Oven controlled crystal oscillator

An oven controlled crystal oscillator, comprising:

• a crystal oscillator that includes a crystal resonator and an oscillator circuit;
• a temperature control circuit including:
• a heater resistor that has one end to which a supply voltage connects to generate a heat;
• a thermistor configured to output a voltage to one end, the voltage corresponding to a temperature;
• a first resistor that has one end to which the supply voltage is supplied and another end connected to the one end of the thermistor;
• a second resistor that has one end to which the supply voltage is supplied;
• a third resistor that has one end connected to another end of the second resistor and another end of the third resistor is grounded;
• a differential amplifier that has one input terminal and another input terminal, a voltage between the another end of the first resistor and the one end of the thermistor being input to the one input terminal, a voltage between another end of the second resistor and the one end of the third resistor being input to the another input terminal, the differential amplifier amplifying a difference between the voltage input to the one input terminal and the voltage input to the another input terminal so as to output as a control voltage;
• a thermosensor disposed in parallel to the first resistor, the thermosensor having one end to which the supply voltage is supplied;
• and
• a fourth resistor that has one end connected to another end of the thermosensor and another end of the fourth resistor is grounded;
• and
• a control integrated circuit that includes a digital variable resistor and a controller, the digital variable resistor being connected to the thermosensor in parallel, the controller adjusting a resistance value of the digital variable resistor based on a digital control signal input from outside.