Ken,

The measuring frequency is dependent on the rise time and the length of the
signal trace. As the trace becomes shorter the TDR tester increases the
frequency so that it can obtain a good sampling along the shorter trace. The
frequency at which the test occurs is not really within the operators control
If you wish to control the test frequency, then you must provide the
fabricator with a test trace length that is calculated to force the TDR
tester to test at a given frequency. your fabricator should be able to
provide that information to you for a given design. Rather than ask for a
specific frequency, you may wish to ask at what frequency did the test occur.
Often it occurs at a higher frequency than you desire, which may be good.

Regards,

Gary Ferrari
Executive Director
IPC Designers Council
860-350-9300

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