Definition
A transistor amplifier circuit in which the collector terminal is connected directly to the common ground (or power supply reference) rather than serving as the output. The input signal is applied to the base, and the output is taken from the emitter. This configuration provides a voltage gain of slightly less than one, but offers high input impedance and low output impedance, making it useful as a buffer between a high-impedance source and a low-impedance load. Also known as an emitter-follower or common-collector amplifier.
Plain English
A type of transistor circuit where the output closely follows the input signal in voltage but can deliver more current. It does not boost voltage, but it allows a weak signal source to drive a heavier load without being weakened.
Context Anchor
Seen in aircraft electronics, avionics, and maintenance discussions of transistor amplifier circuits.
Derivation
Called 'grounded-collector' because the collector terminal of the transistor is tied to ground (the common reference point of the circuit). The alternative name 'emitter-follower' comes from the fact that the voltage at the emitter follows the voltage at the base.
Why Pilots Care
Pilots don't design these circuits, but understanding the term helps when reading avionics theory or troubleshooting guides. Grounded-collector stages are commonly used inside radios, intercoms, and instrument signal paths as buffers, so the term appears in technical documentation.
Analogy
Think of it like a helper between two people carrying a message: the helper does not change the message much, but makes sure it can be delivered clearly to the next person.
Intuition Check
“Grounded” does not always mean connected to the earth. In this circuit, it means connected to the circuit’s common reference point for the signal.
Example Sentence 1
The technician identified the failed component in the grounded-collector amplifier stage of the communications radio.
Example Sentence 2
A grounded-collector amplifier provides the high input impedance needed before feeding the microphone signal into the transmitter.