[SI-LIST] Re: package SSN model accuracy requirements, now B ehavioral Modeling

  • From: Chris Cheng <Chris.Cheng@xxxxxxxxxxxx>
  • To: "'si-list@xxxxxxxxxxxxx '" <si-list@xxxxxxxxxxxxx>
  • Date: Sun, 20 Mar 2005 14:04:53 -0800

I don't think I/O designers provide IBIS models. I believe I/O designers
provide SPICE deck that can be abstracted into IBIS by the app engineer.

We have to be fair here, while I keep hearing this "I remember this one case
the SPICE circuit doesn't converge, so it must be bad". The IBIS standard
community failed to provide a correct solution for SSO for the pass few
years. I am aware of the late Larry Rubin's proposal for handling SSO noise
in TLC (not even XTK) since the early 90's. What can be done and how long
does it take to become a standard are two different things. Let's not get
into pure academic discussion here by keep say "I think behavioral model can
do this and that". Of course give it enough time and resources it can, but
are you expecting the end user to ignore the problem until the standard
committee settle on the solution ? Worst, to even recognize there is a
problem ?

There is a de facto standard to describe circuits other than i-v curves,
encrypted HSPICE. It may be slow but it gives the end users a chance to
discover potential problems that IBIS can't. That's the bottom line. 

-----Original Message-----
From: lgreen
To: weirsi@xxxxxxxxxx; kumarchi@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Sent: 3/19/2005 7:58 PM
Subject: [SI-LIST] Re: package SSN model accuracy requirements, now
Behavioral Modeling

Hi, Steve,

The real sticking point is that IBIS models is what I/O designers
and IBIS does not model tightly coupled diff pairs.  If you get a SPICE
netlist, you are better off, of course.  But even SPICE models are not
foolproof - back when I used to design I/O buffers, I remember seeing
flaky BSIM models from some of the foundries we dealt with.  ("Little"
things like discontinuities in I vs Vds.)

The links under Peter Lauritzen's page show a number of devices and
where no macromodels could match the transient circuit characteristics,
while a well-built behavioral model provided a better match to data
accuracy) and ran faster.

I guess the bottom line is to do whatever modeling it takes to get the
design out the door, while also verifying models whenever possible.

- Lynne
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