Sensor capacity sensing apparatus and sensor capacity sensing method

1 1 3 3 A capacitor C and an impedance converter Hiz are included in a feedback circuit of the first operational amplifier OPin series; an electrode Pof a capacitive sensor is connected to a connection point of the said capacitor and the converter via a signal line L. The signal line L is connected to a predetermined standard electric potential through resistance Rwhose resistance value is high. When the capacitor is included in the feedback circuit, the signal line becomes in a state of floating and a circuit operation becomes unstable, however, the signal line L is fixed at predetermined electric potential, and therefore, the operation becomes stable. It is acceptable to configure the impedance converter with a voltage follower and connect the resistance Rto the output.