[SI-LIST] Re: Guard traces for differetial pairs

Tonglong,

Guard traces don't "guard".  If you have the bad luck to get just the right
length, they become a band pass filter.  They should not be used.  Handle
cross talk by setting proper spacings.

Lee


> [Original Message]
> From: Tonglong Zhang <tlzhang@xxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 9/25/2003 4:09:32 PM
> Subject: [SI-LIST] Guard traces for differetial pairs
>
> Gurus,
>
> Could you pls make comment on below statement on guard traces for
> differential pairs?
>
> Use gnd traces as guard trace is not very effective if there is gnd =
> plane
> direct underneath the differential pairs. As the current is mostly going
> through the plane (lower impedence path), there will be no (or little)
> current in the guard traces. When there are not current in the guard =
> traces,
> the guard traces will only shield electrical field but not magnatic =
> field.
> So magnatic coupling will not be better with the gnd guard traces.
>
> Thanks
>
>
> Tonglong Zhang=20
> Staff Engineer=20
> IC Packaging Engineering=20
> Broadcom  Corporation=20
>
>
>
>
>
>
>
>
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