N8833A Datasheet, PDF (7/15 Pages) Keysight Technologies – Crosstalk Analysis Application

07 | Keysight | N8833A and N8833B Crosstalk Analysis Application for Real-Time Oscilloscopes - Data Sheet
Test Setup
1. Probing
To create a test setup for crosstalk, simply probe all of the transmission lanes and power
supplies that are to be included in the analysis. The application currently supports a total of
four input waveforms.
For serial data signals, it is best to probe all the victim lanes at the receiver end. This captures
the actual waveforms that are delivered to the receiver. For perfectly-terminated transmission
lines, this probing scheme will capture primarily FEXT since NEXT travels back toward the
receiver end. However, it’s possible for a received waveform to contain elements of both FEXT
and NEXT. To specifically analyze NEXT, one can probe at the transmitter end. In the crosstalk
tool you do not need to specify a NEXT or FEXT measurement; The application will measure the
crosstalk that is present regardless of what type it is.
For power supply aggressor crosstalk, it is also best to probe the victim lanes at the receiver
end. The power supply aggressor can be probed anywhere. Keep in mind that supplies of both
the transmitter and receiver can contribute to crosstalk.
For power supply victim crosstalk, it does not matter where you probe the victim or the
aggressors in this case. It is possible to have up to three aggressors, but all of them must be
serial data aggressors. This requirement is because ground bounce is a result of the current
drawn from a supply during data transitions, so it is necessary to find those transitions. Only
one power supply victim can be analyzed at a time due to the complexity of the algorithm.
2. Synchronization
Another consideration in the test setup is synchronization. Because the application is looking
for correlations between victims and aggressors, all victims and aggressors need to be acquired
simultaneously. That application accommodates time skews between victims and aggressors.
However, minimizing this skew can improve calculation time measurement results.
3. Test patterns
The crosstalk application will work with arbitrary serial data patterns, though periodic patterns
produce better results with a shorter calculation time. Note also that in order to distinguish
between distortions cause by ISI and the various aggressors, each serial data channel must
transmit different patterns or run at different data rates. Note that longer data patterns are not
necessarily helpful or desirable in the crosstalk analysis tool. One reason is simply practicality.
A jitter analysis tool looks only at timing errors in the data, so it only needs to process one
data point per data edge (transition), whereas the crosstalk tool uses all of the waveform data.
Therefore, moderate lengths up to 2¹¹ - 1 or less are recommended.