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

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From: Ritchey Lee (leeritchey@earthlink.net)
Date: Wed Nov 22 2000 - 09:38:00 PST


Those comments are from my class. That is exactly how differential
signals should be routed. Routing them close to each other produces
interaction that reduces the final amplitude. I route 2.5 GB
differential signals as two 50 ohm lines separated by at least 25 mils.

Lee

Gaboian, Jerry wrote:

>
>
> 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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