[SI-LIST] Re: Stub length of a clock


The basic relation is that a shelf will occur at half signal swing at the
receiver that is approx 2 times the time of flight of the stub.  This shelf
may introduce unacceptable timing uncertainty.  You could fix this problem
by routing two traces from the driver to each of the loads.  Use a series
terminator for each line at the source and you should probably simulate to
determine the R values.  Beware that this approach is doubly loading the
clock driver, which may or may not have adequate drive strength to keep
adequate edge rate.

You could also terminate at the teed topology at the receivers to get rid of
the shelf, and once again I would probably simulate in order catch all of
the problems with this.

Hope this helps,
James R. Jones

-----Original Message-----
From: Hora Abu [mailto:arageeb@xxxxxxxxx]
Sent: Thursday, January 23, 2003 5:58 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Stub length of a clock



Dear SI expert,

I have two loads that I need to support with one clock. I route the clock
from the generator to half way between the loads and T off to stubs each
going to its target load. I know that the stub needs to be minimize but I
can only make so short. Transmission line theory suggest there is a
relationship between the stub length and signal rise time? does any know
this relation or can point me to an article.

Thanks

Hura


arag abu deeb


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