Common mode noise reduction in capacitive touch sensing

• US 10,120,509 B2
• Filed: 12/29/2015
• Issued: 11/06/2018
• Est. Priority Date: 12/29/2015
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Inventors: Chandran, Praveesh, Korapati, Lokesh Kumar, Nagarajan, Mythreyi
• Primary Examiner(s): Lu, William
• Application Number:
  US14/982,349
• Publication Number:
  US 20170185182A1
• Time in Patent Office: 1,043 Days
• CPC Class Codes: G06F 2203/04102 Flexible digitiser, i.e. constructional details for allowing the whole digitising part of a device to be flexed or rolled like a sheet of paper
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/04184 Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes

Abstract

The present disclosure is directed to a system and method to remove common mode noise projected onto a touch sensor array from a display. The system is configured to activate two rows of electrodes at the same time, while coupling remaining rows of electrodes to ground. A first one of the two activated rows is used for detection of a touch and a second one of the two activated rows is used to detect common mode noise from the display. The common mode noise detected by the second row is removed from signals received from a plurality of columns of the touch sensor array.

Claims

1. A device, comprising:

a touch sensor array that includes;

a current source;

a plurality of rows, each row having a plurality of electrodes electrically coupled to each other, each of the plurality of rows being electrically isolated from remaining rows of the plurality of rows, the touch sensor, in operation, cycles through and activates one of the plurality of rows at a time, and electrically couples an activated row to the current source;

a plurality of columns, each column having a plurality of electrodes electrically coupled to each other, each of the plurality of columns being electrically isolated from remaining columns of the plurality of columns;

a plurality of first current to voltage amplifiers, each one of the plurality of first current to voltage amplifiers electrically coupled to one the plurality of columns;

a plurality of differential amplifiers, each one of the plurality of differential amplifiers electrically coupled to one of the plurality of first current to voltage amplifiers; and

a second current to voltage amplifier, an output of the second current to voltage amplifier being electrically coupled to each one of the plurality of differential amplifiers, the touch sensor, in operation, electrically couples an inactivated row of the plurality of rows to an input of the second current to voltage amplifier while the activated row is electrically coupled to the current source, the touch sensor, in operation, grounds remaining rows of the plurality of rows while the activated row is electrically coupled to the current source and the inactivated row is electrically coupled to the input of the second current to voltage amplifier, the inactivated row being separated from the activated row by at least one of the remaining rows.

2. The device of claim 1, further comprising a transparent layer on the touch sensor array.

3. The device of claim 2, further comprising a display, the touch sensor array being positioned between the transparent layer and the display.

4. The device of claim 3 wherein the display includes a polarizing layer and a thin film transistor layer.

5. The device of claim 3 wherein the display is flexible.

6. The device of claim 3 wherein a distance between the display and the touch sensor array is less than 10 microns.

7. A method, comprising:

reducing parasitic capacitance in a touch sensor from a display, the reducing including;

electrically coupling a first row of electrodes of a plurality of rows of electrodes to a current source;

electrically coupling, while the first row of electrodes are electrically coupled to the current source, a plurality of columns of electrodes to a plurality of first amplifiers of a noise-reducing circuit;

electrically coupling, while the first row of electrodes is electrically coupled to the current source and the plurality of columns of electrodes are electrically coupled to the plurality of first amplifiers, a second row of electrodes of the plurality of rows of electrodes to a second amplifier of the noise-reducing circuit; and

electrically coupling, while the first row of electrodes is electrically coupled to the current source, the plurality of columns of electrodes are electrically coupled to the plurality of first amplifiers, and the second row of electrodes is electrically coupled to the second amplifier, remaining rows of the plurality of rows of electrodes to ground, at least one of the remaining rows of the plurality of rows of electrodes separating the first row of electrodes from the second row of electrodes.

8. The method of claim 7, further comprising detecting a touch by a user with the plurality of column electrodes.

9. The method of claim 8, further comprising determining a third row of electrodes to activate based on a location of the touch.

10. The method of claim 7, further comprising:

electrically coupling the second row of electrodes to the current source;

electrically coupling, while the second row of electrodes is electrically coupled to the current source and the plurality of columns of electrodes are electrically coupled to the plurality of first amplifiers, a third row of electrodes to the second amplifier; and

electrically coupling, while the second row of electrodes is electrically coupled to the current source, the plurality of columns of electrodes are electrically coupled to the plurality of first amplifiers, and the third row of electrodes is electrically coupled to the second amplifier, remaining rows of the plurality of rows of electrodes to ground.

11. The method of 7, further comprising:

receiving, by the plurality of first amplifiers, a plurality of output signals from the plurality of columns of electrodes;

receiving, by the second amplifier, an output signal from the second row of electrodes; and

removing, by the noise-reducing circuit, noise from the plurality of output signals from the plurality of columns of electrodes using the output signal from the second row of electrodes.

12. A system, comprising:

a display;

a touch sensor array coupled to the display, the touch sensor array including;

a current source;

a plurality of rows of electrodes, each of the plurality of rows of electrodes including a plurality of electrodes electrically coupled to each other, the plurality of rows of electrodes being electrically isolated from each other, a first row of electrodes of the plurality of electrodes being electrically coupled to the current source;

a plurality of columns of electrodes, each of the plurality of columns of electrodes including a plurality of electrodes electrically coupled to each other, the plurality of columns of electrodes being electrically isolated from each other; and

a plurality of amplifiers, a first one of the plurality of amplifiers being electrically coupled to a second row of the plurality of rows of electrodes and each remaining amplifier being electrically coupled to one of the plurality of columns of electrodes, remaining rows of electrodes of the plurality of electrodes being grounded, the first row of electrodes and the second row of electrodes being spaced from each other by at least one of the remaining rows of electrodes.

13. The system of claim 12, wherein the touch sensor array includes a plurality of differential amplifiers, each differential amplifier electrically coupled to the first one of the plurality of amplifiers.

14. The system of claim 13 wherein each differential amplifier is electrically coupled to one of the remaining amplifiers that are electrically coupled to the ones of the plurality of columns of electrodes.

15. The system of claim 12, further comprising a touch sensor controller configured to activate and deactivate the plurality of rows and columns of electrodes of the touch sensor array.

16. The system of claim 12, further comprising an application specific integrated circuit coupled to the remaining amplifiers that are coupled to one of the plurality of columns of electrodes.

17. The system of claim 12 wherein the display is a liquid crystal display.

18. The system of claim 12 wherein the plurality of columns of electrodes includes a first number of columns, and the plurality of amplifiers includes a second number of amplifiers that is greater than the first number.