A crystal oscillator is an electronic circuit that uses the mechanical resonance of a physical crystal of piezoelectric material along with an amplifier and feedback to create an electrical signal with a very precise frequency. It is an especially accurate form of an electronic oscillator. This frequency is 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. Crystal oscillators are a common source of time and frequency signals. The crystal used therein is sometimes called a "timing crystal".

Almost any object made of an elastic material could be used like a crystal, with appropriate transducers, since all objects have natural resonant frequencies of vibration. For example, steel is very elastic and has a high speed of sound. It was often used in mechanical filters before quartz. The resonant frequency depends on size, shape, elasticity and the speed of sound in the material. High-frequency crystals are typically cut in the shape of a simple, rectangular plate. Low-frequency crystals, such as those used in digital watches, are typically cut in the shape of a tuning fork. For applications not needing very precise timing, a low-cost ceramic resonator is often used in place of a quartz crystal.

Also Read: Multi Wave Oscillator, Crystal Oscillator, Voltage Controlled Oscillator, Colpitts Oscillator, Oscillator Circuit, Mcclellan Oscillator, Clock Oscillator, Hartley Oscillator