Common gate

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Common gate amplifier

A common-gate amplifier is one of the possible configurations of FET electronic amplifier. It is normally used to convert low impedance to high impedance, but is very rarely found in practice.

[edit] Characteristics

(The parallel lines indicate components in parallel.)

Inherent voltage gain:

${V_\mathrm{out} \over V_\mathrm{in}} = g_m (R_\mathrm{D} \| R_\mathrm{load})\,$

Input resistance:

$r_\mathrm{in} = R_\mathrm{S} \left\| {1 \over g_m}\right.$

Current gain:

$A_\mathrm{vm} {r_\mathrm{in} \over R_\mathrm{load}}$

Output resistance:

$r_\mathrm{out} = R_\mathrm{D}\,$

The variables not listed in the schematic are:

g_m is the transconductance in siemens

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[edit] See also

Transistor amplifiers
Bipolar junction transistor: Common emitter • Common collector • Common base Field effect transistor: Common source • Common drain • Common gate Multiple transistors: Darlington transistor • Cascode • Parallel circuit