OSCILLATORS

OSCILLATORS

An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave.
A low-frequency oscillator (LFO) is an electronic oscillator that generates an AC waveform at a frequencybelow ≈20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audiofrequency oscillator.
Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters.
The waveform generators which are used to generate pure sinusoidal waveforms of fixed amplitude andfrequency are called oscillators.

 Crystal oscillator
A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers. The most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits designed around them were called "crystal oscillators".

Quartz crystals are manufactured for frequencies from a few tens of kilohertz to tens of megahertz. More than two billion (2×109) crystals are manufactured annually. Most are small devices for consumer devices such as wristwatches, clocks, radios, computers, and cellphones. Quartz crystals are also found inside test and measurement equipment, such as counters, signal generators, and oscilloscopes.

Voltage-controlled oscillator

A voltage-controlled oscillator or VCO is an electronic oscillator designed to be controlled in oscillationfrequency by a voltage input. 

The frequency of oscillation is varied by the applied DC voltage, while modulating signals may also be fed into the VCO to cause frequency modulation (FM) or phase modulation (PM); a VCO with digital pulse output may similarly have its repetition rate (FSK, PSK) or pulse width modulated (PWM).