Subject: RE: High frequency performance of IBIS model
From: Ingraham, Andrew (Andrew.Ingraham@compaq.com)
Date: Fri Oct 19 2001 - 14:07:24 PDT
> IBIS models have only a constant capacitance to account for
> the die capacitance, which means that there is no frequency
> dependency in their impedance.
No voltage dependency either. And various other second-order effects
that are missing, which don't bite you until you push the frequencies
high enough.
Also, most IBIS models you will find, have just the simple package model
which consists of simple RLC parameters, and no specified way in which
they are connected, i.e., lumped vs. distributed, pi vs. tee vs. ell ...
which may be OK for lower speeds but not so hot at higher frequencies.
And no couplings either.
Finally, many IBIS models are garbage simply because the people who made
them, didn't really know what they were doing. It's easy to throw
together an IBIS model using s2ibis, and not understand the first thing
about IBIS, nothing about SPICE modeling, and very little about using
SPICE. It's real hard to make a SPICE model without a solid grounding
in both SPICE usage and SPICE modeling.
Andy
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