Re: [SI-LIST] : What's your favourite Screwy SI Concept?

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From: D. C. Sessions (dc.sessions@vlsi.com)
Date: Mon Jan 10 2000 - 14:19:36 PST


Kim Helliwell wrote:
>
> Chris Heard wrote:
> >
> > Here's another...
> >
> > Use a ground trace in between signal traces to reduce crosstalk....

> I'm curious why this is screwy. Is it because:
>
> 1. The separation of the signal traces alone (because of the ground trace)
> would be enough to reduce the crosstalk, so the ground trace is not needed, or
>
> 2. The ground trace actually contributes more crosstalk.

#2. The reason is that for nontrivial frequencies the "ground trace"
is really floating metal and takes up space. So if you have room for
a 6 mil track between two other 6 mil tracks, you COULD have 18 mils
of space instead. 18 mils of space has 2/3 the capacitance of 12
mils (6 mils of copper is close to a dead short) and thus more coupling.

-- 
D. C. Sessions
dc.sessions@vlsi.com

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