Subject: Avoiding Double Counting

From: [email-masked] (Syed Huq)
Date: Wed, 20 Nov 96 17:30:43 PST

IBISfans:

Got a question about double counting of clamp data(Output models).

I believe simulators combine the Pullup(pu) and Power Clamp(pc)
data and also Pulldown(pd) and GND Clamp(gc). That is why both
pu and pd V/I table should not contain pc and gc information.

This is also why, pu and pd data can be non-monotonic and once
the clamp data is combined, the data becomes monotonic.

If the above statements are true, why not just take pu data
with the pc data included and simply put 0.0mA on the pc V/I
table. Take pd data with the gc data included and leave 0.0ma
for the gc V/I table.

If this can be done then Model providers who are creating models
from actual bench measurements, do not have to go thru the pains
of doing V/I table subtraction. A DC sweep on an enabled output
structure gives you the combination of the output stage + the clamp
structures.

It seems that we go thru too much data crunching and Simulators
simply connect the two tables anyway.

Possible I am missing something very important here. Pls comment.

Regards,
Syed
National Semiconductor Corp.

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From: "D.C. Sessions" <[email-masked]>
Date: Wed, 20 Nov 1996 19:27:14 -0700

> Got a question about double counting of clamp data(Output models).

[...]

> Possible I am missing something very important here. Pls comment.

So how would you handle tristate outputs?  The drive is out
of the picture but the clamp is far from negligible.

-- 
D. C. Sessions
[email-masked]