Patent ID: 7287429

Claim:
An acceleration sensor system comprising: a first fixed electrode and a second fixed electrode; a movable electrode disposed between the first and the second fixed electrodes for providing a first capacitor between the first fixed electrode and the movable electrode and a second capacitor between the second fixed electrode and the movable electrode; a detection capacitor for detecting a capacitance difference between the first capacitor and the second capacitor; a charge voltage conversion circuit for outputting and converting a capacitance change of the detection capacitor to an output voltage, the capacitance change being derived from a displacement of the movable electrode caused by an acceleration applied to the sensor; a detection bias voltage applying means for applying a detection bias voltage between the first fixed electrode and the second fixed electrode; a vibrating means for vibrating the movable electrode in an acceleration detection direction in such a manner that the movable electrode is displaced in a first period in which the vibrating means applies a displacement bias voltage to the movable electrode, the movable electrode is returned in a second period in which no displacement bias voltage is applied to the movable electrode, and the first and the second periods are repeated alternately; a sampling means for sampling the output voltage of the charge voltage conversion circuit to detect the acceleration in such a manner that the sampling means selectively samples the output voltage during the second period in a case where the movable electrode is steadily vibrated; and an acceleration signal generating and outputting means for generating and outputting an acceleration signal on the basis of a sampling result of the output voltage of the charge voltage conversion circuit.