**EMRFD Message Archive 177**

MessageDateFromSubject177 2006-10-22 13:13:23 Steven S. Coles Transconductance Equation Question Hello,

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,

Steven179 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