Patent ID: 8327708

Claim:
An acceleration sensor comprising: a driver circuit for outputting a biased alternating-current (AC) voltage having a variable bias voltage; a detector element including a fixed electrode having the biased AC voltage is applied thereto, and a first movable electrode facing the fixed electrode, wherein a capacitance provided between the fixed electrode and the first movable electrode changes depending on acceleration applied to the detector element; a first current-voltage (CN) converter for converting a current output from the first movable electrode of the detector element into a voltage, and outputting the voltage; a first operational amplifier including a first input port having the voltage output from the first CN converter input thereto, and an output port for outputting a voltage depending on the input voltage; a synchronous demodulator for synchronously detecting the voltage output from the first operational amplifier; and a defect detector for outputting a defect detection signal when the defect detector determines that the voltage output from the first operational amplifier is out of a predetermined range while the biased AC voltage output from the driver circuit is a predetermined voltage, wherein the driver circuit includes an oscillator for generating an AC voltage, and a second operational amplifier including a first input port having the AC voltage generated by the oscillator input thereto, a second input port having selectively a reference voltage and a variable voltage input thereto, and an output port connected to the fixed electrode of the detector element.