Terence: If I understood you correctly, you did not point out how you judge the waveform is accurate or not. Can you provide this information? I guess your simulation results be very accurate when you set your simulation length equal to 200ns, 400ns, 600ns and so on. There is a tricky parameter in hspice: fbase. It controls how touchstone file be interpreted by simulator. It should equal your touchstone file data spacing in frequency. If you do not specify, it will be set to 1/(simulation length). Normally, it should be fine. In special cases, interpolation of s-parameters will incur big error. There is also another parameter fmax, which controls how simulator do the inverse FFT. You should set it to be close to your touchstone file data max range. I hope this helps... regards, Han IDT Corp. TerenceHsieh@xxxxxxxxxxxx wrote: Dear all I have some s-parameter simulation problem. I have s-parameter file extracting from board file and simulate it by Hspice. According to the input signal, I extracted the s-parameter with sufficient bandwidth and points (input signal: 125MHz, S-parameter bandwidth : 5GHz 1000pts/linear). When simulating, the output waveform will vary with input rise/fall time enormously and also simulation time. The most accurate waveform will occur when the input rise/fall time set to 0.8ns and simulation time set to some specific value. Even though the rise/fall time set to larger or smaller than 0.8ns the output waveform will get inaccuracy. The s-parameter bandwidth is larger than knee frequency of input signal and I also filtered out high harmonic component of input signal (input signal is an idea 50/50 duty pulse) by 5 order low-pass filter ( cut-off frequency set to 10 times the input knee frequency). Why the s-parameter can just simulate at specific input condition accurately? How could I use s-parameter more accurately? Thanks. Terence ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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 __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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