[SI-LIST] Re: Causality

Jennifer,

The 'ripple' has half of the sampling frequency, correct?
Have you tried applying a suitable window function?  The Agilent 
solution that Colin referred to
is an elegant way of providing causality without loss of bandwidth, but 
if you have a 4x
oversampling, you should be able to get rid of the Nyquist ripple by 
applying a window
function.

Regards,

Istvan Novak
SUN Microsystems


Jennifer Maharani wrote:
> 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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