CIRCUIT DEVICE FOR ELECTROSTATIC-CAPACITY TYPE ACCELERATION SENSOR

PROBLEM TO BE SOLVED: To precisely estimate the difference of capacitance between two capacitors, by a method wherein an AC voltage is applied to a center electrode, and AC currents generated in the capacitors are estimated for position control. SOLUTION: The amplification actions of operational amplifiers 20 and 26 increase or decrease, in accordance with the reactances of capacitors C1 and C2 to AC currents which are changed by the action of acceleration. The amplification factors change as the ratio of negative feedback resistance R1 and R2 to the reactances of the capacitors C1 and C2 change. As a result, the currents flowing through the capacitors C1 and C2 are estimated by the operational amplifiers 20 and 26, and proper amplified signals are generated and applied to terminals 22 and 28. At this time, the potentials of terminals U1 and U2 are constant on the basis of control characteristics of the operational amplifiers. Thereby a signal proportional to acceleration detected by an acceleration sensor can be obtained through the estimation of the amplified signals of the operational amplifiers 20 and 26.