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Common source

Common source amplifier

A common-source amplifier is one of the common configurations of FET electronic amplifier.

R_D is commonly zero.

Characteristics

(The parallel lines indicate components in parallel)

Inherent voltage gain:

With C_S:

$-g_m (R_D \| R_{load})\,$

Without C_S:

$-g_m (R_D \| R_{load}) \over 1 + g_m R_S$

Input resistance:

$R_1 \| R_2\,$

Current gain:

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

Output resistance:

$R_D\,$