Yhteiskollektorikytkentää

Yhteiskollektorikytkentä, also known as common-collector configuration in English, is a fundamental bipolar junction transistor (BJT) amplifier circuit. In this arrangement, the collector terminal of the transistor is connected to the positive power supply, effectively acting as a common reference point for both the input and output signals. The input signal is applied to the base, and the output signal is taken from the emitter.

The defining characteristic of the common-collector configuration is its high input impedance and low output impedance. This impedance transformation makes it an excellent choice for buffering signals, driving low-impedance loads, or impedance matching between stages of a circuit. It is often referred to as an emitter follower because the output voltage at the emitter closely follows the input voltage at the base, albeit with a slight voltage drop determined by the transistor's characteristics.

Voltage gain in a common-collector circuit is always close to unity (slightly less than 1), meaning it does not amplify voltage significantly. However, it provides substantial current gain. This combination of unity voltage gain and high current gain results in a power gain. Due to its buffering capabilities and efficient current transfer, the common-collector configuration is widely used in amplifier output stages and as impedance matching networks.