Patent ID: 8653420

Claim:
A temperature control circuit in an oven controlled crystal oscillator, comprising: a heater resistor for generating heat, wherein one end of the heater resister is connected to a supply voltage; a thermistor, wherein one end of the thermistor is supplied with the supply voltage, and a resistance value of the thermistor varies with a temperature of the thermistor, and an other end of the thermistor outputs a voltage corresponding to the temperature; a first resistor, wherein one end of the first resistor is connected to the other end of the thermistor; a first digital potentiometer, wherein one end of the first digital potentiometer is connected to an other end of the first resistor and an other end of the first digital potentiometer is connected to a ground, and a resistance value of the first digital potentiometer is adjustable in a digital controlled manner; a second digital potentiometer, wherein one end of the second digital potentiometer is supplied with the supply voltage, wherein a resistance value of the second digital potentiometer is adjustable in the digital controlled manner; a second resistor, wherein one end of the second resistor is connected to an other end of the second digital potentiometer and an other end of the second resistor is connected to the ground; a differential amplifier, having a first input terminal, a second input terminal and an output terminal, wherein a voltage between the other end of the thermistor and the one end of the first resistor is input to the first input terminal, a voltage between the other end of the second digital potentiometer and the one end of the second resistor is input to the second input terminal, the output terminal is connected to the first input terminal via a third resistor to provide a feedback, a difference between the voltage input to the first input terminal and the voltage input to the second input terminal is amplified and output as a control voltage; and a power transistor, having a collector connected to an other end of the heater resistor, a base inputting the control voltage output from the differential amplifier and an emitter connected to the ground, wherein the power transistor controls the heat generated by the heater resistor based on the control voltage from the differential amplifier.