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The Physical Principle of Quartz Crystal Oscillator

Release time: 2020-03-27 Browse times: 786 times
The structure of a crystal oscillator is very simple. Its core is a piece of quartz crystal. Quartz in nature is in a hexagonal state. If the crystal is sliced into a slice according to a certain orientation, it is a quartz wafer. Put a thin layer of silver on both sides of the chip, and then solder two leads. Encapsulated in a metal or glass case, it becomes a quartz crystal oscillator.
 
Quartz is an insulator with silver-plated electrodes on both sides. It is a typical parallel plate capacitor when the crystal is not working. Its capacitance is not large, usually only a few pf to dozens of pf. T
 
Quartz crystal has a very wonderful characteristic: when a mechanical force is applied to the wafer, an electric field is generated in the corresponding direction of the wafer; in turn, an electric field is applied between the two electrodes of the quartz wafer, and the wafer will be mechanically deformed. This physical phenomenon is called the piezoelectric effect. Now apply a voltage alternating to the two poles of the quartz wafer, and it will produce mechanical vibration. The Mechanical vibration will cause an alternating electric field to the wafer. It's just that the amplitude of this mechanical vibration and the change in the alternating electric field are very small. The amplitude will increase sharply only when the frequency of the applied alternating voltage is equal to a certain frequency.This phenomenon is called piezoelectric resonance. The specific frequency is called the natural frequency or resonance frequency of the quartz crystal.The natural frequency is determined by the size of the wafer and the cutting angle.
 
The quartz oscillator has a fairly stable oscillation frequency, because the fixed frequency of the quartz crystal is little affected by temperature changes. This effect is related to the way the quartz crystal is cut into thin slices. The natural frequency parameters of quartz crystals mainly depend on the thickness of the slice and are inversely proportional to the thickness.

 
To give a simple example: our daily quartz clocks use a 32.768KHz crystal, and the travel time error is between 0.5 seconds and 1 second, while the daily error of mechanical clocks may exceed 30 seconds. Affected by temperature, the speed of mechanical watches varies with temperature fluctuations.
 
In radar, navigation, global satellite positioning system (GPS) and other fields, the stability of the signal determines the accuracy of the measurement time. It further determines the accuracy and accuracy of the target bearing and target distance. A timing error of 1 microsecond will cause a positioning error of about 150 meters. Therefore, the frequency stability of the crystal oscillator used is very high.