False touch filtering for capacitance sensing systems

• US 8,294,687 B1
• Filed: 03/29/2012
• Issued: 10/23/2012
• Est. Priority Date: 02/23/2012
• Status: Active Grant

• Current Assignee: Parade Technologies, Ltd.
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Ksondzyk, Petro
• Primary Examiner(s): Lao, Lun-Yi
• Assistant Examiner(s): SHAH, PRIYANK J
• Application Number:
  US13/434,642
• Time in Patent Office: 208 Days
• Field of Search: 345156-175, 178/18.01, 178/18.03, 178/18.06, 382312-314
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/04186 Touch location disambiguation
• CPC Class Codes: G06F 3/044 by capacitive means
• 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

Apparatuses and methods of false touch filtering are described. One device includes a controller and a capacitance sensing array including multiple sense elements (e.g., intersections of TX and RX electrodes). The controller includes a capacitance sensing circuit coupled to the capacitance sensing array, and a filter circuit coupled to the output of the capacitance sensing circuit. The controller is configured to receive, from the capacitance sensing circuit, data representing capacitances of the sense elements, process the data to identify activated sense elements, and filter the data to remove false touch events based on a spatial relationship of activated sense elements.

Claims

1. A method, comprising:

receiving, from a sense network comprising a plurality of electrodes, data representing capacitances of a plurality of sense elements, wherein the plurality of sense elements are intersections between the plurality of electrodes;

processing the data to identify activated sense elements from the plurality of sense elements, wherein the processing comprises;

identifying a local maximum from among the activated sense elements; and

identifying a set of sense elements that are adjacent to the local maximum;

filtering the data to remove false touch events based on a spatial relationship of activated sense elements, wherein the filtering comprises comparing a magnitude value of the local maximum against an aggregate value based on at least three of the set of sense elements to distinguish between an actual touch and a false touch.

2. The method of claim 1, wherein the filtering further comprises distinguishing between the actual touch and the false touch based on the capacitances of the set of sense elements.

3. The method of claim 2, wherein the processing the data to identify the activated sense elements further comprises calculating a sum of magnitude values of the activated sense elements, wherein the comparing comprises comparing the sum against a threshold value to distinguish between the actual touch and the false touch.

4. The method of claim 2, wherein the processing the data to identify the activated sense elements further comprises:

calculating a sum of magnitude values of the activated sense elements; and

subtracting the magnitude value of the local maximum from the sum, wherein the comparing comprises comparing the sum against a threshold value to distinguish between the actual touch and the false touch.

5. The method of claim 2, wherein the processing the data to identify the activated sense elements further comprises calculating a sum of magnitude values of the set of sense elements, wherein comparing comprises comparing the sum against a threshold value to distinguish between the actual touch and the false touch.

6. The method of claim 2, wherein the identifying the set of sense elements comprises identifying a three-by-three square of sense elements around the local maximum.

7. The method of claim 2, wherein the identifying the set of sense elements comprises:

determining whether the local maximum is located at a corner of the sense network; and

identifying at least three sense elements that are adjacent to the local maximum for the set when the local maximum is located at the corner of the sense network.

8. The method of claim 2, wherein the identifying the set of sense elements comprises:

determining whether the local maximum is located at a corner of the sense network;

identifying three sense elements that are adjacent to the local maximum for the set when the local maximum is located at the corner of the sense network;

identifying three or more virtual sense elements for the set when the local maximum is located at the corner of the sense network; and

mirroring the magnitude values of the three sense elements for the magnitude values of the three or more virtual sense elements, and wherein the calculating the sum comprises adding the magnitude values of the three sense elements and the magnitude values of the three or more virtual sense elements.

9. The method of claim 2, wherein the identifying the set of sense elements comprises:

determining whether the local maximum is located at an edge of the sense network;

identifying five sense elements that are adjacent to the local maximum for the set when the local maximum is located at the edge of the sense network;

identifying three or more virtual sense elements for the set when the local maximum is located at the edge of the sense network; and

mirroring the magnitude values of the five sense elements for the magnitude values of the three or more virtual sense elements, and wherein the calculating the sum comprises adding the magnitude values of the five sense elements and the magnitude values of the three or more virtual sense elements.

10. A method comprising:

receiving, from a sense network comprising a plurality of electrodes, data representing capacitances of a plurality of sense elements, wherein the plurality of sense elements are intersections between the plurality of electrodes;

processing the data to identify activated sense elements from the plurality of sense elements; and

filtering the data to remove false touch events based on a spatial relationship of activated sense elements, wherein said processing the data to identify the activated sense elements comprises;

identifying a local maximum from among the activated sense elements;

identifying a set of sense elements that are adjacent to the local maximum, the identifying the set comprises;

determining whether the local maximum is located at an edge of the sense network; and

identifying at least three sense elements that are adjacent to the local maximum for the set when the local maximum is located at the edge of the sense network; and

distinguishing between an actual touch and a false touch based on the capacitances of the set of sense elements.

11. A capacitance sensing system, comprising

a controller coupled to the memory device, wherein the controller is configured to receive signals from a sense network comprising a plurality of electrodes to detect a conductive object proximate to the plurality of electrodes, wherein the controller comprises a filter circuit, wherein the filter circuit is configured to:

receive, from the sense network, data representing capacitances of a plurality of sense elements, wherein the plurality of sense elements are intersections between the plurality of electrodes;

process the data to identify activated sense elements of the plurality of sense elements; and

filter the data to remove false touch events based on a spatial relationship of activated sense elements, wherein the filter circuit is further configured to;

identify a local maximum from among the activated sense elements;

identify a set of sense elements that are adjacent to the local maximum; and

comparing a magnitude value of the local maximum against an aggregate value based on at least three of the set of sense elements to distinguish between an actual touch and a false touch.

12. The capacitance sensing system of claim 11, wherein the filter circuit is configured to:

calculate a sum of magnitude values of the activated sense elements;

subtract the magnitude value of the local maximum from the sum; and

compare the sum against a threshold value to distinguish between the actual touch and the false touch.

13. The capacitance sensing system of claim 11, wherein the filter circuit is configured to:

identify a set of sense elements that are adjacent to the local maximum;

calculate a sum of magnitude values of the set of sense elements; and

compare the sum against a threshold value to distinguish between the actual touch and the false touch.

14. The capacitance sensing system of claim 11, wherein the set of sense elements comprises a three-by-three square of sense elements around the local maximum.

15. The capacitance sensing system of claim 13, wherein the filter circuit is further configured to:

determine whether the local maximum is located at a corner of the sense network or at an edge of the sense network;

identify three sense elements that are adjacent to the local maximum for the set when the local maximum is located at the corner of the sense network; and

identify five sense elements that are adjacent to the local maximum for the set when the local maximum is located at the edge of the sense network.

16. The capacitance sensing system of claim 15, wherein the filter circuit is further configured to mirror the magnitude values of the set for the magnitude values for a second set of virtual sense elements, respectively, and wherein the sum is the magnitude values of the set of sense elements and the magnitude values of the second set of virtual sense elements.

17. The capacitance sensing system of claim 11, further comprising the sense network comprising the plurality of electrodes, and wherein the plurality of electrodes comprises a first set of transmit (TX) electrodes and a second set of receive (RX) electrodes, and wherein the controller is configured to measure a mutual capacitance between at least one of the first set of TX electrodes and an individual one of the second set of RX electrodes for one of the plurality of sense elements.

18. The capacitance sensing system of claim 11, further comprising a capacitance sensing array comprising a plurality of sense elements, the capacitance sensing array coupled to the controller.

19. The capacitance sensing system of claim 18, wherein the controller is configured to:

calculate a sum of magnitude values of the set of sense elements; and

comparing the sum against a threshold value to distinguish between the actual touch and the false touch.