RE: [SI-LIST] : board-level simulation for differential signals

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From: Weber Chuang (WeberChuang@via.com.tw)
Date: Thu Apr 13 2000 - 20:04:10 PDT


Hi Weston and all SI-gurus,

  Thanks for the reply, that is the way we think about the simulation
algorithm and result, but here come the problems:

 1. so the even-odd mode switching cannot be simulated in QUAD/xtk or
similar tools, since while considering the switching direction of
neighboring nets, the impedance on the central net might vary, so would the
waveform. but if MDC won't take this into account, and differential nets is
not appropriate for this, thus this condition cannot be simulated.

 2. While simulating in differential mode, the waveform at receivers would
ramp up (or down ) a little bit far before the time the traveling wave
arrives, somewhat like while we are simulating in Hspice with inductor, the
waveform at driver side would ramp up a little bit before it switches down.
Does anyone know how to explain for this?

 We need to align the cross point of differential signal with single ended
signal, so it cannot be done with an analogy way, we need to be sure the way
we simulating differential signals is correct, before we could align them.

 Your comment is welcome and highly appreciated!

  Best Regards
    Weber Chuang
 Signal & Timing Integrity Engineer,
 VIA Technologies, Inc. Taipei, Taiwan, ROC
 TEL : 886-2-22185452 ext : 6522
 mailto:weber@via.com.tw
 http://www.via.com.tw
 Very Innovative Architecture

-----Original Message-----
From: Weston Beal [mailto:weston_beal@mentorg.com]
Sent: Friday, April 14, 2000 12:24 AM
To: si-list@silab.eng.sun.com
Subject: RE: [SI-LIST] : board-level simulation for differential signals

Daniel,

I have simulated differential signals in IS. I suspect that XTK and HSPICE
have the same issues. Your driver and receiver should be defined as
differential, but also the nets should be defined as differential pairs in
order to account for coupling. This is an important factor in differential
signaling. If you use MultiDriverContention simulation in XTK, it might not
be including coupling. In an HSPICE simulation you would need to make sure
that you use a coupled transmission line model.

Good luck,
Weston

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Daniel Wei
Sent: Thursday, April 13, 2000 4:45 AM
To: 'si-list@silab.eng.sun.com'
Subject: [SI-LIST] : board-level simulation for differential signals

Hi,

Does anyone have the experience in simulating differential signals by QUAD,
HSPICE, or IS ?
I appreciate any suggestion or experience.

However, I had simulated differential signals by QUAD, but there are two
ways to do it.
One method is to simulate by defining Differential Driver and Receiver PINs,
another method is by defining Multi-Driver Control file.
And I found that the results of the above two methods are not the same
(waveform and timing).
Note that the driver model had been adjusted to make both pull-up and
pull-down symmetric.
What make them different ?

If you had the HSPICE simulation experiences, which model did you use ?
Or do you have the IS experience ?

Thanks a million.

Regards,

Daniel Wei

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