Subject: [IBIS] [Series MOSFET] question
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Wed Aug 06 2003 - 14:13:57 PDT
Hello,
I would like to understand why the following assumption was made
for the [Series MOSFET] keyword. Was there a technical reason for
it, was this done only for convenience/shorthand purposes?
| One fundamental assumption in the MOSFET switch model is that
| it operates in a symmetrical manner. The tables and
| expressions are given assuming that Vd >= Vs. If Vd < Vs,
| then apply the same relationships under the assumption that
| the source and drain nodes are interchanged. A consequence of
| this assumption is that the Vds subparameter is constrained to
| values Vds > 0. It is assumed that with Vds = 0 the currents
| will be 0 mA
How would anyone feel if we removed this assumption, or found
some ways to make it possible to provide data for negative
values of Vds?
The reason I am asking is because this keyword could be used
very well to describe the differential currents of a true
differential buffer as I proposed it in my presentation at
http://www.eda.org/pub/ibis/summits/oct02/muranyi.pdf
No additional changes to the IBIS spec would be needed and
we could make real differential models with IBIS 3.2 keywords!
I ran a few tests and it seems that differential buffers do
have some asymmetry, so it would be nice if we didn't have
the assumption with this keyword.
I would appreciate any comments before I start writing any
BIRDs.
Thanks,
Arpad
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