re: [SI-LIST] : Guard banding

Ray Anderson (raymonda@radium.eng.sun.com)
Mon, 10 Nov 1997 16:11:10 -0800 (PST)

The context in which you usually hear about
"guard traces" is in very high impedance
analog circuitry where the designer is
trying to guard a very hi-Z node from
very minute leakage currents flowing across
a board or substrate. In these cases, a grounded
guard trace can be effective.

I tend to agree with Fabrizio, that in
high speed circuitry where one is concerned
with AC crosstalk, that the use of grounded
guard traces may be of dubious value.

So depending on what Ronda was referring
to when she asked about grounded guard traces,
the answer could go either way.

Ray Anderson
raymonda@radium.eng.sun.com

>
>
> Ronda, I don't have any papers to supply to you, but I
will mention one
> thing about the subject. In my experience, I have never
found guard bands
> to be a worthwhile thing to add to a design. It adds
traces, makes the
> board more complex, and the distance you need to space
critical traces from
> each other to fit the guard band is enough to eliminate
crosstalk between
> the traces. Guard bands also lower the impedance of
these critical nets.
> So unless one is running 2GHz+ signals, single ended on a
PC board, I would
> recommend not using guard bands.
> Regards,
> Fabrizio Zanella
>
Sr. Design Engineer
>
Hardware Engineering
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