Analog Electronics with LabVIEW®

4.3. Transconductance Parameter

The transconductance parameter, g_m, was introduced in Unit 2 in the treatment on the rudimentary electronic amplifier; it is the proportionality constant of the linear relationship between the output (responding) current and the input (control) voltage [(2.3)]. For the MOSFET, NMOS, or PMOS, I_d = g_mV_gs, where I_d is into the drain for both transistor types. An ideal transistor can be modeled with this alone. A simple model, which includes no other components, would often be adequate for making estimates of circuit performance.

To obtain an expression for g_m as a function of the general form i_D = f(v_GS, v_DS, v_SB) [e.g., (3.8)], we use the definition [from (4.1)]

Equation 4.2

Using (3.8) to express i_D, the resulting ...