Re: [SI-LIST] : simulating differential pairs in Specctraquest

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From: Aloke Bhattacharya ([email protected])
Date: Thu Aug 24 2000 - 20:46:30 PDT

Hi Ken,
  Thanks a lot for the reply. Can you please explain a little more about the
two alternatives you have
suggested for the simulation of differential pair? Can you please explain
exactly how to
(i)mock up differential pairs interactively in sigxp.
(ii)simulate differential pair at the board level.
It would be nice if you can explain the method in terms of Specctraquest

Regarding the board level simulation of differential pair, you have mentioned
only about post route
analysis- is pre route analysis not possible for diff pairs?

After the board level simulation as you have mentioned in the second
alternative, is it possible to get
the wavefoms(I means the 180 degree phase shifted waveforms of the two lines)
in sigwave?

With regards,

Ken Willis wrote:

> Hi Aloke,
> Today, you can't extract coupled-line circuits into Sigxp. You
> can build coupled-line topologies interactively in Sigxp and
> simulate them, or simulate coupled-line stuff to your heart's
> content at the board lavel, but today you can only extract
> single-line topologies directly from Allegro into Sigxp. The
> reason for this is that, besides being complicated (try to come
> up with an algorithm to auto-place all those symbols in the Sigxp
> canvas legibly!), for a given geometry window you may end up with
> an enormous coupled circuit. It isn't uncommon to drag
> 20 neighbor nets into a crosstalk simulation. While this is routinely
> done at the board-level simulation with SPECCTRAQuest, extraction
> of coupled stuff into Sigxp as topologies won't be supported until
> some kind of intelligent pruining algorithms are written, for example
> to just extract the 2 diff pair nets into Sigxp and nothing else. I
> know this was being kicked around a couple of months back, but don't know
> the status.
> The way I do it today is two-fold:
> - mock up your diff pairs interactively in Sigxp and
> figure out your wiring rules
> - simulate the diff pairs at the board level post-route
> and look at the skews, waveforms, and eye patterns
> It works pretty well, I've gotten good correlation with lab
> measurement well up over 600 MHz for diff pairs.
> Ken Willis
> Sirocco Systems
> -----Original Message-----
> From: Aloke Bhattacharya [mailto:[email protected]]
> Sent: Thursday, August 24, 2000 12:31 PM
> To: [email protected]
> Subject: [SI-LIST] : simulating differential pairs in Specctraquest
> Hello,
> I am facing a problem with simulation of differencial pairs in
> Specctraquest. When I try to extract the topology of a net which is
> defined as part of a differential pair, Sigxp gives error saying
> "differential pair extraction is currently not supported". Does anybody
> know how to simulate a differential pair
> in Specctraquest?
> Thanks in advance,
> With regards,
> Aloke
> ****

* Aloke Bhattacharya,                                                *
* Senior Engineer-VLSI/System Design,
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