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A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency. The most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits incorporating them became known as crystal oscillators,  but other piezoelectric materials including polycrystalline ceramics are used in similar circuits.
A crystal oscillator, particularly one using a quartz crystal , works by distorting the crystal with an electric field , when voltage is applied to an electrode near or on the crystal; a property known as electrostriction or inverse piezoelectricity.
When the electric field is removed, the quartz—which oscillates at a precise frequency—generates an electric field as it returns to its previous shape, and this can generate a voltage.
The result is that a quartz crystal behaves like an RLC circuit , but with a much higher Q. Quartz crystals are manufactured for frequencies from a few tens of kilohertz to hundreds of megahertz. More than two billion crystals are manufactured annually. Quartz crystals are also found inside test and measurement equipment, such as counters, signal generators , and oscilloscopes. 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. Crystals are also used in other types of electronic circuits, such as crystal filters. Piezoelectric resonators are sold as separate components for use in crystal oscillator circuits.
An example is shown in the picture. They are also often incorporated in a single package with the crystal oscillator circuit, shown on the righthand side. Piezoelectricity was discovered by Jacques and Pierre Curie in Paul Langevin first investigated quartz resonators for use in sonar during World War I. The first crystal-controlled oscillator , using a crystal of Rochelle salt , was built in and patented  in by Alexander M.
Pierce and Louis Essen. Quartz crystal oscillators were developed for high-stability frequency references during the s and s. A number of firms started producing quartz crystals for electronic use during this time. Using what are now considered primitive methods, about , crystal units were produced in the United States during Shortages of crystals during the war caused by the demand for accurate frequency control of military and naval radios and radars spurred postwar research into culturing synthetic quartz, and by a hydrothermal process for growing quartz crystals on a commercial scale was developed at Bell Laboratories.
By the s virtually all crystals used in electronics were synthetic. In , Juergen Staudte invented a photolithographic process for manufacturing quartz crystal oscillators while working at North American Aviation now Rockwell that allowed them to be made small enough for portable products like watches. Although crystal oscillators still most commonly use quartz crystals, devices using other materials are becoming more common, such as ceramic resonators.
A crystal is a solid in which the constituent atoms , molecules , or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. Almost any object made of an elastic material could be used like a crystal, with appropriate transducers , since all objects have natural resonant frequencies of vibration. For example, steel is very elastic and has a high speed of sound. It was often used in mechanical filters before quartz. The resonant frequency depends on size, shape, elasticity , and the speed of sound in the material.
High-frequency crystals are typically cut in the shape of a simple rectangle or circular disk. Low-frequency crystals, such as those used in digital watches, are typically cut in the shape of a tuning fork. For applications not needing very precise timing, a low-cost ceramic resonator is often used in place of a quartz crystal.
When a crystal of quartz is properly cut and mounted, it can be made to distort in an electric field by applying a voltage to an electrode near or on the crystal. This property is known as electrostriction or inverse piezoelectricity. When the field is removed, the quartz generates an electric field as it returns to its previous shape, and this can generate a voltage.
The result is that a quartz crystal behaves like an RLC circuit , composed of an inductor , capacitor and resistor , with a precise resonant frequency. Quartz has the further advantage that its elastic constants and its size change in such a way that the frequency dependence on temperature can be very low. The specific characteristics depend on the mode of vibration and the angle at which the quartz is cut relative to its crystallographic axes. This means that a quartz clock, filter or oscillator remains accurate.
For critical applications the quartz oscillator is mounted in a temperature-controlled container, called a crystal oven , and can also be mounted on shock absorbers to prevent perturbation by external mechanical vibrations.
A quartz crystal can be modeled as an electrical network with low- impedance series and high- impedance parallel resonance points spaced closely together. Mathematically using the Laplace transform , the impedance of this network can be written as:. Adding capacitance across a crystal causes the parallel resonant frequency to decrease. Adding inductance across a crystal causes the parallel resonant frequency to increase.
These effects can be used to adjust the frequency at which a crystal oscillates. Crystal manufacturers normally cut and trim their crystals to have a specified resonant frequency with a known "load" capacitance added to the crystal. Without the load capacitance, the resonant frequency is higher. A quartz crystal provides both series and parallel resonance. The series resonance is a few kilohertz lower than the parallel one.
Any small additional capacitance in parallel with the crystal pulls the frequency lower. Moreover, the effective inductive reactance of the crystal can be reduced by adding a capacitor in series with the crystal.
This latter technique can provide a useful method of trimming the oscillatory frequency within a narrow range; in this case inserting a capacitor in series with the crystal raises the frequency of oscillation. For a crystal to operate at its specified frequency, the electronic circuit has to be exactly that specified by the crystal manufacturer.
Note that these points imply a subtlety concerning crystal oscillators in this frequency range: the crystal does not usually oscillate at precisely either of its resonant frequencies. To reach higher frequencies, a crystal can be made to vibrate at one of its overtone modes, which occur near multiples of the fundamental resonant frequency. Only odd numbered overtones are used. Such a crystal is referred to as a 3rd, 5th, or even 7th overtone crystal. To accomplish this, the oscillator circuit usually includes additional LC circuits to select the desired overtone.
A crystal's frequency characteristic depends on the shape or "cut" of the crystal. The crystal oscillator circuit sustains oscillation by taking a voltage signal from the quartz resonator , amplifying it, and feeding it back to the resonator.
The rate of expansion and contraction of the quartz is the resonant frequency, and is determined by the cut and size of the crystal. When the energy of the generated output frequencies matches the losses in the circuit, an oscillation can be sustained. An oscillator crystal has two electrically conductive plates, with a slice or tuning fork of quartz crystal sandwiched between them. During startup, the controlling circuit places the crystal into an unstable equilibrium , and due to the positive feedback in the system, any tiny fraction of noise is amplified, ramping up the oscillation.
The crystal resonator can also be seen as a highly frequency-selective filter in this system: it only passes a very narrow subband of frequencies around the resonant one, attenuating everything else. Eventually, only the resonant frequency is active. As the oscillator amplifies the signals coming out of the crystal, the signals in the crystal's frequency band becomes stronger, eventually dominating the output of the oscillator.
The narrow resonance band of the quartz crystal filters out all the unwanted frequencies. The output frequency of a quartz oscillator can be either that of the fundamental resonance or of a multiple of that resonance, called a harmonic frequency. Harmonics are an exact integer multiple of the fundamental frequency.
But, like many other mechanical resonators, crystals exhibit several modes of oscillation, usually at approximately odd integer multiples of the fundamental frequency. These are termed "overtone modes", and oscillator circuits can be designed to excite them. The overtone modes are at frequencies which are approximate, but not exact odd integer multiples of that of the fundamental mode, and overtone frequencies are therefore not exact harmonics of the fundamental. High frequency crystals are often designed to operate at third, fifth, or seventh overtones.
To produce higher frequencies, manufacturers make overtone crystals tuned to put the 3rd, 5th, or 7th overtone at the desired frequency, because they are thicker and therefore easier to manufacture than a fundamental crystal that would produce the same frequency—although exciting the desired overtone frequency requires a slightly more complicated oscillator circuit.
A major reason for the wide use of crystal oscillators is their high Q factor. A typical Q value for a quartz oscillator ranges from 10 4 to 10 6 , compared to perhaps 10 2 for an LC oscillator.
One of the most important traits of quartz crystal oscillators is that they can exhibit very low phase noise. In many oscillators, any spectral energy at the resonant frequency is amplified by the oscillator, resulting in a collection of tones at different phases. In a crystal oscillator, the crystal mostly vibrates in one axis, therefore only one phase is dominant.
This property of low phase noise makes them particularly useful in telecommunications where stable signals are needed, and in scientific equipment where very precise time references are needed. Environmental changes of temperature, humidity, pressure, and vibration can change the resonant frequency of a quartz crystal, but there are several designs that reduce these environmental effects.
These designs, particularly the OCXO, often produce devices with excellent short-term stability. The limitations in short-term stability are due mainly to noise from electronic components in the oscillator circuits.
Long-term stability is limited by aging of the crystal. Due to aging and environmental factors such as temperature and vibration , it is difficult to keep even the best quartz oscillators within one part in 10 10 of their nominal frequency without constant adjustment.
For this reason, atomic oscillators are used for applications requiring better long-term stability and accuracy. For crystals operated at series resonance or pulled away from the main mode by the inclusion of a series inductor or capacitor, significant and temperature-dependent spurious responses may be experienced.
Though most spurious modes are typically some tens of kilohertz above the wanted series resonance their temperature coefficient is different from the main mode and the spurious response may move through the main mode at certain temperatures. Even if the series resistances at the spurious resonances appear higher than the one at wanted frequency a rapid change in the main mode series resistance can occur at specific temperatures when the two frequencies are coincidental.
A consequence of these activity dips is that the oscillator may lock at a spurious frequency at specific temperatures. This is generally minimized by ensuring that the maintaining circuit has insufficient gain to activate unwanted modes.
Spurious frequencies are also generated by subjecting the crystal to vibration. This modulates the resonant frequency to a small degree by the frequency of the vibrations. SC-cut crystals are designed to minimize the frequency effect of mounting stress and they are therefore less sensitive to vibration.
Acceleration effects including gravity are also reduced with SC-cut crystals as is frequency change with time due to long term mounting stress variation. There are disadvantages with SC-cut shear mode crystals, such as the need for the maintaining oscillator to discriminate against other closely related unwanted modes and increased frequency change due to temperature when subject to a full ambient range.
This is a 3. This is a low cost crystal oscillator withoscillation frequency of Crystal are normally required to provideclock pulses to your microcontroller or other IC''s which require external clocksource. An oscillator crystal has two electrically conductive plates, with a slice ortuning fork of quartz crystal sandwiched between them. The crystal oscillatorcircuit sustains oscillation by taking a voltage signal from the quartzresonator, amplifying it, and feeding it back to the resonator. Quartz has thefurther advantage that its elastic constants and its size change in such a waythat the frequency dependence on temperature can be very low. Shop No.
China 11.0592mhz quartz crystal oscillator