Coordinate input device and display device including the same

1. A coordinate input device comprising:

a coordinate input unit having a plurality of first detection electrodes, which are disposed in parallel to each other, and a plurality of second detection electrodes intersecting the first detection electrodes;

an electrode drive circuit configured to apply a drive signal to one or more of the first detection electrodes;

a capacitance detection circuit configured to detect a capacitance of the second detection electrode in synchronization with the drive signal;

wherein the electrode drive circuit is configured to select one or more of the first detection electrodes to which the drive signal is not applied as a reference electrode;

wherein the capacitance detection circuit is configured to detect a capacitance of the selected reference electrode, which capacitance represents noise;

an input coordinate computing circuit configured to correct a capacitance detection result of the capacitance detection circuit on the basis of the detected capacitance representing noise of the reference electrode, and to calculate an input coordinate from the corrected capacitance detection result.

2. The coordinate input device according to claim 1 , wherein the reference electrode comprises one of the first detection electrode which is disposed in parallel to the vicinity of another one of the first detection electrodes to which the drive signal is applied.

3. The coordinate input device according to claim 1 ,

wherein the electrode drive circuit includes a circuit configured to select one or more from among the plurality of first detection electrodes and to apply the drive signal thereto, and

the capacitance detection circuit includes a circuit configured to measure currents or voltages of the plurality of second detection electrodes in synchronization with the drive signal and to detect capacitances from the measured values.

4. The coordinate input device according to claim 3 ,

wherein the circuit for correcting a capacitance detection result includes a circuit configured to calculate a correction value within a predetermined range by adding or subtracting a predetermined value to or from the capacitance detection result from the reference electrode, and

the input coordinate computing circuit is configured to correct the capacitance detection result of the second detection electrode by subtracting or adding the correction value from or to the capacitance detection result of the second detection electrode.

5. The coordinate input device according to claim 1 , wherein the capacitance detection circuit includes:

a first capacitance detection circuit configured to select one or more of the plurality of first detection electrodes and to detect capacitances of the selected first detection electrodes; and

a second capacitance detection circuit configured to select one or more of the plurality of second detection electrodes and to detect capacitances of the selected second detection electrodes.

6. The coordinate input device according to claim 5 ,

wherein the circuit is configured to correct a capacitance detection result includes:

a circuit to calculate a first correction value within a predetermined range by adding or subtracting a first predetermined value to or from the capacitance detection result of the first reference electrode; and

a circuit to calculate a second correction value within a predetermined range by adding or subtracting a second predetermined value to or from the capacitance detection result of the second reference electrode,

wherein the input coordinate computing circuit is configured to correct the capacitance detection result of the first detection electrode by subtracting or adding the first correction value from or to the capacitance detection result of the first detection electrode, and to correct the capacitance detection result of the second detection electrode by subtracting or adding the second correction value from or to the capacitance detection result of the second detection electrode.

7. A display apparatus comprising:

a display panel configured to display an image based on an image signal from an external system; and

a coordinate input device disposed on a display surface side of the display panel,

wherein the coordinate input device includes

a coordinate input unit in which a plurality of first detection electrodes, which are disposed in parallel to each other, and a plurality of second detection electrodes intersecting the first detection electrodes are formed, and which is disposed on the display surface side of the display panel,

an electrode drive circuit configured to apply a drive signal to one or more of the first detection electrodes,

a capacitance detection circuit configured to detect a capacitance of the second detection electrode in synchronization with the drive signal,

the electrode drive circuit configured to select one or more of the first detection electrodes to which the drive signal is not applied as a reference electrode,

a circuit configured to detect a capacitance of the selected reference electrode, which capacitance represents noise,

an input coordinate computing circuit configured to correct a capacitance detection result of the capacitance detection circuit on the basis of the detected capacitance representing noise of the reference electrode, and to calculate an input coordinate from the corrected capacitance detection result.

8. The display apparatus according to claim 7 , wherein the reference electrode comprises one of the first detection electrodes which is disposed parallel to the vicinity of another one of the first detection electrodes to which the drive signal is applied.

9. The display apparatus according to claim 7 ,

wherein the electrode drive circuit includes a circuit configured to select one or more from among the plurality of first detection electrodes and applying the drive signal thereto, and

the capacitance detection circuit includes a circuit configured to measure currents or voltages of the plurality of second detection electrodes in synchronization with the drive signal and to detect capacitances from the measured values.

10. The display apparatus according to claim 9 ,

wherein the circuit for correcting a capacitance detection result includes a circuit to calculate a correction value within a predetermined range by adding or subtracting a predetermined value to or from the capacitance detection result from the reference electrode, and

the input coordinate computing circuit is configured to correct the capacitance detection result of the second detection electrode by subtracting or adding the correction value from or to the capacitance detection result of the second detection electrode.

11. The display apparatus according to claim 7 , wherein the capacitance detection circuit includes:

a first capacitance detection circuit configured to select one or more of the plurality of first detection electrodes and to detect capacitances of the selected first detection electrodes; and

a second capacitance detection circuit configured to select one or more of the plurality of second detection electrodes and to detect capacitances of the selected second detection electrodes.

12. The display apparatus according to claim 11 , wherein the circuit for correcting a capacitance detection result includes:

a circuit configured to calculate a first correction value within a predetermined range by adding or subtracting a first predetermined value to or from the capacitance detection result of the first reference electrode; and

a circuit configured to calculate a second correction value within a predetermined range by adding or subtracting a second predetermined value to or from the second reference electrode,

wherein the input coordinate computing circuit is configured to correct the capacitance detection result of the first detection electrode by subtracting or adding the first correction value from or to the capacitance detection result of the first detection electrode, and to correct the capacitance detection result of the second detection electrode by subtracting or adding the second correction value from or to the capacitance detection result of the second detection electrode.