I would like to remind you that the IBIS "model" is not rally a model, but a
data exchange vehicle to provide modeling information about devices. It depends
entirely on the tool how it is being utilized.
I mentioned this several times in our IBIS Open Foruum meetings, and let me
repeat it again. There are usually three I-V curves in an IBIS model, taken at
different supply voltages. If you think it through, you will realize that the
supply voltage really is the gate voltage of the driver transistor. Now, if
your simulator simulates GND bounce or Vcc droop, it should also have the
instanteneous supply voltage at every iteration. Using those values, your
simulator could also switch dynamically between these curves and anything
inbetween or even outside them (in other words scale them), depending on the
instantenous supply voltage.
I don't want to go into more detail here, the point I am trying to make is that
there is information in an IBIS model that could be used to model these effects.
It is entirely up to the tool vendor's algorithms. (I did implement this effect
in my HSPICE behaviorals and it works pretty well).
There is an issue on how accurately these effects can be modeled, but that is
I'm convinced IBIS works great if you have no rail collapse so that the IV
curves are valid. I don't think they are valid under heavy bus switching
with significant rail collapse, although I hear people claim otherwise. I
just don't see how IV curves provided at, say 3.3V, work when you have 0.5V
of collapse. Any comments?
Larry Smith wrote:
> ... I have compared the results of IBIS simulation to that of full
> HSPICE model simulation and hardware measurements for several different
> transmission line problems. IBIS model simulation compares very well to
Text item: External Message Header
The following mail header is for administrative use
and may be ignored unless there are problems.
***IF THERE ARE PROBLEMS SAVE THESE HEADERS***.
Content-Type: text/plain; charset=us-ascii; x-mac-type="54455854"; x-mac-creator
Subject: Re: [SI-LIST] : Output Impedance
X-Mailer: Mozilla 4.04 (Macintosh; I; PPC)
From: Brian Young <email@example.com>
Date: Thu, 02 Apr 1998 08:50:00 -0500
Received: from email.sps.mot.com (godfather.ibmoto.com [188.8.131.52]) by styx.
ibmoto.com (8.8.6/8.6.9) with ESMTP id IAA21961 for <si-list@silab.Eng.Sun.COM>;
Thu, 2 Apr 1998 08:53:23 -0600 (CST)
Received: from styx.ibmoto.com (styx.ibmoto.com [184.108.40.206])
by earth.sun.com (8.8.8/8.8.8) with ESMTP id GAA16078
for <si-list@silab.Eng.Sun.COM>; Thu, 2 Apr 1998 06:53:24 -0800 (PST)
Received: from earth.sun.com (earth.EBay.Sun.COM [220.127.116.11])
by Eng.Sun.COM (SMI-8.6/SMI-5.3) with SMTP id GAA10403
for <si-list@silab.Eng.Sun.COM>; Thu, 2 Apr 1998 06:53:23 -0800
Received: from Eng.Sun.COM by silab.eng.sun.com (SMI-8.6/SMI-SVR4)
id GAA10880; Thu, 2 Apr 1998 06:55:00 -0800
Received: by silab.eng.sun.com (SMI-8.6/SMI-SVR4)
id GAA10884; Thu, 2 Apr 1998 06:55:04 -0800
Received: from silab.eng.sun.com (silab.Eng.Sun.COM [18.104.22.168])
by Eng.Sun.COM (SMI-8.6/SMI-5.3) with SMTP id HAA02238;
Thu, 2 Apr 1998 07:06:29 -0800
Received: from Eng.Sun.COM (engmail2 [22.214.171.124]) by mercury.Sun.COM (SMI-8.6
/mail.byaddr) with SMTP id HAA27774; Thu, 2 Apr 1998 07:06:39 -0800
Received: from mercury.Sun.COM (mercury.Sun.COM [126.96.36.199])
by mailbag.jf.intel.com (8.8.6/8.8.5) with SMTP id HAA24244
for <Arpad_Muranyi@ccm.fm.intel.com>; Thu, 2 Apr 1998 07:19:50 -0800 (PST)
Received: from mailbag.jf.intel.com (mailbag.jf.intel.com [188.8.131.52]) by fm
mail.fm.intel.com (8.8.5/8.7.3) with ESMTP id HAA01129 for <Arpad_Muranyi@ccm.fm
.intel.com>; Thu, 2 Apr 1998 07:12:10 -0800 (PST)