On Sun, 08 Dec 2013 10:41:37 -0700, Jim Thompson
wrote:

Anyone have a decent Spice model for a twisted pair... lossy, not the
ideal model in circulation?

...Jim Thompson

There's enormous variation in twisted pairs, even among "standard" things like
compliant CAT5 and CAT6 cables.

The Spice lossy delay line implements The Telegrapher's Equation, but ignores
skin loss variation with frequency. The best thing to usually do is get a chunk
of the actual cable of the expected length and note its step response on a
scope, then fiddle the Spice lossy line parameters to match. An extra RC or two
sometimes helps fine-tune the model to reality.

Multi-pair cables, like CAT5/6, can be expected to have various amounts of
crosstalk and pair delay skews, too.

https://dl.dropboxusercontent.com/u/..._Risetimes.pdf

https://dl.dropboxusercontent.com/u/...tonewall_2.JPG

https://dl.dropboxusercontent.com/u/...P_CAT6A_Tr.pdf

Simple RC equalization helps, if the cables are repeatable.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

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