RE: [SI-LIST] : Bad IBIS models!

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From: Bob Perlman ([email protected])
Date: Fri Mar 17 2000 - 11:48:12 PST

Hi -

> I just want to comment on this, because in some cases such similar
> typ., min., and max. IV curves are correct. There are buffers out
> there which adjust themselves to a known quantity to eliminate most of
> the process, voltage, temperature effects on the strength of the
> buffers. The end result is a group of IV curves which are very close.
> This adjustment circuit may even correct slew rate variations, leading
> to very similar V-t curves also. So we can't jump to conclusions too
> quickly seeing such IBIS models.

I can imagine the phone conversation with the apps engineer:

Me: The min, typ, and max IBIS curves look mighty similar. Are
you using constant-Z buffers?

Apps engineer: Uh...yeah!

I'm familiar with constant-Z buffers. Vendors who go to the trouble
of implementing them should proudly say so in the data sheet.
Otherwise, I'll leap to conclusions (and be right 99% of the time).

Bob Perlman

Bob Perlman
Cambrian Design Works
Digital design and signal integrity consulting

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