[SI-LIST] Re: IBIS Model Quality (or lack thereof)

> Why use IBIS at all ?
> If you are convinced that IBIS is not good enough (which I am), don't
> simulate and just follow whatever the vendors design rules say.

That's fine if you're designing Intel motherboards and have their
design rules to go by.

But what design rules are there for using a "jelly-bean" part like
a level translator or a latch?  They don't come with any.

Or if you are actually designing a new circuit, not just copying
someone else's reference design?

Then you get the models that your IC vendors are willing to give you,
and more often than not, it won't be a SPICE model.  Some even require
you to sign an NDA just to get the IBIS model!

Even the vendors of standard logic ICs that used to have SPICE
models, don't anymore.  It's IBIS, or it's nothing.

One of the big reasons why I hate IBIS, is that many IBIS models
stink.

My own personal experience that set the tone for this, was a few years
ago when a vendor refused to provide SPICE models, even though we
had an NDA, then made us wait 6 weeks while their two IBIS engineers
created the IBIS model.  The model they delivered was so totally bogus
(keywords misspelled, wrong polarities, MIN and MAX columns reversed)
that it was obvious they hadn't checked it out on anything.

They claimed it had to be OK because they had sent it to someone
else for checking before releasing it to us, and that third party
didn't complain about it.

I spent the next several weeks hand-holding said vendor to fix their
model for them.  (Me, who had neither created nor used an IBIS model
before!)  It took many iterations until they got the model reasonably
"correct" ... and who knows if it was accurate?!

To this day, whenever I get an IBIS model from an IC vendor, I need
to check it and often have to fix it before using it.  (I sometimes
need to fix vendor SPICE models too.  There seem to be a lot of
engineers out there who are either stupid or ignorant.)

My most recent IBIS model, which I got directly from a very large
semiconductor manufacturer (not off a web page), had syntax errors,
and a major scaling problem.  Plus it completely omitted a major part
of the device's behavior ... thus forcing us to "wing it".

Not all IBIS models stink.  There are companies that specialize in
making them, some of whom do quite a good job.  There may even be IC
vendors who know how to do it.  Then there's the rest of the world,
who it seems couldn't care.

Regards,
Andy

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