RE: [SI-LIST] : IBIS Modeling

Andrew Ingraham (Andrew.Ingraham@digital.com)
Wed, 25 Mar 1998 11:28:44 -0500

>We have built DIMM and SIMM module modules using IBIS 2.1 that do
>a reasonable simulation job. It requires a bit of playing with the
>package model and it is somewhat simulator dependant. Our simulator
>interpretes
>large RLC package values as transmission lines instead of lumped LC
>parameters
>which allows us to make a reasonable DIMM or SIMM module module
>using
>IBIS 2.1

I don't mean to criticize your approach ... but this seems like a
dangerous way of creating a model.

In an ideal world, IBIS models *ought* to be portable such that they can
be used on different platforms and different simulators and yield
basically the same result, within the accuracy limits of those
simulators.

If there are big differences such as this (where large RLC values are
treated in a fundamentally different way on some simulators), that seems
like a risky thing to take advantage of. It ties your IBIS model to
that simulator. How do you prevent the model from being used on another
simulator?

In essence, you have created a proprietary *.ibs model, similar to an
Hspice model that won't work correctly on someone else's simulator.

As a side note, is it even the right thing to treat large RLC package
values as a transmission line? What if they represent something like a
long bondwire and a big bonding pad? How do you make that choice
between which way to model it in the simulator?

Should the IBIS spec make such loopholes possible?

Regards,
Andy Ingraham