Patent ID: 7795881

Claim:
A capacitive physical quantity detection device for detecting a physical quantity, comprising: a plurality of capacitive physical quantity sensors, wherein each capacitive physical quantity sensor performs a self-diagnosis operation and a normal operation, each capacitive physical quantity sensor including: a detection unit having a movable electrode movable in accordance with the physical quantity and a fixed electrode facing the movable electrode; a C-V conversion circuit having a differential amplifier circuit, wherein a first negative or inverting input terminal of the differential amplifier circuit is coupled with the movable electrode, a second positive or non-inverting input terminal of the differential amplifier circuit inputs a reference voltage therein during a period of the normal operation and inputs a self-diagnosis voltage therein during a period of the self-diagnosis operation, wherein the reference voltage is used for detecting a capacitance change between the movable electrode and the fixed electrode, and the self-diagnosis voltage is used for performing the self-diagnosis operation, and the self-diagnosis voltage is different from the reference voltage, and the C-V conversion circuit outputs an output voltage corresponding to the capacitance change between the movable electrode and the fixed electrode; and a signal processing circuit that performs a signal processing of the output voltage from the C-V conversion circuit so as to produce a signal corresponding to the physical quantity, wherein the reference voltage in each capacitive physical quantity sensor is substantially the same; the plurality of capacitive physical quantity sensors perform the self-diagnosis operation simultaneously, the self-diagnosis voltage in one of the plurality of capacitive physical quantity sensors is a first self-diagnosis voltage, the self-diagnosis voltage in another one of the plurality of capacitive physical quantity sensors is a second self-diagnosis voltage, and, the first self-diagnosis voltage is greater than the reference voltage, and the second self-diagnosis voltage is less than the reference voltage, a signal that is output from the one of the plurality of capacitive physical quantity sensors is a first signal, a signal that is output from the another one of the plurality of capacitive physical quantity sensors is a second signal, and the capacitive physical quantity detection device further comprises a control circuit that is connected with the plurality of capacitive physical quantity sensors and is configured to compare the first signal and the second signal.