Re: [SI-LIST] : Differential Signalling and Crosstalk

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From: Fred Balistreri (fred@apsimtech.com)
Date: Thu Apr 20 2000 - 15:28:09 PDT


Your logic is backward. Ideally you would want diff signals coupled.
Sometimes
its easier to attain the Zo goals on a PCB if the diff signals are not coupled.

However electrically speaking a coupled diff pair is preferable assuming you
meet any critical Zo requirements.

Best Regards,

Lisa Desandoli wrote:

> Could anyone recommend guidelines for routing differential PECL signals at
> ~1.25GHz?
> What I'm concerned about is the relationship between coupling the
> differential pair and the cross talk induced because of that close coupling.
> I could be way off base here, but if the signals are closely coupled then
> there will be a lot of noise induced on both lines by the switching on the
> other. Since the signals are switching differentially, the noise induced on
> either line should be opposite in polarity. Since differential receivers
> are only good at rejecting common mode noise, wouldn't this be
> counterproductive? Is there a minimum spacing requirement for high-speed
> differential signals so that the cross talk noise is minimized?
>
> Thanks for your help,
>
> Lisa DeSandoli
> PMC-Sierra, Inc
>
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--
Fred Balistreri
fred@apsimtech.com

http://www.apsimtech.com

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