1. 4/1/2017
Cable Testing using TDR and TDT methods Presented by Christopher Skach Tektronix Dima Smolyansky TDA Systems

2. Agenda Cable specifications and standards
4/1/2017
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
Tektronix Net Seminar 2003

3. Higher Clock and Data Rate Challenge
4/1/2017
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
These are some of the standards of today. This is only the beginning of technology reaching for the speed that consumers expect.
Tektronix Net Seminar 2003

4. Cable and Connector Specifications
4/1/2017
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:
With digital systems requiring faster edges these signal integrity issues are concerns that not only analog engineers have to deal with but digital engineers also need to understand. Impedance issues are at the core of SI and TDR is the fastest and easiest way to determine impedance related issues.
EIA standard testing documents can be found at:
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5. Cable and Connector Specifications
4/1/2017
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.
Some of but not all electrical tests required. All of which can be accomplished with TDR/TDT and software methods.
Tektronix Net Seminar 2003

6. Why use TDR/TDT Methods?
4/1/2017
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.
Signal Integrity is the current theme that everyone is concerned with today. With digital systems requiring faster edges these signal integrity issues are concerns that not only analog engineers have to deal with but digital engineers also need to understand. Impedance issues are at the core of SI and TDR is the fastest and easiest way to determine impedance related issues.
Tektronix Net Seminar 2003

7. Example of TDR results on production sample
4/1/2017
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
Here we see how TDR signatures can be used to observe quality issues and quickly identify sources to these issues.
Tektronix Net Seminar 2003

8. Agenda Cable specifications and standards
4/1/2017
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
Tektronix Net Seminar 2003

9. 4/1/2017
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.
What is TDR, Time Domain Reflectometry, basically it is sending a fast edge down a transmission line and looking at it’s reflection. This reflection can tell us many things about the transmission line.
Fast
Step
Source
Characteristic
Impedance Z2 > Z0
Characteristic
Impedance Z1 =Z0
Impedance
Change Point
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10. TDR Fundamentals – Oscilloscope Monitoring
4/1/2017
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.
Oscilloscope Measurement Point
Knowing the reference source allows the instrument to quantifiably measure the reflection.
Transmission Line
Z2 > Z0
Fast
Step
Source
Z1 = Z0
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11. 4/1/2017
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.
What is TDT, Time Domain Transmission, basically it is sending a fast edge down a transmission line and looking at it’s effect down the line.
Tektronix Net Seminar 2003

12. TDT Fundamentals – Oscilloscope Monitoring
4/1/2017
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.
Time
Delay/Skew measurements
First Oscilloscope Measurement Point
Second Oscilloscope Measurement Point
Knowing the reference source allows the instrument to quantifiably measure the effects of the transmission line.
Transmission Line
Fast
Step
Source
Amplitude
Rise-Fall time measurements
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13. TDT Measurements – Cross Talk
4/1/2017
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.
Other measurements can also be made such as crosstalk where the incident pulse is launched down one line and the other line is measured for effects created form power or energy fields dissipated between the two lines.
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14. TDR Measurements – Differential TDR Measurement
4/1/2017
TDR Measurements – Differential TDR Measurement
With the signal integrity issues many designs have gone to differential transmission lines to achieve:
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
So far we have talked about single transmission lines. Differential transmission lines give us the benefits listed here but do require special care when making the TDR measurements.
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15. TDR Measurements – Differential Clock Coupling
4/1/2017
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.
Here we can see some of these effects and it is important to understand why special care has to be made when making differential TDR measurements.
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16. TDR Measurements – Differential TDR Measurement
4/1/2017
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
Although Differential TDR is basically just two TDRs of opposite polarities it is important to understand that in order to simulate actual differential transmission effects that these two incidents pulses must be launched simultaneously.
Tektronix Net Seminar 2003

17. TDR Measurements – Differential TDR Step Timing Skew
4/1/2017
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.
To guarantee the incident pulses are launched simultaneously a skew adjust is available.
Tektronix Net Seminar 2003

18. Agenda Cable specifications and standards
4/1/2017
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
Tektronix Net Seminar 2003

19. Impedance Measurement (TDR)
4/1/2017 Z1
Impedance Measurement (TDR)
Impedance = Z1
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
Test Fixture
Unused lines terminated with 50 Ohms to Ground
80E04 Differential TDR Module
When making any precision measurement common practices such as high quality cables and connectors and use of such devices as sampler extender cables to move the sampler as close to the DUT as possible will increase measurement repeatability. The TDS8000 incorporates built in airlines and automatically compensates ohms and rho values at the sma connectors. So keeping the cables short and the DUT close to the sampler removes the need for external calibration.
High Speed SMA cables
Sampler Extender Cable
DUT Test Cable
Test Fixture
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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.
Tektronix Net Seminar 2003

21. Differential Impedance Measurement Procedure (TDR)
4/1/2017
Differential Impedance Measurement Procedure (TDR)
Cable & Connector Impedance
M1 = Filter(ChA+ChB)
Using the TDS8000 MagView allows measurement parameters on the full amplitude of the signal. MagView does not compromise resolution because it is acquiring at the magnified rate. Also using features such as user masks allow for quick pass – fail testing. For many standards it is required to provide a means of a TDR pulse of a specific rise time. This is accomplished using the filter function in the math definition of the differential display.
Just Cable Impedance
Use of template and measurement gates to automate test
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22. Rise Time Measurement (TDT)Rt
Measure Rise Time at far end of cable or connector.
Considerations :
Specified with differential TDR applied.
Requires a TDR and an electrical sampling module.
TDS 8000B Sampling Oscilloscope
80Exx Sampling Module
Sampler Extender Cable
80E04 Differential TDR Module
Unused lines terminated with 50 Ohms to Ground
High Speed SMA cables
DUT Test Cable
Test Fixture
Test Fixture
Tektronix Net Seminar 2003

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.
Tektronix Net Seminar 2003

24. Rise Time Measurement Procedure (TDT)
4/1/2017
Rise Time Measurement Procedure (TDT)
Using the TDS8000 MagView allows measurement parameters on the full amplitude of the signal. MagView does not compromise resolution because it is acquiring at the magnified rate.
Most specified at 20% to 80%. Important to find true min max levels. Also important that differential lines are driven simultaneously.
Tektronix Net Seminar 2003

25. Skew Measurement (TDT)
Skew = T2 – T1
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.
TDS 8000B Sampling Oscilloscope
80Exx Sampling Module
Sampler Extender Cable
80E04 Differential TDR Module
Unused lines terminated with 50 Ohms to Ground
High Speed SMA cables
DUT Test Cable
Test Fixture
Test Fixture
Tektronix Net Seminar 2003

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.
Tektronix Net Seminar 2003

27. Skew Measurement Procedure (TDT)
4/1/2017
Skew Measurement Procedure (TDT)
With user math setups, the specific mid level can be defined so absolute values can be obtained.
Most specified at 50%. Important to find true min max levels. Also important that differential lines are driven simultaneously.
Tektronix Net Seminar 2003

28. Crosstalk Measurement (TDT)
CrossTalk = V1 V1
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.
TDS 8000B Sampling Oscilloscope
80Exx Sampling Module
Sampler Extender Cable
80E04 Differential TDR Module
Unused lines terminated with 50 Ohms to Ground
High Speed SMA cables
DUT Test Cable
Test Fixture
Test Fixture
Tektronix Net Seminar 2003

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.
Tektronix Net Seminar 2003

30. Crosstalk Measurement Procedure (TDT)
4/1/2017
Crosstalk Measurement Procedure (TDT)
Math for dB display
With the versatility of the TDS8000’s math features. Displays can be generated in several different formats.
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.
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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.
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32. Tektronix is Enabling Innovation
4/1/2017
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.
With Tektronix’s Open Choice/Open Windows platform. External applications can be used without the need for an external controller to automate and simplify complex measurements.
Tektronix Net Seminar 2003

33. Agenda Cable specifications and standards
4/1/2017
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
Tektronix Net Seminar 2003

34. Frequency Domain Specifications
4/1/2017
Frequency Dependent Specifications
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.
The following are the specification typically requiring frequency domain measurements
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35. S-Parameters in IConnect® TDR software
4/1/2017
Frequency Dependent Specifications
S-Parameters in IConnect® TDR software
However, S-parameters can be easily achieved with TDR/T measurements and IConnect TDR software. For example, TDR can be conveniently converted in S11 or return loss in IConnect, whereas TDT – into S21 or insertion loss
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36. Differential S-parameters in IConnect
4/1/2017
Frequency Dependent Specifications
Differential S-parameters in IConnect
Similarly, a full differential and common mode S-parameters data can be obtained using IConnect with minimum effort.
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37. IConnect Correlation with Network Analyzer
4/1/2017
Frequency Dependent Specifications
IConnect Correlation with Network Analyzer
Correlation to 10 Ghz
And the resulting S-parameter data shows perfect correlation to the VNA data up to Ghz.
Tektronix Net Seminar 2003

38. Serial ATA: Differential Insertion Loss in IConnect
4/1/2017
Frequency Dependent Specifications
Serial ATA: Differential Insertion Loss in IConnect
This particular example shows differential insertion loss for a serial ATA cable. Clearly, the cable does not meet the 6dB specification up to 4.5 Ghz
Serial ATA data courtesy Molex, Inc.
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39. Eye Diagram Options TDT and IConnect Eye Diagram 4/1/2017
Time Domain Reflection and Transmission (TDR/T) measurement based eye diagram is computed in IConnect TDR software using Fourier techniques to compute the convolution of an input with the measured system response function. The modeling assumptions that go into this type of computation are that the system is linear and time-invariant, which are pretty standard assumptions for all interconnect modeling. The modeling equations can be found in a digital signal processing textbook (e.g., Discrete-Time Signal Processing by Oppenheim and Schafer). A time domain transmission waveform through the DUT is required for direct eye diagram prediction from the measurement. Alternatively, the eye can be predicted based on the models extracted for the interconnect, by simulating the transmission through the interconnect, and using it for the eye diagram prediction.
The user can choose between several different stimuli patterns, pattern length, signal amplitude, speed and rise time. Custom pattern can be entered as well.
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40. Predicted and Measured Eye Diagrams
4/1/2017
TDT and IConnect Eye Diagram
Predicted and Measured Eye Diagrams
This is an example of correlation between a pattern generated eye, and an eye generated in IConnect from TDT measurements.
2^10-1 measurement in IConnect based on TDT
2^10-1 measurement
Data courtesy FCI
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41. Eye Diagram Degradation in Interconnects
4/1/2017
TDT and IConnect Eye Diagram
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
The reason the eye diagram correlation is so perfect is because we are only producing deterministic jitter in the cables and connectors. The TDT measurement has all the information about this deterministic jitter, and all that is left to do for us is to reproduce that eye in IConnect TDR software
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42. Predicted and Measured Eye Diagrams
4/1/2017
TDT and IConnect Eye Diagram
Predicted and Measured Eye Diagrams
1.5Gb/s (Gen 1)
3.0Gb/s (Gen 2)
And here is another example, illustrating correlation between the pattern generator measured eye and the eye predicted in IConnect from TDT measurements, for a serial ATA example. Again, good correlation is observed.
Serial ATA data courtesy Molex, Inc.
6.0Gb/s (Gen 3)
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43. Cable Loss Modeling: Time and Frequency
4/1/2017
TDT and IConnect Lossy Lines
Cable Loss Modeling: Time and Frequency
Losses in cables exhibit themselves as rise time and amplitude degradation. It may be useful for a system designer to have SPICE model for the cable loss, and may give a cable manufacturer a competitive edge.
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44. Example: Extraction Results
4/1/2017
TDT and IConnect Lossy Lines
Example: Extraction Results
Extracted skin effect and
dielectric loss parameters
Simulated and measured transmission
Loss modeling and extraction is an easy task in IConnect TDR software. A model that will accurately predict skin effect and dielectric loss can be easily extracted using IConnect loss modeling algorithm
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45. Agenda Cable specifications and standards
4/1/2017
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
Tektronix Net Seminar 2003

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
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47. Tektronix TDS/CSA8000B TDR rise time: 8 acquisition channels
4/1/2017
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
Tektronix Net Seminar 2003

48. TDA IConnect® Software
4/1/2017
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!
Tektronix Net Seminar 2003