Yhteislähtevahvistimet

Yhteislähtevahvistimet, or common-emitter amplifiers in English, are a fundamental configuration of bipolar junction transistor (BJT) amplifiers. They are characterized by having the input signal applied to the base and the output signal taken from the collector, with the emitter terminal common to both the input and output circuits. This commonality is often achieved by grounding the emitter either directly or through a bypass capacitor, which presents a low impedance path to ground for AC signals.

The primary function of a common-emitter amplifier is to provide voltage gain. The input current variation at the base controls a larger current variation through the collector, resulting in an amplified output voltage swing across the collector resistor. A key characteristic of this configuration is its ability to invert the input signal; a positive-going input voltage typically results in a negative-going output voltage.

Common-emitter amplifiers offer a good balance of high voltage gain and moderate input and output impedances. However, their gain can be sensitive to temperature variations and transistor parameter spreads, which can be mitigated through biasing techniques and negative feedback. This amplifier configuration is widely used in various electronic circuits, including audio amplifiers, radio frequency circuits, and signal processing stages, due to its versatility and amplification capabilities.