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. >> ------------------------------------------------------------------ >> >> ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu