[SI-LIST] : differential pair routing

Mario Appiani (mappiani@attotech.com)
Tue, 10 Aug 1999 15:18:18 -0400

From: Mario Appiani@ATTO TECHNOLOGY on 08/10/99 03:18 PM

To: si-list@silab.eng.sun.com
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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