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

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From: Doug Brooks (doug@eskimo.com)
Date: Thu Apr 20 2000 - 16:02:32 PDT


Lisa,

There is an article on our web site entitled
"Impedance Terminations: What's the Value?"
It specifically describes the coupling that occurs when two traces are
routed close together, and why this mutual coupling can be beneficial in
the case of differential signals.

http://www.ultracad.com

Doug Brooks

At 03:06 PM 4/20/00 -0700, you 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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.
Doug Brooks, President doug@eskimo.com
UltraCAD Design, Inc. http://www.ultracad.com

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