Single-Transistor Linear Configurations

For MOSFETs and BJTs, there are three basic configurations used for linear signal-flow analysis. These configurations most commonly appear in analog amplifier designs, but are also relevant for some types of digital circuits. This section gives a brief summary and schematic for each configuration. In each case, the configuration is defined by its input terminal and output terminal, and is named for the idle terminal. In small-signal models, the idle terminal is called “common”, so we have names like “Common Source”, “Common Emitter”, and so on.

MOSFET Configurations

Common-Source

Ideal NMOS and PMOS Common-Source circuits with active bias current sources.
Ideal NMOS and PMOS Common-Source circuits with active bias current sources.

Common-Gate

Ideal NMOS and PMOS Common-Gate circuits with active bias current sources.
Ideal NMOS and PMOS Common-Gate circuits with active bias current sources.

Common-Drain (Source Follower)

Ideal NMOS and PMOS Common-Drain (Source Follower) circuits with active bias current sources.
Ideal NMOS and PMOS Common-Drain (Source Follower) circuits with active bias current sources.

BJT Configurations

Common-Emitter

Ideal NMOS and PMOS Common-Emitter circuits with active bias current sources.
Ideal NMOS and PMOS Common-Emitter circuits with active bias current sources.

Common-Base

Ideal NMOS and PMOS Common-Base circuits with active bias current sources.
Ideal NMOS and PMOS Common-Base circuits with active bias current sources.

Common-Collector (Emitter Follower)

Ideal NMOS and PMOS Common-Collector (Emitter Follower) circuits with active bias current sources.
Ideal NMOS and PMOS Common-Collector (Emitter Follower) circuits with active bias current sources.