Hi,
How do you guys measure skew on PCBs in the 2ps range?
We just made a test board, tried to measure skew but the results varied
randomly by +/-8ps. The test board had very good spread glass. So I'm
worried that the measurement inaccuracy was larger than the actual value to
be measured.
Actually the measurement was single-ended delay measurement with TDR (20GHz
TDR scope), then it was redone with a VNA as well. Both had similar results.
With the 65GHz VNA (65GHz probes under microscope) the measurement was for
frequency of dips on S11, then converted to delay. Different traces had
different delay, even at the same length, due to skew, as expected. But the
actual number varied over time (~1sec) too.
Is there a better setup to get lets say 1ps accuracy? What instrument to
use, or what's the secret?
Do you measure delay on each leg, or measure diffpairs for skew directly?
Regards,
Istvan Nagy
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