Capacitive touch panel with balanced parallel driving

• US 9,727,187 B2
• Filed: 04/16/2015
• Issued: 08/08/2017
• Est. Priority Date: 04/16/2015
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Brown, Christopher James, Slamkul, Dauren, Kay, Andrew
• Primary Examiner(s): Eisen, Alexander
• Assistant Examiner(s): Sarma, Abhishek
• Application Number:
  US14/688,666
• Publication Number:
  US 20160306456A1
• Time in Patent Office: 845 Days
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• 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

Abstract

A capacitive touch sensor includes an array of electrode elements, each electrode element including a drive electrode and a sense electrode, the drive electrode and the sense electrode forming at least one mutual coupling capacitor in each electrode element. A controller is operatively coupled to the array of electrode elements, the controller configured to measure the at least one mutual coupling capacitance over at least one measurement period. In addition, excitation signals applied during the at least one measurement period are balanced to reduce the effect of baseline capacitance.

Claims

1. A capacitive touch sensor, comprising:

an array of electrode elements, each electrode element including a drive electrode and a sense electrode, the drive electrode and the sense electrode forming at least one mutual coupling capacitor in each electrode element; and

a controller operatively coupled to the array of electrode elements, the controller configured to provide excitation signals to the array of electrode elements over at least one measurement period, and to measure the at least one mutual coupling capacitance over the at least one measurement period, wherein the excitation signals applied during the at least one measurement period are balanced to reduce the effect of baseline capacitance,

wherein the controller is configured to represent the excitation signals applied to the drive electrodes over one frame as a drive matrix D having dimension N×

T, where N is the number of drive electrodes in the array of electrode elements and T is the number of measurement periods in the one frame, each row of the matrix representing a pattern of excitation signals applied to the drive electrodes during a measurement period, and each column of the matrix representing a pattern of excitation signals applied to one drive electrode over the course of a single frame.

2. The touch sensor according to claim 1, wherein the at least one measurement period comprises a first measurement period and a second measurement period, and the excitation signal applied during the first measurement period is different from the excitation signal applied during the second measurement period.

3. The touch sensor according to claim 2, wherein the number of drive electrodes excited by the excitation signal during the first measurement period is substantially the same as the number of drive electrodes excited during the second measurement period.

4. The touch sensor according to claim 1, wherein the excitation signals comprise at least one of a first voltage signal having a first amplitude and first phase, a second voltage signal having a second amplitude and second phase, or a constant voltage.

5. The touch sensor according to claim 1, where the controller is configured to represent measurements of each sense electrode during the one frame as a sense matrix S having dimension T×

M, where M is the number of sense electrodes.

6. The touch sensor according to claim 5, wherein the controller is configured to determine the capacitances of the mutual coupling capacitors by multiplying the sense matrix S by the inverse of the drive matrix D.

7. The touch sensor according to claim 1, wherein a first excitation signal is represented in the drive matrix D as a 1 and a second excitation signal is represented in the drive matrix D as a −

1, and wherein the drive matrix D is chosen such that the sum of each row of the drive matrix is approximately 0.

8. The touch sensor according to claim 1, wherein the controller is configured to measure the mutual capacitances in the array during a frame period that includes multiple measurement periods.

9. The touch sensor according to claim 1, further comprising:

a drive unit coupled to the array of electrode elements, the drive unit configured to provide a drive excitation signal to the drive electrodes of the array of electrode elements,

wherein the controller is operatively coupled to the drive unit to cause the drive unit to provide the drive excitation signal to the drive electrodes of the electrode array.

10. The touch sensor according to claim 9, wherein the drive unit comprises a plurality of signal generating circuits, each signal generating circuit providing a drive excitation signal to a respective drive electrode of the array of electrode elements.

11. The touch sensor according to claim 1, further comprising a sense unit coupled to the array of electrode elements, the sense unit configured to measure a signal generated on the sense electrodes in response to the drive excitation signal applied to the drive electrodes.

12. The touch sensor according to claim 11, wherein the sense unit comprises a plurality of signal sensing circuits, each signal sensing circuit operative to measure a signal generated on a respective sense electrode of the array of electrode elements in response to the drive excitation signal.

13. The touch sensor according to claim 1, wherein each electrode of the array of electrode elements comprises a sense electrode and a pair of drive electrodes, the pair of drive electrodes arranged such that a first drive electrode of the pair is adjacent to the sense electrode, and a second drive electrode of the pair is separated from the sense electrode by the first drive electrode.

14. The touch sensor according to claim 13, wherein the controller is configured to represent the excitation signals applied to the drive electrodes over one frame as a drive matrix D2 having dimension 2N×

2N, where N is the number of drive electrode pairs in the array of electrode elements, and wherein a first half of the columns of the drive matrix D2 represents signals supplied to each first drive electrode over the course of a frame period and a second half of the columns represents signals supplied to each second drive electrode over the course of the frame period, a first half of the rows of the drive matrix D2 represent a first phase of the frame period and a second half of the rows of the drive matrix D2 represent a second phase of the frame period.

15. The touch sensor according to claim 14, where the controller is configured to represent measurements of each sense electrode during the one frame as a sense matrix S having dimension T×

M, where T is the number of measurement periods in the one frame and M is the number of sense electrodes.

16. The touch sensor according to claim 15, wherein the controller is configured to determine the capacitances of the mutual coupling capacitors by multiplying the sense matrix S by the inverse of the drive matrix D2.

17. The touch sensor according to claim 14, wherein a sum of all elements in a first half of each row of the drive matrix is approximately 0, and a sum of all elements in a second half of each row of the drive matrix is approximately 0.

18. The touch sensor according to claim 14, wherein the drive matrix is constructed such that all drive electrodes are supplied with a first excitation signal or a second excitation signal during any measurement.

19. The touch sensor according to claim 1, wherein each electrode element comprises a sense electrode pair, further comprising a differential sensing device operatively coupled to the sense electrode pairs.