Patent ID: 7570789

Claim:
A capacitance detecting circuit that detects the variations of capacitances at intersections of a plurality of column lines and a plurality of row lines opposite to the column lines and that converts the variations of capacitances into electrical signals, comprising: a column line driving means that drives the column lines; a comparator that is connected to the row lines to convert charges stored in capacitors formed at the intersections of the driven column lines and the row lines into a measured voltage, and that compares the measured voltage with a predetermined set value to output charging or discharging signals; a constant current source that performs charging or discharging of charges in response to the charging or discharging signals; and a capacitor that stores charges by means of charging or discharging current, wherein a voltage between both ends of the capacitor is output as the electrical signal, wherein the comparator outputs, as the charging or discharging signal, a charging signal indicating the charging when the measured voltage is larger than the predetermined set value, and outputs a discharging signal indicating the discharging when the measured voltage is smaller than the predetermined set value, wherein the constant current source includes a constant current source for charging and a constant current source for discharging, and wherein the constant current source performs a charging operation on the capacitor when the charging signal is input and performs a discharging operation on the capacitor when the discharging signal is input.