From: Phil Hobbs
Subject: Re: Ebers-Moll equation
Date: Fri, 29 Nov 2002 22:18:52 -0500
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> The Ebers-Molls equation is almost completely useless, other than for
> exploring "how transistors work". There is, for example, just one
> parameter that defines the device, namely Is. No Ohmic resistances,
> parasitic capacitances, parasitic diodes or parasitic pnp's are simulated.
> You need to look at Gummel-Poon, or even Mextram models for decent
Whoa! Any physicist or engineer who isn't a one-trick pony will tell
you that an intuitive approximation is much more useful than an unusably
complicated exact result. Ebers-Moll is massively incomplete as a
circuit description, but it is a wonderfully intuitive summary of the
basic device physics, and is highly accurate over a wide range of
conditions at low frequency. For my work, at least, these make it
absolutely indispensable. Furthermore, it can be fixed up by hand
easily when these other effects are important, resulting in a good
intuitive understanding of the circuit, and, crucially, a good idea of
what to change to make it better.
I certainly wouldn't want to rely on Ebers-Moll SPICE models, but then I
wouldn't want to rely on Gummel-Poon for dreaming up new circuits, or
figuring out how they work. Would you?