Touch sensor using capacitance detection and liquid crystal display having the same

1. A touch sensor configured to be disposed within a liquid crystal display panel, the touch sensor comprising:

a plurality of x-axis read-out lines;

a plurality of y-axis read-out lines crossing the x-axis read-out lines, wherein the x-axis read-out lines are insulated from the y-axis read-out lines;

a plurality of sensor units provided in a plurality of regions defined by the x-axis read-out lines and the y-axis read-out lines,

wherein each sensor unit comprises:

a reset unit having a first transistor, wherein the first transistor comprising a control terminal receiving a first control signal, an input terminal receiving a first reset signal and an output terminal outputting the first reset signal based on the first control signal;

a capacitance detector having a liquid crystal capacitor that changes the first reset signal based on a variation of a cell gap of the liquid crystal display panel caused by a touch event, wherein the output terminal of the first transistor is directly connected to a first electrode of the liquid crystal capacitor;

a first output unit having a second transistor that changes an electric potential of a corresponding x-axis read-out line in response to the first reset signal changed in the liquid crystal capacitor; and

a second output unit having a third transistor that changes an electric potential of a corresponding y-axis read-out line in response to the first reset signal changed in the liquid crystal capacitor; and a line reset unit comprising:

a fourth transistor comprising a control terminal receiving the first control signal, an input terminal directly receiving a second reset signal, and an output terminal directly connected to one of the x-axis and y-axis read-out lines; and

a first capacitor connected in parallel with the fourth transistor between the input and output terminals.

2. The touch sensor of claim 1 , wherein the first electrode of the liquid crystal capacitor is connected to a node connecting a control terminal of the first and second output units to an output terminal of the reset unit, and a second electrode receiving a common voltage.

3. The touch sensor of claim 2 , wherein the first control signal has a high duration repeatedly occurring at a predetermined period, and the reset unit is turned on for the high duration to initialize the node with the first reset signal.

4. The touch sensor of claim 2 , wherein the output terminal of the reset unit is connected to the node.

5. The touch sensor of claim 4 , wherein the second transistor comprising a control terminal connected to the node, an input terminal receiving a source supply voltage, and an output terminal connected to the corresponding x-axis read-out line, and the third transistor comprising a control terminal connected to the node, an input terminal receiving the source supply voltage, and an output terminal connected to the corresponding y-axis read-out line.

6. The touch sensor of claim 2 , wherein the capacitance detector further comprises a coupling capacitor comprising a first electrode connected to the node and a second electrode connected to a terminal receiving a second control signal.

7. The touch sensor of claim 6 , wherein the second control signal has a high duration repeatedly occurring at a predetermined period, and has a voltage level identical to a voltage level of the common voltage for the high duration.

8. The touch sensor of claim 7 , wherein the first control signal has a period identical to a period of the second control signal.

9. The touch sensor of claim 1 , further comprising:

a plurality of the line reset units configured to output the second reset signal to the x-axis read-out lines based on the first control signal; and

a plurality of the line reset units configured to output the second reset signal to the y-axis read-out lines based on the first control signal.

10. The touch sensor of claim 1 , wherein the capacitance of the first capacitor is greater than that of the liquid crystal capacitor.

11. A liquid crystal display comprising:

a liquid crystal display panel that comprises a plurality of pixels to display an image;

a touch sensor disposed within the liquid crystal display panel to detect a touch event;

a coordinate detection circuit connected to the touch sensor to detect coordinates of a point at which a touch event occurs; and

a driver that drives the liquid crystal display panel based on the coordinates,

wherein the touch sensor comprises:

a plurality of x-axis read-out lines;

a plurality of y-axis read-out lines crossing the x-axis read-out lines, wherein the x-axis read-out lines are insulated from the y-axis read-out lines; and

a plurality of sensor units provided in a plurality of regions defined by the x-axis read-out lines and the y-axis read-out lines,

wherein each sensor unit comprises:

a reset unit having a first transistor, wherein the first transistor comprising a control terminal receiving a first control signal, an input terminal receiving a first reset signal and an output terminal outputting the first reset signal based on the first control signal;

a capacitance detector having a liquid crystal capacitor that changes the first reset signal based on a variation of a cell gap of the liquid crystal display panel caused by a touch event, wherein the output terminal of the first transistor is directly connected to a first electrode of the liquid crystal capacitor;

a first output unit having a second transistor that changes an electric potential of a corresponding x-axis read-out line in response to the first reset signal changed in the liquid crystal capacitor;

a second output unit having a third transistor that changes an electric potential of a corresponding y-axis read-out line in response to the first reset signal changed in the liquid crystal capacitor; and

a line reset unit comprising:

a fourth transistor comprising a control terminal receiving the first control signal, an input terminal directly receiving a second reset signal, and an output terminal directly connected to one of the x-axis and y-axis read out lines; and

a first capacitor connected in parallel with the fourth transistor between the input and output terminals,

wherein the first capacitor having a capacitance greater than that of the liquid crystal capacitor.

12. The liquid crystal display of claim 11 , wherein the liquid crystal capacitor is disposed in the liquid crystal display panel, and the first electrode of the liquid crystal capacitor is connected to a node connecting a control terminal of the first and second output units to the output terminal of the reset unit, and a second electrode receiving a common voltage.

13. The liquid crystal display of claim 12 , wherein the output terminal of the first transistor is connected to the node.

14. The liquid crystal display of claim 13 , wherein the second transistor comprising a control terminal connected to the node, an input terminal receiving a first voltage, and an output terminal connected to the corresponding x-axis read-out line, and the third transistor comprising a control terminal connected to the node, an input terminal receiving the first voltage, and an output terminal connected to the corresponding y-axis read-out line.

15. The liquid crystal display of claim 12 , wherein the capacitance detector further comprises a coupling capacitor comprising a first electrode connected to the node and a second electrode connected to a terminal receiving a second control signal.

16. The liquid crystal display of claim 11 , wherein the touch sensor comprises:

a first plurality of the line reset units configured to output the second reset signal to the x-axis read-out lines based on the first control signal; and

a second plurality of the line reset units configured to output the second reset signal to the y-axis read-out lines based on the first control signal.

17. The liquid crystal display of claim 16 , wherein each of the first plurality of the line reset units comprises a fifth transistor comprising a control terminal receiving the first control signal, an input terminal receiving the second reset signal, and an output terminal connected to a corresponding x-axis read-out line of the x-axis read-out lines, and each of the second plurality of the line reset units comprises a sixth transistor comprising a control terminal receiving the first control signal, an input terminal receiving the second reset signal, and an output terminal connected to a corresponding y-axis read-out line of the y-axis read-out lines.

18. The liquid crystal display of claim 11 , wherein the coordinate detection circuit comprises:

an x-axis comparator that is connected to the x-axis read-out lines, and compares signals output from the x-axis read-out lines with a preset reference signal to output a first comparative signal; a

y-axis comparator that is connected to the y-axis read-out lines, and compares signals output from the y-axis read-out lines with the preset reference signal to output a second comparative signal; and

a coordinate generator that generates coordinates of a point, at which the touch event occurs, based on the first and second comparative signals.

19. A liquid crystal display comprising:

a liquid crystal display panel that comprises a plurality of pixels to display an image;

a touch sensor disposed within the liquid crystal display panel to detect a touch event;

a coordinate detection circuit connected to the touch sensor to detect coordinates of a point at which a touch event occurs; and

a driver that drives the liquid crystal display panel based on the coordinates,

wherein the touch sensor comprises:

a plurality of x-axis read-out lines;

a plurality of y-axis read-out lines crossing the x-axis read-out lines,

wherein the x- axis read-out lines are insulated from the y-axis read-out lines; and

a plurality of sensor units provided in a plurality of regions defined by the x-axis read-out lines and the y-axis read-out lines,

wherein each sensor unit comprises:

a reset unit having a first transistor, wherein the first transistor comprising a control terminal receiving a first control signal, an input terminal receiving a first reset signal and an output terminal outputting the first reset signal based on the first control signal;

a capacitance detector having a liquid crystal capacitor that changes the first reset signal based on a variation of a cell gap of the liquid crystal display panel caused by a touch event, wherein the output terminal of the first transistor is directly connected to a first electrode of the liquid crystal capacitor;

a first output unit having a second transistor that changes an electric potential of a corresponding x-axis read-out line in response to the first reset signal changed in the liquid crystal capacitor;

a second output unit having a third transistor that changes an electric potential of a corresponding y-axis read-out line in response to the first reset signal changed in the liquid crystal capacitor; and

a line reset unit comprising:

a fourth transistor comprising a control terminal receiving the first control signal, an input terminal directly receiving a second reset signal, and an output terminal directly connected to one of the x-axis and y-axis read out lines; and

a first capacitor connected in parallel with the fourth transistor between the input and output terminals,

wherein the coordinate detection circuit comprises:

an x-axis comparator that is connected to the x-axis read-out lines, and compares signals output from the x-axis read-out lines with a preset reference signal to output a first comparative signal;

a y-axis comparator that is connected to the y-axis read-out lines, and compares signals output from the y-axis read-out lines with the preset reference signal to output a second comparative signal; and

a coordinate generator that generates coordinates of a point, at which the touch event occurs, based on the first and second comparative signals.