Definition
A transistor amplifier circuit in which the base terminal is shared by, or common to, both the input and output sides of the circuit. The input signal is applied between the emitter and the base, and the output signal is taken between the collector and the base. This configuration provides voltage gain but no current gain, and it has a low input impedance with a high output impedance.
Plain English
A type of small electronic amplifier built around a transistor, wired so that one of the transistor's three legs (the base) is connected to both the input and the output. It boosts the strength of a voltage signal but not the current.
Context Anchor
Seen in avionics and aircraft electronics maintenance, especially in descriptions of radio, navigation, or signal-processing circuits.
Derivation
Named for the way the circuit is wired: the base terminal of the transistor is the leg that is 'common' (shared) between the input and output paths. The other two transistor configurations are named the same way: common-emitter and common-collector.
Why Pilots Care
A pilot normally does not operate this circuit directly, but the term can appear in avionics descriptions or maintenance discussions when a radio or navigation unit has a weak signal problem.
Intuition Check
“Common” does not mean “ordinary” here. It means the base connection is shared by the input side and the output side of the circuit.
Example Sentence 1
The technician identified the stage as a common-base amplifier because the input was applied to the emitter and the output was taken from the collector, with the base grounded.
Example Sentence 2
During equipment checks, the technician verified that the common-base amplifier stage was providing stable gain at high frequencies.