IBIS models and i2spice

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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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