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

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From: Marc Humphreys (mhumphreys@nexabit.com)
Date: Thu Apr 13 2000 - 11:56:28 PDT


Daniel,

So as a follow-on, you had mentioned the use of XTK in your original post.
If
you are not familiar with all the capabilities XTK as a tool,
XTK will handle the coupling. As Weston mentioned it is an
important capability in simulating differential signals because
it speaks to the very reason one would use differential signalling - ie
noise immunity. Not only will XTK accurately calculate the single and
differential impedance on all the traces in the design but all the coupling
coefficients too - this is not a single ended vs. diffential problem, rather
in one
case you try to avoid it, in the other you exploit it.
When it comes to simulating coupling in the system (intentional or not) it
makes no difference to XTK what CAD system was used to route the etch
since XTK produces a CAD/Board neutral model
of the system interconnect for simulations purposes, from which it
determines, based
on proximity, what nets are coupled to what. No configuration is required to
indicate to XTK if a signal is coupled to neighboring nets,
wether it be a differential of single ended signal.
Noise couples between any two signals using the same principles, regardless
of intent,
and thats how XTK treats each and every net. Noise coupling and differential
coupling use the same physical principles.

Additionaly (with a little creativity), simulating the coupling within
connectors
is not hard to do either with XTK.

Marc

> -----Original Message-----
> From: Weston Beal [SMTP:weston_beal@mentorg.com]
> Sent: Thursday, April 13, 2000 12:24 PM
> 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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