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

From: Ritchey Lee ([email protected])
Date: Wed Nov 22 2000 - 09:38:00 PST

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• In reply to: Gaboian, Jerry: "[SI-LIST] : Routing Differential Pairs as 100 differentially Vs individually 50 ohm lines"

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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• Next message: Ritchey Lee: "Re: [SI-LIST] : Matched Length Traces"
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