[SI-LIST] Re: Transmission line match
- From: Ross_Amans@xxxxxxxx
- To: doug@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Wed, 12 Nov 2003 17:55:08 -0600
Doug -
So now, don't you go into under-damped, damped, and over-damped
discussions?
Thanks
Ross Amans
-----Original Message-----
From: Doug Brooks [mailto:doug@xxxxxxxxxx]
Sent: Wednesday, November 12, 2003 4:43 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Transmission line match
I am trying to develop a *qualitative* (NOT quantitative) explanation of
what happens at the terminating end of a transmission line. I think I am on
the track with this model and discussion:
1. The transmission line model is a lumped model of a string of Ls and Cs.
2. The termination value forms a time constant with these. That is, if
R=Z=(L/C)^.5, then RC=L/R. That is, when correctly terminated, the time
constants are matched.
3. If the terminating resistance is high, then the RC time constant is
relatively longer. If it is low, then the L/R time constant is relatively
longer.
At this point I am having trouble getting over the "so what?" and
completing the argument. What is the next step in this argument..... or am
I on the wrong track altogether?
Thanks
Doug Brooks
Doug Brooks' new book, "Signal Integrity Issues and Printed Circuit Board
Design" has just been released by Prentice Hall. See details and ordering
info at www.ultracad.com. Also check out UltraCAD's new differential
impedance calculator.
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