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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.
Crystal oscillators can be manufactured for oscillation over a wide range of frequencies, from a few kilohertz up to several hundred megahertz.Many applications call for a crystal oscillator frequency conveniently related to some other desired frequency, so hundreds of standard crystal frequencies are made in large quantities and stocked by electronics distributors.
An OCXO inside an HP digital frequency counter Miniature crystal oven used to stabilize the frequency of a vacuum-tube mobile radio transmitter. A crystal oven is a temperature-controlled chamber used to maintain the quartz crystal in electronic crystal oscillators at a constant temperature, in order to prevent changes in the frequency due to variations in ambient temperature.
Allan variance is used as a measure of frequency stability in a variety of precision oscillators, such as crystal oscillators, atomic clocks and frequency-stabilized lasers over a period of a second or more. Short-term stability (under a second) is typically expressed as phase noise.
In nearly all quartz clocks and watches, the frequency is 32 768 Hz, [1] and the crystal is cut in a small tuning fork shape on a particular crystal plane. [2] This frequency is a power of two ( 32 768 = 2 15 ), just high enough to exceed the human hearing range , yet low enough to keep electric energy consumption , cost and size at a modest ...
Short term stability, startup time, and power consumption, are similar to those of quartz. [citation needed] In some cases, MEMS oscillators show lower power consumption than that of quartz. High precision MEMS temperature-compensated oscillators (TCXOs) have recently been announced with ±0.1 ppm frequency stability over temperature. [65]
In particular, quartz crystals can exhibit mechanical resonances with a very high Q factor (from 10,000 to 100,000 and greater – far higher than conventional resonators built from inductors and capacitors). The crystal's stability and its high Q factor allow crystal filters to have precise center frequencies and steep band-pass characteristics.
The crystal in combination with C 1 and C 2 forms a pi network band-pass filter, which provides a 180° phase shift and a voltage gain from the output to input at approximately the resonant frequency of the crystal. To understand the operation, note that at the frequency of oscillation, the crystal appears inductive.