Manual - TMG Test Equipment
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1. Green is life ABN 43 064 478 842 T 231 osborne avenue clayton south vic 3169 PO box 1548 clayton south vic 3169 t 03 9265 7400 f 03 9558 0875 J freecall 1800 680 680 www tmgtestequipment com au Test amp Complimentary Reference Material Measurement This PDF has been made available as a complimentary service for you to assist in e sales evaluating this model for your testing requirements e rentals TMG offers a wide range of test equipment solutions from renting short to long term buying refurbished and purchasing new Financing options such as Financial Rental and Leasing are also available on application calibration repair disposal TMG will assist if you are unsure whether this model will suit your requirements Call TMG if you need to organise repair and or calibrate your unit If you click on the Click to Call logo below you can all us for FREE TMG Corporate Website TMG Products Website e Leuel 4 Disposal Click to Call TMG Now Review amp Leuel5 Leuel 3 KGE Renew Review amp Renew epair a G amp Leuel e Reh MK Calibration Recycled Leuel 1 e MALO Rcquisition e jr Purchase LU ff Lease Rent Solution Centre Product Lifecycle Management System Disclaimer All trademarks appearing within this PDF are trademarks of their respective owners NY E E v oW NA Form 080 01 cM User Manual Tektronix S SD 24 TDR Sampling Head 070 7052 022. Instrument Serial Numbers Each instrument manufactured by Tektronix has a serial number on a panel insert or tag or stamped on the chassis The first letter in the serial number designates the country of manufacture The last five digits of the serial number are assigned sequentially and are unique to each instrument Those manufactured in the United States have six unique digits The country of manufacture is identified as follows B010000 Tektronix Inc Beaverton Oregon USA E200000 Tektronix United Kingdom Ltd London J300000 Sony Tektronix Japan H700000 Tektronix Holland NV Heerenveen The Netherlands Instruments manufactured for Tektronix by external vendors outside the United States are assigned a two digit alpha code to identify the country of manufacture e g JP for Japan HK for Hong Kong IL for Israel etc Tektronix Inc PO Box 500 Beaverton OR 97077 Printed in U S A Copyright Tektronix Inc 1988 1993 All rights reserved Tektronix products are covered by U S and foreign patents issued and pending The following are registered trademarks TEKTRONIX TEK TEKPROBE and SCOPE MOBILE WARRANTY Tektronix warrants that this product will be free from defects in materials and workmanship for a period of one 1 year from the date of shipment If any such product proves defective during this warranty period Tektronix at its option either will repair the defective product without charge for parts and la
3. Initially the diode switch is conducting Since the step generator output is connected to a 50 Q load the resistance to ground at the acquisition point is 25 Q because of the internal 50 O impedance The 10 mA current source places 250 mV at the acquisition point 250 mV Figure 9 Step Generation with a 50 Q Load When the diode switch opens reverse biased the return path to ground is broken and the acquisition point rises to 0 V The matched impedance allows the acquisition point to remain at 0 V See Figure 9 SD 24 User Manual Taking TDR Measurements Operation Into an Open Circuit Initially the diode switch is conducting Since the step generator output is open the resistance to ground at the acquisition point is 50 O because of the internal 50 Q impedance The 10 mA current source places 500 mV at the acquisition point as a starting condition 250mV 500 mV Figure 10 Step Generation with an Open Circuit When the diode switch opens reverse biased apparent resistance to ground at the acquisition point and at the channel connector is 25 Q because the internal circuit impedance is 50 O and the connector imped ance is 50 Q This causes the acquisition point to rise to 250 mV The transition propagates to the open in the device under test and is reflected back to the acquisition point causing the voltage at the acquisition point to rise to O V At the acquisition point t
4. The reflected rise time is 35 ps or less A 20 GHz typical bandwidth provides high speed signal capture Displayed noise is 750 p Vnys typical without smoothing and 350 uV typical with smoothing on Older sampling heads have a different noise specification see Specifications on page 33 Precision 3 5 mm connectors A Channel Select button for quick trace acquisition and selection from the sampling head front panel As shown in Figure 1 the SD 24 has two independent channels each has its own acquisition and step generation circuitry The strobe drive signal from the mainframe controls the timing of the strobe assertion to each acquisition system The strobe generator in the sampling head is common to both channels guaranteeing sampling coincidence between the two channels Introduction Step Generator O e Acquisition System Strobe Generator Acquisition System TDR Drive Strobe Drive Strobe Sense Variable Delay 50Q To from Mainframe Step Generator Figure 1 SD 24 Sampling Head Block Diagram The strobe sense signal is a part of the strobe signal returned to the main frame The mainframe monitors the time duration of the strobe drive strobe sense loop and adjusts a delay inside the mainframe to maintain correct strobe timing Both channels have a step generator The step generators can indepen dently assert a negative going or positive going step Using both channels you can
5. 24 User Manual F Factory defaults 18 Front panel buttons 11 12 connectors 11 12 lights 11 12 Input voltage maximum 11 L Loop gain adjusting 20 described 19 O Offset null adjusting 21 described 21 R Reference plane 31 Remote commands 15 Rho units selecting 28 Rise time acquisition 2 Index S Sampling head parameters 17 18 19 20 21 22 loop gain 19 20 offset null 27 TDR amplitude 22 SELECT CHANNEL button 11 12 26 Smoothing 13 14 15 Step generator circuitry 1 2 control 12 13 operation 23 24 25 Stored parameter values 78 T TDR 23 24 25 26 28 29 30 31 control 12 13 14 15 delay 13 14 15 differential and common mode measurements 29 30 31 plus alignment 37 polarity 18 14 15 taking measurements 26 27 28 29 30 31 TDR pulse amplitude adjusting 22 described 22 U User constants 18 V Variable delay 2 39 Index 40 Index
6. perform differential and common mode Time Domain Reflectometry TDR and two port time domain network analysis The acquisition risetime is 17 5 ps or less The displayed TDR reflected risetime is 35 ps or less To ensure proper timing between the two step outputs the second channel is equipped with a variable delay SD 24 User Manual SD 24 User Manual Safety Terms in Manuals CAUTION statements identify conditions or practices that could result in damage to the equipment or other property WARNING statements identify conditions or practices that could result in personal injury or loss of life Terms on Equipment CAUTION indicates a personal injury hazard not immediately accessible as one reads the marking or a hazard to property including the equipment itself DANGER indicates a personal injury hazard immediately accessible as one reads the marking Symbols in Manuals Static Sensitive Devices Symbols on Equipment 7 A DANGER Protective ATTENTION High Voltage ground earth Refer to terminal manual Grounding the Instrument The sampling head is grounded through the instrument To avoid electric shock make sure that the instrument is plugged into a properly wired recep tacle where earth ground has been verified by a qualified service person Without the protective ground all parts of the instrument and the sampling head are shock hazards This includes knobs and controls that may appear to be insula
7. the Connector Care section Each channel has a SELECT CHANNEL button a yellow channel light and a red TDR ON light The yellow channel light can have three states off on steady or blinking The operation of the channel button depends on the state of the light m If the yellow light is off then the channel is not acquiring trace data and no trace is displayed from that channel When the light is off pressing the SELECT CHANNEL button causes the channel to acquire trace data and display a trace of that channel Input from that channel becomes the selected trace so the yellow light blinks m If the yellow light is on steady the channel is acquiring trace data The trace data is displayed as a single trace and or may be part of another displayed trace However the trace is not the selected trace When the light is on steady pressing the SELECT CHANNEL button selects that trace causing the light to blink m If the yellow light is blinking the channel is part or all of the selected trace When the light is blinking pressing the button removes all traces displaying that channel The channel stops acquisitions and the yellow light turns off The red TDR ON light indicates whether or not the SD 24 is sending out a step from the step generator through the signal connector You cannot control the TDR function from the SD 24 front panel the main frame instrument turns this feature on or off SD 24 User Manual Instrument Sampl
8. the end of the cable SD 24 User Manual 27 Taking TDR Measurements Changing Graticule Units for TDR The units of measure commonly used in TDR are units of rho p measured on the vertical axis and time measured on the horizontal axis You can change the measurements by using the Graticules selector on the Wave form major menu Graticules Cheste Second braticule aches Maan S za i88 div id b62H88ns Gerp ono Hore Head Poole Trace Status Figure 13 The Graticules Pop Up Menu L Step 8 Touch Graticules in the Waveform major menu and Feet or Meters in the pop up menu If you know that the propagation velocity of your cable differs from the default touch the Propagation Velocity selector and adjust this parameter If you don t know the velocity or are using Tektronix SMA cables accept the 0 7 default This unitless number represents the fraction of the speed of light at which signals pass through your network or transmission line 28 SD 24 User Manual Example Differential and Common Mode TDR SD 24 User Manual Taking TDR Measurements The SD 24 TDR Sampling Head is able to perform differential and common mode TDR measurements As described earlier the sampling head has two sampling input channels and two independent step generators The step generator output for each channel is selectable for positive or negative polarity and amplitude This example will show
9. DRDELAY lt NRx gt This command specifies the delay lt NRx gt of the channel 2 step genera tor step lower channel relative to channel 1 upper channel CH lt alpha gt lt ui gt EXTAttenuation lt NRx gt This command specifies the External Channel Attenuation of the speci fied channel where lt NRx gt is a floating point attenuation factor For complete information about how to use the SD 24 to display traces see the appropriate mainframe user reference manual 15 Using the Sampling Head 16 SD 24 User Manual Adjusting Parameters To get the best performance from your SD 24 TDR Sampling Head you may need to adjust sampling head parameters These parameters affect how the sampling head acquires signals and affect the accuracy of the resulting trace Typically you may want to adjust sampling head parameters whenever you have moved the sampling head to another slot or if the ambient temperature has changed more than 5 C since the parameters were last adjusted At the factory the parameters are set in an environment with an ambient tem perature of 25 C NOTE You should adjust sampling head parameters after a 20 minute warm up You can adjust sampling head parameters at any time However during instrument warm up the values may change as the temperature varies You should adjust the sampling head parameters after the instrument has been on for at least 20 minutes There are three different paramet
10. LIED TEKTRONIX AND ITS VENDORS DISCLAIM ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE TEKTRONIX RESPONSIBILITY TO REPAIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND EXCLUSIVE REMEDY PROVIDED TO THE CUSTOMER FOR BREACH OF THIS WARRANTY TEKTRONIX AND ITS VENDORS WILL NOT BE LIABLE FOR ANY INDIRECT SPECIAL INCIDENTAL OR CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER TEKTRONIX OR THE VENDOR HAS ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES Table of Contents List of Figures 00 cece eee cece eee eee II iii Listof Tables 2 u OR ee ee te V Introduction Iu a Edu nme erre led 1 Safety 2 usua een ae ee ie ee fere a rers 3 Electrostatic Discharge sees 5 Connector Care iii ec etee eee ne tei ea 7 Installing the Sampling Head sseeeeeeeeee 9 Using the Sampling Head eeeeeeeeesee 11 Front Panel 2 ea en 11 Connecting Signals 0cceeee eect nn nenn nn 12 Buttons and Lights ce cece eee nennen nenn nenn 12 Instrument Sampling Head Interaction 13 Commands From the Mainframe Front Panel 14 Programmer Interface Commands usssuuue 15 Adjusting Parameters eese 17 Stored Parameters uuuueeeeeeeeeeeeee 18 LO0pP G in 2 unite EE EE REGINE MEME 19 Adjusting Loop Gain 0 0 eee 20 Offset Null rnia even crc cepere na d
11. Maximum Safe Input Signal Voltage Maximum Signal Voltage Dot Transient Response Accuracy after calibration at operating temperature Adjustment Range Displayed Noise Unity Dot Response With Smoothing Input Termination Impedance SD 24 User Manual Specifications 20 GHz typical 200 kHz 100 Hz 17 5 ps or less 10 to 90 3 or less typical 10 5 or less typical 3 or less typical 1 or less typical 0 5 or less typical 3V 1 0 Vp p 5 for signals up to 0 5 Vp p Adjustable to unity for signals up to 1 0 Vp p SN B020652 and above 1 2 mVams max 750 UVRMS typical SN B010651 and below 1 3 mVnys typical SN B020652 and above 550 u Vnus max 350 uVnys typical SN B010651 and below 600 uVnys typical 50 0 50 33 Specifications Table 1 Acquisition Electrical Specifications Cont Characteristics Specifications Isolation Between Channels lt 1 p p voltage transmission from channel driven with 067 1338 00 to quiescent channel Time Coincidence Between Channels Accuracy 10 ps Stability 0 2 ps C Table 2 Step Generator Electrical Specifications Characteristics Specifications Maximum Repetition Rate 100 kHz Output Amplitude 250 mV Channel 2 Delay Adjustment 50 ps typical relative to channel 1 Insertion Delay Stability One Channel 1 ps C Between Channels 0 2 ps C Table 3 TDR Electrical Specifications Characteristics Specific
12. alize the instrument press UTILITY and touch Initialize L Step 2 Connect your wrist strap to the antistatic connector on the front of your instrument C Step 3 Attach one end of the cable to any SD 24 sampling head input Leave the other end unattached See Figure 11 CSA 803A amm Not Connected Not Connected Figure 11 Connections for Example L Step 4 Press the SELECT CHANNEL button on the sampling head input channel to which you have connected the cable L Step 5 Press the WAVEFORM button and touch the Sampling Head Fnc s selector C Step 6 Touch TDR Preset to turn it on set Trigger to Internal Clock and autoset the trace Touch Exit to remove the pop up menu The sampling head will turn on a red light next to the channel input connec tor indicating that TDR is activated for that channel TDR can be used on each channel independently SD 24 User Manual Taking TDR Measurements L Step 7 Adjust the display sizes and positions to show a trace similar to that shown in Figure 12 The vertical 1 and horizontal icons will let you make fine adjustments NOTE Leave at least one division of baseline trace to the left of the first rise pae _ _ Bsp S32 75mV S8mV diy tris d 4B mV Bo lens Snaesdiu SB lzns Figure 12 TDR Step and Reflection The first rise of this trace is the incident TDR step leaving the sampling head the second rise is the reflection of the step returning from
13. ampling Head Fnc s pop up menu Both ofthese are shown in Figure 5 You first select the channel you want to set in the Selected Channel section ofthe pop up menu Touch the Smoothing TDR TDT or TDR Polarity selectors to change those settings Touch the TDR Head A Delay selector to assign the knobs to that parameter 50 24 TEF Polar duu Duro TIR Preset TEF h Delau 382 2m i External Channel Soroa hiina Brtenustugnn Maan mike 1885a div Main Pos 34 66289ne Status Figure 5 The Sampling Head Fnc s Pop Up Menu 14 SD 24 User Manual SD 24 User Manual Using the Sampling Head Programmer Interface Commands Commands from a remote computer to the 11800 Series or CSA 803 Series instrument via an IEEE 488 or RS 232 C interface can control the sam pling head functions These commands are described below Forthese commands lt alpha gt indicates the unit letter M for mainframe or A B C or D for an SM 11 Multi Channel unit for the CSA 803 Series lt alpha gt is always M and lt ui gt indicates the channel number for the channel you want to affect CH lt alpha gt lt ui gt SMOOTHING ON OFF This command turns smoothing on or off CH lt alpha gt lt ui gt TDRSTATE ON OFF This command turns the TDR step generator on or off CH lt alpha gt lt ui gt TDRPOLARITY PLUS MINUS This command selects a negative going or positive going TDR step CH lt alpha gt lt ui gt T
14. an assign the user parameter value to equal the factory default value The factory default value offers a reasonable parameter value for many conditions See the Enhanced Accuracy section in your instrument s User Manual for more information SD 24 User Manual Loop Gain SD 24 User Manual Adjusting Parameters Loop gain determines the sampling head s ability to accurately follow an input voltage change that occurs between two adjacent samples How accurately the sampling head output follows the input signal is termed the dot transient response When loop gain is unity 1 the value of the first sample acquired after an input voltage change accurately reflects the voltage change indicating a good dot transient response Figure 6 shows this condition If loop gain is adjusted too low then the value of the first sample acquired after an input voltage change will lie somewhere between the value of the last sample and the new voltage If loop gain is adjusted too high the value of the first sample acquired after the input voltage change will be greater than the new voltage level Figure 6 shows displayed trace results for the three loop gain conditions Unity Loop Gain Insufficient Loop Gain Excessive Loop Gain Figure 6 Displayed Trace with Three Loop Gain Settings 19 Adjusting Parameters 20 Adjusting Loop Gain For the 11800 Series and CSA 803 Series you can adjust loop gain auto matically or manually from
15. ations Displayed Rise Time Incident 28 ps typical 10 to 90 at 250 mV or 250 mV output Reflected 35 ps or less 10 to 90 at 250 mV or 250 mV output Maximum Repetition Rate 100 kHz Incident Aberrations at 250 mV or 250 mV 10 ns to 20 ps before step 3 or less lt 300 ps after step 10 5 or less typical 300 ps to 5 ns after step 3 or less 5 ns to 100 ns 1 or less elsewhere 0 5 or less 34 SD 24 User Manual SD 24 User Manual Specifications Table 4 Environmental and Mechanical Specifications Characteristics Weight Height Width Depth Ambient Temperature Operating Non operating Altitude Operating Non operating Humidity MilSpec Electromagnetic Compatibility United States Specifications 314 grams 11 oz 71 05 mm 2 9 in 23 28 mm 0 95 in 91 39 mm 3 8 in 0 C to 50 C 32 F to 122 F 40 C to 75 C 40 F to 167 F to 4 5 km 15 000 feet to 15 km 50 000 feet to 95 relative humidity at up to 50 C 122 F Meets MIL T 28800E Type Ill Class 5 MIL STD 461B CE 03 Pt 4 Curve 1 CS 01 Pt 7 CS 02 Pt 4 CS 06 Pt 5 RE 02 Pt 7 RS 01 Pt 4 RS 02 Pt 5 RS 03 Pt 7 limited to 1 GHz 35 Specifications 36 SD 24 User Manual SD 24 User Manual Glossary Autoset A means of letting the instrument mainframe set itself to provide a stable and meaningful display of a given trace Baseline Correction The pr
16. bor or will provide a replacement in exchange for the defective product In order to obtain service under this warranty Customer must notify Tektronix ofthe defect before the expiration ofthe warranty period and make suitable arrangements for the performance of service Customer shall be responsible for packaging and shipping the defective product to the service center designated by Tektronix with shipping charges prepaid Tektronix shall pay for the return of the product to Customer if the shipment is to a location within the country in which the Tektronix service center is located Customer shall be responsible for paying all shipping charges duties taxes and any other charges for products returned to any other locations This warranty shall not apply to any defect failure or damage caused by improper use or improper or inadequate maintenance and care Tektronix shall not be obligated to furnish service under this warranty a to repair damage resulting from attempts by personnel other than Tektronix representatives to install repair or service the product b to repair damage resulting from improper use or connection to incompatible equipment or c to service a product that has been modified or integrated with other products when the effect of such modification or integration increases the time or difficulty of servicing the product THIS WARRANTY IS GIVEN BY TEKTRONIX WITH RESPECT TO THIS PRODUCT IN LIEU OF ANY OTHER WARRANTIES EXPRESSED OR IMP
17. ents You can adjust the ampli tude of the TDR step The TDR step amplitude setting is highly stable and insensitive to tempera ture variations You should not need to adjust this parameter very often You can adjust the TDR amplitude automatically or manually using the Enhanced Accuracy menu You can adjust the TDR step for a negative or positive polarity With the channel output terminated by a 50 O load the TDR amplitude is adjustable from 0 V to 250 mV positive or negative The repetition rate of the TDR step is set by the mainframe If you adjust the TDR step automatically using the Enhanced Accuracy menu the instrument adjusts the amplitude for both the positive and negative going steps The SD 24 contains nonvolatile memory that stores two values the factory default value and the user value for the TDR amplitude adjustment See Stored Parameters earlier in this section for more information 22 SD 24 User Manual TDR Step Generation SD 24 User Manual Taking TDR Measurements This section describes how to use the SD 24 to perform time domain reflectometry TDR measurements Both channels in the SD 24 TDR Sampling Head have a step generator which gives both channels TDR measurement capabilities You can use the outputs of both generators to perform differential and common mode TDR measurements The step generator circuitry consists fundamentally of an adjustable current source and a diode switch Initially bef
18. ers that you can adjust on each channel of your sampling head m Loop gain m Offset null TDR step amplitude The actual procedure for performing the adjustment is dependent on the mainframe instrument For the 11800 Series and the CSA 803 Series you can use the Enhanced Accuracy feature to adjust sampling head parame ters It is a quick and simple process See the User Manual for your instru ment for instructions to perform these adjustments SD 24 User Manual 17 Adjusting Parameters Stored Parameters 18 The SD 24 contains nonvolatile memory that stores two values the factory default value and the user constant for each of the above parameters These values are always remembered in the sampling head even if you remove the sampling head from the instrument The factory default values for the sampling head parameters are set at the factory These default values are appropriate for many conditions If you decide to adjust a sampling head parameter the parameter is immedi ately applied to the head but is lost when you power off the instrument However you can store the new parameter value as the user constant The user constants are stored in an EEPROM in the sampling head so that they are not lost at power off and are restored at power on If you initialize the mainframe instrument the last used values are applied to the sampling head If you are not sure of the current user value for a sampling head parameter you c
19. hat the two steps arrive at the same time at the reference plane usually the connection point to the device under test To check and adjust this condition disconnect the transmission cables from the device under test at the point where the cables connect to the device Then adjust the TDR step delay for the second channel so that the propagation delay between the incident edges is equal to the propagation delay between the reflected edges as shown in Figure 14 For some measurements and comparisons you may want to visually line up the leading edges of both TDR steps even though you have delayed the step assertion time for one channel To do this create a window of each trace and place each window trace in the lower graticule Then select one of the window traces and using the vertical icon and the lower knob position the leading edge of the trace This does not affect the arrival of the TDR steps at the reference plane See the User Manual for your instrument for more information about windows trigd i a Propagation Propagation Delay Delay Incident Reflected Figure 14 TDR Propagation Delay 31 Taking TDR Measurements 32 SD 24 User Manual Specifications Table 1 Acquisition Electrical Specifications Characteristics Bandwidth Sampling Repetition Rate Maximum Minimum Rise Time Aberrations 10 ns to 20 ps before step lt 300 ps after step 300 ps to 5 ns after step 5 ns to 100 ns elsewhere
20. he time displayed from the first step to the second step is the propagation time from the acquisition point to the open in the device under test and back See Figure 10 Baseline Correction Baseline correction is a feature of the11800 Series and CSA 803 Series This feature holds the displayed baseline of a trace in one location despite vari ations of the offset in the sampling head These offset variations are caused by changes in impedance at the device under test Baseline correction is especially useful with TDR TDT measurements With out baseline correction changes in the DC resistance to ground for the cable or device under test would cause the entire step to move vertically on the display Baseline correction keeps the baseline in one location vertically For the 11800 Series and CSA 803 Series you can enable baseline correction from the Graticules pop up menu For more information on baseline correction see the User Manual for your instrument SD 24 User Manual 25 Taking TDR Measurements Example Taking TDR Measurements 11801B B 26 This example demonstrates the TDR feature of the SD 24 sampling heads TDR is a method of examining and measuring a network or transmission line by sending a step into the network and monitoring the reflections For this example you will need a instrument mainframe with at least one SD 24 installed Also you will need one SMA cable preferably of 5 ns length L Step 1 Initi
21. ing Head Interaction SD 24 User Manual Using the Sampling Head The SD 24 TDR Sampling Head is a part of a larger instrument system Most ofthe SD 24 functions are controlled automatically by the mainframe instru ment These include such things as vertical scaling and horizontal sampling rate You do not directly control these parameters they are controlled for you as you perform tasks on the mainframe The parameters that you can control from the SD 24 front panel are covered in the Buttons and Lights section There are additional SD 24 functions that you control directly but from the mainframe instrument These functions are Smoothing when enabled reduces noise in the signal before it is digitized NOTE Turning smoothing on or off on one channel affects both SD 24 channels m TDR TDT when enabled turns on the step generator and sends a step out the signal connector This step is synchronized with the internal clock of the mainframe m TDR Polarity determines whether the TDR step is negative going or positive going m TDR Head A Delay adjusts the time delay of the channel 2 TDR step lower channel with respect to the channel 1 TDR step upper channel m External Channel Attenuation enables you to enter a number repre senting any external attenuation you have added to a channel 13 Using the Sampling Head Commands From the Mainframe Front Panel The Waveform major menu lets you access the S
22. ing Head Front Panel Figure 4 shows the front panel ofthe SD 24 TDR Sampling Head and identi fies the buttons lights and connectors Lock Down Screw SELECT CHANNEL SELECT CHANNEL Button Channel Indicator Light Yellow Signal Connector Top Channel TDR ON Light Red Bottom Channel SELECT CHANNEL e SD 24 TDR SAMPLING HEAD Figure 4 Sampling Head Front Panel Each channel has a 3 5 mm connector for signal input step output a SELECT CHANNEL button and a yellow channel indicator light caution amp Applying a voltage outside the range 3 V can result in damage to the sampling head or instrument Use a wrist strap to prevent electrostatic damage to the sampling head or instrument The input diodes used in the sampling heads are very susceptible to dam age from overdrive signal or DC voltages and from electrostatic discharge Never apply a voltage outside the range of 3 V Operate the instrument only in a static controlled environment Always use a wrist strap when handling sampling heads or making connections SD 24 User Manual 11 Using the Sampling Head Connecting Signals Buttons and Lights 12 The signal connector for each channel is used to connect signals for sam pling and to output TDR steps These are precision 3 5 mm connectors which are mechanically compatible with the SMA standard Input impedance is 50 Q Use extra care with the sampling head connectors See
23. king TDR measurements the ratio of the incident step to the reflected step A value of one 1 indicates complete reflection 37 Glossary 38 Setting The state of the front panel and system at a given time Smoothing Processing applied by the sampling head prior to the digitization of a trace to reduce apparent noise With smoothing the sampling head samples the signal eight times instead of once and the average of the samples is then used by hardware measurements and the digitizing circuitry Time Domain Reflectometry TDR A method of characterizing a transmission line or network by transmit ting a signal from one end and monitoring the electrical reflections Time Domain Transmission TDT A method of characterizing a transmission line or network by transmit ting a signal through the network and monitoring the output Trigger An electrical event that initiates acquisition of a trace as specified by the time base Waveform The visible representation of an input signal or combination of signals Identical to trace SD 24 User Manual A Acquisition circuitry 7 2 rise time 7 2 ASCII interface commands 15 B Baseline correction 25 C Common mode TDR measurements 23 29 Connectors 7 Constants Factory defaults 18 User constants 18 D Delay step generator 2 13 Differential TDR measurements 23 29 E Electro static discharge precautions 5 Enhanced Accuracy menu 17 SD
24. lay touch Sampling Head Fnc s Touch 2 and the TDR Polarity selector This causes channel 2 to assert a positive TDR step Touch Exit Notice that the upper channel is asserting a positive TDR step This is com mon mode TDR When the TDR steps on the two channels are the same polarity both posi tive or negative you can define a trace that represents the true common mode signal by touching the DefTra icon and touching Mainframe 11801 Series only 1 Mainframe 11800 Series only 2 Enter 29 Taking TDR Measurements 30 When the TDR steps on the two channels are opposite one positive and one negative you can now define a trace that represents the true differen tial signal by touching the DefTra icon and touching Mainframe 77801 Series only 1 Mainframe 11801 Series only 2 Enter TDT Measurements You can make forward and reverse Time Domain Transmission TDT meas urements using the SD 24 To perform a TDT measurement connect one sampling head channel to the input of the device under test and the other sampling head channel to the output of the device under test You can then alternately enable the step generators on both channels and sample the transmitted signal on the other channel to perform forward and reverse TDT measurements SD 24 User Manual More About TDR Measurements SD 24 User Manual Taking TDR Measurements When making differential or common mode TDR measurements it is impor tant t
25. nce ponia oon ona e Dre 21 Adjusting Offset Null 000 cece eee eee 21 TDR Amplitude 0 ccc eee eee eee eee III 22 Taking TDR Measurements 2 00e eee eee eee ee ee eeeneee 23 TDR Step Generation 00 0c cece eee eee eee 23 Operation Into a Short Circuit 000 0008 24 Operation Into a 50 Q Load 00 24 Operation Into an Open Circuit 0 00 eee 25 Baseline Correction 0 00 cc cece eee eens 25 Example Taking TDR Measurements 26 Changing Graticule Units for TDR 0005 28 Example Differential and Common Mode TDR 29 TDT Measurements 0 00 eee e eee 30 More About TDR Measurements sees 31 Specifications cr doleo SE a ea ce ke Le 33 Glossary sli ede a sed te eee gee reo 37 NAR sto cee Sea rae a MM MEC 39 SD 24 User Manual i Table of Contents ii Contents SD 24 User Manual List of Figures Figure 1 SD 24 Sampling Head Block Diagram Figure 2 Sampling Head Compartments in an 11801B and a CSA803A ssss Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Installing a Sampling Head in an Instrument Sampling Head Front Panel 00 cece eens The Sampling Head Fnc s Pop Up Menu Displayed Trace with Three Loo
26. ocess of maintaining the displayed vertical placement of a trace correcting for changes in the signal levels that would ordinarily move the trace up or down Channel A place to connect a signal or attach a network or transmission line to sampling heads Also the smallest component of a trace expression Channel Number The number assigned to a specific signal input connector The top channel of the left most sampling head compartment of the instrument mainframe is always mainframe channel 1 regardless of any reposition ing or omission of sampling heads Common Mode A circumstance where a signal is induced in phase on both sides of a differential network Default Measurement Parameter A value from the default set of measurement parameters The operator can change the default values Whenever a trace is created the meas urement parameters are copied from the default set Differential Mode A method of signal transmission where the true signal and its logical compliment are transmitted over a pair of conductors Incident Step When making TDR measurements the initial transmitted step ona single conductor Initialize Setting the instrument mainframe to a completely known default condition Internal Clock A trigger source that is synchronized with the Calibrator signal Reflected Step When making TDR measurements the step returned due to the reflec tion of the incident step due to a mismatch in impedance Rho p When ma
27. ofthe sampling head has two precision 3 5 mm connectors one for each channel They are for attaching the signal cable or the device under test These are high precision connectors with a closer mechanical tolerance than standard SMA cables Never attach a cable to asampling head con nector if the cable has a worn or damaged connector because the sampling head connector may be damaged Use extra care when attaching or removing a cable from the connectors Turn only the nut not the cable When attaching a cable to a sampling head connector align the connectors carefully before turning the nut Use light finger pressure to make this initial connection Then tighten the nut lightly with a wrench For best repeatability and to prolong the life of both connectors use a torque wrench and tighten the connection to the range of 7 10 Ib in 79 112 N cm If the sampling head connectors will receive heavy use such as in a produc tion environment you should install adapters for example connector sav ers on the sampling head to make connections to the device under test Connector Care 8 SD 24 User Manual SD 24 User Manual Installing the Sampling Head The SD 24 TDR Sampling Head fits into the front panel of a compatible instrument such as the 11801 Series Digital Sampling Oscilloscopes or CSA 803 Series Communications Signal Analyzers Figure 2 shows the front panel of an 11801B Digital Sampling Oscilloscope and a CSA 803A Commu nica
28. ore the step the diode switch is biased to conduct current to the output When the diode switch opens the step occurs Figure 7 a simplified diagram shows the switch and the cur rent source Acquisition Point Figure 7 Step Generator Simplified Schematic Diagram Because of the architecture of the step generator the output voltage of the step depends on the DC resistance to ground of the device under test The following sections describe the operation with a short circuit an open circuit and a 50 O load 23 Taking TDR Measurements 24 Operation Into a Short Circuit Initially the diode switch is conducting 10 mA Since the step generator output is initially shorted the resistance to ground is 0 O and the output voltage is O V When the diode switch opens reverse biased apparent resistance to ground at the acquisition point and at the channel connector is 25 O because the internal termination resistance is 50 O and the connector impedance is 50 Q The voltage at the acquisition point rises to 250 mV The transition propagates to the short in the device under test and is nega tively reflected back to the acquisition point cancelling the transition The time displayed from the first transition to the second transition is the propa gation time from the acquisition point to the short in the device under test and back See Figure 8 Figure 8 Step Generator with a Shorted Output Operation Into a 50 Q Load
29. p Gain Settings Step Generator Simplified Schematic Diagram Step Generator with a Shorted Output Step Generation with a 50 Q Load LL Step Generation with an Open Circuit Connections for Example 2 22 2222 nennen nenn TDR Step and Reflection The Graticules Pop Up Menu seesssse TDR Propagation Delay 10 11 14 19 23 24 24 25 26 27 28 31 lii List of Figures iv Contents SD 24 User Manual List of Tables Table 1 Acquisition Electrical Specifications Table 2 Step Generator Electrical Specifications Table 3 TDR Electrical Specifications Table 4 Environmental and Mechanical Specifications 33 34 34 35 List of Tables vi Contents SD 24 User Manual Introduction The SD 24 TDR Sampling Head is a high performance sampling head that can be installed in the 11800 Series Digital Sampling Oscilloscopes the SM 11 Multi Channel Unit and the CSA 803 Series Communications Signal Analyzers The SD 24 TDR Sampling Head provides the following features Two independent channels with signal acquisition and step generator capabilities In addition to signal sampling the two channels let you perform differential and common mode TDR and TDT measurements Both step generators have switchable polarity with 250 mV amplitude A 28 ps typical displayed TDR incident rise time and a 17 5 ps or less acquisition risetime
30. rsors displayed on the trace will also be incorrect Adjusting Offset Null You can adjust offset null automatically or manually from the Enhanced Accuracy menu If you prefer to adjust offset null manually be sure to adjust the loop gain first You can adjust offset null by terminating the channel input connector with a 50 Q terminator and adjusting the offset null with the knob so that the displayed trace is set to the O V position on the screen If you adjust offset null manually the offset null setting is valid only for the current setting of the smoothing parameter on or off For example if smoothing is set to off and you adjust offset null manually and you then turn smoothing on the offset null value may not be valid However the SD 24 remembers the offset null values for when smoothing is on and off so if you change the smoothing setting the correct offset null value is applied Note that the SD 24 stores four offset null values the two factory default values for when smoothing is on and smoothing is off and the two user constants for when smoothing is on and smoothing is off If you adjust offset null automatically using the Enhanced Accuracy menu the 11800 Series and CSA 803 Series instruments adjust both offset null values smoothing on and smoothing off 21 Adjusting Parameters TDR Amplitude The SD 24 has an internal step generator that is used with the acquisition channel to let you perform TDR measurem
31. the Enhanced Accuracy menu If you prefer to adjust loop gain manually the 11800 Series and CSA 803 Series also pro vide a divide by two feature This feature is helpful if you are using the Calibrator signal or TDR signal generator output to adjust loop gain You can also use the divide by two feature if you are using the trigger output of the instrument to trigger an external generator You might consider adjusting the loop gain whenever you are sampling a trace that has peak to peak voltages and transition speed characteristics that are substantially different from the previous trace In this case you can use the actual signal that you want to measure and turn off vectoring so that you can see each sample individually For instructions to adjust the loop gain see the Enhanced Accuracy section in your instrument s User Manual The SD 24 contains nonvolatile memory that stores two values for the loop gain adjustment the factory default value and the user value These were discussed at the beginning of this section SD 24 User Manual Offset Null SD 24 User Manual Adjusting Parameters The offset null adjustment removes unwanted DC offset that may be present in the sampling head This adjustment effectively zeroes the sampling head so that a0 V amplitude input signal delivers a 0 V output If offset null is not adjusted correctly measurements taken at the mainframe will be incorrect The absolute voltage values for any cu
32. tions Signal Analyzer and the locations of the sampling head compart ments Note that on the CSA 803 Series only two compartments provide signal acquisition capability The other two compartments only provide power for example to power an optical to electrical converter At least one sampling head must be installed in an 11800 Series or a CSA 803 Series instrument to sample signals Sampling Head Compartments 11801B m E m a E L Sampling Head Compartments CSA 803A e a Power Only Sampling Head Compartments Figure 2 Sampling Head Compartments in an 11801B and a CSA 803A Installing the Sampling Head With the ON STANDBY switch set to STANDBY place the sampling head in a compartment and slowly push it in with firm pressure Once the sampling head is seated turn the lock down screw to tighten the sampling head into place To prevent damage to the sampling head or instrument never install or remove a sampling head when the instrument s PRINCIPAL POWER SWITCH is ON powered on To install a sampling head first power off the instrument Then place the sampling head in a compartment and slowly push it in with firm pressure Once the head is seated turn the lock down screw on the sampling head to tighten the head into place See Figure 3 Mainframe iv Lock Down Screw Sampling Head Figure 3 Installing a Sampling Head in an Instrument 10 SD 24 User Manual Using the Sampl
33. tors Safety Do Not Operate in Explosive Atmospheres The sampling head provides no explosion protection from static discharges or arcing components Do not operate the instrument in an atmosphere of explosive gases 4 SD 24 User Manual SD 24 User Manual Electrostatic Discharge To prevent electrostatic damage to the instrument and sampling heads follow the precautions described in this manual and other manuals accom panying your sampling head and instrument Acquisition circuitry in the sampling heads is very susceptible to damage from electrostatic discharge and from overdrive signals and DC voltages Be sure to operate the mainframe instrument only in a static controlled environ ment Be sure to discharge to ground any electrostatic charge that may be present on cables before attaching the cable to the sampling head j caution amp To prevent damage from electrostatic discharge install short circuit terminations on the sampling head connectors before removing from an instrument or storing a sampling head Be sure to store the head in a static free container such as the shipping container Whenever you move the sampling head from one instrument to another use a Static free container to carry the sampling head Always use a wrist strap provided with your instrument when handling your sampling head or making connections Electrostatic Discharge 6 SD 24 User Manual SD 24 User Manual Connector Care The front
34. you how to use the two channels and step generators ofthe SD 24 to perform differential and common mode TDR measurements For this example you need an instrument with at least one SD 24 installed in the left most slot You also need two SMA cables preferably of 5 ns length L Step 1 Initialize the instrument press UTILITY and touch Initialize L Step 2 Connect your wrist strap to the antistatic connector on the front of your instrument L Step 3 Attach one end of each cable to the upper and lower channel connectors on the same sampling head Step 4 Press the SELECT CHANNEL button for the upper channel on the sampling head L Step 5 Press the WAVEFORM button and touch the Sampling Head Fnc s selector Step 6 Touch Diff TDR Preset to turn both TDRs on set Trigger to Internal Clock and autoset the upper channel The display should be similar to Figure 14 L Step 7 Touch the Sampling Head Fnc s selector again The lower channel on each sampling head has an internal delay adjustment This lets you set the time at which the step generator for the lower channel asserts the TDR step Touch the TDR Head A Delay selector Then touch Exit to remove the pop up menu C Step 8 Turn either knob on the mainframe to adjust the delay for channel 2 This varies the time when channel 2 asserts the TDR step Notice that the second edge moves horizontally relative to the first edge C Step 9 Press the WAVEFORM button On the disp
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