[SI-LIST] Re: how to simulate with S parameters
- From: "Raj Raghuram" <raghu@xxxxxxxxxxx>
- To: <Giovanni.Guasti@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 27 Feb 2003 09:03:46 -0800
Giovanni,
I did not see many responses to this and I thought I would offer my opinion
for what it is worth. Some approaches to model a given n-port S-parameter
description versus frequency are:
1. You can refrain from making any assumptions at all about the nature or
topology of a circuit which physically represents the S-parameters. You can
fit a rational function ( a ratio of polynomials in the Laplace variable s)
to the variation of S-parameters with frequency. HSPICE will directly take
in the rational functions. If you are using generic SPICE, you can always
make a model with RLC elements and controlled sources to represent the
rational polynomial or transfer function.
2. Since you are modeling a cable, you will probably need a high order
polynomial in the transfer function to model the cable. This is okay if care
is taken to see that the rational function is stable, causal, passive, etc.
3. You could try pulling out the variation of a lossless line from the
S-parameters, especially if the cable is very long. You can estimate the
electrical length from the number of times the phase variation goes through
zero. You can estimate the characteristic impedance from the quarter-wave
impedance. You could match the rest of the variation with a rational
function or make circuits and use the HSPICE optimization routines to find
the values for the circuit elements. . For example, RL ladders can
approximate the skin effect loss and RC circuits the dielectric loss.
I can try to dig up references on some of these if you are interested. Or,
of course, you can always get software to do this from us or anybody else.
Best Regards,
Raj Raghuram
Sigrity, Inc.
"Achieve what others can't"
raghu@xxxxxxxxxxx
http://www.sigrity.com
4675 Stevens Creek Blvd. , Ste 130
Santa Clara, CA-95051
PH: 408-260-9344 x116
CELL: 408-390-7614
FAX: 408-260-9342
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Guasti Giovanni
Sent: Tuesday, February 25, 2003 12:04 AM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] how to simulate with S parameters
Hi All,
I would like to make some transient and ac simulation of a lossy cable,
modeled with frequency Scatter parameters.
Does anybody know the right way to do it? Does Hspice permit it? Could you
indicate some interesting lectures to me?
Thanks in advance.
Regards,
Giovanni Guasti
giovanni.guasti@xxxxxxxxxx <mailto:giovanni.guasti@xxxxxxxxxx>
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