RE: Subtracting clamp curves from pull-up/down curves

Mike,
        Not trying to play devil's advocate, but I have always wondered
why the model maker has to subtract the clamps out, then the software vendor

puts the clamps back in ? Why not just have syntax (in IBIS) for a pullup
and pulldown model WITH the clamp ? Thus reducing everyone's work ?

My old (internal) simulator and models were defined this way (IV curves
included clamps)
and it seemed a lot easier. We could feed bench data from a curve tracer (or
semiconductor analyzer)
directly into the model without any math, and when you looked model curves
they were intuitive.
I know its probably now water over the dam, but I was just wondering....

regards,
Bob

Cereva Networks
100 Locke Drive
Marlboro MA. 01752
Phone: 508-486-9660 X 3365
FAX: 508-486-9661
Email: rhaller@cereva.com

-----Original Message-----
From: Mike LaBonte [mailto:mikelabonte@cadence.com]
Sent: Friday, July 07, 2000 8:28 AM
To: ibis-users@eda.org
Subject: Re: Subtracting clamp curves from pull-up/down curves

Stephen,

Arpad's reply indicates that both clamp curves are indeed subtracted
to produce pullup and pulldown curves. I can verify the other side of
your question; that simulators (at least Cadence SPECCTRAQuest)
re-combine the curves as follows:

   low state: pulldown + powerclamp + groundclamp
  high state: pullup + powerclamp + groundclamp

So the clamps are never disabled (unless Submodel is used).

Mike LaBonte
Cadence

Stephen Nolan wrote:
>
> Hello IBIS gurus,
>
> When creating a model for a three-state device, it is necessary to
subtract the
> clamp curves from the pull-up/down curves to avoid double counting, as the
EDA
> tool adds the clamp-curves back in to the pull-up/down curves to obtain
the
> devices output charactersitics in the enabled state. Right so far?
>
> The question is this, do you only subtract the corresponding clamp curve
from
> the related pull-up/down curve, or do you subtract BOTH clamp curves from
each
> pull-up/down curve?
>
> For example, if I am creating the pull-down curve, do I subtract only the
> ground-clamp curve, or do I subtract both the power-clamp and ground-clamp
> curves? Does the EDA tool add only the ground-clamp data back in, or does
it add
> both curves back in?
>
> --
> Regards,
> Stephen M. Nolan
Received on Fri Jul 7 07:21:07 2000