Quartz Crystal Oscillators For Electronic Circuits
A crystal of quartz can be made to bend in an electric field, by applying a voltage to an electrode, with proper cutting and mounting. This property of quartz crystal oscillator is known as piezoelectricity. This piezoelectric property of quartz crystals helps to develop an electric potential upon the application of mechanical stress. The piezoelectric properties of quartz are most commonly used in a crystal oscillator.
A crystal oscillator is an electronic circuit that by using the mechanical resonance of a vibrating crystal of piezoelectric material generates an electrical signal. The signal produced is of very precise frequency. The most common type of piezoelectric resonator used is the quartz crystal, so the oscillator circuits designed around them are known as crystal oscillators.
The advantages offered by quartz makes it most suitable for making oscillators. Or, we can say that crystal oscillators are the oscillators where a quartz crystal is used to provide the primary frequency element. The characteristics of high degree of frequency stability and accuracy of the quartz crystal make them most suitable for crystal oscillators.
The mode of vibration and the angle at which quartz crystal is mounted defines the specific characteristics of the crystal. The resonant frequency of the quartz is determined by the cut and size of the crystal. Its elastic constants and its size change in such a way that the frequency dependence on temperature can be very low.
Quartz crystal can be cut and designed for specific purposes. Crystals for AT-cut are most common that are used for oscillator material. Its shape and dimensions are optimized for the high yield of the required wafers. High quality quartz crystals are usually created with low content of aluminium, alkali metal and other impurities ensuing minimum defects. Crystals for watches, for tuning fork are created with these etch channel density. The frequency produced is commonly used to keep the track of time, to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers, etc. Crystals designed for SAW devices are created as flat, with large X-size seed. On the other hand, special high-Q crystals are used in highly stable oscillators. They are grown at slow speed and have constant low infrared absorption. Hence, the shape or 'cut' of the crystal is very important in defining its functionality.
There are several manufacturers in the market that can deliver wide range of quartz crystals in various package styles, frequencies and specifications. Custom specific crystals can also be produced. Therefore, one needs to be very specific before employing oscillators in the application.