Hi Yongjin, We'll often just cascade another small W element on the end to cause the mis-match. You can then sweep or alter its length to find out when the problems start. There's a PCI Bus example in the Hspice manual that shows you how to do that. Donald ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Donald Telian SI Consultant telian@xxxxxxx 559-760-5793 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of yc2158 > Sent: Wednesday, March 29, 2006 5:44 PM > To: si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: How to simulate length mismatch of PCB traces > > Steve, > Thanks for your reply. I should clarify my question with Hspice W > model as follows: > > in1 --------------------- out1 > in2 --------------------- out2 > in3 --------------------- out3 > |<---length=3D10cm---->| > > W1 N=3D3 in1 in2 in3 gnd out1 out2 out3 gnd RLGCMODEL=3Dex_rlgc l=3D10cm > > Here I want to change the length of (in1,out1) to 10.1cm and the > others are the same length (10cm). If then, I think it is hard to > specify the different lengths for each line with W model. > Hope this would clarify my question. > > Yongjin > > --- In si-list@xxxxxxxxxxxxxxx, steve weir <weirsi@...> wrote: > > > > YongJin, if I understand you correctly, you would like to see skew > > effects from lines with mismatched lengths. Just build a SPICE > > simulation with different W elements of like impedance but different > > lengths. Alternatively, you can just calculate the timing difference > > from the material effective eR and the length offset. > > > > Steve. > > At 12:38 PM 3/29/2006, YongJin CHOI wrote: > > >Dear SI members, > > >I am looking for a simple simulation method to get a > > >rough idea if one or two of the four traces is a > > >little bit longer like 1~2mm. The transmission line > > >models I am having are W-model from Hspice field > > >solver(2-D) and S-parameter model from HFSS. I can use > > >Hspice or Spectre depending on the simplicity. > > >Any comments would be appreciated. > > >Thanks, > > > > > >Yongjin CHOI > > > > > >__________________________________________________ > > >Do You Yahoo!? > > >Tired of spam? Yahoo! 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