Transconductance

Transconductance is a property of certain electronic components. It is a contraction of "transfer conductance". Whereas conductance is the creation of a current through two points where a voltage is applied, transconductance is the creation of a current through two output points caused by a voltage at two input points, as if the conductance is transferred from one junction to another. When referring to a value, it is the ratio between these changes in voltage and current, and is sometimes written g_m:

<math>

g_m = {\Delta I_{out} \over \Delta V_{in}} <math>

or sometimes defined as simply

<math>

g_m = {I_{out} \over V_{in}} <math>

In the world of vacuum tubes, transconductance is the relationship between the plate current and the grid voltage, with a constant plate voltage.

Similarly, in field effect transistors, it is the derivative of the output current divided by the input voltage.

A transconductance amplifier is one which outputs a current proportional to the input voltage.

Transresistance

Transresistance is the dual of transconductance. It is a contraction of "transfer resistance", and is the origin of the term transistor. It refers to the ratio between a voltage at two output points and a current through two input points, and is sometimes notated r_m:

<math>

r_m = {\Delta V_{out} \over \Delta I_{in}} <math>

See also

• Transistor
• Vacuum tube