Subject: IBIS models and i2spice

From: Arpad Muranyi <[email-masked]>
Date: Tue, 28 Oct 97 12:52:00 PST

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All interested,

I just came back from a week of vacation and read the EMAIL correspondence on 
the IBIS to SPICE conversion issues with great interest.  I agree with the 
statement that there is a great need for IBIS support in the SPICE tools.  
Ideally, I would like to have a SPICE/behavioral combo tool that has the 
advantages and capabilities of both worlds.  If needed, this tool could run 
transistor level SPICE models for detailed buffer design work, or higher level 
behavioral simulations for fast interconnect design work.  Due to this double 
feature, this tool would also cover the situation when one has both types of 
models which need to be simulated together.  Unfortunately, a standard would 
still be required for covering the various flavors and levels of transistor 
descriptions.

I vould like to make a couple of comments on what I have read in the 
correspondence.

1)  IBIS actually started on HSPICE when I wrote behavioral models (for internal
use) using HSPICE.  Just because a specific SPICE tool vendor does not support 
IBIS, it doesn't mean that the user cannot write behavioral models that use IBIS
data.  Bob Ross gave an excellent example for how to do this in one of the most 
recent replies to this subject.  Most SPICE flavors have behavioral elements 
(controlled voltage and current sources) which can be used to create a 
behavioral model.  However, the support from the SPICE tool vendor is still 
badly needed because of the problems that arise with the usage of these 
elements, such as non convergence, time step too small errors, etc...  
Specialized features (such as event triggered sources to detect a threshold 
crossing, for example) would significantly improve behavioral modeling.  Of 
course, the ideal solution would be if the user would not have to develop the 
behavioral model at all, just plug in the IBIS data into something that the 
vendor provides.

2)  Another reason I use IBIS models under a SPICE tool is actually something 
that I have not read in any of the replies.  The problem I see with most (if not
all) of the IBIS simulator tools is that they all lack substantial amounts of 
freedom.  In my work I have to specify buffer characteristics as well as 
interconnect guidelines.  For this I run sweep simulations on many of the buffer
as well as interconnect parameters.  I like to plot the simulation results in 
many different ways, such as flight time vs. buffer strength, amount of cross 
talk vs. signal pattern, etc... to make the data meaningful.  Many tools don't 
have variable sweeping or scaling capabilities, scaling factors for altering the
I-V curves of the IBIS models for sweeps, or arbitrary measurement definition 
capabilities, and have nothing but a voltage vs. time (waveform) plotting 
capability.  Some tools provide some of these features, but in very primitive 
shape and form.  Even though it is painful some times, I can do most of these 
tasks fairly well in HSPICE, but I could still use better features and support.

To sum it up, IBIS tool vedors could eliminate part of the need for running IBIS
simulations in SPICE tools by adding a bunch of much desired felixibility 
features to their tools which can only be done today in SPICE tools.  These 
tools are only useful if they provide the necessary user interface, and 
automation features which are required for the work at hand and for being more 
productive.  But I would still prefer a tool that can do both worlds together...

Arpad Muranyi
Intel Corporation
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Subject: Re: low budget IBIS tools
Reply-To: <fabrizio=[email-masked]>
From: "fabrizio zanella" <fabrizio=[email-masked]>
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From: Fred Balistreri <[email-masked]>
Date: Tue, 28 Oct 1997 15:48:19 -0800

Arpad Muranyi wrote:
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We have looked into the enemy's face and the enemy is us. Such tools
alredy exist. The user community needs to look at the various SI
companies and solutions carefully! We are just one of several SI spice
based tools that have had IBIS models working together with Spice
transistors and coupled lossy transmission lines since 1991! WAKE UP!
Where have you guys been! We attend the various converences and
marketing shows for a REASON. In our particular case interfaces exist
into the most popular CAD products. These type of products have been put
to good use for quite some time by hundreds of companies! 

-- 
Fred Balistreri
[email-masked]
408-434-0967 ext. 102