Re: [SI-LIST] : Differential pairs and place splits

Vinu Arumugham (vinu@cisco.com)
Tue, 10 Feb 1998 09:17:18 -0800

It depends on the amount of coupling between the differential pairs. In
many implementations of differential pair traces, there is a tighter
coupling to the reference plane than between the traces. Since the bulk of
the return current would flow through the lowest impedance path ( in this
case the plane ), a split in the plane would remain a signal quality and
EMI concern.

Vinu

Young, Randy wrote:

> Hi,
> I understand that in general, routing high-speed digital traces across
> plane splits is a bad idea from both a signal quality perspective and an
> EMI perspective due to return current paths. My question is concerning
> differential pairs - specifically, USB and 1394. Do the same rules
> apply? Is routing a differential pair across a plane split bad from
> either signal quality or EMI perspective? My assumption is that the
> return current path for a differential pair is the other trace of the
> pair, and that this would greatly reduce any signal quality or EMI
> problems associated with crossing splits. Is this correct?
>
> Randy Young
> ryoung@scdc.cirrus.com