Patent ID: 8378755

Claim:
An oscillation circuit, connected to an external piezoelectric resonator, comprising: a first inverter circuit that includes an input terminal and an output terminal which are connected to both terminals of the piezoelectric resonator, respectively; a first feedback resistor that is disposed between the input terminal and the output terminal of the first inverter circuit; first and second variable capacitive elements that are connected to the input terminal and the output terminal of the first inverter circuit, respectively, and have capacitance values that are variably settable by a control signal; a charging circuit that supplies the input terminal or the output terminal with a certain reference current in order to charge the first or second variable capacitive element; a comparator that compares a charging voltage of the input terminal or the output terminal with a reference voltage; and a control circuit that, in a calibration operation, at a first time, causes the charging circuit to start supply the reference current to the input terminal or the output terminal, and, at a second time after the first time, generates the control signal for setting a capacitance value of the first or second variable capacitive element so that the charging voltage becomes close to the reference voltage according to a comparison result of the comparator.