Oscillators

An oscillator is a device or system that generates a periodic signal, typically a waveform such as a sine wave, square wave, or triangle wave, without requiring a periodic input after startup. In electronics, it converts a steady dc energy source into an ac signal with a well-defined frequency. Oscillators rely on feedback: a portion of the output is returned to the input with appropriate phase and gain to sustain oscillations. The Barkhausen criterion formalizes this idea: at the desired frequency, the loop gain must be at least one in magnitude and the total phase shift around the loop must be 0 degrees (or a multiple of 360 degrees). Practical oscillators include amplitude stabilization mechanisms to limit growth and ensure a steady amplitude.

Electronic oscillator types include LC oscillators, which use an inductor-capacitor tank to set the frequency; crystal oscillators, which use a quartz crystal with a high quality factor for stable timing; and RC oscillators, which use resistors and capacitors to produce lower frequencies and often employ a Wien bridge or phase-shift network. Voltage-controlled oscillators provide tunable frequency via a control input. Other domains feature mechanical oscillators (pendulums, tuning forks) and optical oscillators (laser cavities) where feedback yields coherent light.

Performance characteristics include operating frequency, frequency stability, phase noise, spectral purity, amplitude stability, startup behavior, and sensitivity to temperature and supply variations. Common applications are timing references (clocks and microprocessors), radio transmitters and receivers, signal generators and test equipment, and synchronization utilities in communications systems.