The Main Types of Crystal Oscillator
1. General Crystal Oscillator Quartz crystal
Basically this type of oscillator is composed of the crystal unit and feedback amplifier that operates the crystal unit. There are different output waves corresponding to different applications.


 

3. Temperature-Compensated Crystal Oscillators, TCXO, OSC VC-TCXO

The biggest factor that affects the frequency stability is the temperature characteristics. With the help of temperature-compensated circuit, this type of oscillator realizes higher stabilization of temperature characteristics than the crystal unit. Because the specified temperature-compensated voltage is applied, TCXO can output much more stable frequency against the ambient temperature. It is mainly applied for the standard oscillator used for frequency synthesizer of mobile communications device. PDC (Personal Digital Cellular), GSM (Global System for Mobile Communication), GPS (Global Positioning System) and so on require frequency with high temperature stability of +/-2.5ppm Maximum. Such requirement cannot be satisfied with the AT cut crystal unit only. Moreover, there is subtle difference with different crystal units in temperature characteristics. So, there is need to make compensation with the temperature compensation circuit in order to acquire frequency of high temperature stability.