What is Crystal Oscillator ?

　　A crystal oscillator is an electronic oscillator circuit that uses a piezoelectric resonator, a crystal, as its frequency-determining element. Crystal is the common term used in electronics for the frequency-determining component, a wafer of quartz crystal or ceramic with electrodes connected to it. A more accurate term for it is piezoelectric resonator.

　　In crystal oscillators, the usual electrical resonant circuit is replaced by a mechanically vi­brating crystal. The crystal (usually quartz) has a high degree of stability in holding con­stant at whatever frequency the crystal is originally cut to operate. The crystal oscillators are, therefore, used whenever great stability is needed, for example, in communication trans­mitters, and receivers, digital clocks etc.

　　A quartz crystal exhibits a very important property known as piezo-electric effect. When a mechanical pressure is applied across the faces of the crystal, a voltage proportional to the applied mechanical pressure appears across the crystal. Conversely, when a voltage is applied across the crystal surfaces, the crystal is distorted by an amount proportional to the applied voltage. An alter­nating voltage applied to a crystal causes it to vibrate at its natural frequency.

　　There are numerous applications for crystal oscillator in various fields and a few crystal oscillator applications are shown below:

　　The use of crystal oscillator in military and aerospace, is to establish an efficient communication system, for the navigation purpose, electronic warfare, in the guidance systems, and so on.

　　The crystal oscillator is used in research and measurement for celestrial navigation, space tracking purpose, in the measuring instruments and medical devices, and so on.

　　There are a huge number of industrial applications of crystal oscillator such as in computers, digital systems, instrumentation, phase locked loop systems, marine, modems, sensors, telecommunications, disk drives, and so on.

　　Crystal oscillator is used for engine controlling, stereo, clock and to trip computer, and in GPS system.

　　Crystal oscillators are used in many consumer goods such as cable television systems, personal computers, video cameras, toys and video games, radio systems, cellular phones, and so on.

　　Sources:

　　1. https://en.wikipedia.org/wiki/Crystal_oscillator

　　2. www.crystal-bj.com