Coordinate input device and display device with the same

摘要

A capacitance detection device of a capacitance system includes: a capacitance sensor electrode for detecting a capacitance; a power source for supplying charges to be charged in the capacitance sensor electrode; an electric charge storage capacitor in which an amount of charges to be charged therein changes according to the electric charges charged in the capacitance sensor electrode; and a switch for changing a reference potential of the electric charge storage capacitor. The reference potential of the electric charge storage capacitor is changed in a period of measuring the capacitance.

主权项

1. A capacitance detection device of a capacitance system, comprising:
a first capacitor including a coordinate electrode for detecting a capacitance; a power source for supplying electric charges to be charged in the first capacitor; an electric charge storage capacitor in which charges to be charged therein changes according to the electric charges charged in the first capacitor; the electric charge storage capacitor includes a first electrode which connects with the coordinate electrode and a second electrode which is opposed to the first electrode; a first switch and a second switch for changing a reference potential of the second electrode of the electric charge storage capacitor; and a second capacitor including the coordinate electrode and a conductor which touches the capacitance detection device; wherein the first switch electrically connects between the second electrode of the electric charge storage capacitor and a first reference voltage; wherein the second switch electrically connects between the second electrode of the electric charge storage capacitor and a second reference voltage; further comprising an amplifier for detecting electric charges which are transferred from the coordinate electrode via a third switch, wherein the third switch directly connects between the coordinate electrode and the amplifier in order to transfer the electric charges, wherein the capacitance detection device is configured so that when the second reference voltage is applied to the second electrode of the electric charge storage capacitor a noise voltage of the coordinate electrode is reduced, wherein the reference potential of the electric charge storage capacitor is changed in a period of measuring the capacitance due to turning on of the first and second switch alternately, wherein the second switch is turned ON corresponding to a term comprising a start time and an end time in which the electric charges are transferred via the third switch, and wherein the third switch is configured to be turned ON at the same start time as the second switch during the term.