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Cable Testing using TDR and TDT methods Presented by Christopher Skach Tektronix Dima Smolyansky TDA Systems.

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Presentation on theme: "Cable Testing using TDR and TDT methods Presented by Christopher Skach Tektronix Dima Smolyansky TDA Systems."— Presentation transcript:

1 Cable Testing using TDR and TDT methods Presented by Christopher Skach Tektronix Dima Smolyansky TDA Systems

2 Tektronix Net Seminar 2003Slide 2 Agenda Cable specifications and standards Introduction to TDR and TDT measurements Measurement Techniques Using TDA IConnect® software for frequency domain measurements Conclusion Questions and Answers

3 Tektronix Net Seminar 2003Slide 3 Higher Clock and Data Rate Challenge Infiniband 2.5Gb/s Firewire 1394b 1.6Gb/s Serial ATA 1.5Gb/s DVI 1 Gb/s High Speed USB 480 Mb/s

4 Tektronix Net Seminar 2003Slide 4 Cable and Connector Specifications Standard committees and trade associations are specifying the exact methods and measurements required to meet the signal integrity and interoperability requirements. These specifications are developed for compliance testing requirements and used to guarantee interoperability between many vender devices. Specifications can be found on Trade Association web sites such as: EIA standard testing documents can be found at:

5 Tektronix Net Seminar 2003Slide 5 Cable and Connector Specifications Electrical testing required for most cables and connectors: Impedance (for these new standards this is Differential Impedance and is a TDR measurement) Crosstalk ( This requires TDR & TDT Differential measurements) Rise Time (Differential TDR & TDT measurements) Skew (Differential TDR & TDT measurements) All of these measurements can be made using direct TDR/TDT methods. Loss, Jitter and Eye opening ( Frequency domain measurement) Can be obtained using TDA Iconnect software and TDR and TDT methods.

6 Tektronix Net Seminar 2003Slide 6 Why use TDR/TDT Methods? TDR can identify mismatches and variations of impedance which cause signal integrity problems. These SI problems can lead to data and logic errors and severe, hard-to-identify reliability problems especially in cables and connectors. TDR/TDT measurements are easier to setup and use than many other devices such as a VNA. One instrument can accomplish all tests required Substantially lower test costs! Automation can accommodate increased testing requirements. Can also be used as a troubleshooting - design tool.

7 Tektronix Net Seminar 2003Slide 7 Example of TDR results on production sample Initial inspection found excess solder on center pin of SMA connector, shown as yellow TDR trace Blue TDR trace is after solder removal

8 Tektronix Net Seminar 2003Slide 8 Agenda Cable specifications and standards Introduction to TDR and TDT measurements Measurement Techniques Using TDA IConnect® software for frequency domain measurements Conclusion Questions and Answers

9 Tektronix Net Seminar 2003Slide 9 So What is TDR? Time Domain Reflectometry - a measure of reflection in an unknown device, relative to the reflection in a standard impedance. Compares reflected energy to incident energy on a single-line transmission system. Known stimulus applied to the standard impedance is propagated toward the unknown device Reflections from the unknown device are returned toward the source and measured. Fast Step Source Characteristic Impedance Z 1 =Z 0 Impedance Change Point Characteristic Impedance Z 2 > Z 0

10 Tektronix Net Seminar 2003Slide 10 TDR Fundamentals – Oscilloscope Monitoring Use an oscilloscope to monitor the transmission line signal at the step source input point. The oscilloscope waveform will show the combined sum of the incident and reflected propagating signals in proper time sequence. Fast Step Source Z 1 = Z 0 Z 2 > Z 0 Oscilloscope Measurement Point Transmission Line

11 Tektronix Net Seminar 2003Slide 11 What is TDT? Time Domain Transmission - a measure of propagation transmission in an unknown device. A TDR step is propagated down a transmission line and then measured. Amplitude can be measured to determine the loss of the line or cross talk and other measurements such as rise and fall time can be measured to determine signal integrity through the line. Requires a TDR step and a separate sampling channel to acquire transmitted signal.

12 Tektronix Net Seminar 2003Slide 12 TDT Fundamentals – Oscilloscope Monitoring Use an oscilloscope to monitor the transmission line signal at the step source input point and at specific points of the transmission line. Fast Step Source Second Oscilloscope Measurement Point First Oscilloscope Measurement Point Time Amplitude Transmission Line Delay/Skew measurements Rise-Fall time measurements

13 Tektronix Net Seminar 2003Slide 13 TDT Measurements – Cross Talk Mutual coupling and crosstalk between signal lines can be characterized with TDT measurements. Apply the TDR step on one signal line and measure the signal strength on the other.

14 Tektronix Net Seminar 2003Slide 14 TDR Measurements – Differential TDR Measurement Higher noise immunity due to common mode rejection Less radiated noise due to canceling fields More precise timing characteristics Less crosstalk due to noise immunity and less radiated energy Less power supply noise due to current transients With the signal integrity issues many designs have gone to differential transmission lines to achieve:

15 Tektronix Net Seminar 2003Slide 15 TDR Measurements – Differential Clock Coupling Attempting to measure the two halves of the differential pair separately can produce misleading results. Two traces in close proximity tend to read a lower impedance than their characteristic impedance as a pair. Proper characterization of the differential impedance of the transmission line to maintain voltage and timing margins.

16 Tektronix Net Seminar 2003Slide 16 TDR Measurements – Differential TDR Measurement A differential TDR measurement is performed much like a single-ended TDR measurement Use two TDR sampling head channels with the simultaneous step generators set to opposite polarities

17 Tektronix Net Seminar 2003Slide 17 TDR Measurements – Differential TDR Step Timing Skew Another important consideration when making differential TDR measurement is the alignment of the TDR step pulses. The positive and negative going TDR steps must be adjusted so there is not any time skew between them at the transmission launch point.

18 Tektronix Net Seminar 2003Slide 18 Agenda Cable specifications and standards Introduction to TDR and TDT measurements Measurement Techniques Using TDA IConnect® software for frequency domain measurements Conclusion Questions and Answers

19 Tektronix Net Seminar 2003Slide 19 Impedance Measurement (TDR) Measure Characteristic Impedance of Cable and\or Connector. Considerations: Specified as differential pair. Some applications specify a specific rise time of the incident pulses. Test fixture required. TDS 8000B Sampling Oscilloscope Sampler Extender Cable 80E04 Differential TDR Module Test Fixture High Speed SMA cables DUT Test Cable Unused lines terminated with 50 Ohms to Ground Test Fixture Impedance = Z1 Z1

20 Tektronix Net Seminar 2003Slide 20 Differential Impedance Measurement Procedure (TDR) Connect differential TDR channels to test fixture using High Quality SMA cables and sampler extender cable so sampler can be close to the DUT. Create differential TDR pulse with specified rise time if required. De-skew differential incident pulses at the connector of the test fixture. Identify near and far end connector positions. Measure cable, making sure not to measure connector artifacts. Document Results.

21 Tektronix Net Seminar 2003Slide 21 Differential Impedance Measurement Procedure (TDR) Cable & Connector Impedance M1 = Filter(ChA+ChB) Just Cable Impedance Use of template and measurement gates to automate test

22 Tektronix Net Seminar 2003Slide 22 Rise Time Measurement (TDT) Measure Rise Time at far end of cable or connector. Considerations : Specified with differential TDR applied. Requires a TDR and an electrical sampling module. Unused lines terminated with 50 Ohms to Ground Rt 80E04 Differential TDR Module Sampler Extender Cable High Speed SMA cables TDS 8000B Sampling Oscilloscope 80Exx Sampling Module DUT Test Cable Test Fixture

23 Tektronix Net Seminar 2003Slide 23 Rise Time Measurement Procedure (TDT) Connect TDR channels to test fixture using High Quality SMA cables and sampler extender cable. Create differential TDR pulse with specified rise time if required. De-skew differential incident pulses at the connector of the test fixture. Connect High quality SMA cable to far end of DUT cable and high bandwidth sampling module. Measure cable DUT, by measuring Rise Time from incident TDR pulse at the connector to connector on far end of cable. Document Results.

24 Tektronix Net Seminar 2003Slide 24 Rise Time Measurement Procedure (TDT) Most specified at 20% to 80%. Important to find true min max levels. Also important that differential lines are driven simultaneously.

25 Tektronix Net Seminar 2003Slide 25 Skew Measurement (TDT) Measure time skew from near end differential pair to far end of cable or connector. Considerations : Specified in time to a specific tolerance. Requires care taken to de-skew the differential pairs. Unused lines terminated with 50 Ohms to Ground Skew = T2 – T1 T1 T2 80E04 Differential TDR Module Sampler Extender Cable High Speed SMA cables TDS 8000B Sampling Oscilloscope 80Exx Sampling Module DUT Test Cable Test Fixture

26 Tektronix Net Seminar 2003Slide 26 Skew Measurement Procedure (TDT) Connect TDR channels to test fixture using High Quality SMA cables and sampler extender cable. Connect High quality SMA cable to far end of DUT cable and high bandwidth sampling module. De-skew differential TDR at near end of connector. Measure cable DUT, by measuring skew in time from each differential line at far end of cable. Document Results.

27 Tektronix Net Seminar 2003Slide 27 Skew Measurement Procedure (TDT) Most specified at 50%. Important to find true min max levels. Also important that differential lines are driven simultaneously.

28 Tektronix Net Seminar 2003Slide 28 Crosstalk Measurement (TDT) Measures crosstalk on adjacent lines to driven lines on near end of cable or connector. Considerations : Specified in amplitude percentage of input TDR pulse to a specific tolerance or in dB. Requires a Differential TDR and an electrical sampling module. Unused lines terminated with 50 Ohms to Ground CrossTalk = V1 V1 80E04 Differential TDR Module Sampler Extender Cable High Speed SMA cables TDS 8000B Sampling Oscilloscope 80Exx Sampling Module DUT Test Cable Test Fixture

29 Tektronix Net Seminar 2003Slide 29 Crosstalk Measurement Procedure (TDT) Connect TDR channels to test fixture using High Quality SMA cables and sampler extender cable. Connect High quality SMA cable to near end adjacent lines and high bandwidth sampling module. Create differential TDR with specific rise time if required. De-skew differential TDR at near end of connector. Measure cable DUT, by measuring amplitude of TDR input taking care to remove effects of the connector and fixture if possible when measuring a cable. Repeat for each differential pair available. Document Results.

30 Tektronix Net Seminar 2003Slide 30 Crosstalk Measurement Procedure (TDT) Important that differential lines are driven simultaneously and lines are de-skewed properly on both ends. In some cases, fixture is difficult to remove but is usually minimal effect. Math for dB display

31 Tektronix Net Seminar 2003Slide 31 Measurement Considerations Care taken with connector and cable connections, use Sampler Extender cable if required to keep sampler close to DUT and perform ESD protection procedures. True Differential TDR capability. Care taken to de-skew signals properly. Care taken to find min-max levels. Care taken to get best resolution. Automated testing will increase repeatability.

32 Tektronix Net Seminar 2003Slide 32 Tektronix is Enabling Innovation Open Choice – Open Windows Platform enables automation and repeatability. Custom apps enable easy setup and accurate performance. Enable use of external applications to compliment tasks without the requirement for more equipment.

33 Tektronix Net Seminar 2003Slide 33 Agenda Cable specifications and standards Introduction to TDR and TDT measurements Measurement Techniques Using TDA IConnect® software for frequency domain measurements Conclusion Questions and Answers

34 Tektronix Net Seminar 2003Slide 34 Frequency Domain Specifications Insertion loss Serial ATA: <6dB to 4.5Ghz Return loss Crosstalk in frequency domain Serial ATA: lower than 26dB EASILY ACHIEVABLE WITH IConnect® TDR software running directly on TDS8000B. Frequency Dependent Specifications

35 Tektronix Net Seminar 2003Slide 35 S-Parameters in IConnect® TDR software Frequency Dependent Specifications

36 Tektronix Net Seminar 2003Slide 36 Differential S-parameters in IConnect Frequency Dependent Specifications

37 Tektronix Net Seminar 2003Slide 37 IConnect Correlation with Network Analyzer Frequency Dependent Specifications Correlation to 10 Ghz

38 Tektronix Net Seminar 2003Slide 38 Serial ATA: Differential Insertion Loss in IConnect Frequency Dependent Specifications Serial ATA data courtesy Molex, Inc.

39 Tektronix Net Seminar 2003Slide 39 Eye Diagram Options TDT and IConnect Eye Diagram

40 Tektronix Net Seminar 2003Slide 40 Predicted and Measured Eye Diagrams 2^10-1 measurement in IConnect based on TDT 2^10-1 measurement TDT and IConnect Eye Diagram Data courtesy FCI

41 Tektronix Net Seminar 2003Slide 41 Eye Diagram Degradation in Interconnects Interconnect losses Pattern-dependent, crosstalk induced jitter Method to improve the eye Equalization Pre-emphasis and de-emphasis Other signal conditioning techniques TDT and IConnect Eye Diagram

42 Tektronix Net Seminar 2003Slide 42 Predicted and Measured Eye Diagrams 1.5Gb/s (Gen 1) 6.0Gb/s (Gen 3) 3.0Gb/s (Gen 2) TDT and IConnect Eye Diagram Serial ATA data courtesy Molex, Inc.

43 Tektronix Net Seminar 2003Slide 43 Cable Loss Modeling: Time and Frequency TDT and IConnect Lossy Lines

44 Tektronix Net Seminar 2003Slide 44 Example: Extraction Results Extracted skin effect and dielectric loss parameters Simulated and measured transmission TDT and IConnect Lossy Lines

45 Tektronix Net Seminar 2003Slide 45 Agenda Cable specifications and standards Introduction to TDR and TDT measurements Measurement Techniques Using TDA IConnect® software for frequency domain measurements Conclusion Questions and Answers

46 Tektronix Net Seminar 2003Slide 46 Conclusion TDR/TDT measurements are sufficient for electrical cable testing. Differential TDR is required. Automation increases productivity and reliability of tests. Keeping connections close to DUT reduce setup and increase reliable measurements. Resolution is important when making precise measurements. Software solutions such as IConnect® compliment measurement capabilities and enables frequency domain measurements

47 Tektronix Net Seminar 2003Slide 47 Tektronix TDS/CSA8000B TDR rise time: 35 ps reflected 25 ps typical 8 acquisition channels 8-port TDR 4-port True Differential TDR TDR/TDT measurements High resolution and measurement repeatability Open Choice- Open Windows Platform

48 Tektronix Net Seminar 2003Slide 48 TDA IConnect® Software IConnect TDR software for gigabit interconnect… Signal integrity modeling and analysis Accurate impedance measurements Cost effective eye diagram testing Easy S-parameter analysis, differential and single ended Efficient, easy-to-use and cost-effective!


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