Crystal oscillator

Crystal resonator
	A miniature 16 MHz quartz crystal enclosed in a hermetically sealed HC-49/S package, used as the resonator in a crystal oscillator.
Type	Electromechanical
Working principle‍	Piezoelectricity, Resonance
Invented	Alexander M. Nicholson, Walter Guyton Cady
First production	1918
Electronic symbol

A crystal oscillator is an electronic oscillator circuit that uses a piezoelectric crystal as a frequency-selective element.^[1]^[2]^[3] The oscillator frequency is often 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 a quartz crystal, so oscillator circuits incorporating them became known as crystal oscillators.^[1] However, other piezoelectricity materials including polycrystalline ceramics are used in similar circuits.

A crystal oscillator relies on the slight change in shape of a quartz crystal under an electric field, a property known as inverse piezoelectricity. A voltage applied to the electrodes on the crystal causes it to change shape; when the voltage is removed, the crystal generates a small voltage as it elastically returns to its original shape. The quartz oscillates at a stable resonant frequency, behaving like an RLC circuit, but with a much higher Q factor (less energy loss on each cycle of oscillation). Once a quartz crystal is adjusted to a particular frequency (which is affected by the mass of electrodes attached to the crystal, the orientation of the crystal, temperature and other factors), it maintains that frequency with high stability.^[4]

Quartz crystals are manufactured for frequencies from a few tens of kilohertz to hundreds of megahertz. As of 2003, around two billion crystals are manufactured annually.^[5] Most are used for consumer devices such as wristwatches, clocks, radios, computers, and cellphones. However, in applications where small size and weight is needed crystals can be replaced by thin-film bulk acoustic resonators, specifically if ultra-high frequency (more than roughly 1.5 GHz) resonance is needed. Quartz crystals are also found inside test and measurement equipment, such as counters, signal generators, and oscilloscopes.

^ ^a ^b Graf, Rudolf F. (1999). Modern Dictionary of Electronics, 7th Ed. US: Newnes. pp. 162, 163. ISBN 978-0750698665.
^ Amos, S. W.; Roger Amos (2002). Newnes Dictionary of Electronics, 4th Ed. US: Newnes. p. 76. ISBN 978-0750656429.
^ Laplante, Phillip A. (1999). Comprehensive Dictionary of Electrical Engineering. US: Springer. ISBN 978-3540648352.
^ Paul Horowitz, Winfield Hill, The Art of Electronics Second Edition, Cambridge University Press, 1989, ISBN 0-521-37095-7, pg. 300 ff
^ Lombardi, Michael (2003). Encyclopedia of Physical Science and Technology (3rd ed.).

[Graf1999-1] Graf, Rudolf F. (1999). Modern Dictionary of Electronics, 7th Ed. US: Newnes. pp. 162, 163. ISBN 978-0750698665.

[Amos-2] Amos, S. W.; Roger Amos (2002). Newnes Dictionary of Electronics, 4th Ed. US: Newnes. p. 76. ISBN 978-0750656429.

[Laplante-3] Laplante, Phillip A. (1999). Comprehensive Dictionary of Electrical Engineering. US: Springer. ISBN 978-3540648352.

[4] Paul Horowitz, Winfield Hill, The Art of Electronics Second Edition, Cambridge University Press, 1989, ISBN 0-521-37095-7, pg. 300 ff

[5] Lombardi, Michael (2003). Encyclopedia of Physical Science and Technology (3rd ed.).

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