Re: Verifying IBIS models

Luke Chang wrote:

> When IC vendors create IBIS models for their components, how do they
> verify whether they are correct or not, compared to either the original
> SPICE models or to physical measurement data? Do they actually do this
> comparison? Is there a simulation methodology to do this comparison?
>
> I am just a user of IBIS models and will never create them. So I am
> mainly interested in knowing whether I can always (blindly) trust the
> models I get from the vendor Web sites or directly from the vendors.

I suppose the usual disclaimers (I can't, strictly speaking,
speak for VLSI, much less other manufacturers) are in order.
That said, here's a little about our approach:

1) We SPICE the dickens out of I/O designs.
2) We verify the SPICE characteristics in design
   validation and test against them.
3) We generate IBIS models from the SPICE models.
4) We spot-compare SPICE simulations made from
   hand-translating IBIS back to SPICE.

We're in the process of converting the canonical
model for testing purposes from old-fashioned data
sheets to IBIS. We *intensely* wish we had a
working IBIS-to-SPICE translator that we could use
for closing the loop, but at present there don't
seem to be any around.

-- 
D. C. Sessions
dc.sessions@tempe.vlsi.com