Patent ID: 8749314

Claim:
An oven-controlled crystal oscillator comprising: a thermostatic oven; a crystal unit housed in the thermostatic oven; an oscillator circuit which uses the crystal unit; a heater that heats the thermostatic oven; and a temperature control circuit that drives the heater so as to make temperature in the thermostatic oven equal to temperature of a zero temperature coefficient point of the crystal unit, wherein said temperature control circuit includes: a power transistor installed in series with said heater; a differential amplifier that drives said power transistor; a thermistor that installed in said thermostatic oven, provided with negative resistance-temperature characteristics, and connected between a power supply voltage and an inverting input terminal of said differential amplifier; a first resistor installed between the inverting input terminal and a ground point and used to adjust the temperature of the zero temperature coefficient point; a second resistor installed between the power supply voltage and a non-inverting input terminal of said differential amplifier; and a third resistor installed between the ground point and the non-inverting input terminal, and wherein one of said second resistor and said third resistor is configured as a resistor assembly provided with a first end and a second end, wherein the resistor assembly comprises: a first resistance element; a second resistance element; and a temperature-detecting resistance element provided with positive resistance-temperature characteristics and adapted to detect ambient temperature wherein the first resistance element is installed between the first end of the resistor assembly and a connection node while the second resistance element is installed between the connection node and the second end of the resistor assembly, and the temperature-detecting resistance element is installed between the connection node and the second end of the resistor assembly, and wherein a resistance-temperature coefficient of the temperature-detecting resistance element is larger than each of absolute values of resistance-temperature coefficients of the first resistance elements and the second resistance elements.