Patent ID: 7205776

Claim:
A capacitance measuring apparatus including a circuit in which a first capacitor formed of known capacitance is serially connected to a second capacitor formed of unknown capacitance and the circuit having one end part grounded, the circuit measuring capacitance of the second capacitor, the apparatus comprising: a third capacitor which has one end part thereof connected to the other end part of the circuit and the other end part thereof grounded, and applies charging voltage thereof to the other end part of the circuit to charge the first capacitor and the second capacitor with electric charge; a first discharging module which partially discharges the electric charge charged in the third capacitor, and discharges the entire electric charge charged in the first capacitor; a second discharging module which discharges the entire electric charge charged in the second capacitor at almost the same timing as the first discharging module; a number counting module which counts numbers of discharges of the first discharging module and the second discharging module; a comparison module which compares charging voltage of the second capacitor with reference voltage; a computing module which computes capacitance of the second capacitor, when discharge of the first discharging module and the second discharging module is repeated, at a time when the charging voltage of the second capacitor is matched with the reference voltage or when the charging voltage of the second capacitor is smaller than the reference voltage from the compared result of the comparison module, based on the number of discharges counted by the number counting module.