[SI-LIST] : Routing Differential Pairs as 100 differentially Vs individually 50 ohm lines

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From: Gaboian, Jerry (j-gaboian@ti.com)
Date: Thu Nov 09 2000 - 06:31:49 PST


I am looking for some feedback on the topic routing LVDS differential pairs
as 100 ohms
with respect to each other Vs. 2 separate 50 ohm lines.

At the PCB East conference several keynote speakers referenced the following
comment:

"No need to specify differential impedance between two lines. Routing traces
side by side
does not guarantee noise immunity from common mode noise. On the contrary,
noise from an
adjacent line will couple as a differential signal"

The length of the pairs should be matched and kept close to a reference
plane (about 5 mils)is the must important criteria.

Comments, suggustions.......

Thanks,
Jerry Gaboian

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