An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillators convert direct current (DC) from a power supply to an alternating current (AC) signal. They are widely used in many electronic devices ranging from simplest clock generators to digital instruments (like calculators) and complex computers and peripherals etc. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games.

Oscillators are often characterized by the frequency of their output signal:

• A low-frequency oscillator (LFO) is an electronic oscillator that generates a frequency below approximately 20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.
• An audio oscillator produces frequencies in the audio range, about 16 Hz to 20 kHz.
• An RF oscillator produces signals in the radio frequency (RF) range of about 100 kHz to 100 GHz.

There are two main types of electronic oscillator – the linear or harmonic oscillator and the nonlinear or relaxation oscillator. The most common linear oscillator today is the crystal oscillator, in which the frequency is controlled by a resonator consisting of a vibrating quartz crystal. It is ubiquitous in modern electronics, used to generate the clock signal in computers and digital watches and radio frequency signals in radio transmitters and receivers.