IN-CELL CAPACITIVE TOUCH PANEL

• US 20100079406A1
• Filed: 03/17/2009
• Published: 04/01/2010
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: HannStar Display Corporation
• Original Assignee: HannStar Display Corporation
• Inventors: SHIH, PO-SHENG, CHEN, PO-YANG, YANG, KEI-HSIUNG
• Granted Patent: US 8,441,459 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

An in-cell capacitive touch panel is disclosed. The present invention utilizes a sensing unit that comprises a sensing liquid crystal capacitor and three transistors to detect touch events. A first transistor is connected to a first gate line and the sensing liquid crystal capacitor and controlled by the first gate line to charge the sensing liquid crystal capacitor. A second transistor together with a third transistor functions as a capacitance-current converter. The second transistor generates an output current according to the voltage of a first electrode of the sensing liquid crystal capacitor. A second gate line controls the third transistor to transfer the output current through a readout line to a readout unit that determines the touch positions. Thus, the in-cell capacitive touch panel of the present invention can use a simple-structure readout circuit to achieve superior readout accuracy and is adaptive to various sizes of touch panels.

Claims

1. An in-cell capacitive touch panel comprising

a first gate line and a second gate line;

and

a sensing unit further comprising;

at least one sensing liquid crystal capacitor;

a first transistor connected to said first gate line and said sensing liquid crystal capacitor and controlled by said first gate line to charge said sensing liquid crystal capacitor; and

a second transistor and a third transistor coupled to each other, wherein said second transistor is connected to a first electrode of said sensing liquid crystal capacitor;

said third transistor is connected to said second gate line and a readout line;

said second transistor generates an output current to said third transistor according to voltage of said first electrode of said sensing liquid crystal capacitor;

said second gate line controls said third transistor to transfer said output current to said readout line.

2. The in-cell capacitive touch panel according to claim 1, wherein said first transistor, said second transistor and said third transistor are thin film transistors (TFTs).

3. The in-cell capacitive touch panel according to claim 1 further comprising a readout unit, which is connected to said readout line and receives said output current to detect touch events and find out touch positions.

4. The in-cell capacitive touch panel according to claim 1, wherein a gate and a drain of said first transistor are connected to said first gate line;

a source of said first transistor is connected to said first electrode of said sensing liquid crystal capacitor and a gate of said second transistor.

5. The in-cell capacitive touch panel according to claim 4, wherein a second electrode of said sensing liquid crystal capacitor is connected to a first bias source;

a source of said second transistor is connected to a second bias source.

6. The in-cell capacitive touch panel according to claim 5, wherein said first bias source and said second bias source are connected to a common voltage source.

7. The in-cell capacitive touch panel according to claim 1, wherein a gate of said second transistor is connected to said first electrode of said sensing liquid crystal capacitor and a source of said first transistor;

a drain of said second transistor is connected to a drain of said third transistor.

8. The in-cell capacitive touch panel according to claim 7, wherein a second electrode of said sensing liquid crystal capacitor is connected to a first bias source;

a source of said second transistor is connected to a second bias source.

9. The in-cell capacitive touch panel according to claim 8, wherein said first bias source and said second bias source are connected to a common voltage source.

10. The in-cell capacitive touch panel according to claim 1, wherein a gate of said third transistor is connected to said second gate line;

a drain of said third transistor is connected to a drain of said second transistor;

a source of said third transistor is connected to said readout line.

11. The in-cell capacitive touch panel according to claim 1, wherein said sensing unit comprises following stages:

in stage one, letting said first gate line and said second gate line respectively have a high voltage level and a low voltage level to turn on said first transistor and turn off said third transistor;

via said first transistor charging said sensing liquid crystal capacitor;

in stage two, letting voltage of said first gate line rapidly descend from said high voltage level to said low voltage level and maintaining voltage of said second gate line at said low voltage level to generate a voltage variation of said first electrode of said sensing liquid crystal capacitor to switch said second transistor and generate said output current to said third transistor;

in stage three, letting voltage of said second gate line increase to said high voltage level to turn on said third transistor and control said output current to flow to said readout line; and

in stage four, letting voltages of said first gate line and said second gate line both descend to said low voltage level to turn off said first transistor and said third transistor.

12. The in-cell capacitive touch panel according to claim 1, wherein said sensing liquid crystal capacitor further comprises two transparent substrates, two electrode layers respectively arranged on said two transparent substrates, and a liquid crystal layer arranged in between said two electrode layers.

13. The in-cell capacitive touch panel according to claim 12, wherein a protrusion is formed on said transparent substrate corresponding to said sensing liquid crystal capacitor to make a liquid crystal cell within a range of said protrusion has a smaller cell gap than a liquid crystal cell outside said range of said protrusion.

14. The in-cell capacitive touch panel according to claim 1, wherein a protrusion is formed on a color filter corresponding to said sensing liquid crystal capacitor to make a liquid crystal cell within a range of said protrusion has a smaller cell gap than a liquid crystal cell outside said range of said protrusion.

15. The in-cell capacitive touch panel according to claim 14, wherein said protrusion is formed via stacking at least two color resists.

16. The in-cell capacitive touch panel according to claim 1, wherein a gate-source capacitance of said first transistor is slightly greater than or equal to a capacitance of said sensing liquid crystal capacitor.

17. An in-cell capacitive touch panel comprising:

a first gate line and a second gate line; and

a sensing unit further comprising;

a sensing liquid crystal capacitor;

a first transistor, wherein a gate and a drain of said first transistor are connected to said first gate line, and a source of said first transistor is connected to a first electrode of said sensing liquid crystal capacitor;

a second transistor, wherein a gate of said second transistor is connected to said source of said first transistor and said first electrode of said sensing liquid crystal capacitor; and

a third transistor, wherein a gate, a drain and a source of said third transistor are respectively connected to said second gate line, a drain of said second transistor and a readout line.

18. The in-cell capacitive touch panel according to claim 17, wherein a second electrode of said sensing liquid crystal capacitor is connected a first bias source, and a source of said second transistor is connected to a second bias source.

19. The in-cell capacitive touch panel according to claim 18, wherein said first bias source is connected to a common voltage source.

20. The in-cell capacitive touch panel according to claim 18, wherein said first bias source and said second bias source are connected to a common voltage source.