[SI-LIST] Re: Causality

  • From: "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 15 May 2009 09:56:39 -0600

Hi Jennifer,

Did you try Hyperlynx's S-parameter Fitter/Viewer? It is an application inside 
Hyperlynx. With that, you can enforce causality and passivity of any 
S-parameter data file. The output is available in a form of tables of 
poles/residues, or as a SPICE compatible subcircuit. All stages of 
transformation are graphically viewable so you can control accuracy.

With that transformer, you simple will not be able to generate non-causal 
model, even if you want to :-)

If you can share your data, I'd be glad to build the model for you.


P.S. On thing I'm curious, how exactly you observed non-causality from time 
domain simulation? Since time domain simulators all work in sequential manner 
(step after step, with increasing time) the response can never come ahead of 
the input. Although, I agree that time response could be very different from 
what you'd expect from you frequency dependence.

Jennifer Maharani jennifer.maharani@xxxxxxxxx wrote:
To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
Sent: Thursday, May 14, 2009 12:48:44 PM
Subject: [SI-LIST] Causality

Dear all,

I have non-passive non-causal S-parameter. I can use some commercial  
tools that can generate broadband spice with passivity enforcement.  
Not with causality enforcement, though.

In transient simulation it clearly shows non-causal response.

Does anybody know how to resolve this issue? Quick and dirty solution  
will also be appreciated.

Many thanks. 

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