Coordinate input device and display device with the same

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.

2. A capacitance detection device according to claim 1 , wherein at least one of the first switch and the second switch sets the reference potential of the electric charge storage capacitor as a potential of a portion which causes noise to be generated in a charging potential at which the charges are charged in the electric charge storage capacitor.

3. A capacitance detection device according to claim 2 , wherein a period in which the at least one of the first switch and the second switch sets the reference potential of the electric charge storage capacitor as the potential of the portion which causes the noise to be generated in the charging potential at which the charges are charged in the electric charge storage capacitor overlaps with at least one of a period in which the electric charges charged in the coordinate electrode of a measuring target are moved to the electric charge storage capacitor and a period in which the charges are charged in the coordinate electrode of the measuring target.

4. A capacitance detection device according to claim 1 , further comprising a filter in a portion for connecting a terminal to which the reference potential of the electric charge storage capacitor is input with a portion which causes noise to be generated in a charging potential at which the charges are charged in the electric charge storage capacitor.

5. An input coordinate detecting 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 including a first electrode which connects with the coordinate electrode and a second electrode which is opposed to the first electrode; and

a first and second switch for changing a reference potential of the second electrode of the electric charge storage capacitor,

wherein the first switch electrically connects between the second electrode and a first reference voltage,

wherein the second switch electrically connects between the second electrode 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 coordinate detecting 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.

6. An input coordinate detection device according to claim 5 , wherein at least one of the first switch and the second switch sets the reference potential of the electric charge storage capacitor as a potential which causes noise to be generated in a charging potential at which the charges are charged in the first capacitor.

7. A capacitance detection device according to claim 5 , wherein a period in which the at least one of the first switch and the second switch sets the reference potential of the electric charge storage capacitor as the potential of the portion which causes the noise to be generated in the charging potential at which the charges are charged in the electric charge storage capacitor overlaps with at least one of a period in which the electric charges charged in the coordinate electrode of a measuring target are moved to the electric charge storage capacitor and a period in which the charges are charged in the coordinate electrode of the measuring target.

8. A capacitance detection device according to claim 5 , further comprising a filter in a portion for connecting a terminal to which the reference potential of the electric charge storage capacitor is input with a portion which causes noise to be generated in a charging potential at which the charges are charged in the electric charge storage capacitor.

9. A display device comprising:

an LCD panel and a touch sensor panel, wherein the touch sensor panel includes a first transparent electrode facing the LCD panel, wherein the LCD panel includes a second transparent electrode facing the touch sensor panel, and wherein a capacitance is formed between the first and second transparent electrodes, wherein the touch panel sensor includes a capacitance detection device for detecting an input coordinate 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 including a first electrode which connects with the coordinate electrode and a second electrode which is opposed to the first electrode; and

a first and second switch for changing a reference potential of the second electrode of the electric charge storage capacitor,

wherein the first switch electrically connects between the second electrode and a first reference voltage,

wherein the second switch electrically connects between the second electrode 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 display 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 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.

10. A display device according to claim 9 , wherein the capacitance detection device further includes a second capacitor including the coordinate electrode and a conductor which touches the capacitance detection device.

11. A display device according to claim 10 , wherein a period in which the at least one of the first switch and the second switch sets the reference potential of the electric charge storage capacitor as a potential of a portion which causes the noise to be generated in the charging potential at which the charges are charged in the electric charge storage capacitor overlaps with at least one of a period in which the electric charges charged in the coordinate electrode of a measuring target are moved to the electric charge storage capacitor and a period in which the charges are charged in the coordinate electrode of the measuring target.

12. A display device according to claim 10 , further comprising a filter in a portion for connecting a terminal to which the reference potential of the electric charge storage capacitor is input with a portion which causes noise to be generated in a charging potential at which the charges are charged in the electric charge storage capacitor.