Re: [SI-LIST] : trace width for clock routing- wider/narrower?

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From: Gerald Johnson (jjohnson@minn.teradyne.com)
Date: Mon Mar 13 2000 - 10:53:19 PST


Doug,

>From: Doug Brooks <doug@eskimo.com>
>Subject: Re: [SI-LIST] : trace width for clock routing- wider/narrower?

>Assuming you ARE controlling for impedance and crosstalk, trace width is
>not an issue UNLESS there is a power (trace heating) issue. Absent that,
>width is not an issue.
>

UNLESS, of course you're dealing with fast clocks where
the high frequency line losses (not DC heating) become
important. I've routed clocks on very wide lines specifically
to keep the edge rates from rolling off due to skin effect.
These were faster than "normal" clocks (up to 1.2 GHz) with
GaAs drivers. Again points out the problems of a "rule of
thumb". One persons clock frequency is not another persons
clock frequency. As usual it all depends on the details.

Jerry Johnson
Senior Staff Engineer
Teradyne Inc.

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