Capacitive physical quantity detection device

Abstract

A capacitive semiconductor acceleration sensor capable of efficiently performing a self-diagnostic procedure without having to provide any separate electrodes for self-diagnosis purposes. The acceleration sensor includes a beam portion that is deformable upon application of acceleration thereto in a direction at right angles to the elongate direction thereof to thereby exhibit a spring function. The sensor also includes a movable electrode and fixed electrodes which are integrally formed with the beam portion. The sensor is operable to detect the acceleration while applying between the movable electrode and fixed electrodes a periodically changeable signal to derive an output voltage variable in potential with a differential capacitance change of capacitors between the both electrodes. Here, a detection signal for detection of such acceleration and a self-diagnosis signal are selectively applied while permitting creation of quasi-acceleration at the movable electrode due to application of the self-diagnosis signal, wherein a ratio of a frequency of the self-diagnosis signal to a resonance frequency of the beam portion in its deformation direction is set so that the resultant resonance magnification of such beam portion is more than or equal to one time upon application of the self-diagnosis signal.