We only know that the crystal is a kind of frequency components, and for a fundamental and overtone crystal oscillator of the crystal may be less and less. So what is the fundamental and overtone crystal oscillator, what, two in the circuit in the use of what is the difference.
The crystal generally consists of quartz material or ceramic material are added to the chip and a combination of internal, and the crystal frequency depends on the thickness of the wafer effect. First of all, in the production process, the wafer size and wafer thickness and crystal oscillator frequency is closely related, generally speaking, the higher the frequency of quartz crystal, quartz crystal need more thin. For example, 40MHZ quartz crystal wafer thickness required is 41.75 microns, so the thickness can be done, but 100MHZ quartz crystal, the required thickness of the wafer is 16.7 microns. Even if the thickness can be done, but the loss is very high, the finished product after a slight fall on the chip fragmentation. It is generally in the high frequency crystal will be used three times, five times, seven harmonic overtone overtone techniques to achieve. For example, the fundamental frequency of 20MHZ crystal, after the five overtone can be 100MHZ crystal. In general, experience, 40MHZ is the basic frequency crystal, rather than 40MHZ, is the harmonic oscillator. Therefore, we are not difficult to understand why many are high active crystal frequency, and the cost is relatively expensive, in addition to the cost of internal active crystal thin wafer, then add a piece of self oscillation.
Then the fundamental and overtone crystal oscillator in use and what not. Both in use is certainly different, such as fundamental frequency crystal, only need to access the appropriate capacitor can work, and is in need of inductance and capacitance crystal overtone vibration can be used in conjunction with only the overtone frequency or just, vibration frequency.