Subject: Re[2]: Spice Model of IBIS

From: Arpad Muranyi <[email-masked]>
Date: Mon, 30 Mar 98 09:24:00 PST

Text item: 

John,

Short of proposing a standard, we have done just that (last paragraph in 
included message below).  About five or so years ago we asked several SPICE 
vendors to support IBIS (behavioral) modeling by improving the existing 
controlled sources.  Neither one of the companies responded positively, because 
they felt that their main strengths was in transistor level modeling.  Since 
then all I can do is tell people who are asking for behavioral SPICE models to 
go to their SPICE vendor and let them know about their need.  Maybe customer 
demand will change their mind.

By the way, the whole IBIS idea started from my behavioral modeling work in 
HSPICE, so it can be done, but it would be a lot easier and more robust with 
more IBIS specific controlled elements.

Sincerely,

Arpad Muranyi
Intel Corporation
================================================================================

Thank you to all those people who responded to my last posting. I guess my
previous question wasn't very clear, and so I got the standard response that
SPICE is a functional simulator, not a behavioral simulator.

I wasn't proposing to use SPICE as a functional simulator, but rather I was
proposing to use SPICE as a behavioral simulator. If you construct a SPICE
model equivalent to IBIS 2.1 or 3 model, using tables in the same way IBIS
does, then SPICE can be used as a behavioral simulator.

Ian Dodd pointed out that the syntax used by various SPICE simulators for
behavioral simulation tends to be proprietary to each SPICE vendor. Is this
really the case?

If proprietary syntax is the problem, then why not propose a standard
behavioral syntax be added to SPICE?

Regards

John Synesiou               [email-masked]
U.S. Power, Inc               Phone (612)826-1111
6497 City West Parkway     Fax (612)826-1003
Eden Prairie               Date: 03/28/98
MN, 55344               Time: 5:59 PM

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Date: Sat, 28 Mar 1998 18:12:58 -0600
Subject: RE: Spice Model of IBIS
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From: "John Synesiou" <[email-masked]>
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From: "John Synesiou" <[email-masked]>
Date: Mon, 30 Mar 1998 20:42:48 -0600

Thank you to all those members who provided me with feedback regarding the
use of SPICE for behavioral simulation. What I found interesting was
everyone agreed that SPICE can be used to do exactly what IBIS was intended
to do, however no standard SPICE syntax exists to make the model available
across different platforms.

I have included a response I obtained from my SPICE vendor as I believe it
provided further insight to the issues, and presents several possible
solutions. I'm not sure I agree with his conclusion, because if members of
this newsgroup and other SPICE users are willing to choose one of the
solutions presented below, most SPICE vendors lacking this functionality
would probably add this to their product.

Since multiple vendors support XSPICE syntax, then why not use a syntax
based on XSPICE to implement a behavioral model?

Regards

John Synesiou			[email-masked]
U.S. Power, Inc			Phone (612)826-1111
6497 City West Parkway	Fax (612)826-1003
Eden Prairie			Date: 03/30/98
MN, 55344			Time: 7:23 PM

John
I could write a novel in response to some of these emails. But a couple of
points.
As a spice vendor we are committed to supporting IBIS. It's really not that
big a deal for SPICE vendors to make subcircuits from IBIS data sheets.
While we have made IBIS to spice conversions for customers, the task was
rather timeconsuming and manual. We will be putting out a software utility
to do the job. Syntactically IBIS is a good standard that spice vendors can
use to make models. The other issue of IBIS tools being better solution for
pcb analysis is a NON-ISSUE as far as IBIS syntax is concerned. A spice
engine could be fitted with all such features so IBIS tools really have no
inherent advantage. The underlying syntax would in any case be transparent
to the user. Users should be able to use their SPICE simulators if they want
to. If features to do a job are lacking in SPICE products that's a
completely different question.
As for SPICE, it is far more than a functional simulator. People who think
otherwise need to wake up. They are living in the past by 5-10 years. Today
spice simulators handle C code, ActiveX servers, Visual basic scripts, as
well as full behavioral circuit descriptions using math equations,
if-then-else statements, and table models. Virtually every commercial SPICE
program has a full behavioral simulation capability allowing system, board
and IC design to be simulated in ANY combination.
With regard to a SPICE standard. True there is no standard spice behavioral
syntax. I was able to derive a SPICE model from an IBIS data sheet using
SPICE 2G6 syntax (See May 1993 Intusoft Newsletter).  This would be
compatible with ALL SPICE simulators. So this is one possibility.  The
Berkeley SPICE B element is the closest thing to a standard in the SPICE 3
world. The syntax problem is largely due to other SPICE vendors lack of
desire to be cooperative (this is not sour grapes, its the hard truth. All
attempts to get them to change\adapt to Berkeley spice or XSPICE syntax have
met with indifference).  But XSPICE, from Georgia Tech, could be the
standard EVERYONE is looking for. Its public domain, its used by seven
different SPICE vendors (Intusoft, Deutsch, Cad-Migos, Visionics, Electronic
Workbench, Circuit maker), it hides the model implementation because its
compiled (good for vendors), and the language is based on the most popular
AHDL there is; C. The C part could make the model easily portable to those
tools, SPICE or other, that don't have XSPICE.
With regard to the need for IBIS, I stated from the outset when IBIS was
being developed that a SPICE description could be found to solve the
problem. Indeed, in most cases, the SPICE description DOES NOT reveal any
hidden secrets about the technology or device architecture. These types of
claims are usually made by people who only know SPICE as a transitor level
simulator. They are often ignorant of SPICE's ability to model behavior in
various ways as to hide the real circuits nature. Clearly, it is possible to
even use a transistor topology since Philips, Texas Instruments, and
Motorola freely distribute model done in this fashion. However, silly,
people refuse to extend SPICE, probably because its syntax is not IEEE
controlled. I wish it were. Anyway IBIS is here to stay.