Subject: RE: removing non-monotonic points?!
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Thu Feb 07 2002 - 08:06:30 PST
Prabhu,
You are correct, the recommendation in that presentation will result
in double counting the clamps. What the author of that paper really
should have recommended is to check the monotonocity after summing
the pullup with the power clamp and the pulldown with the GND clamp
IV curves. Unfortunately the IBIS checker doesn't do this, and in
my opinion it should be corrected. It has mislead way too many
people already.
When I brought this up in the meeting Scott's response was that your
signals will never go into that range at the driver anyway, so it
really doesn't matter. Even though this maybe true in most cases,
the correct way for monotonocity check is after the summation.
Arpad Muranyi
Intel Corporation
====================================================================
-----Original Message-----
From: Mohan, Prabhu [mailto:Prabhu.Mohan@actel.com]
Sent: Wednesday, February 06, 2002 6:59 PM
To: ibis-users@eda.org
Subject: removing non-monotonic points?!
Hi all,
I have a few questions regarding a paper that was presented at the last IBIS
Summit, that suggested various methods to remove non-monotonic points from
the IBIS model file.
http://www.eda.org/pub/ibis/summits/jan02/bell2.pdf
For example, on page11, the pulldown curve is just extrapolated in the -ve
region to remove non-monotonic behavior.
Question#1: Won't we double count the clamp current by doing this (since
simulation tools add the Pulldown/up curves with the clamp curves)?
Question#2: What do we do if the silicon really does behave like this? (true
in my case. i do get a similar -ve bump when i subtract the 'tristate' curve
from the 'ouput low' curve)
Question#3: Is it advisable to remove the non-monotonic points completely,
since they almost always seem to occur outside the normal operating range?
ie. flatten the -ve/+ve bumps?
There might not be a simple solution. But I'd really like to know what the
possibilities are.
Thanks in advance,
Prabhu/~
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