Definition
A transistor amplifier circuit in which the emitter terminal is shared (common) between the input and output sides of the circuit. The input signal is applied between the base and the emitter, and the amplified output signal is taken between the collector and the emitter. This configuration produces both voltage gain and current gain, and inverts the signal — meaning the output waveform is 180 degrees out of phase with the input.
Plain English
A small electronic circuit built around a transistor that takes a weak signal and makes it stronger. It's called "common-emitter" because one of the transistor's three legs — the emitter — is connected to both the input side and the output side of the circuit, acting as a shared reference point.
Context Anchor
Seen in aircraft electronics, radio, audio, and avionics maintenance discussions, especially when describing how small electrical signals are strengthened inside equipment.
Derivation
A transistor has three terminals: base, collector, and emitter. The name describes which terminal is shared between input and output. "Emitter" comes from the Latin emittere, meaning "to send out" — it's the terminal that emits charge carriers into the transistor. "Common" here simply means "shared by both sides of the circuit."
Why Pilots Care
Pilots don't design these circuits, but understanding the term helps when reading avionics manuals, troubleshooting guides, or studying for exams that cover aircraft electrical and radio systems. It explains how weak signals — like those from a microphone or antenna — are boosted to usable levels.
Intuition Check
Common does not mean ordinary here. It means the emitter connection is shared by both the input and output sides of the amplifier circuit.
Example Sentence 1
The microphone signal in the intercom system is boosted by a common-emitter amplifier before being sent to the headsets.
Example Sentence 2
A failed common-emitter amplifier can reduce signal strength in avionics equipment, making transmissions hard to hear.