[SI-LIST] Re: Causality

I guess there are some hyperlinx users in my office. I might give it a  
try.

How do I know it non-causal? I used my Spar block for transient  
simulation and fed in a measured current activity. This current  
activity is only active starting let's say 1ns. From 0ns to 1ns it is  
flat zero. At the output side of my Spar block I see some transient  
behavior (ripple like). That is how I concluded that my Spar is indeed  
non-causal.

I also tried to use the broadband spice generator from Agilent. It too  
gives warning message that the Spar is non-causal. The tool is able to  
enforce passivity, but not causality.

Based on the frequency and rise time of my signal, I only need a model  
up to around 5 GHz. Just to be safe, I ran my EM simulation up to  
20GHz. While the energy level converged nicely down to -60dB and the  
power balance looks well, my Spar is still non passive and non causal.

Confused :(



On May 15, 2009, at 5:56 PM, "Dmitriev-Zdorov, Vladimir" 
<vladimir_dmitriev-zdorov@xxxxxxxxxx 
 > wrote:

>
>
> 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.
>
> Vladimir
>
> 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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