RE: [SI-LIST] : Differential Pair Theory

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From: Phares, Charles C (charles.c.phares@intel.com)
Date: Mon Nov 15 1999 - 15:15:30 PST


-----Original Message-----
From: Mike Degerstrom [mailto:degerstrom.michael@mayo.edu]
Sent: Monday, November 15, 1999 2:18 PM
To: si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : Differential Pair Theory

<snip>
100 ohms. One thing to keep in mind is that if you route your
t/c pair closely together on your pcb then you must design for
the odd mode impedance which is typically several ohms lower
than your single-ended Zo.
<snip>

could you elaborate on what you mean by "design for the odd mode impedance"?

there is a pretty good article regarding differential impedances in both
microstip and stripline layouts. i would like some other people to look
over it and comment on whether they think that some information regarding
the trace thickness has been overlooked, especially in very tightly spaced
layouts. ie a 1/2 oz. trace has a thickness of about .7mils. if the traces
are spaced 20- mils appart, then the thickness, t, isn't a big factor in the
eqn. but if the traces are spaced only 5-mils or so apart, then t should
start to have an effect. i am likely wrong about this, but i would like
someone to tell me why.

here is the link to the article...
http://www.edtn.com/analog/tn025.htm

also, thanks for the responses on my quad model question a few days ago.

Charles Phares

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