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What is the PSpice Optimizer?

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1. aus en ngs asithey appear tthe Edit To display the Edit Specifications dialog Specification dialog box are shown below box double dick the lower right hand corner of the specification box of interest in Name Power Enabled the PSpice Optimizer window Reference Internal External Weight fo Internal i External IV Power Target o1uw e pies Foe IK ear lie i Adouble dick here iF Constraint Y Column Name bee mas el pren 1 When finished browsing click Cancel Rue Profile or Circuit File CAC CDC Tran Probe File Containing Goal Functions Evaluate feam OK Cancel Setting the method for a single goal optimization The amplifier design is set up to use minimization to assess To see the Minimize setting from the performance because this optimization has one goal Options menu choose Defaults and click minimize the power consumption The default method Advanced Options least squares is appropriate when minimizing the square of a function 135 Chapter 7 Tutorial Using constrained optimization MOS amplifier 136 Performing the optimization You are now ready to run the optimization To optimize the amplifier design 1 From the Tune menu choose Update Performance to calculate initial performance The results are as shown in Figure 29 IV Power M Gain M BW 2 36776mw I 23 7998 2 16111Meg 23 7998 2 16111Meg PERIZIE
2. 37 Design flow for running an optimization LL 42 PSpice Optimizer automatic optimization process 44 Optimization results for the diode designexample 45 Results after adding the power constraint oaoa aa 47 Results after changing the constraint type ooa a 49 Report summary for the diode optimization 50 Updated diode schematic usi 1a zu Roe Bus a fo ein 51 The PSpice Optimizer window este fad eee 58 Example of a specification box 6 ee ee 59 Example of a parameter box su nu ea dee ted men bee OK BR 61 Sample format for an external specification 67 Sample excerpt from a report as sss keen ir 80 Sample excerpt from a Log file 4 5 cee ED EAE ER eS 81 sample derivative data 6 bee 0 80 u 40 su wu 0 HK Hee sun 81 Resistive terminator circuit var 24 456 od ae Ra a 86 Global and local minima of a function LL 92 Hypothetical function 22 24 02 en 4 sus er dep ur Bas 96 Hypothetical data glitch 322 2 9 Ree eee hee Se Dees 102 Resistive terminator circuit e en ed a wand eR pe an ern 106 Schematic for the terminator Example TERM DSN 107 Optimization results for the passive terminator example 116 Schematic for the active filter example BPF DSN 121 Optimized values for the active filter example 127 Schematic for CMOS amplifier example M2 DSN 130 Upda
3. Adding a parameter There are two ways to add a parameter using the PSpice Optimizer e Create the parameter from scratch e Copy an existing parameter and change its name To create a parameter from scratch 1 From PSpice Optimizer s Edit menu choose Parameters Any optimization parameters that you have already established in the schematic appear in the selection list 2 Inthe Parameters dialog box either e click Add or e double click the blank line following the parameter list 3 Inthe Edit Parameter dialog box set the controls as described in Table 3 Adding and editing parameters You can also define parameters in Capture using the OPTPARAM part See Defining design parameters on page 2 38 for an example Name Br M Enabled Current Value 5 Initial Value 5 Upper Limit 10 Lower Limit 1 Tolerance 63 Chapter 3 Using the PSpice Optimizer Table3 Edit parameter dialog box controls Control Name Meaning Name Parameter name for a new parameter double click lt lt new gt gt and enter a text string that is unique to the current optimization file Current Value Latest parameter value for a new parameter set Current Value equal to Initial Value Initial Value Starting value for the parameter Upper Limit Highest allowable value for the parameter Lower Limit Lowest allowable value for the parameter Tolerance Tolerance level 1 5 etc to use when standardizin
4. Advanced options This section describes the advanced configuration options for the PSpice Optimizer To display the Advanced options dialog box 1 From the Options menu choose Defaults 2 Click the Advanced Options button Controlling cutback Cutback option The Cutback option defines the minimum fraction by which an internal step is reduced while the PSpice Optimizer searches for a reduction in the goal s target value To set cutback 1 In the Cutback text box enter a decimal fraction that defines the minimal percent reduction in internal step size If the data is noisy consider increasing the Cutback value from its default of 0 25 Controlling parameter value changes between iterations Threshold option The Threshold option defines the minimum step size the PSpice Optimizer uses to adjust the optimization parameters during the optimization process The optimizer assumes that the values measured for the specifications change continuously as the parameters are varied In practice this assumption is not justified For some analyses especially transient analyses the goal function values show discontinuous behavior for small Advanced options Advanced Options x Cutback 0 25 Threshold fo r One Goal Least Squares C Minimize Cancel The PSpice Optimizer saves option settings to the opt file so that they remain with the optimization s parameter and specification settings To ge
5. CenterFreg vdb out 1 cancel Note that to measure performance all three goals are evaluated using goal functions 123 Chapter 6 Tutorial Exploring design tradeoffs active filter To remeasure performance select Update Performance from the Tune menu 124 Testing performance Initial performance has already been measured for the active filter ensuring that the design simulated as expected that current values for the goals were calculated and that initial values were updated Initial performance calculated to Table 6 2 Goal Current Initial value Target value Fe 8 322 Hz 10 Hz BW 0 7122 Hz 1Hz Gain 14 81 10 Calculating derivatives To estimate performance effects with small changes in parameters or specifications the PSpice Optimizer uses derivatives of each specification with respect to each of the parameters To calculate the derivatives 1 From the Tune menu choose Update Derivatives The message Updating Derivatives appears in the status bar while this takes place Tweaking parameters Once the derivatives are calculated you can use the PSpice Optimize to explore how small changes in the parameters affect the performance of the design To examine the performance effect w hen changing aGain from 0 5 to 0 4 1 Highlight the current value for a Gain and type 0 4 2 Press Enter lt 4 The value of the Gain specification changes from the initial value of 14 811 to a new valu
6. e Thevenin equivalent resistance of the combination Requiv must equal a specified value Assume that the DC supply has negligible internal resistance and that Veenter must be 3 75 0 1 V Requiv must be 10041 Q Your objective is to find the best values for R1 and R2 that meet the stated specifications You can manually solve this problem using the following simultaneous equations 5R R R 2 5375 and H gt R R R R mp These equations solve to R1 133 3 Q and R2 400 Q an exact solution As you complete this tutorial compare this solution to that produced by the PSpice Optimizer Loading the design into Capture Loading the design into Capture To begin set up a design with e Parameters for the resistor values e Away to measure the performance of the two specifications Your OrCAD installation includes a schematic for the passive terminator design To load the passive terminator schematic 1 From the Windows Start menu choose the OrCAD Design Desktop program folder and then the Capture shortcut to start Capture 2 From the File menu choose Open then choose Project 3 Move to the directory containing TERM OPJ Program Files OrCA D PSpice Samples Optimize Term and select the project file in the File Name list TT This design contains two sections The first section connects an instance of the terminator to a DC source and to ground The output is connected to a bubble port
7. e With manual recalculation selected you can change the current value for several parameters or specifications and initiate recalculation when you are ready Exploring the effect of parameter and specification changes Derivative calculations When tweaking values the See Derivatives on page 4 95 for PSpice Optimizer does not perform any simulations more information on how the PSpice Instead the optimizer requires derivative data and uses Optimizer computes derivative data See this to estimate what will happen when you change a Viewing derivatives on parameter or specification page 3 81 for instructions on how to The PSpice Optimizer calculates derivatives either e once when you choose Update Derivatives from the Tune menu or e for each iteration of an optimization run when you choose Auto from the Tune menu Use the first method Update Derivatives when you are exploring design tradeoffs Note Because the performance of the design usually depends on the parameters in a highly nonlinear way the results are typically reliable only for small changes in values See Ensuring reliable results when tweaking values on page 3 77 for the steps you can take for best results Automatically recalculating performance The PSpice Optimizer automatically recalculates performance after each change provided that e Automatic recalculation is selected the default e Derivatives are available To test performance us
8. Table2 Valid Operators and Functions for PSpice Optimizer Expressions Operator Meaning addition subtraction multiplication division exponentiation exp amp log In x log10 10g10 x sin sine cos cosine tan tangent atan arctangent Note Unlike trace functions and goal functions PSpice Optimizer expressions are evaluated without using a simulation Derivative A derivative defines mathematically how a specification value changes with a small change in parameter value For a given design the PSpice Optimizer calculates derivatives for each specification with respect to each parameter Within an applicable range the optimizer uses the derivatives to estimate new values for the goals and constraints Terms you need to understand See Derivatives on page 4 95 fora detailed discussion 29 Chapter 1 Things you need to know 30 Primer How to optimize a design Chapter overview This chapter guides you through the basic steps needed to setup and run an optimization using a simple diode biasing design e Optimizing a diode biasing circuit the objective on page 2 33 describes the sample circuit and its ideal operating characteristics e Why use optimization on page 2 34 explains why fine tuning your design using the PSpice Optimizer saves time e Phase One Developing the design on page 2 35 walks you through the steps needed to create a working design e Phase Two Setting up th
9. Target text box 67 target value 25 scaling raw measurements 97 Terminate command Auto submenu Tune menu 72 Threshold option 101 Tolerance text box 64 68 tolerance component values 82 trace function Probe 27 tradeoffs design 34 74 active filter example 119 and starting points 89 between goals and constraints 86 ensuring reliable results 77 tweaking values 74 Tune menu Auto submenu 2 Start command 72 Terminate command 2 Show Derivatives command 81 Update Derivatives command 75 76 Update Performance command 72 Type list constraints 67 U Update Derivatives command Tune menu 75 76 Update Performance command Tune menu 72 Update Schematic command Edit menu 84 174
10. choose Edit Simulation Then click the Include Files tab 141 Chapter 8 Tutorial Fitting model data bipolar transistor Refer to Q devices in the online OrCA D PSpice A D Reference Manual for more information on the parameters used for bipolar transistor models To display the Optimizer Parameters dialog box double click the OPTPARAM partin the design The parameters The model parameters to fit are Is Ikf Br Bf Ise and Ne These parameters are a subset of the parameters PSpice uses to determine the BJT s DC characteristics To fit all of the BJT model parameters you would need more measured data than is provided in this tutorial PSpice Optimizer parameters There are six PSpice Optimizer parameters each corresponding to one of the BJT model parameters listed above The initial and current values for each of these parameters are set up using the OPTPARAM part as follows Property Parameters Is Ikf Br Bf Ise Ne Initial Value le 13 5 5 50 le 10 1 5 Current Value le 13 5 5 50 le 10 1 5 Lower Limit le 14 1 1 20 le 11 1 2 Upper Limit le 11 10 10 200 le 8 2 Tolerance 0 0 0 0 0 To see the parameterized expression assignments for the model parameters 1 Click Q1 2 Fromthe Edit menu choose Model 3 Click Edit Instance Model Text 4 When finished click Cancel 142 Parameterized expression assignments The model definition is set up with parameterized expression assignments for the model param
11. m N Current source Options Model ty Y Global parameter C Model parameter Primary Sweep Secondary Sweep 0 Monte CarloAW orst Case C Temperature Parametric Sweep Temperature Sweep 7 Sweep type Save Bias Point al Start valle Load Bias Point iake ss Logarithmic Dec ade v Inerement Value list av Cancel Apply Help 4 Click OK to save the profile Developing performance measures To measure performance you must define an evaluation algorithm for each specification There are three alternatives e Trace function for single point simulations e Goal function e PSpice Optimizer expression When the evaluation is anything other than a single point simulation or PSpice Optimizer expression you must develop goal functions to derive values from the simulation results Developing goal functions is an iterative process that involves writing the goal function simulating the design and testing the goal functions against actual results to make sure you are measuring the waveform characteristics you intended A goal function is not required for the diode design example You are examining the trace of R1Val versus I D1 which shows the relationship between the value of R1 and the diode forward current Because only a single point on the curve is of interest the trace function I D1 is the appropriate evaluation Defining spedfications goals and cons
12. performance results and seeing what parameter values would produce these results To investigate the parameter changes when changing Gain to a new target value of 10 1 Note Make sure that automatic recalculation is selected a From the Options menu choose Recalculate b Inthe When frame click Auto co Click OK Highlight the current value for Gain and type 10 Press Enter The PSpice Optimizer automatically adjusts the parameters to satisfy the results and then updates the results to match The result changes from the value you specified to the nearest value which still satisfies all of the parameter limits In this case the lower limit of the aGain parameter 0 1 is violated so the optimizer uses the smallest allowed parameter value This gives a value of 10 8 for Gain Because the PSpice Optimizer computes estimates using the previously calculated derivatives results are typically reliable for only small changes in parameter values After significant tweaking you should resimulate and recompute the derivatives to see true performance See Ensuring reliable results when tweaking values on page 3 77 Completing optimization Completing optimization To finish exploring the active filter design run an optimization To start optimizing 1 From the Tune menu choose Auto and click Start The PSpice Optimizer finds a set of parameters for which the specifications are met Figure 27 shows the resu
13. the optimizer displays the Save As dialog box and you must enter the name of a new file To save optimization results to a new or different file 1 From the File menu choose Save As 2 Enter anew file name 3 Click OK If an optimization file with this name already exists the PSpice Optimizer requests confirmation to overwrite the file 83 Chapter 3 Using the PSpice Optimizer Edit menu Parameters Specifications Store Values Reset Values Round Nearest Round Calculated 84 Updating the design Once the optimization is complete and you have optionally standardized component values you can update the underlying schematic with the final parameter values To back annotate the schematic with the latest parameter values 1 From PSpice Optimizer s Edit menu choose Update Schematic The optimizer writes the optimized parameter values to the schematic file On the schematic the new values appear in the Current column of the OPTPARAM part To use the new parameter values in subsequent simulations run from Capture 1 From Capture s PSpice menu choose Use Optimized Values Understanding optimization prindples and options Chapter overview This chapter explains optimization concepts and how you can influence the outcome of an optimization The concepts covered in this chapter include constrained optimization function characteristics convergence and the effect of starting points and how the PS
14. weight 1 satisfied yes circuit mydiode analysis DC allsections no evaluate i r1 u r1 1 r1 2 using default goal functions file reference internal type gt target 4mU range 466UW constraint xxx Options x Delta 1 Threshold 8 Cutback 6 25 Max Iterations 20 One Spec least squares Recalculate auto xxx Derivatives xxx Rival Idi 2 43e 007 Pc 9 96e 007 7 la gt Figure 16 Sample excerpt from a report To print an optimization report 1 Open the report file in a standard text editor such as Notepad Use the Print command to print the report Viewing the optimization log The PSpice Optimizer automatically creates an audit trail of optimization progress and saves the information to a file named design_name OLG You can use this file as a debugging tool when an optimization fails to converge To view the optimization log file 1 Activate Notepad or another text editor 2 Open the log file for browsing Viewing derivatives You can display a matrix showing the most recent derivative data the PSpice Optimizer uses to calculate performance To display the derivative data 1 From the Tune menu choose Show Derivatives Each entry in the matrix represents the partial derivative of one specification the row label with respect to one active parameter the column heading If a specification is completely independent of a parameter the derivative is zero 2 When finished
15. 01 1 310E 05 3 989E 06 4 300E 01 1 928E 05 4 897E 06 8 100E 01 8 002E 00 1 922E 01 8 200E 01 9 092E 00 2 371E 01 Figure 35 Sample external data file 160 Defining specification criteria in the external data file The external data file contains the measured data used in the optimization e g when fitting data to model parameters Data is formatted as labeled columns of values Typically the first column contains the independent values at which all other data was measured this corresponds to the X Column Name in the optimizer s Edit Specification dialog box All other columns contain the dependent measured values and correspond to the Y Column Name in the dialog box To set up an external file Using a standard text editor 1 Online 1 enter the column headings for the data separated by spaces or tabs 2 Onall lines following line 1 a Enter data values that correspond to the column headings separated by spaces or tabs D Sort the lines of data in ascending X Column Name order 3 Save the file using any file extension that does not conflict with other OrCAD standard file extensions We recommend using the naming convention design_name MDP For an example of an optimization that uses an external data file see Chapter 8 Tutorial Fitting model data bipolar transistor File type summary Table 1 briefly describes all of the file types that the PSpice Optimizer uses directly File type summary Ta
16. 10 accuracy To load the active filter design 1 From the Windows Start menu choose the OrCAD Design Desktop program folder and then the Capture shortcut to start Capture 2 In the Project Manager from the File menu choose Open then choose Project 3 Move to the directory containing BPF OPJ Program Files OrCA D PSpice Samples Optimize Bpf and select the project file in the File Name list RI 10k Honing pot OPTIMIZER PARAMETERS CI C2 Name Initial Current JL IF aFe 0 5 0 5 a 4 aBW 0 5 0 5 u u R 620 aGain 048 0 5 ug74 Figure 26 Schematic for the active filter example BPF DSN The parameters The three variable resistors Rfc Rbw and Rgain are implemented as potentiometers The potentiometer part has an property called SET which describes the slider position a value between 0 and 1 To optimize slider position the optimization parameters afc aBW and AGain are assigned to the SET property for the parts Rfc Rbw and Rgain respectively The parameters are shown in the OPTPARAM part on the schematic Each parameter is set up to range from 0 1 to 0 9 with an initial value for each set to 0 5 each The active filter design To see the assignment for SET double click on one of the variable resistor parts to bring up its list of properties 121 Chapter 6 Tutorial Exploring design tradeoffs active filter To display the Optimizer Parameters di
17. 74 for more information 61 Chapter 3 Using the PSpice Optimizer 4 862e 001 e I See Target value scaling on page 4 97 for a discussion of normalization and scaling 62 Error gauge area The error gauge area has an error indicator and shows information reflecting the overall condition of the optimization The error gauge shows how far the goals are from their target values Initially the indicator displays 100 As the optimization proceeds the error falls as the goals approach their target values The PSpice Optimizer displays the RMS of the normalized value of the goals in the RMS Error field If all of the specifications meet the target values exactly the error is zero If the optimization succeeds by finding a solution that works within the set ranges but does not meet the target values exactly the error represents the combined error of all of the specifications Note The RMS error reflects only those goals that are enabled The error does not include contributions from constraints nor does it reflect any specifications that are disabled Adding and editing parameters This section describes how to create and change optimization parameters using the PSpice Optimizer This means you can also edit the properties of parameters that you defined in a schematic Note You are limited to eight parameters per optimization file This limit indudes parameters that you have defined but disabled for a given run
18. Constrained optimization Many problems in analog circuit optimization are naturally expressed as the minimization of a function representing a goal e g power consumption which is subject to one or more constraints e g bandwidth Constraints are typically complicated nonlinear functions of the parameters of the problem so manual optimization is a difficult task Most other analog circuit optimizers implement only unconstrained optimization of a single goal or a sum of squares of several goals To tackle a problem like the problem outlined above other optimizers must combine the functions for the goals and constraints and then optimize the combination Unfortunately this scheme does not differentiate between reduction of the 87 Chapter 4 Understanding optimization principles and options goals and violation of the constraints In general constraints are given much greater weight than the goals This approach has a number of pitfalls In particular e Ifa very large value is used for the weight of the constraints numerical problems occur e Jfa more reasonable value is used the result is not a true solution of the original problem e Using a sequence of weights and performing a series of minimizations can lead to the true solution but at the expense of a large increase in optimization time because of all of the extra evaluations required to solve the intermediate problems The PSpice Optimizer implements both con
19. Equality constraints are always active e g a constraint of the form Vout 3 75 V is always active Inequality constraints are considered active if the solution violates the constraint or if it is equal to the constraint e g a constraint of the form Req gt 100 is active if Reg is less than or equal to 100 at the solution Lagrange multipliers The result of a constrained optimization is typically a compromise between further reduction of the goals and violation of one or more constraints A set of numbers the Lagrange multipliers provide valuable information about the tradeoffs between the goals and the constraints The PSpice Optimizer calculates Lagrange multipliers only for those constraints which are active at the solution A constraint which is inactive can be removed from the problem without affecting the solution which means there is no tradeoff between the goals and the constraint Think of Lagrange multipliers as the incremental cost of each active constraint on the solution Example Consider optimizing propagation delay through a gate subject to a constraint on gate width and a constraint on bias current Suppose that at the optimum both constraints are active There are two Lagrange multipliers for this problem e Incremental cost of propagation delay versus gate width e Incremental cost of propagation delay versus bias current For this problem the units of the Lagrange multipliers are seconds meter
20. Max Iterations option defines how many attempts at most the PSpice Optimizer can make before giving up on the solution even if the optimizer is making progress To limit the simulation iterations 1 Inthe Max Iterations text box enter an integer value that defines the maximum number of attempts you will allow the PSpice Optimizer to make 99 Chapter 4 Understanding optimization principles and options Specifying a waveform display Waveform Data File and Display options The Display option defines the name of the waveform display the PSpice Optimizer uses to display simulation results in PSpice A D The Probe File option specifies a nondefault PRB file in which the Probe display information has been stored To use a specific Probe display when optimizing Refer to online Help in PSpice A D for 1 In PSpice A D configure the plots as you want to information on using PSpice A D Display view them LEN le 2 Save and name the display a From the Window menu choose Display Control b Enter the name for the display c Click Save 3 Inthe PSpice Optimizer specify the waveform display a From the Options menu choose Defaults to display the Defaults dialog box b Inthe Display frame type the Probe waveform display name in the text box c Select the appropriate analysis type AC DC or Tran d Ifyou saved the waveform display to a nondefault PRB file enter the name of the file in the Probe File text box 100
21. Optimizer s Options menu choose a Rew Delta 1 Max Iterations 7 Probe File b Inthe Display text box enter the name of the Probe waveform display Display c Select the analysis type corresponding to the o Probe waveform display CAC DC Tran d Click OK Advanced Options Cancel 73 Chapter 3 Using the PSpice Optimizer 74 Exploring the effect of parameter and specification changes The PSpice Optimizer provides three easy ways to examine tradeoffs between goals constraints and parameters You can e Tweak parameter values to explore performance effects or change specification values to see how parameters change by entering new current values directly into the PSpice Optimizer window e Exclude specifications and or parameters that you previously defined e Add new or edit existing parameter definitions and specification descriptions Testing performance when changing current values In the PSpice Optimizer window you can quickly examine the effects of a small change to either a parameter s current value or a specification s current value Recalculation modes When changing current values sing you can choose between automatic and manual recalculation of performance e With automatic recalculation selected you can change the current value upper text box for one parameter or a specification value and see the impact on other values almost immediately
22. ____ External Target 4mW ie T Be lt Range 400uW Range 400uW X Column Name V Constraint Y Column Name Constraint selected type EEE Tolerance fix Type lt target Analysis Circuit File CAC DC Tran Analysis DC DT Circuit File mydiode Probe File Containing Goal Functions prb Evaluate r1 v r1 1 r1 2 Evaluate 46 i r1 v r1 1 r1 2 Cancel The Evaluate text box contains the expression for measuring dissipated power For each iteration PSpice A D will compute dissipated power by taking Phase Three Running an optimization the product of the voltage across the resistance and the current through it 4 To calculate the performance of the design for initial parameter and specification values only one iteration a From the Edit menu choose Reset Values b From the Tune menu choose Update Performance Note the appearance of the progress indicator in FR n the Pc box Since Pc is a less than or equal to Blei progress Indicator constraint the progress indicator has a tick mark rn 1 4 of the way up The vertical bar within the See Progress indicator on indicator is below the tick mark this means that page 3 60 for more on the different the constraint is currently satisfied kinds of progress indicators and how to 5 From the Tune menu choose Auto and click Start to interpret them start optimization After a number of iterations the optimization en
23. and seconds ampere respectively In a problem with several goals which have been combined as a sum of squares the target value is dimensionless In this case the units of the Lagrange multipliers are the reciprocal of the units of their associated constraint Example A multiplier associated with a width constraint has units of meter Characteristics of functions The success of an optimization depends highly on the behavior of the functions related to each specification Generally the PSpice Optimizer obtains values measures performance for each of the specifications by evaluating a trace which results from a simulation with varying parameter values The optimizer can experience difficulties if the accuracy of the measurement is decreased by e Discontinuities in the simulation results e Anerror in the goal function definition e Inaccuracies in the simulation results on which the evaluation is based Generally simulations and measurements using AC and DC analyses behave better than simulations using transient analyses This is particularly true if the evaluations are set up to measure the value of a single point e g the time when a trace crosses a specified level This kind of measurement tends to behave discontinuously as the parameters change creating difficulties for the optimizer Characteristics of functions To review the PSpice Optimizer measures performance in one of three ways by taking the value of
24. ccm LP Figure 29 Updated performance values for the amplifier example 2 From the Tune menu choose Update Derivatives to compute the partial derivatives of each goal and constraint with respect to each parameter 3 Display the derivatives a From the Tune menu choose Show Derivatives b Click Close when finished 4 From the Tune menu choose Auto and click Start to start the optimization Performing the optimization Notice that the performance indicators change as the optimization proceeds When complete optimized values should appear as shown in Figure 30 Ei Optimizer M2 opt Derivs Avail File Edit Tune Options Help Specifications W Power M Gain MW BW 914 414uw 19 9614 999 392k 2 36776mw 23 7998 2 16111Meg RMS Error _ Pwi F F ret 33 4944u 6 55869u Bra u er Optimization ended reached iteration limit Figure 30 Optimized values for the amplifier example This optimization stops after reaching the maximum number of allowed iterations Even so power consumption is minimized the objective within the iteration limits Note For a minimization problem like this one you can still effectively use the PSpice Optimizer to improve the circuit s performance even though the goal is not attainable 137 Chapter 7 Tutorial Using constrained optimization MOS amplifier 138 Tutorial Fitting model data bipolar transistor Tutorial overview T
25. circuit file in PSpice compatible format 2 Create a separate file containing the optimization parameter definitions 3 Using the PSpice Optimizer complete the setup and run the optimization as usual Refer to your PSpice A D user s guide for any questions you might have on circuit file syntax The remaining sections explain what you need to do once your design is defined as a circuit file Setting up the circuit file Setting up the circuit file To use the PSpice Optimizer to optimize a design defined as a netlist 1 Decide on the design parameters you want the optimizer to vary 2 Place parameter definitions PARAM in a separate parameters file PAR 3 Include the parameters file in the circuit file using the INC command 4 Replace component values that are dependent on the parameters with expressions All of these steps use standard PSpice A D syntax see your PSpice A D user s guide for details The following section explains why you need to set up a separate parameters file and how to do it steps 2 and 3 above The parameters file PAR When optimizing the PSpice Optimizer uses a separate parameters file to track changes to parameter values with each iteration This file contains nothing but PSpice A D parameter definitions reflecting the last used values The optimizer automatically looks for a file with the name circuit_file_name PAR Example If the design is contained in MYAMP CIR the opti
26. click Close Viewing result summaries PSpice Optimizer Optimization Run E File Bpf ope Wed Jan 08 10 50 17 1997 One Spec least squares Recalculate auto method Unconstrained Least Squares Iteration 1 x 0 5 0 5 0 5 F 16 78 2 878 4 811 In xada i 2 S9et001 9 22 4001 2 46e 000 1 78e 000 3 86e 001 2 002 002 1 06e 000 4 99e 001 9 86e 000 gtest 1 2129e 001 0 ssian 1 29e 009 3 19e 003 9 8764001 3 1924003 1 25e 004 2 65e 002 9 87e 001 2 65e 002 1 03e 002 0 2512 0 08625 0 07804 2512 0 08625 0 07804 i Do 000 1 7 216804000 Iteration 2 x i For Help press F1 Uni Coli C NN 4 Figure 17 Sample excerpt from a Log file Figure 18 Sample derivative data 81 Chapter 3 Using the PSpice Optimizer Edit menu Parameters Specifications Store Values Reset Values Round Nearest Round Calculated Update Schematic 82 Finalizing the design This section describes how to use the PSpice Optimizer to e Standardize part values once the optimization is complete e Save results e Back annotate the schematic with the final part and parameter values Using standard part values When optimization parameters directly correspond to part values you can use the PSpice Optimizer to select standard part values by either e rounding to the nearest values or e computing values based on the most recent optimization run
27. e scaling zz 2242 22 mocs a ma so naam a Reed 97 Default options lt cc sceme HE rien 98 Controlling finite differencing when calculating derivatives Delta option 21k 4 lt ewe deuce a ore oe ox 98 Limiting simulation iterations Max Iterations option 99 Specifying a waveform display Waveform Data File and Display options 100 Advance pone 52 SER oat Er Ran heine 101 Controlling cutback Cutback option 101 Controlling parameter value changes between iterations Threshold option 4 101 Choosing an optimization method for single goal problems Least Squares Minimization options 103 Tutorial Optimizing a design passive terminator 105 Tutorial overview 2 HH m on 105 The passive terminator design iii 54584 00 dae we 0 106 Contents Chapter 6 Chapter 7 Chapter 8 vi Loading the design into Capture 4c skew ina Setting part values to expressions ws er unser ip Lee Defining optimization parameters 2 22m en Defining the analysis type aus an ee er Br re E Running an initial circuit analysis oaoa Starting the PSpice Optimizer 2 0 su u 05 00 ees oe Eee Re a Viewing the parameter description ss bed a wba ee o Defining the goals and constraints 00 00000 Checking that the design will simulate Starting the optimization u u Sur 2 Seb eee ea Changing a goal to a constraint ex 6
28. evaluate performance simulation in a run PAR Generated by Capture when Parameters file Contains the latest optimization parameter activating the PSpice Optimizer and updated by the optimizer when running an optimization values You can use any file extension for an external data file 161 Chapter B File types used by the PSpice Optimizer 162 Optimizing a netlist based design Appendix overview This appendix describes how to set up and run an optimization for a design defined in a circuit file e Optimizing without a schematic on page C 164 gives an overview on optimizing a netlist based design e Setting up the circuit file on page C 165 describes the steps that you must complete using a text editor to parameterize the circuit file for optimization e Setting up and running the PSpice Optimizer on page C 166 describes the steps that you must complete using the PSpice Optimizer to define parameters and specifications run the optimization and save the results e Example Parameterizing the circuit file on page C 168 steps through parameterizing a simple diode biasing circuit file Chapter C Optimizing a netlist based design 164 Optimizing without a schematic Although the PSpice Optimizer is designed to optimize a Capture based design you can optimize a design for which a netlist but no schematic is available To optimize your design without using Capture 1 Implement your design as a
29. labeled Vc The second section connects the top and bottom ends of an instance of the terminator to ground and a1 A current source to its output This output is connected to a bubble port labeled Vr The voltage at Vc gives the value of the Venter Figure 24 Schematic for the terminator specification The voltage at Vr gives the equivalent Example TERM DSN resistance of the network the Requiv specification 107 Chapter 5 Tutorial Optimizing a design passive terminator The curly braces are PSpice syntax for an expression You can specify any expression that PSpice can evaluate 108 Setting part values to ex pressions The parameters varied between iterations must relate to the components you are optimizing For this example R1 and R2 resistor values are already parameterized To see how the resistor values are set up to use optimization parameters 1 Double click the part for R1 or R2 The Edit Part dialog appears 2 Within the Edit Part dialog box note the value of the VALUE property R1val or R2val depending on the part you selected 3 Click OK to close the Edit Part dialog box Defining optimization parameters Next set up the optimization parameters that the PSpice Optimizer will vary between iterations these are the same parameters used in the value expressions for R1 and R2 For this example Rival and R2val are already defined using an OPTPARAM part as shown below OPTIMIZER PARAMETERS N
30. menu If you have the demo version The demonstration version of the PSpice Optimizer has the following requirements and limitations e Requires OrCAD PSpice A D with Capture demonstration package e Is limited to one goal one parameter and one constraint xvii Before you begin xviii Things you need to know Chapter overview This chapter introduces the purpose and function of the PSpice Optimizer the optimization process and related terms e What is the PSpice Optimizer on page 1 20 describes optimizer capabilities and the criteria designs must meet for successful optimization e Using the PSpice Optimizer with other OrCAD programs on page 1 22 presents the high level design flow for optimization and how other OrCAD programs are integrated into each design phase e Terms you need to understand on page 1 23 defines the terms that are important for optimizing designs successfully Chapter 1 Things you need to know 20 What is the PSpice Optimizer The OrCAD PSpice Optimizer is a circuit optimization program that improves the performance of analog and mixed analog digital circuits Run optimizations The PSpice Optimizer performs iterative simulations while adjusting the values of design parameters until performance goals subject to specified constraints are nearly or exactly met Constraints can include simple bounds on parameter values and nonlinear functions The PSpice Optimizer also comp
31. numeric field shows the total error the sum of the squares of the normalized errors for the active specifications and the gauge shows the error relative to the starting point Final results are shown in Figure 25 Ei Optimizer Term opt Derivs Avail File Edit Tune Options Help Rt I 09 5833 250 M Reval a Optimization complete Specs met Figure 25 Optimization results for the passive terminator 116 example Compare the parameter values of 133 5 for Rlval and 393 7 for R2val with the calculated values on page 5 106 They are very close Changing a goal to a constraint Changing a goal to a constraint Try examining what happens when you change one ofthe For an example see See Goals versus specifications from a goal to a constraint constraints on page 4 86 for more information To change a goal to a constraint 1 Edit a specification a Inthe PSpice Optimizer window double click the hot spot lower right hand corner in either the Vc or Rt specification box Select the Constraint check box Inthe Type list select the type of constraint 2 From the Edit menu choose Reset Values to set the current values back to the original initial values 3 From the Tune menu choose Update Performance 4 Ifyou want to run a complete optimization a From the Tune menu choose Auto b Click Start For this example the PSpice Optimizer should produce approximately the sa
32. or PSpice Optimizer expression to track the independent data value To set up an evaluation for an external specification 1 Create the goal function or PSpice Optimizer expression 2 Inthe Edit Specification dialog box enter the evaluation in the Evaluate text box as follows Substitute the character for every X value argument i e wherever a measured subgoal value should appear For example Suppose that you want to fit a set of data measured at different values of Vtest 2 0 2 5 and 3 0 volts using the goal function YatX V out x_value to measure the output of the design To use this with an external specification replace x_value with the character and enter the evaluation YatX V out into the Evaluate text box for the specification As the fitting process proceeds the PSpice Optimizer passes the following goal functions one for each measured data point to PSpice A D YatX V out 2 0 YatX V out 2 5 YatX V out 3 0 Selecting a specification to edit You can change the properties of an existing specification at any time using the Edit Specification dialog box To display the Edit Specification dialog box for a goal or constraint 1 Doone of the following e In the specifications area of the PSpice Optimizer window double click the lower right hand corner of the box for the specification you want to edit e From the Edit menu choose Specifications then select the speci
33. specifications e Optimize a design in which the circuit has several states where a small change in a parameter value causes a change of state For example A flip flop is on for some parameter value and off for a slightly different value 21 Chapter 1 Things you need to know Using the PSpice Optimizer with other OrCAD programs Because you can use Capture and The PSpice Optimizer is fully integrated with other PSpice A D to design and simulate at the OrCAD programs This means you can design your circuit system subcircuit or component level use with OrCAD Capture simulate with OrCAD PSpice A D the PSpice Optimizer to optimize at or OrCAD PSpice analyze results with the PSpice A D whatever level is most appropriate waveform viewer and optimize performance within the same environment Figure 1 illustrates the typical design flow for circuit optimization Phase One OrCAD Capture Develop the d OrCAD PSpice A D eag Phase Two OrCAD Capture Set up the OrCAD PSpice A D optimization OrCAD PSpice Optimizer Phase Three OrCAD PSpice A D See Chapter 2 Primer How to optimize a design for a detailed description of each design phase OrCAD PSpice Optimizer Fit the model parameters Run the optimization Figure 1 Optimization design flow 22 Terms you need to understand Optimization Optimization is the process of fine tuning a design by varying design parameters between succes
34. subgoals and five are satisfied the current value field reads 5 20 and the bar in the progress indicator rises to the one quarter mark Parameters area The parameters area can show up to eight parameter boxes Figure 13 illustrates the fields contained in each box enable disable check box 4 14799k current value edit parameter hot spot initial value Figure 14 Example of a parameter box The following sections explain the initial and current value fields in the parameter box Initial value The initial value field displays a single value taken from the parameter specification that you set up either in Capture using the OPTPARAM part or in the PSpice Optimizer from the Edit menu choose Parameters Current value Initially the current value is taken from the parameter specification you set up in either the schematic or the PSpice Optimizer With each iteration of an optimization the optimizer updates the current value field with the new set of parameter values The PSpice Optimizer Window For more information on the enable disable check box see Excluding parameters and specifications from optimization on page 3 78 For more information on the edit hot spot see Selecting a parameter to edit on page 3 65 If derivative data is available you can change the value in this field to explore how specification values might change See Testing performance when changing current values on page 3
35. the problem as specified e The simulation and or evaluations are not accurate enough to allow the solution to be found 93 Chapter 4 Understanding optimization principles and options 94 e A limit on the number of simulations or elapsed time is encountered e The optimizer finds a spurious numerical minimum which is not the desired solution To improve convergence consider the following techniques e Inthe second case use more accurate measurement techniques possibly with the aid of help circuitry e Inthe last case restart from a different starting point which might lead to a different solution Parameter bounds The PSpice Optimizer performs bound constrained minimization This means it will solve problems where one or more of the parameters are limited by the specified upper or lower bound for that parameter In other words the optimizer finds a solution if one exists even if one or more parameters are at their limit However solving this kind of problem is intrinsically more difficult than performing unconstrained minimization If one or more parameters appear to be limited during the optimization run and you don t expect the final solution to have limited parameters you could save time by using one or both of the following techniques e Useastarting point that is further from the parameter limits e Loosen the limits on the parameter s in question Derivatives Derivatives To perform optim
36. the single point trace trace function in PSpice A D by applying a goal function to the trace or by evaluating a PSpice Optimizer expression Trace functions and goal functions require a simulation PSpice Optimizer expressions do not 91 Chapter 4 Understanding optimization principles and options M2 Figure 20 Global and local minima of a function 92 To improve measurement accuracy consider any of the following techniques e Use several points rather than a single point for the Probe goal function That is specify several points on a waveform instead of a single point e Reduce the step ceiling in Transient analysis to produce a more finely sampled set of data e Increase simulator accuracy e g reduce RELTOL The first proposed technique is preferred because it does not affect the time required to run each simulation usually the determining factor in how long an optimization run takes Global and local minima The curve in Figure 20 shows a 1 dimensional function with 2 minima Point M1 is a local minimum it satisfies the conditions for a minimum but there is another minimum which is smaller Point M2 is the global minimum for the function There are no points within the range of the function which are smaller All practical optimization techniques find local minima including the algorithms used by the PSpice Optimizer This may or may not present a problem The application may not have any local min
37. those lines the estimates are not reliable When for a given parameter the difference between its initial value and the value of interest is large that is the relative difference is much bigger than Delta modify its initial value and restart the simulation Note When you modify the current value for a parameter to recalculate specification values by editing the value appearing in the PSpice Optimizer window the PSpice Optimizer uses the derivative data rather than a resimulation to determine the new values Therefore you should periodically verify the results with another simulation see Ensuring reliable results when tweaking values on page 3 77 Target value scaling When there is more than one goal or a combination of goals and constraints the PSpice Optimizer needs to scale the raw measurements before combining them Example Consider a least squares optimization with two specifications e Collector base capacitance e Collector resistance The first of these can have values of several picofarads the second of tens of Kohms Clearly adding the squares of the errors for these specifications will lose the significance of the capacitance term Instead the optimizer scales the values as follows T _ T measured target Scaled Range Suppose the specified target and measured values are as shown below Table 4 1 sei agi Target Allow ed Measured Specification value range value collector base 10
38. want to design a resistive terminator that produces an output voltage of 3 75 V 0 1 V at the junction of the two resistors and the Thevenin equivalent resistance of the resistor combination must equal 100 Q 1 Q Your objective is to find the best resistor values to meet these two specifications e output voltage of 3 75 V Ve e equivalent resistance of 100 Q Re You can manually solve this problem using the following simultaneous equations SR R R 2 3 75 and 100 R R R R These equations solve to R1 133 3 Q and R2 400 Q an exact solution Constrained optimization When using the PSpice Optimizer you can set up this problem in one of three ways e Consider V and R as equally important set up both as goals e Consider V as the most important requirement to meet even at the expense of R set up Vi as a constraint and R as a goal e Consider Re as the most important requirement to meet even at the expense of Ve set up R as a constraint and V as a goal Note Because at least one optimization goal is necessary the case where both V and Re are constraints is excluded If the problem like this one has a solution the PSpice Optimizer might arrive at the same answer for all three methods However most problems do not have a single exact solution as this one does For most designs the result is a compromise that minimizes the goals while not violating the constraints
39. 42 au kan a na Saving TESUle tee Reha eee Sees od eee ERDAS 4 Tutorial Exploring design tradeoffs active filter 119 Tutorial overview LL The active filter designi o o aus eee Re oe ke en ind The parameters ods 0 eh 5 0 8 400 neh ED ELE ae OR he goals aa ea a EK a a Oe mer En Brei Testing performance os Fhe Phe a ee See BIG da Ehe Calculating derivatives un ae Ch Er ee Tweaking parameters sr aw eae nae Gee ee de Shey ann Tweaking goals and constraints 00500004 Completing optimization 244 perla Rea Peek Bee pe RS Tutorial Using constrained optimization MOS amplifier 129 Tutorial overview 2 2 2 0 ce eseri sa n arosa akt The CMOS amplifier design 4 suas Eau a es an Bug ewe RA The Paramielern se Reit eee we ESE EES POSS CA ES The evaluations 2 22 Co Como The goals and constraints us 22 34 oes de eae ee we ee eo Setting the method for a sinigle soal optimization 2 42 4 54 eee a a Performing the optimization iii ees ee be owe ee ee Tutorial Fitting model data bipolar transistor 139 Tutorial overview 0 a a Using the PSpice Optimizer to fit data to model parameters The bipolar transistor test case u au sau eb an a Ihe Paramelets sa ss ss doioro ao a ann Bien A The analysis ssi ans saga tata The external file of measured data Appendix A Appendix B Appendix C Contents The goals and constraints 2 2 0 0 ba 65 os ee ee Rew oS 144 Monitoring progress
40. Optimizer with the help of PSpice generates intermediate results which you can view in PSpice A D This is especially useful when fitting model parameters For the BJT example this means you can monitor how closely the Ic and Ib values match the target values To set up PSpice A D and the PSpice Optimizer to monitor the fitting process 1 From Capture s PSpice menu choose Run to simulate the circuit 2 Create or use an existing waveform display configuration For the BJT example a display named icibe is predefined To see what the icibe display looks like a From PSpice A D s Window menu choose Display Control In the display list click icibe DC C Click Restore d Click Close From the File menu choose Close Monitoring progress with PSpice A D 3 Define the display configuration to use when optimizing For the BJT example this is predefined To R pe verify the display name dnan D a From PSpice Optimizer s Options menu choose Probe File Defaults bitpar prb The display name icibe appears in the Display ais text box and the DC analysis type is selected C AC DC C Tran b When finished click Cancel Advanced Options 4 Measure performance and re display the traces in PSpice A D Cancel a From PSpice Optimizer s Tune menu choose Update Performance In some regions of the device characteristic the measured currents are relatively The optimizer automatically updates th
41. OrCAD PSpice Optimizer User s Guide Copyright 1998 OrCAD Inc All rights reserved Trademarks OrCAD OrCAD Layout OrCAD Express OrCAD Capture OrCAD PSpice and OrCAD PSpice A D are registered trademarks of OrCAD Inc OrCAD Capture CIS and OrCAD Express CIS are trademarks of OrCAD Inc Microsoft Visual Basic Windows Windows NT and other names of Microsoft products referenced herein are trademarks or registered trademarks of Microsoft Corporation All other brand and product names mentioned herein are used for identification purposes only and are trademarks or registered trademarks of their respective holders Part Number 60 30 637 First edition 30 November 1998 Technical Support 503 671 9400 Corporate offices 503 671 9500 OrCAD Japan K K 81 45 621 1911 OrCAD UK Ltd 44 1256 381 400 Fax 503 671 9501 General email info orcad com Technical Support email techsupport orcad com World Wide Web http www orcad com OrCAD Design Network ODN http www orcad com odn 9300 SW Nimbus Ave Beaverton OR 97008 USA Contents Chapter 1 Chapter 2 Before you begin xiii Welcome to OrCAD aaa aa xiii OrCAD PSpice Optimizer overview 2 2 2 Kr Au ri xiv How t use this guide so ca scara cete s keta datas eera ai XV Typographical conventions siii iii ce ene a XV Related documentation 2 20 0 0 0 nen xvi Onlinehelp e ea 2 20 4 4 ese eae ed nen ERE ent xvii If you have the demo
42. SPECIAL OLB Double click on the OPTPARAM part then click the User Properties button Set Rival properties as shown in the Optimizer Parameters dialog box Optimizer Parameters EI Name Initial Value Current Value R1 val 5k 5k Lower Limit Upper Limit Tolerance fo 00 fx Ok 1 fox Name Initial Value Current Value Add Param Save Param Cancel Click OK Phase Two Setting up the optimization 5 Double click the 1 k label for R1 and enter Rlval to parameterize the value of R1 6 Click OK Setting up goals and constraints Before you can evaluate and improve the circuit s performance answer these questions e What operating characteristics do I want to measure e How do the parameters affect the operating characteristics After you ve answered these questions you are ready to e Set up the analyses needed to evaluate the performance measures e Develop the performance measure algorithms e Fully define the goals and constraints in terms of these performance measures and analyses Setting up analyses for each goal and constraint For each specification you must define an analysis type AC DC or transient This is the analysis that PSpice will run in order to generate results that will be used by the PSpice Optimizer to measure performance For the diode design example you want to monitor the value of I D1 at a fixed input voltage of 5 V while the optimization parameter R1va
43. The Evaluate text box in the Specification dialog box must contain a valid Probe output variable Probe goal function or PSpice Optimizer expression Refer to application examples in the your PSpice user s guide The first line of an external data file must contain names for each column of data The first column should contain the X axis data and each succeeding column should contain Y axis data for each external specification The column names on the first line must be identical to those used in the Specification dialog box X Column Name Y Column Name There is a maximum of 8 parameters allowed for an optimization There is a maximum of 8 specifications allowed for an optimization At least one parameter must be selected to perform an optimization The opt file could not be opened by the PSpice Optimizer Make sure that this file is not locked by a word processor or other application See 11021 for a description of the external specification data file The maximum number of iterations can be increased by selecting Defaults from the Options menu The default limit is 20 iterations It is often more helpful to refine the specifications than to increase this limit The optimization was terminated by the user No improvement was made by going back to the last good step and recalculating derivatives Try refining the specifications The external file typed in the Edit Specification dialog box could not be found See 11021 fo
44. The PSpice Optimizer considers the tolerance specified for the parameters using tables of preferred values for 1 5 and 10 tolerance components Other tolerance values cause the optimizer to use the nearest calculated value for that tolerance Parameters with zero tolerance are not changed To round component values to the nearest standard values 1 From the Edit menu choose Round Nearest Finalizing the design To compute standard component values based on the most recent optimization From the Edit menu select Round Calculated Edit menu Parameters The PSpice Optimizer replaces the parameter values Ee with the standardized values only if the new values Bose Vaie Round Nearest remain within the specified limits If so the optimizer Found Caeusted automatically calculates new performance values ein based on derivative data using the new parameter values and displays an e in the upper right hand corner of each specifications area to indicate that the performance measure is an estimate Saving results Performance results are not written to the optimization file until you deliberately initiate a save operation To save optimization results to the current optimization file 1 From the File menu choose Save By default the PSpice Optimizer saves the results and the latest optimization settings to a file named design_name OPT If you started your design from a schematic this file already exists If not
45. The amplifier design is set up to measure power by performing a single point DC analysis and then applying the trace function I V2 10V to the simulation results Gain The amplifier design is set up to measure the spot gain at 1 kHz assuming that the bandwidth is much greater than this by performing an AC analysis and then applying the waveform analysis goal function YatX V Vout 1K to the simulation results YatX is provided with your OrCAD programs The goal function definition is as follows value at given x Yatx 1 1 sf xvalue where 1 where yl YatX V Vout 1k gives the Y value on the V Vout trace for the X value corresponding to 1 k 3 dB bandwidth The amplifier design is set up to find the frequency where the output has fallen by 3 dB from its low frequency value by performing an AC analysis same as for Gain and then applying the waveform analysis goal function LPBW Vdb Vout 3 LPBW is provided with your OrCAD programs The goal function definition is as follows bandwidth of low pass response LPBW 1 db_level yl 1 sf level max db_level n 1 LPBW Vdb Vout 3 gives the low pass cutoff value on the Vdb Vout trace where the output is 3 dB below the maximum value on the trace The CMOS amplifier design The goal functions YatX and LPBW are contained in the file PSPICE PRB Every OrCAD PSpice A D installation indudes this file When loading a data file int
46. alog box double click the OPTPARAM part 122 potentiometer s center point The settings for aGain are shown below Optimizer Parameters Name Initial Value Current Value JaGain Jos Lower Limit Upper Limit Tolerance Jor 0 9 o Save Param Delete The goals The example circuit is set up with predefined goals which you can view using the PSpice Optimizer To start the PSpice Optimizer 1 From Capture s PSpice menu choose Run Optimizer The PSpice Optimizer window shows the three parameters aFc aBW and aGain and the three corresponding goals Fc BW and Gain The goals are defined as follows Table 6 1 Setting n Bandw idth Gain Name Fe BW Gain Target 10 1 10 Range 0 1 0 1 1 Analysis AC AC AC Circuit File bpf bpf bpf Evaluate CenterFreq Bandwidth max v out vdb out 1 vdb out 3 The active filter design The Fc settings as they appear in the Edit Specification dialog box are shown below nn To display the Edit Specifications dialog Name Fe RW Enabled eon Ferla 7 box double dick the lower right hand uu acai si corner of the specification box of interest in Target 10 File the PSpice Optimizer Window Range jo 1 X Column Name I Constraint Y Column Name N Fe target J olerance 18 3222 en ii Zu EN here Circa Fie eac CDC Tran bpi When finished browsing click Cancel Probe File Containing Goal Functions prb Evaluate
47. als and constraints in any combination but there must always be at least one goal You can easily change a goal to a constraint and vice versa The PSpice Optimizer accepts specifications in two formats internal and external Internal specifications An internal specification is composed of goals and constraints defined in terms of target values and ranges which are entered into the PSpice Optimizer through dialog boxes Terms you need to understand External specifications An external specification is composed of measurement data which are defined in an external data file that is read by the PSpice Optimizer Target value A target value is the ideal operating value for a characteristic of the design as defined by a goal or constraint specification Goal A goal defines the performance level that the design should attempt to meet for instance minimum power consumption A goal specification includes e The name of the goal e A target value and an acceptable range e A circuit file to simulate e An evaluation for measuring performance e Ananalysis type used for simulation based evaluations The goal specification can also include e The name of the file containing the PSpice A D goal function definitions PRB file e When using an external specification the name of the file containing measured data and the columns of data to be used as reference Note Typically the PSpice Optimizer measures performance u
48. ame Initial Current Rival 500 500 R2val 500 500 To see the settings for Rlval and R2val 1 On the schematic double click OPTIMIZER PARAMETERS By default the settings for Rival are displayed 2 To view settings for R2val click the R2val entry in the parameter list Optimizer Parameters EI Name Initial Value Current Value R1 val 500 500 Lower Limit Upper Limit Tolerance po KR BR Initial Value Current Value Save Param Delete OK Cancel 3 Click OK to close the Optimizer Parameters dialog box Defining optimization parameters The optimization parameter settings are the same for R1val and R2val as follows Setting Value Initial Value 500 Current Value 500 Lower Limit 100 Upper Limit 5k Tolerance 5 109 Chapter 5 Tutorial Optimizing a design passive terminator 110 Defining the analysis type For each specification set up an analysis which PSpice will run for each iteration of the optimization This example is already set up for a 1 point DC analysis with the supply set to 5 V To see the analysis settings 1 From the PSpice menu choose Edit Profile The Simulation Settings dialog box appears Simulation Settings DC Sweep Monte Carlo Worst Case Parametric Sweep Temperature Sweep Save Bias Point Load Bias Point 2 Under Analysis type select DC Sweep and verify the settings Running an initial circuit analysis Before optimizing ver
49. analysis other than a single point sweep analysis A goal function computes a single number from a waveform This can be done by finding a characteristic point e g time of a zero crossing or by some other operation e g RMS value of the waveform For example you can use PSpice A D goal functions to e Find maxima and minima in a trace e Find distance between two characteristic points such as peaks e Measure slope of a line segment e Derive aspects of the circuit s performance which are mathematically described such as 3 dB bandwidth power consumption and gain and phase margin To write effective goal functions determine what you are attempting to measure then define what is mathematically special about that point or set of points Note Be sure that the goal functions accurately measure what they are intended to measure Optimization results highly depend on how well the goal functions behave Discontinuities in goal functions i e sudden jumps for small parameter changes can cause the optimization process to fail PSpice Optimizer expression A PSpice Optimizer expression defines a design characteristic The expression is composed of optimizer parameter values constants and the operators and functions shown in Table 2 For example To measure the sum of resistor values for two resistors with parameterized values named Rival and R2val respectively use the PSpice Optimizer expression Rival R2val
50. andwidth at 1 MHz or greater To load the CMOS amplifier design 1 From the Windows Start menu choose the OrCAD Design Desktop program folder and then the Capture shortcut to start Capture i 2 In the Project Manager from the File menu choose Open then choose Project 3 Move to the directory containing M2 OPJ Program Files OrCA D PSpice Samples Optimize M2 and select the project file in the File Name list Vdd Il OPTIMIZER PARAMETERS Jame nitia Curren di wi 75u 75 10u Li Su Su M5 tet Iref 100uA 7OduA MP MP M2 Vin H n R4 so 10Meq a MN 50 vai jlreft I A L 10u T cpa SU MI Ro Q 10u a vi lve 19 MO g ciod A va we swit 10kT Spr L fL1 4 4 a Figure 28 Schematic for CMOS amplifier example M2 DSN The circuit consists of a common source stage M1 with active load M3 and M4 and a source follower M2 130 The CMOS amplifier design The parameters For this example there are three circuit values that you must optimize and three corresponding parameters that the PSpice Optimizer will vary e Channel length for M1 W1 e Channel width for M1 L1 e Bias current for M3 and M4 Iref Parameterized expression assignments In the schematic you can see the parameterized component values for MOSFET M1 w w1 L L1 and the current source Il Iref In preliminary tests the parameter values W1 75 m L1 5 m and Iref 100 mA produce the following pe
51. ate simulate and test analog only circuit designs OrCAD PSpice Optimizer which is an analog performance optimization program that lets you fine tune your analog circuit designs xvi The following table provides a brief description of those manuals available online only This online manual If you have the demo version Provides this OrCAD PSpice A D Online Reference Manual OrCAD Application Notes Online Manual Online Library List Reference material for PSpice A D Also included detailed descriptions of the simulation controls and analysis specifications start up option definitions and a list of device types in the analog and digital model libraries User interface commands are provided to instruct you on each of the screen commands A variety of articles that show you how a particular task can be accomplished using OrCAD s products and examples that demonstrate a new or different approach to solving an engineering problem A complete list of the analog and digital parts in the model and symbol libraries Online help Choosing Search for Help On from the Help menu brings up an extensive online help system The online help includes e step by step instructions on how to use OrCAD PSpice Optimizer features e reference information about OrCAD PSpice Optimizer e Technical Support information If you are not familiar with Windows NT or 95 Help System select How to Use Help from the Help
52. blel Summary of PSpice Optimizer related file types File type Source Description NET Generated by Capture or Netlist file and alias file respectively Define components ALS user entered with a text and connectivity analysis directives and simulation editor control directives for the circuit Refer to your PSpice user s guide for more information MDP User entered with a text External data file Contains measured data to which the editor optimization must adhere OLG Generated by the PSpice Optimization log file Contains an optimization audit trail Optimizer when running an that is useful as a debugging aid when the optimization optimization doesn t converge Have this file available when contacting Technical Support OOT Generated by the PSpice Optimization report file Provides a formatted description Optimizer when generating of the optimization specifications and parameters and a report results including derivatives and Lagrange multipliers OPT Generated by Capture when Optimization file Defines the optimization settings for the activating the PSpice circuit When an optimization is complete the PSpice Optimizer or by the PSpice Optimizer saves results on command to this file Capture Optimizer when saving also reads this file on command to back annotate the results schematic opt_0 DAT Generated by the PSpice Interim data files Contain simulation results which are opt_1 DAT Optimizer for each read by Probe to
53. bove the progress indicator shows red while the specification is violated and changes to green when the specification is satisfied You can monitor progress as the optimization runs by watching the progress indicator and observing the height of the vertical black bar relative to the tick mark s to the right The number and relative position of the tick mark s varies depending on the type of specification e Twotick marks fora goal or equality constraint denote the acceptable range around the target value e A single tick mark one quarter of the way up denotes a less than or equal to constraint e A single mark three quarters of the way up denotes a greater than or equal to constraint External spedfications Initial value The initial value field is used in a different way from an internal specification the field contains a pair of numbers separated by a character The first number is the number of subgoals in the external specification that are satisfied The second number is the total number of subgoals in the external specification Current value The current value field is used in a different way from an internal specification the field contains a pair of numbers as described above for initial value Progress indicator The progress indicator shows the fraction of subgoals that are satisfied The indicator turns from red to green when all of the subgoals are satisfied For example If an external specification has 20
54. ce 67 Target 67 Tolerance 68 Type 67 Weight 67 X Column Name 68 Y Column Name 68 Enabled check box 64 67 equality constraint 89 error gauge area 62 Evaluate text box 68 evaluation 27 for external specifications 70 See Also goal function Probe See Also PSpice Optimizer expression See Also trace function Probe examples active filter 119 bipolar transistor 139 diode biasing circuit primer 33 MOS amplifier 129 parameterizing a diode biasing circuit file 168 passive terminator 105 exploration design 74 active filter example 119 ensuring reliable results 77 tweaking values 74 expression PSpice Optimizer 27 28 external data file mdp 160 161 external specification progress indicator 60 setting up the data file 160 F File menu New command 57 Open command 57 Print command 80 Report command 80 Save As command 83 Save command 83 File text box 68 files alias als 161 circuit cir 158 161 external data mdp 160 161 log olg 81 161 netlist net 161 opt_0 dat 161 opt_1 dat 161 optimization opt 55 83 158 161 parameter par 165 parameters par 158 161 Probe goal functions prb 40 159 report oot 80 161 fitting data to model parameters 148 bipolar transistor example 139 G global minima 92 93 goal 24 25 compared to constraints 86 progress indicator 60 target value 25 See Also specification goal function Probe 28 def
55. ch satisfies both the goal current of 1 mA and the constraint power dissipated in the resistor greater than 4 mW Figure 9 shows the results 48 E Optimizer mydiode opt Derivs Avail File Edit Tune Options Help Specifications AMS Ero _ ae e a Optimization complete Specs met Figure9 Results after changing the constraint type Using standard component values When an optimization completes successfully the optimizer displays the new parameter values in the PSpice Optimizer window However each calculated value might not correspond to an actual value that is available with off the shelf components For example resistors are not readily available in all possible values You can use the PSpice Optimizer to select standard component values The optimizer either e rounds to the nearest value or e computes values based on the most recent optimization run To round to the nearest standard component value 1 From the Edit menu select Round Nearest Rival s current value changes to 3 9 k in accordance with the specified 10 tolerance Phase Three Running an optimization See Using standard part values on page 3 82 for more information induding how the PSpice Optimizer uses tolerances and limits when standardizing values Bak rounded resistor value 49 Chapter 2 Primer How to optimize a design Producing reports You can use the PSpice Optimizer to generate a report summarizi
56. dialog box controls continued Control name Meaning File Name of the file that contains the measured data X Column Name Heading for the data column in File containing the independent X values Y Column Name Heading for the data column in File containing the dependent Y values Tolerance Tolerance value used when standardizing component values Syntax lt 0 lt integer value lt 100 gt Analysis Settings Analysis Type Kind of analysis used for simulation based evaluations e Select AC for AC sweep analysis e Select DC for a DC sweep analysis e Select Tran for a transient analysis Circuit File Set to either e the name of the circuit file PSpice uses for simulation or e leave blank if the Evaluate text box contains a PSpice Optimizer expression Evaluate Trace function Probe goal function or PSpice Optimizer expression used to measure performance See Defining an evaluation for an external specification on page 3 70 for the purpose and use of the part in the Evaluate edit control 68 Adding and editing specifications To create a specification based on an existing specification 1 Note From PSpice Optimizer s Edit menu choose Specifications Select the specification that you want to copy and click Copy Notice that the Insert button is now enabled no longer grayed out Click Insert to add a copy of the selected specification to the parameter list The optim
57. ds without satisfying the goal Ei Optimizer mydiode opt Derivs Avail File Edit Tune Options Help Specifications Optimization ended no more progress Figure 8 Results after adding the power constraint Note that the power dissipated in R1 is exactly equal to the target value of the constraint 4 mW In this example there is no feasible solution to the problem 47 Chapter 2 Primer How to optimize a design However the PSpice Optimizer found the lowest value for Id1 which does not violate the constraint Changing the constraint and rerunning the PSpice Optimizer You can examine the effect the Pc constraint has on performance by changing its constraint type so the power dissipation in the resistor must be greater than or equal to 4mW To change the Pc constraint type to greater than or equal FR 1 In PSpice Optimizer double click the lower ow Todi giu right hand corner of the Pc box 2 In the Edit Specifications dialog box change Type to gt target 3 Click OK To run the optimization with the modified constraint 1 Test performance with the updated constraint a From the Edit menu choose Reset Values b From the Tune menu choose Update Performance The Pc constraint is initially violated because the power dissipation is less than 4 mW 2 From the Tune menu choose Auto and click Start to start optimization The PSpice Optimizer finds a solution whi
58. duced by the model More formally given a set of N data points x y a model that has M parameters aj and a model relationship of the form yx yorzay ay the optimizer chooses the parameters aj to minimize N Y by ya ag i 1 The bipolar transistor test case This tutorial fits parameters to a bipolar transistor BJT model using measured data for Ic and Ib versus Vbe at constant Vce To load the BJT design 1 From the Windows Start menu choose the OrCAD Design Desktop program folder and then the Capture shortcut to start Capture 2 In the Project Manager from the File menu choose Open then choose Project 3 Move to the directory containing BJTPAR OPJ Program Files OrCA D PSpice Samples Optimize Bjtpar and select the project file in the File Name list Vee Vor O R Vee Q2N3055 Pi Figure 31 Schematic for the BJT model fitting example The circuit has voltage sources for Vbe and Vce and an instance Q1 of a BJT Q1 is a QbreakN device with its model reference set to Qx the name of a BJT model The schematic also includes an instance of a 2N3055 This is the model that was used to produce the measured data The 2N3055 in the schematic works as a reference during model fitting The bipolar transistor test case The QX model definition for this example is contained in the BITP AR INC include file To check whether this file is included from the PSpice menu
59. e Optimizer is a circuit optimization program that improves the performance of analog and mixed analog digital circuits The PSpice Optimizer is fully integrated with other OrCAD programs This means you can design your circuit with OrCAD Capture simulate and analyze results with OrCAD PSpice A D or OrCAD PSpice and optimize performance within the same environment How to use this guide How to use this guide This guide is designed so you can quickly find the information you need to use the OrCAD PSpice Optimizer This guide assumes that you are familiar with Microsoft Windows NT or 95 including how to use icons menus and dialog boxes It also assumes you have a basic understanding about how Windows manages applications and files to perform routine tasks such as starting applications and opening and saving your work If you are new to Windows please review your Microsoft Windows User s Guide Typographical conventions Before using the OrCAD PSpice Optimizer it is important to understand the terms and typographical conventions used in this documentation This guide generally follows the conventions used in the Microsoft Windows User s Guide Procedures for performing an operation are generally numbered with the following typographical conventions Notation Examples Description Ctrl R Press Ctri R A specific key or key stroke on the keyboard monospacef Type VAC Commands text entered ont from the ke
60. e insensitive to changes in the parameters waveform display When the iterationis complete Because of this the value of Delta is the display should look something like the one increased to 3 from its default value of shown in Figure 32 This display compares the 1 See Controlling finite curves for Ic and Ib with curves for an instance of differencing when calculating a 2N3055 The percentage error for Ic and Ib is also derivatives Delta option on displayed in the uppermost plot page 4 98 for more information E BJTPAR BJTPAR DC Sweep OrCAD PSpice A D BJTPAR BJTPAR DC Sweep dat EE Fie Edit View Simulation Trace Plot Tools Window Help 18 x je szus nun mn mmmm ja amp amp amp 9 m E x E 7 a gt ct P Pees 8 o 199 ic q1 ic q2 1 gt 190 ib q1 ib q2 1 N o ELSE o Ic Q1 Ic Q2 TE SEL gt gt FI Scan vi I I i 4 6uat 460nU 45 0nU 500nU 55 0mU 690nU 650mU 700nU 75 0mU 800nU 850nU v Ib Q1 A Ib Q2 U_Ube T E BUTPARBI mu For Help press Fi 100 EGRESS DI 2 Figure 32 Initial traces for the Ic and Ib parameters 147 Chapter 8 Tutorial Fitting model data bipolar transistor Fitting the data The PSpice Optimizer looks for a set of parameters which minimizes the total squared error between the measured and simulated curves When using external data the optimizer uses the r
61. e of 13 825 The target is 10 0 which is a change in the right direction Center frequency and bandwidth also change In the case of center frequency the change from its initial value of 8 322 to a new value of 8 298 is in the wrong direction This frequently occurs You can try various strategies to get closer to the target values Two common approaches are e Adjust a given parameter to get the best results then vary the other parameters Example Continue to adjust aGain until you are satisfied with the performance Then incrementally change Fc until you are satisfied And finally change BW e Change every parameter in the set by a small amount at a time and continue in this manner to get the best results Example Adjust aGain once by a small amount then Fc then BW Continue with this pattern of adjustments until you are satisfied Testing performance MW aGain 0 4 new parameter value ps M Fe ely BW e M Gain e 8 2976 0 712009 13 8246 8 3222 0 712189 msm pdated goal values 125 Chapter 6 Tutorial Exploring design tradeoffs active filter M Gain e i 14 8106 N new goal value 126 updated param eter values Tweaking goals and constraints The PSpice Optimizer gives you the advantage of doing something not possible on the bench changing the
62. e optimization on page 2 37 walks you through the steps needed to define the parameters goals and constraints that describe the optimization Chapter 2 Primer How to optimize a design e Phase Three Running an optimization on page 2 42 walks you through the steps needed to optimize and finalize the design 32 Optimizing a diode biasing circuit the objective Optimizing a diode biasing circuit the objective Assume that you want to design a circuit that drives a current of 1mA 5 uA through a diode D1N914 using a 5Vvoltage source and a series resistor to control the current through the diode A circuit such as this is shown in Figure 2 y DI D1N914 Figure 2 Diode biasing design example Your objective is to find a value for resistor R1 so that current through diode D1 falls in the range 0 995 mA to 1 005 mA 33 Chapter 2 Primer How to optimize a design When solving complex problems the manual approach can be too unwieldy to consider For example When your design has multiple parameters or complicated parameter interactions you may find it s nearly impossible to know which parameters to change and how best to change them When solving for multiple specifications the solution often depends on the order in which goals and constraints are optimized This sequential approach can miss possible solutions since it is impractical to repeat the process starting with a different goal
63. elative error at each measured point This means that all points have equal weight regardless of the absolute value This is essential for fitting semiconductor curves where the currents may range over many orders of magnitude Automatic normalization is discussed in detail in Target value scaling on page 4 97 To fit the data to the model parameters 1 From the Tune menu choose Auto and click Start The following table compares the model parameter values estimated by the PSpice Optimizer to the data values measured by PSpice for the 2N3055 transistor Table 8 6 Parameter en Measured from PSpice Is 9 744e 13 9 744e 13 Ikf 4 071 4 029 Br 5 2 949 Bf 98 465 99 49 Ise 9 920e 10 9 025e 10 Ne 1 960 1 941 The estimated parameters compare well with the original values The results of the optimization are shown in Figure 33 148 Fitting the data EEE i Optimizer Bitpar opt Derivs Avail File Edit Tune Options Help Specifications 143 743 0743 W Ib 143 743 0743 W le Parameters RMS Error kt V Br W Bf Vils 9 327e 002 98 4652 4 07062 5 V Ne 1 96049 1 5 Optimization complete Specs met 19 744059e 013 11 000000e 013 11 000000e 010 9 920115e 010 M Ise Simulations Iteration 11 Figure 33 Optimization results for the BJT model fitting example Eee ee re spere Ta
64. eters the PSpice Optimizer will vary All other model parameters are left unchanged For example using the Model Editor the forward beta is specified as bf bf The bipolar transistor test case The analysis The BJT example is set up for a DC sweep of the voltage source which provides a range of values for Vbe These values should match the measurement points contained in the external data file Ic and Ib are measured at values of Vbe starting from 0 4 V incrementing by 0 01 V toa maximum of 0 82 V The external file of measured data There are two measured curves Ic and Ib Each of these has an associated PSpice Optimizer specification When fitting model parameters specifications are different from those used in other kinds of optimizations because they reference an external data file For the BJT example both sets of measured data are contained in the 3055 MDP file A portion of this file is shown below Vbe Ic Ib 4 000E 01 6 047E 06 2 655E 06 4 100E 01 8 900E 06 3 253E 06 A 200E 01 1 310E 05 3 989E 06 4 300E 01 1 928E 05 4 897E 06 8 100E 01 8 002E 00 1 922E 01 8 200E 01 9 092E 00 2 371E 01 The file contains 3 columns of data Vbe Ic and Ib The first non blank line in the file contains names for the columns of data These map to the specification setup in the PSpice Optimizer 143 Chapter 8 Tutorial Fitting model data bipolar transistor To display the Edit Specifications dialog box double click the l
65. ether the design still meets specifications You can also change the value of the specification s and immediately determine how parameter values change If you are dissatisfied with the result after any change you can always return to the last set of values Phase One Developing the design Phase One Developing the design Before optimizing you must have a working circuit This Phase 1 is also the time to investigate means first drawing the design then iteratively e The effects of individual components simulating with PSpice A D and adjusting the design by replacing component values with until the circuit operates with the intended behavior parameters or parameterized expressions e Using PSpice A D to perform a DC AC or parametric sweep of each parameterized value OrCAD Capture Design schematic OrCAD PSpice A D Figure 3 Design flow for developing the design To draw the schematic page for the diode biasing design 1 In Capture s Project Manager choose New under the File menu then choose Project 2 Enter MYDIODE as the name of the new project 3 Select Analog or Mixed signal Circuit Wizard to make this a design that can be simulated with PSpice 4 Click OK then click Finish A blank schematic page will appear gt From the Place menu choose Part to select and place the following parts on the schematic page 35 Chapter 2 Primer How to optimize a design Note When you initially place resist
66. fication you want to edit and click Change Measuring and Optimizing Performance This section describes how to e Optimize your design once all of the parameters and specifications are defined e Monitor progress using the waveform viewer in PSpice A D Optimizing Your Design Optimization is a two stage process 1 Running one evaluation to ensure that the circuit is valid and that it simulates 2 Starting the optimization process Measuring and Optimizing Performance A double click here Edit menu Parameters Store Values Reset Values Round Nearest Round Calculated Update Schematic 71 Chapter 3 Using the PSpice Optimizer Tune menu Tune menu Update Performance Update Derivatives 10w Derivative See Viewing the optimization log on page 3 81 for information on the audit trail the PSpice Optimizer generates when running an optimization 72 To optimize your design 1 From the Tune menu choose Update Performance The PSpice Optimizer measures the design s performance using both the initial and current values for each of the parameters The optimizer updates the initial and current fields respectively for each specification and sets the progress indicators showing how closely these initial measures match each of the target values From the Tune menu choose Auto and click Start The PSpice Optimizer computes the derivatives for each specif
67. fine goals amp constraints Figure 4 Design flow for setting up the optimization Phase Two Setting up the optimization 37 Chapter 2 Primer How to optimize a design You can also define optimization parameters in the PSpice Optimizer by selecting Parameters from the Edit Menu See Adding and editing parameters on page 3 63 for more information The parameter settings are Name R1Val Initial Value 5k Current Value 5k Lower Limit 100 Upper Limit 10k Tolerance 10 Later in Capture when you select Run Optimizer from the PSpice menu the parameters specified with the OPTPARAM part are loaded into the PSpice Optimizer and displayed in its main window 38 Defining design parameters To define parameters for optimization you must Identify the parameters to adjust for optimization and assign a unique name to each one Set up each parameter as a global optimization parameter using Capture Select which components in the design are affected by the parameter and for each component replace its value e g the value of its VALUE property with an expression that includes the parameter name To prepare the diode design example for optimization you need to parameterize the value of R1 and specify its optimization properties To set up the value of R1 as a parameter named R1Val 1 4 From Capture s PSpice menu choose Place Optimizer Parameters to place an instance of the OPTPARAM part from
68. formance using information in the circuit file and PRB file Remember that for a simulation based optimization you must define how to evaluate performance This means that for each specification goal or constraint you must define the following What drauit file to use Typically an optimization uses only one simulation profile or circuit file based on the design that is active in Capture when you start the PSpice Optimizer But you can set up the optimization to use a different circuit file for each specification Which analysis to run The circuit file contains the analysis directives for any PSpice simulations e g DC sweep transient etc that you set up for the schematic However you control which analyses are actually run for an optimization when you define how to evaluate each specification in the Edit Specifications dialog box How to measure performance If to evaluate performance your optimization is based on a multi point simulation you must define goal functions Goal functions reside in the GOAL FUNCTIONS section of a PRB file By default a given design references the global PRB file shipped with all OrCAD programs PSPICE PRB in the OrCAD root directory PSpice Common and a local PRB file design_name PRB in the working directory File and program relationships 159 Chapter B File types used by the PSpice Optimizer Vbe Ic Ib 4 000E 01 6 047E 06 2 655E 06 4 100E 01 8 900E 06 3 253E 06 4 200E
69. g 79 saving final values 83 saving for netlist based design 167 saving intermediate values 79 Results Recalculate command Options menu 77 RMS error 62 Round Calculated command Edit menu 83 Round Nearest command Edit menu 82 S Save As command File menu 83 Save command File menu 83 Schematics 22 back annotating 84 defining optimization parameters OPTPARAM symbol 38 OPTPARAM symbol 55 61 84 Show Derivatives command Tune menu 81 simulation monitoring with Probe 73 single point analyses 27 specification 24 adding from scratch 66 conflicting 27 copying 69 Edit Specification dialog box controls 67 enable disable 78 excluding from optimization 78 external 25 60 160 function behavior and accuracy 91 internal 24 59 target value 25 tweaking values 74 See Also constraint See Also goal specifications area Optimizer Window Enable check box 78 specifications area optimizer window 59 edit hot spot 78 external current value 60 173 Index initial value 60 W internal current value 59 initial value 59 Weight text box 67 progress indicator 60 X progress indicator 60 Start command Auto submenu Tune menu 72 X Column Name text box 68 starting points and global and local minima 92 93 and parameter bounds 94 Y feasible 89 improving convergence 93 infeasible 89 Store Values command Edit menu 79 subgoal progress indicator 60 Y Column Name text box 68 T
70. g component values Enabled When selected includes the parameter in the next optimization run If cleared excludes the parameter To create a parameter based on an existing parameter 1 From PSpice Optimizer s Edit menu choose Parameters 2 Select the parameter that you want to copy and click Copy Notice that the Insert button is now enabled no longer grayed out 3 Click Insert to add a copy of the selected parameter to the parameter list The optimizer inserts the new parameter immediately above the highlighted parameter 4 Select the new parameter in the list and click Change gt Change the Name text box to a unique name and change any other controls as needed 64 6 When finished click OK to return to the Parameters dialog box Note You cannot copy a parameter description from one optimization file to another Instead save an entire optimization file under a new name then edit the new version as needed Selecting a parameter to edit You can change the properties of an existing parameter at any time using the Edit Parameter dialog box To display the Edit Parameter dialog box for a parameter 1 Doone of the following or In the parameters area of the PSpice Optimizer window double click the lower right hand corner of the box for the parameter you want to edit From the Edit menu choose Parameters then select the parameter you want to edit and click Change Adding and editing parame
71. g values Because the PSpice Optimizer uses derivative data to estimate what will happen when a parameter or a specification is changed and because the design usually depends on the parameters in a highly nonlinear way results are typically reliable only for small changes in values Once you have significantly changed values resimulate and recompute the derivatives before adjusting values any further To ensure that results are reliable after significant tw eaking 1 From the Tune menu choose Update Performance The PSpice Optimizer will run the appropriate simulations and update the specifications 2 From the Tune menu choose Update Derivatives You are now ready to continue exploring the design Recalculate click here to recalculate specifications Results Parameters click here to recalculate parameters 77 Chapter 3 Using the PSpice Optimizer enable disable check box FM Ne ni double dick here 78 Excluding parameters and specifications from optimization Every specification and parameter has a check box that you can select to exclude that specification or parameter from the next optimization run To exclude a parameter or specification from an optimization 1 Do one of the following e Inthe PSpice Optimizer window clear the check box check box should be empty to the left of the parameter or specification name e Double click the lower right
72. hand corner of the box for the parameter or specification you want to exclude clear the Enabled check box check box should be empty in the dialog box and click OK Note When you exclude a specification from optimization the PSpice Optimizer still re evaluates its performance when you update the parameters or derivatives It is also included in the matrix of partial derivatives Testing performance when adding or changing parameters or specifications Even after running an optimization you can add new parameters and specifications or change the properties of existing definitions to see their effect on performance To test performance after changing the parameters or specifications 1 From the Edit menu choose Reset Values 2 From the Tune menu choose Update Performance 3 If you want to run a complete optimization a From the Tune menu choose Auto b Click Start Saving intermediate values You can save a set of parameter and specification values and then continue to investigate performance To save intermediate values 1 From the Edit menu choose Store Values The PSpice Optimizer copies the current values to the initial values for all specifications and parameters To restore the previous settings 1 From the Edit menu choose Reset Values The PSpice Optimizer copies the initial values to the current value fields View ing result summaries This section describes how to e Generate a report that summarizes
73. he dbias par file containing the parameter definition for Rbias using this syntax PARAM Rbias 5k 2 Parameterize the circuit file as shown added or changed items are in bold diode bias circuit INC dbias par this line added LIB V1 10 5v R1 1 2 Rbias this line modified D1 2 0 DIN914 DC Vl LIST 5V Probe END Now you are ready to start the PSpice Optimizer complete setup and run the optimization Index 1 70 als file 161 cir file 158 161 dat file 95 mdp file 160 161 net file 161 olg file 81 161 oot file 80 161 opt file 55 83 158 161 par file 158 161 165 prb file 40 159 A accuracy and Delta value 99 and derivatives 96 and failed convergence 93 and RELTOL 99 and Threshold value 102 improving 92 99 activation automatically loading an optimization file 57 changing startup options 56 from Schematics 55 from Windows 95 56 with a different initialization file 56 active constraint 90 Add Parameters command Edit menu 63 Add Specifications command Edit menu 66 Advanced Options Defaults command Options menu 101 alias file als 161 analysis type options 68 Auto submenu Tune menu 72 automatic recalculation 74 75 back annotation 84 bound constraint 88 C Change Parameter command Edit menu 64 Change Specifications command Edit menu 69 circuit file cir 158 161 as alternative to a schematic 164 i
74. he following tutorial shows you how to use the PSpice Optimizer to fit a parameterized model to a set of measured data points Using the bipolar transistor example provided with your OrCAD programs you will e Review the bipolar transistor test case schematic parameter definitions and parameterized expression assignments analysis and external file with measured data e Review the goal setup in the PSpice Optimizer e Setup PSpice A D and the PSpice Optimizer to monitor intermediate waveform results e Run the fitting process Chapter 8 Tutorial Fitting model data bipolar transistor 140 Using the PSpice Optimizer to fit data to model parameters The PSpice Optimizer can fit a parameterized model to one or more sets of data points The source for this external data might be e Results from measuring a real device e g using a semiconductor curve tracer e A manufacturer s data sheet e A PSpice simulation To fit a model using the PSpice Optimizer you need a text file containing the measured values and the measurement points For example For static I V characteristic of a diode the external data file would contain pairs of values where each pair consists of the voltage at which the measurement was made and the current through the device at that voltage The PSpice Optimizer performs a least squares estimation of the parameter values that result in the best fit between the external data and the values pro
75. he initial value fields Note that this value example requires one PSpice simulation to update the performance Starting the optimization You are now ready to run the full optimization to find resistor values which satisfy the two specifications output voltage 3 75 V equivalent resistance 100 Q To start optimizing 1 From the Tune menu choose Auto and click Start First the PSpice Optimizer computes the derivative of each specification with respect to each parameter at the initial value While this is in progress the message Updating Derivatives appears in the status bar of the optimizer window In this example two simulations are performed one for each parameter Using the derivative information the optimizer selects a direction in which to vary the parameters The optimizer tries parameter changes along this direction until it achieves a reduction in the overall error The optimizer then updates the parameters and computes new derivatives 115 Chapter 5 Tutorial Optimizing a design passive terminator The optimizer repeats this process until it achieves success failure or you terminate the process from the Tune menu point to Auto and select Terminate For this example let the process run to completion This takes 5 more simulations As the optimization proceeds the vertical gauge and numeric display fields in the error gauge area far left in the PSpice Optimizer window show updated values The
76. he square root of a bias current and as the reciprocal of a transistor dimension Performance The performance of a design is a measure of how closely its specifications calculated values approach their target values for a given set of parameter values When there are multiple specifications at least one of which is a goal the PSpice Optimizer uses the sum of the squares of their deviations from target to measure closeness For a single specification goal the PSpice Optimizer uses either the goal s value or the square of its deviation from target Each aspect of a design s performance is found by either e First performing the appropriate simulation then running PSpice A D to measure characteristics of the resulting waveform s or e Evaluating PSpice Optimizer expressions In many cases particularly if there are multiple conflicting specifications it is possible that the PSpice Optimizer will not meet all of the goals and constraints In these cases optimum performance is the best compromise solution that is the solution that comes closest to satisfying each of the goals and constraints even though it may not completely satisfy any single one Evaluation An evaluation is an algorithm that computes a single numerical value which is used as the measure of performance with respect to a design specification The PSpice Optimizer accepts evaluations in one of these three forms e Single point PSpice A D trace f
77. hen restarting optimization after adjusting parameters or specifications This is useful when exploring design tradeoffs by tweaking parameter and specification values 43 Chapter 2 Primer How to optimize a design 44 Starting parameter values Evaluate performance Compare to specifications Iteration limit reached Evaluate derivatives Compute new parameter values Convergence fails Figure 6 PSpice Optimizer automatic optimization process To start optimizing the diode design 1 From the Tune menu select Auto and click Start The PSpice Optimizer performs several simulations For each iteration of the parameter values the optimizer calculates overall performance and graphically displays the results The optimizer also calculates the value of the trace function I d1 and displays the new value in the specifications area of the PSpice Optimizer window After three iterations the optimizer should converge on a solution of 4 131 k as shown in Figure 7 B Optimizer mydiode opt Derivs Avail Ele Edt Tune Options Heb Specifications M Idi 1 00163ma j Optimization complete Specs met Figure 7 Optimization results for the diode design example Adding a constraint and rerunning the PSpice Optimizer So far you have optimized for a single goal Id1 Now suppose you want to add a condition or constraint on the power dissipated in resistor R1 Pha
78. ication with respect to each parameter and uses this information to determine the direction in which to vary the parameters With each iteration the optimizer tries parameter changes along the chosen direction and measures performance until it achieves a reduction in the overall error The optimizer then updates the parameters calculates new derivatives and repeats the process until one of the following occurs e Specifications are met success e No more progress can be made failure e You manually interrupt the process To cancel the optimization run 1 2 From the Tune menu choose Auto Click Terminate Measuring and Optimizing Performance Graphically monitoring progress To see how well specifications are approaching the optimization requirements use the waveform viewer in PSpice A D to monitor the simulation results from each of the iterations To monitor optimization progress 1 From Capture s PSpice menu choose Simulate Active to simulate the circuit 2 Create a display configuration a InPSpice A D add the traces from the Trace menu choose Add Trace and modify the axes from the Plot menu choose Axis Settings to appear as you want them to when monitoring intermediate results From the Window menu choose Display Control Inthe New Name text box enter a name for the waveform display and click Save d Click Close 3 Define the waveform display to use when optimizing a From PSpice
79. ify that the circuit works and check that the voltages at Vc and Vr are as you expect To test the circuit setup 1 From Capture s PSpice menu choose Run Starting the PSpice Optimizer From PSpice A D s Trace menu choose Add Trace and click v vc and v vr Click OK Verify that the voltages at Vc and Vr are 2 5 V and 250 V respectively Starting the PSpice Optimizer Assuming the circuit simulated successfully you are now ready to start the PSpice Optimizer and complete optimization setup To start the PSpice Optimizer 1 From Capture s PSpice menu choose Run Optimizer The PSpice Optimizer window displays the current optimization file TERM OPT in the title bar i Optimizer Term opt File Edt Tune Options Help Specifications W Rival W Reval The two parameters Rival and R2val appear in the parameters area Because the specifications Vc and Rt are predefined for this example circuit they also appear in the specifications area Initially the error gauge area is empty 111 Chapter 5 Tutorial Optimizing a design passive terminator Name Rival Current Value Initial Yalue Upper Limit Lower Limit 112 500 500 p VW Enabled View ing the parameter description The PSpice Optimizer automatically loads the parameter descriptions defined earlier in Capture To verify the parameter descriptions 1 From the Edit menu choose Parame
80. ile into PSpice A D then from the Trace menu choose Eval Goal Function to test the goal function Refer to online Help in PSpice A D for more information on writing goal functions Optimization was aborted because of an error or user termination PSpice Optimizer numbers are real numbers with an optional suffix T G Meg k m u n p f mil and an optional symbol for units Specifications must be given names Type in an ASCII string in the Name text box in the Edit Specification dialog box The current and initial values for a parameter must be greater than the Lower Limit These values can be changed on the OPTPARAM symbol in Capture or select Parameters from the Edit menu in the PSpice Optimizer The Upper Limit of a parameter must be greater than the Lower Limit and less than the Upper Limit specified These values can be changed on the OPTPARAM symbol in Capture or select Parameters from the Edit menu in the PSpice Optimizer 153 Chapter A Error messages Error message Description 11020 Evaluation Field Required 11021 Column Name Required 11022 Would Exceed Max Params 11023 Would Exceed Max Specs 11024 All Params Are Disabled 11025 Can t Open File 11026 Problem With External Spec 11027 Max Iterations Exceeded 11028 Terminated 11029 Can t Make Progress 11030 No External File 11031 External Spec Bad Format 11032 Unrecognized Expression
81. ima within the domain of interest If local minima do exist the global minimum may be the nearest solution to the starting point This is discussed further in Starting points on page 4 93 Starting points Starting points Itis important to begin with a good estimate of the starting point There are two reasons for this e The process may converge to the wrong solution a local minimum rather than to the right solution the global minimum For example Consider Figure 20 If point A is chosen the PSpice Optimizer will most likely find local minimum M1 If point B is chosen the optimizer will most likely find the global minimum M2 e The PSpice Optimizer may require a large number of simulations to find a region close to a solution It is usually more efficient to find the approximate location of the desired solution perhaps by performing a number of analyses sweeping out ranges of the parameters before starting the optimization process Convergence When running an optimization the PSpice Optimizer varies the parameter values and measures the resulting performance For each subsequent iteration the optimizer chooses each parameter step to reduce the error between the design s measured and specified target performance If the optimizer finds a solution where all of the specifications are met then the process has converged There are several common reasons why the process may fail to converge e There is no solution to
82. ing automatic recalculation 1 Do the following to enable automatic recalculation When frame in the a From the Options menu choose Recalculate Recalculate dialog box b Inthe When frame choose Auto c Click Close 2 From the Tune menu choose Update Derivatives When derivative calculations are complete the message Derivs Avail appears in the title bar display the latest derivative data When Auto Manual Tune menu Auto 75 Chapter 3 Using the PSpice Optimizer The PSpice Optimizer accepts numerical entries in any format supported by PSpice Refer to the online OrCA D PS pice A D Reference Manual for a complete list of supported numeric forms When When frame in the ca Recalculate dialog box Manual Tune menu Update Performance Update Derivatives Update atives Show Derivatives Auto E The PSpice Optimizer accepts numerical entries in any format supported by PSpice Refer to the online OrCA D PS pice A D Reference Manual for a complete list of supported numeric forms 76 3 Change the current value for the parameter or specification you want to investigate a Double click in the current value upper field for a parameter or specification b Enter the new value C Press Enter The PSpice Optimizer immediately recalculates the values When you change parameter values a small e appears next to the progress indicator for each recalculated specificat
83. ings are also saved Updating the schematic Having completed the optimization you can update the data in the schematic file to include the optimized parameter values To update the diode schematic with the current parameter values 1 From the Edit menu select Update Schematic Recall that R1Val was initially set at 5 0 k in the schematic file When you select Update Schematic the PSpice Optimizer sends a message to Capture to update the design file Capture writes the new parameter value of 3 9 k to the OPTPARAM part on the schematic as the current value Figure 11 shows the updated schematic for the diode design OPTIMIZER PARAMETERS Name Initial Current Rival Sk 3 9k x7 DI M DINYI4 Figure 11 Updated diode schematic 51 Chapter 2 Primer How to optimize a design 52 Using the PSpice Optimizer Chapter overview This chapter describes in general terms how to complete any task using the PSpice Optimizer including How to activate the PSpice Optimizer and load a design page 3 55 How to interact with the PSpice Optimizer window page 3 58 How to add and edit optimization parameters page 3 63 How to add and edit goals and constraints page 3 66 How to measure and optimize performance page 3 71 How to explore design tradeoffs page 3 74 How to generate result summaries including Lagrange multipliers and derivative values page 3 79 Chapter 3 Using the PSpice Optimi
84. ining prb file 40 159 discontinuities 28 Index inactive constraint 90 inequality constraint 88 initial value external specification 60 internal specification 59 parameter 61 Initial Value text box 64 Insert Parameters command Edit menu 64 Insert Specifications command Edit menu 69 interactive design exploration 34 interim data file opt_x dat 161 iterations and Cutback 101 controlling parameter value changes 101 limiting 99 L Lagrange multipliers 88 90 least squares 103 constrained 23 unconstrained 23 Least Squares option 104 local minima 92 93 log file olg 161 viewing 81 Lower Limit text box 64 M manual recalculation 76 Max Iterations option 99 minima and starting points 92 93 constrained 89 global 92 93 local 92 93 minimization 103 bound constrained 94 constrained 23 unconstrained 23 94 Minimize option 104 model parameters fitting 148 bipolar transistor example 139 171 Index Name text box 64 67 netlist file net 161 netlist based design 164 New command File menu 57 nonlinear constraint 88 O Open command File menu 57 opt_0 dat file 161 opt_1 dat file 161 optimization 23 aborting 72 adding editing parameters and specifications and specification functions 91 choosing least squares or minimization 103 constrained least squares 23 constrained minimization 23 constrained vs unconstrained 87 controlling parameter per
85. ion to show that the value is an estimate based on derivative data Manually recalculating performance When you want to change multiple values before recalculating performance disable recalculation As with automatic recalculation derivative data is required To test performance using manual recalculation 1 Disable automatic recalculation a From the Options menu choose Recalculate b Inthe When frame choose Manual c Click Close From the Tune menu choose Update Derivatives When derivative data is calculated the message Derivs Avail appears in the title bar Change the current value for the parameter or specification you want to investigate a Double click in the current value upper field for a parameter or specification b Enter the new value C Press Enter From the Options menu choose Recalculate to recalculate performance Exploring the effect of parameter and specification changes 5 Select the kind of recalculation as follows e Ifyou entered a new parameter value click Results The PSpice Optimizer recalculates performance A small e appears next to the progress indicator for each recalculated specification to show that the value is an estimate based on derivative data e Ifyou entered a new specification value click Parameters The PSpice Optimizer recalculates values for all of the parameters based on the current specification values Ensuring reliable results when tweakin
86. itial and current value fields and the progress indicator Internal specifications Initial value The initial value field displays a single performance measure that the PSpice Optimizer sets when you start an optimization The optimizer derives this value from the initial optimization parameter values you defined in the schematic or the optimizer Current value The current value field displays the performance measure that corresponds to the current parameter values Current values are updated each time an optimization iteration makes progress When the current value satisfies the specification that is the current value is within the allowed range of the target then the progress indicator turns from red to green and the PSpice Optimizer considers the specification satisfied The PSpice Optimizer Window For more information on the enable disable check box see Excluding parameters and specifications from optimization on page 3 78 For more information on the edit hot spot see Selecting a specification to edit on page 3 71 If derivative data is available you can change the value in this field to explore how parameter values might change See Testing performance when changing current values on page 3 74 for more information 59 Chapter 3 Using the PSpice Optimizer goal or equality constraint less than or equal to constraint greater than or equal to constraint 60 Progress indicator As mentioned a
87. ization the PSpice Optimizer computes The PSpice Optimizer calculates derivatives the matrix of partial derivatives the Jacobian either e once when you select Update Derivatives from the Tune menu or e automatically for each iteration when How the PSpice Optimizer estimates derivatives on Sartopkinization by decine The PSpice Optimizer approximates derivatives using a pee TUG MEN finite difference approach In one dimensional terms this See Exploring the effect of method computes an approximation to the first derivative parameter and specification of a function f x by changes on page 3 74 for more information f x fa t f x where h is a small perturbation The optimizer organizes the simulations and evaluations to compute the Jacobian in the most efficient way possible Example If there are two specifications each of which requires a DC analysis of the same circuit file the optimizer will run a single simulation for each parameter then load the data file DAT into PSpice A D and evaluate the perturbed values of f If there are M specifications all using the same analysis type and the same circuit file and N parameters then forming the Jacobian takes e N simulations and e M Probe goal function evaluations per simulation Note The time needed to simulate is usually much greater than the time needed to evaluate the goal functions This means that the time taken to optimize a design depends heavil
88. izer inserts the new specifications immediately above the highlighted specification Select the new specification in the list and click Change Change the Name text box to a unique name and change any other controls as needed When finished click OK to return to the Specifications dialog box You cannot copy a specification description from one optimization file to another Instead save an entire optimization file under a new name then edit the new version as needed 69 Chapter 3 Using the PSpice Optimizer After substitution the PSpice Optimizer does one of the following depending on the kind of evaluation e For a waveform analysis goal function the optimizer sends the substituted goal function to PSpice A D for evaluation e For a PSpice Optimizer expression the optimizer evaluates the expression directly See Chapter 8 Tutorial Fitting model data bipolar transistor for another example using this technique 70 Defining an evaluation for an external specification When defining evaluations for external specifications use the part within the evaluation as a placeholder for data in the external file For each of the subgoals in the external file the PSpice Optimizer first replaces the character with the X column data value defined in the X Column Name text box in the Edit Specification dialog box and then proceeds with evaluation This approach allows a waveform analysis goal function
89. l Constraint check box is cleared The analysis type is DC and the evaluation to measure performance is the trace function V Vc as in the preliminary test simulation 3 Click Cancel to leave the specification unchanged 4 To see the settings for the Rt goal click Rt then click Change Name Rt Enabled Reference B Internal C External Weight fo r Internal External Target 100 File panged X Column Name T Constraint Y Column Name Type target E Tolerance 196 Analysis Circuit File CAC DC C Tran term Probe File Containing Goal Functions prb Evaluate RO Cancel Again the analysis type is DC and the evaluation to measure performance is the trace function V Vr gt Click Cancel to leave the specification unchanged 6 Click Close to exit the Edit Specification dialog box 114 Checking that the design will simulate Checking that the design will simulate Before running a full optimization you should run a single iteration to make sure the design still simulates by selecting Update Performance from the Tune menu The PSpice Optimizer performs the simulations and trace function evaluations required to find the current value for each active specification and updates their initial values For this example an initial iteration has already been run are FA The Vc specification shows 2 5 and the Rt specification a a inital shows 250 in t
90. l is varied This means setting up a single point voltage sweep To set up a single point voltage sweep analysis at 5 volts 1 From Capture s PSpice menu choose New Simulation Profile then enter aname DC Sweep for the profile The Simulation Settings dialog box appears 2 Under Analysis type select DC Sweep 39 Chapter 2 Primer How to optimize a design The DC Sweep settings are Swept Var Type Voltage Source Sweep Type Value List Name V1 Values 5v See Evaluation on page 1 27 and the sections that follow for definitions of trace function goal function and PSpice Optimizer expression OrCAD supplies standard goal functions for AC DC and transient analyses in the file PSPICE PRB This file resides in the OrCAD root PSpice directory You can add goal functions to this file or create a local PRB file for use with a specific design See Chapter 7 Tutorial Using constrained optimization MOS amplifier for examples of Probe goal functions used to evaluate performance Refer to your PSpice A D User s Guide for instructions on creating goal functions and for a description of the global and local PRB files 40 3 To fix the voltage of VI fill in the DC Sweep dialog box as shown Simulation Settings DC Sweep x General Analysis Include Files Libraries Stimulus Options Data Collection Probe Windows Analysis type r Sweep variable foc Sweep Voltage source Name
91. liable results when tweaking values 77 Excluding parameters and specifications from optimization 78 Testingperformancewhenaddingorchangingparametersorspecifications 78 Saving intermediate values 4 444 2a 24 40828 EE Era 79 Viewing result summaries au Sa 684 Birken sees 79 Chapter 4 Chapter 5 Contents Producing optimization reports 79 Viewing the optimization log 81 Viewing derivatives i S EARLE 81 Finalizing the design was a bee eee Oe BS 82 Using standard part values i ugo po 22 Bu Ree RES R 82 Saving results s e cac 00 su sa ERROR OS ek 83 Updating the design s so gt sea omacka 22 be macsom ea i aE S 84 Understanding optimization principles and options 85 Chapter overview Lire lieto Rd ete tues SPERM ES EA 85 Goals versus constraints sr an an er eA eS RR ERS 86 Constrained optimization ass 0a aa wenn be EO 87 Types of constraints a sun ses 8 bee en 88 Feasible and infeasible points 22 iii 222 Kan 89 Active and inactive constraints LL 90 Lagrange multipliers zur 2 2 ns ke oe ee ey RO 90 Characteristics of functions 5 24 4 400 6404 aaa a 91 Global and local minima aaa aa 92 STAEHNE POINTS inca REG eH REDE a ARIE 93 CORSI cha Pee by eee oe ia reden 93 Parameter bounds 0 nen 94 Derivatives Lu oe see 0 age Pe ee ee Re a a ee i EUA ee a 95 How the PSpice Optimizer estimates derivatives 95 Limitations of derivative data 96 Target val
92. lts Ei Optimizer Bpf opt Derivs Avail File Edit Tune Options Help Specifications Vv BW W Gain rorez8 0 712189 10 4255 14 8106 Parameters V aBW M aGain iteration 0 710379 0 502658 R Optimization complete Specs met Figure 27 Optimized values for the active filter example Note The number of simulations required to complete the optimization varies depending on the starting values in the current value fields when you initiate optimization 127 Chapter 6 Tutorial Exploring design tradeoffs active filter 128 Tutorial Using constrained optimization MOS amplifier 7 Tutorial overview The following tutorial shows you how to use the PSpice Optimizer to set up and run constrained optimization Using the MOS amplifier example provided with your OrCAD programs you will e Review the optimization setup in Capture parameter definitions and parameterized expression assignments e Review the goal and constraint setup in the PSpice Optimizer including the evaluations used to measure performance e Review the optimization method selected for single goal problems e Run the optimization Chapter 7 Tutorial Using constrained optimization MOS amplifier The CMOS amplifier design For this optimization the CMOS amplifier requirements are e Minimize power consumption e Maintain gain at 20 e Maintain 3 dB b
93. matic 4 606 eta 40 eee ee wu a na 51 Using the PSpice Optimizer 53 Chapter overview e aerea oe eed ee he 53 Starting and loading the PSpice Optimizer 55 Starting the Popice Optimizer au ser euer re 55 From Capt re socs s son a gosoy Oe a ae 55 From the Windows Start menu 000 000085 56 Changing startup options u 0 0 2 ARA 56 Loading a different optimization file 57 The PSpice Optimizer Window 3 ieri sa ren 58 Specifications area aaa een an he 59 Internal specifications sce oe ewe nF RR I 59 External specifications 23 2 2 24 RS ee 8 OTS Pe BERS 60 Parameters area 61 Error ga gearea eea q kos aeut ir been 444 Ri 62 Adding and editing parameters sun sen sauna nen 63 Adding a parameter win ones ee Gas eR eae eR Os PELA 63 Selecting a parameter to edit 65 Adding and editing specifications LL 66 Adding a specification x as ie 284 meee de kein 66 Defining an evaluation for an external specification 70 Selecting a specification to edit 71 Measuring and Optimizing Performance 0 71 Optimizing Your Design ipsa aaa ee 71 Graphically monitoring progress aoaaa 73 Exploring the effect of parameter and specification changes 74 Testing performance when changing current values 74 Automatically recalculating performance 75 Manually recalculating performance 76 Ensuring re
94. me result for each configuration of the two specifications one goal and one constraint Saving results At this point you would ordinarily choose Save from the File menu to save the results However to avoid modifying the tutorial files either e From the File menu choose Save As to store the results under another file name or e Omit the save process entirely 117 Chapter 5 Tutorial Optimizing a design passive terminator 118 Tutorial Exploring design tradeoffs active filter Tutorial overview The following tutorial shows you how to use the PSpice Optimizer to explore design tradeoffs Using the simple active filter example provided with your OrCAD programs you will e Review the optimization setup in Capture parameter definitions and parameterized expression assignments e Review the goal and constraint setup in the PSpice Optimizer e Change a parameter value to see the effect on goal and constraint values e Change a goal value to see the effect on parameter values Chapter 6 Tutorial Exploring design tradeoffs active filter 120 The active filter design The filter has three adjustable resistors These resistors adjust center frequency bandwidth and gain In this case the adjustments are interdependent Requirements for the filter are e Center frequency Fc must be 10 Hz with 1 accuracy e 3 dB bandwidth BW must be 1 Hz with 10 accuracy e Gain Gain must be 10 with
95. meters to a set of measurements or when minimizing more than one goal 23 Chapter 1 Things you need to know See Chapter 6 Tutorial Exploring design tradeoffs active filter for a working example showing parameterized slider values For more information see Goal and Constraint on page 1 26 24 Parameter A parameter defines a property of the design for which the PSpice Optimizer attempts to determine the best value within specified limits A parameter can e Represent component values such as resistance R for a resistor e Represent other component property values such as slider settings in a potentiometer e Participate in expressions used to define component values or other component property values The PSpice Optimizer can optimize designs with up to eight variable parameters For example A potentiometer part in a schematic uses the SET property to represent the slider position You can assign a parameterized expression to this property to represent variable slider positions between 1 and 0 During optimization the PSpice Optimizer varies the parameterized value of the SET property Spedfication A specification describes the ideal behavior of a design in terms of goals and constraints For example For a given design the gain shall be 20 dB 1 dB for a given design the 3 dB bandwidth shall be 1 kHz for a given design the rise time must be less than 1 usec A design can have up to eight go
96. mizer writes updated parameter definitions to MYAMP PAR To create a parameters file for a design 1 Start any text editor 2 For each parameter in the circuit enter a line using the syntax PARAM parameter_name starting_value 3 Save the file as circuit_file_ name PAR 165 Chapter C Optimizing a netlist based design To make the parameter definition in the PAR file available to PSpice A D 1 Inserta INC command anywhere after the first line of the circuit file using the syntax INC parameters_file_name where parameters_file_name is the same file in which you entered the PARAM statements for the circuit Example To MYAMP CIR add the following statement anywhere after the first line in the file INC myamp par Setting up and running the PSpice Optimizer Before optimizing you need to define all of the parameters declared in the circuit file and the goals and constraints Setup is exactly the same as for a schematic based design To complete setup and optimize the design 1 Start the PSpice Optimizer by doing one of the following e From the Windows Start menu choose the OrCAD program folder and then the PSpice Optimizer shortcut e From the Windows Start menu choose Run enter the command line for OPTIMIZE EXE and click OK 2 Adda parameter definition for each of the parameters used in the circuit file a From the Edit menu choose Parameters b Click Add 166 Setting up and r
97. n opt i myinit ini Loading a different optimization file Once you have started the PSpice Optimizer you can change to a new or different optimization file at any time To start a new optimization 1 From the File menu choose New To load an existing optimization setup 1 From the File menu choose Open 2 Locate and select the appropriate optimization file 57 Chapter 3 Using the PSpice Optimizer The PSpice Optimizer Window The PSpice Optimizer window contains three areas e Specifications area e Parameters area e Error gauge area Figure 12 illustrates their position in the window error gauge area specifications area Ei Optimizer Bitpar opt Derivs Avail Edit i p 9 744059e 013 Fi 9 920115e 010 000000e 010 Optimization complete Specs met Fer E 15 Gone m parameters area Figure 12 The PSpice Optimizer window 58 Specifications area The specifications area can show up to eight specification boxes where each box represents either a goal or a constraint Figure 13 illustrates the fields contained in each box enable disable check box progress indicator current value edit specification hot spot Figure 13 Example of a specification box The contents of the box varies depending on the source for the specifications either internal or external The following sections describe the differences in the in
98. n optimization method for single goal problems Least Squares Minimization options The PSpice Optimizer implements two general classes of algorithm to measure design performance least squares and minimization These algorithms are applicable to both unconstrained and constrained problems Least squares A reliable measure of performance for a design with multiple targets is to take the deviation of each output from its target square all deviations so each term is positive and sum all of the squares The PSpice Optimizer then tries to reduce this sum to zero This technique is known as least squares Note that the sum of the squares of the deviations becomes zero only if all of the goals are met Minimization Another measure of design performance considers a single output and reduces it to the smallest value possible For example Power or propagation delay each of which is a positive number with ideal performance corresponding to zero Choosing the algorithm When optimizing for more than one goal the PSpice Optimizer always uses the least squares algorithm For a single goal however you must specify the algorithm for the optimizer Advanced options 103 Chapter 4 Understanding optimization principles and options To set the optimization method for a single goal 1 Do one of the following e Click the Least Squares button to minimize the square of the deviation between measured and target value e Click Minimize to
99. ncluding a parameters file netlist based design 166 Index Circuit File text box 68 component values tolerance 82 using standard 82 constraint 24 26 active 90 bound 88 compared to goals 86 equality 89 inactive 90 inequality 88 nonlinear 88 progress indicator 60 target value 25 See Also specification Constraint check box 67 convergence 93 Copy Parameters command Edit menu 64 Copy Specifications command Edit menu 69 current value changing interactively 75 76 external specification 60 internal specification 59 parameter 61 Current Value text box 64 Cutback option 101 D Defaults command Options menu 98 Delta option 98 derivatives 29 accuracy 96 and linearity 96 and tweaking values 75 calculating 75 95 98 finite differencing 95 98 limitations 96 viewing 81 when excluding specifications 78 Edit menu Parameters command Add 63 Change 64 Copy 64 Insert 64 170 Reset Values command 78 79 Round Calculated command 83 Round Nearest command 82 Specifications command Add 66 Change 69 Copy 69 Insert 69 Store Values command 79 Update Schematic command 84 Edit Parameter dialog box Current Value 64 Enabled 64 Initial Value 64 Initial Value text box 64 Lower Limit 64 Name 64 Tolerance 64 Edit Specification dialog box analysis type 68 Circuit File 68 Constraint 67 Enabled 67 Evaluate 68 File 68 Name 67 Range 67 Referen
100. nerate a summary of the option settings for a given design select Report from the File menu 101 Chapter 4 Understanding optimization principles and options parameter changes This can be caused by accumulation of errors in iterative simulation algorithms Figure 22 demonstrates a typical case The effect of the Goal Glitch i Rio Function glitch is serious the optimizer can get stuck in the spurious local minimum represented by the glitch The optimizer s threshold mechanism limits the effect of unreliable data Parameter Figure 22 Hypothetical data glitch To control parameter perturbation betw een iterations 1 Inthe Threshold text box enter a value that defines a fraction of the current parameter value For example A Threshold value of 0 01 means that when the PSpice Optimizer changes a parameter value the value will change by at least 1 of its current value By default Threshold is set to 0 so that small changes in parameter values are not arbitrarily rejected To obtain good results however you may need to adjust the Threshold values When making adjustments consider the following e If data quality is good and Threshold is greater than zero reduce the Threshold value to find more accurate parameter values e If data quality is suspect has potential for spurious peaks or glitches increase the Threshold value to ensure that the optimizer will not get stuck during the run 102 Choosing a
101. ng e current settings for parameter specification and program options e calculated derivatives and Lagrange multipliers To generate a summary report 1 From the File menu choose Report The PSpice Optimizer saves the final results to MYDIODE OPT as shown in Figure 10 mydiode out Notepad O x File Edit Search Help PSpice Optimizer Report mydiode opt xx Parameters x Rival on current 3 9k initial 5k min 100 max 10k tolerance 16 xx Specifications name Id1 on current value 1 09687ma weight 1 satisfied no circuit mydiode analysis DC allsections no evaluate I d1 using default goal functions file reference internal type eq target 1ma range 5ua goal name Pc on current value 4 53348nU weight 1 satisfied yes circuit mydiode analysis DC allsections no type gt target 4mU range 400UW constraint xxx Options Max Iterations 20 One Spec least squares Recalculate auto xxx Derivatives Rival 2 43e 007 9 96e 007 Figure 10 Report summary for the diode optimization 50 Phase Three Running an optimization Saving results When you have finished optimizing you can save all of the optimizer data including the current values for all parameters and specifications To save the optimizer data for the diode design 1 From the File menu choose Save The PSpice Optimizer updates the MYDIODE OPT file All of the options sett
102. o PSpice A D PSpice automatically loads the global PSPICE PRB file located by default in your OrCAD root common directory and any local PRB file located in the working directory corresponding to the current design You can freely update PSPICE PRB or any other PRB file with new goal function definitions Refer to online Help in PSpice for more information on the PRB files 133 Chapter 7 Tutorial Using constrained optimization MOS amplifier 134 The goals and constraints The example circuit is set up with predefined goals and constraints which you can view using the PSpice Optimizer To activate the PSpice Optimizer 1 From Capture s PSpice menu choose Run Optimizer The PSpice Optimizer window shows the three parameters W1 L1 and Iref and the three specifications Power is defined as a goal and gain and bandwidth are defined as constraints as shown below Table 7 4 Setting Power Gain Bandwidth Name Power Gain BW Target 1uW 20 1MHz Range 100 uW 2 100 kHz Constraint Type N A target gt target Analysis DC AC AC Circuit File m2 m2 m2 Evaluate i v2 10v YatX LPBW v vout 1k vdb vout 3 Since Power is a goal constraint type does not apply Gain is defined as a constraint because circuit gain MUST remain at 20 1 BW is defined as a constraint because the 3dB bandwidth MUST be at least 900 kHz or greater Setting the method for a single goal optimization
103. om the File menu choose Properties and dick the Shortcut tab 56 From the Windows Start menu From the Start menu there is a program folder which contains Windows shortcuts for all installed OrCAD programs including the PSpice Optimizer To start the PSpice Optimizer from the Windows Start menu From the Windows Start menu select the OrCAD program folder and then the PSpice Optimizer shortcut to start optimizer The optimizer starts without an optimization setup See Loading a different optimization file on page 3 57 for further instructions Changing startup options The PSpice Optimizer supports two command line options which are used to e Start the optimizer with an initialization file other than the default PSPICE INI e Automatically load an optimization file OPT after startup You can add one or both options to the command line To change the initialization file used by the PSpice Optimizer In the Optimizer command line use the i option as follows OPTIMIZE i initialization_file_name Starting and loading the PSpice Optimizer To automatically load an optimization file after startup In the PSpice Optimizer command line add the name of the optimization file as follows OPTIMIZE optimization_file_name The following command line example shows how to start the optimizer at all times with an initialization file named MYINIT INI and an optimization file named MYDESIGN OPT OPTIMIZE mydesig
104. optimization Now that you have defined the parameters specifications and evaluations for the design you are ready to optimize adjust and finalize your design OrCAD PSpice Optimizer OrCAD PSpice A D Optimize Simulate Standardize part values Generate reports Update the design Improved design Figure5 Design flow for running an optimization Running the PSpice Optimizer You can use the PSpice Optimizer to e Optimize the circuit to completion from the Tune menu select Auto e Evaluate performance for a single set of parameter values from the Tune menu select Update Performance e Compute derivatives of each specification with respect to each parameter from the Tune menu select Update Derivatives When you select Auto from the Tune menu the PSpice Optimizer automatically computes the derivatives for each specification with respect to each parameter Figure 6 Using the derivatives the optimizer determines the direction in which to vary the parameters and changes parameter values accordingly until it achieves a reduction in the overall error After updating the parameters the optimizer computes new derivatives and repeats the process until one of the following occurs e Specifications are met success e No more progress can be made failure e You manually interrupt the process Phase Three Running an optimization This is useful when initially validating the circuit or w
105. or R1 its value is 1 k Later when you set up the optimization you will parameterize R1 s value as shown in Figure 2 36 10 R resistor R1 D1N914 diode D1 VSRC voltage source V1 Choose Place Ground to select and place the following simulaton parts on the schematic page 0 analog ground 0 From the Place menu choose Wire to connect the parts as shown in Figure 2 Click on the VSRC part V1 to select it From the Edit menu choose Properties then User Properties to set V1 s DC property to 5v From the File menu choose Save The PSpice optimizer advantage To determine a value for R1 manually you can set up a parametric analysis of a DC sweep where The value of R1 steps from 4 k to 5 k in increments of 0 1k The DC sweep analysis is a single point voltage analysis at 5 V Such an analysis requires eleven PSpice simulations Using Probe the resistor value giving rise to 1 mA current through D1 is 4 14 k The remainder of this chapter shows how to use the PSpice Optimizer to determine the same solution automatically using fewer simulations Phase Two Setting up the optimization Now that preliminary design development is complete you are ready to define the optimization parameters goals and constraints OrCAD Capture OrCAD Capture OrCAD PSpice A D OrCAD PSpice A D OrCAD PSpice Optimizer Define design parameters Set up analyses Develop performance measures De
106. or constraint each time Because the PSpice Optimizer solves for all specifications at once and simultaneously adjusts all parameters between iterations you end up examining fewer possible solutions 34 Why use optimization To solve the problem manually you could assign an arbitrary value to R1 manually calculate the current then make an educated guess to adjust the values until a satisfactory solution is found Or you might use a simulation to sweep the value for R1 with a DC Sweep analysis carefully analyzing the results to find the best solution These manual methods have two major disadvantages e Because the diode is a non linear device manual calculations can be time consuming e Sweeping a parameterized value can take a large number of simulations depending on the range and increment selected The PSpice Optimizer automates these processes by handling calculations for you and intelligently directing the series of simulations Given results of the previous simulations the optimizer automatically adjusts the parameterized value of R1 for the next run thus eliminating unnecessary iterations which in turn provides a solution more quickly and with less effort Once the PSpice Optimizer settles on the best solution you can still explore available tradeoffs When done manually this iterative process can be difficult and frustrating With the optimizer you can tweak the parameter s and immediately determine wh
107. ower right hand corner of the specification box of interest in the PSpice Optimizer window F Ib A double click here When finished browsing click Cancel 144 The goals and constraints The example circuit is set up with predefined goals which you can view using the PSpice Optimizer To start the PSpice Optimizer 1 From Capture s PSpice menu choose Run Optimizer The PSpice Optimizer window shows the six parameters Is Ikf Br Bf Ise and Ne and the two specifications Ic and Ib Ic and Ib are defined as a goals as shown below Table 8 5 Setting Ic Ib Name Ic Ib Reference External External File 3055 MDP 3055 MDP X Column Name Vbe Vbe Y Column Name Ic Ib Tolerance 5 5 Analysis DC DC Circuit File bjtpar bjtpar Evaluate YatX ic q1 YatX ib q1 The Ib settings as they appear in the Edit Specification dialog box are shown below Name Ib Enabled Reference C Internal External Weight 1 Internal External Target p File 3055 mdp a pange or X Column Name Ybe F Constraint Y Column Name jib Type target nd Tolerance 5 F Analysis s Simulation Profile or Circuit File CAC DC Tran Probe File Containing Goal Functions pesi Evaluate lyatx ib q1 OK Cancel Mappings to the external data file Note the reference to the external data file 3055 MDP and the values assigned to X Column Name and Y Column Name The column values map
108. ox controls Control name Meaning Name Reference Weight Enabled Internal specification Target Range Constraint Type Specification name for a new specification double click lt lt new gt gt and enter a text string that is unique to the current optimization file e Select Internal when defining the specification s target value and range in this dialog box e Select External when defining the specification s measurement data using a file e g for curve fitting Relative weight of the specification To give a specification more weight assign a number that is higher than that for the other specifications When enabled includes the specification in the next run If cleared excludes the specification Ideal value for the specification Delta applied to Target defining the acceptable range of values i e Target Range For example If Target 10 and Range 2 then the PSpice Optimizer accepts values from 9 to 11 When enabled defines the ee X column name specification as a constraint not a Y column name goal Defines whether constraint values Vbe Ic must equal the target value be less 4 0E 01 6 05E 06 than or equal to the target value or be _ greater than or equal to the target le SEN value 4 2E 02 1 31E 05 External Specification Figure 15 Sample format for an external specification 67 Chapter 3 Using the PSpice Optimizer Table4 Edit specification
109. pF 1 pF 8 pF capacitance collector 10k 1 k 12k resistance Then the scaled values are 8pF 10pPF gt and 21O _ 1 IpF Ik ui respectively Target value scaling 97 Chapter 4 Understanding optimization principles and options Options Ei Delta 1 Max Iterations 7 Probe File Display mydisplay CAC DC C Tran Cancel The PSpice Optimizer saves option settings to the OPT file so that they remain with the optimization s parameter and specification settings To generate a summary of the option settings for a given design choose Report from the File menu 98 Since these numbers are close enough in magnitude the PSpice Optimizer can combine them without losing numerical significance Default options This section describes the basic configuration options for the PSpice Optimizer To display the Options dialog box 1 From the Options menu choose Defaults Controlling finite differencing when calculating derivatives Delta option The Delta option specifies the relative amount as a percentage of current parameter value by which the PSpice Optimizer perturbs each parameter from its initial value when calculating the derivatives The optimizer uses gradient based optimization algorithms that use a finite difference method to approximate the gradients gradients are not known analytically To implement finite differencing the optimizer 1 Perturbs each parame
110. pice Optimizer computes derivatives and scales target values e Default options on page 4 98 describes the options you can set to control derivative calculations maximum simulation iterations and the Probe display e Advanced options on page 4 101 describes the options you can set to control cutback threshold and the method least squares minimization that the PSpice Optimizer uses Chapter 4 Understanding optimization principles and options If there is more than one goal the PSpice Optimizer combines the errors by summing the squares of the normalized values Figure 19 Resistive terminator circuit 86 Goals versus constraints Goals and constraints represent the ideal behavior of a design In practice this behavior is often unattainable For example A gate cannot achieve zero propagation delay but the goal of the optimization process might be to come as close as possible to that target value that is to reduce the error as much as possible When solving problems involving both goals and constraints the PSpice Optimizer trades off meeting the target values for the goals against violation of the constraints This means that the error indicator does not always reduce in value for a given iteration When setting up an optimization you must decide which specifications are goals and which are constraints In many cases there are several legitimate ways to describe the design For example Assume you
111. ptimizer expressions You may need to change the lower or upper limit of a parameter Valid operators and functions in PSpice Optimizer expressions are exp log log10 sin cos tan atan PSpice Optimizer numbers are reals with an optional suffix T G Meg k m u n p f mil and an optional symbol for units Log function log or log10 can not have a zero argument You may need to change the lower or upper limit of a parameter 152 Error message Error message descriptions Description 11012 dat File In Use 11013 No Simulation Result 11014 G F Evaluation Failed 11015 Aborted 11016 Bad Numeric Field 11017 Name Required 11018 MAX Must Be gt MIN 11019 Must Be Between MIN amp MAX You must unload the data file from PSpice A D for the circuit being optimized Click on the Probe window to make it active then select Close from the File menu PSpice A D could not open the dat file for the circuit being optimized The PSpice Optimizer uses two files for optimization opt_0 dat and opt_1 dat Try running a PSpice simulation to investigate the problem If PSpice does not create a dat file check that a DC sweep AC sweep or transient analysis has been selected and that there is adequate hard disk space PSpice A D could not find one or more of the marked points in the goal function error message will contain goal function name Try loading the dat f
112. r a description of the format of this file A column could not be found in the external data file See 11021 for a description of the format for this file The expression used in the Evaluate text box of the Edit Specification dialog box could not be parsed See errors 11014 and 11016 for aids in debugging the problem PSpice Optimizer expressions can only use the following operators exp log log10 sin cos tan atan 154 Error message Error message descriptions Description 11033 Need At Least 1 Enabled Goal 11034 Max External Items 250 11035 Missing External Column 11036 Eval Limits 1 Goal 1 Constraint At least one goal must be used in an optimization An optimization can not be performed with constraints only A maximum of 250 lines of data can be used in the external data file The first line of an external data file must contain names for each column of data The first column should contain the X axis data and each succeeding column should contain Y axis data for each external specification The column names on the first line must be identical to those used in the Specification dialogs X Column Name Y Column Name The evaluation version is limited to a maximum of 1 goal and 1 constraint 155 Chapter A Error messages 156 File types used by the PSpice Optimizer Appendix overview This appendix describes how OrCAD programs used to capture and op
113. reduce a value to the smallest possible value If your optimization problem is to maximize a single goal then set up the specification to minimize the negative of the value For example To maximize gain set up the problem to minimize gain 104 Tutorial Optimizing a design passive terminator Tutorial overview The following tutorial takes you through the steps needed to setup and run an optimization starting with the simple terminator example provided with your OrCAD programs In this tutorial you will e Verify the design setup e Check that part values are parameterized e Check that optimization parameters are defined e Check the analysis settings e Check the goal specification settings e Run the optimization For a complete hands on tutorial in which you draw the schematic and set up the optimization from scratch see Chapter 2 Primer How to optimize a design Chapter 5 Tutorial Optimizing a design passive terminator Figure 23 Resistive terminator circuit 106 The passive terminator design Figure 23 shows a simple terminator that you could use for example for one line of a backplane The top end of R1 connects to a 5 v DC supply the lower end of R2 connects to ground The center point of the two resistors provides the line termination This design must meet two specifications e Voltage at the junction of the two resistors V center must lie within a specified range
114. rformance characteristics gain 23 8 bandwidth 2 2 Mhz power consumption 2 2 mW These initial parameter values yield both excess gain and bandwidth so a reduction in power consumption appears feasible But because the gain bandwidth and power depend nonlinearly on circuit parameters such as transistor dimensions manual optimization is impractical 131 Chapter 7 Tutorial Using constrained optimization MOS amplifier To display the Optimizer Parameters dialog box double click the OPTPARAM partin the design To see the setup for the analyses 1 From Capture s PSpice menu choose Edit Simulation 2 Inthe Analysis type box select either DC Sweep or AC Sweep Noise to examine the simulation settings 3 Click Cancel to return 132 PSpice Optimizer parameters For optimization the parameters for the amplifier are set up using the OPTPARAM symbol as follows Table 7 3 Property Parameters wi L1 Iref Initial Value 75u 5u 100uA Current Value 75u 5u 100uA Lower Limit 10u 2u 10uA Upper Limit 150u 50u 500uA Tolerance 0 0 0 The evaluations The amplifier is set up with three performance characteristics power gain and 3 dB bandwidth To measure performance the PSpice Optimizer needs to know how to calculate response for each of these Power The objective to minimize power consumption is a single point goal This means that a trace function appropriately measures the power response of the circuit
115. s ad ade ici ae red CORI RErR o 108 ic q1 ic q2 1 188 ib q1 ib q2 1 measured curves and shows the percent relative error The PSpice plot in Figure 34 compares fitted and in Ic and Ib 3 opt_1 dat Figure 34 PSpice A D display after optimization is complete 149 Chapter 8 Tutorial Fitting model data bipolar transistor 150 Error messages Appendix overview This appendix lists and explains the error messages you might encounter while using the PSpice Optimizer and where appropriate what action to take Chapter A Error messages Error message descriptions Table Error message descriptions Error message Description 11002 No More Resets 11003 Mismatched Parentheses 11004 Undefined Symbol 11005 Divide by 0 11006 0 to the y 11007 Unknown Operator 11008 Invalid Number 11009 Log of Number lt 0 No improvement was made by going back to the last good step and recalculating derivatives Try refining the specifications Check for mismatched parentheses in the evaluation expression A symbol in a PSpice Optimizer expression was not recognized A division by zero in a PSpice Optimizer expression occurred Try adding a small offset e g 1e 3 to the denominators of fractional terms in the expressions You may need to change the lower or upper limit of a parameter Try adding a small offset e g 1e 3 to bases in PSpice O
116. s critical value is the constrained minimum for this problem Feasible and infeasible points The starting point for an optimization can satisfy all the constraints a feasible point or it can violate one or more of the constraints an infeasible point Depending on the feasibility of the starting point the PSpice Optimizer does the following e From an infeasible point it attempts to reduce the goals and to reduce the amount by which the constraints are violated e From a feasible point it attempts to reduce the goals while keeping the constraints satisfied Note Because the PSpice Optimizer sometimes trades off reduction of the goals against violation of the constraints to make progress an iteration can produce an infeasible point even though the initial starting point was feasible Constrained optimization The PSpice Optimizer can also handle equality constraints where a performance measure is required to be equal to some defined value 89 Chapter 4 Understanding optimization principles and options To view Lagrange multipliers for your design generate a report by selecting Reports from the File menu and browse the design_name oct report file See Producing optimization reports on page 3 79 for instructions 90 Active and inactive constraints An active constraint is one which affects the solution of the optimization problem that is the solution would probably be different if the constraint were removed
117. se Three Running an optimization In the diode example the derivative at R1 5 k is 1 62 x 10 7 or dia 1 62x107 This indicates that a 1 ohm increase in R1 will produce a decrease of 0 162 uA in Idl To verify this try reducing the value of R1 by 100 ohms to 4 9 kohm and simulate This increases the diode current by 16 2 uA and agrees with the derivative information See The PSpice Optimizer Window on page 3 58 for a complete description of the window elements and how you can interact with them 45 Chapter 2 Primer How to optimize a design Constraints are defined like goals using the Edit Specification dialog box with two additions In the Internal frame you must Select the Constraint check box Choose the constraint type gt target target or lt target The constraint type specifies the required relation between what is evaluated as defined in the Evaluate text box and the target value defined in the Target text box To define the constraint for power dissipation in R1 The power dissipated in R1 must be less than or equal to 4mW 400 uW Define the constraint by doing the following 1 From PSpice Optimizer s Edit menu choose Specifications 2 Inthe Specifications dialog box click Add 3 Enter the power Pc constraint properties as shown below The constraint specification settings are lt a mr Name Pc Reference Internal C External Weight i Inema
118. sing an evaluation that requires a simulation and therefore you must specify the circuit file for the simulation However when measuring performance using PSpice Optimizer expressions that do not require a simulation you do not need to specify a circuit file 23 Chapter 1 Things you need to know See Optimization on page 1 23 for more on least squares and minimization algorithms 26 Constraint A constraint defines the performance level that the design must fulfill in which the target value exceeds falls below or equals a specified value for instance an output voltage that must be greater than a specific level The constraint specification includes e The name of the constraint e A target value and an acceptable range e A circuit file to simulate See note on previous page e An evaluation for measuring performance e An analysis type used for simulation based evaluations e An allowed relationship between measured values and the target value which can be one of the following lt measured value must be less than or equal to the target value measured value must equal the target value gt measured value must be greater than or equal to the target value The constraint specification can also include the name of the file containing the PSpice A D goal function definitions PRB file Constraints are often nonlinear functions of the parameters in the design For example Bandwidth can vary as t
119. sive simulations until performance comes close to or exactly meets the ideal performance The PSpice Optimizer solves four types of optimization problems as described in Table 1 Table 1 Optimization problems Terms you need to understand Problem type Unconstrained minimization Constrained minimization Unconstrained least squares Constrained least squares PSpice Optimizer action Reduces the value of a single goal Reduces the value of a single goal while satisfying one or more constraints Reduces the sum of the squares of the individual errors difference between the ideal and the measured value for a set of goals Reduces the sum of squares of the individual errors for a set of goals while satisfying one or more constraints Example Minimize the propagation delay through a logic cell Minimize the propagation delay through a logic cell while keeping the power consumption of the cell less than a specified value Given a terminator design minimize the sum of squares of the errors in output voltage and equivalent resistance Minimize the sum of squares of the figures of merit for an amplifier design while keeping the open loop gain equal to a specified value All four cases allow simple bound constraints that is lower and upper bounds on all of the parameters The PSpice Optimizer also handles nonlinear goals and constraints Use unconstrained least squares when fitting model para
120. strained and unconstrained minimization algorithms This means that the optimizer e Tackles constrained problems directly and efficiently e Calculates Lagrange multipliers for the solution which provide valuable insight to design tradeoffs Types of constraints Constraints are restrictions placed on potential solutions to optimization problems The simplest constraints are bound constraints simple limits on the ranges of the parameters e g a resistor whose value has to be at least 100 Q More challenging constraints that frequently arise in analog circuit optimization have dependencies on other characteristics of the design Example Consider optimizing a MOS amplifier cell which must satisfy these specifications e Reduce power consumption e Make sure gain bandwidth product of the cell is greater than or equal to some minimum value The power consumption of the cell is the goal the characteristic to be minimized and the gain bandwidth product is the inequality constraint To continue the example consider the dependence of power consumption and gain bandwidth product on bias current in one of the amplifier stages Power consumption is proportional to the bias current while the gain bandwidth product is proportional to the square root of the bias current Bias current must be reduced in order to reduce power consumption Below some critical bias current the minimum gain bandwidth requirement will be violated Thi
121. ted performance values for the amplifier example 136 Optimized values for the amplifierexample 137 Schematic for the BJT model fitting example 141 Initial traces for the Ic and Ib parameters 147 Figures Figure 33 Figure 34 Figure 35 Optimization results for the BJT model fitting example PSpice A D display after optimization is complete Sample external data file 424044 ee vas Tables Table 1 Table 2 Table 3 Table 4 Table 4 1 Table 6 1 Table 6 2 Table 7 3 Table 7 4 Table 8 5 Table 8 6 Table 7 Table 1 Optimization problems 4 age 00 2 000 5 ww ee E en 3 23 Valid Operators and Functions for PSpice Optimizer Expressions 29 Edit parameter dialog box controls 2 2 02 000 00 0000 64 Edit specification dialog box controls LL 67 97 122 124 132 134 144 148 Error message descriptions 4 2 04452 ee Er Bas 152 Summary of PSpice Optimizer related filetypes 161 Tables November 6 1998 xii Before you begin Welcome to OrCAD Welcome to the OrCAD family of products Whichever programs you have purchased we are confident that you will find that they meet your circuit design needs They provide an easy to use integrated environment for creating simulating and analyzing your circuit designs from start to finish Before you begin xiv OrCAD PSpice Optimizer overview The OrCAD PSpic
122. ter in turn from its current value by an amount h 2 Evaluates the function at the perturbed value 3 Subtracts the old function value from the new 4 Divides the result by h Note There isa tradeoff If h is too small the difference in function values is unreliable due to numerical inaccuracies However if h is too large the result is a poor approximation to the true gradient Default options To control parameter perturbation w hen calculating derivatives 1 Enter a value in the Delta text box that defines a fraction of the parameter s total range Example If a parameter has a current value of 10 and Delta is set to 1 the default then the PSpice Optimizer perturbs the parameter by 10 The 1 default value is suitable for the accuracy of typical simulations 2 If the accuracy of your simulation is very different from typical perhaps because of the use of a non default value for either RELTOL or the time step ceiling for a Transient analysis then change the value of Delta as follows e If simulation accuracy is better decrease Delta by an appropriate amount e If simulation accuracy is worse increase Delta by an appropriate amount Note The optimum value of Delta varies as the square root of the relative accuracy of the simulation For example if your simulation is 100 times more accurate than typical you should reduce Delta by a factor of 10 Limiting simulation iterations Max Iterations option The
123. ters double click here Edit menu Parameter Specifications Store Values Reset Values 65 Chapter 3 Using the PSpice Optimizer BW Add Gain Change Delete Copy Insert Name lt lt new gt F Enabled Reference Internal C External Weight 1 Internal External Target 0 GE n g X Column Name F Constraint Y Column Name Type target 7 Tolerance fies Analysis Circuit Fite CAC CDC Tran Probe File Containing Goal Functions prb Evaluate Cancel 66 Adding and editing specifications This section describes how to create and change specifications that is goals and constraints using the PSpice Optimizer Note You are limited to eight specifications per optimization file This limit includes specifications that you have defined but disabled for a given run Adding a specification There are two ways to add a specification using the PSpice Optimizer e Create the specification from scratch e Copy an existing specification and change its name To create a specification from scratch 1 From PSpice Optimizer s Edit menu choose Specifications 2 Inthe Specifications dialog box either e click Add or e double click the blank line following the specification list 3 In the Edit Specification dialog box set the controls as described in Table 4 Adding and editing specifications Table4 Edit specification dialog b
124. ters 2 To see Rival settings a Inthe Parameters list click Rival b Click Change to display the Edit Parameter dialog box 3 Click Cancel to leave the parameter unchanged 4 Optionally repeat steps 2 and 3 for R2val gt Click Close to exit the Edit Parameter dialog box Defining the goals and constraints Defining the goals and constraints To review the specifications for this example are e Voltage V at the junction must be 3 75 0 1 V center e Thevenin equivalent resistance Requiv must be 100 1 Q One way to handle the optimization problem is to treat both specifications as a goal For each goal you must define e its name e its target value and range e the analysis to use for simulation e the circuit file containing the netlist description e the way to measure performance For this example these are already defined To see the Vc and Rt goal settings 1 From the Edit menu choose Specifications 2 Click Vc then click Change Name Rt M Enabled Reference Internal External Weight 1 Internal External Target 100 File esa Renge p X Column Name I Constraint Y Column Name Type target z Tolerance fx r Analysis Simulation Profile or Circuit File CAC De Tran Probe File Containing Goal Functions Evaluate Ma o Cancel 113 Chapter 5 Tutorial Optimizing a design passive terminator Notice that Vc is described as a goa
125. the latest run e View the current derivative calculations Producing optimization reports You can produce a report containing e Settings for each of the parameters specifications and options Viewing result summaries Edit menu Parameters Round Nearest Round Calculated Update Schematic Edit menu Parameters Specifications Store Values 79 Chapter 3 Using the PSpice Optimizer File menu New Open Save Save As Exit 1 Term opt 2 msim EXAMPLES OPTIMIZENM2 M2 opt 3 msim EXAMPLES OPTIMIZENBJTPAR Bitpar opt 4 msim EXAMPLES OPTIMIZENBPF Bpf opt 80 Performance results Partial derivatives Lagrange multipliers To generate an optimization report 1 2 From the File menu choose Report The PSpice Optimizer generates the report and saves it to an ASCII file named design_name OOT The optimizer also displays the report in the text editor configured for your installation mydiode out Notepad BEE File Edit Search Help PSpice Optimizer Report mydiode opt xxx Parameters Rival on current 3 9k initial 5k min 166 max 10k tolerance 16 xxx Specifications name Id1 on current value 1 09687ma weight 1 satisfied no circuit mydiode analysis DC allsections no evaluate I d1 using default goal functions file reference internal type eq target 1ma range 5ua goal name Pc on current value 4 53348mU
126. timize your design interact and share information with each other e File and program relationships on page B 158 illustrates and describes the data flow among OrCAD programs e File type summary on page B 161 explains the contents of each file type Chapter B File types used by the PSpice Optimizer 158 Fil e and program relationships Typically you enter your design using Capture and use this as the basis for optimization with the PSpice Optimizer Each design produces a single netlist file des ign_name NET which you create in one of the following ways From Capture s PSpice menu choose Create Netlist or Run or From Capture s PSpice menu choose Run Optimizer In the latter case Capture also produces Note An optimization file design_name OPT which contains optimization settings describing parameters specifications and other options The PSpice Optimizer adds to and keeps the information in this file up to date A parameters file design_name PAR which contains parameter values as of the last optimization iteration The PSpice Optimizer keeps the information in this file up to date The netlist file produced by Capture automatically references the PAR file If you are entering your design using a circuit file instead of a schematic add a inc include command naming the PAR file See Chapter C Optimizing a netlist based design for details Measuring per
127. to the column names defined in 3055 MDP such that the X column gives the data points at which the Y column values were measured For the BJT example the Y column contains measured collector current corresponding to the specified base emitter voltages in the X column The evaluations To measure performance both goals use the waveform analysis goal function YatX see The evaluations on page 7 132 Notice the character appearing in the expression This character allows PSpice A D to make measurements at the multiple X column values When the PSpice Optimizer encounters this character it replaces it with the current X column value before sending it to PSpice A D for evaluation The bipolar transistor test case 145 Chapter 8 Tutorial Fitting model data bipolar transistor Save Restore Display bo 2 New Name E I 1313 p LAST DISPLAYIDC LAST SESSION DC Close Refer to online Help in PSpice A Dfor more on waveform display control 146 Example If Evaluate is set to YatX Ic Q1 and if the X column of the external data file contains the values 1v 2v 3v then the PSpice Optimizer will form the waveform analysis goal function expressions Yat X Ic 01 1v YatX Ic Q1 2v and YatX Ic Q1 3v and send each one to PSpice A D for evaluation against the simulation results Monitoring progress with PSpice A D When optimizing the PSpice
128. traints Now that you ve completed the preliminary groundwork you are ready to define the properties for goals and constraints So far you have performed all steps in Capture To finalize setup you must specify the goal for the diode design example using the PSpice Optimizer To define the design goal Id1 for the diode design example 1 From Capture s PSpice menu choose Run Optimizer to start the PSpice Optimizer The PSpice Optimizer window appears showing the parameter Rival that you defined using the OPTPARAM part in the your design 2 From PSpice Optimizer s Edit menu choose Specifications 3 In the Specifications dialog box click Add 4 Enter Id1 properties as shown below Name Id1 V Enabled Reference e Internal C External Weight 1 Internal r External Target Ima File BE Range Sua X Column Name F Constraint Y Column Name Type target 7 Tolerance 1 Analysis Simulation Profile or Circuit File Cac amp DC Tran mydiode ce Probe File Containing Goal Functions Evaluate CC ok Cancel Phase Two Setting up the optimization The goal specification settings are Name Idl Target 1ma Range 5ua Analysis DC Circuit File mydiode Evaluate I dl The PSpice Optimizer appropriately defaults to the internal specification setting shown in the Reference control 41 Chapter 2 Primer How to optimize a design 42 Phase Three Running an
129. turbation 98 value changes 101 excluding parameters and specifications 78 for one goal 103 improving convergence 93 limiting iterations 99 log 81 loosening parameter bounds 94 purpose 34 restoring previous results 79 running 72 saving final results 83 saving intermediate values 79 scaling 97 setting Cutback value 101 starting points 89 tweaking values 74 unconstrained least squares 23 unconstrained minimization 23 using a netlist based design 164 optimization file opt 55 158 161 loading 55 57 saving results 83 optimizer window 78 error gauge area 62 parameters area 172 current value 61 edit hot spot 78 initial value 61 specifications area 59 current value 59 60 edit hot spot 78 Enable check box 78 initial value 59 60 progress indicator 60 options activation 56 Cutback 101 Delta 98 Least Squares 104 Max Iterations 99 Minimize 104 Threshold 101 Options menu Defaults command 98 Advanced Options 101 Recalculate command 75 76 OPTPARAM symbol Schematics 55 61 84 P parameter 24 adding from scratch 63 back annotating values to the schematic 84 bounds 94 controlling changes between iterations 101 controlling perturbation 98 copying 64 Edit Parameter dialog box controls 64 editing 65 enable disable 78 excluding from optimization 78 fitting 148 loosening bounds 94 tolerance on component values 82 tweaking values 74 using standard component val
130. ues 82 parameters area Optimizer Window Enable check box 78 parameters area optimizer window 61 current value 61 edit hot spot 78 initial value 61 parameters file par 158 161 165 creating for netlist based designs 165 including in a circuit file netlist based design 166 Parameters Recalculate command Options menu TI performance 26 derivative calculations 75 evaluating 72 excluding parameter and specifications 78 measuring when adding editing parameters and specifications 78 recalculating automatically 75 manually 76 saving results 83 scaling measured values 97 tweaking values 74 Print command File menu 80 Probe 22 27 prb file 40 159 data file dat 95 goal function 28 See Also goal function Probe monitoring simulations 73 trace function 27 Probe data file dat 95 Probe goal functions file prb 40 159 progress indicator external specification 60 internal specification 60 PSpice 22 PSpice Optimizer activating 55 loading 55 57 PSpice Optimizer expression 27 28 R Range text box 67 Recalculate command Options menu 75 76 recalculation 74 automatic 75 manual 76 Reference frame 67 RELTOL option 99 Report command File menu 80 reports 79 oot file 80 generating 80 Index printing 80 reports file oot 80 161 requirements see specifications 27 Reset Values command Edit menu 78 79 results opt file 83 improving convergence 93 restorin
131. unction e PSpice A D goal function e PSpice Optimizer expression Given evaluation results the PSpice Optimizer determines whether or not the changes in parameter values are improving performance and determines how to select the parameters for the next iteration Trace function A trace function defines how to evaluate a design characteristic when running a single point analysis such as a DC sweep with a fixed voltage input of 5 V For example V out to measure the output voltage I d1 to measure the current through a component Terms you need to understand Refer to the online OrCAD PSpice A D Reference Manual for the variable formats and mathematical functions you can use to specify a trace function 27 Chapter 1 Things you need to know Refer to the Goal Function Wizard in PSpice A D and your PSpice A D User s Guide for information on how to develop and specify goal functions Here are some quick tips In PSpice A D e To test the value returned by a specified goal function choose Eval Goal Function from the Trace menu e To see the waveforms and marked points used to evaluate a goal function select Display Evaluation in the Options dialog box from the Tools menu choose Options to display this dialog box See Gain on page 7 133 for an example of the YatX goal function definition 28 PSpice A D goal function A goal function defines how to evaluate a design characteristic when running any kind of
132. unning the PSpice Optimizer c Fill in the dialog box Add a specification definition for each goal and constraint a From the Edit menu choose Specifications b Click Add c Fill in the dialog box In the Analysis frame be sure to enter the name of the circuit file you parameterized earlier Run the optimization a From the Tune menu choose Update Performance b From the Tune menu choose Auto and click Start To save the optimization results 1 Save the results to the optimization file a From the File menu choose Save As b Enter the name of the optimization file OPT to contain the setup and results information From the File menu choose Report to create a PSpice Optimizer report file OOT containing a readable summary of the setup and results information 167 Chapter C Optimizing a netlist based design 168 Example Parameterizing the circuit file The following circuit file call it DBIAS CIR contains the netlist for a voltage source resistor diode series combination diode bias circuit LIB V1 10 5v RI 1 2 5k D1 2 0 D1N914 DC V1 LIST 5V Probe END Suppose you want to optimize the bias current in a voltage source resistor diode series combination Specifically your goal is to achieve a current of 1mA through the diode To realize this goal you must vary the value of resistor R1 call the variable value or parameter Rbias To parameterize the circuit file 1 Create t
133. utes Lagrange multipliers that provide information on the cost of each constraint on the solution Explore performance tradeoffs When you enter new values for design parameters the PSpice Optimizer provides graphical feedback showing performance You can also tweak goal and constraint values to examine changes to parameter values Fit model parameters Given a parameterized model a set of measured data points and a good starting point for the parameter values the PSpice Optimizer fits a more accurate model What is the PSpice Optimizer Designs that you can optimize A design that you can optimize must meet the following Optimization problems are not always criteria solvable by a particular algorithm e Itworks that is it simulates with PSpice to completion and behaves as intended e One or more of its components have a variable value and each value that is varied relates to an intended performance goal e An algorithm exists to measure its performance as a function of the variable value If you can visualize which factors should be adjusted to improve performance and how you would manually step through the optimization process even though the computations might seem unwieldy then the design is a good candidate for the PSpice Optimizer Designs that you cannot optimize You cannot use the PSpice Optimizer to e Create a working design This especially applies when you begin with a design that is far from meeting
134. versioni 2254444 ees bee au ea eae xvii Things you need to know 19 Chapter ov rvieW seoseis a k oe wer BOS a a eS ee re Be 19 What is the PSpice Optimizer iii a 20 Designs that you can optimize acc hee Karen He 21 Designs that you cannot optimize oaoa 21 Using the PSpice Optimizer with other OrCAD programs 22 Terms you need to understand iii nn en sa run 23 Primer How to optimize a design 31 Chapter overview dardi Br a aan SS here 31 Optimizing a diode biasing circuit the objective 33 Why use optimization te ohne ee Ra Eee PAY PERLA 34 Phase One Developing the design 2 2 0 00000008 35 The PSpice optimizer advantage si pesi 5424 4 282 36 Phase Two Setting up the optimization LL 37 Defining design parameters i od ee ana re 38 Setting up goals and constraints 2 2222 39 Setting up analyses for each goal and constraint 39 Developing performance measures 40 Defining specifications goals and constraints 41 Phase Three Running an optimization LL 42 Running the Papice Optimizer esa 8 1 u ale ea bles eo 43 Contents Chapter 3 Adding a constraint and rerunning the PSpice Optimizer 45 Changing the constraint and rerunning the PSpice Optimizer 48 Using standard component values 49 Producing reports 2248 Susan ai Ga eee PE Bee EY 50 Saving Testes hae eke a De RES PERS ER HEE SA 51 Updating the sche
135. with PSpice A D 2 22 2220 146 Fitting thedata s i RATE reas cede rare de Bees 148 Error messages 151 Appendix overview prata Eee ip Pr ren hei 151 Error message descriptions s sun es ar u Er ea 152 File types used by the PSpice Optimizer 157 Appendix overview 3a BE i aa har 157 File and program relationships LL 158 Measuring performance using information in the circuit file and PRB file 159 Defining specification criteria in the external datafile 160 File type summary tana u 8 Sen at OR tren 161 Optimizing a netlist based design 163 Appendix overview 254 iii 163 Optimizing without a schematic i iii eee eee ewes 164 Setting up the circuit file 244 234 4204 ase how BREE OSS 165 Setting up and running the PSpice Optimizer 166 Example Parameterizing the circuit file 168 Index 169 vii Contents viii Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27 Figure 28 Figure 29 Figure 30 Figure 31 Figure 32 Optimization design flow gt 4440544 4 0 saw eee eae Ba 22 Diode biasing design example lt i 632 ae sparare fe 33 Design flow for developing the design 2 2 2222 35 Design flow for setting up the optimization
136. y on the number of variable parameters 95 Chapter 4 Understanding optimization principles and options See Controlling finite differencing when calculating derivatives Delta option on page 4 98 for more information on Delta Figure 21 Hypothetical function 96 Limitations of derivative data A derivative analysis calculates a linear relationship between a parameter and a specification It assumes that the function is linear near the initial value within a region defined by the value set for the Delta option If the data is well behaved in this region then this is a valid assumption the PSpice Optimizer can use the derivative to approximate specification values based on the linear relationship However when the function is not well behaved in the region around the initial value the approximation may not be valid For example Assume that the function shown in Figure 21 is the plot of a specification s behavior vs a parameter value Note that the function is approximately linear between the dashed lines but not necessarily linear outside of that region If you pick an initial value for the parameter which is between the two dashed lines then subsequently compute the derivatives the derivative data provides a reasonable approximation for any other parameter value between those lines However if you try to use the same derivative data to estimate new specification values for parameter values outside of
137. yboard XV Before you begin Related documentation Documentation for OrCAD products is available in both hard copy and online To access an online manual instantly you can select it from the Help menu in its respective program for example access the Capture User s Guide from the Help menu in Capture Note The documentation you receive depends on the software configuration you have purchased The following table provides a brief description of those manuals available in both hard copy and online This manual Provides information about how to use OrCAD Capture OrCAD Capture which is a schematic capture front end program User s Guide with a direct interface to other OrCAD programs and options OrCAD Layout OrCAD Layout which is a PCB layout editor that lets you specify User s Guide printed circuit board structure as well as the components metal OrCAD PSpice A D amp Basics User s Guide OrCAD PSpice amp Basics User s Guide OrCAD PSpice Optimizer User s Guide and graphics required for fabrication PSpice A D the Stimulus Editor and the Model Editor utility which are circuit analysis programs that let you create simulate and test analog and digital circuit designs It provides examples on how to specify simulation parameters analyze simulation results edit input signals and create models OrCAD PSpice amp OrCAD PSpice Basics which are circuit analysis programs that let you cre
138. zer e How to finalize the design standardize component values save results and back annotate the schematic page 3 79 54 Starting and loading the PSpice Optimizer Starting and loading the PSpice Optimizer This section describes how to e Start the PSpice Optimizer e Set special startup options e Load a design Starting the PSpice Optimizer Start the PSpice Optimizer program either from e Capture or e The Windows Start menu From Capture To start the PSpice Optimizer from within Capture 1 From Capture s PSpice menu choose Run Optimizer If you have an active schematic loaded in the schematic editor when you choose Run Optimizer any optimization parameters defined with the OPTPARAM part and any existing setup information contained in the corresponding optimization file OPT are automatically loaded into the PSpice Optimizer If no design is active the PSpice Optimizer starts without an optimization setup Instead you must load an optimization file directly into the optimizer as described in Loading a different optimization file on page 3 57 55 Chapter 3 Using the PSpice Optimizer Because you can start the PSpice Optimizer from either Capture or from the Windows Start menu we recommend that you change the command line definition as follows e In Windows Explorer change the Target text box in the Optimizer s Properties dialog box click once on the PSpice Optimizer shortcut then fr

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