Subject: [Series MOSFET] keyword

From: Kim Helliwell <[email-masked]>
Date: Thu, 10 Aug 2000 15:08:34 -0700

I'm trying to understand how series models work, and the explanation
in the 3.2 spec for the [Series MOSFET] keyword has me confused. 

The spec says that Vtable is Vgs = Vcc-Vs.  What I'm unclear on is
the where the subparameter Vds comes in.  From the model, it appears
to be the voltage difference between the pins that are in series.

I think my problem is we are specifying two pins connected by the
series model, so how does the third pin (the gate) get hooked up
and modeled by a simulator?

-- 
Kim Helliwell
Senior CAE Engineer
Acuson Corporation
Phone: 650 694 5030  FAX: 650 943 7260

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From: Mike LaBonte <[email-masked]>
Date: Fri, 11 Aug 2000 09:08:50 -0400

Vds, the drain-to-source voltage, is indeed the voltage between the
the 2 pins of a [Series MOSFET] model. IBIS leaves the gate up to the
simulator - there is no third pin defined for it. In some simulators
(at least SPECCTRAQuest) you can wire the gate to any voltage source
you want.

I like to test series switch models using a gate voltage source that
turns on and off at a frequency that is different from the clock
frequency of the signal passing through the switch. This way you can
study how far in advance the signal must stop changing before it is
safe to switch. You can also inject noise into the gate voltage to
see how much of it appears on the signal.

Mike LaBonte
Cadence Design Systems