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

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From: Chung, Sinh (Sinh_Chung@littonas.com)
Date: Fri Apr 21 2000 - 06:49:30 PDT


For diff. signals, you want the routing of the two to be close
to one another as much as possible and matched length so that even when
noise
coupled to the diff. signals, they will be cancelled out since you only
looking at the
difference of the two signals. I'm implying that the coupled noise is
hopefully common mode noise.
So routing the signals so that they are close to one another is important,
and you need them to be symetric.

> -----Original Message-----
> From: Lisa Desandoli [mailto:Lisa_Desandoli@pmc-sierra.com]
> Sent: Thursday, April 20, 2000 5:07 PM
> To: 'SI'
> Subject: [SI-LIST] : Differential Signalling and Crosstalk
>
>
> 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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