition Name p n pr nr ModelName parameter value Name p n pr nr fourier parameter value The signal between terminals p and n is the test or numerator signal The signal between terminals pr and nr is the reference or denominator signal Fourier analysis is performed on terminal currents by specifying the term or refterm parameters If both term and p orn are specified then the terminal current becomes the numerator and the node voltages become the denominator By mixing voltages and currents it is possible to compute large signal immittances Model Definition model modelName fourier parameter value DC Match Analysis This analysis computes the 3 sigma variance of dc voltages or currents at the specified outputs due to device mismatches You need to specify the mismatch parameters in the model cards for each device that contributes to the deviation The analysis uses the device mismatch models to evaluate an equivalent mismatch current sourc
86. to Gear s second order backward difference formula method gear2only B Ifa low loss resonator exhibits too much loss set the integration method in the transient analysis to the trapezoidal rule method t raponly W Ifthe initial conditions used by the Spectre simulator are not the same as the ones you specified decrease the rforce parameter in the options or set statements until the initial conditions are correct m I the Spectre simulator does not accurately follow the turn on transient of an oscillator set the maxstep parameter of the transient analysis to one tenth the size of the expected period of oscillation or less July 2002 278 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits This appendix contains example netlists for testing the BSIM3v3 standard model Notes on the BSIM3v3 Model on page 280 Spectre Syntax on page 280 SPICE BSIM 3v3 Model on page 280 Spectre BSIM 3v3 Model on page 281 Ring Oscillator Spectre Deck for Inverter Ring with No Fanouts inverter_ring sp on page 281 Ring Oscillator Spectre Deck for Two Input NAND Ring with No Fanouts nand2 ring sp on page 283 Ring Oscillator Spectre Deck for Three Input NAND Ring with No Fanouts nandS ring sp on page 284 Ring Oscillator Spectre Deck for Two Input NOR Ring with No Fanouts nor2 ring sp on page 286 Ring Oscillator Spectre Deck for Three Input NOR Ring with No Fanouts nor3 ring sp on page 287
87. vee NPNbjt Q16 vcc 4 9 vee NPNbjt Q17 11 9 10 vee NPNbjt Q18 13 12 17 vee NPNbjt Q20 vee 17 14 vcc PNPbjt Q23 vee 11 17 vcc PNPbjt Diodes Q8 vec 1 NPNdiode Q19 13 12 NPNdiode Resistors Rl 7 vee resistor r 1k R2 6 vee resistor r 1k R3 8 vee resistor r 50k R4 9 vee resistor r 50k R5 10 vee resistor r 100 R6 12 17 resistor r 40k R8 15 out resistor r 27 R9 14 out resistor r 22 Capacitors C1 4 11 capacitor c 30p Current Sources I1 16 vee isource dc 19u I2 vec 11 isource dc 550u July 2002 imax 5m rb 20 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses I3 vee 13 isource dc 180u ends ua741 Sources Vpos vcc gnd vsource dc 15 Vneg vee gnd vsource dc 15 Vin pin gnd vsource type pulse dc 0 val0 0 vall 10 width 100u period 200u rise 2u fall 2u tdi1 20 taul 20u td2 100u tau2 100u freq 10k ampl 10 delay 5u file sinel0 scale 10 0 stretch 200 0e 6 Vfb nin out vsource Op Amps OA1 pin nin out ua741 Resistors Rload out gnd resistor r 10k Analyses DC operating point pleasel alter param temp value 25 annotate no OpPoint dc print yes readns C r dc25 write C r dc25 Temperature Dependenc Drift dc start 0 stop 50 0 step 1 param temp readns SC r dcO write C r dc0 XferVsTemp xf start 0 stop 50 step 1 probe Rload param temp freq lkHz readns C r dc0 Gain please2 alter dev Vfb param mag value 1 annotate no OpenLoop ac start 1
88. with the nodeset statement include voltages on topological nodes including internal nodes and currents through voltage sources inductors switches transformers N ports and transmission lines The format for specifying signals with the nodeset statement is similar to that used by the save statement This method is described in detail in Saving Main Circuit Signals on page 213 Consult this discussion if you need further clarification about the following example nodeset Voff 0 X3 7 2 5 Ml int_d 3 5 L1 1 1u This example sets the following solution estimates n The voltage of node voff is set to 0 n Node 7 of subcircuit X3 is set to 2 5 V n Theinternal drain node of component M1 is set to 3 5 V See the table in the ic statements section of this chapter for more information about specifying internal nodes n The current for inductor L1 is set to 1p Specifying State Information for Individual Analyses You can specify state information for individual analyses in two ways n You can use the ic parameter of the transient analysis to choose which previous specifications are used n You can create a state file that is read by an individual analysis July 2002 189 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Choosing Which Initial Conditions Specifications Are Used for a Transient Analysis The ic parameter in the transient analysis lets you select among several options for which initia
89. x1 pwr n the power dissipated in the x1 x2 m1 MOSFET Power Options The pwr parameter in the opt ions statement can also be used to save power The following table shows the five possible settings for the pwr option Setting Action all The total power the power dissipated in each subcircuit and the power dissipated in each device is saved subckts The total power and the power dissipated in each subcircuit is saved devices The total power and the power dissipated in each device is saved total The total power dissipated in the circuit is calculated and saved none No power variable is calculated or saved This is the default setting For example opts options pwr total save xl pwr This creates two power signals pwr generated by the options statement and x1 pwr generated by the save statement July 2002 206 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Saving Groups of Signals To save groups of signals as results you use the save and nest 1v1 parameters You specify which signals you want to save with the save parameter You use the nest 1v1 parameter when you save signals in subcircuits The nest 1v1 parameter specifies how many levels deep into the subcircuit hierarchy you want to save signals You can set these parameters as follows n In options statements or set statements If you set the save and nest 1v1 parameters with an options ora set statement the set
90. 0 L2 n12 n2 inductor 1 r0 0 9705 6 2832 bw C3 m2 Q capacitor c 2 2034 6 2832 bw r0 L3 n2 0 inductor l r0 bw 2 2034 6 2832 fc fc ends filter The paramtest component checkFreqs has no terminals and no effect on the simulation results It monitors its parameters and issues a message if a given condition is satisfied by evaluating to a nonzero number In this case errorif specifies that the Spectre simulator issues an error message and stops the simulation If you specify printif the Spectre simulator prints an informational message and continues the simulation If you specify warnif the Spectre simulator prints a warning and continues For more information about specific parameters available with the pa ramt est component see the parameter listings in the Spectre online help spectre h Inline Subcircuits An inline subcircuit is a special case where one of the instantiated devices or models within the subcircuit does not get its full hierarchical name but inherits the subcircuit call name The inline subcircuit is called in the same manner as a regular subcircuit You format inline subcircuit definitions as follows inline subckt SubcircuitName lt nodel gt lt nodeN gt Depending on the use model the body of the inline subcircuit typically contains one of the following m Multiple device instances one of which is the inline component m Multiple device instances one of which is
91. 0 256 Cadence parameter storage format PSF 224 235 Cadence range limits defaults 263 Cadence Signal Scan output format Cadence waveform storage format 224 WSF 224 Calculator Window 34 cards A Z 51 dot 51 title 51 center parameter check statement controlling checks on parameter values 186 269 example 186 269 formatting 186 269 what parameter 186 187 269 270 checking simulation status 230 checkpoint files automatic creation after interrupts 232 creating automatically 232 creating from the commandline 232 specifications for a single analysis 233 checkpoint spectre command option 232 checks on parameter values controlling the number of 269 choosing output file formats 224 circuit age controlling for 175 example 178 circuit parameters 82 CIW Command Interpreter Window ckptperiod parameter in transient analysis 233 closed loop gain in netlist example of measuring 135 CMI compiled model interface description 19 CMI versioning 295 colon modifiers colon character chaining 252 e extension examples 252 formatting 252 th head 251 of input filenames 251 159 34 251 251 Product Version 5 0 Spectre Circuit Simulator User Guide r root 251 t tail 251 colons in Spectre syntax 59 Command Interpreter Window CIW 34 comments formatting for 59 compatible parameter 200 compiled model interface CMI description 19 components naming 28 59 rules fornames 5
92. 0 title card 27 title line 27 51 title parameter in Monte Carlo analysis 168 tnom parameter 90 in alter statement 186 244 tolerances setting with the options statement 199 Toshiba model for hot electron degradation simulation 176 total as pwroption 206 218 tran analysis brief description of 130 transfer curves 157 transfer function analysis xf brief description of 130 transient analysis accuracy 143 brief description of 130 ckptperiod parameter example 233 convergence problems 277 correcting accuracy problems 278 error tolerances See error tolerances 142 ic parameter 187 238 improving convergence 144 integration method 143 read parameter for state files readns parameter for state files 241 restarting 233 specifying initial conditions in 191 241 191 Coo 187 23 July 2002 speed 143 terminations recovering from 231 transistors requesting breakdown region warnings for 269 Spes forbidden operating regions Or trap integration method parameter trapezoidal rule integration method traponly integration method parameter 141 143 trigonometric functions 86 truncate statement 173 truncation factor 173 tutorial for using Spectre 24 two port test circuit sample input file 117 typographical conventions 14 U U 75 uA741 operational amplifier sample input file 134 unif parameter 172 uniform distribution unitless 75 UNIX commands and environment defaults
93. 03 models in 1ibphilips so the developer can create a CMI configuration file in the home directory as follows this is SHOME cmiconfig file I want to include libphilips so released by Cadence so that I can check my BJT with BJT503 load libphilips so I also want to include my BJT model from libmybjt so append SHOME myLib load libmybjt so CMI Versioning The version format for CMI is ma jor minor The value of ma jor is increased when there are major changes that require CMI developers to recompile their components Type spectre cmiversion to display the current CMI version The Spectre circuit simulator checks for CMI version compatibility for each shared object as well as for each primitive This ensures that WB A shared object is compiled with the latest version of CMI m The source code for each device primitive is up to date Note A primitive can be installed only once Different versions of the same primitive cannot be used July 2002 295 Product Version 5 0 Spectre Circuit Simulator User Guide Index Symbols codes 233 predefined 248 predefined percent code 249 in syntax 1 in Spectre syntax 59 colon modifier 251 in syntax 14 in vectors 78 V in Spectre syntax 59 in syntax 15 in syntax 14 A A predefined percent code 248 absolute error tolerance 142 abstol parameter 74 142 AC analysis 139 AC analysis brief description of 129 accuracy correcting pr
94. 10 Creating Recovery Files from the Command Line You can create a checkpoint file when a transient analysis is running with a UNIX interrupt signal from the command line gt Tocreate a checkpoint file from the command line send a USR2 signal with a UNIX k 111 command kill USR2 lt PID gt You find the necessary process identification number by running the UNIX ps utility The Spectre simulator also attempts to write a checkpoint file after QUIT TERM INT or HUP interrupts After other interrupt signals the Spectre simulator might be unable to write a checkpoint file July 2002 232 Product Version 5 0 Spectre Circuit Simulator User Guide Running a Simulation Setting Recovery File Specifications for a Single Analysis When you specify a transient analysis you can also create periodic checkpoint files for that analysis gt Tocreate periodic checkpoint files for a transient analysis set the ckptperiod parameter in the transient analysis statement The following example creates a checkpoint every 20 seconds during the transient analysis SineResponse SineResponse tran stop 150u ckptperiod 20 Restarting a Transient Analysis gt Torestart a transient analysis from the last checkpoint file start the simulation again with the spect re command Make sure to enter the recover command line argument Controlling Command Line Defaults There are many run options you can specify with either the spectre command
95. 2 2 isc 0 nc 1 5 rb 115 re 1 rc 30 5 cje 1 08e 13 vje 0 995 mje 0 46 tf 1le 11 xtf 1 itf 1 5e 2 cjc 2 2e 13 vjc 0 42 mjc 0 22 xcjc 0 1 tr 4e 10 cjs 1 29e 13 vjs 0 65 mjs 0 31 xtb 1 5 eg 1 232 xti 2 148 fc 0 875 The following example creates two instances of a bjt transistor model al C Bl a2 C B2 S NPNbjt S NPNbjt2 y an Dp an Basic model Statement Rules When you use the model statement m You can have several model statements for a particular component type but each instance statement can refer to only one model statement B Occasionally a component allows a parameter to be specified as either an instance parameter or as a model parameter If you specify it as a model parameter it acts as a default for instances If you specify it as an instance parameter it overrides the model parameter July 2002 69 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists m Values for model parameters can be expressions of netlist parameters Input Data from Multiple Files If you want to use data from multiple files you use the include statement to insert new files When the Spectre simulator reads the include statement in the netlist it finds the new file reads it and then resumes reading the netlist file If you have older netlist files you want to incorporate into your new larger netlist the include statement is particularly helpful Instead of
96. 2 Passed x1 m2 0 059703 7 1226 7 1189 7 0997 Passed x10 m2 0 059668 7 1189 7 1151 7 096 Passed x4 m2 0 059025 7 0498 7 0461 7 0271 Passed x8 m2 0 058728 7 0178 7 0141 6 9952 Passed x4 m1 0 055291 6 6471 6 6447 6 6324 Passed x1 m1 0 049069 5 9699 5 9677 5 9566 Passed x10 m1 0 044038 5 4161 5 4141 5 4039 Passed x6 m1 0 044 5 4119 5 41 5 3998 Passed x8 m1 0 04301 5 3021 5 3002 5 2902 Passed x9 m2 0 030815 3 9276 3 9255 3 9145 Passed x5 m2 0 030724 3 9171 3 915 3 9041 Passed x7 m2 0 030223 3 8597 3 8576 3 8468 Passed x11 m2 0 030096 3 845 3 8429 3 8322 Passed July 2002 182 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements The Spectre circuit simulator lets you place a sequence of control statements in the netlist You can use the same control statement more than once Different Spectre control statements are discussed throughout this manual The following are control statements n The alter and altergroup Statements on page 183 n The check Statement on page 186 n Theic and nodeset Statements on page 187 n Theinfo Statement on page 192 n The options Statement on page 198 n The paramset Statement on page 200 n The save Statement on page 201 n The set Statement on page 210 n The shell Statement on page 211 n The statistics Statement on page 211 The alter and altergroup Statements You modify individual parameters for devices models circuit and subcircuit parameters during
97. 200 dcop2 dc tran2 tran start 0 stop lu export slewrate oceanEval slewRate v V voutV 10n t 30n t 10 90 July 2002 169 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses The following Monte Carlo analysis statement applies both process and mismatch variations mc3 montecarlo saveprocessparams yes variations all numruns 200 dcop3 dc tran3 tran start 0 stop 1lu export slewrate oceanEval slewRate v V voutV 10n t 30n t 10 90 Specifying Parameter Distributions Using Statistics Blocks The statistics blocks are used to specify the input statistical variations for a Monte Carlo analysis A statistics block can contain one or more process blocks which represent batch to batch type variations and or one or more mismatch blocks which represent on chip or device mismatch variations in which the distributions for parameters are specified Statistics blocks can also contain one or more correlation statements to specify the correlations between specified process parameters and or to specify correlated device instances such as matched pairs Statistics blocks can also contain a truncate statement that can be used for generating truncated distributions The statistics block contains the distributions for parameters W Distributions specified in the process block are sampled once per Monte Carlo run are applied at global scope and are used typically to represent batch to batch process variatio
98. 22 0 96 0 17 0 96 0 17 0 03 0 23 15 0000 0 10 0 31 0 91 0 26 0 91 0 26 0 08 0 31 20 0000 20 016 0 37 0 85 0 35 0485 0 35 0 T14 0 37 25 0000 0 21 0 41 0 78 0 43 0 78 0 43 0 23 0 40 30 0000 0 27X 50 43 0 697 0 51l 05 69 04 51 0 34 20 38 END A line beginning with is treated as a comment and ignored The translator reads lines beginning with VAR which is uppercase to pick up the number of ports given by parameter NPORT impedance value given by R frequency scale factor given by FREQ UNIT and complex number format given by FORMAT The possible values of and treatments for the frequency scale factor and the complex number format comply with what was described for LIBRA format The translator treats a line beginning with as the S parameter format definition Data is expected after the line Currently the translator supports only a single set of data Anything after the first END line is ignored Spectre Format A Spectre S parameter file for three ports looks as follows S parameter data file port2 data Generated by spectre from circuit file gendata during analysis swp 12 13 06 PM Fri May 8 1998 reference resistance port3 137 is port p3 port2 137 is port p2 porti1 2137 is port pl format freq s33 real imag s23 real imag s13 real imag 32 real imag s22 real imag s12 real imag s31 real imag s21 real imag July 2002 125 Product Version 5 0
99. 229 state files 191 241 write parameter writefinal parameter subcircuit calls 94 subcircuit definitions 90 fourier 190 241 190 241 Product Version 5 0 Spectre Circuit Simulator User Guide component synopsis 151 model definition 151 Fourier analysis improvements in 17 fourier analysis 150 freq parameter 158 functions algebraic 86 hyperbolic 86 trigonometric 86 functions user defined 89 G GaAs traveling wave amplifier sample input file 92 gauss parameter 172 Gaussian distribution 172 gear2 integration method parameter 141 143 gear2only integration method parameter 141 143 gmin parameter increasing value with convergence problems 275 resetting to correct error conditions 255 setting to correct accuracy problems 277 278 warning about size of 259 gmin stepping 245 gmin as homotopy parameter option ground definition of 58 H h colon modifier 251 H predefined percent code 249 hard limit definition 78 homotopy parameter 246 hot electron degradation simulating 175 circuitage parameter 176 degradation parameters 176 177 example 178 failure criteria parameters 177 options and restrictions 175 results files 177 specifying the analysis 176 July 2002 HPMNS format translating 120 huge parameter 74 hyperbolic functions 86 74 iabstol parameter 200 convergence problems and 275 setting to correct accuracy problems 277 ic parameter
100. 3v3 Model model bsim3v3 Berkeley Spice Compatibility Lmin 35 Lmax 20 Wmin 6 Wmax 20 model N1 NMOS tLevel 11 Tnom 27 0 Nch 2 498E 17 Tox 9E 09 Xj 1 00000E 07 Lint 9 36e 8 Wint 1 47e 7 VthO 6322 K1l 756 K2 3 83e 2 K3 2 612 Dvt0 2 812 Dvt1l 0 462 Dvt2 9 17e 2 N1x 3 52291E 08 WO 1 163e 6 K3b 2 233 Vsat 86301 58 Ua 6 47e 9 Ub 4 23e 18 Uc 4 706281E 11 Rdsw 650 U0 388 3203 wr 1 tA0 3496967 Ags 1 B0 0 546 Bl 1 Dwg 6 0E 09 Dwb 3 56E 09 Prwb 213 tKeta 3 605872E 02 A1 2 778747E 02 A2 9 tVoff 6 735529E 02 NFactor 1 139926 Cit 1 622527E 04 Cdsc 2 147181E 05 Cdscb 0 DvtOw 0 Dvtlw 0 Dvt2w 0 Cdscd 0 Prwg 0 Eta0 1 0281729E 02 Etab 5 042203E 03 Dsub 31871233 July 2002 280 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits Pclm 1 114846 Pdiblcl 2 45357E 03 Pdiblc2 6 406289E 03 Drout 31871233 Pscbel 5000000 Pscbe2 5E 09 Pdiblcb 234 Pvag 0 delta 0 01 W1 0 Ww 1 420242E 09 Wwl 0 Wln 0 Wwn 2613948 L1 1 300902E 10 Lw 0 Lwl 0 Ll1n 316394 Lwn 0 kt1 3 kt2 051 At 22400 Ute 1 48 Ual1 3 31E 10 Ub1 2 61E 19 Ucl 3 42e 10 Kt11 0 Prt 764 3 Spectre BSIM 3v3 Model Berkeley Spice Compatibility Lmin 35 Lmax 20 Wmin 6 Wmax 20 simulator lang spectre model nch bsim3v3 tversion 3 1 type n tnom 27 0 tnch 2 498E 17 to
101. 5 53 s Total time required for tran analysis OscResp was 15 58 s Aggregate audit 9 24 38 AM Mon Jul 6 1998 Time used CPU 17 7 s elapsed 23 s util 77 Virtual memory used 1 39 Mbytes Spectre completes with O0 errors 0 warnings and 0 notices July 2002 31 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre Viewing Your Output The waveform display tool for this simulation example is AWD a display tool you receive when you purchase the Spectre simulator In this section you will learn the following m Howto start AWD How to display waveforms with the Results Browser How to extract zero crossing points of a waveform How to select new colors for waveforms How to access data from multiple directories Starting AWD There are several ways to start AWD Using the dataDir Command Line Option gt To start AWD for the simulation example type the following at the command line from the directory where the Spectre simulator was run awd dataDir osc raw Using Just the awd Command 1 To start AWD for the simulation example type the following at the command line from the directory where the Spectre simulator was run awd osc raw 2 In the Browse Project Hierarchy form click OK For this command to work you need to specify which simulator you are using The default is Spectre To specify the simulator create a cdsinit file and put the following line in i
102. 6 where rawfile In the following example a set of analyses is performed on output v n3 0 by sweeping the device parameter w of the device mp6 from 80um to 90um at each increment of 2um sweepl sweep dev mp6 param w start 80e 6 stop 90e 6 step 2e 6 demm5 n3 0 dcmatch mth 1e 3 where rawfile In the following example temperature is swept from 25 C to 100 C at increment of 25 C dcmm7 n3 0 dcmatch mth 0 01 param temp start 25 stop 100 step 25 July 2002 153 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses For more information on the dcmatch parameters see the Spectre Circuit Simulator Reference If you run the dcmatch analysis in Analog Design Environment you can access the output through the Results menu and create a table of mismatch contributors Stability Analysis The loop based and device based algorithms are available in the Spectre circuit simulator for small signal stability analysis Both are based on the calculation of Bode s return ratio The analysis output are loop gain waveform gain margin and phase margin Model Definition name stb parameter value Examples of the stb command stbloop stb start 1 0 stop 1e12 dec 10 probe Iprobe stbdev stb start 1 0 stop 1e12 dec 10 probe mos1 The analysis parameters are similar to the small signal ac analysis except for the probe parameter which must be specified to perform stability analysis When the probe parameter poin
103. 68 example 267 parameter storage format PSF 224 formatting output files 235 parameter sweeps dev parameter 158 159 200 examples linear sweep 160 logarithmic sweep 160 sweeping temperature 160 with vector of values 160 formatting 160 freq parameter 158 159 200 mod parameter 1 param parameter 158 159 200 setting sweep limits 159 specifying 156 temp parameter 158 with vector of values 161 parameter values changing for components 1 changing for models 184 2 checking 186 187 269 Oo 4 24 AR AR 270 all parameter values 187 270 in instance statements 18 3 X 186 269 in model statements 186 2 269 in subcircuit calls 95 operating point parameters 187 270 low co stopping 186 269 controlling the number of checks on 269 example of altering in netlist 109 July 2002 general rules for specifying 82 in instance statements 29 invalid 254 listing 192 222 permissible types 77 scaling 81 testing 271 vector 78 with arithmetic operators 84 with Boolean operators 84 with built in constants 87 with user defined functions 89 parameterized inline subcircuits example of use in netlist 112 parameterized models using inline subcircuits 99 parameters 82 circuit 82 Monte Carlo analysis table of 163 predefined netlist 90 subcircuit 82 parameters statement 82 paramfile parameter Monte Carlo analysis 164 paramset 158 paramset statement 200 paramset statement using 159 200 paramtest statement chec
104. 9 specifying initial conditions for 187 238 Composer to Spectre direct simulation environment 20 conditional if statements example of use in netlist formatting example 106 conditional instantiation 107 specifying 106 warning 108 configuration file default 291 example 294 format 291 precedence 293 connections inherited 75 constants built in table of 87 continuation characters 50 51 continuation methods 245 control statements 66 67 definition 29 formatting 67 paramset 200 statistics 211 use of in instance statement controls specifying 66 conventions typographic and syntax convergence problems 274 backward Euler integration method to correct 276 correcting with current probes 275 correcting with DC sweeps 276 dividing the circuit into parts to correct 276 floating resistors causing 275 gmin parameter increasing 275 loosening iabstol parameter to correct 275 loosening truncation error criteria to correct 276 Iteratio parameter 11 29 14 276 July 2002 298 maxiters parameter 275 nodesets to correct 276 nonlinear component models simplifying 276 numeric pivoting in the sparse matrix factorization 276 options statement settings to prevent 275 oscillators causing 276 pivotdc parameter settings to correct 276 pivrel parameter resetting to correct 276 realistic device models needed 275 reduced in Spectre 18 region parameter settings in bipolar analog circuits causing 276 region parameters
105. 96 July 2002 12 Product Version 5 0 Spectre Circuit Simulator User Guide Preface This manual assumes that you are familiar with the development design and simulation of integrated circuits and that you have some familiarity with SPICE simulation It contains information about the Spectre circuit simulator Spectre is an advanced circuit simulator that simulates analog and digital circuits at the differential equation level The simulator uses improved algorithms that offer increased simulation speed and greatly improved convergence characteristics over SPICE Besides the basic capabilities the Spectre circuit simulator provides significant additional capabilities over SPICE SpectreHDL Spectre High Level Description Language and Verilog A use functional description text files modules to model the behavior of electrical circuits and other systems SpectreRF adds several new analyses that support the efficient calculation of the operating point transfer function noise and distortion of common RF and communication circuits such as mixers oscillators sample holds and switched capacitor filters This Preface discusses the following topics m Related Documents on page 13 m Typographic and Syntax Conventions on page 14 m References on page 15 Related Documents The following can give you more information about the Spectre circuit simulator and related products B The Spectre circuit simulator is often run within
106. Carlo analysis statement specifies using the default that a nominal analysis is performed first The sweep analysis and all child analyses are performed and export statements are evaluated If the nominal analysis fails the Spectre simulator gives an error message and will not perform the Monte Carlo analysis If the nominal analysis succeeds the Spectre simulator immediately starts the Monte Carlo analysis The variations parameter specifies that only process variations variations process are applied this is useful for looking at absolute performance spreads There is a single child sweep analysis sw1 so that for each Monte Carlo run the Spectre simulator sweeps the temperature performs the dc and transient analyses and calculates the slew rate The output of the slew rate calculation is saved in the scalar data file mcl montecarlo variations process seed 1234 numruns 200 swl sweep param temp values 50 27 100 dcopl dc a child analysis tranl tran start 0 stop 1u another child analysis export calculations are sent to the scalardata file export slewrate oceanEval SslewRate v vout 10n t 30n t 10 90 The following Monte Carlo analysis statement applies only mismatch variations which are useful for detecting spreads in differential circuit applications It does not perform a nominal run Note No temperature sweep is performed mc2 montecarlo donominal no variations mismatch seed 1234 numruns
107. Colon Modifiers The Spectre simulator recognizes the following colon modifiers Modifier Description S Signifies the root base name of the given path for the file Signifies the extension for the given path of the file h Signifies the head of the given path for any portion of the file before the last E Signifies the tail of the given path for any portion of the file after the last Signifies the character itself use two consecutive colons to place a single colon in an output filename that is not read as a percent code modifier Any character except a modifier after a colon signals the end of modifications The Spectre simulator appends both the character and the colon to the filename July 2002 251 Product Version 5 0 Spectre Circuit Simulator User Guide Managing Files The Spectre simulator applies a chain of colon modifiers in the sequence you specify them For example if you apply C e C r t to the input filename circuits opamp ckt C e is the extension ckt of the input filename C r is the root opamp ckt of the input filename t is the tail of the input filename after the last opamp The result is the output filename ckt opamp Note If the input filename does not contain a slash and a period the modifiers t and r return the whole filename and the modifier n returns a period Examples of Colon Modifier Use The following table shows the various filenames you can generate f
108. Drift dc XferVsTemp xf OpenLoop ac XferVsFreq xf StepResponse tran StepResponse op SineResponse tran Log file identifies output file format Nonlinear device DC operating point file Node voltages at the operating point DC sweep Transfer function versus temperature AC analysis Transfer function versus frequency Transient analysis Operating point information for transient analysis Transient analysis July 2002 227 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options Filenames for SPICE Input Files If you specify analyses with standard SPICE syntax the name of the output file for the first instance of each type of analysis is the same as the name shown in the following table SPICE Analysis Output Filename OP opBegin dc AC frequencySweep ac DC srcSweep dc TRAN timeSweep tran Note These names have special significance to the Cadence analog design environment If you request multiple unnamed analyses using SPICE syntax the names are constructed by appending a sequence integer to the name of the analysis type and further adding the dot extension that is appropriate for the analysis For example multiple AC analyses would generate this sequence of files frequencySweep ac ac2 ac ac3 ac ac4 ac and so on Specifying Your Own Names for Directories You might want to specify a name for an output directory that is different from the name of your n
109. E T M GE 154 Advanced Analyses sweep and montecarlo 000 e eee eee 156 OWOODJAD ly SIGs Li modit ties goth Sa IAS eh eda ke hake DEL A P iei ead ML 156 Monte Carlo Analysis 5 9 2 95 do ponte o9 P SAU eee Eun E ae ee ad Os 161 Special Analysis Hot Electron Degradation 0 0 0 cc eee 175 Hot Electron Degradation Analysis llle 176 Output Options for Hot Electron Degradation Analysis 177 Example of Hot Electron Degradation lslslllsluss 178 Gontrol Statemmefiis aus ae oponen de need tonsa ee Sted 183 The alter and altergroup Statements 0 c ccc eee 183 Changing Parameter Values for Components 00 cece eee eee ees 184 Changing Parameter Values for Models 02 e eee eee 184 Further Examples of Changing Component Parameter Values 185 Changing Parameter Values for Circuits lllllllssllllslsn 185 Tie CHECK Statement xu eee ER HR RC oen er Pont Row RON e Pre co ee Mees 186 The ic and nodeset Statements 2 2 2 nbd ee Lieder xe eem sie 187 Setting Initial Conditions for All Transient Analyses 187 Supplying Solution Estimates to Increase Speed uss 189 July 2002 7 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying State Information for Individual Analyses
110. FETs JFETs and GaAs MESFETs Specifying Forbidden Operating Regions for Transistors You specify a forbidden operating region in a transistor with the alarm parameter The alarm parameter gives you the following options Option Description none The default condition with no warnings issued off Warns if the transistor is turned off triode Warns if the transistor operates in the triode region available for MOSFETs sat Warns if the transistor operates in the saturation region subth Warns if the transistor operates in the subthreshold region available for MOSFETs fwd Warns if the transistor is forward biased available for BJTs rev Warns if the transistor is reverse biased For example to be sure that a group of MOSFETs always operates in the saturation region you enter this model statement model mos example nmos alarm off alarm triode alarm subth July 2002 270 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Each of the three alarm parameters in this example identifies a forbidden operating condition Operating the device anywhere except in the saturation region triggers a warning The warning looks like the following Warning detected by spectre during transient analysis timesweep M1 Device operated in the triode region Defining BJT Operating Regions The Spectre simulator provides two parameters vbe fwd and vbc fwa that let you specif
111. More accurate simulation techniques Techniques that reduce reliability or accuracy such as device bypass simplified models or relaxation methods are not used in the Spectre circuit simulator m User control of accuracy tolerances For some simulations you might want to sacrifice some degree of accuracy to improve the simulation speed For other simulations you might accept a slower simulation to achieve greater accuracy With the Spectre circuit simulator you can make such adjustments easily by setting a single parameter Improved Speed The Spectre circuit simulator is designed to improve simulation speed The Spectre circuit simulator improves speed by increasing the efficiency of the simulator rather than by sacrificing accuracy Faster simulation of small circuits The average Spectre simulation time for small circuits is typically two to three times faster than SPICE The Spectre circuit simulator can be over 10 times faster than SPICE when SPICE is hampered by discontinuity in the models or problems in the code Occasionally the Spectre circuit simulator is slower when it finds ringing or oscillation that goes unnoticed by SPICE This can be improved by setting the macromodels option to yes Faster simulation for large circuits The Spectre circuit simulator is generally two to five times faster than SPICE with large circuits because it has fewer convergence difficulties and because it rapidly factors and solves large sparse matrice
112. OS devices only library select models section fast select models for fast device based on subckt parameters l w if 1 lt 3um if w lt 3um nmos dg s b fast 1xl l 1 w w ls l1s ld ld else nmos dg s b fast 1x3 l 1 w w ls ls ld ld else if w lt 3um nmos dg s b fast 3x1 l 1 w w ls ls ld ld else July 2002 114 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features nmos dg s b fast 3x3 l 1 w w ls ls ld ld endsection fast section typical if 1 lt 3um if w lt 3um nmos dg s b typ 1x1 1 1 w w ls ls ld ld else nmos dg s b typ 1x3 l 1 w w ls ls ld 1d else if w lt 3um nmos dg s b typ 3x1 1 1 w w ls ls ld 1d else nmos dg s b typ 3x3 1 1 w w ls ls ld 1d endsection typical section slow if 1 lt 3um if w lt 3um nmos dg s b slow 1xl l 1 w w ls l1s ld ld else nmos dg s b slow 1x3 l 1 w w ls ls ld ld else if w lt 3um nmos dg s b slow 3x1 1 1 w w ls ls ld ld else nmos dg s b slow 3x3 1 1 w w ls ls ld ld endsection slow endlibrary Scaling Physical Dimensions of Components Selected components allow their physical dimensions to be scaled
113. Opamp Circuit opamp cir on page 289 Opamp Circuit 2 opamp1 cir on page 289 Original Open Loop Opamp openloop sp on page 289 Modified Open Loop Opamp openloop1 sp on page 290 Example Model Directory q35d4h5 modsp on page 290 July 2002 279 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits Notes on the BSIM3v3 Model The Spectre circuit simulator supports the standard BSIM 3v3 MOS model both BSIM 3v3 1 and BSIM 3v3 2 as published by the University of California at Berkeley Further information about this model can be obtained by using Spectre s online help by typing spectre h bsim3v3 at the command line or by consulting the BSIM3 home page at http www device eecs berkeley edu bsim3 index html Spectre does not add proprietary parameters to its implementation of the standard model Spectre Syntax Notes explaining Spectre syntax are included as comments throughout the example netlists The Spectre circuit simulator reads Spice2G6 input along with its own native format The model card can therefore be specified in either format Below is an example of each Note that the valid parameter list does not change only the primitive name level designation and version type parameters Beginning with the 4 4 3 release the Spectre simulator is compatible with SPICE input language beyond documented SPICE2G6 Contact your local Cadence representative for more details SPICE BSIM
114. Product Version 5 0 Spectre Circuit Simulator User Guide and writefinal parameter 190 241 creating manually 191 241 reading 191 241 special uses for 191 241 using to specify initial conditions and estimate solutions 190 240 write parameter 190 241 state information specifying initial conditions 187 237 nodesets 187 237 state of the simulator modifying initial settings 186 245 statements analysis 64 formatting 64 65 control 66 instance 61 library 72 model 68 examples 69 formatting 68 netlist 57 paramset 200 save 201 statistics 211 statistical analysis performing 161 statistics blocks 161 multiple Monte Carlo analysis 174 specifying parameter distributions 170 statistics statement 211 status checking simulation 230 step parameter 144 160 step size for DC sweep and convergence problems 275 stop parameter 159 stopping asimulation 231 string parameters specifying 117 strobing 144 example 146 skipstart parameter 145 skipstop parameter 145 strobedelay parameter 145 strobeperiod parameter 145 stty utility UNIX 231 sub parameter 158 subcircuit calls checking for invalid parameter values in 95 example 94 formatting 94 names unrestricted 95 July 2002 saving signals 203 214 subcircuit parameters 82 subcircuits calling 90 94 composed of analyses calling 137 example 137 formatting 137 defining 90 example 91 92 formatting 90 expressions within 93 inline 96
115. Pwr 74 pwr 203 205 214 217 pwr parameter 206 217 pxf analysis brief description of 131 Q quantity statement 74 abstol parameter 74 Product Version 5 0 Spectre Circuit Simulator User Guide blowup parameter 74 example 75 huge parameter 74 maxdelta parameter 74 predefined quantities 74 R r colon modifier 251 range checking for subcircuit parameters 271 reading state files 191 241 recover spectre command option 233 recovering from transient analysis terminations automatic recovery customizing 232 restarting a transient analysis 233 setting recovery checkpoint file specifications for a single analysis 233 recursive inclusion 71 redirected files and percent codes 250 reducing simulation time with previous solutions 237 reference direction associated 58 reference to alibrary 73 relative error tolerance 142 relref parameter 141 142 allglobal setting 143 alllocal setting 142 pointlocal setting 142 sigglobal setting 143 reltol parameter 141 142 199 setting to correct accuracy problems 277 reserved words Spectre 59 restart parameter in analyses 237 results controlling destination and format of 233 displaying 32 Results Browser 36 RF capabilities 21 rforce parameter and convergence problems 276 setting to correct accuracy problems 278 run terminations See terminations of Spectre 230 running a simulation introductory July 2002 example 30 S 96S predefined p
116. SIM 3v3 Model slelleeeeeee eee ee eee 281 Ring Oscillator Spectre Deck for Inverter Ring with No Fanouts inverter ring sp 281 Ring Oscillator Spectre Deck for Two Input NAND Ring with No Fanouts nand2 ring sp 283 Ring Oscillator Spectre Deck for Three Input NAND Ring with No Fanouts nand3 ring sp 284 Ring Oscillator Spectre Deck for Two Input NOR Ring with No Fanouts nor2 ring sp 286 Ring Oscillator Spectre Deck for Three Input NOR Ring with No Fanouts nor3 ring sp 287 Opamp Circuit opamp cir Gas eae tede d epee binds eR wade hoon OR ae DECORE 289 Opamp Circuit 2 opamp1 cir 23v 22m Sew ki ke BOP see Cos SROs es BS MG 289 Original Open Loop Opamp openloop sp 0 ee 289 Modified Open Loop Opamp openloop1 sp 2 2 ee 290 Example Model Directory q35d4h5 modsp 00 cee ee 290 July 2002 11 Product Version 5 0 Spectre Circuit Simulator User Guide B Dynamic LO AGING uu cias ds eels Ad orca beet rete te 291 Configuration Fle ca be nie te Ea Peete tees pe at cl Cede ae cdi eU ees 291 Configuration File Format 9 0E abate Maw deh ah Olp oct noc A eed due Rn ede 291 Precedence for the CMI Configuration File elles 293 Configuration File Example 2 sn E Cea UI qur RASA WIRE ES EN e geek eek eee 294 CIMICVOESIODI cuire a Rr Ent exe satu tetra t es d wu aod tun EE sos 295 las 2
117. Spectre simulator looks for filename in your home directory This does not work for include m You can use environment variables in your include statements For example include SMYMODELS filename The Spectre simulator looks for filename in the directory specified by MYMODELS This works for include but not for include There are two major differences between using include and include m You can specify include to run CPP and use macros and defined constants B include does not expand special characters or environment variables in the filename Example of include Statement Use In the following include statement example the Spectre simulator reads initial program options and then inserts two files cmos mod and opamp ckt After reading these files it returns to the original file and reads further data about power supplies July 2002 71 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists example of using include statement global gnd vdd vss simulator lang spectre parameters VDD 5 include cmos mod include opamp ckt power supplies Vdd vdd gnd vsource dc VDD Vss vss gnd vsource dc VDD Reading Piecewise Linear PWL Vector Values from a File You could type the following component description into a netlist v4 in 0 vsource type pwl wave 0 0 1n 0 2n 5 10n 5 lin O 12n 0 You could also enter the vector values from a file in which case the component description migh
118. Spectre simulator uses to increase the accuracy of the initial solution estimate There are three ways to provide a good starting point for a simulation W Start analyses from previous solutions m Specify initial conditions for components and nodes m Specify solution estimates with nodesets Reducing the Number of Simulation Runs With the Spectre simulator you can run many analyses including analyses of the same type in a single simulation With other SPICE like simulators you might require multiple simulations to complete the same tasks In a single simulation run you can run a set of July 2002 236 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques Spectre analyses modify the component temperature or opt ions parameters and then run additional analyses with the new parameters Adjusting Speed and Accuracy You can use the errpreset parameter to increase the speed of transient analyses but this speed increase requires some sacrifice of accuracy Saving Time by Starting Analyses from Previous Solutions A solution for one analysis can be an appropriate starting point for the next analysis For example if a DC analysis precedes a transient analysis you can use the DC solution as the first guess for the initial point in the transient analysis solution There are two Spectre analysis parameters that let you start analyses from previous solutions They are available for most Spectre analyses
119. TNSA plain RPLR no geometrical or process modeling inline subckt RPLR A B parameters R 1 MULT 1 RPLR A B RPLR B R R MULT MULT ends RPLR The following file Process h provides the designer with the geometrical device interface File Process h simulator lang spectre call to the geometrical TNSA model inline subckt TNSA C B E S parameters WE 1u LE 1u MULT 1 dIS 0 dBF 0 TNSA CB E S TNSA PR WE WE LE LE MULT MULT dIS dIS dBF dBF call TNSA PR ends TNSA call to the geometrical RPLR model inline subckt RPLR A B parameters Rnom 1 WB 10u MULT 1 dR 0 RPLR A B RPLR PR Rnom Rnom WB WB MULT MULT dR dR call RPLR PR ends RPLR The following example is a differential amplifier netlist showing how a design can combine process modeling with process and geometry effects a differential amplifier biased with a 1mA current source simulator lang spectre include ProcessSimple h include Process h E 1 10 vsource dc 12 pullup resistors 4k ohms nominal R1 12 RPLR Rnom 4k WB 5 5 units wide model will calc length R2 1 3 RPLR Rnom 4k WB 10 10 units wide model will calc length the input pair TNSA1 2 4 5 0 NSA WE 10 LE 10 TNSA2 3 4 5 0 NSA WE 10 LE 10 no differential input voltage both inputs tied to same source E4 4 0 vsource dc 5 current source biasing J5
120. a seed July 2002 163 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Parameter Description scalarfile This parameter specifies the name of an ASCII file where scalar data calculated by the export state ments the results of export expressions that resolve to scalar values is saved For each iteration of each Monte Carlo child analysis Spectre writes a line to this ASCII file with one scalar expression per column for example slew rate or bandwidth The default name for this file is name mcdata where name is the name of the Monte Carlo analysis instance The file is created in the psf directory by default unless you specify a path in the filename This file contains only the matrix of numeric values The analog design environment Monte Carlo tool can read this ASCII file and plot the data in histograms and scattergrams When you use the analog design environment Monte Carlo tool to generate the Spectre netlist file Spectre merges the values of the statistically varying process parameters into this file containing the scalar data The analog design environment statistical plotting tool can later read the data and create scatter plots of the statistically varying process parameters against each other or against the results of the export expressions You can then see correlations between process parameter variations and circuit performance variations This data merging takes place whenever the scalarfile and proce
121. a string that is 00 in SPICES and thus are interpreted differently The SPICE Reader treats these like SPICES Leading spaces are ignored in SPICE2 and treated as a comment in SPICE3 The SPICE Reader treats these as SPICE2 does lib in PSPICE provides a file to search for each instantiated model in HSPICE it acts as a section specific include statement The SPICE Reader treats these as HSPICE does July 2002 55 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility B alter in SPICE2 allows multiple lines to be relisted with deltas following this statement In SPICES the alter is an interactive command and only allows one parameter to be changed per alter statement The SPICE Reader treats these as SPICE2 does B insome versions of SPICE global parameters values override values specified on instances of subcircuits The SPICE Reader treats all parameter values specified on any instance including subcircuits as the final value instead of allowing a global to override it For more information on specific SPICE Reader limitations please see the SPP Known Problems and Solutions on SourceLink July 2002 56 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists This chapter discusses the following topics Netlist Statements on page 57 Instance Statements on page 61 Analysis Statements on page 64 Control Statements on page 66 Model Statements on page 68 Inpu
122. aE ORE 212 Saving Signals for Individual Nodes and Components lilius 213 Savings Mal GIreulbolglidiS cider UDERXI PE EE ie eset ses ees wad 213 Saving Subcircuit Signals oie te sari atte eter rotto occ ona qe as oro teerdtue 215 Examples of the save Statement ellel lesse 215 Saving Individual Currents with Current Probes 000 cee ences 216 Savi POWGE gt 15 cuna racers b gael pcc Cie Jeg anf dy Du Ole ODA ead Porc de Tei cash Be 217 Saving Groups of Signals 3 rx ene Eee bao d Up eee ae ee ee eases 219 Formatting the save and nestlvl Parameters 2 cee es 219 The save Parameter Options 2 2 fice neu eater ee QE ta eee or eas 219 SAVING Subcircuit Signals 2 oo 2 5 See vba da Pee og Sed a ita dole aac rn cette 220 Saving Groups of Currents 24 2 25 uote tote dentate eed hee o cot re o Ae the 220 Saving All A DL Variables 40 45 25 34 220 tant hate tied XOU Sea es Sk ES 222 Listing Parameter Values as Output 1 ee ee 222 July 2002 8 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying the Parameters You Want to Save ee 223 Specifying the Output Destination uu ieu ere ee Oe Vue dan D 223 Examples of the info Statement 0 ccc eee eee teens 224 Preparing Output for Viewing 2s uo ke bae sw sme e enn a au Re RAT d i wand GY 224 Output Formats Supported by the Spectre Simulator
123. able 7 1 displays the output for the circuit below when det ail nodetonode C3 1p 0 5p doen gra C5 2p n2 e e P pi Ed e Cp July 2002 196 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements In this circuit the total capacitance at node 2 n2 n2 in the table is C4 C5 C3 5p The total capacitance between node 2 and node 1 n2 n1 is C Linear C3 Non Linear 3p Table 7 1 Node Capacitance Table Sorted by Value n2 n2 Fixed 2p Variable 3p Sum 5p n2 n1 Fixed 2p Variable 1p Sum 3p ni nl Fixed 3 5p Variable 1p Sum 4 5p n1 0 Fixed 1p Variable 0 Sum l1p ni n2 Fixed 2p Variable 1p Sum 3p n1 n3 Fixed 0 5p Variable 0 Sum 0 5p n3 n3 Fixed 1 5p Variable 0 Sum 1 5p n3 0 Fixed 1p Variable 0 Sum 1p n3 nl Fixed 0 5p Variable 0 Sum 0 5p The total node capacitance at nodes 1 2 and 3 is represented by the rows n1 n1 n2 n2 and n3 n3 respectively There is no entry for n3 n2 which means there is no capacitance between these two nodes Table 7 1 is sorted by value The rows are first grouped according to node names the rows with the same From Node are kept in a group The row depicting the total capacitance at each node is always displayed first in the group and the row displaying the node to ground capacitance is second The remaining rows within each group are sorted in descending order of the Sum value Note If the threshold is set to 2
124. age at zero body bias has an absolute value less than or equal to 3 Entering a Parameter Range Limits File You can enter a parameter range limits file in two ways B Type the param filename option of the spectre command from the command line or place it in an environment variable i 1ename is the name of the parameter range limits file In the following example 1imits3 is the range limits file for this simulation of test circuit Spectre tparam limits3 test circuit m Read the parameter limits file from within another file by putting an include statement with a syntax like the following example in your netlist include filename filename is the name you give to the range limits file You can nest include statements The only limit on depth is that imposed by the operating system on the number of files that can be open simultaneously in the Spectre simulator Paths you specify in filenames refer to the directory that contains the current file not to the directory in which the Spectre simulator was started For example suppose your directory tree is set up as follows designl ckt1 designl param lmts designl resistor lmts design2 ckt2 design2 param lmts design2 resistor lmts and you run the Spectre simulator in design1 with the following spect re command spectre param design2 param lmts cktl If the file designl param 1mts contains the line include resistor lmts the Spectre simulator reads in the
125. all instead of 1v1pub or allpub to include internal node voltages and currents through other components that compute current Use 1v1pub or allpub to exclude signals at internal nodes on devices the internal collector base emitter on a BJT the internal drain and source on a FET etc 1v1pub and allpub also exclude the currents through inductors controlled sources transmission lines transformers etc Note Setting the save parameter value to selected without any save statements in the netlist is not equivalent to specifying no output Currently the Spectre simulator saves all circuit nodes and branch currents with this combination of settings This might change in future releases of the Spectre simulator Saving Subcircuit Signals To save groups of signals for subcircuits you must adjust two parameter settings n Setthe save parameter to either 1v1 or 1v1pub n Setthe nest1v1 parameter to the number of levels in the hierarchy you want to save The default setting for nest 1v1 is infinity which saves all levels Saving Groups of Currents The currents parameter of the opt ions statement computes and saves terminal currents You use it to create settings for currents that apply to all terminals in the netlist For two terminal components the Spectre simulator saves only the first terminal entering currents You must use a save statement or use the global redundant currents parameter of the opt ions statement to save data for t
126. all instances only input Checks input parameters for all models and all instances July 2002 186 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Option Action output Checks output parameters for all models and all instances all Checks input and output parameters for all models and all instances oppoint Checks operating point parameters for all models and all instances The ic and nodeset Statements The Spectre simulator lets you provide state information to the DC and transient analyses You can specify two kinds of state information n lhitial conditions The ic statement lets you specify values for the starting point of a transient analysis The values you can specify are voltages on nodes and capacitors and currents on inductors n Nodesets Nodesets are estimates of the solution you provide for the DC or transient analyses Unlike initial conditions their values have no effect on the final results Nodesets usually act only as aids in speeding convergence but if a circuit has more than one solution as with a latch nodesets can bias the solution to the one closest to the nodeset values Setting Initial Conditions for All Transient Analyses You can specify initial conditions that apply to all transient analyses in a simulation or to a single transient analysis The ic statement and the ic parameter described in this section set initial conditions for all transient analyses in the netlist
127. alysis information you automatically receive with the AC and DC analyses by placing sens statements in the netlist Output for the sens command is sent to the rawfile or to an ASCII file that you can specify with the sensdata lt filename gt option of the spect re command July 2002 147 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses B If youset senstype partial Spectre calculates partial sensitivity This determines the sensitivity of output variables to input design parameters Results are expressed as a ratio of the change in an output analysis variable to the change in an input design parameter For example if V is the output value and P is the input design parameter sensitivity is computed as follows _ dV Sv p 7 qp WB If you set senstype normalized Spectre calculates normalized sensitivity which removes the dependence of results on the magnitude of the output variable and input design parameters Normalized sensitivity is computed as follows s BIV V P VdP dV _ p4V ifv 0 My pi tap 5 _ ldV itpco V P VdP When both P and V are zero partial sensitivity is used Formatting the sens Command You format the sens command as follows sens output_variables_list to design parameters list for analyses list where output variables list ovar ovars design parameters list dpar dparj analyses list ana anap The ovar are the output variables whose sensit
128. am dc dev vdr start 0 stop 5 step 0 1 end m Mixed language Spectre allows the use of both SPICE and Spectre syntax in the same netlist The SPICE Reader does not read the Spectre statements thus statements in the SPICE sections that are dependent on Spectre statements might get improperly mapped Except for model and subcircuit names do not have any dependencies between these two language sections July 2002 47 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility Language Differences Comparing the SPICE and Spectre Languages When you run the SPICE Reader all SPICE statements are mapped directly to Spectre input There are several important differences between these two languages that are addressed by the SPICE Reader To get a better idea at the differences between the two languages an example netlist is shown below First is the SPICE version of the netlist for an oscillator from Sample Netlist on page 26 BJT ECP Oscillator Vcc 10 5 Tee 2 0 1MA Q1 1 3 2 NPN Q2 4 5 2 NPN L1 4 5 1UH C11 5 1PF C2 5 3272 TRE C3 3 0 3NF C4 5 6 3NF R1 3 0 10K R2 5 6 10K ic V 3 1 model NPN NPN BF 80 RB 100 VAF 50 CJS 2PF TF 0 3NS TR 6NS CJE 3PF CJC 2PF option method trap tran lus 80us 10ns Here is the Spectre version of the same netlist BJT ECP Oscillator simulator lang spectre Vcc vcc 0 vsource dc 5 Tee e 0 isource dc 1mA Q1 vcc bl e
129. an value is taken as the current value of the parameter being varied giving a distribution denoted by Normal mean std Using the example in Specifying Parameter Distributions Using Statistics Blocks parameter rshpi is varied with a distribution of Normal 5k 0 4k The nominal value for the Gaussian distribution is the value of the parameter before the Monte Carlo analysis is run The standard deviation can be specified using the std parameter If you do not specify the percent parameter the standard deviation you specify is taken as an absolute value If you specify percent yes the standard deviation is calculated from the value of the sta parameter multiplied by the nominal value and divided by 100 that is the value of the sta parameter specifies the standard deviation as that percentage of the nominal value B Log normal This distribution is specified using dist 1norm The log normal distribution is denoted by log x Normal log mean std where x is the parameter being specified as having a log normal distribution Note log is the natural logarithm function For parameter xxx in the example in Specifying Parameter Distributions Using Statistics Blocks the process variation is according to log xxx Normal log 20000 12 The nominal value for the log normal distribution is the natural log of the value of the parameter before the Monte Carlo analysis is run If you specify a normal distribution for a
130. an analysis that has a prerequisite analysis the Spectre simulator performs the prerequisite analysis automatically For example if you specify an AC analysis the Spectre simulator automatically performs the prerequisite DC analysis However if you want to run a pac pxf Of pnoise analysis you must specify the prerequisite pss analysis You specify analyses in the order you want the Spectre simulator to perform them You can perform more than one of the same type of analysis in a single Spectre run Consequently you can perform several analyses of the same type and vary parameter values with each analysis You must give each analysis or control statement a unique name The Spectre simulator requires these unique names to identify output data and error messages Control Statements The Spectre simulator lets you place a sequence of control statements in the netlist You can use the same control statement more than once Spectre control statements are discussed throughout this manual The following are control statements alter altergroup check TG info nodeset options paramset save set shell statistics July 2002 66 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists Formatting the Control Statement Control statements often have the same format as analysis statements Like analysis statements many control statements must have unique names These unique names let the Spectre simulat
131. arameter but give it no limits all limits are disabled for that parameter m You can specify limits for integer real or enumerated parameters Enumerated parameters are those that take only predefined values such as yes or no and a11 or none To specify limits on enumerated parameters use the index of the enumeration in the limits declaration for that parameter To find the index of a parameter of component name see the parameter listings for the component name in the Spectre online help spect re h and count the enumerations in the limits declaration starting from zero For example to specify that the BJT operating point parameter region should not be rev reversed look for the region parameter in the parameter listings for the BUT component The region parameter is described as follows region fwd Estimated operating region Possible values are off fwd rev Or sat July 2002 266 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting For this parameter off has index 0 fwd has index 1 rev has index 2 and sat has index 3 To specify a limit that notifies you if any BJT is reversed use either of the following specifications 2 lt region lt 2 or 3 lt region lt 1 B You must give the keyword model when you place limits on model parameters If you do not give the keyword mode1 the limits are applied to instance parameters m You can indicate upper or lower limits fo
132. arameters inst Lists input parameters for instances of all components models Lists input parameters for models of all components input Lists input parameters for instances and models of all components output Lists effective and temperature dependent parameter values all Lists input and output parameter values oppoint Lists operating point parameters terminals The output is a node to terminal map nodes The output is a terminal to node map The info statement gives you some additional options You can use the save parameter of the info statement to specify groups of signals whose values you want to list For more information about save parameter options consult Saving Groups of Signals on page 219 Finally you can generate a summary of maximum and minimum parameter values with the extremes option Specifying the Output Destination You can choose among several output destination options for the parameters you list with the info statement With the info statement where parameter you can n Display the parameters on a screen n Send the parameters to a log file to the raw file or to a file you create July 2002 223 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options Examples of the info Statement You format the info statement as follows StatementName info lt parameter value gt The following example tells the Spectre simulator to send the maximum and minimum input p
133. arameters do have default values these values are given in the parameter listings for that analysis in the Spectre online help spectre h A listing like the following tells you that the default value for parameter 1in is 50 steps lin 50 Emission coefficient parameters Probes in Analyses Some Spectre analyses require that you set probes Remember the following guidelines when you set probes m You can name any component instance as a probe July 2002 133 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses m Ifthe probe component measures a branch current you can use it as either a current probe or a voltage probe Component instances that do not calculate branch currents can be used only as voltage probes m Ifthe probe component has more than two terminals you specify which pair of terminals to use as the probe by specifying a port of the probe In the following instance statement port 1 is nodes 5 and 8 and port 2 is nodes 2 and 4 bjtl 5 8 2 4 bmodl m f the probe component measures more than one branch current you specify which branch current to use as the probe by specifying a port In the following instance statement current port 1 is the branch from node 4 to node 5 and port 2 is the branch from node 8 to node 9 tline2 4 5 8 9 tline m Every component has a default probe type and port number In the following example the netlist contains a resistor named Rocm and a voltage source named vc
134. arameters for all models to a log file Inparams info what models where logfile extremes only For a complete description of the parameters available with the info statement consult the lists of analysis and control statement parameters in the Spectre online help spectre h Preparing Output for Viewing In this section you will learn how to format output data files so you can view them with a postprocessor Output Formats Supported by the Spectre Simulator You can choose from among seven format settings for output data files or directories The default setting is psfbin Option Format wsfbin Cadence waveform storage format WSF binary wsfascii Cadence waveform storage format WSF ASCII psfbin Cadence parameter storage format PSF binary psfascii Cadence parameter storage format PSF ASCII nutbin Nutmeg binary SPICE3 standard output nutascii Nutmeg ASCII SPICES standard output sst2 Cadence Signal Scan format In the Nutmeg format the Spectre simulator writes output data to a raw file For further information about the Nutmeg format consult the Nutmeg Users Manual available from the University of California Berkeley In the other formats the Spectre simulator creates and writes output to a directory of files The Spectre simulator overwrites existing files and July 2002 224 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options directories If the Spectre simulator ca
135. ard compatibility The Verilog A language is an open standard which was based upon SpectreHDL The Verilog A language is preferred because it is upward compatible with Verilog AMS a powerful and industry standard mixed signal language Both languages use functional description text files modules to model the behavior of electrical circuits and other systems Each programming language allows you to create your own models by simply writing down the equations The AHDL lets you describe models in a simple and natural manner This is a higher level modeling language than previous modeling languages and you can use it without being concerned about the complexities of the simulator or the simulator algorithms In addition you can combine AHDL components with Spectre built in primitives Both languages let designers of analog systems and integrated circuits create and use modules that encapsulate high level behavioral descriptions of systems and components The behavior of each module is described mathematically in terms of its terminals and July 2002 20 Product Version 5 0 Spectre Circuit Simulator User Guide Introducing the Spectre Circuit Simulator external parameters applied to the module Designers can use these behavioral descriptions in many disciplines electrical mechanical optical and so on Both languages borrow many constructs from Verilog and the C programming language These features are combined with a minimum number of spe
136. art with an x This is useful if you wantto replace individual components in an existing netlist with subcircuits for more detailed modeling Checking for Invalid Parameter Values When you define subcircuits such as the one in Modifying Subcircuit Parameter Values on page 95 you might want to put error checking on the subcircuit parameter values Such error checking prevents you from entering invalid parameter values for a given subcircuit call The Spectre paramtest component lets you test parameter values and generate necessary error warning and informational messages For example in the example of the bandpass filter in Modifying Subcircuit Parameter Values on page 95 the center frequency needs to be greater than half the bandwidth Here is a version of the previous three pole filter that issues an error message if the center frequency is less than or equal to half the bandwidth July 2002 95 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features define passive 3 pole bandpass filter subckt filter n1 n2 para meters bw 1 r0 1 fc 1 paramtest checkFreqs paramtest errorif bw 2 fc gt 0 VN 4 component message center frequency must be greater than half the bandwidth C1 nl 0 capacitor c 0 3374 6 2832 bw r0 L1 nl 0 inductor l 2 r0 bw 0 3374 6 2832 fc fc C2 nl n12 capacitor c bw 0 9705 6 2832 fc fc r
137. ary to use a current probe rather than a save statement You use a probe instead of a save statement under the following circumstances n Ifyou want increased flexibility for giving currents descriptive names With a current probe you can name the current anything you want With a save statement the name of the current must have a name suffix n Ifyou are saving measurements for current controlled components n l fyouare saving currents for an AC analysis n Ifyou are saving measurements for a current that passes between two parts of a circuit but not through a terminal In the following example you insert a current probe to measure the current flowing between A and B Because there is no component between A and B there is no other July 2002 216 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options way to measure this current except to insert a current probe that has an identical current to the one you want to measure A B Current probe inserted to measure current from A to B Probe Statement Example To specify a current probe place a statement with the following syntax in your netlist lt Name gt lt in gt lt out gt iprobe n Name is the unique netlist name for the current probe component The measured current also receives this name n in isthe name you choose for the input node of the probe n out is th
138. asic Formatting of Analysis Statements You format analysis statements in the same way you format component instance statements except that you usually do not put a list of nodes in analysis statements You specify most analysis statements as follows Name nodel nodeN Analysis Type parameter value Name is a unique name you give to the analysis nodel nodeN arethe names you give to the nodes that connect to the analysis You have the option of putting the node names in parentheses to improve the clarity of the netlist See the examples later in this chapter For most analyses you do not need to specify any nodes July 2002 64 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists Analysis Type isthe Spectre name of the type of analysis you want such as ac tran or xf You can find this name by referring to the topics list in the Spectre online help spectre h parameter value isthe list of parameter values you specify for the analysis You can specify values for any number of parameters You can find parameter listings for an analysis by referring to the Spectre online help spectre h Note The noise xf pnoise and pxf analyses let you specify nodes p and n which identify the output of the circuit When you use this option you should use the full analysis syntax as follows Name p n Analysis Type parameter value If you do not specify the p and n terminals you must specify th
139. atements m When the statementi Or statement2 field is a single instance or if statement an else statement is associated with the closest previous i f statement Binning by Conditional Instantiation You can use conditional instantiation to select an appropriate model based on certain ranges of specified parameters model binning This technique lets you decide and implement which parameters to bin on and is valid for any device that supports a model The Spectre Netlist Language has conditional instantiation For example subckt sl dg s b parameters l 1u w lu TP ics 10 5 4 ml dg s b shortmod 1 1 w w short channel model else m2 dg s b longmod 1 1 w w long channel model model shortmod vto 0 6 gamma 2 etc model longmod vto 0 8 gamma 66 etc ends sl Based on the value of parameter 1 one of the following is chosen B Ashort channel model m A long channel model Previously the transistor instances had to have unique names such as m1 and m2 in the preceding example even though only one of them could actually be chosen Now you can use the same name for both instances provided certain conditions are met The following example shows a powerful modeling approach that combines model binning based on area with inline subcircuits for a bipolar device July 2002 107 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features general pur
140. ax for the five formats LIBRA Format An input file for LIBRA format must have a header and a data section The header consists of all comments An exclamation mark begins a comment and the first line of the header must be a comment line with the keyword Libra A line beginning with 4 can include information July 2002 121 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features on frequency scale factor impedance data complex number format definition and so on The following is an input file example with five frequency data points and three ports Libra TM Ver 3 500 103 3 Cfg 800 14999 5 0 8613 0 1 2F3FCF9DE Wed May 12 10 54 31 1998 makes3p ckt GHZ S MA R 50 0000 SCATTERING PARAMETERS L 00000 0 99602 7 18399 0 06256 84 5886 0 06256 84 5886 0 06256 84 5886 0 99801 3 59201 0 00196 172 762 0 06256 84 5886 0 00196 172 762 0 99801 3 59201 2 00000 0 98439 14 2738 0 12351 79 2690 0 12351 79 2690 0 12351 79 2690 0 99220 7 13736 0 00775 165 618 0 12351 79 2690 0 00775 165 618 0 99220 7 13736 3 00000 0 96600 21 1845 0 18146 74 1238 0 18146 74 1238 0 18146 74 1238 0 98299 10 5954 0 01704 158 654 0 18146 74 1238 0 01704 158 654 0 98299 10 5954 4 00000 0 94210 27 8472 0 23535 69 2195 0 23535 69 2195 0 23535 69 2195 0 97101 13 9360 0 02938 151 939 0 23535 69 2195 0202938 151 939 0 97101 13 9360 5 00000 0 91416 34 2126
141. but r 500hms is rejected because units are provided without a scale factor For the last example use r 50_Ohms July 2002 81 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features SPICE mode simulator lang spice accepts only the following SPICE scale factors t 10 2 g 10 meg 10 k 10 p 10 m 10 mil 25 4x 10 u 10 n 10 210 Note SPICE scale factors are not case sensitive Any other scale factor is ignored treated as 1 0 caution If you are not clear about the scaling rules for each simulation mode you can cause errors in your simulation For example 1 0M is interpreted as 10 in the SPICE mode but as 10 in the Spectre mode Parameters Statement In this section you will learn about the circuit and subcircuit parameters collectively known as netlist parameters as defined by the parameters statement Circuit and Subcircuit Parameters The Spectre Netlist Language allows real valued parameters to be defined and referenced in the netlist both at the top level scope and within subcircuit declarations run spectre h subckt for more details on parameters within subcircuits The format for defining parameters is as follows parameters param value lt param value gt Once defined you can use parameters freely in expressions The following are examples simulator lang spectre parameters pl 1 p2 2 declare some parameters
142. cOp dc creates sweepl1 000 dcOp dc and sweep1_001_dcOp dc The following example contains a number of analysis statements from a netlist It shows the name of the output file the Spectre simulator creates for each analysis In some cases the Spectre simulator creates more than one output file for an analysis This is because the analysis statement contains a parameter that specifies that certain output information be sent to a file July 2002 226 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options OpPoint dc p Drift dc p XferVsTemp xf B OpenLoop ac e XferVsFreq xf p gt StepResponse tran OpPoint op ANALYSES DC operating point OpPoint dc print yes oppoint fil write 2 ua741 dc Drift dc start 0 stop 50 0 step 1 param temp nestlvl 0 XferVsTemp xf start 0 stop 50 step 1 probe Rload param temp freq 1k readns ua741 dc Gain pleasel alter dev Vfb param mag value 1 annotate no OpenLoop ac start 1 stop 10M dec 10 nestlvl 0 please2 alter dev Vfb param mag value 0 annotate no XF XferVsFreq xf start 1 stop 10M dec 10 probe Rload Transient StepResponse op l7 3 StepResponse tran stop 250u oppoint fWle SineResponse tran stop 150u method trap SineResponse tran Results File please3 alter dev Vin param type value sin rrpreset moderate Description logFile OpPoint op OpPoint dc
143. cadence Spectre Circuit Simulator User Guide Product Version 5 0 July 2002 2000 Cadence Design Systems Inc All rights reserved Printed in the United States of America Cadence Design Systems Inc 555 River Oaks Parkway San Jose CA 95134 USA Trademarks Trademarks and service marks of Cadence Design Systems Inc Cadence contained in this document are attributed to Cadence with the appropriate symbol For queries regarding Cadence s trademarks contact the corporate legal department at the address shown above or call 1 800 862 4522 All other trademarks are the property of their respective holders Restricted Print Permission This publication is protected by copyright and any unauthorized use of this publication may violate copyright trademark and other laws Except as specified in this permission statement this publication may not be copied reproduced modified published uploaded posted transmitted or distributed in any way without prior written permission from Cadence This statement grants you permission to print one 1 hard copy of this publication subject to the following conditions 1 The publication may be used solely for personal informational and noncommercial purposes 2 The publication may not be modified in any way 3 Any copy of the publication or portion thereof must include all original copyright trademark and other proprietary notices and this permission statement and 4 Cadence reserves the r
144. cal potential in Volts 74 end 50 end 50 enumerations setting parameter limits with 79 envelope following analysis 22 130 environment variables changing defaults in 234 environments in which Spectre can be used 23 envlp 22 130 equal sign in Spectre syntax 59 error conditions terminate simulation internal errors 256 invalid parameter values 254 singular Jacobian or matrix 255 Product Version 5 0 Spectre Circuit Simulator User Guide errormessages 19 caused by invalid parameters in subcircuit calls 95 customizing 262 specifying conditions for in subcircuit calls 95 error options of spectre command 274 error tolerances abstol parameter error tolerance parameter 142 errpreset parameter 140 Iteratio error tolerance parameter 142 relref error tolerance parameter 142 reltol parameter error tolerance parameter 142 errpreset parameter 141 escaping special characters 61 estimating solutions with the nodeset statement 189 239 euler integration method parameter 143 example in netlist conditional if statement 112 parameterized inline subcircuit 112 paramtest statement 112 specifying N ports 117 exit codes Spectre 230 explosion region warnings 257 expressions 84 as model parameters 70 in subcircuit parameters 93 extending statements beyond a single line formatting for 59 F failure criteria parameters for hot electron degradation simulation 177 field separators inpu
145. cale and scalem affect only parameters whose default measurement units are in meters For example vmax is affected because its units are m sec but ucrit is not affected because its units are V cm Similarly n sub is not affected because its units are 1 cm You can check the effects of scale and scalem by adding an info statement with what output and look for the effective length 1e or width wef of a device For more information about the info statement see Specifying the Parameters You Want to Save on page 193 The following table shows you the effects of scale and scalem with different units scale or scalem Units Scaling action scale meters m Multiplied by scale scalem meters m Multiplied by scalem scale meters m Multiplied by scale With n a real number scalem meters m Multiplied by scalem With n a real number scale 1 meters 1 m Divided by scale scalem 1 meters 1 m Divided by scalem July 2002 116 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features scale or scalem Units Scaling action scale 1 meters 1 m Divided by scale With n a real number scalem 1 meters 1 m Divided by scale With n a real number String Parameters You can use quoted character strings as parameter values String values you might use as Spectre parameter values include filenames and labels When you use a string as
146. ce bsim1 2 3 3v3 gm Common source transconductance btasoi gm Common source transconductance CCCS gain Current gain CCVS rm Transresistance ekv gm Common source transconductance gaas gm Common source transconductance hbt dice_dvbe Intrinsic dice dVbe hvmos gm Common source transconductance jfet gm Common source transconductance mos0 1 2 3 gm Common source transconductance tom2 gm Common source transconductance July 2002 155 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Component Dominant Controlled Source Description vbic dic_dvbe Intrinsic dic dVbe VCCS gm Transconductance VCVS gain Voltage gain In general the stability information produced by the device based algorithm can be used to assess the stability of that particular device Most often a feedback network consists of a global feedback loop and numerous nested local loops around individual transistors The loop based algorithm can determine the stability of the whole network as long as all nested loops are stable while the device based algorithm can be used to ensure all local loops are stable For more information on the stability analysis parameters see the Spectre Circuit Simulator Reference Advanced Analyses sweep and montecarlo There are two advanced analyses sweep and montecarlo Sweep Analysis The sweep analysis sweeps a parameter processing a list of analyses or multiple analyses for each value of the parameter The swe
147. ch and stb on page 147 Advanced Analyses sweep and montecarlo on page 156 Special Analysis Hot Electron Degradation on page 175 Types of Analyses This section gives a brief description of the Spectre circuit simulator analyses you can specify Spectre analyses frequently let you sweep parameters estimate or specify the DC solution specify options that promote convergence and select annotation options You can specify sequences of analyses any number in any order For a more detailed description of each analysis and its parameters consult the Spectre online help spectre h m DC analysis dc Finds the DC operating point or DC transfer curves of the circuit B AC small signal analyses Q AC analysis ac Linearizes the circuit about the DC operating point and computes the steady state response of the circuit to a given small signal sinusoidal stimulus July 2002 129 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses This analysis is useful for obtaining small signal transfer functions For more information about the AC analysis see Chapter 4 Analysis Statements of the Spectre Circuit Simulator Reference Noise analysis no ise Linearizes the circuit about the DC operating point and computes the total noise spectral density at the output The output can be either a voltage or a current If you specify an input probe the Spectre simulator computes the transfer function and the equivalent in
148. ch a message check the parameter If the unusual parameter value is correct you can ignore this message The limits settings that generate these warning messages are soft limits as opposed to hard limits settings Hard limits stop a simulation if they are violated the Spectre simulator has automatic soft limits on a few parameter values However you can override these limits or specify your own limits for parameters that do not have automatic limits For more information see Customizing Error and Warning Messages on page 262 gmin Is Large Enough to Noticeably Affect the DC Solution Warning detected by spectre during DC analysis oppoint Gmin 1pS is large enough to noticeably affect the DC solution By default the Spectre simulator and SPICE adds a very small conductance of 107 siemens called gmin across nonlinear devices This conductance prevents nodes from floating if the nonlinear devices are turned off By default GMIN 1e 12 Siemens The gmin parameter usually has a minimal effect on circuit behavior However some circuits such as charge storage circuits are very sensitive to the small currents that flow through gmi n July 2002 259 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting You see a message such as the one given above if the current flowing through the gmin conductors when treated as an error current does not meet the gmin criteria That is the messa
149. characters not included in the preceding list You must enter required characters exactly as shown References Text within brackets is a reference See Appendix A References of the Spectre Circuit Simulator Reference manual for more detailed information July 2002 15 Product Version 5 0 Spectre Circuit Simulator User Guide 1 Introducing the Spectre Circuit Simulator This chapter discusses the following Improvements over SPICE on page 16 Analog HDLs on page 20 RF Capabilities on page 21 Mixed Signal Simulation on page 23 Environments on page 23 The Spectre circuit simulator is a modern circuit simulator that uses direct methods to simulate analog and digital circuits at the differential equation level The basic capabilities of the Spectre circuit simulator are similar in function and application to SPICE but the Spectre circuit simulator is not descended from SPICE The Spectre and SPICE simulators use the same basic algorithms such as implicit integration methods Newton Raphson and direct matrix solution but every algorithm is newly implemented Spectre algorithms the best currently available give you an improved simulator that is faster more accurate more reliable and more flexible than previous SPICE like simulators Improvements over SPICE The Spectre circuit simulator has many improvements over SPICE Improved Capacity The Spectre circuit simulator can simulate larger circuits t
150. check analysis you must also enter the param command line argument with the spect xe command to specify a file that contains the soft limits The following example illustrates the syntax of the check statement It tells the Spectre simulator to check the parameter values for instance statements ParamChk check what inst B ParamChk is your unique name for this check statement m The keyword check is the component keyword for the statement WB The what parameter tells the Spectre simulator which parameters to check The what parameter of the check statement gives you the following options Option Action none Disables parameter checking models Checks input parameters for all models only inst Checks input parameters for all instances only input Checks input parameters for all models and all instances July 2002 269 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Option Action output Checks output parameters for all models and all instances all Checks input and output parameters for all models and all instances oppoint Checks operating point parameters for all models and all instances Selecting Limits for Operating Region Warnings The Spectre simulator lets you specify forbidden operating regions for transistors If a transistor operates in a forbidden operating region the Spectre simulator sends you a warning message This feature is available for BJTs MOS
151. cial constructs for behavioral simulation These high level constructs make it easier for designers to use a high level description language for the first time RF Capabilities SpectreRF adds several new analyses that support the efficient calculation of the operating point transfer function noise and distortion of common analog and RF communication circuits such as mixers oscillators sample and holds and switched capacitor filters SpectreRF adds four types of analyses to the Spectre simulator The first is periodic steady state PSS analysis a large signal analysis that directly computes the periodic steady state response of a circuit With PSS simulation times are independent of the time constants of the circuit so PSS can quickly compute the steady state response of circuits with long time constants such as high Q filters and oscillators You can also embed a PSS analysis in a sweep loop referred to as an SPSS analysis in the Cadence analog design environment which allows you to easily determine harmonic levels as a function of input level or frequency making it easy to measure compression points intercept points and voltage controlled oscillator VCO linearity The second new type of analysis is the periodic small signal analysis After completing a PSS analysis SpectreRF can predict the small signal transfer functions and noise of frequency translation circuits such as mixers or periodically driven circuits such as oscil
152. cje 3pf cjc 2pf When you create an instance statement that refers to a model statement for its parameter values you must specify the model name as the master name For example an instance statement that receives its parameter values from the previous model statement might look like this Q1 vcc bl e vcc npn Check documentation for components to determine which parameters are expected to be provided on the instance statement and which are expected on the model statement Analysis Statements The last section of the sample netlist has the analysis statement An analysis statement has the same syntax as an instance statement except that the analysis type name replaces the master name To specify an analysis you must include the following information in a netlist statement m A unique name for the analysis statement W Possibly a set of node names B The name of the type of analysis you want m Any additional parameter values associated with the analysis To find the analysis type name and the parameters you can specify for an analysis consult the parameter listing for that analysis in the Spectre online help spectre h The following analysis statement specifies a transient analysis The analysis name is stepResponse and the analysis type name is t ran stepResponse tran stop 100ns Instructions for a Spectre Simulation Run When you complete a netlist you can run the simulation with the spect re command gt Torun a simu
153. component or analysis parameter value is a group of numbers or names you specify the group as a vector of values by enclosing the list of items in square brackets for example coeffs 0 0 1 0 2 0 5 to specify the parameter values 0 0 1 0 2 and 0 5 You can specify a group of number pairs such as time voltage pairs to specify a waveform as a vector of the individual numbers Remember these guidelines when you specify vectors of value m You can mix numbers and netlist or subcircuit parameter names in the same vector coeff 0 coeffl coeff2 0 5 m You cannot leave a list of items empty m You can use expressions such as formulas to specify numbers within a vector When you use a vector of expressions each expression must be surrounded by parentheses coeff 0 A B C 0 5 m You can use subcircuit parameters within vectors Parameter Ranges Parameter ranges have hard limits and soft limits Hard limits are enforced by the Spectre simulator if you violate them the Spectre simulator issues an error and terminates You specify soft limits if you violate them the Spectre simulator issues a warning and continues Soft limits are used to define reasonable ranges for parameter values and can help find unreasonable values that are likely errors You can change soft limits which are defined in July 2002 78 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features o
154. computed for node 2 is in error by 755 152 uV To reduce error in computed initial conditions decrease rforce However setting rforce too small may result in convergence difficulties or in the matrix becoming singular The Spectre simulator sets initial conditions on a node by attaching a voltage source through a resistor The default value of this resistor is 1 but you can control the value through the options parameter r force This notice indicates that the initial condition calculated for this node is about 755uV from the value specified in the netlist You can lower the value of rforce to bring the voltage values into agreement in one of the following ways m Through the Analog Options window in the Analog Design Environment B Inserting an options statement in the netlist An example is given below myOptions options rforce 1m Output Messages Notice from spectre during transient analysis tranl No outputs found Loosening output filter criterion to lvlpub If you set save selected the Spectre simulator saves the voltages in the save statement If the save statement does not contain any voltage values Spectre issues the above warning and changes the save option default to 1v1lpub This saves all node voltages Customizing Error and Warning Messages You can customize the Spectre error and warning messages to some extent to fit the needs of a simulation This section tells you about these customization options
155. cond sorted table This table lists all the degradations of the threshold voltage V 4 the mobility factor U the transconductance g and the drain current I 4 of each device for the period specified in the circuitage parameter The degradation of Vj is given in absolute values The degradations of U 9m and lgs are expressed as a percentage of their original values All four degradations are compared to failure criteria that you can specify with the model statement parameters crivth criuo crigm and criids If any degradation is greater than its corresponding failure criterion the device is listed as having failed In the transient analysis you can also save waveforms of the following quantities for any device B Voltage B Any operating point parameter m Stress July 2002 177 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses B Effective device age m Substrate current You create these output files with the save statement You use a waveform display tool such as the Cadence Analog Waveform Display AWD tool to view the waveforms Example of Hot Electron Degradation This netlist of an 11 stage ring oscillator demonstrates the statements required to simulate hot electron degradation in the Spectre simulator You must properly characterize and extract the degradation parameters dvthc dvthe duoc and duoe These are usually obtained from DC stress measurements Because device degradations are
156. conservative the simulation is the most accurate but also slowest The conservative setting is appropriate for sensitive analog circuits If you still require more accuracy than that provided by conservative tighten error tolerance by setting xe1to1 to a smaller value July 2002 140 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Description of errpreset Parameter Settings The effect of errpreset on other parameters is shown in the following table In this table T stop start errpreset reltol relref method maxstep lteratio liberal x10 0 allglobal gear2 lt 7 10 3 5 moderate x1 0 sigglobal traponly lt 17 50 3 5 conservative x0 1 alllooal gear2only T 100 10 0 The description in the previous table has the following exceptions B The errpreset parameter sets the value of reltol as described in the table except that the value of reltol cannot be larger than 0 01 m Except for reltol and maxstep errpreset does not change the value of any parameters you have specified m With naxstep the specified value in the preceding table is an upper bound You can always specify a smaller maxstep value If you need to check the errpreset settings for a simulation you can find these values in the log file Uses for errpreset You adjust errpreset to the speed and accuracy requirements of a particular simulation For example you might set errpreset to liberal for your first sim
157. ction At the end of the longer parameter listings is the parameter index This index lists the parameters alphabetically and gives the number that corresponds to where the parameter is in the numbered list For components parameters are divided into up to four sections Instance Parameters Model Parameters Output Parameters and Operating Point Parameters At the end of longer parameter listings is the parameter index This index indicates where to find a parameter s description with a letter and a number The letter refers to the section for example refers to the instance parameters section M refers to the model parameters section O refers to the output parameters section and OP refers to the operating point parameters section and the number refers to where the parameter is in the numbered list spectre helpsort When you type spectre helpsort name Where name is the name of a component or analysis you get the same information as you do with spectre h name but the parameters are sorted alphabetically instead of divided into related groups spectre helpfull When you type spectre helpfull name where name is the name of a component or analysis you get related parameters grouped as you do with spectre h name and you get the following additional information m Parameter type m Parameter dimension scalar or vector m Parameter range spectre helpsortfull When you type spectre helpsortfull name wher
158. ction with the same name as a built in function the Spectre simulator issues a warning and runs the user defined function Calling the Function Functions can be called from anywhere that an expression can currently be used in the Spectre simulator Functions can call other functions however the function must be declared before it can be called The following example defines the function my func and then calls it July 2002 89 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features real myfunc real a real b return atb 2 sqrt a sin b real yourfunc real a real b return atb myfunc a b call myfunc The next example shows how a user defined function can be called from an expression in the Spectre netlist rl 1 0 resistor r myfunc 2 0 4 5 Predefined Netlist Parameters There are two predefined netlist parameters B temp is the circuit temperature in degrees Celsius and can be used in expressions BH tnomis the measurement nominal temperature in degrees Celsius and can be used in expressions For example rl 1 0 res r temp tnom 15 10k ol options TEMP 55 Note If you change temp or t nom using a set statement alter statement or simulator options card all expressions with temp or tnom are reevaluated Hence you can use the temp parameter for temperature dependent modeling this does not include self heating however Subcirc
159. ctre netlister allows each of these fields to be greater than 200 characters In the SPICE language instance statements often have their parameter values listed in a particular order In the Spectre language you can specify parameter values in any order using parameter name This allows for a more readable netlist Spectre netlists are case sensitive and use lower case for all keywords SPICE netlists are case insensitive This means that you can name one model myMode1 and another mymodel and Spectre treats them as two distinct models In SPICE they would be considered to be the same model Spectre always tries to match the case of a model subcircuit s name when there is a call to a model subcircuit from an instance line an alter statement or other part of the netlist During the netlist conversion process the SPICE Reader converts included models subcircuits to lower case which can prevent Spectre from identifying the right model subcircuit for a given device For this reason the SPICE Reader will insert the flag insensitive yes atthe beginning of each converted netlist on the simulator command statement that is simulator lang spectre insensitive yes The insensitive yes language directive marks the models subcircuits that were converted so that Spectre can perform a lower case compare Because the SPICE language is case insensitive the scale factors are different from the Spectre scale factors see Scaling Numerical Literals
160. d v Default absolute tolerance 1 uV Default maximum allowable change per iteration 300mV m Magnetic flux in Webers named wb Default absolute tolerance 1 nWb B Temperature in Celsius named Temp Default absolute tolerance 100 uC B Power in Watts named Pwr Default absolute tolerance 1 nW July 2002 74 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists m Unitless named U Default absolute tolerance 1 x 10 For more information see spectre h quantity quantity Statement Example The electrical potential quantity has a normal default setting of 1 uV for absolute tolerance abstol and 300 mV for maximum change per Newton iteration maxdelta You can change abstol to 5 uV reset maxdelta to 600 mV define the estimate of the maximum voltage to be 1000 V and set the maximum permitted voltage to be 10 with the following statement VoltQuant quantity name V abstol 5uV maxdelta 600mV huge 1000V blowup 1e9 VoltQuant is a unique name you give to the quant ity statement The keyword quantity is the primitive name for the statement The name parameter identifies the quantity you are changing v is the name for electrical potential abstol maxdelta huge and blowup are the parameters you are resetting Note The quantity statement has other uses besides setting tolerances You can use the quantity statementto create new quantities or to redefine properties of an ex
161. dcmat ch Computes the statistical deviation in the DC operating point of the circuit caused by device mismatch For more information about the dcmatch analysis see DC Match Analysis on page 151 Stability Analysis stb Linearizes the circuit about the DC operating point and computes loop gain gain margin and phase margin for a specific feedback loop or an active device The stability of the circuit can be determined from the loop gain waveform The probe parameter must be specified to perform stability analysis For more information about the stability analysis see Chapter 4 Analysis Statements of the Spectre Circuit Simulator Reference m Advanced analyses ua July 2002 Sweep analysis sweep Sweeps a parameter executing a list of analyses or multiple analyses for each value of the parameter The sweeps can be linear or logarithmic Swept parameters return to their original values after the analysis Sweep statements can be nested For more information about the sweep analysis see Sweep Analysis on page 156 132 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Q Monte Carlo analysis montecarlo Varies netlist parameters according to specified distributions and correlations runs nested child analyses and extracts specified circuit performance measurements You can apply both process and device to device mismatch variations and tag device instances as correlated or matched pairs
162. de e Ro Rs 65 GCOntrol StatementS 323 5 doe ELENCO ER EE VAM LL ERE EER OSS 66 Formatting the Control Statement 0 0 eee 67 Examples of Control Statements 0 teens 67 Medel Statements 2 cer sos eu eek MeO Seca aac a tuU d RE RU Eua wars 68 Formatting the model Statement eee eee eee 68 Examples of model Statements lllllll leer 69 Basic model Statement Rules 225 s Soke kh EE era eise heu issu s s 69 Input Data from Multiple Files 3E SALIS eee tied ye eed ts ek eee Sed 70 Formatting the include Statement 0 0 eee eee 70 Rules for Using the include Statement 0 eee eee 70 Example of include Statement Use 23 26 x e rcx atate HE CER CR EA 71 Reading Piecewise Linear PWL Vector Values from a File 72 Using Library Statements nannaa ome eh ve Rake had koe ox EP eters oe 72 Multidisciplinary Modeling 5 9 gta gere one EP sea eee pex Rs 73 Setting Tolerances with the quantity Statement sues 74 Inherited Connections zu scabies ira d e AS Dea pios Cedo Da duco S OO SASS 75 5 Parameter Specification and Modeling Features 77 Instance Component or Analysis Parameters 0 cece eee 77 Types of Parameter Values cs ces mese te seme SO aka a eee ae ee Pen dade io e 77 Parameter DIMENSION 34 9 ed ci ee hg Mane Reet de c ede ee o t tel Aot 78 Parameter Ranges oie poian
163. dels here model nch bsim3v3 model pch bsim3v3 type p Op simulator lang spectre tf 3 0 xf save lvlpub nestlvl 1 start 1 stop 1K dec 20 simulator lang spice dc vinp 0 10 0 10 10u print dc v 3 ac dec 10 1 10MEG print ac vdb 3 vp 3 end Gl Example Model Directory q35d4h5 modsp example model directory simulator lang spectre library mosmodels section tt model n bsim3v3 tox 1 194e 08 model p bsim3v3 type p tox 7 4e 09 endsection section ss model n bsim3v3 tox 1 242e 08 model p bsim3v3 type p tox 7 724e 09 endsection section ff model n bsim3v3 tox 1 1544e 08 model p bsim3v3 type p tox 7 148e 09 endsection endlibrary July 2002 290 Product Version 5 0 Spectre Circuit Simulator User Guide Dynamic Loading The Spectre circuit simulator supports dynamic loading of device models This feature allows you to dynamically load device primitives stored in shared objects at run time This is useful for developing and distributing models Configuration File The Spectre circuit simulator can be configured to load a specific set of shared objects based on the content of a set of configuration files The default CMI compiled model interface configuration file is shown below The default search path is SCDS ROOT tools spectre lib cmi M This file is automatically generated Any changes made to it will not be saved load libnortel s
164. der maps this to a parameter if a param statement is encountered with this assignment or to a model name if a model card with the name myres is found If neither is present the field is assumed to be a model name In the case of the convert mode where these assignments could be part of included files this assumption could be incorrect and the instance statement would need to be fixed m Global nodes In Spectre global nodes must be at the very beginning of the netlist while they can be present anywhere in a SPICE netlist If a converted file contains global nodes these July 2002 45 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility Spp must be moved to the top level of the netlist before the file can be included in a higher level netlist Multiple global statements cause fatal errors in Spectre Location of measurement data The SPICE Reader converts Hspice style measure statements to Measurement Description Language MDL statements The SPICE Reader does this by creating an MDL control file which can then be used in the simulation In normal operation using the spectrespp netlist command the control file that is created takes on the name of the netlist with the suffix md1 When a netlist is converted with the convert option the MDL control file that is created is always named Net list mdl If this control file is used in a subsequent simulation the results output is written to a file
165. design2 resistor lmts file but not the designl resistor lmts file July 2002 268 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Requesting Breakdown Region Warnings for Transistors If you want warning messages about the breakdown regions of transistors you must set the appropriate parameters for each component when you identify the component with an instance or model statement For most transistors you set the bvj parameter For BJTs you must set three parameters bvbe bvbc and bvsub These are breakdown parameters for the base emitter the base collector and the substrate junctions Diodes are also exceptions because you can set both the bv j and bv parameters You need two different parameters for the diode breakdown voltage because of the Zener breakdown model in the diode When you use the diode as a Zener diode it is purposely biased in the breakdown region and you do not want to be warned about the Zener breakdown By specifying the bv parameter you tell the Spectre simulator to implement the Zener diode model at bv Telling Spectre to Perform Additional Checks of Parameter Values You can perform a check analysis at any point in a simulation to be sure that the values of component parameters are reasonable You can perform checks on input output or operating point parameters The Spectre simulator checks parameter values against parameter soft limits To use the
166. digit followed by Q Underscores digits or backslash escaped characters This accommodates model or subcircuit libraries that use names like 2N2222 Instance Statements In this section you will learn to place individual components into your netlist and to assign parameter values for them Formatting the Instance Statement To specify components you use the instance statement You format the instance statement as follows name nodel nodeN master parami valuel paramN valueN When you specify components with the instance statement the fields have the following values name The unique name you give to the statement Unlike SPICE instance names the first character in Spectre instance names is not significant nodel nodeN The names you give to the nodes that connect to the component July 2002 61 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists master You have the option of putting the node names in parentheses to improve the clarity of the netlist See the examples later in this chapter This is the name of one of the following A built in primitive Such as resistor A model A subcircuit An AHDL module SpectreHDL or Verilog A language Note The instance statement is used to call subcircuits and refer to AHDL modules as well as to specify individual components For more information about subcircuit calls see Subcircuits on page 90 For
167. e n in isthe name you choose for the input node of the probe n out is the name you choose for the output node of the probe n The keyword iprobe is the primitive name of the component In the following example the current probe measures the current between nodes src and in names the measured current Iin and saves I in to the raw file Iin src in iprobe Note You can also direct the Spectre simulator to save currents with probes with a save statement option For further information see the description of save statement keywords in this chapter Saving Power To save power dissipated on a circuit subcircuit or device you use the pwr parameter Power is calculated only during DC and transient analyses The results are saved as a waveform representing the instantaneous power dissipated in the circuit subcircuit or device July 2002 205 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Formatting the pwr Parameter The syntax for the pwr parameter is illustrated by the following examples To save the power dissipated on a device or instance of a subcircuit the syntax is save instance_name pwr To save the total power the syntax is save pwr You can explicitly save particular power variables For example save pwr xl pwr x1l x2 ml pwr This statement saves three power signals n the total power dissipated pwr n the power dissipated in the x1 subcircuit instance
168. e De aec RC la cg s ED ED ve 93 Calling ouUbOllGUulls e KAAS E Siok Eee oa AAT Rt LU e ito ft teat 94 Modifying Subcircuit Parameter Values llllllllllsssn 95 Checking for Invalid Parameter Values 0 0002 es 95 Ile SUDCILGUH S us aci au pa ERO XRERCE E RRIDR TEC DH EA ER RE Row S CRT ENIRO R 96 Mod ling Parasiti s Aedui ye ox CREER ED ad aret d de RR RA n 97 Paramelterzed MOGdels ried ouod doa pt aa adir zone Mc oc crar aee EE DP AE REG 99 Inline Subcircuits Containing Only Inline model Statements 100 Process Modeling Using Inline Subcircuits llle 101 Yann ss kes 88 06 eek Dae women ans BORMAN heii a a a e Utd Ma Um 104 Auto Model Selection 5a gore iur dou as rrr pedo One We dur eS Gd v eee 105 Conditional l st riees Luo pe YEA OD ENIEd p XE e Eb Rok EIA E THEOCR RS 106 Scaling Physical Dimensions of Components 0 00 115 PNR CNET ITUR TIT TS EIL UOLUIT 117 NPort Example eno deeper eroe Ro es rap eO ree Rae aad ee AE dire 117 Creating an S Parameter File Automatically 0 00000 eee eee eee 118 Creating an S Parameter File Manually 0 00 118 Example of an S Parameter File 2 2 5 cece eee eves eee ae ewe eee aw ee 119 Reading the S Parameter File 0 ccc cee eens 120 S Parameter File Format Translator 0 0 ccc cece ee 120 6 PANNA SOS i erdt toc let at adh iA eire ead 129 Types oft Analyses Woe xd dre Ae sa Vete ee cM
169. e Spectre simulator can perform the analysis while sweeping a parameter The parameter can be frequency temperature component instance parameter component model parameter or netlist parameter If changing a parameter affects the DC operating point the operating point is recomputed on each step You can sweep the circuit temperature by giving the parameter name as t emp with no dev or mod parameter You can sweep a netlist parameter by giving the parameter name with no dev or mod parameter After the analysis has completed the modified parameter returns to its original value The syntax is as follows Name ac parameter value You can specify sweep limits by giving the end points or by providing the center value and the span of the sweep Steps can be linear or logarithmic and you can specify the number of July 2002 139 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses steps or the size of each step You can give a step size parameter step lin log dec to determine whether the sweep is linear or logarithmic If you do not give a step size parameter the sweep is linear when the ratio of stop to start values is less than 10 and logarithmic when this ratio is 10 or greater All frequencies are in Hertz The small signal analysis begins by linearizing the circuit about an operating point By default this analysis computes the operating point if it is not known or recomputes it if any significant component or circ
170. e easily identifiable Subcircuit Example GaAs Traveling Wave Amplifier GaAs Traveling wave distributed amplifier 2 26 MWTD Hewlett Packard Co Designed by Jerry Orr 1986 MTT symposium global gnd vdd simulator lang s Models model nGaAs gaas subckt cell o gl g2 TI o d d g2 Gb s s d c ends cell subckt stage i0 Devices Q1 ol Q2 02 Q3 03 Q4 04 Q5 05 Q6 06 Q7 07 Transmission TLil i0 TLi2 il TLi3 i2 TLi4 i3 TLi5 i4 TLi6 i5 TLi7 16 TLi8 i7 TLo1 00 July 2002 unpublished material pectre type n vto gnd d gnd tline len 355u vel g2 S nGaAs S capacitor c 0 033p gnd capacitor c 3p gi gnd nGaAs gnd capacitor c 0 033p C resistor r 4k gnd capacitor c 0 165p o8 LI b2 cell 152 b2 cell i3 b2 cell i4 b2 cell i5 b2 cell i6 b2 cell iy b2 cell lines gnd il gnd tline gnd 12 gnd tline gnd 13 gnd tline gnd i4 gnd tline gnd i5 gnd tline gnd i6 gnd tline gnd i7 gnd tline gnd i8 gnd tline gnd o1 gnd tline 92 5GHz 0 36 len 185u len 675u len 675u len 675u len 675u len 675u len 675u len 340u len 360u Z0 96 z0 96 z0 96 z0 96 z0 96 z0 96 z0 96 z0 96 z0 96 2 beta 0 012 cgs 148p cgd 016p fc 0 5 vel vel vel vel vel vel vel 36 36 36 36 36 36 36 36 36 OOOO Product Version 5 0 Spectre Circu
171. e file is the name of the library file to be included The library reference statement looks like an include statement except for the specification of the library section When the file is being inserted only the named section is actually included Library Definition The library definition has to be in a separate file The library has to have a name Each section in the library has to be named because this name is used by the library reference statement to identify the section to include The statements within each section can be any valid statement This is importantto remember when using libraries in conjunction with alter groups because the altergroup statement is restrictive in what can be specified The optional names are allowed at the end of the section and library These names must match the names of the section or library The following is the syntax for library definition library libraryName section sectionName statements endsection sectionName section anotherName statements endsection anotherName library libraryName One common use of library references is within altergroup statements For example al altergroup change models to FAST process corner include MOSLIB section FAST Multidisciplinary Modeling Multidisciplinary modeling involves setting tolerances and using predefined quantities July 2002 73 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists Setting Tole
172. e name is the name of a component or analysis you get the same information as you do with spectre helpsort name but the parameters are sorted alphabetically instead of divided into related groups July 2002 80 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features Scaling Numerical Literals If a parameter value is an integer or a floating point number you can scale it in the following ways m Follow the number with an e or an E and an integer exponent for example 2 6563 5 32e 4 1E 14 3 04E6 m Use scale factors for example 5u 3 26k 4 2m You cannot use both scale factors and exponents in the same parameter value For example the Spectre simulator ignores the p in a value such as 1 234E 3p Caution The Spectre simulator also accepts additional data files such as the waveform and noise files accepted by the independent sources or the S parameter file accepted by the N port Generally these files do not accept numbers with scale factors The Spectre mode simulator lang spectre accepts only the following ANSI standard SI scale factors T2107 G 10 M 10 K 10 k 10 E 2107 c 10 m 10 u 10 n 10 p 10 2 10 az107 Note SI scale factors are case sensitive The Spectre simulator allows you to specify units but only if you specify a scale factor If specified units are ignored Thus c lpf units f l 1uH units H are accepted
173. e name you choose for the output node of the probe n Thekeyword iprobe is the primitive name of the component In the following example the current probe measures the current between nodes src and in names the measured current Iin and saves Iin to the raw file Iin src in iprobe Note You can also direct the Spectre simulator to save currents with probes with a save statement option For further information see the description of save statement keywords in this chapter Saving Power To save power dissipated on a circuit subcircuit or device you use the pwr parameter Power is calculated only during DC and transient analyses The results are saved as a waveform representing the instantaneous power dissipated in the circuit subcircuit or device Formatting the pwr Parameter The syntax for the pwr parameter is illustrated by the following examples July 2002 217 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options To save the power dissipated on a device or instance of a subcircuit the syntax is save instance_name pwr To save the total power the syntax is save pwr You can explicitly save particular power variables For example save pwr xl pwr xl x2 ml pwr This statement saves three power signals n The total power dissipated pwr n The power dissipated in the x1 subcircuit instance x1 pwr n The power dissipated in the x1 x2 m1 MOSFET Power Option
174. e output with a probe component Examples of Analysis Statements The following examples illustrate analysis statement syntax XferVsTemp xf start 0 stop 50 step 1 probe Rload param temp freq 1kHz This statement specifies a transfer function analysis x with the user supplied name XferVsTemp With all transfer functions computed to a probe component named R1oad it sweeps temperature from 0 to 50 degrees in 1 degree steps at frequency 1 kHz For long statements you must place a backslash at the end of the first line to let the statement continue on the second line Sparams sp stop 0 3MHz lin 100 ports Pin Pout This statement requests an S parameter analysis sp with the user supplied name Sparams A linear sweep starts at zero the default and continues to 3 MHz in 100 linear steps The ports parameter defines the ports of the circuit ports are numbered in the order given The following example statement demonstrates the proper format to specify optional output nodes p n FindNoise out gnd noise start 1 stop 1MHz Basic Analysis Rules When you prepare netlists for the Spectre simulator remember these basic analysis rules July 2002 65 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists The Spectre simulator has no default analysis If you do not put any analysis statements into a netlist the Spectre simulator issues a warning and exits For most analyses if you specify
175. e that is placed in parallel to the device These current sources have zero mean and some variance The simulation results are displayed in descending order For MOSFET devices bsim3v3 the analysis displays threshold voltage mismatch current factor mismatch gate voltage mismatch and drain current mismatch For bipolar devices vbic it displays base emitter junction voltage mismatch For resistors limited to two terminal resistance it displays resistor mismatches July 2002 151 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses The analysis replaces multiple simulation runs and tedious calculations in the estimation of mismatch performance It automatically identifies the set of critical matched components during circuit design For example when there are matched differential pairs in the circuit the contribution of two matched transistors will be equal in magnitude and opposite in sign Model Definition name pnode nnode dcmatch parameter value Examples of the dcmatch command The following example investigates the 3 sigma dc variation at the output of the current flowing through the device vd which is a voltage source in the ciruit netlist dcmm1 is the name of the analysis dcmatch is a keyword indicating the dc mismatch analysis and the parameter settings oprobe vd and port i 1 specify that the output current is measured at the first port of vd Device mismatch contributions less than 1e 3 of the maximu
176. e voltages and currents through other components that compute current Use 1v1pub or allpub to exclude signals at internal nodes on devices the internal collector base emitter on a BJT the internal drain and source on a FET etc Ivlpub and allpub also exclude the currents through inductors controlled sources transmission lines transformers etc Note Setting the save parameter value to selected without any save statements in the netlist is not equivalent to specifying no output Currently the Spectre simulator saves all circuit nodes and branch currents with this combination of settings This might change in future releases of the Spectre simulator Saving Subcircuit Signals To save groups of signals for subcircuits you must adjust two parameter settings n Setthe save parameter to either 1v1 or 1v1pub n Setthe nest1v1 parameter to the number of levels in the hierarchy you want to save The default setting for nest 1v1 is infinity which saves all levels Saving Groups of Currents The currents parameter of the opt ions statement computes and saves terminal currents You use it to create settings for currents that apply to all terminals in the netlist For two terminal components the Spectre simulator saves only the first terminal entering currents You must use a save statement or use the global redundant currents parameter of the opt ions statement to save data for the second terminal of a two terminal component For mo
177. ectre online help spectre h n The Spectre simulator saves all terminal currents for nonlinear components currents specified with the save statement and routinely computed currents optl options currents nonlinear n The Spectre simulator saves all terminal currents opt2 options currents all Setting Multiple Current Probes Sometimes you might need to set a large number of current probes This could happen for example if you need to save a number of ACs Current probes can find such small signal currents when they are not normally computed You can specify that all currents be calculated with current probes by placing useprobes yes in an options statement July 2002 221 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options Setting multiple current probes can greatly increase the DC and transient analysis simulation times Consequently this method is typically used only for small circuits and AC analysis Important Adding probes to circuits that are sensitive to numerical noise might affect the solution In such cases an accurate solution might be obtained by reducing reltol Saving Subcircuit Terminal Currents You use the subcktprobelvl parameter to control the calculation of terminal currents for subcircuits Current probes are added to the terminals of each subcircuit up to subcktprobelvl deep You can then save these terminal currents by setting the save parameter The nest 1v1 param
178. ectre Circuit Simulator User Guide Analyses You may specify values to force for the DC analysis by setting the parameter force The values used to force signals are specified by using the force file the ic statement or the ic parameter on the capacitors and inductors The force parameter controls the interaction of various methods of setting the force values The effects of individual settings are force none Any initial condition specifiers are ignored force node The ic statements are used and the ic parameter on the capacitors and inductors are ignored force dev The ic parameters on the capacitors and inductors are used and the ic statements are ignored force all Boththe ic statements and the ic parameters are used with the ic parameters overriding the ic statements If you specify a force file with the readforce parameter force values read from the file are used and any ic statements are ignored Once you specify the force conditions the Spectre simulator computes the DC analysis with the specified nodes forced to the given value by using a voltage source in series with a resistor whose resistance is rforce see options AC Analysis The AC analysis linearizes the circuit about the DC operating point and computes the response to all specified small sinusoidal stimulus For more information on specifying small sinusoidal stimulus see Chapter 4 Component Statements Part 2 in the Spectre Simulator Reference Th
179. ectre provides three ways to gain access to its language in a SPICE netlist 1 Change the input language to Spectre using the simulator lang command 2 Append Spectre parameters to a SPICE statement 3 Hide Spectre text from SPICE Each of these methods is discussed in the following sections Spectre s simulator lang Command You can use the Spectre Netlist Language or an extended form of the SPICE2 3 input language for your simulation You specify which language with a simulator lang command You can change the input processing mode with the simulator lang command A simulator lang spice command causes subsequent input to be processed in the SPICE extension mode a simulator lang spectre command causes the input processing to conform to the Spectre Netlist Language Remember that you can give the simulator lang command anywhere that you can enter an instance statement and it affects all subsequent input regardless of whether the command is part of an if statement Use of Spectre syntax in the SPICE mode or SPICE syntax in the Spectre mode results in an error The simulator lang command has the following format simulator lang spice simulator lang spectre Although the simulator lang command is expected to be the first line in the netlist it does not have to be The commands take effect immediately and remain in effect until the end of input or until the next simulator lang command For example you can include Spectre li
180. eep and the second example writes the state file from the final point in the DC sweep Drift dc param temp start 0 stop 50 0 step 1 readns ua741 dc write ua741 dc Drift dc param temp start 0 stop 50 0 step 1 readns ua741 dc writefinal ua741 dc Creating a State File Manually The syntax for creating a state file in a text editor is simple Each line contains a signal name and a signal value Anything after a pound sign 4 is ignored as a comment The following is an example of a simple state file State file generated by Spectre from circuit file wilson during stepresponse at 5 39 38 PM jan 21 1992 1 588793510612534 2 1 17406247989272 3 14 9900516233357 pwr 15 vcc p 9 9483766642647e 06 Reading State Files To read a state file as an initial condition use the read transient analysis parameter To read a state file as a nodeset use the readns parameter This example reads the file inc Cond as initial conditions DoTran z12 tran start 0 stop 0 003 step 0 00015 maxstep 6e 06 read intCond This second example reads the file soluEst as a nodeset DoTran z12 tran start 0 stop 0 003 step 0 00015 maxstep 6e 06 readns soluEst Special Uses for State Files State files can be useful for the following reasons July 2002 241 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques m You can save state files and use them in later simulations
181. el selection parameters are out of range Models are assigned to instances depending on the initial values of their parameters when the circuit is input Note that the instances are not reassigned to new models if the selection parameters later change However the models are updated if the circuit temperature is changed Notice that even though nmos is defined as a subcircuit it is called as if itis a MOSFET primitive July 2002 112 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features The MOSFET model parameters are deleted to keep this example to a reasonable length and ordinarily both the N and P channel models are in the same file If you added the model parameters and a pmos model this file could replace cmos mod in the previous example N CHANNEL MOS 1u NMOS PROCESS The following group of models represent N channel MOSFETs over the following ranges lu lt 1 lt oo lu lt w lt oo Q0 lt T lt 55 process corners FAST TYPICAL SLOW Warnings are issued if these limits are violated This model takes 4 parameters l w ls and ld The defaults for each of these parameters is lum Source Gate Drain simulator lang spectre Complain if global constants are out of rang TooCold paramtest warnif temp lt 0 message The nmos model is
182. ells the Spectre simulator how to construct the filename You can use percent codes in environment variables in spectre command parameters or in your netlist wherever you need to specify filenames for simulation results For example C is the predefined percent code for the name of the input circuit file If your circuit file is named opamp1 and you place the following raw setting for your UNIX environment variable setenv SPECTRE DEFAULTS raw C raw the Spectre simulator sends simulation results to a file named opamp1 raw Description of Spectre Predefined Percent Codes These are the percent code options that can help you organize your simulation data oe A A is replaced by the name of the current analysis that is running If it is specified in a device statement it is expanded to a blank string because there is no current analysis C is replaced by the input circuit filename as it is used in the command line If the circuit filename is opamp1 the specification C raw generates a file named opampl raw oe Q When the Spectre simulator does not know the name of the input file as when the circuit is read from the standard input from a pipe or from a redirected file the Spectre simulator substitutes the name stdin for C July 2002 248 Product Version 5 0 Spectre Circuit Simulator User Guide Managing Files oe J D is replaced by the date when the program started For example the specif
183. eps can be linear or logarithmic Swept parameters return to their original values after the analysis However certain other analyses also allow you to sweep a parameter while performing that analysis For more details check spectre h for each of the following analyses The following table shows you which parameters you can sweep with different analyses A component A component Time TEMP FREQ instance model ipe parameter parameter p DC analysis dc e e AC analysis ac 3 e e e July 2002 156 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Acomponent Acomponent Time TEMP FREQ instance model parameter parameter A netlist param eter Noise analysis A e e e noise S parameter e e e analysis sp Transfer function e b e e analysis xf Transient analysis tran Time domain reflectometer analysis t dr Periodic steady 2 state analysis pss Periodic AC analysis pac Periodic transfer function analysis pxf Periodic noise s analysis pnoise Envelope following analysis env1p Sweep analysis a sweep DC Match Analysis e e dcmatch Stability Analysis P s e e e stb Note To generate transfer curves with the DC analysis specify a parameter and a sweep range If you specify the oppoint parameter for a DC analysis the Spectre simulator computes the linearized model for each nonlinear component If you specify both a DC
184. er in the filename which is not interpreted as a percent code indicator The predefined percent codes feature does not perform recursive substitutions For example if you have an input file named A SD xyz and you create an output file with the percent code designation C raw the Spectre simulator creates the output file A SDxyz raw The Spectre simulator does not substitute the simulator name for 5 in this case Customizing Percent Codes You can define your own percent codes or redefine existing codes with the lt x gt option of the spect re command Names of customized percent codes can be any single uppercase or lowercase letter You can define percent codes in two ways July 2002 249 Product Version 5 0 Spectre Circuit Simulator User Guide Managing Files m You can define percent codes for a single simulation by typing this option into the command line with the spect re command at the start of the simulation m You can specify the customized percent code as a default by typing the spectre command into the SPECTRE_DEFAULTS environment variables For example if you type in the following instruction at the command line spectre E opampl test3 the Spectre simulator runs a simulation for circuit test 3 During this simulation the Spectre simulator substitutes the name opamp1 for any E it finds in results filename specifications You undefine customized percent codes with the x spectre command op
185. ercent code 249 S DEFAULTS 234 sample input file differential amplifier 109 GaAs traveling wave amplifier 92 process file 112 two port test circuit 117 uA741 operational amplifier save parameter example 206 207 217 219 formatting 207 219 options 207 219 setting with an analysis statement 134 setting with the options statement save statement 201 examples 203 215 formatting 201 213 keywords 202 203 214 operating point parameters of individual components saving 202 214 saving signals by keywords 202 214 by terminal index 202 214 by terminalname 202 213 of individual components 202 213 of individual nodes 202 213 of individual subcircuits 203 215 voltages of individual nodes saving 202 213 saveahdivars 222 savefamilyplots parameter Monte Carlo analysis 168 saveprocessparams parameter Monte Carlo analysis 164 saveprocessvec parameter Monte Carlo analysis 166 saving all ahdl variables 222 currents for AC analysis 204 216 groups of currents with the currents parameter 220 with the save and nestlvl parameters 207 219 208 307 Product Version 5 0 Spectre Circuit Simulator User Guide groups of signals in main circuits with the save parameter 207 219 in subcircuits 208 220 in subcircuits with the nestlvl parameter 207 219 individual currents with current probes 204 216 with the save statement 201 21 individual signals of subcircui
186. ese results you need to know the names of the files and directories where the Spectre simulator stores these results In this section you will learn how the Spectre simulator names its output directories and files and how you can change these naming conventions to fit your needs The information in this section applies to psf and wsf formats July 2002 225 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options How the Spectre Simulator Creates Names for Output Directories and Files When you create a netlist you give the netlist a filename When you simulate the circuit the Spectre simulator adds the suffix raw to this filename to create the name of the output directory for the simulation For example results from the simulation of a file named test are stored in a directory named test raw In the output directory results from each analysis you specify are stored in separate files The root of each filename is the name you gave the analysis in the netlist and the suffix for each filename is the type of analysis you specified For example if you run the following analysis the Spectre simulator stores the results in a file named Sparams sp Sparams sp start 100M stop 100G dec 100 For the sweep and montecarlo analyses the names of the filenames are a concatenation of the parent analysis name the iteration number and the child analysis name For example sweepl sweep param temp values 25 50 d
187. et to the default for the parameter July 2002 243 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques Changing Parameter Values for Models To change a parameter value for model files with the altergroup statement you list the device model and circuit parameter statements as you do in the main netlist Within an alter group each model is first defaulted and then the model parameters are updated You cannot nest alter groups You cannot change from a model to a model group and vice versa The following example demonstrates altergroup statement syntax agl altergroup parameters pl 1 model myres resistor rl le3 af pl model mybsim bsim3v3 lmax pl lmin 3 5e 7 Further Examples of Changing Component Parameter Values This example changes the is parameter of a model named SH3 to the value le 15 modify2 alter mod SH3 param is value 1e 15 The following examples show how to use the param default in an alter statement The first parameter listed for resistors in the Spectre online help spectre h is the default For resistors this is the resistance parameter r Consequently if R1 is a resistor the following two alter statements are equivalent changel alter dev R1 param r value 50 changel alter dev R1 value 50 Changing Parameter Values for Circuits When you change a circuit parameter you use the same syntax as when you change a device or model parameter except that you do not enter a d
188. eter controls how many levels are returned Saving All AHDL Variables If you want to save all the ahdl variables belonging to all the ahdl instances in the design set the saveahdlvars option to a11 using a Spectre options command For example Saveahdl options saveahdlvars all Listing Parameter Values as Output You can generate lists of component parameter values with the info statement With this statement you can access the values of input output and operating point parameters These parameter types are defined as follows n Input parameters Input parameters are those you specify in the netlist such as the given length of a MOSFET or the saturation current of a bipolar resistor n Output parameters Output parameters are those the simulator computes such as temperature dependent parameters and the effective length of a MOSFET after scaling n Operating point parameters Operating point parameters are those that depend on the operating point July 2002 222 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options You can also list the minimum and maximum values for the input output and operating point parameters along with the names of the components that have those values Specifying the Parameters You Want to Save You specify parameters you want to save with the info statement what parameter You can give this parameter the following settings Setting Action none Lists no p
189. etlist For example if you use the same netlist in more than one simulation you probably want different names for the output files You can specify names in two ways n You can specify your directory name from the command line or in an environment variable with the spect re command raw option For example if you want your output directory to be named test circuit raw you start your simulation as follows spectr raw test circuit lt inputFilename gt n You can set the rawfile parameter of the options statement For example the following opt ions statement creates an output directory named test circuit raw Setup options rawfile test circuit Note The Spectre simulator has some additional features that help you manage data by letting you systematically specify or modify filenames For more information about these features see Chapter 11 Managing Files July 2002 228 Product Version 5 0 Spectre Circuit Simulator User Guide Running a Simulation This chapter discusses the following topics W Starting Simulations on page 229 Checking Simulation Status on page 230 Interrupting a Simulation on page 231 Recovering from Transient Analysis Terminations on page 231 Controlling Command Line Defaults on page 233 Starting Simulations To start a simulation you type the spect re command at the command line with the following syntax Spectre options lt inputfile gt The spectre command starts a simula
190. ev or a mod parameter This example changes the ambient temperature to 0 C change2 alter param temp value 0 The following table describes the circuit parameters you can change with the alter statement Parameter Description temp Ambient temperature tnom Default measurement temperature for component parameters July 2002 244 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques Parameter Description scalem Component model scaling factor scale Component instance scaling factor Note If you change temp or tnom using an alter statement all expressions with temp or tnom are reevaluated Modifying Initial Settings of the State of the Simulator You can change the initial settings for the state of the simulator by placing a set statement in the netlist The set statement is similar to the options statement that sets the state of the simulator but it is queued with the analysis statements in the order you place them in the netlist You use the set statement to change previous options or set statement specifications The modifications apply to all analyses that follow the set statement in the netlist until you request another parameter modification The set and options statements have many identical parameters but the set statement cannot modify all options statement parameters The parameter listings in the Spectre online help spectre h tell you which parameters you can reset with the se
191. explosion region 257 missing diode would be forward biased 258 pnoise analysis brief description of 131 pointlocal relative error parameter 142 power in Watts power supply rejection netlist example of measurement discussed 135 power saving 205 217 predefined netlist parameters 90 predefined percent code character 249 CMlVersion 249 date 249 July 2002 described 248 host name network name 249 input circuit file name 248 process ID 249 program starting time 249 simulator name 249 substitution in 249 version string 249 predefined quantities 74 prepend path 292 previous solutions starting analyses from 237 prevoppoint parameter in analyses 237 printout to screen example 31 probe statement 205 217 probes setting in analyses 133 process block 170 process corners example 111 process file sample input file 1 ie process identification number PID 230 use of 163 process modeling using inline subcircuits 101 process parameter correlation statement 174 processparamfile parameter Monte Carlo analysis 165 processscalarfile parameter Monte Carlo analysis 165 profile file and Cadence range limits 263 ps utility UNIX 230 pseudotransient method 245 PSF parameter storage format 224 formatting output files 235 psfascii output format 224 psfbin output format 224 pss analysis brief description of 131 ptran as homotopy parameter option 246 punctuation characters in Spectre syntax 59 PWL definition 72
192. f Spectre s native language When Spectre syntax is not an acceptable solution the SPICE Reader can be used to ensure access to as much of Spectre s capabilities as possible Running the SPICE Reader In order for Spectre to properly process a SPICE netlist the SPICE Reader must be enabled By default the SPICE Reader is disabled when you invoke Spectre Use the command spectrespp rather than the spect re command to enable the SPICE Reader For example the following command invokes Spectre with the SPICE Reader for the input netlist amp sp spectrespp amp sp July 2002 42 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility The Spice Reader runs on the top level netlist as well as on any included files that contain SPICE syntax The SPICE Reader converts the netlist to Spectre native syntax before it sends the design to the Spectre netlist reader From the 5 0 release any measure statements found in the Spice input file are converted to MDL Measurement Description Language before being passed on to Spectre The conversion is done via the creation of an MDL control file which is written to the current directory This control file takes on the name of the netlist with a suffix of md1 The simulation that immediately follows the conversion uses the MDL option to Spectre with this control file to evaluate the measure expressions Results are written to a file with the same name as the control file netlist wit
193. f you have File Transfer Protocol FTP access on the Internet You can also get information about the performance of several simulators with these circuits The Spectre circuit simulator has successfully simulated all of these circuits Sometimes the netlists required minor syntax corrections such as inserting balancing parentheses but circuits were never altered and options were never changed to affect convergence Improved Models The Spectre circuit simulator has MOSFET Level 0 3 BSIM1 BSIM2 BSIM3 BSIM3v3 EKV MOSS JFET TOM2 GaAs MESFET BJT VBIC HBT diode and many other models It also includes the temperature effects noise and MOSFET intrinsic capacitance models The Spectre Compiled Model Interface CMI option lets you integrate new devices into the Spectre simulator using a very powerful efficient and flexible C language interface This CMI option the same one used by Spectre developers lets you install proprietary models Spectre Usability Features and Customer Service The following features and services help you use the Spectre circuit simulator easily and efficiently m You can use Spectre soft limits to catch errors created by typing mistakes July 2002 19 Product Version 5 0 Spectre Circuit Simulator User Guide Introducing the Spectre Circuit Simulator B Spectre diagnosis mode available as an options statement parameter gives you information to help diagnose convergence problems m You can r
194. file Option Description file format freq Scale input file output file sim hpmns Input or output is in HPMNS S parameter file format sim libra Input or output is in LIBRA S parameter file format sim mharm Input or output is in MHARM S parameter file format sim Inm Input or output is in LNM S parameter file format The file format default is Spectre If the option is not specified the input file must be in LIBRA or Spectre format The translator always automatically checks the input file format to determine the output file format For example if you specify the option as sim hpmns and the input file is found to be in Spectre or HPMNS format the translator generates an output file for HPMNS or Spectre format If the input file format does not match the option the translator reports an error message and exits f FreqScale If the frequency scale is not explicitly given it is taken to be FreqScale Thus TrueFreq GivenFreq FreqScale The default is 1 This option is ignored if the scale is specified on the first frequency or the line beginning with This is the input filename If both filenames are not given or if the input file is specified as the input is taken from the standard input This is the output filename If it is not given or if itis specified as the output is delivered to the standard output Input File Syntax This section describes the input file synt
195. first iteration number are as follows m You can reproduce a particular run from a previous experiment when you know the starting seed and run number but not the corresponding seed m If you are a standalone Spectre user you can run a Monte Carlo analysis of 100 runs analyze the results decide they are acceptable and then decide to do a second analysis July 2002 168 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses of 100 runs to give a total of 200 runs By specifying the irstrun 101 for the second analysis the Spectre simulator retains the data for the first 100 runs and runs only the second 100 runs This gives the same results and random sequence as if you ran just a single Monte Carlo analysis of 200 runs Sample Monte Carlo Analyses For a Monte Carlo analysis the Spectre simulator performs a nominal run first if requested calculating the specified outputs If there is any error in the nominal run or in evaluating the export statements after the nominal run the Monte Carlo analysis stops If the nominal run is successful then depending on how the variations parameter is set the Spectre simulator applies process variations to the specified parameters and mismatch variations if specified to those parameters for each subcircuit instance If the export statements are specified the corresponding performance measurements are saved as a new file or appended to an existing file The following Monte
196. g exp as Cvs i omer wo cox cos ass pas gt 10x am emot vie we 7 0 9 an atm ren aero yr vx mt e opt a 5 6 stm sse imag amo x2 sort mue mw 1 2 9 eme n e oj n pit m 1 a oe tm sam JH Calculator Window July 2002 34 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre y Results Browser Filter 4 Commands Help A 100m Apache MM Navajo adm barbaral log lost found nsmail opt osce osc cir osc raw psf stuff swap2 tmp var Results Browser July 2002 35 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre F Waveform Window Active 2 Window Zoom Axes Curves Markers Annotation Edit Tools Help mouse L awviMouseSingleSele M hiRepe at Waveform Window Displaying a Waveform 1 In the Results Browser scroll if necessary until osc raw is visible and then click on osc raw July 2002 36 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre The display in the Results Browser now looks like this is Results Browser Filter 4 Commands Help 100m In Ripache MM Navajo adm barbaral log lost found nsmail opt osc L1 cc analysisType osc cir osc rau psf stuff swap2 tmp syeepVariable var
197. g Output for Viewing on page 224 n Accessing Output Files on page 225 Signals as Output Signals are quantities that the simulator must determine to solve the network equations formulated to represent the circuit The signals must be known before other output data can be computed Signals are mainly the physically meaningful quantities of interest to the user such as the voltages on the topological nodes and naturally computed branch currents such as those for inductors and voltage sources Other examples of signals are the voltages at the internal nodes of components and the terminal currents computed by using current probes at device or subcircuit terminals Note If there are more than four terminals on a device such as vbic hbt or bta soi the fifth and higher terminals do not return actual currents but return 0 0 You can save signals and include them as simulation results Signals you can save include the following n Voltages at topological nodes n All currents July 2002 212 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options n Other quantities the Spectre circuit simulator computes to determine the operating point and other analysis data Saving Signals for Individual Nodes and Components You can include signals for individual nodes and components in the save list by placing save statements not to be confused with the save parameter in your netlist When you specify signals
198. ge for transistor m1 in the x1 subcircuit These waveforms are shown in Figure 6 1 on page 179 Figure 6 2 on page 179 and Figure 6 3 on page 180 The ring oscillator output waveform is shown before and after degradation in Figure 6 4 on page 180 Figure 6 1 Transistor m1 Substrate Current 0 20 0 15 1 Substrate Current 0 10 uA 0 05 0 0 0 0 0 002 0 004 0 006 0 008 0 010 Time usec Figure 6 2 Transistor m1 Stress 0 025 0 020 Stress 0 015 0 010 0 005 f 0 0 0 002 0 004 0 006 0 008 0 010 Time usec July 2002 179 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Figure 6 3 Transistor m1 Effective Device Age 4 00e 18 3 00e 18 Age Sec 2 00e 18r 1 00e 18 t 0 00e 00 0 0 0 002 0 004 0 006 0 008 0 010 Time usec Figure 6 4 Oscillator Output at Two Different Ages 6 0 4 0 Vout 2 0 0 0 2 0 i i i 0 0 0 002 0 004 0 006 0 008 0 010 Time usec The Spectre simulator also creates two files called moslev3_dgt_0 and moslev3_dgt_4 0 These files are the sorted tables that contain the results of hot electron analysis The filenames show that the outputs are for level 3 MOSFETs The numbers 0 and 4 0 in the filenames further specify that the degradations are for circuitage 0 and July 2002 180 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses circuitage two files are shown in the following table
199. ge is displayed if the current that enters any node from all attached gmin conductors is larger than either iabstol or reltol multiplied by the sum of the absolute value of the individual currents that enter the node If your circuit is not sensitive to small leakage currents you can ignore this message If your circuit is sensitive to these currents reduce the gmin value or set it to zero Minimum Timestep Used If this problem occurs the Spectre circuit simulator discards the timepoint that does not meet the convergence criteria and cuts the timestep 1 Make sure devices have junction and overlap capacitance specified 2 Increase maxiters but do not go higher than 200 3 Change to the gear2 or gear2on1y method of integration 4 Reduce other occurrences of the local truncation error cutting the timestep Increase lteratio and increase the absolute error tolerances vabstol and iabstol Do not go too high with any of these 5 Combine 2 3 and 4 and set cmin to prevent instantaneous change at every node in the circuit 6 Relax reltol in combination with 5 Syntax Errors Warning from spectre in indab 7 during circuit read in na300 scs 27 c11 Encountered statement in Spectre format while in Spice language mode This will not be supported in a future release The Spectre parser is dual mode and accepts both the Spectre native language and documented Spice2G6 The default for the Spectre simulator is SPICE If you i
200. gn opamp sp Specifying the spp binary to be used By default the spp binary that is located in the Cadence hierarchy CDS INSTALL tools dfII bin spp isusedbythe spect respp command You can specify the use of other spp executables with the sppbin command line option In the following example spp from the current directory is used spectrespp sppbin spp opamp sp Specifying the location of the measurement output Also by default the output of the measure statements is written to a file with the base name of the netlist and a suffix of measure In the example of opamp sp A measurement file named opamp measure would be created This can be overridden with the measure command line option spectrespp measure design measure design opamp sp Notice that when specifying the measure option you must also specify the design option to identify the netlist All other command line options are passed to Spectre Please type spectrespp usag for the online help July 2002 44 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility Using the SPICE Reader to Convert Netlists In many cases the SPICE data to be used with Spectre is a library of models or reusable blocks that is subcircuits Rather than using the SPICE Reader to interpret these files each time they are used you can convert the netlist to Spectre s native syntax This is done by running the SPICE Reader alone spp and us
201. gs Warning from spectre at dc 191 mA during DC analysis srcSweep mos mod The bulk drain junction current exceeds imelt The results computed by Spectre are now incorrect because the junction current model has been linearized Or xram d3247 The junction is melting increase imax The Spectre simulator provides two parameters imax and imelt that limit the current across a PN junction These parameters aid convergence and prevent numerical overflow July 2002 257 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting The junction characteristics of the device are assumed to be accurately modeled for current up to imax If imax is exceeded during iterations the linear model is substituted until the current drops below imax or until convergence is achieved If convergence is achieved with the current exceeding imax the results are inaccurate and Spectre prints a warning similar to the first one above The imelt parameter is used as a limit warning for the junction current This parameter can be set to the maximum current rating of the device By default it is set to the value of imax When any component of the junction current exceeds imelt Spectre issues a warning and again the results become inaccurate The junction current is linearized above the value of imelt to prevent arithmetic exceptions Both these parameters have current density counterparts jmax and jme1t
202. h a measure suffix For example the amp sp SPICE netlist above creates a control file named amp md1 and a measurement output file named amp measure You simply enter the spect respp command with the netlist and the rest of the steps are completed for you automatically The MDL control file is left behind for future use Note In previous releases the command line option spp was used to invoke the SPICE Reader While this method is still supported it is advised that you use the spect respp command if measure statements are included in the input file For more information on MDL see the SpectreMDL User Guide and Heference For backward compatibility a limited SPICE2 netlist reader is embedded into the Spectre netlist reader This reader supports much of SPICE2G6 syntax and has as its primary use the processing of SPICE style model cards If the SPICE Reader is not used this limited SPICE netlist reader is used This is only for backwards compatibility and might be removed in a future release to be replaced by the SPICE Reader This limited SPICE netlist reader is no longer documented as of the 4 4 3 release In the rest of this chapter SPICE Reader refers to the full SPP SPICE Reader and not this limited version Running the SPICE Reader from Analog Artist When using Spectre within Analog Artist the need to read SPICE netlists is usually limited to model files and information from extraction tools that comes into the netlist by
203. han other simulators because its convergence algorithms are effective with large circuits because it is fast and because it is frugal with memory and uses dynamic memory allocation For large circuits the Spectre circuit simulator typically uses less than half as much memory as SPICE July 2002 16 Product Version 5 0 Spectre Circuit Simulator User Guide Introducing the Spectre Circuit Simulator Improved Accuracy Improved component models and core simulator algorithms make the Spectre circuit simulator more accurate than other simulators These features improve Spectre accuracy m Advanced metal oxide semiconductor MOS and bipolar models Q The Spectre BSIM3v3 is a physics based metal oxide semiconductor field effect transistor MOSFET model for simulating analog circuits Q The Spectre models include the MOSO model which is even simpler and faster than MOS for simulating noncritical MOS transistors in logic circuits and behavioral models MOS 9 EKV BTA HVMOS BTA SOI VBIC95 TOM2 HBT and many more m Charge conserving models The capacitance based nonlinear MOS capacitor models used in many SPICE derivatives can create or destroy small amounts of charge on every time step The Spectre circuit simulator avoids this problem because all Spectre models are charge conserving m Improved Fourier analyzer The Spectre circuit simulator includes a two channel Fourier analyzer that is similar in application to the SPICE
204. hat is piped to the spect re command As a default action it puts the output simulation data in the directory stdin raw setenv SPECTRE DEFAULTS raw C raw sed e s S g cktfile spectre In the second example redefining the C percent code causes the Spectre simulator to base the output filename on the input filename The spect re command in the environment variable redefines the normal predefined c code The Spectre simulator substitutes the July 2002 250 Product Version 5 0 Spectre Circuit Simulator User Guide Managing Files name ckt file for all C specifications and puts the output simulation data in the directory cktfile raw setenv SPECTRE DEFAULTS raw C raw sed e s S g cktfile spectre C cktfile Note For more information about Spectre defaults see Selecting Limits for Parameter Value Warning Messages on page 263 and the Spectre Circuit Simulator Reference manual Creating Filenames from Parts of Input Filenames Colon modifiers x create filenames from parts of input filenames You can use colon modifiers with all percent codes except the code For example if you apply C r raw to the input filename opamp ckt C is the input filename opamp ckt r is the root of the input filename opamp raw is the new filename extension The result is the output filename opamp raw In this example x is the colon modifier Definitions of
205. he alter group and can use the simulator lang spice command to switch language mode For more details on the include command see the Spectre online help spectre h include A model defined in the netlist has to have the same model name and primitive type Such as bsim2 bsim3 or bjt in the alter group For model groups you can change the number of models in the group You cannot change from a model to a model group and vice versa For details on model groups see the Spectre online help spectre h bsim3v3 Further Examples of Changing Component Parameter Values This example changes the is parameter of a model named SH3 to the value le 15 modify2 alter mod SH3 param is value 1e 15 The following examples show how to use the param default in an alter statement The first parameter listed for resistors in the Spectre online help is the default For resistors this is the resistance parameter r Consequently if R1 is a resistor the following two alter statements are equivalent changel alter dev R1 param r value 50 changel alter dev R1 value 50 Changing Parameter Values for Circuits When you change a circuit parameter you use the same syntax as when you change a device or model parameter except that you do not enter a dev or a mod parameter This example changes the ambient temperature to 0 C change2 alter param temp value 0 July 2002 185 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements
206. he instance parameter q1 area and the model parameter nbjt 1 rb The values are computed for analysis analDC1 sens 1 n2 7 for analAC This command computes the AC sensitivities of nodes 1 n2 and 7 to all available device and model parameters Note This can result in a lot of information Fourier Analysis The ratiometric Fourier analyzer measures the Fourier coefficients of two different signals at a specified fundamental frequency without loading the circuit The algorithm used is based on the Fourier integral rather than the discrete Fourier transform and therefore is not subject to aliasing Even on broad band signals it computes a small number of Fourier coefficients accurately and efficiently Therefore this Fourier analyzer is suitable on clocked sinusoids generated by sigma delta converters pulse width modulators digital to analog converters sample and holds and switched capacitor filters as well as on the traditional low distortion sinusoids produced by amplifiers or filters The analyzer is active only during a transient analysis For each signal the analyzer prints the magnitude and phase of the harmonics along with the total harmonic distortion at the end of the transient analysis The total harmonic distortion is found by summing the power in all of the computed harmonics except DC and the fundamental Consequently the distortion is not accurate if you request an insufficient number of harmonics The Fourier analyze
207. he second terminal of a two terminal component For more information about the save statement see Saving Signals for Individual Nodes and Components on page 201 July 2002 208 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Setting the currents Parameter The currents parameter has the following options Setting Action selected Saves only currents that you specifically request with save statements or save parameters Also saves naturally computed branch currents currents through current probes voltage sources and inductors This is the default setting nonlinear Saves all terminal currents for nonlinear devices naturally computed branch currents currents through current probes voltage sources and inductors and currents you specify with save statements Can significantly increase simulation time all Saves all terminal currents and currents available from selected settings to the raw file Can significantly increase simulation time Note Currently if you set the currents parameter value to nonlinear orall and do not specify a save parameter value in an options statement the Spectre simulator saves circuit nodes as well as the currents you requested This might change in future releases of the Spectre simulator Examples of the currents Parameter You use the following syntax for the currents parameter in the opt ions statement For more information about the opt io
208. he use of the cmos process models simulator lang spectre Folded Cascode Operational Amplifier subckt opamp pout nout pin nin input differential pair M1 4 pin 1 1 nmos w 402 4u 1 7 6u M2 5 nin 1 1 nmos w 402 4u 1 7 6u M18 1 12 VSS VSS nmos w 242 4u 1 7 6u upper half of folded cascode M3 4 pl vdd vdd pmos w 402 4u 1 7 6u M4 5 11 vdd vdd pmos w 402 4u 1 27 6u M5 nout 16 4 vdd pmos w 122 4u 1 7 6u M6 pout 16 5 vdd pmos w 122 4u 1 7 6u lower half of folded cascode M7 nout 13 8 vss nmos w 72 4u 1 7 6u M8 pout 13 9 vss nmos w 72 4u 1 7 6u M9 8 T2 vss vss nmos w 122 4u 1 7 6u M10 9 12 vss vss nmos w 122 4u 1 7 6u common mode feedback amplifier M11 10 nout vss vss nmos w 12 4u 1 62 6u M12 10 pout vss vss nmos w 12 4u 1 62 6u M13a 11 gnd vss vss nmos w 12 4u 1 62 6u M13b 11 gnd vss vss nmos w 12 4u 1 62 6u M14 10 10 vdd vdd pmos w 52 4u 1 7 6u M15 11 10 vdd vdd pmos w 52 4u 1 7 6u Ccl nout 11 capacitor c l1p Cc2 pout 11 capacitor c lp bias network M16 12 12 VSS vss nmos w 22 4u 1 11 6u M17 21 T2 VSS vss nmos w 22 4u 1 11 6u M19 13 T3 14 vss nmos w 22 4u 1 21 6u M20 13 21 16 vdd pmos w 52 4u 1 7 6u M21 21 16 X vdd pmos w 26 4u 1 11 6u M22 16 16 17 vdd pmos w 26 4u l 11 6u D1 15 vss dnp area 400n D2 14 15 dnp area 400n D3 18 17 dnp area 400n D4 vdd 18 dnp area 400n Ib gnd 12 isource dc 10u ends opamp The following file c
209. his section also tells you how to restart a simulation after a transient analysis termination July 2002 231 Product Version 5 0 Spectre Circuit Simulator User Guide Running a Simulation Customizing Automatic Recovery By default the Spectre simulator creates checkpoint files every 30 minutes during a transient analysis The Spectre simulator deletes these checkpoint files when the simulation ends successfully Reactivating Automatic Recovery for a Single Simulation If you have deactivated the default setting by putting the checkpoint setting in an environment variable you can reactivate the default value for a given simulation run with the following procedure gt Type checkpoint as a command line argument to the spect re command that starts the simulation Determining How Often the Spectre Simulator Creates Recovery Files If you want to change how often the Spectre simulator creates checkpoint files for a particular simulation or if you want your checkpoint files saved after a successful completion you should set the ckpt clock parameter of the opt ions statement For more information about the options statement consult the parameter listings in the Spectre online help spectre h The following opt ions statement tells the Spectre simulator to create checkpoint files every 3 1 2 minutes for all transient analyses in a simulation You indicate parameters for ckptclock in seconds SetCkptInterval options ckptclock 2
210. ibility Guidelines 212 25b ue weds eaa ET usu ek d sd tors 51 General Input Compatibility i3 xk Miwa bets REA Ec bI d EYE XE ERES 51 Compatibility Limitations sse donat enoncr od OH AY ded aD Sora td SOS eo eo 55 4 SPECIE NGMISIS stove ho atu dup that densus 57 Nets Statements ack cusan Ss chad ca en e C REESE o Ea AER haa Lotta a E AU 57 INetist C OHDVebiltOFis armier 308 dra tta E ari bg e e ot E arated Go a MES SP aE 58 BASICS YMC S955 sen cpa aed va aie seh eben Raro fand rdi a Ua RO x T en dh ceed ee oS 58 Spectre Language Modes llleeeleeeee eee 59 Creating Component and Node Names eee eens 59 Escaping Special Characters in Names 0 0 0 61 Inst ce Statements drsi mara dare ecco me Ne dee End utu p e Rudd ad enin od esq ul 61 Formatting the Instance Statement 0 eee 61 Examples of Instance Statements llleeeeeeeeeeee 62 Basic Instance Statement Rules eee 63 Identical Components or Subcircuits in Parallel 0 0 0 0 cece eeee 63 July 2002 4 Product Version 5 0 Spectre Circuit Simulator User Guide AMAIVSIS SIAIE MEMS wate eok we es reete a HER eee ene euin Eee RE RE sete aie 64 Basic Formatting of Analysis Statements 0 cece eee 64 Examples of Analysis Statements 00 ete eee 65 Basic Analysis Rules 2559 mg ee hak eto cesis Sat tae Roe e A pe
211. ication D opamp1 might generate a file named 94 09 19 opamp1 The date is in year month day format All leading zeros are included This format generates filenames that you can sort alphabetically into chronological order oe HH H is replaced by the host name network name of the system on which the Spectre simulator is running oe Z M is replaced by the current CMIVersion o FU P is replaced by the process ID The process ID is a unique integer assigned to the Spectre process by the operating system oe 05 S is replaced by the simulator name For example the specification S opampl might generate a file named spectre opampl If you use a different name or a symbolic link with a different name to access a copy of the executable program the new name becomes the program name oe H T is replaced by the time when the program started For example the specification T opamp1 might generate a file named 14 44 07 0pamp1 Time is in 24 hour format and all leading zeros are included This format generates filenames that sort alphabetically into chronological order oe lt V is replaced by the simulator version string For example the specification out V raw might generate a file named out 1 0 2 raw oe oe This specifies the character by itself This option lets you use percent characters in filenames Two percent characters 3 in a filename specification produce a single percent charact
212. icular psf directory and expand down to the data Data can be overlaid on top of data from a previous data directory If you are accessing data from multiple directories and the data directory path names do not end with psf as the last directory you can still use the awd command by itself July 2002 40 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre When you expand down to a data directory and select the Create ROF command the system creates a soft link from that data directory to psf You can now expand down to the data If you then move to a different data directory in the Results Browser you have to again select the Create ROF command even if a run object file already exists This removes the old link if the two data directories exist in the same level of hierarchy and reestablishes the psf link to the new data directory Now you can expand down to data If you want to plot from the calculator a net you had previously plotted already for example overlay the same net from two different runs you need to first flush out the cache memory Learning More about AWD The AWD display tool gives you a number of additional options for displaying your data To learn more about using AWD with the Spectre simulator see the Cadence application note Using awd with Standalone Spectre available from Cadence Customer Support and the Analog Waveform User Guide about displaying results for the Cadence a
213. iculties during simulation When clamping is completed Spectre displays a message indicating that it is using clamped values There is no way to disable these clamps Invalid Parameter Warnings Warning from spectre during circuit read in pchmod tox is not a valid parameter for bsim4 models pchmod nch is not a valid parameter for bsim4 models This type of warning is issued any time you specify an invalid parameter in a model definition The models included with Spectre have predefined model parameters For more information See spectre h Only these predefined parameters can be used within a model definition The Spectre circuit simulator issues similar warnings for invalid instance and subcircuit parameters Redefine Primitives Messages Warning from spectre in q2 during circuit read in July 2002 261 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting redefPrim scs 6 q2 resistor redefines the primitive named resistor Spectre displays this message if you define a model or subcircuit with the same name as a built in primitive device The following message tells you that the local definition will override the built in definition model resistor bjt ql 1 2 3 resistor q1 is considered a bjt device rather than a resistor Initial Condition Messages Notice from spectre during IC analysis during transient analysis tranl Initial condition
214. ide Analyses Important Adding probes to circuits that are sensitive to numerical noise might affect the solution In such cases an accurate solution might be obtained by reducing reltol Telling Spectre to Save Operating Point Data at Specific Times In addition to saving operating point data in a ac analysis Spectre allows this data to be saved during a transient analysis This data is saved as a waveform and can be plotted along with node voltages and other output data See Chapter 8 Specifying Output Options to learn how to select and save this data Often all that is needed is the operating data at specific times which can be achieved by linking an info analysis with the tran analysis To control the amount of data produced for operating point parameters use the following two transient analysis parameters to specify at which time points you would like to save operating point output for all devices infotimes vector of numbers infoname analysis name where analysis name points to an info analysis For example mytran tran stop 30n infotimes 10n 25n infoname opinfo opinfo info what oppoint where rawfile The opinfo statement is called at 10 and 25 nanoseconds The data for all devices is reported at these specified time points Other Analyses sens fourier dcmatch and stb There are four analyses in this category sens fourier dcmatch and stb Sensitivity Analysis You can supplement the an
215. ier This netlist describes and analyzes a CMOS operational amplifier and demonstrates several sophisticated uses of Spectre features The example includes top level netlist parameters model library section statements multiple analyses and configuring a test circuit with the alter statement The first file in the example is the main file for the circuit This file contains the test circuit and the analyses needed to measure the important characteristics of the amplifier The main file is followed by files that describe the amplifier and the various models that can be selected These additional files are placed in the netlist with include statements Voltage controlled voltage sources transform single ended signals to differential and common mode signals and vice versa This approach does not generate or dissipate any power The power dissipation reported by the Spectre simulator is that of the differential amplifier Fully Differential Operational Amplifier Test Circuit define PROCESS CORNER TYPICAL simulator lang spectre global gnd vdd vss parameters VDD 5 0_V GAIN 0 5 include cmos mod section typical include opamp ckt power supplies Vdd vdd gnd vsource dc VDD Vss vss gnd vsource dc VDD compute differential input Vem cmin gnd vsource type dc dc 0 val0 0 vall 2 width 1u delay 10ns July 2002 109 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specificatio
216. if you have altered a circuit it is usually faster to start the DC analysis from a previous solution than to start from the beginning The info Statement You can generate lists of component parameter values with the info statement With this statement you can access the values of input output and operating point parameters and print the node capacitance table These parameter types are defined as follows n Input parameters Input parameters are those you specify in the netlist such as the given length of a MOSFET or the saturation current of a bipolar resistor n Output parameters Output parameters are those the simulator computes such as temperature dependent parameters and the effective length of a MOSFET after scaling n Operating point parameters Operating point parameters are those that depend on the operating point n Node Capacitance Table The node capacitance table displays the capacitance between the nodes of a circuit You can also list the minimum and maximum values for the input output and operating point parameters along with the names of the components that have those values Parameter Setting Action Taken what oppoint Prints the oppoint parameters Other possible values are none inst input output nodes all terminals oppoint models and captab where logfile Prints the parameters to the logfile Other possible values are nowhere screen file and rawfile July 2002 192 Product Version 5
217. ight to revoke this authorization at any time and any such use shall be discontinued immediately upon written notice from Cadence Disclaimer Information in this publication is subject to change without notice and does not represent a commitment on the part of Cadence The information contained herein is the proprietary and confidential information of Cadence or its licensors and is supplied subject to and may be used only by Cadence s customer in accordance with a written agreement between Cadence and its customer Except as may be explicitly set forth in such agreement Cadence does not make and expressly disclaims any representations or warranties as to the completeness accuracy or usefulness of the information contained in this document Cadence does not warrant that use of such information will not infringe any third party rights nor does Cadence assume any liability for damages or costs of any kind that may result from use of such information Restricted Rights Use duplication or disclosure by the Government is subject to restrictions as set forth in FAR52 227 14 and DFAR252 227 7013 et seq or its successor Spectre Circuit Simulator User Guide Contents mit A AA 13 Related Documents clle rh 13 Typographic and Syntax Conventions 0 00 ee 14 Heferenc s Le ee ee Ba BS lw ni SED IRURE hed eg eee ee ER
218. in the following example you can avoid the problem t t2 m2 b1 b2 subckt ct xfmr tl bl t2 m2 b2 Tt t1 bl t2 m2 transformer n1 2 Tb t1 bl m2 b2 transformer n1 2 end ct xfmr Circuits that contain ideal transformers N ports or transmission lines can have floating nodes or loops of zero resistance branches because the topology checker cannot adequately verify these components Finding these currents is difficult because all these components act like ideal transformers at DC When you look into one port of a transformer you can see either a short or an open circuit depending on what you see looking out of the other port Internal Error Messages If the Spectre simulator detects an internal error it displays a message like one of the following Internal error detected by spectre Please s http sourcelink cadence com supportcontacts html for Customer Support contact information Error detected in file file c at line 101 Internal error detected by spectre Please s http sourcelink cadence com supportcontacts html for Customer Support contact information Arithmetic exception Cadence can help you find solutions to these problems If you get one of these messages call Cadence Customer Support or contact a Cadence application engineer July 2002 256 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Time Is Not Strictly Increasing
219. in transient analyses 238 ic statement example 188 238 formatting 188 238 specifying initial conditions ifstatements 106 imelt 258 include statements examples 70 71 formatting 70 include statements 70 examples 71 formatting 70 of use in netlist 109 rules for using 70 individual components specifying 28 61 info spectre command option 274 info statement 192 222 choosing the output destination 223 187 187 238 194 example 194 224 formatting 194 224 options 193 223 informational messages specifying conditions for in subcircuit calls 95 infotime 144 inheritance 75 inherited connections 75 initial conditions specifying 187 examples 187 188 238 individual analyses 190 24 transient analyses 187 23 initial settings of the state of the simulator modifying 186 245 inline model statements inside of inline subcircuits 100 inline subcircuits containing inline model statements 100 237 Product Version 5 0 Spectre Circuit Simulator User Guide modeling parasitics 97 parameterized models 99 probing 98 process modeling 101 using 96 input data reading from multiple files 70 input files examples differential amplifier 109 GaAs traveling wave amplifier 92 process file 112 two port test circuit 117 uA741 operational amplifier 134 input language mixing SPICE and Spectre 54 input parameters listing 192 222 input as info sta
220. ina save statement Spectre sends these signals to the output raw file as long as the nest1v1 setting does not filter them In this section you will learn the following n How to save voltages for individual nodes n Howto save all signals for an individual component n How to save selected signals for an individual component The syntax for the save statement varies slightly depending on whether the requested data is from the main circuit or a subcircuit You will learn about the syntax for main circuit statements first and then you will learn how to modify the save statement to store signals from subcircuits Saving Main Circuit Signals The save statement general syntax has the following arguments You can specify more than one argument with a single save statement and you can mix the types of arguments in a single statement save signalName save compName save compName modifier save subcircuitName terminallndex n signalName is generally the netlist name of a node whose voltage you want to save n compName is the netlist name of a component whose signals you want to save n modifier Specifies signals you want to save for a particular component It can have the following types of values q A terminal name Terminal names for components are the names for nodes in component instance definitions You can find instance definitions for each component in the component parameter listings in the Spectre online
221. inal currents associated with component Q4 save D8 cap Saves the junction capacitance for component D8 Assumes D8 is a diode and therefore cap is an operating point parameter save Q5 D9 oppoint Saves all signal information for component Q5 and the operating point parameters for component D9 July 2002 203 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements save Statement Action save Ql c Saves the collector current for component o1 Example assumes Q1 is a BJT and therefore c is a terminal name save Q1 1 Same effect as the previous statement Saves the collector current for component Q1 Identifies the terminal with its terminal index instead of its terminal name save M2 d displacement Saves capacitive current associated with the drain terminal of component M2 Example assumes v2 is a MOSFET so d is a terminal name save Q3 currents M1 all Saves all currents for component Q3 and all signals for component M1 save F4 S1 BUT3 oppoint Saves operating point parameters for terminal BJT3 BJT3 is in subcircuit S1 Subcircuit S1 is nested within subcircuit F4 Saving Individual Currents with Current Probes A current probe is a component that measures the current passing between two nodes Its effect is like placing an amp meter on two points of a circuit It creates a new branch in the circuit between the two nodes forces the voltages on the two nodes to be equal
222. inal value with a standard deviation of 0 4 K ohms square In the mismatch block the parameter rshsp is then subject to further statistical variation on a per subcircuit instance basis for on chip variation Here it varies a little for each subcircuit instance this time with a standard deviation of 2 For the first Monte Carlo run if there are multiple instances of a subcircuit that references parameter rshsp then assuming variations all it might get a process random value of 210 and then the different instances might get random values of 209 4 211 2 210 6 and so on The parameter xisn also varies on a per instance basis with a standard deviation of 0 5 In addition the parameters rshsp and rshpi are correlated with a correlation coefficient cc of 0 6 Specifying Distributions Parameter variations are specified using the following syntax July 2002 171 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses vary PAR NAME dist type std lt value gt N lt value gt percent yes no Three types of parameter distributions are available Gaussian log normal and uniform corresponding to thet ype keywords gauss lnorm and unif respectively For both the gauss and the 1norm distributions you specify a standard deviation using the std keyword The following distributions and associated parameters are supported m Gaussian This distribution is specified using di st gauss For the Gaussian distribution the me
223. inary Plus Minus Sum difference of the operands Shift lt lt gt gt First operand shifted left by the number of bits specified by the second operand first operand shifted right by the number of bits specified by the second operand Relational LU LM NE Less than less than or equal greater than greater than or equal respectively Equality True if the operands are equal true if the operands are not equal Bitwise AND amp Bitwise AND of integer operands July 2002 85 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features Operator Symbol s Value Bitwise Exclusive or Bitwise exclusive NOR of integer NOR operands Bitwise OR Bitwise OR of integer operands Logical AND amp amp True only if both operands true Logical OR ll True if either operand is true Conditional selection cond X Returns x if cond is true y if not where x and y are expressions Algebraic and Trigonometric Functions The trigonometric and hyperbolic functions expect their operands to be specified in radians The atan2 and hypot functions are useful for converting from Cartesian to polar form Function Description Domain log x Natural logarithm x gt 0 log10 x Decimal logarithm x gt 0 exp x Exponential x 80 sqrt x Square root x gt 0 min x y Minimum value All x all y max x y Maximum value All x all y abs x Ab
224. index line The data file must mark the end of the file with LNM Format The following is an example of an LNM file This file has two sets of S parameter data which correspond to two width values MS bend model as a function of frequency strip width W and dielectric constnat ER 10GHz lt FREQ lt 30GHz 0 6mm lt W lt 0 8mm 2 lt ER lt 7 July 2002 124 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features VAR MODELFMT MAFET NEUTRAL MODEL FORMAT VAR NPORTS 2 2 ports VAR MODELTYPE S S parameters VAR FORMAT RI S data in real imaginary format VAR R 50 VAR PARAMETER W UNIT MM INTERPOLATION YES VAR PARAMETER ER INTERPOLATION YES VAR PARAMETER FREQ UNIT GHZ INTERPOLATION YES VAR W 0 6 VAR ER 2 BEGIN ACDATA FREQ reS11 imS11 reS21 imS21 reS12 imS12 reS22 imS22 10 0000 0 05 0 24 0 96 0 12 0 96 0 12 0 01 0 24 15 0000 0 10 0 33 0 92 0 18 0 92 0 18 0 03 0 34 20 0000 0 16 0 40 0 87 0 24 0 87 0 24 0 07 0 42 25 0000 0 23 0 44 0 81 0 30 0 81 04 30 0 1IT 0 49 30 0000 20 29 0 47 0 75 0 35 0 75 0 35 0 18 0 53 END VAR W 0 8 VAR ER 2 BEGIN ACDATA 5 FREQ reS11 imS11 reS21 imS21 reS12 imS12 reS22 imS22 10 0000 0 05 0
225. ing required to make it true MDS format Title file Date time No Variables number of variables Variables 0 freq frequency type real indep yes 1 S LL S param type complex indep no 2 S 1 2 Ss param type complex indep nol k2 S k K s param type complex indep no k 2 1 PORTZ 1 port impedance type complex indep n0 K 2 K PORT K port impedance type complex indep n0 Values data section k is the number of ports number of variables shows the total number of frequency S parameters and ports data section shows S parameter data in the format specified in the Variables section of the header LNM Format An output file for LNM format looks like the following LNM format VAR MODELFMT VAR NPORTS MAFET NEUTRAL MODEL FORMAT number July 2002 127 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features VAR MODELTYPE VAR FORMAT VAR R BEGIN ACDATA S parameter format Data Section S format resistance number shows the number of ports S parameter format specifies the S parameter data format that must be followed The S parameter data for a LNM output file is in the LIBRA format Spectre Format An output file for Spectre format looks like the following S parameter data translated from file file time reference resistance portl resistance portk resistance forma
226. ing the convert option Spp convert lt netlist spice gt netlist spectre An example is given below Spp convert amp sp gt amp scs converts the SPICE netlist amp sp to an equivalent Spectre netlist with the name amp scs The convert option removes special embedded codes for tracking the line numbers of the original netlist returning a cleanly converted netlist This option does not descend into included files to convert them but only converts the include statement For this reason included files must be converted independently In this case the SPICE Reader cannot always resolve conflicts and ambiguities and the resulting netlist files must be verified Great care must be taken when converting hierarchically arranged netlists Some of the possible issues include the following m Namespace conflicts Spectre has a single namespace for instance names nodes master model names and parameters When running on an entire netlist the SPICE Reader can map these name conflicts In the convert mode where only sections of the netlist can be considered spp might not resolve all conflicts m Distinguishing instance models from instance parameters For some devices such as resistors SPICE instance statements can use an order dependent mechanism to define the values of parameters An example could be rl 1 0 myres The field myres could be either a model name or a parameter representing the resistance value in SPICE The SPICE Rea
227. inition fourier 151 model binning rules 108 model scaling factor changing with alter statement 186 245 model statement 29 examples 29 69 formatting 68 inline 100 using 68 July 2002 modeling identical components in parallel 63 71 identical subcircuits in parallel 64 multidisciplinary 73 N ports 117 parasitics in inline subcircuits 97 process using inline subcircuits 101 models as info statement parameter charge conservation of 17 formatting for multiple components 62 selecting automatically 105 use of expressions in 70 Monte Carlo analysis brief description of 133 characterization 175 examples 169 modeling 175 parameters table of 163 performing 161 specifying statistics 174 specifying the first iteration number 168 MOS models advantages of Spectre version 17 MOSO model brief description 17 multidisciplinary modeling 73 multiple analyses example in netlist 109 multiple components creating models 193 223 for 68 multiple directories accessing data from 40 multiplication factor 63 N n terminals formatting in analysis statements 65 names rules for components 59 nodes 59 old netlists 61 nestlvl parameter 207 219 netlist conventions 58 definition 26 elements of 27 introduction to 27 Spectre example 26 netlist parameters predefined 90 netlist statements 57 Product Version 5 0 Spectre Circuit Simulator User Guide use of in example 28 newlink keywo
228. ir parent enclosing subcircuit definition or top level definition This inheritance continues across all levels of nesting of subcircuit definitions that is if a subcircuit s1 is defined which itself contains a nested subcircuit definition s2 then any parameters accessible within the scope of s1 are also accessible from within s2 Also any parameters declared within the top level circuit description are also accessible within both s1 and s2 However any subcircuit definition can redefine a parameter that it inherited In this case if no value is specified for the redefined parameter when the subcircuit is instantiated then the redefined parameter uses the locally defined default value rather than inheriting the actual parameter value from the parent See how the r2 resistor is used in the examples in Circuit and Subcircuit Parameters on page 82 Parameter Namespace Parameter names must not conflict with node component or analysis names That is it is not possible to reference a parameter called r1 if there is an instance of a resistor or other device or analysis called r1 Parameter names must also not be used where a node name is expected Parameter Referencing Spectre netlist parameters can be referenced anywhere that a numeric value is normally specified on the right hand side of an sign or within a vector where the vector itself is on the right hand side of an sign This includes referencing of parameters in expressio
229. ircuit creates a simple MOS device instance M1 and calls the inline subcircuit sl twice M2 and M3 M1 210 0 mos mod 2 5 6 sl 1 6u w 7u 3 6 7 sl This circuit flattens to the following equivalent circuit M1 2 1 0 0 mos mod 2 560 0 mos mod 1 6u w 7u the inline component inherits call name 2 capl 5 0 capacitor c 1n a regular hierarchical name 2 cap2 6 0 capacitor c 1n 3 67 0 0 mos mod 1 1u w 2u the inline component inherits call name capl 6 0 capacitor c 1n cap2 7 0 capacitor c 1n 3 3 The final flattened names of each of the three MOSFET instances are M1 M2 and v3 If s1 was a regular subcircuit the final flattened names would be M1 M2 s1 and M3 s1 However the parasitic capacitors have full hierarchical names You can create an instance of the inline subcircuit cell in the same way as creating an instance of the specially tagged inline device You can use save statements to probe this instance in the same way as a regular device without having to July 2002 97 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features W Realize that the instance is actually embedded in a subcircuit m Know that there are possible additional parasitic devices present m Figure out the hierarchical name of the device of interest A modeling engineer can create several of these inline subcircuits and place them in a library
230. isting quantity and you can use the node statement to set the quantities for a particular node For more information about the quantity statement see the Spectre online help spectre h quantity and the SpectreHDL Reference manual For more information on the node statement see spectre h node The following is an example of a node statement setToMagnetic tl t2 node value Wb flow MMF strength insist Inherited Connections Inherited connections is an extension to the connectivity model that allows you to create global signals and override their names for selected branches of the design hierarchy The flexibility of inherited connections allows you to use m Multiple power supplies in a design m Overridable substrate connections W Parameterized power and ground symbols July 2002 75 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists You can use an inherited connection so that you can override the default connection made by a signal or terminal This method can save you valuable time You do not have to re create an entire subbranch of your design just to change one global signal For more detailed information on how to use inherited connections and net expressions with various Cadence tools in the design flow see the Inherited Connections Flow Guide July 2002 76 Product Version 5 0 Spectre Circuit Simulator User Guide o Parameter Specification and Modeling Features You can use the Spectre
231. istor Vin input 0 dc 1 AC 1 0 X1 mainnetlist in out Rload out 0 1k isnoisy no isnoisy is spectre parameter include main ckt ac dec 10 1k 100k noise v out end If the netlist is to be run by a SPICE simulator at a later time these Spectre parameters must be hidden or removed See the next section for information on how to hide Spectre text Hiding Spectre Text from SPICE You can create a SPICE mode input file that you can use with both a SPICE based simulator and the Spectre simulator When you run the Spectre simulator you can use Spectre features unavailable in SPICE For example if you want to specify a Spectre parameter that SPICE does not support you write the Spectre statements so they do not cause syntax errors when you run the SPICE based simulator To create such an input file follow these steps 1 Insert the special prefix spectre atthe beginning of a line in your SPICE netlist The line should start with an asterisk optionally followed by blanks or tabs followed by the string spectre spectre Spectre text Be sure to leave a space after the colon 2 Place Spectre specific input language statements after the Notepecial prefix The Spectre simulator recognizes the Spectre statements after the prefix as input but the SPICE based simulator ignores the whole line as a comment spectre Rp 15 0 resistor r 50m July 2002 54 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE
232. it Simulator User Guide Parameter Specification and Modeling Features TLo2 ol gnd o2 gnd tline len 750u z0 96 vel 0 36 TLo3 02 gnd o3 gnd tline len 750u z0 96 vel 0 36 TLo4 03 gnd o4 gnd tline len 2750u z0 96 vel 0 36 TLo5 04 gnd o5 gnd tline len 2750u z0 96 vel 0 36 TLo6 05 gnd o6 gnd tline len 2750u z0 96 vel 0 36 TLo7 06 gnd o7 gnd tline len 2750u z0 96 vel 0 36 TLo8 07 gnd o8 gnd tline len 220u z0 96 vel 0 36 Bias network drain bias Ldd vdd o0 inductor l 1u R1 o0 b1 resistor r 50 C1 bl gnd capacitor c 9p gate 2 bias R2 bl b2 resistor r 775 R3 b2 gnd resistor r 465 C2 b2 gnd capacitor c 21p gate 1 bias R4 i8 b3 resistor r 50 R5 b3 gnd resistor r 500 C3 b3 gnd capacitor c 12p ends stage Two stage amplifier Pl in gnd port r 50 num 1 mag 0 Cin in inl capacitor clin X1 inl out1 stage Cmid outl in2 capacitor c 1n X2 in2 out2 stage Cout out2 out capacitor c 1n P2 out gn port r 50 num 2 Power Supply Vpos vdd gnd vsource dc 5 Analyses OpPoint dc Sparams sp start 100M stop 100G dec 100 Rules to Remember When you use subcircuits m You must place the same number of nodes in the same order in subcircuit definitions and their respective subcircuit calls m Models and subcircuits defined within a subcircuit definition are accessible only from within that subcircuit You cannot use the model names in a subcircuit defini
233. iteration that might not be achievable If the gain is even higher the numerical resolution of the machine might be approached About 15 digits of resolution is available in a 64 bit floating point number In this case the gain needs to be reduced Note In this case one node the output controls convergence and all the other nodes are more accurate than the convergence criteria by itself would predict This is typical for most circuits Enable the topology checker set topcheck fu11 onthe opt ions statement and pay attention to any warnings Increase maxiters for the DC analysis If you have convergence problems during a DC sweep reduce the step size Check for unusual parameter values using the parameter range checker add param param limits filetothe spectre command line arguments and pay attention to any warnings Print out the minimum and maximum parameter values by placing an info statement in the netlist Make sure that the values for the instance model output temperature dependent and if possible operating point parameters are reasonable Avoid using very small floating resistors particularly small parasitic resistors in semiconductors Use voltage sources or iprobes to measure currents instead Small floating resistors connected to high impedance nodes can cause convergence difficulties rbm in the bipolar model is especially troublesome If the minr model parameter is set make certain it is set to 1 mOhm or larger
234. ivities are calculated These are normally node names deviceInstance parameter Or modelName parameter specifications Examples are 5 n1 and Qout betadc The dpar are the design parameters to which the output variables are sensitive You can specify them in a format similar to ova r However they must be input parameters that you can specify for example R1 x If you do not specify a to clause sensitivities of output variables are calculated with respect to all available instance and model parameters July 2002 148 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Note The method for specifying design parameters and output variables is described in more detail in the documentation for the save statement in Chapter 8 Specifying Output Options The following table shows you the types of design and output parameters that are normally used for both AC and DC analyses AC Analysis DC Analysis Design Instance parameters Instance parameters parameisis Model parameters Model parameters Output Node voltages Node voltages paramere Branch currents Branch currents Instance operating point parameters You can also specify device instances or models as design parameters without further specifying parameters but this approach might result in a number of error messages The Spectre simulator attempts sensitivity analysis for every device parameter and sends an error message for each parameter that cannot
235. ix possible settings that permit different combinations of these three methods to be used The following table shows the possible settings and what integration methods are allowed with each Backward Euler Trapezoidal Rule Second Order Gear euler traponly e trap e gear2only e gear2 trapgear2 The trapezoidal rule is usually the best setting if you want high accuracy This method can exhibit point to point ringing but you can control this by tightening the error tolerances The trapezoidal method is usually not a good choice to run with loose error tolerances because it is sensitive to errors from previous time steps If you need to use very loose tolerances to get a quick answer it is better to use second order Gear While second order Gear is more accurate than backward Euler both methods can overestimate a system s stability This effect is less with second order Gear You can also reduce this effect if you request high accuracy July 2002 143 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Artificial numerical damping can reduce accuracy when you simulate low loss high Q resonators such as oscillators and filters Second order Gear shows this damping and backward Euler exhibits heavy damping Improving Transient Analysis Convergence If the circuit you simulate can have infinitely fast transitions for example a circuit that contains nodes with no capacitance the Spectre
236. ize parameter the sweep is linear when the ratio of stop to start values is less than 10 and logarithmic when this ratio is 10 or greater If you specify the oppoint parameter Spectre computes and outputs the linearized model for each nonlinear component Nodesets help find the DC or initial transient solution You can supply them in the circuit description file with nodeset statements or in a separate file using the readns parameter When nodesets are given Spectre computes an initial guess of the solution by performing a DC analysis while forcing the specified values onto nodes by using a voltage source in series with a resistor whose resistance is r force Spectre then removes these voltage sources and resistors and computes the true solution from this initial guess Nodesets have two important uses First if a circuit has two or more solutions nodesets can bias the simulator towards computing the desired one Second they are a convergence aid By estimating the solution of the largest possible number of nodes you might be able to eliminate a convergence problem or dramatically speed convergence When you simulate the same circuit many times we suggest that you use both the write and readns parameters and give the same filename to both parameters The DC analysis then converges quickly even if the circuit has changed somewhat since the last simulation and the nodeset file is automatically updated July 2002 138 Product Version 5 0 Sp
237. ke simulators before you can skim Elements of a Spectre Netlist on page 27 With this method you can learn a fair amount about the Spectre simulator in a short time Approach this chapter as an overview You will probably have unanswered questions about some topics when you finish the chapter Each topic is covered in greater depth in subsequent chapters Do not worry about learning all the details now To give you a complete overview of a Spectre simulation the example in this chapter includes the display of simulation results with Analog Waveform Display AWD a waveform display tool that is included with the Spectre simulator If you use another display tool the procedures you follow to display results are different This user guide does not teach you how to display waveforms with different tools If you need more information about how to display Spectre results consult the documentation for your display tool July 2002 24 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre The example used in this chapter is a small circuit an oscillator you run a transient analysis on the oscillator and then view the results The following sections contain the schematic and netlist for the oscillator If you have used SPICE like simulators before looking at the schematic and netlist can help you compare Spectre syntax with those of other simulators If you are new to simulation looking at the schematic a
238. king subcircuit parameter values with 95 checking values of subcircuit parameters 271 errorif option 272 example 272 example of use in netlist 112 formatting 271 message option 272 printif option 272 severity option 272 warnif option 272 parasitic elements in parallel with device terminals 99 in series with device terminals 99 parasitics modeling in inline subcircuits 97 parentheses in Spectre syntax 59 pdisto analysis brief description of 22 131 percent codes 233 customizing 249 example 250 formatting 250 removing customized settings 250 305 Product Version 5 0 Spectre Circuit Simulator User Guide predefined 248 249 A 248 C 248 D 249 H 249 M 249 P 249 S 249 substitution in 249 T 249 V 249 redirected files 250 use with piped files 250 percent parameter Monte Carlo analysis 171 173 periodic AC analysis pac brief description of 131 periodic distortion analysis pdisto brief description of 131 periodic noise analysis pnoise brief description of 131 periodic small signal analyses description 21 periodic steady state analysis pss brief description of 21 131 periodic transfer function analysis pxf brief description of 131 physical dimensions of components scaling 115 PID process identification number 230 use of 163 piecewise linear PWL vector values reading 72 piped files and percent codes 250 P N junction warnings 257 breakdown region 258
239. l conditions to use You can choose the following settings Parameter Setting Action Taken dc Initial conditions specifiers are ignored and the existing DC solution is used node The ic statements are used and the ic parameter settings on the capacitors and inductors are ignored dev The ic parameter settings on the capacitors and inductors are used and the ic statements are ignored all Both the ic statements and the ic parameters are used If specifications conflict ic parameters override ic statements Specifying State Information with State Files You can also specify initial conditions and estimate solutions by creating a state file that is read by the appropriate analysis You can create a state file in two ways n Youcaninstruct the Spectre simulator to create a state file in a previous analysis for future use n You can create a state file manually in a text editor Telling the Spectre Simulator to Create a State File You can instruct the Spectre simulator to create a state file from either the initial point or the final point in an analysis To write a state file from the initial point in an analysis use the write parameter To write a state file from the final point use the writefinal parameter Each of the following two examples writes a state file named ua741 dc The first example writes the state file from the initial point in the DC sweep and the second example writes the state file from the final point in
240. lag specifies whether to save the multiple waveform data in parameter storage format PSF for family plotting The default is no If the flag is set to yes a separate PSF file is saved for each analysis in each Monte Carlo iteration in addition to the export scalar results that are saved to the ASCII scalar data file at the end of each iteration Saving the PSF files between runs allows you to m Cloud plot overlaid waveforms in the analog design environment m Define and evaluate new calculator measurements after the simulation has been run using the analog design environment calculator and or the Analog Waveform Display tool Note This feature can result in many very large data files You might want to monitor the disk space available after each iteration or perhaps after just the nominal simulation and extrapolate to see if sufficient disk space is available If savefamilyplots is set to no PSF files are overwritten by each Monte Carlo iteration annotate This specifies the degree of annotation such as percentage done Possible values are no title sweep Or status similar to the Spectre simulator s nested sweep analysis Use the maximum value of status to print a summary of which runs did not converge or had problems evaluating export statements and so on The default is sweep title This specifies the analysis title Specifying the First Iteration Number The advantages of using the irstrun parameter to specify the
241. lation for the sample circuit type the following at the command line Spectre osc cir Note osc ciris the file that contains the netlist July 2002 30 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre Following Simulation Progress As the simulation runs the Spectre simulator sends messages to your screen that show the progress of the simulation and provide statistical information In the simulation of osc cir the Spectre simulator prints some warnings and notifications The Spectre simulator tells you about conditions that might reduce simulation accuracy When you see a Spectre warning or notification you must decide whether the information is significant for your particular simulation Screen Printout The printout for the osc cir simulation looks like this spectre ver 4 4 3 52 339 02 Jul 1998 Simulating osc cir on cds8616 at 9 24 15 AM Mon Jul 6 1998 Circuit inventory nodes equations bjt capacitor inductor isource resistor vsource LS NH m B qs P2 Q0 KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK Transient Analysis OscResp time 0 s gt 80 us KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK Narration of transient analysis progress Oa Ose ecelesie estet Oc ere eure Dreher Bee ai be Ete Gea ete e ea wena a beate de cel Number of accepted tran steps 11090 Initial condition solution time 10 ms Intrinsic tran analysis time 1
242. lator User Guide Parameter Specification and Modeling Features Caution Parasitic Elements in Series with Device Terminals If the parasitic elements are in series with the device terminals the reported operating point currents are correct but reported operating point voltages might be incorrect For example consider the case of an inline MOSFET device with parasitic source and drain resistances inline subckt mos_r d gs b parameters pl lu p2 2u mos r dp g sp b mos mod l pl w p2 inline component rd d dp resistor r 10 series drain resistance rs s sp resistor r 10 series source resistance ends mos r If an instance M1 is created of this mos r inline subcircuit and the operating point of v1 is probed the drain to source current ids is reported correctly However the reported vds is not the same as V d V s the two wires that connect the subcircuit drain and source terminals Instead vas is V dp V sp which are nodes internal to the inline subcircuit Caution Parasitic Elements in Parallel with Device Terminals If the parasitic elements are in parallel with the device terminals the reported voltages are correct but the reported currents might be incorrect For example consider the following case of a MOSFET with source to bulk and drain to bulk diodes inline subckt mos d dg s b parameters pl 1u p2 2u mos d dg s b mos mod 1 pl w p2 inline component d1 d b diodel r 10 drain
243. lators or switched capacitor or switched current filters The periodic small signal analyses periodic AC PAC analysis periodic transfer function PXF analysis and periodic noise Pnoise analysis are similar to Spectre s AC XF and Noise analyses but the traditional small signal analyses are limited to circuits with DC operating points The periodic small signal analyses can be applied to circuits with periodic operating points such as the following Mixers VCOs Switched current filters Phase frequency detectors Frequency multipliers Chopper stabilized amplifiers July 2002 21 Product Version 5 0 Spectre Circuit Simulator User Guide Introducing the Spectre Circuit Simulator Oscillators Switched capacitor filters Sample and holds Frequency dividers m Narrow band active circuits The third SpectreRF addition to Spectre functionality is periodic distortion PDISTO analysis PDISTO analysis directly computes the steady state response of a circuit driven with a large periodic signal such as an LO local oscillation or a clock and one or more tones with moderate level With PDISTO you can model periodic distortion and include harmonic effects PDISTO computes both a large signal the periodic steady state response of the circuit and also the distortion effects of a specified number of moderate signals including the distortion effects of the number of harmonics that you choose This is a common scenario when tryi
244. le After you create the S parameter file you must place instructions in the netlist for the Spectre simulator to read it You give these instructions with an nport model statement The following example shows how to enter an S parameter file into a netlist This model statement reads S parameters from the file Spara data model Sdata nport file Spara data If the S parameter file is not in the same directory as the Spectre simulator you can use a path to the S parameter file as a value for the nport statement file parameter or you can specify a search path using the 1 command line argument S Parameter File Format Translator The S parameter data file format translator spt r is a separate program from the Spectre simulator It translates files from LIBRA MHARM HPMNS or Linear Neutral Model LNM format to Spectre format or from Spectre format to LIBRA MHARM HPMNS or LNM format The input or output can be files that you specify or standard input or output For standard input or output the input must be LIBRA format and the output must be Spectre format The translator supports the S parameter file format translation with any number of ports Command Arguments The following is a synopsis of the command line and arguments used to run the translator July 2002 120 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features sptr file format freq scale input file output
245. le defines a subcircuit called sweepVcc that contains the following B A list of parameters with default values for start stop Ib omega and steps This list of defaults is optional These defaults are for the subcircuit call For example if you call sweepvcc and do not specify values for the start and stop parameters in the subcircuit call the sweeps for analyses SwpVccDC and SwpVccAc start at 0 and end at 10 the values specified as defaults If however you specify start 1 and stop 5 as parameter values in the subcircuit call the start and stop parameters in SwpVccDC and SwpVccAC take the values 1 and 5 respectively B A control statement set Ibb which alters the ac parameter of the component named Ibb to the numerical value of Ib m Two analysis statements SwoVccDC and SwpVccAC which run a DC analysis followed by an AC analysis Calling Analysis Subcircuits Each subcircuit call for sweepVcc in the netlist causes all the analyses in the sweepVcc to be performed Each of the following statements is a subcircuit call to subcircuit sweepVcc IbbluA sweepVcc stop 2 Ib 1lu Ibb3uA sweepVcc stop 2 Ib 3u IbblO0uA sweepVcc stop 2 Ib 10u Ibb30uA sweepVcc stop 2 Ib 30u Ibbl00uA sweepVcc stop 2 Ib 100u Note the following important syntax features m Each subcircuit call has a unique name W Each subcircuit call overrides the default values for the stop and Ib parameters July 2002 137 Product Version 5 0
246. les a voltage versus time td file and an amplitude phase versus time fd file for each of specified harmonic of the clock fundamental For more information about the envelope following analysis see SpectreRF Help Periodic AC analysis pac After the periodic steady state analysis computes a periodic solution this analysis computes the response of a circuit in periodic steady state to a small sinusoidal stimulus The frequency of the sinusoidal stimulus is not constrained by the period of the large periodic solution The periodic AC analysis lets you sweep the frequency over a range of values This analysis is similar to the AC analysis except that it linearizes the circuit about a periodically varying operating point and accurately models frequency conversion effects For more information about the periodic AC analysis see SpectreRF Help Periodic distortion analysis pdisto Models periodic distortion and includes harmonic effects pdisto computes both a large signal the periodic steady state response of the circuit and also the distortion effects of a specified number of moderate signals including the distortion effects of the number of harmonics that you choose For more information about the periodic distortion analysis see SpectreRF Help Periodic noise analysis pnoi se After the periodic steady state analysis computes a periodic solution this analysis linearizes the circuit about the periodic steady state and perf
247. line must be the data line The first data entry at each frequency must be the frequency value which can include a frequency scale factor If the frequency scale factor is not given as shown previously it can be given by using the command option In general the data entry format is required to be the same as described for the LIBRA format HPMNS Format An input file for HPMNS format is expected to have a header preceding its data section The following is an HPMNS S parameter file with two ports and two frequency points File Format MD Revision 2 01 Title sp net Date Oct Plotname Flags complex No Sweep Variables No Variables Variables 0 BOwNE July 2002 Sweep Variables S 0 10 freq 6 17215253 1998 SP scatter 1 lt sp net gt freq 2 GHz gt 18 GHz frequency type real indep yes mixop neg 1 s param type complex indep no 2 s param type complex indep no 1 s param type complex indep no 2 s param type complex indep no 123 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features PORTZ 1 port impedance type complex indep n0 PORTZ 2 port impedance type complex indep n0 sopt none type complex indep no rn none type real indep no nfmin none type real indep no o00 10 01 Values 0 2 000000e 09 0 000000eE 00 8 158130e 01 5 296380e 01 2 341800e 02 6 210130e 02 2 025200e 00 1 043630e 00
248. ll the Spectre simulator to save every Nth data point with the following parameters m With the skipcount parameter which you set to N to make the Spectre simulator save every Nth data point m The skipstart parameter which tells the Spectre simulator when to start skipping parameters This parameter is also used in strobing m The skipstop parameter which tells the Spectre simulator when to stop skipping parameters This parameter is also used in strobing July 2002 145 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Examples of Strobing and Skipping In the following example the Spectre simulator starts skipping data points at Time 10 seconds and continues to skip points until Time 35 seconds During this 25 second period the Spectre simulator saves only every third data point ExSkipSt tran skipstart 10 skipstop 35 skipcount 3 In this example the Spectre simulator starts strobing at Time 5 seconds and continues until Time 20 seconds During this 15 second period the Spectre simulator saves data points every 10 seconds ExStrobe tran skipstart 5 skipstop 20 strobeperiod 10 This example is identical to the previous one except that it sets a delay of 2 seconds between the skipstart time and the first strobe point ExStrobe2 tran skipstart 5 skipstop 20 strobeperiod 10 strobedelay 2 Data Compression Some circuits such as mixed analog and digital designs and circuits with switching
249. log design environment and also into the Cadence analog workbench design system You can also use the Spectre circuit simulator by itself with several different output format options Assura interactive verification Dracula distributed multi CPU option and Assura hierarchical physical verification produce a netlist that can be read into the Spectre circuit simulator However only interactive verification when used with the Cadence analog design environment automatically attaches the stimulus file All other situations require a stimulus file as well as device models July 2002 23 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre This chapter discusses the following topics m Using the Example and Displaying Results on page 24 Sample Schematic on page 25 Sample Netlist on page 26 Instructions for a Spectre Simulation Run on page 30 Viewing Your Output on page 32 Using the Example and Displaying Results In this chapter you examine a schematic and its Spectre circuit simulator netlist to get an overview of Spectre syntax You also follow a sample circuit simulation The best way to use this chapter depends on your past experience with simulators Carefully examine the schematic Sample Schematic on page 25 and netlist Sample Netlist on page 26 and compare Spectre netlist syntax with that of SPICE like simulators you have used If you have prepared netlists for SPICE li
250. lowing subsections Q Degradation related parameters Q The Spectre simulator stress parameters for Toshiba analysis Q BERT stress parameters for BERT analysis July 2002 176 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses caution Be careful to set the following parameters correctly dvthc dvthe duoc and duoe These are degradation parameters which are usually obtained from DC stress measurements Errors in setting these parameters can lead to inaccurate results m You must set the circuitage parameter correctly in the transient analyses In the following example the Spectre simulator makes a baseline measurement and then examines changes in circuit behavior after 1 5 and 10 years new tran 1n 100n circuitage 0 yearl tran 1n 100n circuitage 1 year5 tran 1n 100n circuitage 5 yearl0O tran 1n 100n circuitage 10 Note After you establish the baseline value you can enter subsequent circuitage parameters in any order Output Options for Hot Electron Degradation Analysis After the transient analyses are completed the Spectre simulator produces a sorted table of device lifetimes Two device lifetimes are calculated for each device that receives hot electron degradation analysis The first lifetime is based on the threshold voltage and the second lifetime is based on the low mobility shift For each transient analysis in which circuitage is greater than 0 the Spectre simulator generates a se
251. ly 2002 210 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Note If you want to change temp or tnom use the alter statement The shell Statement The shell analysis passes a command to the operating system command interpreter given in the SHELL environment variable The command behaves as if it were typed into the Command Interpreter Window except that any sx codes in the command are expanded first The default action of the shell analysis is to terminate the simulation The following is the syntax for the shell statement Name shell parameter value The statistics Statement The statistics blocks allow you to specify batch to batch process and per instance mismatch variations for netlist parameters These statistically varying netlist parameters can be referenced by models or instances in the main netlist and can represent IC manufacturing process variation or component variations for board level designs For more information about the statistics statement see Specifying Parameter Distributions Using Statistics Blocks on page 170 July 2002 211 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options This chapter discusses the following topics n Signals as Output on page 212 n Saving Signals for Individual Nodes and Components on page 213 n Saving Groups of Signals on page 219 n Listing Parameter Values as Output on page 222 n Preparin
252. m These components are used as probes for the noise analysis statement The parameters oprobe and iprobe specify the probe components and the parameters oportv and iportv specify the port numbers cmNoise noise start 1k stop 1G dec 10 oprobe Rocm oportv 1 iprobe Vcm iportv 1 Multiple Analyses This netlist demonstrates the Spectre simulator s ability to run many analyses in the order you prefer In this example the Spectre simulator completely characterizes an operational amplifier in one run In analysis OpPoint the program computes the DC solution and saves it to a state file whose name is derived from the name of the netlist file On subsequent runs the Spectre simulator reads the state information contained in this state file and speeds analysis by using this state information as an initial estimate of the solution Analysis Drift computes DC solutions as a function of temperature The Spectre simulator computes the solution at the initial temperature and saves this solution to a state file to use as an estimate in the next analysis and in subsequent simulations Analysis XferVsTemp computes the small signal characteristics of the amplifier versus temperature Analysis XferVsTemp starts up quickly because it begins with the initial temperature of the DC solution that was placed in a state file by the previous analysis Analysis OpenLoop computes the loop gain of an amplifier in closed loop configuration Analysis OpenLoop starts
253. m contribution of all mismatch devices to the output are not reported as specified by the paramter mth The mismatch that is the equivalent mismatch current sources in parallel to all the devices that use model n1 is modeled by the model parameters mvt wl mvtwl2 mvt0 mbewl and mbeO dcmml dcematch mth 1e 3 oprobe vd porti 1 model nl bsim3v3 type n mvtwl 6 15e 9 mvtwl2 2 5e 12 mvt0 0 0 mbewl 16 5e 9 mbe0 20 0 The output of the analysis is displayed on the scree logfile DC Device Matching Analysis mismatchl at vd Local Variation 3 sigma random device variation sigmaOut sigmaVth sigmaBeta sigmaVg sigmalds 13 8 uA 2 21 mV 357 m 2 26 mV 1 71 mp6 6 99 uA 1 63 mV 269 m 1 68 mV 1 08 m01 2 71 uA 1 11 mV 187 m 1 16 mV 648 m m02 999 nA 769 uV 131 m 807 uV 428 m m04x4_4 999 nA 769 uV 131 m 807 uV 428 m m04x4 3 999 nA 769 uV 131 m 807 uV 428 m m04x4 2 999 nA 769 uV 131 m 807 uV 428 m m04x4 1 999 nA 769 uV 131 m 807 uV 428 m m04 718 nA 1 09 mV 185 m 1 15 mV 599 m m40x04 520 nA 1 55 mv 263 m 1 63 mV 835 m m20x04 378 nA 2 21 mV 376 m 2 34 mV 1 16 m10x04 363 nA 539 uV 92 m 567 uV 293 m m08 131 nA 379 uV 64 9 m 400 uV 203 m m16 July 2002 152 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses 46 7 nA 267 uV 45 9 m 283 uV 142 m m32 vd 3 477 mA 15 91 uA 3 sigma variation This says that the 3 sigma variation at i vd due to the mismatch models is 3 477
254. m temperature sweep to the extreme temperature and write the last solution to a nodeset file m Use numeric pivoting in the sparse matrix factorization Set pivotdc yes with the options statement Sometimes you must also increase the pivot threshold to between 0 1 to 0 5 by resetting the pivrel parameter with the opt ions statement M Divide the circuit into pieces and simulate them individually Make sure that results for a part alone are close to results for that part combined with the rest of the circuit Use the results to create nodesets for the whole circuit B Try replacing the DC analysis with a transient analysis Modify all the independent sources to start at zero and ramp to the independent source DC values Run the transient analysis well beyond the time when all the sources have reached their final values Write the final point to a nodeset file You can make this transient analysis more efficient with one of the following procedures Q Set the integration method to backward Euler method euler Q Loosen the local truncation error criteria by increasing 1teratio to 50 or more Occasionally an oscillator in the circuit causes the transient analysis to terminate or work very slowly July 2002 276 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Correcting Transient Analysis Convergence Problems You can use two approaches to eliminate transient analysis convergence
255. m4 nq vdd 6 vss n 1 0 35u w 1 70u ad 1 25p pd 4 86u as 0 18p ps 1 91u cO a vdd capacitor c 1 0512057e 15 cl ang capacitor c 7 308e 17 GZ vdd vss capacitor c 6 12359e 16 e3 nq vss capacitor c 5 175377e 16 c4 nq vdd capacitor c 1 1668172e 15 c5 a vss capacitor c 29 530671e 16 ends Begin top level circuit definition xna21 1 90 na2 xna22 2 1 na2 xna23 3 2 na2 xna24 14 3 na2 xna25 5 4 na2 July 2002 283 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits xna26 6 5 na2 xna27 7 6 na2 xna28 8 7 na2 xna29 9 8 na2 xna210 10 9 na2 xna211 11 10 na2 xna212 12 11 na2 xna213 13 12 na2 xna214 14 13 na2 xna215 115 14 na2 xna216 116 15 na2 xna217 90 16 na2 Next couple of lines sets variables for vdd and vss parameters vdd S1 23 3 parameters vss S1 20 0 vdd Il vdd gnd vsource dc vdd S1 vss Il vss gnd vsource dc vss S1 Next line initializes nodes within ring ic 220 420 6 20 8 20 1020 include q35d4h5 modsp section tt Next line defines transient steps and total simulation time tempOption options temp 25 tt tran tran step 0 010n stop 35n alter ss altergroup include q35d4h5 modsp section ss parameters vdd S1 3 0 alterTempTo100 alter param temp value 100 ss_tran tran step 0 010n stop 35n alter_ff altergroup include q35d4h5 modsp section ss parameters vdd_S1 3
256. ment in the netlist n In most analysis statements If you set the save and nest 1v1 parameters with an analysis statement the setting applies to that analysis only It overrides any previous save or nest1v1 settings Formatting the save and nestlvl Parameters The syntax for both the save and nest1v1 parameters is illustrated by the following options statement settingl options save lvlpub nestlvl 2 The save Parameter Options The following table shows the possible settings for the save parameter Setting Action none Does not save any data currently does save one node chosen at random selected Saves only signals specified with save statements This is the default setting lvlpub Saves all signals that are normally useful up to nest 1v1 deep in the subcircuit hierarchy This option is equivalent to a11pub for subcircuits Normally useful signals include shared node voltages and currents through voltage sources and iprobes lvl Saves all signals up to nest 1v1 deep in the subcircuit hierarchy This option is relevant for subcircuits July 2002 219 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options Setting Action allpub Saves only signals that are normally useful Normally useful signals include shared node voltages and currents through voltage sources and iprobes all Saves all signals Use 1v1 or all instead of 1v1pub or allpub to include internal nod
257. mes yes MyAcct2 info what models extremes yes MyAcct3 info what input extremes yes MyAcct5 info what terminals extremes yes MyAcct6 info what oppoint extremes yes Next section is the subckt for inv subckt inv nqa ml nq a vdd vdd p 1 0 35u w 2 60u ad 1 90p pd 6 66u as 1 90p ps 6 66u m2 vss a nq vss n 1 0 35u w 1 10u ad 0 80p pd 3 66u as 0 80p ps 3 66u Interconnect Caps for inv c0 a vdd capacitor c 1 0824323e 15 cl ang capacitor c 3 0044e 16 c2 nq vss capacitor c 5 00186e 16 cs nq vdd capacitor c 6 913993e 16 c4 a vss capacitor c 8 5372566e 16 ends Begin top level circuit definition xinvl 1 90 inv xinv2 2 1 inv xinv3 32 inv xinv4 4 3 inv xinv5 5 4 inv xinv6 6 5 inv xinvy y 6 inv xinv8 8 7 inv xinv9 9 8 inv xinv10 10 9 inv xinvll 11 10 inv xinv12 12 11 inv xinvl13 13 12 inv xinvl4 14 13 inv xinv15 15 14 inv xinvl6 1615 inv xinv17 90 16 inv Next couple of lines sets variables for vdd and vss parameters vdd S1 3 3 parameters vss S1 20 0 vdd I1 vdd gnd vsource dc vdd S1 vss Il vss gnd vsource dc vss S1 Set initial conditions ic 2 0 420 6 20 8 20 1020 Next line makes the call to the model NOTE The user may utilize the lib syntax with Spectre s spp command line option if they are using Spectre 4 43 or greater There is also a Spectre native syntax for equivalent functi
258. meters instances and models are updated when the altergroup statement is executed These statements must be bound within braces The opening brace is required at the end of the line defining the alter group Alter groups cannot be nested or be instantiated inside subcircuits Also no topology changes are allowed to be specified in an alter group The following is the syntax of the a1tergroup statement July 2002 67 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists Name altergroup lt netlist parameter statements gt and or lt device instance statements gt and or lt model statements gt and or lt parameter statements gt The following is an example of the altergroup statement vl 1 0 vsource dc 1 R1 1 0 Resistor R 1k dcl dc this analysis uses a 1k resistance value al altergroup R1 1 0 Resistor R 5k dc2 dc this analysis uses a 5k value Model Statements model statements are designed to allow certain parameters which are expected to be shared over many instances to be given once However for any given component it is predetermined which parameters can be given on model statements for that component This section gives a brief overview of the Spectre model statement For a more detailed discussion on modeling issues including parameterized models expressions subcircuits and model binning see Chapter 5 Parameter Specification and Modeling Features
259. meters for component D9 save Ql c Saves the collector current for component Q1 Example assumes Q1 is a BJT and therefore c is a terminal name save Q1 1 Same effect as the previous statement Saves the collector current for component Q1 Identifies the terminal with its terminal index instead of its terminal name save M2 d displacement Saves capacitive current associated with the drain terminal of component m2 Example assumes v2 is a MOSFET so d is a terminal name save Q3 currents M1 all Saves all currents for component Q3 and all signals for component M1 July 2002 215 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options save Statement Action save F4 S81 BJT3 0ppoint Saves operating point parameters for terminal BJT3 BJT3 is in subcircuit S1 Subcircuit S1 is nested within subcircuit F4 Saving Individual Currents with Current Probes A current probe is a component that measures the current passing between two nodes Its effect is like placing an amp meter on two points of a circuit It creates a new branch in the circuit between the two nodes forces the voltages on the two nodes to be equal and then measures the flow of current Important Adding probes to circuits that are sensitive to numerical noise might affect the solution In such cases an accurate solution might be obtained by reducing reltol When to Use Current Probes Sometimes it is preferable or necess
260. mi M The default search path is the path to the directory that contains Spectre shared objects SCDS_ROOT tools spectre lib cmi CMIVersion July 2002 292 Product Version 5 0 Spectre Circuit Simulator User Guide Dynamic Loading To load a shared object load path soname ext Example 1 load libnortel so Example 2 load HOME myLib cmi M libmydevice so To unload a shared object unload path soname ext version Example 1 unload libsiemens so 1 Example 2 unload SHOME myLib cmi M libmydevice so The name of the shared object file includes an extension and can also have a version number The path to the shared object is optional If you do not specify the path the Spectre simulator uses the search path from the current configuration file A line that begins with a semicolon is a comment and is ignored Empty lines are allowed and are ignored Precedence for the CMI Configuration File The Spectre simulator reads configuration files in the following order m The default Cadence CMI configuration file B The configuration file specified by the value of the ScMI_CONFIG environment variable B The file SHOME cmiconfig if it exists B The CMI configuration file specified in the cmiconfig argument Each configuration file modifies the previous configuration July 2002 293 Product Version 5 0 Spectre Circuit Simulator User Guide Dynamic Loading libmybjt so with the BUT5
261. more information about the SpectreHDL product see the SpectreHDL Reference manual For more information about Verilog A see the Verilog A Language Reference manual parameteri valuel parameterN valueN This is an optional field you can repeat any number of times in an instance statement You use it to specify parameter values for a component Each parameter specification is an instance parameter followed by an equal sign followed by your value for the parameter You can find a list of the available instance parameters for each component in the Spectre online help spectre h As with node names you can place optional parentheses around parameter specifications to improve the clarity of the netlist For example c 10E 12 For subcircuits and ahdl modules the available instance parameters are defined in the definition of the subcircuit or AHDL module In addition all subcircuits have an implicit instance parameter m for defining multiplicity For more details about m see Identical Components or Subcircuits in Parallel on page 63 Examples of Instance Statements In this example a capacitor named c1 connects to nodes 2 and 3 in the netlist Its capacitance is 10E 12 Farads C1 2 3 capacitor c 10 E 12F The following example specifies a component whose parameters are defined in a model statement In this statement npn is the name of the model defined in a model statement that July 2002 62 Product
262. mos mod contains the models and uses the Library and section statements to bin models into various process corners See Process File on page 112 for a more sophisticated example which also includes automatic model selection cmos mod Spectre MOSFET model parameters CMOS process Empirical parameters best typical and worst cases simulator lang spectre library cmos_mod July 2002 111 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features section fast MOSFETS and DIODES for process corner FAST model nmos mos3 type n vto 1 04 gamma 1 34 phi 55 nsub 1e15 cgso 290p cgdo 290p cgbo 250p cj 360u tox 700e 10 pb 0 914 js 1e 4 xj 1 2u ld 1 2u wd 0 9u uo 2793 bvj 14 model pmos mos3 type p vto 0 79 gamma 0 2 phi 71 nsub 1 7e16 cgso 140p cgdo 140p cgbo 250p cj 80u tox 700e 10 pb 0 605 js 1e 4 xj 0 8u 1d20 9u wd 0 9u uo 2245 bvj 14 model dnp diode is 3 1e 10 n 1 12 cjo 3 1e 8 pb 914 m 5 bvj 45 imax 1000 model dpn diode is 1 3e 10 n 1 05 cjo 9 8e 9 pb 605 m 5 bvj 45 imax 1000 endsection fast section typical MOSFETS and DIODES for process corner TYPICAL model nmos mos3 type n vto 1 26 gamma 1 62 phi 58 nsub 1e15 cgso 370p cgdo 370p cgbo 250p cj 400u tox 750e 10 pb 0 914 js 1e 4 xj 1u l1d 20 8u wd 1 2u uo 2717 bvj 14 model pmos mos3 type p vto 1 11 gamma 0 39 phi 72 nsub 1 7e16 cgso 220p cgdo 220p cgbo 250p cj 100u tox 750e
263. mple if you have the parameters XISN XIS XIB you cannot specify distribution for XISN or a correlation of this parameter with another The percent flag indicates whether the standard deviation sta or uniform range N are specified in absolute terms percent no or as a percentage of the mean value percent yes For parameter uuu in the example in Specifying Parameter Distributions Using Statistics Blocks the mean value is 200 and the variation is 200 10 200 that is 200 20 For parameter rshsp the process variation is given by Normal 200 12 200 that is Normal 200 24 Cadence recommends that you do not use the percent yes with the log normal distribution Truncation Factor The default truncation factor for Gaussian distributions and for the Gaussian distribution underlying the log normal distribution is 4 0 sigma Randomly generated values that are outside the range of mean 4 0 sigma are automatically rejected and regenerated until they fall inside the range You can change the truncation factor using the truncate statement The following is the syntax truncate tr lt value gt Note The value of the truncation factor can be a constant or an expression Note Parameter correlations can be affected by using small truncation factors July 2002 173 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Multiple Statistics Blocks You can use multiple statistics blocks which accumula
264. mple is a passive Bessel three pole bandpass filter with default parameter values for bandwidth termination resistance and center frequency The bw r0 and fc parameters are given default values in the subcircuit but you can change these values when you call the subcircuit Changing the value of bw x0 and c in a subcircuit call changes the values of many parameters in instance statements that refer to these three parameters Default specifications forbw r0 and fc define passive 3 pole bandpass filter 4 subckt filter n1 n2 parameters bw 1 r0 1 fc 1 Gl ni 0 capacitor c 0 3374 6 2832 bw r0 L1 n1 0 inductor l rO0 bw 0 3374 6 2832 fc fc C2 nl n12 capacitor c bw 0 9705 6 2832 fc fc r0 L2 n12 n2 inductor 1 r0 0 9705 6 2832 bw C3 n2 0 capacitor c 2 2034 6 2832 bw r0 L3 n2 0 inductor l r0 bw 2 2034 6 2832 fc fc ends filter instantiate 50 Ohm filter with 10 4MHz center frequency and 1MHz bandwidth Parameter values F1 in out filter bw 1MHz fc 10 4MHz r0 50 a changed from instantiate 1 Ohm filter with 10Hz defaults center frequency and 1Hz bandwidth for these F2 nl n2 filter fc 10 lt q Ssubcircuit calls You can use such parameterized subcircuits when the Spectre simulator is reading either Spectre or SPICE syntax Unlike subcircuit calls in SPICE the names of Spectre subcircuit calls do not have to st
265. n compName is the netlist name of a component whose signals you want to save n modifier Specifies signals you want to save for a particular component It can have the following types of values A terminal name q Terminal names for components are the names for nodes in component instance definitions You can find instance definitions for each component in the component parameter listings in the Spectre online help spectre nh For example the following is the instance definition of a microstrip line The terminal names are t 1 b1 t2 and b2 Name tl bl t2 b2 msline parameter value q A terminal index The terminal index is a number that indicates where a terminal is in the instance definition You give the first terminal a terminal index of 1 the second a terminal index of 2 and so on In this example the terminal indexes are 7 for sink and 2 for STC Name sink src isource parameter value q A name of an operating point parameter from the lists of parameters for each component in the Spectre online help q The name of a SpectreHDL Verilog A internal variable q One of the following keywords currents To save all currents of the device static To save resistive currents of the device displacement To save capacitive currents of the device dynamic To save charge or flux of the device oppoint To save the operating points of the device probe To measure current of the device with a probe July 2002 202 Product Version 5 0
266. n and Modeling Features Vdif in gnd vsource type dc dc 0 val0 0 vall 2 width lu delay 10ns Ridif in gnd resistor Eicmp pin cmin in gnd VCVS gain GAIN Eicmn nin cmin in gnd VCVS gain GAIN feedback amplifier Al pout nout pvg nvg opamp CEL pout tl capacitor c 8p Ctf2 E t2 capacitor c 8p VEL t nvg vsource mag 0 Vt2 t pvg vsource mag 0 C11 ae gnd capacitor c 8p C12 out gnd capacitor c 8p Cil pin pvg capacitor c 2p Cag nin nvg capacitor c 2p compute differential output Edif out gnd pout nout vcvs gain 1 Rodif out gnd resistor Ecmp cmout mid pout gnd vcvs gain GAIN Ecmn mid gnd nout gnd vcvs gain GAIN Rocm cmout gnd resistor Perform measurements spectre options save lvlpub nestlvl 1 printParams info what output where logfile operating point opPoint dc readns C r dc write C r dc printOpPoint info what oppoint where logfile differential mode characteristics closed loop gain Av Vdif p power supply rejection ratio Vdd PSR Vdd p Vss PSR Vss p dmXferFunctions xf start 1k stop 1G dec 10 probe Rodif dmNoise noise start 1k stop 1G dec 10 oprobe Edif oportv 1 iprobe Vdif iportv 1 step response dmEnablePulse alter dev Vdif param type value pulse annotate no dmStepResponse tran stop 2us errpreset conservative dmDisablePulse alter dev Vdif param type value dc annotate no loop gain Tv tl nvg open loop gain av out pvg nvg
267. nalog design environment July 2002 41 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility While SPICE is an industry standard language there are many variations of SPICE syntax on the market today Most of the language is common across the major commercial simulators but each vendor has extended or modified it with different capabilities and or slightly different syntax For the convenience of SPICE users the Spectre circuit simulator provides a SPICE Reader as an extension to its native language that accepts most variations of SPICE input The SPICE Reader provides support for SPICE2 SPICE3 and common extensions found in other simulators such as PSPICE and HSPICE This chapter focuses on how to use the SPICE Reader with Spectre This chapter is not intended to describe the syntax variations of SPICE as they are well documented in other places nor an exact listing of syntax supported by the SPICE Reader m Reading SPICE Netlists on page 42 m Language Differences on page 48 W Scope of the Compatibility on page 50 Reading SPICE Netlists Spectre provides the SPICE Reader to let you simulate existing SPICE netlists with Spectre While it is possible to gain access to many of Spectre s features with a SPICE netlist the Spectre syntax is a much more powerful language designed to give the Spectre user features beyond those provided by SPICE Whenever possible you are encouraged to take advantage o
268. name You can load processscalarfile and processparamfile into the analog design statistical postprocessing environment to plot verify the process parameter distributions If you later merge processparamfile with the data in scalarfile you can then plot export scalar values against the corresponding process parameters by loading this merged file into the analog design statistical postprocessing environment processparamfile This specifies the output file where process parameter scalar data labels are saved This file contains the titles and sweep variable values for each of the columns in processscalarfile These titles are the names of the process parameters processparamfile is equivalent to paramfile except that paramfile contains the name of the export expressions whereas processparamfile contains the names of the process parameters The default name for this file is instname process mcparam where instname is the name of the Monte Carlo analysis instance This file is created in the psf directory by default unless you specify some path information in the filename July 2002 165 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Parameter Description Saveprocessvec firstrun variations July 2002 This specifies an array of statistically varying process parameters which are subject to process variation to save as scalar data in processscalarfile For example saveprocessvec RSHSP TOX This acts
269. named Netlist measure For example say that you have an SPICE netlist named amp sp In order to convert this netlist without executing the simulation use spp with the convert option convert amp sp gt amp scs Upon completion of this command the Spectre equivalent for amp sp is in the amp scs file In addition a file called Net 1ist mdl is created This additional file contains the MDL expressions that correspond to any measure statements in the original netlist In order to run the Spectre simulation using the new netlist and control file use the following command spectremdl batch Netlist mdl design amp scs Upon completion of the simulation you ll find a file named Net list measure which contains the values calculated for each of the MDL expressions For more information on the expression evaluation capabilities in Spectre see the SpectreMDL User Guide and Reference Netlist parameters In Spectre parameters are order dependent that is they must be defined before being used When the SPICE Reader is run on the entire design parameters are moved to the top of the netlist but in convert mode they are moved to the top of each file If a parameter is accessed before inclusion it will fail until it is fixed Order dependent statements Some statements in SPICE are mapped into multiple statements in Spectre Things like temp sweeps analysis sweeps and alter sections all get converted into multiline
270. nclude a file written in Spectre native syntax you must either specify simulator 1ang spectre or name the file with a scs suffix After Spectre processes the file it reverts to the default mode It is illegal to include Spectre syntax in the SPICE mode or vice versa For the MOS instance line given below M1 12 0 0 NCH W 10u L 2u Spectre displays the following warning July 2002 260 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting ml Encountered statement in Spectre format while in SPICE language mode This will not be supported in a future release Since the instance statement is valid in both languages you can ignore this warning Topology Messages Notice from spectre during topology check Only one connection to the following node 4 No DC path from node 4 to ground Gmin installed to provide path The Spectre topology checker identifies floating nodes and automatically inserts a gmin resistor 1e12 Ohms to prevent a non isolated solution The Spectre simulator then displays a message telling you what it did Model Parameter Values Clamped Warning from spectre during initial setup The value of vj pb at T 25 C is 50e 03 V which is too small Q lamped to 0 1 V n The value of vj pb at T 27 C is 41 7617e 03 V which is too small Clamped to 0 1 V The Spectre simulator clamps model parameter values to prevent numerical diff
271. nd netlist can prepare you to understand the later chapters of this book You can also get more information about command options components analyses controls and other selected topics by using the spectre h command to access the Spectre online help Sample Schematic A schematic is a drawing of an electronic circuit showing the components graphically and how they are connected together The following schematic has several annotations m Names of components Each component is labeled with the name that appears in the instance statement for that component The names for components are in italics for example Q2 m Names of nodes Each node in the circuit is labeled with its unique name or number This name can be either aname you create or anumber Names of nodes are in boldface type for example b1 Ground is node 0 B Sample instance statements The schematic is annotated with instance statements for some of the components Arrows connect the components in the schematic with their corresponding instance statements July 2002 25 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre Bold Type Names of nodes All connections to ground have the same node name Italic Type Names of components also appear in the instance statement for each component lt q p gt Link between components and instance statements cc Vcc cc cc il Cl LI out Vcc C2 ce bl b2 Q1
272. nd statement that is simulator lang spectre insensitive yes The insensitive yes language directive marks the models subcircuits that were converted so that Spectre can perform a lower case compare m The SPICE Reader treats the character as a math function if found inside of an expression and as a comment if found outside of an expression B Lines beginning with lt CPP keywords are not treated as comments by the SPICE Reader but will result in an syntax error unless you run CPP on the netlist m You can force the SPICE Reader to treat all bjt devices as having four terminals with the q4term command line option to spp By default the fourth field after the device name of an instance statement is treated as a terminal unless one of the following occurs Q There is a model name within the netlist that is named the same as the fourth field a Itis the last item on the instance line For example ql 1 2 3 4 mybjt The 4 is treated as a device terminal q112 3 neh mybjt The nch is treated as a device terminal unless Q mybjt is defined as a parameter in the netlist Q nchis defined as a model in the netlist In the second case the q4t erm option can be used to override the default behavior of the converter July 2002 52 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility You can gain full access to Spectre and its features with a SPICE netlist by controlling the input language Sp
273. ne or more files Use the param command line option to use the suggested parameter range limits You can specify limits for any scalar parameter that takes either a real number an integer or an enumeration To specify the limits of a parameter that takes enumerations use the indices or index values associated with the enumerations For example consider the region parameter of the bjt There are four possible regions see spectre h bjt B off B fwd B rev B sat Each enumeration is assigned a number starting at 0 and counting up Thus B off 0 B fwd 1 B rev 2 E sat 3 The specification bjt 3 lt region lt 1 indicates that a warning is printed if region rev because the conditions 3 lt region and region lt 1 exclude only region 2 and region 2is rev For more information on parameter range checking see Checking for Invalid Parameter Values on page 95 Help on Parameters There are four main ways to get online help about Spectre component or analysis parameters spectre help When you type spectre help name where name is the name of a component or analysis you get the following information BH Parameter names Related parameters are grouped together July 2002 79 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features BH Parameter defaults BH Units B Parameter description For analyses and controls parameters are listed in the Parameters se
274. nes in the middle of a SPICE netlist by surrounding the Spectre lines with the simulator lang command HI T Ouk vl 1 0 1 simulator lang spectre r2 1 0 resistor r 1k simulator lang spice Op If you do not specify an input language the Spectre simulator uses SPICE mode by default You do not need to place simulator lang commands around include statements but you must specify simulator lang spectre in include files written in the Spectre Netlist Language July 2002 53 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility Spectre allows you to specify the netlist input format to be Spectre without the simulator lang command by naming the file with the Spectre circuit simulator extension of scs Files ending in this extension are treated as Spectre syntax Appending Spectre Parameters While you can gain full access to Spectre features by switching to the Spectre syntax you can also gain access to specific parameters on the SPICE input statements The SPICE Reader maps each SPICE statement to the Spectre equivalent statement Mapping of parameters is done first for order dependent parameters and then for name value based parameters The SPICE reader tries to map parameters in the name value form if they are known otherwise they are passed directly to Spectre as is This allows you to add Spectre parameters to the end of any SPICE statement For example Additional Spectre parameter to res
275. nfluence the speed of the simulation by setting parameters that control accuracy requirements and the number of data points saved For more information about the transient analysis see Transient Analysis on page 140 Time domain reflectometer analysis t dr Linearizes the circuit about the DC operating point and computes the reflection and transmission coefficients versus time This is the time domain equivalent of the S parameter analysis For more information about time domain reflectometer analysis see Chapter 4 Analysis Statements of the Spectre Circuit Simulator Reference m RF analyses Q July 2002 Envelope Following Analysis env1p Computes the envelope response of a circuit The simulator automatically determines the clock period by looking through all the sources with the specified name Envelope following analysis is most efficient 130 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses July 2002 for circuits where the modulation bandwidth is orders of magnitude lower than the clock frequency This is typically the case for example in circuits where the clock is the only fast varying signal and other input signals have a spectrum whose frequency range is orders of magnitude lower than the clock frequency For another example the down conversion of two closely placed frequencies can also generate a slow varying modulation envelope The analysis generates two types of output fi
276. ng Problems and Troubleshooting to find information about installing Cadence defaults or creating your own range limits file if you need to customize defaults m Youcanfind additional information about percent code defaults in Description of Spectre Predefined Percent Codes on page 248 Overriding Defaults You can override defaults in the UNIX environment variables for a given simulation with either spectre command line arguments or opt ions statement specifications The spectre command line arguments also override opt ions statement specifications July 2002 235 Product Version 5 0 Spectre Circuit Simulator User Guide 10 Time Saving Techniques In this chapter you will learn about different methods to reduce simulation time This chapter discusses the following topics W Specifying Efficient Starting Points on page 236 Reducing the Number of Simulation Runs on page 236 Adjusting Speed and Accuracy on page 237 Saving Time by Starting Analyses from Previous Solutions on page 237 Saving Time by Specifying State Information on page 237 Saving Time by Modifying Parameters during a Simulation on page 242 Saving Time by Selecting a Continuation Method on page 245 Specifying Efficient Starting Points The Spectre circuit simulator arrives at a solution for a simulation by calculating successively more accurate estimates of the final result You can increase simulation speed by providing information that the
277. ng reserved words case specified should not be used as node names net names instance names model names or parameter names M_1 PI M 2_PI M_2_ SQRTPI M DEGPERRAD M EM LN10M LN2M LOG10E M LOG2EM PI M PI 2M PI 4 M SORT12 M SQRT2M TWO PI P C P CELSIUSO0 P EPSOP HP K POP U0abs acos acosh altergroupasinasinh atanatan2atanhceil correlate cos cosh else nd endsexp export floor for function global hypot ic if inline int library local log log10 march max min modelnodeset parameters paramset plot pow print pwr real returnsave sens sinsinh sqrt statistics subckt tan tanh to truncate vary July 2002 60 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists Escaping Special Characters in Names If you have old netlists that contain names that do not follow Spectre syntax rules you might still be able to run these netlists with the Spectre simulator The Spectre Netlist Language permits the following exceptions to its normal syntax rules to accommodate old netlists Use these features only when necessary If you place a backslash before any printable ASCII character including spaces and tabs you can include the character in a name You can create a name from the following elements in the order given A string of digits followed by Q Letters underscores or backslash escaped characters followed by Q A
278. ng to predict the intermodulation distortion of a mixer amplifier or a narrow band filter In this analysis the tones can be large enough to create significant distortion but not so large as to cause the circuit to switch or clip The frequencies of the tones need not be periodically related to each other or to the large signal LO or clock Thus you can make the tone frequencies very close to each other without penalty which allows efficient computation of intermodulation distortion of even very narrow band circuits The fourth analysis that SpectreRF adds to the Spectre circuit simulator is the envelope following analysis This analysis computes the envelope response of a circuit The simulator automatically determines the clock period by looking through all the sources with the specified name Envelope following analysis is most efficient for circuits where the modulation bandwidth is orders of magnitude lower than the clock frequency This is typically the case for example in circuits where the clock is the only fast varying signal and other input signals have a spectrum whose frequency range is orders of magnitude lower than the clock frequency For another example the down conversion of two closely placed frequencies can also generate a slow varying modulation envelope The analysis generates two types of output files a voltage versus time td file and an amplitude phase versus time fd file for each specified harmonic of the clock fundame
279. nnot open files or create the necessary directories it stops Defining Output File Formats You can redefine the output file format in two ways n With a spectre command you type from the command line or place in an environment variable n With an options statement you put in the netlist You use the opt ions statement in the netlist to override an environment default setting and you use the spect re command at run time to override any settings in the netlist The parameter values you enter are the same for either method Example Using the spectre Command The following example shows you how to set format options with the spect re command This statement which you type at the command line or place in an environment variable directs the Spectre simulator to run a simulation on a circuit named circuitfile and format the results in binary Nutmeg spectre format nutbin circuitfile Example Using the options Statement You set format options with the rawfmt parameter of the opt ions statement as shown in the following example This statement which you place in the netlist instructs the Spectre simulator to create an output file in binary Nutmeg For more information about the opt ions statement see the parameter listings in the Spectre online help spectre h Settings options rawfmt nutbin Accessing Output Files After you run a simulation you will want access to results of the various analyses you specified To access th
280. ns W Distributions specified in the mismatch block are applied on a per subcircuit instance basis are sampled once per subcircuit instance and are used typically to represent device to device on chip mismatch for devices on the same chip When the same parameter is subject to both process and mismatch variations the sampled process value becomes the mean for the mismatch random number generator for that particular parameter Note Statistics blocks can be specified using combinations of the Spectre keywords statistics process mismatch vary truncate and correlate Braces are used to delimit blocks The following example shows some sample statistics blocks which are discussed after the example along with syntax requirements define some netlist parameters to represent process parameters such as sheet resistance and mismatch factors parameters rshsp 200 rshpi 5k rshpi std 0 4K xisn 1 xisp 1 xxx 20000 uuu 200 define statistical variations to be used with a MonteCarlo analysis statistics process process generate random number once per MC run vary rshsp dist gauss std 12 percent yes vary rshpi dist gauss std rshpi std rshpi std is a parameter July 2002 170 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses vary xxx dist lnorm std 12 vary uuu dist unif N 10 percent yes mismatch mismatch generate a random number per instance vary rshsp dist gauss std 2
281. ns run spectre h expressions for more details on netlist expression handling as indicated in the preceding examples You can use expressions containing parameter references when specifying component or analysis parameter values for example specifying the resistance of July 2002 83 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features a resistor or the stop time of a transient analysis as outlined in the preceding example when specifying model parameter values in model statements for example specifying bf p1 0 8 for a bipolar model parameter bf or when specifying initial conditions and nodesets for individual circuit nodes Altering Sweeping Parameters Just as certain Spectre analyses such as sweep alter ac dc noise sp and xf can sweep component instance or model parameters they can also sweep netlist parameters Run spectre h analysis to see the particular details for any of these analyses where analysis is the analysis of interest Expressions An expression is a construct that combines operands with operators to produce a result that is a function of the values of the operands and the semantic meaning of the operators Any legal operand is also an expression in itself Legal operands include numeric constants and references to top level netlist parameters or subcircuit parameters Calls to algebraic and trigonometric functions are also supported The complete list
282. ns statement see the parameter listings in the Spectre online help spectre h n The Spectre simulator saves all terminal currents for nonlinear components currents specified with the save statement and routinely computed currents optl options currents nonlinear n The Spectre simulator saves all terminal currents opt2 options currents all Setting Multiple Current Probes Sometimes you might need to set a large number of current probes This could happen for example if you need to save a number of ACs Current probes can find such small signal currents when they are not normally computed You can specify that all currents be calculated with current probes by placing useprobes yes in an options statement July 2002 209 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Setting multiple current probes can greatly increase the DC and transient analysis simulation times Consequently this method is typically used only for small circuits and AC analysis Important Adding probes to circuits that are sensitive to numerical noise might affect the solution In such cases an accurate solution might be obtained by reducing reltol Saving Subcircuit Terminal Currents You use the subcktprobelvl parameter to control the calculation of terminal currents for subcircuits Current probes are added to the terminals of each subcircuit up to subcktprobelvl deep You can then save these terminal currents by
283. nt The correlation coefficients are specified in the va 1 ue gt field and must be between 1 0 not including 1 0 or 1 0 Note Correlation coefficients can be constants or expressions aS can std and N when specifying distributions Characterization and Modeling The following statistics blocks can be used with the example in Process Modeling Using Inline Subcircuits on page 101 if they are included in the main netlist anywhere below the main parameters statement These statistics blocks are meant to be used in conjunction with the modeling and characterization equations in the inline subcircuit example for a Monte Carlo analysis only statistics process vary RSHSP dist gauss std 5 vary RSHPI dist lnorm std 0 15 vary SPDW dist gauss std 0 25 vary SNDW dist gauss std 0 25 correlate param RSHSP RSHPI cc 0 6 mismatch vary XISN dist gauss std 1 vary XBFN dist gauss std 1 vary XRSP dist gauss std 1 statistics correlate dev R1 R2 cc 0 75 correlate dev TNSA1 TNSA2 cc 0 75 Special Analysis Hot Electron Degradation The Spectre simulator lets you control the age of the circuit when simulating hot electron degradation This feature has the following options and restrictions m Only the transient analysis supports hot electron calculations July 2002 175 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses m Hotelectron calculations are available with the following components
284. nt Codes 248 Customizing Percent Codes uus ae 2 08 x Sar op o TOI EORR qd 9 da d dui sj et deu e 249 Creating Filenames from Parts of Input Filenames 0000005 251 12 Identifying Problems and Troubleshooting 254 Error Conditions 3 3 Lteners e eo So ba or ee s d Dm ee ORC et Go d a ae ae ncn pcne rd 254 Invalid Parameter Values That Terminate the Program s 254 Sing lar Matrices 24 viminet sot cette lo hehe eek ct M bU SUE SES SES 255 Internal Error Messages 25 bee Sidmetenacd ORG PACES One dae Oh aOR 256 Time lIs Not Strictly Increasing 2 56 de we duds Se bowers ve sous P EE Seb RW 257 Spectre Warning Messages xt4 acs sea PEE Dewar enti eh we E OC DESEE 257 P N Junction Warning Messages xusrasiace dren c3 cx CS oin ac ri er et c gos 257 Parameter Is Unusually Large or Small eee 259 gmin Is Large Enough to Noticeably Affect the DC Solution 259 Mititm trm Timestep Used 3 9be tei studee these Aves ool shed eb hates 260 Sylt XJ ETTOLS gt gia aats ae hehe eae Renee en eee oe dole Los OR tet ora aad ewe 260 Top logy Messages scins raain E dex cg dea ded duae eta RO RUE ELE aded aoa ric fh ecto ENR RAG 261 Model Parameter Values Clamped leeeel eee 261 Invalid Parameter Warnings 3 3 vacuae aora neo ce Bos gat ada eta a et C 261 Redefine Primitives Messages 000 eee teens 261 Initial
285. nt between multiple process parameters You can specify multiple process parameter correlation statements in a statistics block to build a matrix of process parameter correlations During a Monte Carlo analysis process parameter values are randomly generated according to the specified distributions and correlations m Instance or mismatch correlation statements matched devices The following is the syntax of the instance or mismatch correlation statement correlate dev list of subckt instances param list of parameters cc lt value gt where the device or subcircuit instances to be matched are listed in ist of subckt instances and list of parameters specifies exactly which parameters with July 2002 174 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses mismatch variations are to be correlated Use the instance mismatch correlation statement to specify correlations for particular subcircuit instances If a subcircuit contains a device you can effectively use the instance correlation statements to specify that certain devices are correlated matched and give the correlation coefficient You can optionally specify exactly which parameters are to be correlated by giving a list of parameters each of which must have had distributions specified for it in a mismatch block or by specifying no parameter list in which case all parameters with mismatch statistics specified are correlated with the given correlation coefficie
286. nt defaults 234 loop gain example of measuring in netlist 109 Iteratio parameter 141 142 convergence problems and 27 293 142 lvl as save parameter option 207 219 Ivipub as save parameter option 207 219 M m factor 63 M predefined percend code 249 magnetic fluxin Webers 74 magnetomotive force in Amperes 74 main circuit signals saving See save statement 201 213 masternames 29 definition 28 model statements 29 Product Version 5 0 Spectre Circuit Simulator User Guide maxdelta parameter 74 maximum and minimum parameter values listing 192 223 maxiters parameter 275 maxstep parameter 141 144 setting to correct accuracy problems 278 MCNC benchmark suite 19 measuring differential signals example in netlist 109 loop gain example in netlist 109 134 output resistance netlist example discussed 135 power supply rejection netlist example discussed 135 melting current warnings 258 message control specifying the destination of 273 suppressing 274 method parameter 141 euler setting 143 gear2 setting 143 gear2only setting 143 setting to correct accuracy problems 278 trap setting 143 trapgear2 integration method parameter 143 traponly setting 143 MHARM format translating 120 minimum timestep used fixing warning 260 mismatch block 170 mismatch correlation statement 174 missing diode would be forward biased warning message 258 mixed signal simulation 23 MMF 74 mod parameter 158 model def
287. ntal In summary with periodic small signal analyses you apply a small signal at a frequency that might not be harmonically related noncommensurate to the periodic response of the undriven system the clock This small signal is assumed to be small enough so that the circuit is unaffected by its presence With PDISTO you can apply one or two additional signals at frequencies not harmonically related to the large signal and these signals can be large enough to drive the circuit to behave nonlinearly July 2002 22 Product Version 5 0 Spectre Circuit Simulator User Guide Introducing the Spectre Circuit Simulator For complex nonlinear circuits hand calculation of noise or transfer function is virtually impossible Without SpectreRF these circuits must be breadboarded to determine their performances SpectreRF eliminates unnecessary breadboarding saving time Mixed Signal Simulation You can use the Spectre circuit simulator coupled with the Verilog XL simulator in the Cadence analog design environment to simulate mixed analog and digital circuits efficiently This mixed signal simulation solution can easily handle complex designs with tens of thousands of transistors and tens of thousands of gates The digital Verilog data can come from the digital designer as either an RTL block or gates out of synthesis Environments The Spectre circuit simulator is fully integrated into the Cadence design framework II for the Cadence ana
288. numeric values are expected on the right hand side of an sign or within a vector where the vector itself is on the right hand side of an sign Expressions can be used when specifying component or analysis instance parameter values for example specifying the resistance of a resistor or the stop time of a transient analysis as outlined in the preceding example when specifying model parameter values in model statements for example specifying bf p1 0 8 fora bipolar model parameter bf or when specifying initial conditions and nodesets for individual circuit nodes Operators The operators in the following table are supported listed in order of decreasing precedence Parentheses can be used to change the order of evaluation For a binary expression like a b a is the first operand and b is the second operand All operators are left associative with the exceptions of the to the power of operator and the ternary operator which are right associative For logical operands any nonzero value is considered true The relational and equality operators return a value of 1 to indicate true or 0 to indicate false There is no short circuiting of logical expressions involving amp amp and Operator Symbol s Value Unary Unary Value of the operand negative of the operand To the power of First operand to be raised to the power of the second operand Multiply Divide X2 Product quotient of the operands B
289. o load libphilips so load libsiemens so load libstmodels so The CMI file allows legal UNIX file paths and Spectre predefined percent codes For more information on predefined percent codes see Description of Spectre Predefined Percent Codes on page 248 Configuration File Format The following commands can be used in the configuration file Command Action setpath Specifies the search path July 2002 291 Product Version 5 0 Spectre Circuit Simulator User Guide Dynamic Loading Command Action prepend Adds a path before the current search path append Adds a path after the current search path load Adds a shared object to the list of shared objects to load unload Removes a shared object from the list of shared objects to load The following examples show the syntax for these commands To specify a search path setpath path path2 path N Example 1 setpath SHOME cds 4 4 6 tools CDS_SYSNAME spectre lib cmi M Example 2 setpath SHOME myLib cmi M SHOME cds 4 4 6 tools CDS SYSNAME spectre lib cmi SM To prepend a path prepend path path 2 path N Example 1 prepend SHOME myLib cmi M Example 2 prepend SHOME myLib cmi M SHOME cds 4 4 6 tools S CDS SYSNAME spectre lib cmi SM To append a path append path path2 path N Example 1 append S HOME myLib cmi M Example 2 append SHOME myLib cmi M SHOME expLib c
290. oblems 277 improving 18 user control of tolerances 18 AHDL variables saving 222 AHDL definition 20 alarm parameter 270 Tapora functions 86 all as homotopy parameter option 246 as info statement parameter 193 223 as pwr option 206 218 as save parameter option 208 220 allglobal relative error parameter 141 143 alllocal relative error parameter 141 142 allpub as save parameter option 208 22 alter statement 67 186 244 245 changing parameter values with example 184 243 formatting 184 243 use with circuit parameters 244 e 185 example of use in netlist 109 July 2002 altergroup statement changing parameter values with 184 244 using 67 Analog Artist Calculator 34 case sensitivity of scale factors 81 use in mixed signal simulation 23 use of with Spectre 20 Waveform Window 36 Analog Waveform Display AWD brief description of 14 20 definition of 24 using 32 analog workbench design system use of with Spectre 23 analyses AC 139 basic rules 65 brief description of types 129 DC 138 envelope following 22 130 example of analysis statement 30 formatting 64 65 fourier 150 handling of prerequisite 66 Monte Carlo performing 161 no default analysis 66 order performed 66 parameter sweep examples 160 parameter value defaults 133 rules fornaming 66 sens 147 setting probes 133 specifying 30 64 133 statistical 161 subcircuits composed of calling 137 format
291. odels called modl mod2 modl bjtmod le 4u we 4u mod2 bjtmod le 1u area 50e 12 99 instances of mod1 all share mod1 and 1 instance of mod2 ql 23 1 0 modl region fwd q2 23 2 0 modl trise 2 q99 23 99 0 modl q100 23 100 0 mod2 Because the syntax of creating an instance of a model is the same as the syntax of creating an instance of a subcircuit in the Spectre netlist you can easily replace model instances with more detailed subcircuit instances To do this replace the model statement itself with a subcircuit definition of the same name When you do this in the Spectre Netlist Language you do not have to change the instance statements In SPICE inline subcircuits start with x so you need to rename all instance statements to start with x if you replaced a model with a subcircuit Process Modeling Using Inline Subcircuits Another modeling technique is to specify geometrical parameters such as widths and lengths to a device such as a bipolar transistor and then to create a parameterized model based on that geometry In addition the geometry can be modified according to certain process equations allowing you to model nonideal etching effects for example You use inline subcircuits and some include files for process and geometric modeling as in the following example files The ProcessSimple h file defines the process parameters and the bipolar and resistor devices File ProcessSimple h simulator lang s
292. ol gnd tline z0 25 f 1M Port2 01 gnd port num 2 Port3 i2 gnd port r 50 num 3 X1 02 gnd o2 gnd Sp data Port4 02 gnd port r 50 num 4 Analyses Op Point dc Sparams sp stop 0 3MHz lin 100 port Portl port Port3 Creating an S Parameter File Automatically To create an S parameter file automatically run an sp analysis that sweeps frequency and set the output file parameter to file filename The parameter filename is the name you select for the S parameter file For more information about specifying an sp analysis see Chapter 6 Analyses and the parameter listings for the sp analysis in the Spectre online help spectre h sp Creating an S Parameter File Manually To create an S parameter file manually in a text editor observe the following guidelines and rules m The Spectre simulator accepts the following formats for S parameters real imag mag deg mag rad db deg and db rad The formats do not have to be the same for each S parameter For clarity use a comma to separate the two parts of an S parameter Begin each file with a semicolon Semicolons indicate comment lines Use spaces commas and newlines as delimiters You can enter S parameters in any order You can specify any number of frequency points The frequency points do not have to be equally spaced but the frequency index must be in ascending or descending order m You must place the frequency specification before the S parameters and you must
293. om the file you specify Specifying param tells the Spectre simulator to ignore the param given in SPECTRE DEFAULTS without giving the Spectre simulator a new location to find range limits Note For more information about Spectre defaults see the Spectre Circuit Simulator Reference manual and Customizing Percent Codes on page 249 Creating a Parameter Range Limits File In some circumstances you might want to set your own parameter limits for warning messages This might be the case for example if you are maintaining your own sets of model libraries If you want to choose your own parameter limits for warnings you must use a text editor to create a parameter range limits file A parameter range limits file requires the following syntax Fields enclosed by single brackets 11 are optional ComponentKeyword model LowerLimit lt Param lt UpperLimit Observe the following syntax rules for a parameter limits file July 2002 263 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting m You can specify limits for input output or operating point parameters for either component instances or models You can also specify limits for analysis parameters m You must specify the limits for each parameter on a single line m You can specify open bounds using angle brackets lt or closed bounds using an angle bracket with an equal sign If yo
294. on does not converge Correcting DC Convergence Problems If you have DC convergence problems these suggestions might help you Simple solutions generally precede more radical or complex measures in the list m Evaluate and resolve any warning or error messages W Check for circuit connection errors Check to see that the polarity and value are correct for independent sources Check to see if the polarity and multiplier are correct for controlled sources Try all of the homotopy methods gmin source ptran and dpt ran These are tried by default W Check for an incorrect estimated operating region The default estimated operating region in the Spectre simulator is on in the forward region for all devices If there are a July 2002 274 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting reasonable number of devices that are really off set them off in the schematic For a large number of devices this might not be practical Check for extremely high gain circuits with nonlinearities and feedback The convergence criteria are applied to all nodes in the circuit The output of the gain block meets Kirchhoff s Current Law and delta reltol V about 1 part in 10 by default Because of the gain the input must move by this value divided by the gain If the gain is high for example 109 the input must move less than 1 part in 1011 This is an extremely small motion from iteration to
295. on page 219 Finally you can generate a summary of maximum and minimum parameter values with the extremes option July 2002 193 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Specifying the Output Destination You can choose among several output destination options for the parameters you list with the info statement With the info statement where parameter you can n Display the parameters on a screen n Send the parameters to a log file to the raw file or to a file you create When the info analysis is called from a transient analysis or used inside of a sweep the name of the info analysis is prepended by the parent analysis If the file option is used to save the results use the A percent code described in Description of Spectre Predefined Percent Codes on page 248 in the filename to prevent the file from being overwritten For example the following info statement tempSweep sweep param temp start 27 stop 127 step 10 dcl dc dcInfo info what oppoint where file file infodata A Produces infodata tempSweep 000 dcInfo infodata tempSweep 001 dcInfo infodata tempSweep 002 dcInfo infodata tempSweep 003 dcInfo and so on Examples of the info Statement You format the in o statement as follows StatementName info parameter value The following example tells the Spectre simulator to send the maximum and minimum input parameters for all models to a log file Inparams
296. on page 81 for more information The Spectre Netlist Language uses the ANSI standard SI scale factors Options that are analysis specific are found on the global options card in SPICE In Spectre options pertaining to an analysis are listed on the analysis card Spectre supports the idea of named analyses which allows you to include multiple analyses of the same type in a single netlist The SPICE Reader takes advantage of Spectre s ability to have more than one analysis of each type mapping each analysis July 2002 49 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility statement to the equivalent Spectre analysis and providing each a unique name If multiple analysis of the same type are listed within the SPICE deck each will be simulated instead of the last one wins mode of SPICE m In both Spectre and Spice the first line is always the title card and ignored by the simulator m Acard other than the title or a comment can be continued onto the next card by putting the continuation character in the first column of the next card Spectre also supports continuations at the end of the line in its native mode with the backslash character B In many versions of Spice there are punctuation characters such as parentheses and commas that are treated as white space Spectre will treat all characters as relevant input The SPICE Reader will treat all of these characters as literals m The S
297. onality It is shown in q35d4h5 modsp include q35d4h5 modsp section tt July 2002 282 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits Analysis Statement tempOption options temp 25 typ_tran tran step 0 010n stop 35n alter_ss altergroup include q35d4h5 modsp section ss parameters vdd S1 23 0 alterTempTo100 alter param temp value 100 ss_tran tran step 0 010n stop 35n alter_ff altergroup include q35d4h5 modsp section ff parameters vdd S1 23 3 alterTempTo0O alter param temp value 0 ff_tran tran step 0 010n stop 35n Ring Oscillator Spectre Deck for Two Input NAND Ring with No Fanouts nand2_ring sp This example uses Spectre syntax Ring oscillator Spectre deck for 2 Input NAND ring with no fanouts simulator lang spectre global 0 gnd vdd vss aliasGnd gnd 0 vsource type dc dc 0 Spectre options to be used SetOptionl options iabstol 1 00n audit full MyAcctl info what inst extremes yes MyAcct2 info what models extremes yes MyAcct3 info what input extremes yes MyAcct5 info what terminals extremes yes yAcct6 info what oppoint extremes yes Next section is the subckt for na2 9 subckt na2 nga ml nq a vdd vdd p 1 0 35u w 2 70u ad 1 03p pd 3 46u as 1 98p ps 6 86u m2 nq vdd vdd vdd p 1 0 35u w 2 70u ad 1 03p pd 3 46u as 1 98p ps 6 86u m3 vss a 6 vss n 1 0 35u w 1 70u ad 1 25p pd 4 86u as 0 18p ps 1 91u
298. ons component statements analysis statements or model statements ends SubcircuitName The keyword ends or ends in SPICE mode optionally followed by the subcircuit name A Subcircuit Definition Example The following subcircuit named twisted models a twisted pair It has four terminals p 1 n1 p2 and n2 The parameter specification field for the subcircuit sets subcircuit call default values for parameters zodd zeven veven vodd and 1en Remember that the specified parameters are defaults for subcircuit calls not for the instance statements in the subcircuit For example if the subcircuit call leaves the zodd parameter unspecified the value of zodd in odd is 50 If however the subcircuit call sets zodd to 100 the value of zodd in odd is 100 July 2002 91 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features subckt twisted pl nl p2 n2 parameters zodd 50 zeven 50 veven 1 vodd 1 len 0 odd pl nl p2 n2 tline z0 zodd vel vodd len len tfla pl 0 el cl transformer t1 2 t2 1 tflb nl 0 cl 0 transformer tl1 2 t2 ven el 0 e2 0 tline z0 zeven vel veven len len tf2a p2 0 e2 c2 transformer tl1 2 t2 tf2b n2 0 c2 0 transformer tl1 2 t2 ends twisted Indenting the contents of a subcircuit definition is not required However it is recommended to make the subcircuit definition mor
299. onstant in joules Kelvin Planck s constant in joules times seconds Permittivity of vacuum in farads meter Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features Constant Name Value Description P UO nx 4 0x10 7 Permeability of vacuum in henrys meter P CELSIUSO 273 15 Zero Celsius in Kelvin User Defined Functions The user defined function capability allows you to build upon the provided set of built in mathematical and trigonometric functions You can write your own functions and call these functions from within any expression The Spectre function syntax resembles that of C or the SpectreHDL language Defining the Function The following is a simple example of defining a function with arguments of type real and results of type real real myfunc real a real b return atb 2 sqrt a sin b When you define a function follow these rules B Functions can be declared only at the top level and cannot be declared within subcircuits m Arguments to user defined functions can only be real values and the functions can only return real values You must use the keyword real for data typing B The Spectre function syntax does not allow references to netlist parameters within the body of the function unless the netlist parameter is passed in as a function argument B The function must contain a single return statement Note If you create a user defined fun
300. oose the following settings Parameter Setting Action Taken dc Initial conditions specifiers are ignored and the existing DC solution is used node The ic statements are used and the ic parameter settings on the capacitors and inductors are ignored dev The ic parameter settings on the capacitors and inductors are used and the ic statements are ignored all Both the ic statements and the ic parameters are used If specifications conflict ic parameters override ic statements Specifying State Information with State Files You can also specify initial conditions and estimate solutions by creating a state file that is read by the appropriate analysis You can create a state file in two ways m You can instruct the Spectre simulator to create a state file in a previous analysis for future use July 2002 240 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques m You can create a state file manually in a text editor Telling the Spectre Simulator to Create a State File You can instruct the Spectre simulator to create a state file from either the initial point or the final point in an analysis To write a state file from the initial point in an analysis use the write parameter To write a state file from the final point use the writefinal parameter Each of the following two examples writes a state file named ua741 dc The first example writes the state file from the initial point in the DC sw
301. or devices models circuit and subcircuit parameters during a simulation with the a1ter statement The modifications apply to all analyses that follow the alter statement in your netlist until you request another parameter modification Changing Parameter Values for Components To change a parameter value for a component device or model you specify the device or model name the parameter name and the new parameter value in the alter statement You can modify only one parameter with each alter statement but you can put any number of alter statements in a netlist The following example demonstrates a1ter statement syntax SetMag alter dev Vtl param mag value 1 B SetMag is the unique netlist name for this alter statement Like many Spectre statements each alter statement must have a unique name B The keyword alter is the primitive name for the alter statement B dev Vt1 identifies vc 1 as the netlist name for the component statement you want to modify You identify an instance statement with dev and a mode1 statement with mod When you use the alter statement to modify a circuit parameter you leave both dev and mod unspecified B param mag identifies mag as the parameter you are modifying If you omit this parameter the Spectre simulator uses the first parameter listed for each component in the Spectre online help as the default B value 1 identifies 1 as the new value for the mag parameter If you leave value unspecified it is s
302. or identify the control statement if there are error messages or other output associated with the control statement You specify most control statements as follows Name Control Statement Type parameter value Name is a unique name you give to the control statement Control Statement Type is the Spectre name of the type of control statement you want such as alter You can find this name by referring to the topics list in the Spectre online help spectre h parameter value isthe list of parameter values you specify for the control statement You can specify values for any number of parameters You can find parameter listings for a control statement by referring to the Spectre online help spectre h Examples of Control Statements SetTemp alter param temp value 27 The preceding example of an alter statement sets the temperature for the simulation to 27 C The name for the alter statement is Set Temp and the name of the control statement type is alter You cannot alter a device from one primitive type to another For example instl 1 2 capacitor c 1pF alterfail altergroup instl 1 2 resistor r 1k is illegal Another example of a control statement is the altergroup statement which allows you to change the values of any modifiable device or netlist parameters for any analyses that follow Within an alter group you can specify parameter instance or model statements the corresponding netlist para
303. or the options statement The Spectre simulator provides defaults for many of these options so you can avoid the inconvenience of specifying many options for each simulation Spectre defaults are satisfactory for most situations but if you have specialized needs you can also set your own defaults Spectre command line defaults control the following general areas Messages from the Spectre simulator Destination and format of results Default values for the C preprocessor Default values for percent codes Creating checkpoints and initiating recoveries Screen display Name of the simulator Simulation environment Such as opus edge and so on July 2002 233 Product Version 5 0 Spectre Circuit Simulator User Guide Running a Simulation Examining the Spectre Simulator Defaults You can identify the various Spectre defaults by consulting the detailed description of spectre command options in the Spectre Circuit Simulator Reference manual Setting Your Own Defaults You can set your own defaults by setting the UNIX environment variables S_DEFAULTS or SPECTRE_DEFAULTS In S_DEFAULTS S is replaced by the name of the simulator so this variable is typically SPECTRE_DEFAULTS However the name created by the S substitution is different if you move the executable to a file with a different name or if you call the program with a symbolic or hard link with a different name Consequently you can create multiple sets of defaults which
304. ormation for single loop circuits and multi loop circuits in which a probe component can be placed on a critical wire to break all loops For a multi loop circuit in which such a wire may not be available the loop based algorithm can be performed only on individual feedback loops to ensure they are stable Although the stability of all feedback loops is only a necessary condition for the whole circuit to be stable the multi loop circuit tends to be stable if all individual loops are associated with reasonable stability margins Device Based Algorithm The device based algorithm produces accurate stability information for circuits in which a critical active device can be identified such that nulling the dominant gain source of this device renders the whole network to be passive Examples are multistage amplifier single transistor circuit and S parameter characterized microwave component This algorithm is often applied to assess the stability of circuit design in which local feedback loops cannot be neglected the loop based algorithm cannot be performed for these applications because the local feedback loops are inside the devices and are not accessible from the schematic level or netlist level to insert the probe component The supported active device and its dominant gain source are summarized in the table below Component Dominant Controlled Source Description b3soipd gm Common source transconductance bjt gm Common emitter transconductan
305. orms a small signal analysis The small signal analysis computes the total noise spectral density at the output If you specify an input probe the transfer function and the input noise for an equivalent noise free network are computed pnoise is like noise except it models frequency conversion effects and the effect of time varying bias on noise sources For more information about the periodic noise analysis see SpectreRF Help Periodic steady state analysis p s s Computes the periodic steady state response of a circuit at either a given fundamental frequency or the corresponding steady state analysis period The pss analysis also determines the circuit s periodic operating point This operating point is used for periodic time varying small signal analyses such as pac px f and pnoise For more information about the periodic steady state analysis see SpectreHF Help Periodic transfer function analysis px After the periodic steady state analysis computes a periodic solution this analysis linearizes the circuit about the periodic steady state and performs a small signal analysis The small signal analysis 131 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses computes the transfer function from every independent source in the circuit to a designated output The variable of interest at the output can be voltage or current The analysis is similar to the transfer function analysis except that it linearizes the
306. orted In general this error is produced for any analysis that changes the value of the conditional expression Rules for General Purpose Model Binning The following set of rules exists for general purpose model binning as outlined in the preceding example Within subcircuit npn mod the inline device npn mod is referenced three times each with a different model Allowing multiple instances or references to the same named device is possible only under the following strict topological conditions m The reference to the same named device is possible only in a structural if statement that has both an if part and an else part July 2002 108 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features m Both the if part and the else part must be either a simple one statement block or another structural i statement to which these same rules apply m Both the if part and the else part must evaluate to a single device instance whose instance name terminal list and type of primitive are identical Multiple references to the same named device are only possible if there can only ever be one single instance of this device after all expressions have been evaluated and each instance must be connected to the same nodes and represent the same device Examples of Conditional Instances The following two examples show how to use conditional instances Fully Differential CMOS Operational Amplif
307. p thresh 2p the row n1 n3 will not be printed since the capacitance between them is less than the threshold The row n1 0 will be printed since the node to ground capacitance is always printed The group n3 n3 n3 0 and n3 n1 will not be printed because the total node capacitance at node 3 n3 n3 is less than the threshold If you sort the table by name sort name it would look as follows July 2002 197 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Table 7 2 Node Capacitance Table Sorted by Name ni nl Fixed 3 5p Variable 1p Sum 4 5p nii Fixed 1p Variable 0 Sum 1p ni n2 Fixed 2p Variable 1p Sum 3p ni n3 Fixed 0 5p Variable 0 Sum 0 5p n2 n2 Fixed 2p Variable 3p Sum 5p n2 0 Fixed 0 Variable 2p Sum 2p n2 nl Fixed 2p Variable 1p Sum 3p n3 n3 Fixed 1 5p Variable 0 Sum 1 5p n3 n0 Fixed 1p Variable 0 Sum 1p nom Fixed 0 5p Variable 0 Sum 0 5p In this case the From Node To Node column is sorted alpha numerically However the row depicting the total capacitance at each node is always displayed first in the group and the row displaying the node to ground capacitance is second The options Statement To enter initial parameters for your simulation that you do not specify in your environment variables or on your command line you use the options statement You can control parameters in a number of areas with the opt ions statement n Parameters that specify tolerances for accuracy
308. page 273 Correcting Convergence Problems on page 274 Correcting Accuracy Problems on page 277 Error Conditions Error conditions terminate a Spectre run If you receive any of the messages described in this section you must fix the problem and rerun the simulation Invalid Parameter Values That Terminate the Program If you enter a parameter that causes the Spectre simulator to stop or puts a model in an invalid region such as giving z0 0 to a transmission line the Spectre simulator sends you a message like this one and exits Error from spectre during hierarchy flattening tll Value of z0 should be nonzero Spectre terminated prematurely due to fatal error To run the simulation you must change the parameter to an acceptable value July 2002 254 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Singular Matrices If you receive an error message that says a matrix is singular your netlist contains either a floating node which is causng the problem or a loop of zero resistance branches for example a loop of voltage sources or inductors The following procedures might help you find the problem B Check the options statement in your netlist to ensure that topcheck yes in at least one statement The topology checker normally helps you identify singular matrix problems but it cannot do so if it is disabled m If the error message appears only for particular com
309. pecify initial conditions that apply to all transient analyses in a simulation or to a single transient analysis The ic statement and the ic parameter described in this section set initial conditions for all transient analyses in the netlist In general you use the ic parameter of individual components to specify initial conditions for those components and you use the ic statement to specify initial conditions for nodes You can specify initial conditions for inductors with either method Specifying cmin for a transient analysis does not satisfy the condition that a node has a capacitive path to ground Note Do not confuse the ic parameter for individual components with the ic parameter of the transient analysis The latter lets you select from among different initial conditions specifications for a given transient analysis Specifying Initial Conditions for Components You can specify initial conditions in the instance statements of capacitors inductors and windings for magnetic cores The ic parameter specifies initial voltage values for capacitors and current values for inductors and windings In the following example the initial condition voltage on capacitor Cap13 is set to two volts Cap13 11 9 capacitor c 10n ic 2 Specifying Initial Conditions for Nodes You use the ic statement to specify initial conditions for nodes or initial currents for inductors The nodes can be inside a subcircuit or internal nodes to a component The follo
310. pectre define process parameters including mismatch effects parameters RSHSP 200 RSHPI 5k sheet resistance pinched sheet res SPDW 0 SNDW 0 etching variation from ideal XISN 1 XBFN 1 XRSP 1 device mismatch mm July 2002 101 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features parameters XISNafac 100m XISNbfac 1m IS scaling factors for mm eqns XBFNafac 100m XBFNbfac 1m BF x XRSPafac 100m XRSPbfac 1m RS RSHSPnom 200 RSHPInom 5k sheet resistance nom values FRSHPI RSHPI RSHPInom ratio of PI sheet res to nom define simple bipolar and resistor devices a base TNSA subckt that is a simple TNSA bipolar transistor subcircuit with model statement inline subckt TNSA B C B E S parameters MULT 1 IS 1e 15 BF 100 model modX bjt type npn is IS bf BF a model statement TNSA B CB E S modX m MULT inline device instance ends TNSA B a base resistor a simple RPLR resistor subcircuit inline subckt RPLR B A B parameters R MULT 1 RPLR B A B resistor r R m MULT inline device ends RPLR B define process geometry dependent bipolar and resistor devices a geometrical process TNSA subcircuit a BJT subcircuit with process and geometry effects modeled bipolar model parameters IS and BF are functions of effective emitter area perimeter taking process facto
311. pectre Circuit Simulator User Guide Identifying Problems and Troubleshooting il q0 Missing collector substrate diode returns to normal bias condition Most p n junctions in semiconductor models include both a resistive the diode and a capacitive the junction capacitance model If the diode reverse saturation current is set to zero the resistive part of the junction is turned off and the Spectre simulator assumes that the resistive portion of the junction does not exist but the junction capacitance may still be present In this case if the voltage across the missing diode is larger than 10 Vt where Vt is the thermal voltage Spectre will issue a warning message telling you that the junction which is missing will be forward biased A follow up notice is issued if and when the device returns to a normal bias condition Parameter Is Unusually Large or Small The Spectre simulator checks the parameter values to see if they are within a normal range of expected values This check can catch data entry errors or identify situations that can cause the Spectre simulator to have difficulties simulating the circuit The Parameter is unusually large or small message issues a notice about a parameter value The message looks like one of the following NPNbjt rb has the unusually small value of 1mOhms PNPbjt tf has the unusually large value of 1Gs OA1 Q16 of ua741 region has the unusual value of rev If you receive su
312. pectre simulator does not require an end statement it assumes the end of the input file is the end of the input statements The ena statement if included in a SPICE netlist is treated like the end of file and the SPICE Reader does not read beyond the end Reading SPICE and Spectre Files When the Spectre simulator opens a netlist file the simulator determines whether the file is a SPICE or Spectre netlist and interprets it accordingly This is true regardless of whether the file is the main netlist or an included netlist The Spectre simulator recognizes Spectre files because they start with the line simulator lang spectre or the filename ends in the Spectre circuit simulator extension of scs Files that do not start with this line or end in the scs extension are taken to be SPICE files Thus SPICE files do not need to be modified to work with the Spectre simulator as the SPICE Reader will automatically map them correctly to Spectre input The scs extension allows users to write netlists included files and library files using only the Spectre Netlist Language without having to switch from SPICE mode To learn more about controlling the input language see General Input Compatibility on page 51 Scope of the Compatibility Many current variants of SPICE have their own alterations to the SPICE input language The SPICE Reader in Spectre does support many of these variations using the following sources and guidelines July 2002
313. ponents or circuit parameters or only for particular voltages or currents try one of the following procedures Q Set gmin 1e 12 the default value Q Ifyou are working with simplified semiconductor models try using more complex models A CMOS complementary metal oxide semiconductor inverter whose model parameters have infinite output impedance in saturation demonstrates the usefulness of these techniques When either the N or P type device is in the ohmic region the solution is unique However when both devices are saturated there is a range of output voltages that all satisfy Kirchhoff s Current Law In this situation the Newton Raphson method forms a linearized circuit that is singular for that iteration m Check ideal transformers N ports or transmission lines for floating nodes or loops of zero resistance branches and modify the circuit to eliminate them For example consider this center tapped transformer m1 m2 b1 b2 subckt ct xfmr tl bl t2 m2 b2 Tt t1 ml t2 m2 transformer n1 2 Tb m1 bl m2 b2 transformer n1 2 end ct xfmr July 2002 255 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting If you use this transformer and leave the center tap terminal m2 floating the Spectre simulator notifies you of a singular matrix Because both m1 and m2 are floating the DC solution is not unique If you choose a different topology for the transformer like the one
314. pose binning and inline models simulator lang spectre parameters VDD 5 vec 2 0 vsource dc VDD vin 1 0 vsource dc VDD qi 1 2 0 0 npn mod area 350e 12 gets 20x20 scaled model q2 1 3 0 0 npn_mod area 25e 12 gets 10x10 scaled model q3 13 0 0 npn mod area 1000e 12 gets default model inline subckt npn mod cbe s generalized binning based on area parameters area 5e 12 if area 100e 12 npn mod cbe s npn10x10 10u 10u inline device else if area lt 400e 12 npn mod cbe s npn20x20 20u 20u inline device else npn mod cbe s npn default 5u 5u inline device model npn_default bjt is 3 2e 16 va 59 8 model npnl10x10 bjt is 3 5e 16 va 61 5 model npn20x20 bjt is 3 77e 16 va 60 5 ends npn_mod The transistors end up having the name that they were called with q1 q2 and q3 but each has the correct model chosen for its respective area Model binning can be now achieved based on any parameter and for any device such as resistor Or bjt A Warning about Conditional Instantiation If you run a sweep analysis on the previous circuit sweeping the parameter area for device instance q1 from 350 x 10 to 50 x 10 the Spectre simulator issues an error and stops once the value of area exceeds 100 x 10 This is because the condition in i area lt 100e 12 changes from being true to being false and this can result in a topology change that is not supp
315. power functions of the substrate current if you do not accurately determine the degradation parameters the predicted device lifetimes and degradations might lead to false conclusions Hot Electron Degradation Circuit Spectre degradation model subckt inv 1 2 3 cl 3 0 0 1p ml 3 2 1 1 pmen 1 1 5u w 30u ad 120p as 75p pd 36u ps 6u m2 3 2 0 0 nmen 1 1 5u w 15u ad 60p as 37 5p pd 23u ps 6u ends x1 21 2 3 inv x2 13 4 inv x3 145 inv x4 15 6 inv x5 1 6 7 inv x6 17 8 inv x7 18 9 inv x8 19 10 inv x9 X0 El an x10 1 11 12 inv xli k LZ 2 rnv vddl 1 0 vsource dc 5 0 vdd 21 0 pulse 0 5 0 0 0 1m 1n 500n tran 0 1n 10n circuitage 0 0 tran 0 1n 10n circuitage 4 0 model nmen nmos level 3 vto 0 6876 gamma 0 5512 kappa 5 0 kp 0 8675e 4 tox 0 206e 7 nsub 0 197e17 vmax 4e5 theta 0 2 cbs 10f cbd 10f degramod spectre degradation yes strc 1 5e 6 sube 1 duoc 0 9 duoe 0 9 wnom 15u lnom 2u model pmen pmos level 3 vto 0 6893 gamma 0 4411 kappa 5 0 ld 0 45e 6 kp 0 3269e 4 tox 0 206e 7 nsub 0 197e17 vmax 4e5 theta 0 2 cbs 10f cbd 10f degramod spectre degradation yes strc 3 0e 6 sube 1 duoc 0 9 duoe 0 9 wnom 30u lnom 2u save xl ml isub xl ml stress xl ml age end July 2002 178 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses The save statement in the previous netlist saves the waveforms of the substrate current the stress and the effective device a
316. ps 3 81u m2 7 vss 8 vdd p 1 0 35u w 3 60u ad 0 38p pd 23 81u as 0 38p ps 3 81u m3 nq vss 8 vdd p 1 0 35u w 3 60u ad 1 37p pd 4 36u as 0 38p ps 3 81lu m4 nq vss 9 vdd p 1 0 35u w 3 60u ad 1 37p pd 4 36u as 0 38p ps 3 81lu P p m5 9 vss 10 vdd 1 0 35u w 3 60u ad 0 38p pd 23 81u as 0 38p ps 3 81u m6 vdd a 10 vdd 1 0 35u w 3 60u ad 2 63p pd 8 66u as 0 38p ps 3 81lu July 2002 287 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits m7 vss a nq vss n 1 0 35u w 1 40u ad 1 02p pd 4 26u as 0 53p ps 2 16u m8 vss vss nq vss n 1 0 35u w 1 40u ad 0 53p pd 2 16u as 0 53p ps 2 16u m9 vss vss nq vss n 1 0 35u w 1 40u ad 0 53p pd 2 16u as 1 02p ps 4 26u c1 9 nq capacitor c 3 7995e 17 ez vdd vss capacitor c 1 3996057e 15 c3 nq vss capacitor c 3 1546797e 15 c4 nq vdd capacitor c 5 5551875e 16 c5 a vss capacitor c 1 2907233e 15 c6 a vdd capacitor c 2 1779808e 15 c7 10 nq capacitor c 2 0115e 17 c8 ang capacitor c 5 233362e 16 ends Begin top level circuit definition xno31 1 90 no3 xno32 2 1 no3 xno33 32 no3 xno34 14 3 no3 xno35 5 4 no3 xno36 6 5 no3 xno37 7 6 no3 xno38 8 7 no3 xno39 09 8 no3 xno310 10 9 no3 xno311 11 10 no3 xno312 12 11 no3 xno313 13 12 no3 xno314 14 13 no3 xno315 15 14 no3 xno316 16 15 no3 xno317 90 16 no3 Next couple of lines sets variables for vdd and vs
317. put referred noise for a noise free network For more information about the noise analysis see Chapter 4 Analysis Statements of the Spectre Circuit Simulator Reference Transfer function analysis x Linearizes the circuit about the DC operating point and performs a small signal analysis It calculates the transfer function from every source in the circuit to a specified output The output can be either a voltage or a current For more information about the transfer function analysis see Chapter 4 Analysis Statements of the Spectre Circuit Simulator Reference S parameter analysis s p Linearizes the circuit about the DC operating point and computes S parameters of the circuit taken as an N port You define the ports of the circuit with port statements You must place at least one port statement in the circuit The Spectre simulator turns on each port sequentially and performs a linear small signal analysis The Spectre simulator converts the response of the circuit at each port into S parameters For more information about the S parameter analysis see Chapter 4 Analysis Statements of the Spectre Circuit Simulator Reference B Transient analyses Q Transient analysis t ran Computes the transient response of the circuit over a specified time interval You can specify initial conditions for this analysis If you do not specify initial conditions the analysis starts from the DC steady state solution You can i
318. quickly because it begins with the initial temperature of the DC solution that was placed in a state file during analysis OpPoint July 2002 134 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Analysis XferVsF req computes several small signal quantities of interest such as closed loop gain the rejection ratio of the positive and negative power supply and output resistance The analysis again starts quickly because the operating point remains from the previous analysis Analysis StepResponse computes the step response that permits the measurement of the slew rate and settling times The alter statement please4 then changes the input stimulus from a pulse to a sine wave Finally the Spectre simulator computes the response to a sine wave in order to calculate distortion ua741 operational amplifier global gnd vcc vee Simulator lang spectre Spectre options audit detailed limit delta maxdeltav 0 3 save lvlpub nestlvl 1 ua741 operational amplifier model NPNdiode diode is 1f model NPNbjt bjt type npn bf 80 vaf 50 imax 5m cje 3p cjc 22p cjs 2p tf 3n tr 6n rb 100 model PNPbjt bjt type pnp bf 10 vaf 50 imax 5m cje 6p cjc 24p tf 1n tr 20n subckt ua741 pin nIn out Transistors Q1 1 pIn 3 vee NPNbjt Q2 1 nIn 2 vee NPNbjt Q3 5 16 3 vec PNPbjt Q4 4 16 2 vcc PNPbjt Q5 5 8 7 vee NPNbjt Q6 4 8 6 vee NPNbjt Q7 vec 5 8 vee NPNbjt Q9 16 1 vcc vee PNPbjt Q14 vcc 13 15
319. r 350s Edeka thet Denis ee ERE IS 78 Help or Parameters 52 089 Sun Ara Rid eror st OS ARO LAND aed eld ca d e ee 79 Scaling Numerical Literals 3 52 24 rur dut O9 eee dd ER Ge all Se Gres 81 Pararreters SItaterment 23241 EXE RIDERE Du AA Er EVI at si anm e 82 Circuit and Subcircuit Parameters nanana aaa eq OT V astra tate wie evden rue Ea 82 Par meter D claration n osten S err to a oet e ban AEN SS M tero EROS 83 Parameter Inheritance 4 i isis hee ERE ee ek e REOS 83 Parameter Namespace suci rii ERU ONDE REDE ei ead ER EVER E d 83 Parameter Referencing isc 9s 242 25 rex dor rmt ORC OGRE xD koc edere soia d edel 83 July 2002 5 Product Version 5 0 Spectre Circuit Simulator User Guide Altering Sweeping Parameters 0 200 cee eee 84 EEXPICSSIONS Aisa n parece III T LU IUE m 84 EXHI GO ODSLBS aaepe teese hob Ea dor Qo Mor deta tw a o eap ee a ee 87 User Defined E NGUONS masaker oe de vox e e e eg aA e tpe x 89 Predefined Netlist Parameters usus Ru RERaIDEEX A ea oh RNC ERE EE 90 SSUDGIDGHIES 3 odis kot donet aid oe eol ace Aes wale Bk dol RU dod One E o E WR FUP IG ACIER 90 Formatting Subcircuit Definitions 530 eee pe WOSREEY Ev ee qe Rex PUSH TRE 90 A Subcircuit Definition Example 34 36 x ER IE MRG a Ru e cR CUR RE ke Rx ERE 91 SUDCIEGUIT Example uo eec alin court ene aae aah at Case aoe ge RE Qt go adf a be rer effc 92 Rules to Remember 1 nencueci t tke ex SE o Y D
320. r also prints the ratio of the spectrum of the first signal to the fundamental of the second so you can use the analyzer to compute large signal gains and immittances directly If you are concerned about accuracy perform an additional Fourier transform on a pure sinusoid generated by an independent source Because both transforms use the same time points the relative errors measured with the known pure sinusoid are representative of the errors in the other transforms In practice this second Fourier transform is performed on the reference signal To increase the accuracy of the Fourier transform use the points parameter to increase the number of points Tightening reltol and setting errpreset conservative are two other measures to consider The accuracy of the magnitude and phase for each harmonic is independent of the number of harmonics computed Thus increasing the number of harmonics while keeping points constant does not change the magnitude and phase of the low order harmonics but it does July 2002 150 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses improve the accuracy of the total harmonic distortion computation However if you do not specify points you can increase accuracy by requesting more harmonics which creates more points The large number of points required for accurate results is not a result of aliasing Many points are needed because a quadratic polynomial interpolates the waveform between the
321. r settings on the capacitors and inductors are used and the ic statements are ignored all Both the ic statements and the ic parameters are used If specifications conflict ic parameters override ic statements Specifying State Information with State Files You can also specify initial conditions and estimate solutions by creating a state file that is read by the appropriate analysis You can create a state file in two ways m You can instruct the Spectre simulator to create a state file in a previous analysis for future use July 2002 240 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques B The voltage of node voff is set to 0 m Node 7 of subcircuit X3 is set to 2 5 V m The internal drain node of component M1 is set to 3 5 V See the table in the ic statements section of this chapter for more information about specifying internal nodes B The current for inductor L1 is set to 1y Specifying State Information for Individual Analyses You can specify state information for individual analyses in two ways m You can use the ic parameter of the transient analysis to choose which previous specifications are used M You can create a state file that is read by an individual analysis Choosing Which Initial Conditions Specifications Are Used for a Transient Analysis The ic parameter in the transient analysis lets you select among several options for which initial conditions to use You can ch
322. r the absolute value of a parameter with the vertical line character vto For example resistor 0 1 lt r lt 1M specifies that the absolute value of r should be greater than 0 1 ohm and less than 1 megohm There can be no spaces between the absolute value symbols and the parameter name m You currently cannot place limits on vector parameters m You can write parameter limits using Spectre native mode scale factors For example you can write the limit f lt 1 0e6 as f lt 1M Example of a Parameter Range Limits File This example shows a parameter limits file with correct syntax mos3 0 5u lt 1 lt 100u 0 5u lt w 0 lt as lt 1e 8 0 lt ad lt le model vto lt 3 You can find the parameter names 1 w as ad vto and component keywords mos3 in the parameter listings in the Spectre online help spectre h This example instructs the Spectre simulator to accept without warnings mos3 components for these conditions W f channel length is more than or equal to 0 5 um or less than or equal to 100 um B f channel width is greater than or equal to 0 5 um July 2002 267 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting B Ifthe area of source diffusion is greater than 0 or less or equal to 1e 8m m iif the area of drain diffusion is greater than O or less or equal to 1e 8 m B If the mos3 model parameter vto the threshold volt
323. rances with the quantity Statement Quantities are used to hold convergence related information about particular types of signals such as their units absolute tolerances and maximum allowed change per Newton iteration With the quantity statement you can create quantities and change the values of their parameters You set these tolerances with the abstol and maxdelta parameters respectively You can set the huge parameter which is an estimate of the probable maximum value of any signal for that quantity You can also set the blowup parameter to define an upward bound for signals of that quantity If a signal exceeds the blowup parameter value the analysis stops with an error message Generally a reasonable value for the absolute tolerance of a quantity is 10 times smaller than its greatest anticipated value A reasonable definition for the huge value of a quantity is 10 to 10 times its greatest expected value A reasonable definition of the blowup value for a quantity is 108 to 10 times its greatest expected value Predefined Quantities The Spectre Netlist Language has seven predefined quantities that are relevant for circuit simulation and you can set tolerance values for any of them These seven predefined quantities are B Electrical current in Amperes named I x Default absolute tolerance 1 pA m Magnetomotive force in Amperes named MMF Default absolute tolerance 1 pA turn W Electrical potential in Volts name
324. rcuit it is usually faster to start the DC analysis from a previous solution than to start from the beginning Saving Time by Modifying Parameters during a Simulation The Spectre simulator lets you place specifications in the netlist to modify parameters and then resimulate This lets you accomplish tasks with a single Spectre run that might require multiple runs with another simulator To change parameter settings during a run you use the following Spectre control statements m Thealter statement You use this statement to change the parameters of circuits subcircuits and individual models or components You also use it to change the following options statement temperature parameters and scaling factors Q temp Q tnom Q scale July 2002 242 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques m Scalem You can use the altergroup statement to specify device model and netlist parameter statements that you want to change the values of with analyses m The set statement Except for temperature parameters and scaling factors you use the set statement to modify any opt ions statement parameters you set at the beginning of the netlist The new settings apply to all analyses that follow the set statement in the netlist The alter and set statements are queued up with analysis statements and are processed in order Changing Circuit or Component Parameter Values You modify parameters f
325. rds 202 214 newlink save statement 201 213 Newton Raphson iteration 245 255 node capacitance table printing 194 nodes as info statement parameter 193 223 definition of 58 naming 59 rules fornames 59 specifying initial conditions with 188 238 nodeset statement nodesets 187 237 convergence problems and 276 specifying for individual analyses 190 240 node to terminal map 193 223 noise analysis brief description of 130 none as homotopy parameter option 246 as info statement parameter 193 as pwr option 206 218 as save parameter option 207 21 nonlinear component models and convergence problems 276 notifications responding to 31 nport component and S parameter files 120 nport statement example in netlist 117 N ports example 117 modeling 117 numerical error improved control of 17 numruns parameter Monte Carlo analysis 163 nutascii output format 224 nutbin output format 224 Nutmeg format 224 O online help 20 open loop gain in netlist example of measuring 134 operating regions determining for BJTs 271 189 239 N Co 2 co selecting limits for warnings about 270 specifying forbidden regions for July 2002 transistors 270 operating point parameters listing 192 222 saving with save statement 202 214 operational amplifier example of characterization in one simulation run 134 oppoint as DC analysis parameter 157 as info s
326. re m SPICE mode You can specify the language mode for subsequent statements by specifying simulator lang mode where mode S spectre Or spice Spectre mode input is fully case sensitive In contrast except for letters in quoted strings SPICE mode converts input characters to lowercase Creating Component and Node Names When you create node and component names in the Spectre simulator follow these rules m Use unique names for components and nodes The Spectre Netlist Language uses the same syntax for the names for nodes device instances models nets subcircuit parameters enumerated named values for parameters and netlist parameters that are expressions so there is no way for the Spectre simulator to distinguish between duplicate names m Donotuse the name of an analysis such as t ran or built in primitive such as resistor m Except for node names names must begin with a letter or underscore Node names can also be integers July 2002 59 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists m If the node name is an integer leading zeros are significant in the Spectre language mode m Names can contain any number of letters digits or underscores m Names cannot contain nonalphanumeric characters blanks tabs punctuation characters or continuation characters unless they are escaped with a backslash The exception is bang for example vdd m The followi
327. re information about the save statement see Saving Signals for Individual Nodes and Components on page 213 July 2002 220 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options Setting the currents Parameter The currents parameter has the following options Setting Action selected Saves only currents that you specifically request with save statements or save parameters Also saves naturally computed branch currents currents through current probes voltage sources and inductors This is the default setting nonlinear Saves all terminal currents for nonlinear devices naturally computed branch currents currents through current probes voltage sources and inductors and currents you specify with save statements Can significantly increase simulation time all Saves all terminal currents and currents available from selected settings to the raw file Can significantly increase simulation time Note Currently if you set the currents parameter value to nonlinear orall and do not specify a save parameter value in an options statement the Spectre simulator saves circuit nodes as well as the currents you requested This might change in future releases of the Spectre simulator Examples of the currents Parameter You use the following syntax for the currents parameter in the options statement For more information about the options statement see the parameter listings in the Sp
328. rl 1 0 resistor r pl use a parameter value 1 r2 1 0 resistor r pltp2 use parameters in an expression value 3 xl sl p4 8 subckt sl is defined below pass in value 8 for p4 subckt sl parameters pl 4 p3 5 p4 6 note no p2 here pl redefined rl 1 0 resistor r pl local definition used value 4 r2 1 0 resistor r p2 inherit from parent top level value 2 r3 1 0 resistor r p3 use local definition value 5 r4 1 0 resistor r p4 use passed in value value 8 r5 1 0 resistor r pl p2 p3 use local inherited local 4 2 5 4 4 ends July 2002 82 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features time sweep tran start 0 stop pl p2 50e 6 use 5 50e 6 150 us dc sweep dc param pl values 0 5 1 p2 sqrt p2 p2 sweep pl Parameter Declaration Parameters can be declared anywhere in the top level circuit description or on the first line of a subcircuit definition Parameters must be declared before they are used referenced Multiple parameters can be declared on a single line When parameters are declared in the top level their values are also specified When parameters are declared within subcircuits their default values are specified The value or default value for a parameter can be a constant expression a reference to a previously defined parameter or any combination of these Parameter Inheritance Subcircuit definitions inherit parameters from the
329. rm storage format 224 wsfascii output format 224 wsfbin output format 224 X xf analysis brief description of 130 July 2002 312 Product Version 5 0 Spectre Circuit Simulator User Guide July 2002 313 Product Version 5 0
330. roduct Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists B If filename is not an absolute path specification it is considered relative to the directory of the including file that the Spectre simulator is reading not from the directory in which the Spectre simulator was called m You must surround the filename in quotation marks m You can place a space and then a backslash escaped newline X between include and filename for line continuation m You can place other include statements in the inserted file recursive inclusion m With any ofthe include formats you can set the language mode for the inserted file by placinga simulator lang command at the beginning of the file For more information about the simulator lang command see Chapter 3 SPICE Compatibility The Spectre simulator assumes that the file to be included is in the SPICE language unless one of the following conditions occurs Q The file to be included has a simulator lang spectre line at the beginning of the file The first line is not a comment title line even in SPICE mode a The file to be included has a scs file extension m With the include format if you change the language mode in an inserted file the language mode returns to that of the original file at the end of the inserted file m You cannot start a statement in an original file and end it in an inserted file or vice versa B Youcanuse include filename and the
331. rom an input filename C of users maxwell circuits opamp ckt Colon Modifier Comments Output Filename Result C Input filename users maxwell circuits opamp ckt BOT Root of the input filename users maxwell circuits opamp C e Extension of the input ckt filename C h Head of the input filename users maxwell circuits SC t Tail of the input filename opamp ckt SC Second colon is appended users maxwell circuits to the input filename and opamp ckt the end of the modification C h h The head of C h sucha users maxwell recursive use of h might be useful if you want to direct your output to a different directory from that of the input file SC ltr The root of C t opamp Se ese The tail of C r opamp July 2002 252 Product Version 5 0 Spectre Circuit Simulator User Guide Managing Files Colon Modifier Comments Output Filename Result tmp C t r raw The suffix raw is tmp opamp raw appended to the root of C t and the full path is altered to put opamp raw in the tmp file SC exec E PTE Extension of C followed by ckt opamp the tail of C r July 2002 253 Product Version 5 0 Spectre Circuit Simulator User Guide 12 Identifying Problems and Troubleshooting This chapter discusses the following topics Error Conditions on page 254 Spectre Warning Messages on page 257 Customizing Error and Warning Messages on page 262 Controlling Program Generated Messages on
332. ronment Variables If you specify log file options in a SPECTRE_DEFAULTS environment variable you might want to name log files according to some system that helps you keep track of log files from different simulations Spectre predefined percent codes are useful for this The following example uses the predefined percent code C to create log filenames based on the input filename If you run a simulation for smps circuit the Spectre simulator creates a log file named smps circuit logfile You place the SPECTRE DEFAULTS environment variable in the cshrc Or profile files setenv SPECTRE DEFAULTS log C logfile July 2002 273 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting For more information about predefined percent codes and the SPECTRE_DEFAULTS environment variable see Chapter 11 Managing Files Suppressing Messages There are also spect re command options that let you print or suppress error warning or informational messages terror Prints error messages error Does not print error messages warning Prints warning messages warning Does not print warning messages info Prints informational messages info Does not print informational messages As a default the Spectre simulator prints all these messages Correcting Convergence Problems In this section you will learn about procedures that can help you if a simulati
333. rridmgDefa lts 23 535 253 3 3 9 X 3e RR OUR ECOUTER edad oe vue Ea 235 10 Time Saving Techniques 00 0 00 eee 236 Specifying Efficient Starting Points ccc ees 236 Reducing the Number of Simulation Runs eee ee 236 Adjusting Speed and Accuracy agas rrr o eur ose Pee dI ra a ee RE 237 Saving Time by Starting Analyses from Previous Solutions 237 Saving Time by Specifying State Information 0 0 0 0 cee eee 237 July 2002 9 Product Version 5 0 Spectre Circuit Simulator User Guide Setting Initial Conditions for All Transient Analyses llle 238 Supplying Solution Estimates to Increase Speed 239 Specifying State Information for Individual Analyses 240 Saving Time by Modifying Parameters during a Simulation 242 Changing Circuit or Component Parameter Values 243 Modifying Initial Settings of the State of the Simulator 245 Saving Time by Selecting a Continuation Method illius 245 11 Managing mil iE ET EE TOO 247 About Spectre Filename Specification 0 0 20 eee 247 Creating Filenames That Help You Manage Data 000 cece eee 247 Creating Filenames by Modifying Input Filenames sues 248 Description of Spectre Predefined Perce
334. rs for example nonideal etching into account inline subckt TNSA PR CB E S parameters WE LE MULT 1 dIS 0 dBF 0 WEA WE SNDW effective or Actual emitter width LEA LE SNDW effective or Actual emitter length AE WEA LEA effectiv mitter area IS 1e 18 FRSHPI AE 1 XISNafac sqrt AE XISNbfac dIS 2 XISN 1 sqrt MULT rr E mea E TXBFNbfac t dBF 24XBFN 1 sqrt MULT TNSA PR CB E S TNSA B IS IS BF BF MULT MULT Lf T 3nline ends TNSA PR a geometrical process RPLR resistor subcircuit resistance is function of effective device geometry taking process factors for example nonideal etching into account inline subckt RPLR PR A B parameters Rnom WB MULT 1 dR 0 t LB Rnom WB RSHSPnom AB LB WB SPDW RPLR_PR A B RPLR_B R RSHSP LB WB SPDW 1 XRSPafac sqrt AB XRSPbfac dR 2 XRSP 1 sqrt MULT ends RPLR_PR The following file Plain h provides the designer with a plain device interface without geometrical or process modeling July 2002 102 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features File Plain h Simulator lang spectre plain TNSA no geometrical or process modeling inline subckt TNSA C B E S parameters MULT 1 IS 1e 15 BF 100 TNSA CB E S TNSA B IS IS BF BF MULT MULT call TNSA B ends
335. s parameters vdd S1 23 3 parameters vss S1 0 0 vdd I1 vdd gnd vsource dc vdd S1 vss Il vss gnd vsource dc vss S1 Next line initializes nodes within ring ic 220 420 6 20 8 20 1020 include q35d4h5 modsp section tt Analysis tempOption options temp 25 typ tran tran step 0 010n stop 35n alter ss altergroup include q35d4h5 modsp section ss parameters vdd S1 23 0 alterTempTo100 alter param temp value 100 ss_tran tran step 0 010n stop 35n alter_ff altergroup include q35d4hn5 modsp section ff parameters vdd S1 3 3 alterTempTo0 alter param temp value 0 ff_tran tran step 0 010n stop 35n July 2002 288 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits Opamp Circuit opamp cir This example uses Spectre s SPICE syntax subckt opamp 1 2 6 8 9 ml 4 2 3 3 nch w 43u 1 10u ad 0 3n as 0 3n pd 50u ps 50u m2 5 1 3 3 nch w 43u 1 10u ad 0 3n as 0 3n pd 50u ps 50u m3 4 4 8 8 pch w 10u 1 10u ad 0 3n as 0 3n pd 20u ps 20u m4 5 4 8 8 pch w 10u 1 10u ad 0 3n as 0 3n pd 20u ps 20u m5 3 7 9 9 nch w 38u 1 10u ad 0 3n as 0 3n pd 40u ps 40u m6 6 5 8 8 pch w 344u 1 10u ad 1 3n as 1 3n pd 350u ps 350u m7 6 7 9 9 nch w 652u 1 10u ad 2 3n as 2 3n pd 660u ps 660u m8 7 7 9 9 nch w 38u 1 10u ad 0 3n as 0 3n pd 40u ps 40u cc 5 6 4 4p ibias 8 7 8 8u ends opamp Opamp Circuit 2 opamp1 cir This example uses Spectre s SPICE syntax subckt opamp 12 6
336. s Device Lifetime Years in Ascending Order Device Vin lifetime Uj lifetime Age sec x7 m1 4 5372 3 9493 6 9888e 18 x3 m1 4 563 3 9718 6 9493e 18 x9 m1 4 5865 3 9922 6 9138e 18 x2 m1 4 5935 3 9983 6 9032e 18 x11 m1 4 6045 4 0078 6 8867e 18 x5 m1 4 6269 4 0273 6 8534e 18 x2 m2 5 6758 4 9404 5 5868e 18 x3 m2 6 5803 5 7277 4 8189e 18 x6 m2 6 6639 5 8004 4 7585e 18 x1 m2 6 6998 5 8317 4 733e 18 x10 m2 6 7037 5 8351 4 7302e 18 x4 m2 6 7768 5 8986 4 6792e 18 x8 m2 6 8111 5 9285 4 6556e 18 x4 m1 7 2344 6 297 4 3832e 18 x1 m1 8 1518 7 0956 3 8899e 18 x10 m1 9 0831 7 9062 3 4911e 18 x6 m1 9 0909 7 9129 3 4881e 18 x8 m1 9 3002 8 0952 3 4096e 18 x9 m2 12 981 11 299 2 4428e 18 x5 m2 13 019 11 332 2 4356e 18 x7 m2 13 235 11 52 2 3959e 18 x11 m2 13 291 11 569 2 3858e 18 July 2002 181 4 0 the values requested in the t ran statements The contents of these Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Device Degradations after Four Years in Descending Order Device Delta Vth V Delta Uo Delta Gm Delta Id Status x7 m1 0 08816 10 115 10 112 10 094 Failed x3 m1 0 087661 10 064 10 06 10 042 Failed x9 m1 0 087213 10 018 10 014 9 9962 Failed x2 m1 0 087079 10 004 10 9 9824 Failed x11 m1 0 086872 9 9824 9 9789 9 961 Passed x5 m1 0 086451 9 9389 9 9354 9 9176 Passed x2 m2 0 070474 8 2693 8 265 8 243 Passed X3 m2 0 060787 7 2389 7 2351 7 2157 Passed x6 m2 0 060025 7 1572 7 1534 7 134
337. s Improved Reliability The Spectre circuit simulator offers you the following improvements in reliability Improved convergence Spectre proprietary algorithms ensure convergence of the Newton Raphson algorithm in the DC analysis The Spectre circuit simulator virtually eliminates the convergence problems that earlier simulators had with transient simulation July 2002 18 Product Version 5 0 Spectre Circuit Simulator User Guide Introducing the Spectre Circuit Simulator B Helpful error and warning messages The Spectre circuit simulator detects and notifies you of many conditions that are likely to be errors For example the Spectre circuit simulator warns of models used in forbidden operating regions of incorrectly wired circuits and of erroneous component parameter values By identifying such common errors the Spectre circuit simulator saves you the time required to find these errors with other simulators The Spectre circuit simulator lets you define soft parameter limits and sends you warnings if parameters exceed these limits B Thorough testing Automated tests which include over 1 000 test circuits are constantly run on all hardware platforms to ensure that the Spectre circuit simulator is consistently reliable and accurate m Benchmark suite There is an independent collection of SPICE netlists that are difficult to simulate You can obtain these circuits from the Microelectronics Center of North Carolina MCNC i
338. s The pwr parameter in the options statement can also be used to save power The following table shows the five possible settings for the pwr option Setting Action all The total power the power dissipated in each subcircuit and the power dissipated in each device is saved subckts The total power and the power dissipated in each subcircuit is saved devices The total power and the power dissipated in each device is saved total The total power dissipated in the circuit is calculated and saved none No power variable is calculated or saved This is the default setting For example opts options pwr total save xl pwr This creates two power signals pwr generated by the options statement and x1 pwr generated by the save statement July 2002 218 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options Saving Groups of Signals To save groups of signals as results you use the save and nest 1v1 parameters You specify which signals you want to save with the save parameter You use the nest 1v1 parameter when you save signals in subcircuits The nest 1v1 parameter specifies how many levels deep into the subcircuit hierarchy you want to save signals You can set these parameters as follows n In options statements or set statements If you set the save and nest 1v1 parameters with an opt ions or a set statement the setting applies to signal data from all analyses that follow that state
339. s You can create an inline subcircuit that contains only a single model statement and nothing else where the model name is identical to the subcircuit name This syntax is used to generate a parameterized model statement for a given set of parameters where the model is then exported and can be referenced from one level outside the subcircuit Instantiating the inline subcircuit in this case merely creates a model statement with the same name as the subcircuit call The Spectre simulator knows that because the subcircuit definition contains only a model statement and no other instances the definition is to be used to generate named models that can be accessed one level outside of the subcircuit Regular device instances one level outside of the subcircuit can then refer to the generated model Because these are now instances of a model rather than of a subcircuit you can specify device instance parameters with enumerated types such as region fwd July 2002 100 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features This technique is shown in the following example declare an inline subcircuit that exports a parameterized model inline subckt bjtmod parameters le lu we 2u area le w model bjtmod bjt type npn bf 100 letwe 2 area le 12 is le 12 le we area 1e 12 ends bjtmod now create two instances of the inline subcircuit that is create two actual m
340. s allowed only in the top level of the input file The following is the syntax for the paramset statement Name paramset lt list of netlist parameters gt lt list of values foreach netlist parameter gt list of values foreach netlist parameter Here is an example of the paramset statement parameters pl 1 p2 2 p3 3 data paramset pl pZ p3 5 5 5 4 3 2 Combining the paramset statement with the sweep analysis allows you to sweep multiple parameters simultaneously for example power supply voltage and temperature Setting Sweep Limits For all analyses that support sweeping you specify the sweep limits with the parameters in the following table Parameter Value Comments start Start of sweep value Default 0 start and stop are used stop End of sweep value together to specify sweep limits center Center value of sweep center and span are used span Span of sweep Default 0 together to specify sweep limits July 2002 159 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Parameter Value Comments step Step size for linear sweeps step and lin are used to specify lin Number of steps for linear sweeps linear sweeps Default is 50 dec Number of points per decade for dec and log are used to specify log sweeps logarithmic sweeps log Number of steps for logarithmic sweeps default is 50 values Array of sweep values values specifies each sweep value with a vector of values
341. s of operators algebraic and trigonometric functions are given after some examples The following are examples simulator lang spectre parameters pl 1 p2 2 declare some top level parameters rl 1 0 resistor r pl the simplest type of expression r2 1 0 resistor r plt p2 a binary expression r3 1 0 resistor r 5 6 2 expression of constants 8 xl sl p4 8 instantiate a subcircuit defined in the following lines subckt sl parameters pl 4 p3 5 p4 p1 p3 subcircuit parameters rl 1 0 resistor r pl another simple expression r2 1 0 resistor r p2 p2 a binary multiply expression r3 1 0 resistor r pl p2 p3 a more complex expression r4 1 0 resistor r sqrt pl p2 an algebraic function call r5 1 0 resistor r 3 atan pl p2 a trigonometric function call r6 1 0 RESMOD r pl p4 1 p3 the ternary operator ends a model statement containing expressions model RESMOD resistor tcl pl p2 tc2 sqrt pl p2 some expressions used with analysis parameters time sweep tran start 0 stop pl p2 50e 6 use 5 50e 6 150 us a vector of expressions see notes on vectors below dc sweep dc param pl values 0 5 1 p2 sqrt p2 p2 sweep pl July 2002 84 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features Where Expressions Can Be Used The Spectre Netlist Language allows expressions to be used where
342. s the title card Generally ignores the case of alphabetic characters in the input The program internally converts them to lowercase Quoted strings are exceptions to this rule Interprets scale factors following numerical values according to SPICE conventions Accepts the SPICE comment and continuation conventions July 2002 51 Product Version 5 0 Spectre Circuit Simulator User Guide SPICE Compatibility W Accepts the and characters as valid parts of a node or an instance or parameter name You can also use the Escape backslash convention to include otherwise illegal characters in the names m Spectre statements are not allowed in the SPICE mode and SPICE statements are not allowed in the Spectre mode B n simulator lang spectre mode you can refer to model names and subcircuit names defined with the simulator lang spice mode model and subckt statements even though they are in another portion of the netlist Spectre always tries to match the case of a model subcircuit s name when there is a call to a model subcircuit from an instance line an alter statement or other part of the netlist During the netlist conversion process the SPICE Reader converts included models subcircuits to lower case which can prevent Spectre from identifying the right model subcircuit for a given device For this reason the SPICE Reader will insert the flag insensitive yes atthe beginning of each converted netlist on the simulator comma
343. s variations be applied unless you have specified process statistics in the statistics block More details on statistics blocks are given in Specifying Parameter Distributions Using Statistics Blocks on page 170 166 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Parameter Description donominal appendsd July 2002 This flag determines whether a nominal run of all child analyses is performed yes or no before starting the Monte Carlo runs The default is yes If the flag is set to yes and the Spectre simulator cannot calculate an output expression during the nominal run for example convergence problems or incorrect export expressions the Spectre simulator issues an error message and immediately exits the Monte Carlo analysis If donominal is set to no the Spectre simulator runs the Monte Carlo iterations without performing a nominal analysis If there are convergence problems or the output expressions cannot be successfully calculated for the first or any iteration the Spectre simulator issues a warning and continues with the next iteration of the Monte Carlo loop This specifies whether to append scalar data to the existing scalarfile yes or to overwrite the existing file no The default is no This flag applies to both scalarfile and processscalarfile 167 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Parameter Description savefamilyplots This f
344. save operating point data instead of for all time points July 2002 144 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Telling the Spectre Simulator to Change the Time Interval between Data Points Strobing Strobing changes the interval between data points You use strobing to eliminate some unwanted high frequency signal from the output just as a strobe light appears to freeze rapidly rotating machinery With strobing you can demodulate AM signals or hide the effect of the clock in clocked waveforms You can also dramatically improve the accuracy of external Fast Fourier Transform FFT routines To perform strobing you set the following parameters in the transient analysis m The strobeperiod parameter which sets the time interval between the data points that the Spectre simulator saves m The skipstart parameter optional which tells the Spectre simulator when to start strobing This parameter is also used to skip data points m The skipstop parameter optional which tells the Spectre simulator when to stop strobing This parameter is also used to skip data points m The strobedelay parameter optional which lets you set a delay between the skipstart time and the first strobe point Telling the Spectre Simulator How Many Data Points to Save By telling the Spectre simulator to save only every Nth data point you can reduce the size of the results database generated by the Spectre simulator You te
345. separate the frequency specification from the S parameters with a colon July 2002 118 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features m There is no limit to the number of ports If either port number is greater than nine place a colon between the two port numbers when you specify the S parameter format S13 15 Note The s parameters can be given in any order and in any supported format but the order and format used must be consistent through out the file and must match the order and format specified in the format line Example of an S Parameter File The following is a correctly formatted S parameter file S parameter data file nport data Generated by spectre from circuit file y 4 42 38 PM Tue Jul 28 1998 reference resistance port2 50 port1 50 format freq 0 00000000e 00 1 00000000e 05 2 00000000e 05 3 00000000e 05 4 00000000e 05 5 00000000e 05 6 00000000e 05 7 00000000e 05 8 00000000e 05 9 00000000e 05 1 00000000e 06 July 2002 22 real imag s21 real imag OO C3 CY OO One IC T 09 703 CX CY C3 C X 4C C is port p2 is port pl 7 0 0 665775 Sls 334225 0 665775 3 334225 0 665775 D 334224 0 665775 EH 0 334224 0 665775 95 334224 0 665776 0 334224 O 665776 0 334224 0 665776 zs 334224 0 665776 0 334223
346. simulator might have convergence problems To avoid these problems set cmin which is the minimum capacitance to ground at each node to a physically reasonable nonzero value You also might want to adjust the time step parameters step and maxstep step iS a suggested time step you can enter Its default value is 001 stop start maxstep is the largest time step permitted Controlling the Amount of Output Data The Spectre simulator normally saves all computed data in the transient analysis Sometimes you might not need this much data and you might want to save only selected results At other times you might need to decrease the time interval between data points to get a more precise measurement of the activity of the circuit You can control the number of output data points the Spectre simulator saves for the transient analysis in these ways m With strobing which lets you select the time interval between the data points the Spectre simulator saves The simulator forces a time step on each point it saves so the data is computed not interpolated m With skipping time points which lets you select how many data points the Spectre simulator saves m With data compression which eliminates repetitive recording of signal values that are unchanged m With the outputstart parameter which lets you specify the time when the Spectre simulator starts saving data points m With the infotime parameter which lets you specify specific times to
347. solute value All x pow x y x to the power of y All x all y sin x Sine All x cos x Cosine All x tan x Tangent All x except x n x 2 where n is odd asin x Arc sine 1 lt x lt 1 acos x Arc cosine 1 2 x lt 1 atan x Arc tangent All x atan2 x y Arc tangent of x y All x all y July 2002 86 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features Function Description Domain hypot x y sqrt x x y y All x all y sinh x Hyperbolic sine All x cosh x Hyperbolic cosine All x tanh x Hyperbolic tangent All x asinh x Arc hyperbolic sine All x acosh x Arc hyperbolic cosine x gt 1 atanh x Arc hyperbolic tangent 1 lt x lt 1 int x Integer part of x number before the decimal ceil x Smallest integer All x greater than or equal to X floor x Largest integer less All x than or equal to x fmod x y Floating point y 0 remainder of x y Using Expressions in Vectors Expressions can be used as vector elements as in the following example dc sweep dc param pl values 0 5 1 p2 sqrt p2 p2 sweep pl Note When expressions are used within vectors anything other than constants parameters or unary expressions unary unary must be surrounded by parentheses Vector elements should be space separated The preceding dc sweep example shows a vector of four elements 0 5 1 p2 and sqrt p2 p2 Note that the
348. square root expression is surrounded by parentheses Built in Constants You can use built in constants to specify parameter values July 2002 87 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features The Spectre Netlist Language contains the built in mathematical and physical constants listed in the following table Mathematical constants start with M_ and physical constants start with P_ Constant Name Value Description M M M M M M M_ My Mo Me M Me M_ M M Pos July PET DEGPERRAD E LOG2E LOG10E LN2 LN10 IWO PI PI 2 PIA TPI 2_PI 2_SQRTPI SORT2 SORT1 2 EPSO 2002 2 7182818284590452354 1 4426950408889634074 0 434294481 90325182765 0 69314718055994530942 2 30258509299404568402 3 14159265358979323846 6 2831853071 7958647652 1 57079632679489661923 0 78539816339744830962 0 3183098861 8379067154 0 63661977236758134308 1 12837916709551257390 1 41421356237309504880 0 70710678118654752440 57 2957795130823208772 1 6021918x10 1 2 997924562x108 1 3806226x10 23 6 6260755x10 34 8 85418792394420013968x10 88 e or escp 1 log2 e log10 e In 2 In 10 T Qn x 2 x 4 1 x 2 r 2 n A2 4172 Number of degrees per radian equal to 180 z Charge of electron in coulombs Speed of light in vacuum in meters second Boltzman s c
349. ssscalarfile are written in the same directory paramfile This file contains the titles sweep variable values and the full expression for each of the columns in scalarfile The default name for this file is name mcparam where name is the name of the Monte Carlo analysis instance The file is created in the psf directory by default unless you specify some path information in the filename saveprocessparams This specifies yes or no whether to save scalar data for statistically varying process parameters that are subject to process variation July 2002 164 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Parameter Description processscalarfile If saveprocessparams is set to yes the process batch to batch values of all statistically varying parameters are saved to this scalar data file You can use saveprocessvec to filter out a subset of parameters in which case the Spectre simulator saves only the parameters specified in saveprocessvec 0 processscalarfile processscalarfile is equivalent to scalarfile except that the data in scalarfile contains the values of the scalar export statements whereas the data in processscalarfile contains the corresponding process parameter values The default name for this file is instname process mcdata Where instname is the name of the Monte Carlo analysis instance This file is created in the psf directory by default unless you specify some path information in the file
350. sweeping of multiple parameters defined by the paramset statement For all analyses that support sweeping to sweep the circuit temperature use param temp with no dev mod or sub parameter You can sweep a top level netlist parameter by giving the parameter name with no dev mod or sub parameter You can sweep a subcircuit parameter for a particular subcircuit instance by specifying the subcircuit instance name with the sub parameter and the subcircuit parameter name with the param parameter You can do the same thing for a particular device instance by using dev for the device instance name or for a particular model by using mod for the device model name July 2002 158 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses Note If frequency is a sweep option for an analysis the Spectre simulator sweeps frequency if you leave dev mod and param unspecified That is frequency is the default swept parameter for that analysis Specifying Parameter Sets You Want to Sweep For the sweep analysis only the paramset statement allows you to specify a list of parameters and their values This can be referred by a sweep analysis to sweep the set of parameters over the values specified For each iteration of the sweep the netlist parameters are set to the values specified by a row The values have to be numbers and the parameters names have to be defined in the input file netlist before they are used The paramset statement i
351. t envSetVal asimenv startup Simulator string spectre Save the cdsinit file in the directory from which you start AWD or in your home directory AWD looks for the cdsinit file first in the directory from which AWD was started if the file is not there AWD looks for it in your home directory Another option is to place the following entry in a cdsenv file asimenv startup simulator string spectre July 2002 32 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre Save the cdsenv file in your home directory If AWD does not find the cdsenv file in your home directory AWD looks for the system defined default settings July 2002 33 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre AWD and Other Windows Once AWD is running four windows appear on your screen They are shown in the following figures T File Tools Options Help COPYRIGHT 1992 1999 CADENCE DESIGN SYSTEMS INC ALL RIGHTS RESERVED 1992 1999 UNIX SYSTEMS Laboratories INC Reproduced with permission is Cadence Design Systems program and online documentation are Loading asimenv cxt Command Interpreter Window CIW Window Memories Constants Options Help 3 1 Evaluate Buffer Display Stack 4 standard RF browser vt Ea lasts xeoy dwn wp sto rel Special Functions wave vt it cea cst app an asin ma
352. t Data from Multiple Files on page 70 Multidisciplinary Modeling on page 73 Inherited Connections on page 75 Netlist Statements A Spectre circuit simulator netlist describes the structure of circuits and subcircuits by listing components the nodes that the components are connected to the parameter values that are used to customize the components and the analyses that you want to run on the circuit You can use SpectreHDL or Verilog A to describe the behavior of new components that you can use in a netlist like built in components You can also define new components as a collection of existing components by using subcircuits A netlist consists of four types of statements m Instance Statements on page 61 Analysis Statements on page 64 a W Control Statements on page 66 a Model Statements on page 68 July 2002 57 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists Before you can create statements for a Spectre netlist you must learn some basic syntax rules of the Spectre Netlist Language Netlist Conventions These are the netlist conventions followed by the Spectre simulator Associated Reference Direction The reference direction for the voltage is positive when the voltage of the terminal is higher than the voltage of the terminal A positive current arrives through the terminal and leaves through the terminal Current Voltage Ground Gro
353. t freq S11 mag deg S21 mag deg Skk mag deg Data section Comment lines can appear before the t ime line These comment lines are notes on complex number formats in the input file Data section enters S parameter data in the format specified in the header Error Handling The translator provides the following error handling mechanisms m When the incorrect filename has been given the translator exits with an error message such as sptr Unable to open input file filename No such file or directory m When the input file format does not match the sim option the translator exits and reports an error message such as Input format does not match sim option m When reading a file that is inconsistent with the standard format for example upon scanning a line in the data section that does not match the specified format the translator exits with an error message such as sptr error in file at line XXX Generally the translator ignores blank lines in data sections when reading a file July 2002 128 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses This chapter discusses the following topics Types of Analyses on page 129 Analysis Parameters on page 133 Probes in Analyses on page 133 Multiple Analyses on page 134 Multiple Analyses in a Subcircuit on page 136 DC Analysis on page 138 AC Analysis on page 139 Transient Analysis on page 140 Other Analyses sens fourier dcmat
354. t language syntax 59 file formats defining output filenames creating by modifying input filenames percent codes 248 creating from parts of input filenames colon modifiers 251 generation 226 files S parameter 119 state reading 191 241 firstrun parameter Monte Carlo analysis 166 225 July 2002 using 168 floating resistors and convergence problems 275 forbidden operating regions for transistors specifying 270 formatting alarm parameter 270 analyses composed of subcircuits 137 analysis parameters 133 analysis statements 64 check statement 186 269 colon modifiers 252 commentlines 59 conditional if statement 106 control statements 67 currents parameter 209 221 customized percent codes 250 ic statement 188 238 identical components in parallel 63 71 identical subcircuits in parallel 64 include statements 70 info statement 194 224 instance statements 61 line extension 59 model statements 68 models for multiple components 62 nestlvl parameter 207 219 nodeset statement 189 239 options statement 199 parameter range limits file 263 parameter sweeps 156 160 paramtest specification 271 probe statement 205 217 pwr parameter 206 217 rules for names 59 save parameter 206 207 217 219 save statement 201 213 scaling parameter values 81 scaling physical dimensions 115 sens command 148 set statement 210 245 S parameter files 118 specifying parameter values 82 spectre command 229 starting a simulation
355. t look like this v4 in 0 vsource type pwl file test in You can use the 1 command line option followed by a path to have the Spectre simulator look for the inserted files in a specified directory if they cannot be found in the current directory If you place PWL vector values in an input file that is read by the component do not specify scale factors in your parameter values If you use an input file the values in the file must look like this without scale factors 0 1e 9 2e 9 10e 9 11e 9 12e 9 OOOO O Using Library Statements Another way to insert new files is to use the library statements There are two statements one to refer to a library and one that defines the library A library is a way to group statements into multiple sections and selectively include them in the netlist by using the name of the section As for the include statement the default language of the library file is SPICE unless the extension of the file is scs then the default language is the Spectre Netlist Language July 2002 72 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists Library Reference This statement refers to a library section This statement can be nested To see more information on including files see spectre h include The name of the section has to match the name of the section defined in the library The following is the syntax for library reference include file section Nam wher
356. t statement Formatting the set Statement The following example demonstrates the set statement syntax This example turns off several annotation parameters Quiet set narrate no error no info no B Quiet is the unique name you give to the set statement B The keyword set is the primitive name for the set statement B narrate error and info are the parameters you are changing Note If you want to change t emp or t nom use the alter statement Saving Time by Selecting a Continuation Method The Spectre simulator normally starts with an initial estimate and then tries to find the solution for a circuit using the Newton Raphson method If this attempt fails the Spectre simulator automatically tries several continuation methods to find a solution and tells you which method July 2002 245 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques was successful Continuation methods modify the circuit so that the solution is easy to compute and then gradually change the circuit back to its original form Continuation methods are robust but they are slower than the Newton Raphson method If you need to modify and resimulate a circuit that was solved with a continuation method you probably want to save simulation time by directly selecting the continuation method you know was previously successful You select the continuation method with the homotopy parameter of the set or options statements In addition to the
357. t warnif ls lum warnif ld lt lum message Strip width for nmos must be greater than lu July 2002 272 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Controlling Program Generated Messages The Spectre simulator normally sends error warning and informational messages to the screen To prevent confusion the Spectre simulator limits the amount of material it sends to the screen You can however get a more complete printout of messages if you send the messages to a log file that you can generate with the spectre command orina SPECTRE_DEFAULTS environment variable Specifying Log File Options You can choose from among the following command line options log file The Spectre simulator sends all messages to a log file as well as printing to the screen You specify the name for the file You can use 1 as an abbreviation of 10g log file The Spectre simulator sends all messages to a log file but does not print to the screen You specify the name for the file You can use 1 as an abbreviation of 210g log The Spectre simulator does not create a log file You can use 1 as an abbreviation of 1og This is the default option Command Line Example The following entry on the command line runs a simulation for circuit smps circuit and sends all messages to a log file named smps logfile spectre log smps logfile smps circuit Setting Envi
358. tatement parameter 193 223 options statement ckptclock option example 232 correcting convergence problems 275 defining output file formats 225 example 199 formatting 199 generating output directory names 228 overriding environment defaults 235 parameters compatible 200 iabstol 200 rawfile 228 rawfmt 225 reltol 199 tempeffects 200 topcheck 255 275 vabstol 200 resetting options 245 setting tolerances with 199 OR bars in syntax 14 order of analyses netlist example of effective use 134 output as info statement parameter data controlling the amount of outputstart parameter 144 skipping 144 strobing 144 directory names how Spectre generates 226 specifying yourown 228 file format options 224 225 filenames how Spectre generates 226 parameters listing 192 222 viewing 32 output resistance netlist example of measurement discussed 135 outputstart parameter 144 overriding defaults 235 193 223 Product Version 5 0 Spectre Circuit Simulator User Guide P P predefined percent code 249 p terminals formatting in analysis statements 65 pac analysis brief description of 131 param parameter 158 param spectre command option 263 parameter checking stopping 186 269 parameter range checker convergence problems 275 parameter range limits file creating 263 absolute value specifications 267 exclusive boundaries in 264 inclusive boundaries in 264 model specifications 267 entering 2
359. te or overlay each other Typically process variations mismatch variations and correlations between process parameters are specified in a single statistics block This statistics block can be included in a process include file such as the ones shown in the example in Process Modeling Using Inline Subcircuits on page 101 Asecond statistics block can be specified in the main netlist where actual device instance correlations are specified as matched pairs The following statistics block can be used to specify the correlations between matched pairs of devices and probably is placed or included into the main netlist by the designer These statistics are used in addition to those specified in the statistics block in the preceding section so that the statistics blocks overlay or accumulate define correlations for matched devices ql and q2 Statistics correlate dev ql q2 param XISN cc 0 75 Note You can use a single statistics block containing both sets of statements however it is often more convenient to keep the topology specific information separate from the process specific information Correlation Statements There are two types of correlation statements that you can use m Process parameter correlation statements The following is the syntax of the process parameter correlation statement correlate param list of parameters cc lt value gt This allows you to specify a correlation coefficie
360. tement parameter 193 22 inst as info statement parameter 193 223 instance correlation statement 174 instance scaling factor changing with alter statement 186 245 instance statements 61 annotated example 28 control statements 29 examples 62 formatting 61 model statements 29 parameter values 29 rules for using 63 use of in example 28 INT signal 231 interrupting a simulation 231 introductory netlist how to use 24 invalid parameter values 254 iprobes and convergence problems 275 italics in syntax K keywords 14 for save statement Spectre 60 kill command UNIX kill 9 warning about use of 231 kill 1 as interrupt method 231 USR1 option example 230 USR2 option example 232 Kirchhoff s Current Law KCL 17 58 143 Kirchhoff s Flow Law KFL 17 58 14 202 21 July 2002 L lang spectre command 81 lang spice command 82 language title line 51 language modes 59 LIBRA format translating 120 library definition 73 library reference 73 library statements using 72 limits selecting for operating region warnings 270 lin parameter 160 line extension formatting 59 listing parameter values 192 222 literal characters 14 LNM definition 120 translating format 120 Inorm parameter 172 LO definition of 22 load shared object local truncation error log 273 log 273 log 273 log files specifying options 273 log normal distribution 172 log parameter 160 login file and environme
361. test conditions the specified actions are taken and the message is printed unconditionally This option is useful for using the paramtest component with the i statement The paramtest instruction can be followed whenever a given if statement option is executed The paramtest Options The following table explains the possible paramtest options Parameter Instruction printif Informational message is printed if test condition is satisfied warnif Warning is printed if test condition is satisfied errorif Program quits and error message is printed if testing condition is satisfied message Parameter value is the message text severity You set this parameter when you use paramtest without a test condition It specifies the type of message printed and the action to be taken if any The possible values are debug status warning error and fatal If you specify error the current analysis quits with an error message If you specify fatal the whole simulation stops A paramtest Example This example uses three consecutive paramtest statements to check the values of four parameters 1 w 1s and 1d If a parameter value satisfies a test condition one of three different warning messages is printed TooShort paramtest warnif l lt lum message Channel length for nmos must be greater than lu TooThin paramtest warnif w lum message Channel width for nmos must be greater than lu TooNarrow paramtes
362. the inline component and one or more parameterized models B A single inline device instance and a parameterized model to which the device instance refers m Only asingle parameterized model July 2002 96 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features The inline component is denoted by giving it the same name as the inline subcircuit itself When the subcircuit is flattened as shown in the following section the inline component does not acquire a hierarchical name such as x1 M1 but rather acquires the name of the subcircuit call itself x1 Any noninline components in the subcircuit acquire the regular hierarchical name just as if the concept of inline subcircuits never existed Typically a modeling engineer writes inline subcircuit definitions for a circuit design engineer to use Modeling Parasitics You can model parasitics by adding parasitics components to a base component using inline subcircuits The body of the inline subcircuit contains one inline component the base component and several regular components which are taken to represent parasitics The following example of an inline subcircuit contains a MOSFET instance and two parasitic capacitances inline subckt sl a b si is name of subcircuit parameters l 1u w 2u sl ab 0 0 mos mod 1 1 w w sl is inline component capl a 0 capacitor c 1n cap2 b 0 capacitor c 1n ends sl The following c
363. ting applies to signal data from all analyses that follow that statement in the netlist n In most analysis statements If you set the save and nest 1v1 parameters with an analysis statement the setting applies to that analysis only It overrides any previous save or nest 1v1 settings Formatting the save and nestlvl Parameters The syntax for both the save and nest1v1 parameters is illustrated by the following options statement settingl options save lvlpub nestlvl 2 The save Parameter Options The following table shows the possible settings for the save parameter Setting Action none Does not save any data currently does save one node chosen at random selected Saves only signals specified with save statements This is the default setting lvlpub Saves all signals that are normally useful up to nest 1v1 deep in the subcircuit hierarchy This option is equivalent to a11pub for subcircuits Normally useful signals include shared node voltages and currents through voltage sources and iprobes lvl Saves all signals up to nest 1v1 deep in the subcircuit hierarchy This option is relevant for subcircuits July 2002 207 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Setting Action allpub Saves only signals that are normally useful Normally useful signals include shared node voltages and currents through voltage sources and iprobes all Saves all signals Use 1v1 or
364. ting example 137 analysis order netlist example of effective use 134 analysis statement 64 examples 30 65 formatting 64 annotate parameter in Monte Carlo analysis 168 Product Version 5 0 Spectre Circuit Simulator User Guide in Spectre analyses 231 append path 292 appendsd parameter Monte Carlo analysis 167 associated reference direction 58 automated testing 19 automatic model selection examples in netlist 112 automatic recovery in transient analyses customizing 232 AWD Analog Waveform Display definition of 24 using 32 105 B backslash in Spectre syntax 59 backward Euler integration method benchmark suite MCNC 19 BERT model for hot electron degradation 14 simulation 176 stress parameters 176 binning 104 auto model selection 105 by conditional instantiation 107 conditional instances 106 rules 108 BJT operating regions determining 271 blowup parameter 74 braces in syntax 15 brackets in syntax 14 breakdown region warnings example of messages 258 requesting for transistors 269 BSIM 3v3 brief description 17 built in constants 87 bvbc parameter and breakdown region warnings 269 bvbe parameter and breakdown region warnings 269 bvj parameter and breakdown region warnings 269 bvsub parameter and breakdown region warnings 269 C C predefined percent code 248 C preprocessor CPP July 2002 297 defaults 233 using the include statement with Cadence Customer Support contacting 2
365. ting point to debug the circuit Check the topology the component parameters the models and the power supplies B Be sure you are using appropriate models and that the model parameters are consistent and correct m f the circuit might have more than one solution use nodeset statements to influence the Spectre simulator to compute the solution you want B Be sure that gmin is not influencing the solution If possible set gmin to 0 in an options Or set statement July 2002 277 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Suggestions for Improving Transient Analysis Accuracy W Verify that the circuit biased up properly If it did not there might be a problem in the topology the models or the power supplies B Be sure you are using appropriate models and that the model parameters are consistent and correct Check the operating point of each device B Set the transient analysis parameter errpreset to conservative B If there is a charge conservation problem use only charge conserving models if you are not already doing so Then tighten reltol to increase accuracy With the Spectre simulator only customer installed models might not be charge conserving B Be sure that gmin is not influencing the solution If possible set gmin to 0 in an options Or set statement m f a solution exhibits point to point ringing set the integration method in the transient analysis
366. ting you create filenames that are variants of input filenames For example with Spectre you can m Identify simulation data by date time process ID or other defining characteristics in the results filenames m Keep multiple circuits in a single directory without having subsequent simulations overwrite previous results To do this you set environment variables so that output filenames are automatically different variants of input filenames m Construct filenames at run time July 2002 247 Product Version 5 0 Spectre Circuit Simulator User Guide Managing Files This is convenient if your input data comes from several files For example you can use an include statement to insert several different circuit files into main input files that each contain analyses Each circuit file can also be used with several stimulus files To prevent confusion you can create filenames at run time for the stimulus files that associate them with the appropriate main input files In this section you will learn how to use the various Spectre features for creating filenames Creating Filenames by Modifying Input Filenames The Spectre simulator gives you predefined percent codes you can put in your filenames These predefined codes let you construct filenames that add defining characteristics such as date or time to input filenames You specify predefined percent codes with a percent character followed by an uppercase letter The uppercase letter t
367. tion For example if you customize percent codes with the SPECTRE DEFAULTS environment variable you might want to undefine them for a given simulation run To do this you include the x command line option in the spect re command that starts the simulation Undefined percent codes return to predefined values If an undefined percent code has no predefined value it is treated like an empty string Enabling the Spectre Simulator to Recognize the Input Names of Piped or Redirected Files One practical application for customized percent codes is to enable the Spectre simulator to recognize the input filenames of piped or redirected files If the Spectre simulator reads the circuit from standard input as it does when it reads from a pipe the Spectre simulator cannot determine the name of the original input file If you want the results filename to be a variant of the input filename you can enable the Spectre simulator to recognize the input filename by redefining the Spectre simulator s predefined percent codes In the following two examples the circuit file is passed through sea 1 The resulting file cktfile is then piped to the Spectre simulator as input The first example shows the problem created if you want the results filename to be a modification of the input filename and the second example shows how you can correct this difficulty In the first example the Spectre simulator cannot identify the name ckt file ofthe file t
368. tion in statements from outside the subcircuit You can however use both the model name and the subcircuit definitions in new subcircuits within the original subcircuit Local models or subcircuits hide nodes or subcircuits with the same names defined outside the subcircuit m When you use model statements within subcircuit definitions where model parameters are expressions of subcircuit parameters definitions a new model is created for every July 2002 93 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features instance of the subcircuit These different models are expanded models which are derived from the original mode1 statement Each of the new models has a unique name and component instances created from the original model statement are instances of the new model created for the subcircuit The full name of each new model is the flattened name of the subcircuit followed by a dot followed by the name of the model as given in the model statement If you request the output of model data you can see these expanded models in the output B Subcircuit parameter names are local only You cannot access the value of a subcircuit parameter outside of the scope of the subcircuit in which it was declared B Parameter names must be lowercase if you want to instantiate components from SPICE mode Calling Subcircuits To call a subcircuit place an instance statement in your netlist
369. tion of input file The simulation includes any options you request For a given simulation the spect re command options override any settings in default environment variables or opt ions statement specifications The simplest example is to simulate a circuit with no run options The following example starts a simulation of the input file cest 1 Spectre testl Specifying Simulation Options Many simulation runs require more complicated instructions than the previous example Spectre circuit simulator run options can be specified in two ways Which method you use depends on the run option July 2002 229 Product Version 5 0 Spectre Circuit Simulator User Guide Running a Simulation m You specify some Spectre options by typing a minus in front of the option The v in the following example specifies that version information be printed for the simulation of circuit test1 spectre V testl m You activate some Spectre options by typing a plus before the option You deactivate these options by typing a minus before the option For example the following spectre command starts a simulation run for circuit cest 1 In this simulation the Spectre simulator sets checkpoints but does not print error messages spectre checkpoint error testl Some Spectre options have abbreviations You can find these abbreviations in Chapter 2 Spectre Command Options of the Spectre Circuit Simulator Reference manual For example you can t
370. to that used by the save statement This method is described in detail in Saving Main Circuit Signals on page 213 Consult this discussion if you need further clarification about the following example ic Voff 0 X3 7 2 5 Ml int_d 3 5 L1 1 1u This example sets the following initial conditions n The voltage of node voff is set to 0 n Node 7 of subcircuit X3 is set to 2 5 V n Theinternal drain node of component M1 is set to 3 5 V See the following table for more information about specifying internal nodes n The current for inductor L1 is set to 1p Specifying initial node voltages requires some additional discussion The following table tells you the internal voltages you can specify with different components Component Internal Node Specifications BJT int c int b int e BSIM int d int s MOSFET int d int s GaAs MESFET ini dnt s int_g JFET inbtod intos 2b ww nt 3b Winding for Magnetic Core int Rw Magnetic Core with Hysteresis flux July 2002 188 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements Supplying Solution Estimates to Increase Speed You use the nodeset statement to supply estimates of solutions that aid convergence or bias the simulation towards a given solution You can use nodesets for all DC and initial transient analysis solutions in the netlist The nodeset statement has the following format nodeset signalName value Values you can supply
371. tre Circuit Simulator User Guide Running a Simulation You can use the default settings to specify alternative conditions for running the Spectre simulator Suppose you create the following environment variables setenv SPECTRE DEFAULTS param range lmts log C r o E setenv SPECSIM DEFAULTS param corner lmts log C r log f psfbin If spectre and specsim are both links to the Spectre executable and you run the executable as spect re the Spectre simulator does the following m Reads the file cange 1mts for the parameter limits W Directs all messages to the screen and to a log file named after the circuit file with o appended see Chapter 11 Managing Files for more information about specifying filenames m Runs the C preprocessor Running the executable as specsim causes the Spectre simulator to select a different set of defaults and to do the following m Read the range limits from the file corner lmts m Direct log messages to a file named after the circuit file with log appended the log specification suppresses the log output to the screen W Format output files in binary parameter storage format PSF References for Additional Information about Specific Defaults In some cases you need to consult other sections of this book before you can set defaults If you want to set default limits for warning messages about parameter values consult Chapter 12 Identifyi
372. ts 203 215 main circuit signals See save statement 201 213 measurements for current controlled components 204 216 parameter values 192 222 signals from subcircuit calls 2 saving power 205 217 scalarfile parameter Monte Carlo analysis 164 scale factors 81 scale parameter devices scaled by 115 how affected by default units of components 116 in alter statement 186 245 scalem parameter devices scaled by D how affected by default units of component at in alter statement 186 245 scaling parameter values in Spectre 81 inSPICE 81 physical dimensions of components 115 schematic 25 screen printout example 31 second order Gear integration method 143 seed parameter Monte Carlo analysis 163 selected as save parameter option 207 219 3 21 Fon sens analysis 147 sens command example 149 formatting 148 sensitivity analysis 147 set statement to modify options statement settings 245 setting tolerances July 2002 with the quantity statement 74 shell initialization file and Cadence range limits 263 shell status variable 230 sigglobal relative error parameter 141 143 Signal Scan output format signals defined 212 simulation checking status 230 following the progress of 31 improved accuracy 18 interrupting 231 introductory Spectre run 30 sample narration of progress 31 specifying options 229 starting 229 termination See terminations of Spectre 230
373. ts to a current probe or voltage source instance the loop based algorithm will be invoked when it points to a supported active device instance the device based algorithm will be invoked The gain margin and phase margin are automatically determined from the loop gain waveform by detecting zero crossing in the gain plot and phase plot If margins cannot be determined for a particular stability analysis a log file displays the corresponding reason Loop Based Algorithm The loop based algorithm is based on considering the feedback loop as a lumped model with normal and reverse loop transmission It calculates the true loop gain which consists of normal loop gain and reverse loop gain Stability analysis approaches for low frequency applications assume that signal flows unilaterally through the feedback loop and they use the normal loop gain to assess the stability of the design However the true loop gain provides more accurate stability information for applications involving significant reverse transmission You can place a probe component current probe or zero DC valued voltage source on the feedback loop to identify the loop of interest The probe component does not change any of the circuit characteristics and there is no special requirement on the polarity configuration of the probe component July 2002 154 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses The loop based algorithm provides accurate stability inf
374. u specify closed bounds there can be no space between and m You can specify inclusive or exclusive ranges If you specify exclusive ranges the upper limit must be smaller than the lower limit The diagram on the following pages shows you the proper formats for range specifications July 2002 264 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Examples of Range Limits Specifications Single boundary 1 p Inclusive boundaries 1 p 2 1 lt p lt 2 lt p lt 2 lt p lt 2 Exclusive boundaries 2 lt p lt 1 2 lt p lt 1 July 2002 265 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Examples of Range Limits Specifications continued 2 lt p lt 1 2 p 1 BRE Single point boundaries 1 lt p lt 1 fi 2 p 2 Invalid boundaries 2 lt p lt 2 B The component keyword must be a Spectre name not a name used for SPICE compatibility For example use mos3 rather than mos m f you specify more than one parameter limit for a component you need to specify the component keyword only once The Spectre simulator assumes the keyword is unchanged from the previous parameter unless you specify a new component keyword B f you give a parameter limit more than once your last instructions override previous limits B f you mention a p
375. u want to save by the terminal index Note To save all terminal currents for subcircuit calls you use a save statement or specify the subcktprobelvl parameter in an options statement The currents all option of the opt ions statement saves currents only for devices July 2002 214 Product Version 5 0 Spectre Circuit Simulator User Guide Specifying Output Options Saving Subcircuit Signals To save a subcircuit signal with the save statement modify the main circuit syntax as follows Give a full path to the subcircuit name Start with the highest level subcircuit and identify the signals you want to save at the end of the path Separate each name with a period Examples of the save Statement The following table shows you examples of save statement syntax When you specify node names the Spectre simulator saves node voltages Currents are identified by the terminal node name or the index number Exception Currents through probes take the name of the probe save Statement Action save 7 Saves voltage for a node named 7 save Q4 currents Saves all terminal currents associated with component Q4 save Q4 c static Saves resistive terminal currents associated with component Q4 save D8 cap Saves the junction capacitance for component D8 Assumes D8 is a diode and therefore cap is an operating point parameter save Q5 D9 oppoint Saves all signal information for component Q5 and the operating point para
376. ual nodes and components or save groups of signals Saving Signals for Individual Nodes and Components You can include signals for individual nodes and components in the save list by placing save statements not to be confused with the save parameter in your netlist When you specify signals in a save statement the Spectre simulator sends these signals to the output raw file as long as the nest 1v1 setting does not filter them In this section you will learn the following n How to save voltages for individual nodes n Howto save all signals for an individual component n How to save selected signals for an individual component The syntax for the save statement varies slightly depending on whether the requested data is from the main circuit or a subcircuit You will learn about the syntax for main circuit statements first and then you will learn how to modify the save statement to store signals from subcircuits Saving Main Circuit Signals The save statement general syntax has the following arguments You can specify more than one argument with a single save statement and you can mix the types of arguments in a single statement July 2002 201 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements save signalName save compName save compName modifier save subcircuitName terminallndex n signalName is generally the netlist name of a node whose voltage you want to save
377. uit parameter has changed However if a previous analysis computed an operating point you can set prevoppoint yes to avoid recomputing it For example if you use this option when the previous analysis was a transient analysis the operating point is the state of the circuit on the final time point Transient Analysis You can adjust transient analysis parameters in several useful ways to meet the needs of your simulation Setting different Spectre parameters that control the error tolerances the integration method and the amount of data saved let you choose between maximum speed and greatest accuracy in a simulation You normally use reltol or errpreset to control accuracy but you can use additional methods in special situations to improve performance This section also tells you about parameters you can set that improve transient analysis convergence Trading Off Speed and Accuracy with a Single Parameter Setting You can set transient analysis speed and accuracy parameters individually or you can set a group of parameters that control transient analysis accuracy with the errpreset parameter You can set errpreset to three different values E liberal M moderate M conservative At liberal the simulation is fast but less accurate The liberal setting is suitable for digital circuits or analog circuits that have only short time constants At moderate the default setting simulation accuracy approximates a SPICE2 style simulator At
378. uits The Spectre simulator helps you simplify netlists by letting you define subcircuits that you can place any number of times in the circuit You can nest subcircuits and a subcircuit definition can contain both instances and definitions of other subcircuits The main applications of subcircuits are to describe the circuit hierarchy and to perform parameterized modeling In this section you learn to define subcircuits and to call them into the main circuit Formatting Subcircuit Definitions You format subcircuit definitions as follows subckt SubcircuitName nodel nodeN July 2002 90 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features parameters namel valuel nameN valueN instance model ic or nodeset statements or further subcircuit definitions ends SubcircuitName subckt The keyword subckt subckt is used in SPICE mode SubcircuitName The unique name you give to the subcircuit nodel nodeN The external or connecting nodes of the subcircuit to the main circuit parameters namel valuel nameN This is an optional parameter specification field You can specify default values for subcircuit calls that refer to this subcircuit The field contains the keyword parameters followed by the names and values of the parameters you want to specify component instance statement The instance statements of your subcircuit other subcircuit definiti
379. ulation to see if the circuit works After debugging the circuit you might switch to noderate to get more accurate results If the application requires high accuracy or if you want to verify that the moderate solution is reasonable you set errpreset to conservative You might also have different ex rpreset settings for different types of circuits For logic gate circuits the 1iberal setting is probably sufficient A moderate setting might be better for analog circuits Circuits that are sensitive to errors or circuits that require exceptional accuracy might require a conservative setting July 2002 141 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses m The relref sigglobal or relref allglobal settings compare relative errors in each of the circuit signals to the maximum of all the signals in the circuit m In addition the relref allglobal setting compares equation residues the amount by which Kirchhoff s Current Law also known as Kirchhoff s Flow Law is not satisfied for each node to the maximum current floating onto the node at any time in that node s past history Setting the Integration Method The method parameter specifies the integration method You can setthe met hod parameter to adjust the speed and accuracy of the simulation The Spectre simulator uses three different integration methods the backward Euler method the trapezoidal rule and the second order Gear method The met hod parameter has s
380. un the Spectre circuit simulator standalone or run it under the Cadence analog design environment To see how the Spectre circuit simulator is run under the analog circuit design environment read the Cadence Analog Design Environment User Guide You can also run the Spectre circuit simulator in the Composer to Spectre direct simulation environment The environment provides a graphical user interface for running the simulation m The Spectre circuit simulator gives you an online help system With this system you can find information about any parameter associated with any Spectre component or analysis You can also find articles on other topics that are important to using the Spectre circuit simulator effectively m The Spectre circuit simulator also includes a waveform display tool Analog Waveform Display AWD to use to display simulation results For more information about AWD see the Analog Waveform User Guide m If you experience a stubborn convergence or accuracy problem you can send the circuit to Customer Support to get help with the simulation For current phone numbers and e mail addresses see the following web site http sourcelink cadence com supportcontacts html Analog HDLs The Spectre circuit simulator works with two analog high level description languages AHDLs SpectreHDL and Verilog A These languages are part of the Spectre Verilog A option SpectreHDL is proprietary to Cadence and is provided for backw
381. und is a common reference point in an electrical circuit The value of ground is zero Node A node is an infinitesimal connection point The voltage everywhere on a node is the same According to Kirchhoff s Current Law also known as Kirchhoff s Flow Law the algebraic sum of all the flows out of a node at any instant is zero Basic Syntax Rules The following syntax rules apply to all statements in the Spectre Netlist Language July 2002 58 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists m Field separators are blanks tabs punctuation characters or continuation characters m Punctuation characters such as equal signs parentheses and colons are significant to the Spectre simulator m You can extend a statement onto the next line by ending the current line with a backslash You can use a plus sign to indicate line continuation at the beginning of the next line The preferred style is the at the end of the line m You can indicate a comment line by placing a double slash at the beginning of the comment The comment ends at the end of that line You can also use an asterisk to indicate a comment line The preferred style is using m You can indicate a comment for the remainder of a line by placing a space and double slash anywhere in the line Spectre Language Modes The Spectre netlist supports two language modes m Spectre mode mostly discussed he
382. ur ports Sd S12 freq 13 mag mag mag mag 14 S11 deg S12 deg 13 deg S11 deg 12 deg 13 deg S14 deg 21 mag 22 mag 23 mag S21 S22 mag S23 mag mag mag S24 S21 deg S22 deg S23 deg S21 deg S22 deg S23 deg S24 deg S31 mag S31 deg S32 mag S32 deg S33 mag S33 deg S31 mag S31 deg S32 mag S32 deg S33 mag S33 deg S34 mag S34 deg S41 S42 mag S43 mag mag mag S44 S41 deg S42 deg S43 deg S44 deg and so on where the complex number format is specified as MA on the line The frequency entry must be first and can include a scale factor The data entries need to be separated with at least a space The data entries at the first frequency point specify the number of ports MHARM Format The following is an example MHARM file with three frequency data points and three ports 1 0GHz 0 99602 0 06256 0 06256 2 0GHz 0 98439 0 12351 0 123951 18999 84 5886 84 5886 14 2738 79 2690 79 2690 06256 99801 00196 sli 2352 99220 00775 C5 CO CO C CO 84 5886 3 59201 172 762 79 2690 7 13736 165 618 0 0 0 0 0 0 06256 84 5886 00196 172 762 99801 3 59201 12351 79 2690 00775 165 618 99220 7 13736 An input file for MHARM format has no header The first
383. uses Spectre syntax Ring oscillator Spectre deck for 2 Input NOR ring with no fanouts simulator lang spectre global 0 gnd vdd vss aliasGnd gnd 0 vsource type dc dc 0 Spectre options SetOptionl options iabstol 1 00n audit full MyAcctl info what inst extremes yes MyAcct2 info what models extremes yes MyAcct3 info what input extremes yes MyAcct5 info what terminals extremes yes yAcct6 info what oppoint extremes yes Next section is the subckt for no2 subckt no2 nga ml vdd a 6 vdd p 1 0 35u w 4 80u ad 3 50p pd 11 06u as 0 50p ps 5 01u m2 nq vss 6 vdd p 1 0 35u w 4 80u ad 3 50p pd 11 06u as 0 50p ps 5 01u m3 vss a nq vss n 1 0 35u w 1 20u ad 0 88p pd 3 86u as 0 46p ps 1 96u m4 vss vss nq vss n 120 35u w 1 20u ad 0 88p pd 3 86u as 0 46p ps 1 96u cO a vdd capacitor c 6 3676066e 16 cl ang capacitor c 5 3592e 17 c2 vdd vss capacitor c 5 39538e 16 c3 nq vss capacitor c 8 780327e 16 c4 nq vdd capacitor c 5 577428e 16 c5 a vss capacitor c 1 1100392e 15 ends begin top level circuit definition xno21 1 90 no2 xno22 2 1 no2 xno23 3 2 no2 xno24 4 3 no2 xno25 5 4 no2 xno26 6 5 no2 xno27 7 6 no2 xno28 8 7 no2 xno29 9 8 no2 xno210 10 9 no2 xno211 11 10 no2 xno212 12 11 no2 xno213 13 12 y no2 xno214 14 13 no2 July 2002 286 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits
384. uto model selection see the following section B Conditional instances For more information on using conditional instances see Conditional Instances on page 106 For more information on using inline subcircuits for model selection see Scaling Physical Dimensions of Components on page 115 Auto Model Selection Automatic model selection is a simulator feature that automatically assigns the correct models to devices based on their device sizes without using conditional instantiation Binning is usually used together with automatic model selection Model selection is now automatic for MOSFETs BSIM1 BSIM2 and BSIMS Help on any one of these devices for example spectre h mos1 gives you more details For the auto model selector program to find a specific model the models to be searched need to be grouped together within braces Such a group is called a model group An opening brace is required at the end of the line defining each model group Every model in the group is given a name followed by a colon and the list of parameters Also you need to specify the device length and width using the four geometric parameters 1max 1min wmax and wmin The selection criteria to choose a model is as follows Imin lt inst length lt lmax and wmin lt inst width lt wmin For example model ModelName ModelType Js lmin 2 lmax 4 wmin 1 wmax 2 vto 0 8 23 lmin 1 lmax 2 wmin 2 wmax 4 vto 0 7 3 lmin 2 lmax 4 wmin 4 wmax 6 vto
385. value The nodes for which the total node capacitance is below the threshold value will not be printed in the output table detail node Displays the total node capacitances Other possible values are nodetoground and nodetonode sort value Sorts the captab output according to value The other possible value is name For a complete list of captab parameters and values consult the Spectre online help spectre h July 2002 195 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements You may use the infotimes option of the transient analysis when you bind the captab analysis to a transient analysis This runs the capt ab analysis at specified time intervals The syntax for the infotimes option is infotimes xl x2 where x1 and x2 are time points for which the info analysis should be performed The following is an example of binding a captab analysis to a transient analysis tranl tran stop 1U infotimes 0 1 0 5U infoname capiInfo capInfo info what captab where file file capNodes detail nodetonod Output Table The output for the captab analysis is printed in the following format n The first column displays the names of the two nodes From_node To_Node n The second column displays the fixed linear capacitance between the two nodes n _ The third column is the variable non linear capacitance between the two nodes n The last column displays the total capacitance between the nodes T
386. vary xisn dist gauss std 0 5 vary xisp dist gauss std 0 5 some process parameters are correlated correlate param rshsp rshpi cc 0 6 specify a global distribution truncation factor truncate tr 6 0 6 sigma a separate statistics block to specify correlated i e matched components where m1 and m2 are subckt instances statistics correlate dev ml m2 param xisn xisp cc 0 8 Note You can specify the same parameter for example rshsp for both process and mismatch variations In the process block the process parameter rshsp is varied with a Gaussian distribution where the standard deviation is 12 percent of the nominal value percent yes When percent is set to yes the value for the standard deviation std is a percentage of the nominal value When percent is set to no the specified standard deviation is an absolute number This means that parameter rshsp should be varied with a normal distribution where the standard deviation is 12 percent of the nominal value of rshsp The nominal or mean value for such a distribution is the current value of the parameter just before the Monte Carlo analysis starts If the nominal value of the parameter rshsp was 200 the preceding example specifies a process distribution for this parameter with a Gaussian distribution with a mean value of 200 and a standard deviation of 24 12 percent of 200 The parameter rshpi sheet resistance varies about its nom
387. varying netlist parameters can be referenced by models or instances in the main netlist and can represent IC manufacturing process variation or component variations for board level designs The following description gives a simplified example of the Monte Carlo analysis flow perform nominal run if requested if any errors in nominal run then stop for each Monte Carlo iteration if process variations specified then apply process variation to parameters if mismatch variations specified then for each subcircuit instance apply mismatch variation to parameters for each child analysis run child analysis evaluate any export statements and store results in a scalar data file July 2002 161 Product Version 5 0 Spectre Circuit Simulator User Guide Analyses The following is the syntax for the Monte Carlo analysis Name montecarlo lt parameter value gt analysis statements export statements The Monte Carlo analysis m Refers to the statistics block s for how and which netlist parameters to vary M Generates statistical variation random numbers according to the specified distributions m Runs the specified child analyses similar to the Spectre nested sweep analysis where the child analyses are either Q Multiple data producing child analyses such as DC or AC analyses Q A single sweep child analysis which itself has child analyses m Calculates the export quantities Each Monte
388. viewing output 32 simulation language use of in example netlist 28 simulator lang command default 53 singular Jacobian or matrix error message 255 skipping data points skipcount parameter 145 skipstart parameter 14 skipstop parameter skipping time points example 146 explanation 144 soft limits definition 78 useof 19 source stepping 245 source as homotopy parameter option 246 span parameter 159 S parameter analysis sp brief description of 130 S parameter file format translator 120 S parameter files creating manually db deg 118 db rad 118 example 1 formattin b 1 224 145 145 118 119 118 y Spectre 11 118 g generate mag deg Product Version 5 0 Spectre Circuit Simulator User Guide mag rad 118 reading example of nport statement 120 format of nport statement 120 real imag 118 special characters escaping 61 specify search path 292 specifying analyses 30 control statements 67 individual components 28 models for multiple components 29 percent codes 249 Spectre accuracy improvements 17 annotated netlist example 26 capacity improvements 16 case sensitivity 59 coupling with Verilog 23 customer service 19 differences from SPICE 183 280 environments 23 exit codes 230 improvements 16 introduction to netlists 27 keywords 60 language title line 51 model improvements 19 netlist elements of 27 reliability improvements 18 RF capabilities 21 run terminations 230 schematic example
389. wing is the format for the ic statement ic lt signalName value gt The format for specifying signals with the ic statement is similar to that used by the save statement This method is described in detail in Saving Main Circuit Signals on page 213 July 2002 238 Product Version 5 0 Spectre Circuit Simulator User Guide Time Saving Techniques B The voltage of node voff is set to 0 m Node 7 of subcircuit X3 is set to 2 5 V m The internal drain node of component M1 is set to 3 5 V See the table in the ic statements section of this chapter for more information about specifying internal nodes B The current for inductor L1 is set to 1y Specifying State Information for Individual Analyses You can specify state information for individual analyses in two ways m You can use the ic parameter of the transient analysis to choose which previous specifications are used M You can create a state file that is read by an individual analysis Choosing Which Initial Conditions Specifications Are Used for a Transient Analysis The ic parameter in the transient analysis lets you select among several options for which initial conditions to use You can choose the following settings Parameter Setting Action Taken dc Initial conditions specifiers are ignored and the existing DC solution is used node The ic statements are used and the ic parameter settings on the capacitors and inductors are ignored dev The ic paramete
390. with global scale factors When you want to scale the physical dimensions of these instances and models you use the scale and scalem parameters in the options statement Use scale for instances and scalem for models The default value for both scale and scalem is 1 0 For more information about the options statement see options Statement Form at on page 199 and the documentation for the opt ions statement in Spectre online help spectre h options You can scale the following devices with scale and scalem m Capacitors length 1 or width w m Diodes length 1 or width w July 2002 115 Product Version 5 0 Spectre Circuit Simulator User Guide Parameter Specification and Modeling Features m Resistors length 1 or width w m Physical resistors phy res length 1 or width w m MOSFET length or width Finding Default Measurement Units The effects of scale and scalem depend on the default measurement units of the components you scale To find the default measurement units for a component parameter look up that parameter in the parameter listings of your Spectre online help spectre h The default for measurement units is in parentheses For example the m in this entry from the mos8 parameter descriptions in the Spectre online help spectre h tells you that the default measurement unit for channel width is meters w m Channel width Effects of scale and scalem with Different Default Units s
391. x 9E 09 xj 1 00000E 07 tlint 9 36e 8 wint 1 47e 7 tvth0 6322 k1 756 k2 3 83e 2 k3 2 612 tdvt0 2 812 dvt1 0 462 dvt2 9 17e 2 tn1x 3 52291E 08 w0 1 163e 6 k3b 2 233 tvsat 86301 58 ua 6 47e 9 ub 4 23e 18 uc 4 706281e 11 rdsw 650 u0 388 3203 wr 1 a0 3496967 ags 1 b0 0 546 bl 1 dwg 6 0e 09 dwb 2 3 56e 09 prwb 213 tketa 3 605872e 02 al 2 778747e 02 a2 9 tvoff 6 735529e 02 nfactor 1 139926 cit 1 622527e 04 tcdsc 2 147181e 05 cdscb 0 tdvtO0w 0 dvtlw 0 dvt2w 0 cdscd 0 prwg 0 teta0 1 0281729e 02 etab 5 042203e 03 dsub 31871233 tpcim 1 114846 pdiblcl 2 45357e 03 pdiblc2 6 406289e 03 tdrout 31871233 pscbel 5000000 psche2 5e 09 pdiblcb 234 pvag 0 delta 0 01 twl 0 ww 1 420242e 09 wwl 0 twln 0 wwn 2613948 11 1 300902e 10 t lw 0 lwl 0 Ilin 316394 lwn 0 kt1 3 kt2 051 tat 22400 tute 1 48 tual 3 31e 10 ub1 2 61e 19 ucl 3 42e 10 kt11 0 prt 764 3 Ring Oscillator Spectre Deck for Inverter Ring with No Fanouts inverter_ring sp This example uses Spectre syntax July 2002 281 Product Version 5 0 Spectre Circuit Simulator User Guide Example Circuits Ring oscillator Spectre deck for INVERTER ring with no fanouts simulator lang spectre global 0 gnd vdd vss aliasGnd gnd 0 vsource type dc dc 0 Spectre options to be used SetOptionl options iabstol 1 00n audit full temp 25 MyAcctl info what inst extre
392. y the boundaries between BJT operating regions The default value for each parameter is 0 2 volts The following table shows you the criteria the Spectre simulator uses to determine BJT operating regions Region Bias Conditions off Vbe lt vbefwd and V5 lt vbcfwd saturation Vbe gt vbe wd and Vp gt vbcfwd forward Vbe gt vVbefwd and Vp lt vbcfwd reverse Vbe lt vbe fwd and Vp gt vbcfwd Range Checking on Subcircuit Parameters You can test the value of subcircuit parameters with the paramtest component If the parameters meet your testing criteria you can print an informational message print a warning or print an error message and terminate the program Formatting the paramtest Component The paramtest component has the following format Name paramtest parameter value B Name is your unique name for this paramtest component m The keyword paramtest is the component keyword for the component B The parameters specify the tests that are applied to the parameters the action taken if parameters satisfy the test conditions and the text of the message that is printed when parameters satisfy the test conditions July 2002 271 Product Version 5 0 Spectre Circuit Simulator User Guide Identifying Problems and Troubleshooting Rules and Guidelines to Remember B f you specify more than one test the conditional action is taken if any test passes B If you use the paramtest component without specifying
393. y positive real number B The multiplication factor does not affect short channel or narrow gate effects in MOSFETSs B Ifyou use the m factor with components that naturally compute branch currents such as voltage sources and current probes the computed current is divided by m Terminal currents are unaffected m Youcansetthe built in m factor property on a subcircuit to a parameter and then alter it July 2002 63 Product Version 5 0 Spectre Circuit Simulator User Guide Spectre Netlists Example of Using m to Specify Parallel Components In the following example a single instance statement specifies four 4000 Ohm resistors in parallel Ro d C resistor r 4k m 4 The preceding statement is equivalent to Ro d C resistor r 1lk Specifying Subcircuits in Parallel If you place a multiplication factor parameter in a subcircuit call you model m copies of the subcircuit in parallel For example suppose you define the following subcircuit subckt LoadOutput a b rl a b resistor r 50k cl a b capacitor c 2pF ends LoadOutput If you place the following subcircuit call in your netlist the Spectre simulator models five LoadOutput cells in parallel x1 out 0 LoadOutput m 5 Analysis Statements In this section you will learn to place analyses into your netlist and to assign parameter values for them For more information on analyses see Chapter 6 Analyses and the Spectre online help spectre h B
394. ye ro odo e ecd e hee obe Mete o Ad Kd 129 AnalysIS PaFaImelBIS 5515 uroiseci eters CE HDI EDD I PG E ees ES 133 Probes in Analyses Nude aon Oe ak aena 133 July 2002 6 Product Version 5 0 Spectre Circuit Simulator User Guide M l iple Analyses ete int tein uter pid e wre ee teda RE ele 134 Multiple Analyses in a Subcircuit 3 9 0 acea nea e eR OE QR RE Dro ra ara e D D enue 4 136 Examples oa ead or ots obo ed tucd th i deae c dtd weder eid diae EO aedi 137 DDG AralySIS 4 5 ato Buts reveren er a a MURANO ee Vrbe Ed soa ona A SA RAC DO eL Lr odere e Dd 138 AGAMA SIS 3 3554 1 21 3 ETE Edo eos visa E Eie epo PLE Qu SP SE Seis 139 Transient Analysis RECETTE 140 Trading Off Speed and Accuracy with a Single Parameter Setting 140 Controlling the Acc rac asian id va eaa eee E a oe a a SE ER id 142 Setting the Integration Method voor nde Bd a ae ena whee ee ens 143 Improving Transient Analysis Convergence 0 0 cece eee 144 Controlling the Amount of Output Data ee 144 Other Analyses sens fourier dcmatch and stb 0 cee eee eeee 147 Sensitivity Analysis 5 credi EIER PESO PEUT WIPEpEDE UE WU SUE qe ME 147 EOULIBE AD SIS ss ache cede d Rr Y TRAE deh don d dean dnte qu A a ae av ame Drs ek ine 150 DG Matelr Analysis ues d ui ee eR CREE EE atat ate dd e EUR C es 151 Stability Analysis xf Draig uem acd Sok ea wea exi ea LEE FO ahh uS db RR SE UE NES
395. you identify with different s substitutions Initially the Spectre simulator looks for defaults settings in s DEFAULTS If this variable does not exist it looks for default settings in SPECTRE DEFAULTS To set these environment variables use the following procedure gt In an appropriate file such as cshrc or login use the appropriate UNIX command to create settings for the environment variables 8 DEFAULTS or SPECTRE DEFAULTS Format the new default settings like spect xe command line arguments and place them in quotation marks The following example changes the default output format from ps fbin to wsfbin It also sets an option that is normally deactivated It sends all messages from the Spectre simulator to a C r 1og file For csh setenv SPECTRE DEFAULTS format wsfbin log C r log For sh or ksh SPECTRE DEFAULTS format wsfbin log C r log EXPORT SPECTRE DEFAULTS This second example a typical use of the SPECTRE_DEFAULTS environment variable tells the Spectre simulator to do the following m Write a log file named ckt file out where ckt file is the name of the input file minus any dot extension m Use the parameter soft limits file in the Cadence software hierarchy setenv SPECTRE DEFAULTS log C r out V param cds etc spectre range lmts July 2002 234 Product Version 5 0 Spec
396. ype the previous command as follows Spectre tcp error testl Specific spect re command options are discussed throughout this guide For a complete list of options and formats consult the Spectre Circuit Simulator Reference manual Determining Whether a Simulation Was Successful When the Spectre simulator finishes a simulation it sets the shell status variable to one of the following values 0 If the Spectre simulator completed the simulation normally 1 l fthe Spectre simulator stopped any analysis because of an error 2 Ifthe Spectre simulator stopped the simulation early because of a Spectre error condition 3 If a Spectre simulation was stopped by you or by the operating system Checking Simulation Status If you want to check the status of a simulation during a run type the following UNIX command kill USR1 lt PID gt P TD is the Spectre process identification number which you can find by activating the UNIX ps utility The Spectre simulator displays the status information on the screen or sends it to standard output if it cannot write to the screen If you check the status from a remote terminal the July 2002 230 Product Version 5 0 Spectre Circuit Simulator User Guide Running a Simulation Spectre simulator also writes the status to the SpectreStatus file in the directory from which the Spectre simulator was called The Spectre simulator deletes this file at termination of the run Note You can also give
397. yses and control statements in a Spectre netlist All topics discussed here such as model statements or the simulator lang command are presented in greater depth in later chapters If you want more complete reference information about a topic consult these discussions Title Line The first line is taken to be the title It is used verbatim when labeling output Any statement you place in the first line is ignored as a comment For more information about comment lines see Basic Syntax Rules on page 58 July 2002 27 Product Version 5 0 Spectre Circuit Simulator User Guide Getting Started with Spectre Simulation Language The second line of the sample netlist indicates that the netlist is in the Spectre Netlist Language instead of SPICE For more information about the simulator lang command see Chapter 3 SPICE Compatibility Instance Statements The next section in the sample netlist consists of instance statements To specify a single component in a Spectre netlist you place all the necessary information for the component in a netlist statement Netlist statements that specify single components are called instance statements The instance statement also has other uses that are described in Chapter 4 Spectre Netlists To specify single components within a circuit you must provide the following information m A unique component name for the component m The names of nodes to which the component is connected
398. ysis and then continue the analysis in a later simulation by using the state file as the starting point for another transient analysis n You can use state files to create automatic updates of initial conditions and nodesets The following example demonstrates the usefulness of state files altTemp alter param temp value 0 Drift dc param temp start 0 stop 50 0 step 1 readns ua741 dc0 write ua741 dc0 XferVsTemp xf param temp start 0 stop 50 step 1 probe Rload freq 1lkHz readns ua741 dc0 The first analysis computes the DC solution at T20C saves it to a file called ua741 dc0 and then sweeps the temperature to T 50C The transfer function analysis x resets the temperature to zero Because of the temperature change the DC solution must be recomputed Without the use of state files this computation might slow the simulation July 2002 191 Product Version 5 0 Spectre Circuit Simulator User Guide Control Statements because the only available estimate of the DC solution would be that computed at T 50C the final point in the DC sweep However by using a state file to preserve the initial DC solution at T 0C you can enable the Spectre simulator to compute the new DC solution quickly The computation is fast because the Spectre simulator can use the DC solution computed at T 0C to estimate the new solution You can also make future simulations of this circuit start quickly by using the state file to estimate the DC solution Even

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