Re: Differential Pair Skew

Mike Jenkins (jenkins@lsil.com)
Fri, 26 Jul 1996 09:59:30 -0700

Sometimes it seems skew is given too much importance, but it does
have a number of subtle effects. While the differential signal
timing is theoretically insensitive to small skew, a common mode
signal is created. This is certainly a consideration in receiver
design, and needs to be limited by specification.

A second effect is on the dif'l risetime. Skew will "round off"
the corners of the differential signal, increasing the risetime.

A third effect is another aspect of the resulting common mode
signal. Perfect differential signals have the virtue of creating
zero net ground return current, so connectors with poor (or no)
ground connection and PC boards with split power/ground planes
are not a problem. Skew can turn these into real design issues.

Regards,
Mike Jenkins

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