[SI-LIST] Re: Preparing S-Parameters for Simulation
- From: <colin_warwick@xxxxxxxxxxx>
- To: <scott@xxxxxxxxxxxxx>, <amolak_badesha@xxxxxxxxxxx>
- Date: Thu, 26 Feb 2009 01:46:07 -0700
Hi Scott,
Here's a 2007 paper about our (patented) technique for getting causal impulse
responses from S-parameters, including a comparison:
http://eesof.tm.agilent.com/pdf/si_seminar_2007_transient_simulation.pdf
The key thing to bear in mind is that applying an IFFT to S-parameters to try
to get an impulse response will guarantee the wrong answer: the output of an
IFFT is by definition a piece of periodic waveform: not a single impulse at
all, but a truncation (one period of a train of impulses). It's true you can
use band-aids like windowing to try to minimize the Gibbs phenomenon but this
doesn't get the heart of the problem, which is this:
To get an impulse response in general you'd need the frequency response in the
complex plane (s = alpha + j*omega) and then do an inverse *Laplace* transform.
Fortunately, it turns out that don't need all that data because for causal
systems the Kramers-Kroenig relations:
http://en.wikipedia.org/wiki/Kramers-Kronig_relations
...allow you to reconstruct the response using just the steady state frequency
response (alpha=0 locus) i.e. the information in the S-parameters file. The
resulting fit is guaranteed causal.
For more info on our implementation please see:
http://www.agilent.com/find/signal-integrity
Hope this helps,
-- Colin
http://signal-integrity-tips.com <http://signal-integrity-tips.com/>
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Scott McMorrow
Sent: Wednesday, February 25, 2009 4:08 PM
To: BADESHA,AMOLAK (A-SantaClara,ex1)
Cc: shlepnev@xxxxxxxxxxxxx; tim@xxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Preparing S-Parameters for Simulation
Amolak
Is there documentation on how those causality/passivity corrections are
performed? Any way to compare the before and after results?
regards,
Scott
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