Date: Fri Aug 11 2000 - 09:08:37 PDT
After rereading my earlier transmittal on this topic, I noted a minor
inconsistency that matters little, but might serve to confuse some. Scott's
sliding paper example centered the transitions of both lines at "zero" time.
This assignment makes the crossover disappear after a 200 ps skew of either
signal with respect to the other. I originally stated "If one signal is
skewed by the magnitude of the rise time (400 ps)..." which is in error; Only
200 ps is required.
Scott's subsequent clarification/elaboration on keeping "the differential
switch point well away from the high and low signaling levels where noise can
cause some terribly nasty glitches to occur in receivers" still applies. The
key factor here is that any critical timing edge/transition (differential or
not) that is degraded/slowed and/or experiences possible ringing/ripple in
the transition region can cause problems. (By "critical" I mean that other
circuit operations key off of this timing edge.)
Michael L. Conn
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