Touch sensitive active matrix display and method for touch sensing

• US 20060012575A1
• Filed: 11/27/2003
• Published: 01/19/2006
• Est. Priority Date: 12/12/2002
• Status: Abandoned Application

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Knapp, Alan G., Johnson, Mark T.
• Application Number:
  US10/538,278
• Publication Number:
  US 20060012575A1
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G02F 1/13338 Input devices, e.g. touch panels
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: G06F 3/0447 Position sensing using the local deformation of sensor cells

Abstract

A touch sensitive active martix display device has an array of capacitive display element pixels (16), each associated with a pixel storage capacitor (20) and a pixel transistor. One or more common electrode contacts (18a) are provided and connected to a terminal of a plurality of the display elements (16). Each common electrode contact is individually connectable to a charge measurement device (50) for measuring a flow of charge to the common electrode contact. The charge flowing through the capacitive display element can thus be measured while the pixel transistor is switched off. This flow of charge represents the transfer of charge between the pixel storage capacitor (20) and the display element (16) and results from a change in capacitance, and is therefore indicative of a touch input.

Claims

1. A touch sensitive display device comprising an array of capacitive display element pixels, each display element being associated with a pixel circuit including a pixel storage capacitor, each display element being connected at a first terminal to the storage capacitor,

wherein the device further comprises one or more common electrode contacts, the or each common electrode contact being connected to a second terminal of a plurality of the display elements, and wherein each common electrode contact is individually connectable to a charge measurement means for measuring a flow of charge to the common electrode contact.

2. A device as claimed in claim 1, wherein a plurality of common electrode contacts are provided.

3. A device as claimed in claim 2, wherein each common electrode contact is connected to a respective charge measurement means.

4. A device as claimed in claim 1, wherein the or each charge measurement means comprises a charge sensitive amplifier.

5. A device as claimed in claim 4, wherein each charge sensitive amplifier connects the common electrode contact to a virtual earth potential.

6. A device as claimed in claim 1, wherein the array of display element pixels is arranged in rows and columns, and wherein each common electrode contact is connected to the second terminals of the display elements of a plurality of adjacent columns of display element pixels.

7. A device as claimed in claim 6, wherein each row of display element pixels shares a common row conductor for providing a pixel address signal, and wherein the storage capacitor of each pixel is connected between the display element and the row conductor of an adjacent row of display element pixels.

8. A device as claimed in claim 6, wherein each row of display element pixels shares a common capacitor row conductor, and the storage capacitor of each pixel is connected between the display element and the capacitor row conductor.

9. A device as claimed in claim 7, wherein a plurality of groups of adjacent rows are defined with each group individually connectable to a charge measurement means for measuring a flow of charge to the group of row conductors.

10. A device as claimed in claim 1, wherein each pixel circuit comprises a transistor which is addressed by a signal on a row conductor associated with a row of display element pixels, and which provides a signal from a column conductor associated with a column of display element pixels to the display element.

11. A device as claimed in claim 1, wherein the capacitive display elements comprise liquid crystal display elements.

12. A method of detecting a touch input in a touch sensitive display device, the device comprising an array of capacitive display element pixels each comprising a capacitive display element and a pixel storage capacitor, the method comprising:

applying display signals to the pixels of the array, by charging the display element of each pixel to a desired voltage through a pixel transistor;

isolating each pixel by switching off the pixel transistor, and storing the voltage on the display element using the pixel storage capacitor; and

whilst the pixel is isolated, sensing the charge flowing between the storage capacitor and the capacitive display element.

13. A method as claimed in claim 12, wherein the sensing is carried out by monitoring the charge flowing to a terminal of the capacitive display element.

14. A method as claimed in claim 13, wherein the charge flowing to a terminal of a plurality of display elements is monitored, the plurality of display elements sharing a common contact and comprising a column or columns of display elements.

15. A method as claimed in claim 14, wherein the sensing is carried out by also monitoring the charge flowing to a terminal of the pixel storage capacitor.

16. A method as claimed in claim 15, wherein the charge flowing to a terminal of a plurality of pixel storage capacitors is monitored, the plurality of pixel storage capacitors sharing a common contact and comprising the pixel storage capacitors of a row or rows of pixels.

17. A method as claimed in claim 12, wherein a subset of the pixels of the array are used for touch sensing and display, the remaining pixels being used only for display.

18. A method as claimed in claim 17, wherein substantially static images are provided to the subset of pixels.

19. A method as claimed inclaim 17, wherein the subset comprises a plurality of rows of pixels.

20. A method as claimed in claim 17, wherein the display data for the subset is repeated, and touch sensing is performed in the first or in a subsequent repetition.

21. A method as claimed in claim 20, wherein the subset is different for different frames.