Quartz-Crystal Oscillator

Quartz-Crystal Oscillator 

a low-power generator of high-frequency electrical oscillations in which the resonant circuit is a quartz resonator, which is a plate, ring, or bar cut in a certain way from a quartz crystal. Upon deformation of the plate, electric charges appear on its surface. The magnitude and sign of the charges depend on the magnitude and direction of the deformation. In turn, the appearance of electric charges on the surface of the plate causes mechanical deformation. As a result, mechanical vibrations of the plate are accompanied by synchronous oscillations of electric charges on its surface, and vice versa. Quartz-crystal oscillators are characterized by great stability of the frequency of the generated oscillations: Δv/v, where Δv is the frequency deviation (drift) from its nominal value v, is 10^-3 to 10^-5 percent for short time intervals as a result of the high quality factor (10⁴-10⁵) of quartz resonators (the quality factor for commonly used oscillatory circuits is about 10²).

The oscillation frequency of a quartz-crystal oscillator (several kilohertz to several dozen megahertz) depends on the size of the quartz resonator, on the elasticity and piezoelectric constants of the quartz, and on the manner in which the resonator was cut from the crystal. For example, for an X-cut of a quartz crystal, the frequency (in megahertz) will be v = 2.86/d, where d is the thickness of the plate in millimeters.

A layer of silver may be deposited on the lateral surfaces of the plate (electrodes), or the plate may be placed in a special holder that acts as the capacitor plates.

To produce a high quality factor, the resonator is placed in a vacuum and its temperature is kept constant to within 0.001°C. The power of a quartz-crystal oscillator does not exceed several dozen watts. At higher power the quartz-crystal resonator breaks down because of mechanical stresses that arise within it.

Quartz-crystal oscillators with subsequent conversion of oscillatory frequency by division or multiplication are used for time measurements (quartz-crystal clocks and quantum clocks) or as frequency standards.

REFERENCE

Plonskii, A. F. P’ezokvarts v tekhnike sviazi. Moscow-Leningrad, 1951.