RE: [IBIS-Users] Conditions for clamp and pullup/down tables

Rene,
 
You are raising very good questions, and your observation
is correct.  We were aware of this problem, but didn't
concern ourselves too much because this clamping diode
behavior is only effecting the overshooting signals.  In
general, designs with overshoot should not rely on the
clamping diodes of the devices for various reasons, and
because of that we shouldn't expect hair splitting accuracy
from the simulations based on clamping diode behavior.
 
In addition to that, the parasitic clamps of MOSFET models
in SPICE tools are quite often very inaccurate due to
inadequate modeling techniques which adds another reason
for not relying too much on the claming effects.
 
Also, more modern signaling schemes use terminations which
means that the signals will not get into the active region
of the clamping diodes in which case they can be neglected
in the models.
 
In summary, even though your observations are correct, we
didn't feel that this was an important deficiency in the
IBIS specification and models.  If you can show us an example
which would justify to make corrections to this situation
we could certainly address this issue.
 
Thanks,
 
Arpad
=============================================================

________________________________

From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Rene Voshol
Sent: Friday, August 08, 2008 7:25 AM
To: ibis-users@server.eda.org
Subject: [IBIS-Users] Conditions for clamp and pullup/down tables



Hi, 

I have a question about the conditions used to extract the data for the clamp and the pullup/down curves. I understand that the temperature range given in the model should correspond to the min. and max. conditions of the device. Meaning that for the pullup/down curve of a CMOS device  you will have maximum performance with low temperature, and vice versa. But the clamp of this same the device will most likely be a diode, of some sorts, which will have the reverse temperature behavior. Since both curves are substracted, you need to apply the same conditions when extracting the curves. In which case I use the pullup/down curve as reference. 

My questions are: 


1.	Is this correct thinking? (Or am I perhaps overthinking things here?) 
2.	What about an input model? This has only clamp curves. Is it OK to use a different temperature ranges for input and output of the same device? 
3.	Or a switch where the clamps and the series current are in separate models?


Clarifications on this matter will be highly appreciated. 

Kind Regards, 

René Voshol
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