Re: [SI-LIST] : differential pair routing

Steve Weir (weirsp@a.crl.com)
Tue, 10 Aug 1999 15:48:22 -0700

Mario,

Both are important, but my vote is to keep the traces together. Even a
small bump greatly impairs the radiation, and susceptibility. Variations
in the trace length introduce common mode currents where it counts during
the signal transitions.

Regards,

Steve.
At 03:18 PM 8/10/99 -0400, you wrote:
>
>
>From: Mario Appiani@ATTO TECHNOLOGY on 08/10/99 03:18 PM
>
>
>To: si-list@silab.eng.sun.com
>cc:
>Subject: differential pair routing
>
>Hello all,
>
>I have a question about routing differential pairs. Is it more important
>to maintain trace lengths between the pairs (one spec says to keep trace
>lengths within .100") or to maintain the trace spacing throughout the trace
>run? I 've noticed on several boards that in order to maintain trace
>lengths between pairs, many designers have had to add loops or bumps in one
>of the pairs' lines. When I see this, I wonder about how the impedance
>change, due to the increased trace pair separation, has on the signal.
>
> _____
>_____/ \________________ + leg
>
>___________________________ - leg
>
>
>Do I need to worry more about jitter or impedance mismatches? If loops are
>ok, does it matter where they are placed (i.e. in the middle of the run or
>at the end) ?
>
>Thanks in advance,
>
>Mario Appiani ext. 130
> Sr. Digital Systems Engineer
> ATTO Technology, Inc.
> 40 Hazelwood Drive
> Suite 106
> Amherst, NY 14228
> Tel. 716.691.1999
> Fax. 716.691.3724
> Email. mappiani@attotech.com
>
>
>
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