Constant temperature crystal oscillator is called constant temperature crystal oscillator for short. OCXO (oven controlled crystal oscillator) is a crystal oscillator that uses constant temperature bath to keep the temperature of quartz crystal resonator in crystal oscillator constant and reduce the change of output frequency caused by the change of surrounding temperature to the minimum. OCXO is composed of constant temperature bath control circuit and oscillator circuit. Usually people use the differential series amplifier composed of thermistor "bridge" to realize temperature control.