Device and method for detecting multiple touch points

• US 8,072,441 B2
• Filed: 05/31/2009
• Issued: 12/06/2011
• Est. Priority Date: 05/20/2009
• Status: Active Grant

• Current Assignee: Vimicro Corporation, Wuxi Vimicro Corporation
• Original Assignee: Vimicro Corporation, Wuxi Vimicro Corporation
• Inventors: Zhang, Chen
• Primary Examiner(s): SHERMAN, STEPHEN G
• Application Number:
  US12/475,591
• Publication Number:
  US 20100295815A1
• Time in Patent Office: 919 Days
• Field of Search: 345173-178, 178 1801- 1809, 178/18.11, 178/20.01
• US Class Current: 345/174
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

Techniques for detecting multiple touch points for touch screens are disclosed. A touch screen includes a first conductive layer and a second conductive layer, each conductive layer having a positive terminal and a negative terminal. Efficient operations of detecting multiple points on the touch screen are described using various voltage/currents differences from the positive and negative terminals of the first and second conductive layers.

Claims

1. A method for detecting a touch screen, the touch screen including a first conductive layer and a second conductive layer, each conductive layer having a positive terminal and a negative terminal, the method comprising:

coupling the positive terminal of the second conductive layer to a positive reference voltage, coupling the negative terminal of the second conductive layer to a negative reference voltage, sampling the positive terminal of the first conductive layer to obtain a series of first voltage samples V1(i), sampling the negative terminal of the first conductive layer to obtain a series of second voltage samples V2(i);

coupling the positive terminal of the first conductive layer to the positive reference voltage, coupling the negative terminal of the first conductive layer to the negative reference voltage, sampling the positive terminal of the second conductive layer to obtain a series of third voltage samples V3(i), sampling the negative terminal of the second conductive layer to obtain a series of fourth voltage samples V4(i), wherein i is a sampling number;

calculating a rotating parameter X(i) according to the first voltage samples V1(i), the second voltage samples V2(i), the third voltage samples V3(i) and the fourth voltage samples V4(i); and

determining a rotating direction of two touch points in the touch screen according to the rotating parameter X(i), wherein

the rotating parameter X(i) is a function of

2. The method according to claim 1, wherein

3. The method according to claim 1, wherein

4. The method according to claim 1, wherein

5. The method according to claim 1, wherein

6. The method according to claim 1, further comprising:

determining a rotating angle of the two touch points by counting how many times of differences V1(i)−

V2(i) between the first voltage samples and the first voltage samples passing though zero.

7. The method according to claim 1, further comprising:

concluding that a motion tendency of the two touch points on the touch screen is a rotation when some differences V1(i)−

V2(i) between the first voltage samples and the first voltage samples are larger than 0 and some differences V1(i)−

V2(i) between the first voltage samples and the first voltage samples are less than 0.

8. The method according to claim 1, further comprising:

determining whether all or most of differences V1(i)−

V2(i) between the first voltage samples and the first voltage samples are larger than a second threshold or less than a third threshold;

determining whether absolute values of the differences V1(i)−

V2(i) tend to increase if yes;

concluding that a motion tendency of the two touch points on the touch screen is rotation when differences V1(i)−

V2(i) between the first voltage samples and the first voltage samples are larger than a third threshold or less than a second threshold.

9. The method according to claim 8, wherein the second threshold is less than or equal to zero, and the third threshold is larger than or equal to zero.

10. The method according to claim 1, further comprising:

counting a number of absolute values of differences V1(i)−

V2(i) between the first voltage samples and the first voltage samples being larger than a first threshold; and

concluding that there are two touch points on the touch screen when the number is larger than a predefined number threshold.

11. A device for detecting touch screen, comprising:

a touch screen having a first conductive layer and a second conductive layer, each of the first and second conductive layers having a positive terminal and a negative terminal;

a selector configured to couple the positive terminal of the second conductive layer to a positive reference voltage, couple the negative terminal of the second conductive layer to a negative reference voltage, couple the positive terminal of the first conductive layer to the positive reference voltage, and couple the negative terminal of the first conductive layer to the negative reference voltage;

an analog-to-digital converter configured to sample the positive terminal of the first conductive layer to obtain a series of first voltage samples V1(i), sample the negative terminal of the first conductive layer to obtain a series of second voltage samples V2(i), sample the positive terminal of the second conductive layer to obtain a series of third voltage samples V3(i), and sample the negative terminal of the second conductive layer to obtain a series of fourth voltage samples V4(i), wherein i is a sampling sequence number;

a micro-processor configured to calculate a rotating parameter X(i) according to the first voltage samples V1(i), the second voltage samples V2(i), the third voltage samples V3(i) and the fourth voltage samples V4(i) and determine a rotating direction of two touch points on the touch screen according to the rotating parameter X(i); and

wherein

the rotating parameter X(i) is a function of and