An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or square wave.

A low frequency oscillator (or LFO) is an electronic oscillator that generates an alternating current waveform between 0.1 Hz and 10 Hz. This term is typically used in the field of audio frequency synthesizers, to distinguish it from an audio frequency oscillator.

There are two main types of electronic oscillator: the harmonic oscillator and the relaxation oscillator.

The harmonic oscillator produces a sine wave at the output.

The basic form of a harmonic oscillator is an electronic amplifier whose output is connected to a narrowband electronic filter. The output of the filter is in turn connected to the input of the amplifier.

When the amplifier is turned on, noise feeds it and the output is filtered and reconnected to the input. Nonlinear phenomena prevent the feedback from increasing to infinity, causing saturation in the amplified signal.

A piezoelectric crystal (commonly quartz) can be integrated into the circuit to stabilize the frequency of the oscillation, resulting in a crystal oscillator or Pierce Oscillator.

There are several types of harmonic oscillators, given the different ways of amplifying and filtering. For example:.