Amplifiers

An amplifier is a device that increases the amplitude of a signal. In electronics, amplifiers employ an active element—such as a transistor, a vacuum tube, or an operational amplifier—along with passive components to produce an output that is a larger replica of the input within specified limits of bandwidth, linearity, and load impedance. Amplifiers are described by gain (voltage, current, or power), bandwidth, input and output impedance, noise, distortion, and efficiency.

Common types include voltage amplifiers (which produce larger voltages), current amplifiers, transconductance amplifiers, transimpedance amplifiers, and power amplifiers. In integrated circuits, operational amplifiers use feedback to set gain and improve linearity, stability, and bandwidth. Preamplifiers condition weak signals; power amplifiers deliver rated output into a load such as a loudspeaker or antenna.

Topologies such as common-emitter (or common-source), common-base, and common-collector (emitter/source follower) describe the relationship between input, output, and the signal ground. In RF and microwave work, RF amplifiers are designed for high frequency and impedance matching; in optics, optical amplifiers boost light signals in fiber communications (e.g., EDFA).

Amplifier performance is constrained by linearity, distortion, noise figure, and power efficiency. Small-signal amplifiers assume linear operation near a bias point, while large-signal or saturated operation yields significant distortion. Stability and feedback are used to control gain and reduce distortion.

Applications span audio and home theater, telecommunications and wireless, instrumentation and sensors, and measurement equipment. History traces from vacuum tubes to bipolar and field-effect transistors to modern integrated circuits, enabling compact, low-noise, and high-gain devices.