Subject: IBIS modeling questions response to greg Edlund

From: Kellee Crisafulli <[email-masked]>
Date: Thu, 9 Nov 1995 14:32:06 -0800

Hi Greg, 

I will take a crack at answering your questions:

>1. I was discussing IBIS model support with one of
>   our IC vendors, and they raised a concern about
>   ESD diode SPICE models not being accurate at
>   -5 V and + 10 V.  Any clues about how to get
>   around this without setting up a test lab?  Why
>   do you need such a wide range in the first place,
>   since nobody operates out there?

    You can extrapolate the data relatively easily to -5V and +10V.
    If each vendor extrapolates the data independently there is
    no way to sure how it will be extrapolated.  Linear? exponential?,
    clipped?.  For many devices it needs to be clipped, for others
    a linear extrapolation is better.
    The reason we specified it out that far is to prevent anything
    strange from happening with any given simulator after the last
    data point.  This way we know that all the simulators at least
    in theory should operate the same at least within -5V to +10V.
    This should insure stable and accurate operation under all
    normal operating conditions.

>2. When will s2ibis 2.0 be available on Windows?
>   Actually, I'd be happy with DOS, but that's
>   probably not in the plan...

   I have given this a first pass and had some trouble getting the
   source code to compile.  I will try it again soon when I get a
   few spare hours.

>3. Has anybody written a "theory of operations"
>   paper on behavioral simulators?  For instance, if
>   I have a simple behavioral driver model (no ESD
>   diodes, no package) driving a 50 Ohm transmission
>   line terminated at the far end into 50 Ohms, how
>   do I calculate the current and voltage vs. time at
>   the output of the driver?  At the far end?  This
>   must be an easy problem to solve.  I'd like to
>   write a little C program to do this so I can better
>   understand IBIS and critically compare it to SPICE.
>   (For the sake of accuracy in system design issues,
>   not so I can write another simulator!)

    There are several books on this subject.  Visit your local
    book store and look under transmission lines, signal integrity,
    microstrip, and stripline.
    The easier method is to buy one of the cheaper programs on the
    market that already does the it for you.  There are several
    that support IBIS.  If you need a reference let me know.

>4. Has anybody thought about organizing an IBIS
>   users group and mailing list?

    This has been talked about a few times.  It hasn't gotten
    enough steam up to make the engine run yet.
Have a great day...Kellee Crisafulli, HyperLynx Inc.