Transconductance

Transconductance, also known as mutual conductance, is a property of certain electronic components. Conductance is the reciprocal of resistance; transconductance, meanwhile, is the ratio of the current change at the output port to the voltage change at the input port. It is written as g_m. For direct current, transconductance is defined as follows:

$g_m = {\Delta I_\mathrm{out} \over \Delta V_\mathrm{in}}$

For small signal alternating current, the definition is simpler:

$g_m = {i_\mathrm{out} \over v_\mathrm{in}}$

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