Patent ID: 7102364

Claim:
A capacitance detecting circuit for detecting, in terms of voltage, change in capacitance at intersections of a plurality of column lines and a plurality of row lines crossing each other, the capacitance detecting circuit comprising: column-line driving means for driving a column line; row-line selecting means for selecting a specific row line from the plurality of row lines; and a capacitance calculator for calculating a capacitance at an intersection of the specific rowline and the driven column line based on a reference current that flows in relation to a reference capacitance and a current that flaws in relation to the capacitance at the intersection, wherein the row-line selecting means selects a first row line and a second row line adjacent to each other, wherein the capacitance calculator includes differential-voltage outputting means for amplifying a difference between values of currents corresponding to capacitances at respective intersections associated with the first and second row lines, and outputting the amplified difference as a differential voltage signal; and calculating means for calculating values of voltages corresponding to capacitances at intersections based on differential voltage signals sequentially input to the calculating means, wherein the row-line selecting means, in a first detecting period, selects a line connected to the reference capacitance as a first row line, and a row line adjacent to the first row line as a second row line, wherein the row-line selecting means, in and after a second detecting period, selects row lines adjacent to each other from the plurality of row lines as first and second row lines, and wherein the calculating means cumulatively adds differential voltage signals sequentially input thereto, thereby obtaining voltage values corresponding to capacitances at intersections.