SENSOR CAPACITY SENSING APPARATUS AND SENSOR CAPACITY SENSING METHOD

摘要

A capacitor C and an impedance converter Hiz are inserted in series in a feedback circuit of a first calculation amplifier OP1. An electrode P1 of a capacitor sensor is connected via a signal line L to a connection point between the capacitor and the converter. The signal line L is connected to a predetermined reference potential via a resistor R3 having a high resistance. When the capacitor is inserted into the feedback circuit, the signal line is in a floating state and the circuit operation becomes unstable. However, the signal line L is fixed to a predetermined potential via the high resistor R3 and accordingly, the operation is stabilized. It is also possible to constitute the impedance converter by a voltage follower whose output is connected to the resistor R3.