[SI-LIST] Re: How to simulate length mismatch of PCB traces

  • From: "Donald Telian" <telian@xxxxxxx>
  • To: <yc2158@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Wed, 29 Mar 2006 18:16:18 -0800

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
> > >
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> 
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