EMRFD Message Archive 177

Message Date From Subject
177 2006-10-22 13:13:23 Steven S. Coles Transconductance Equation Question

I thought "Radio Frequency Design" contained a form of

Gm = n*Ie/26

In which n ~= 1 for germanium and a range (1.2 – 1.8?) for silicon.
Now I can't find the form or range for silicon. I'd appreciate the
correct equation and range.

Thank you,

179 2006-10-23 21:15:20 Wes Hayward Re: Transconductance Equation Question
Hi Steven, et al,

I'm not familiar with the form that you mention. The simple
equation with gm=Ie/26 is one that holds for all sorts of
materials. It is the first derivative of the common exponential
expression for Ie(Vbe) which is the Ebers-Moll equation, a model
that comes directly from the semiconductor physics. The number 26
is actually .026 when we deal with I in amps and is the ratio kT/q
where k is Boltzman's constant, T is absolute temperature in Kelvin
and q is the electronic charge in columbs. A good reference to
this stuff is the text by Gray and Meyer.

You make reference to "Radio Frequency Design." Did you
mean "Experimental Methods in RF Design," or the
earlier "Introduction to Radio Frequency Design," or something
else? I don't recall having talked about anything other than the
things that follow from the Ebers-Moll model, which is what is used
in SPICE for all kinds of bipolar transistors, including Silicon
parts and wild things like GaAs heterojuncti