[SI-LIST] Re: Preparing S-Parameters for Simulation

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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