What is a "Quartz"? The crystalline form of SiO2 or quartz is relatively abundant in nature, but in the highly pure form required for the manufacture of quartz crystal units, the supply tends to be small. The limited supply and the high cost of natural quartz have resulted in the development of a synthetic quartz manufacturing industry. The synthetic quartz manufacturing technology turns quartz crystals an indispensable component of modern electronic production. What is the "Quartz Crystal Units"?
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Ham Radio Store How a Quartz Crystal Resonator Works The operation of quartz crystals depends upon the piezo-electric effect that links mechanical resonances to the electrical system. The electrical signals are converted from their electrical form into mechanical vibrations. It is these vibrations that are affected by the mechanical resonances of the quartz crystal and then linked back into electrical system.
The losses associated with quartz crystals are very low and this means that the selectivity or Q - quality factor is exceedingly high. Circuit symbol for a quartz crystal resonator, xtal Piezo-electric effect When looking at how a quartz crystal works, it is first necessary to understand the basics of the piezo-electric effect. It is an effect that occurs in a number of materials, both naturally occurring and synthetic. The piezo electric effect occurs in quartz as well as a number of ceramic materials used in the electronics industry as well as a number of organic substances.
It is for this reason that some ceramic resonators are available, although their performance does not equal that of quartz in terms of being used as a resonator. The peizo-electric effect is not only used in resonators, but it can also be used for electric transducers - motion sensors, stress gauges, crystal microphones and many more. When the piezo-electric effect occurs, an electric charge develops in certain solid materials as a result of an applied mechanical stress.
This effect converts a mechanical stress in a crystal to a voltage and vice versa, i. How does a quartz crystal resonator work: the basics For the operation of a quartz crystal it is found that the piezo-electric effect converts the electrical impulses to mechanical stress which is subject to the very high Q mechanical resonances of the crystal, and this is in turn linked back into the electrical circuit.
The quartz crystal can vibrate in several different ways, and this means that it has several resonances - each on a different frequency. Fortunately the way in which the quartz crystal blank is cut from the original crystal itself can very significantly reduce this. In fact the angle of the faces relative to the original crystal axes determines many of its properties from the way it vibrates to its activity, Q, and its temperature co-efficient.
This causes the centre to become thinner as the crystal extends and thicker as it shortens. Quartz crystal resonator longitudinal vibration Low frequency face shear mode: For crystals that work in this mode, the whole rectangular shape of the crystal vibrates as shown below. Quartz crystal resonator high frequency shear vibration The way in which the crystal blank is cut from the bulk crystal affects the way in which it vibrates.
In particular the angle it is cut relative to the axes of the bulk quartz crystal has a major effect. A cut known as the AT cut is used for most crystals found in traditional radio and electronics circuits and this typically vibrates using the high frequency shear mode.
Equivalent circuit of a quartz crystal resonator To analyse the electrical response of a quartz crystal resonator, it is very often useful to depict it as the equivalent electrical components that would be needed to replace it.
This equivalent circuit is can then be used to analyse its response and predict its performance as in the diagram below: The equivalent circuit given below is often called the 4-parameter crystal model and it is sufficient for many calculations and to illustrate the operation of the crystal.
The largest of these arises from the frictional losses of the mechanical vibration of the crystal. This is often refered to as the shunt capacitance. Apart from their use in oscillators, quartz crystals find uses in filters. Here they offer levels of performance that cannot be achieved by other forms of filter. Often several crystals may be used in one filter to provide the correct shape.
Crystal parallel and series resonance There are two modes in which a crystal oscillator can operate and these can be seen from the equivalent circuit diagram. At the resonant frequency, fs, the capacitive and inductive reactances cancel and the impedance falls to a minimum equal to the resistance in the circuit, i.
Understanding The Quartz Crystal Resonator
January 17, Accurate timing is one of the most basic requirements for so much of the technology we take for granted, yet how many of us pause to consider the component that enables us to have it? The quartz crystal is our go-to standard when we need an affordable, known, and stable clock frequency for our microprocessors and other digital circuits. Tuned circuits are cheap and easy to produce, however their frequency stability is extremely affected by external factors such as temperature and vibration. Thus an RF oscillator using a tuned circuit can drift by many kHz over the period of its operation, and its timing can not be relied upon. Long before accurate timing was needed for computers, the radio transmitters of the s and s needed to stay on frequency, and considerable effort had to be maintained to keep a tuned-circuit transmitter on-target. The quartz crystal was waiting to swoop in and save us this effort. Good Vibrations Equivalent circuit of a quartz crystal.
JoJozahn To reach higher frequencies, a crystal can be made to vibrate at one of its overtone modes, resonatoes occur near multiples of the fundamental resonant frequency. The oscillation frequency depends mainly on the thickness of the ceramic core of the resonator and the type of material used while it is little affected by external variable elements. Placing a capacitor in series with the crystal and a several-megaohm resistor in parallel can minimize such voltages. These include single crystals of lithium tantalatelithium niobatelithium borateberlinitegallium arsenidelithium tetraboratealuminium phosphatebismuth germanium oxidepolycrystalline zirconium crytsal ceramics, high-alumina ceramics, silicon — zinc oxide composite, or dipotassium tartrate. Vig High sensitivity temperature sensor and sensor array U.