Engineers usually only know that the crystal is a frequency component, and there may be few people who are interested in the crystal is divided into fundamental frequency crystal and overtone crystal. So what is the fundamental frequency crystal, what is the overtone crystal, and what is the difference between the use of the two in the circuit.
The vibration of the crystal is like a spring; the vibration frequency of the crystal is related to the area, thickness and cutting orientation of the quartz crystal.
The longer it is, the slower it shakes.
the thicker it is, the slower it shakes.
The softer the crystal, the slower it will vibrate.
But too short, too thin, too hard can not shake.
Crystal oscillator is mechanical vibration, with the characteristics of mechanical vibration: shape, geometry, quality, etc., determine the frequency of vibration.
Crystal oscillators are generally made of quartz or ceramic material plus the combination of the internal wafer, and the frequency of the crystal oscillator depends on the thickness of the wafer impact.
In terms of manufacturing process, the size of the wafer and the thickness of the wafer are closely related to the frequency of the crystal. Generally speaking, the higher the frequency of the quartz crystal, the thinner the quartz wafer is required. For example, a 40MHz quartz crystal requires a wafer thickness of 41.75 microns, which is quite achievable, but a 100MHz quartz crystal requires a wafer thickness of 16.7 microns. Even though the thickness is achievable, the loss is very high, and the wafer will be broken when it is dropped gently after the finished product is made. Therefore, it is necessary to use three times overtone, five times overtone, and seven times overtone technology to achieve high frequency crystals. For example, for a crystal with a fundamental frequency of 20MHz, a crystal of 100MHz can be obtained after five overtones. Generally speaking, in terms of experience, below 40MHz is basically the fundamental frequency crystal, while above 40MHz, it is the overtone crystal. Therefore, it is easy to understand why many active crystal frequency is basically considered high frequency, and the cost is relatively expensive, the cost of the active crystal in addition to the internal chip is thinner, and then there is an oscillation piece added to itself.
Then the fundamental frequency crystal and overtone crystal in the use of what will not be used. There is definitely a difference in the use of the two, such as the base frequency crystal, only need to access the appropriate capacitance can work, while the overtone crystal requires inductance and capacitance with the use of the overtone frequency, otherwise it can only vibrate the base frequency.
Overtone crystal oscillator introduction: quartz crystal oscillator is made of quartz wafer, and different frequencies of quartz crystal oscillator corresponding to the size, thickness of the quartz wafer is not the same.
