Touch Sensor With Adaptive Touch Detection Thresholding

• US 20130147752A1
• Filed: 12/08/2011
• Published: 06/13/2013
• Est. Priority Date: 12/08/2011
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Simmons, Martin John, Golbourn, Darren, Pickett, Daniel
• Granted Patent: US 9,411,472 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• 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

In one embodiment, a method includes receiving, by a controller coupled to a touch sensor, a plurality of signals from a plurality of sense electrodes, the plurality of signals indicative of an amount of capacitance between the touch sensor and an external object. The method further includes accessing a stored threshold value, determining a strength of a charge return path between the touch sensor and a ground, and adjusting the stored threshold value based on the determined strength of the charge return path. The threshold value indicates a threshold magnitude of the signals from the plurality of sense electrodes to process as a touch by the external object.

Claims

1. A touch sensor comprising:

a plurality of sense electrodes; and

a controller communicatively coupled to the plurality of sense electrodes, the controller configured to;

receive a plurality of signals from the plurality of sense electrodes, the plurality of signals indicative of an amount of capacitance between the touch sensor and an external object;

access a stored threshold value, the threshold value indicating a threshold magnitude of the signals from the plurality of sense electrodes to process as a touch by the external object;

determine a strength of a charge return path between the touch sensor and a ground; and

adjust the stored threshold value based on the determined strength of the charge return path.

2. The touch sensor of claim 1, wherein:

the plurality of sense electrodes comprises a plurality of x-axis sense electrodes and a plurality of y-axis sense electrodes;

the plurality of x-axis sense electrodes visually intersect the plurality of y-axis sense electrodes; and

the visual intersections of the x-axis sense electrodes and the y-axis sense electrodes comprises a plurality of nodes.

3. The touch sensor of claim 2, wherein determining the strength of the charge return path between the touch sensor and ground comprises:

determining that the external object has touched the touch sensor at a location that at least partially covers a particular one of the nodes;

determining a maximum magnitude of a particular signal received from sense electrodes associated with the particular node; and

calculating a new threshold value using the determined maximum magnitude of the particular signal received from sense electrodes associated with the particular node.

4. The touch sensor of claim 3, wherein:

calculating the new threshold value comprises multiplying the determined maximum magnitude of the particular signal received from sense electrodes associated with the particular node by a predetermined percentage; and

adjusting the stored threshold value based on the determined strength of the charge return path comprises storing the calculated new threshold value as the stored threshold value.

5. The touch sensor of claim 1, the controller further configured to, after adjusting the stored threshold value based on the determined strength of the charge return path:

determine that the external object has not touched the touch sensor within a predetermined amount of time; and

periodically drift, at a predetermined rate, the stored threshold value back to an original value, the original value comprising a value of the stored threshold value before it was adjusted based on the determined strength of the charge return path.

6. The touch sensor of claim 1, wherein:

adjusting the stored threshold value based on the determined strength of the charge return path comprises replacing the stored threshold value with a new threshold value; and

the stored threshold value is adjusted at a predetermined rate.

7. A method comprising:

receiving, by a controller coupled to a touch sensor, a plurality of signals from a plurality of sense electrodes, the plurality of signals indicative of an amount of capacitance between the touch sensor and an external object;

accessing, by the controller, a stored threshold value, the threshold value indicating a threshold magnitude of the signals from the plurality of sense electrodes to process as a touch by the external object;

determining, by the controller, a strength of a charge return path between the touch sensor and a ground; and

adjusting, by the controller, the stored threshold value based on the determined strength of the charge return path.

8. The method of claim 7, wherein:

the plurality of sense electrodes comprises a plurality of x-axis sense electrodes and a plurality of y-axis sense electrodes;

the plurality of x-axis sense electrodes visually intersect the plurality of y-axis sense electrodes; and

the visual intersections of the x-axis sense electrodes and the y-axis sense electrodes comprises a plurality of nodes.

9. The method of claim 8, wherein determining the strength of the charge return path between the touch sensor and ground comprises:

determining that the external object has touched the touch sensor at a location that at least partially covers a particular one of the nodes;

determining a maximum magnitude of a particular signal received from sense electrodes associated with the particular node; and

calculating a new threshold value using the determined maximum magnitude of the particular signal received from sense electrodes associated with the particular node.

10. The method of claim 9, wherein:

calculating the new threshold value comprises multiplying the determined maximum magnitude of the particular signal received from sense electrodes associated with the particular node by a predetermined percentage; and

adjusting the stored threshold value based on the determined strength of the charge return path comprises storing the calculated new threshold value as the stored threshold value.

11. The method of claim 7, further comprising, after adjusting the stored threshold value based on the determined strength of the charge return path:

determining that the external object has not touched the touch sensor within a predetermined amount of time; and

periodically drifting, at a predetermined rate, the stored threshold value back to an original value, the original value comprising a value of the stored threshold value before it was adjusted based on the determined strength of the charge return path.

12. The method of claim 7, wherein:

adjusting the stored threshold value based on the determined strength of the charge return path comprises replacing the stored threshold value with a new threshold value; and

the stored threshold value is adjusted at a predetermined rate.

13. A touch-sensitive device comprising a controller, the controller communicatively coupled to a plurality of sense electrodes, the controller operable to:

receive a plurality of signals from the plurality of sense electrodes, the plurality of signals indicative of an amount of capacitance between the touch-sensitive device and an external object;

access a stored threshold value, the threshold value indicating a threshold magnitude of the signals from the plurality of sense electrodes to process as a touch of the touch-sensitive device by the external object;

determine a strength of a charge return path between the touch-sensitive device and a ground; and

adjust the stored threshold value based on the determined strength of the charge return path.

14. The touch-sensitive device of claim 13, wherein:

the plurality of sense electrodes comprises a plurality of x-axis sense electrodes and a plurality of y-axis sense electrodes;

the plurality of x-axis sense electrodes visually intersect the plurality of y-axis sense electrodes; and

the visual intersections of the x-axis sense electrodes and the y-axis sense electrodes comprises a plurality of nodes.

15. The touch-sensitive device of claim 14, wherein determining the strength of the charge return path between the touch sensor and ground comprises:

determining that the external object has touched the touch sensor at a location that at least partially covers a particular one of the nodes;

determining a maximum magnitude of a particular signal received from sense electrodes associated with the particular node; and

calculating a new threshold value using the determined maximum magnitude of the particular signal received from sense electrodes associated with the particular node.

16. The touch-sensitive device of claim 15, wherein:

calculating the new threshold value comprises multiplying the determined maximum magnitude of the particular signal received from sense electrodes associated with the particular node by a predetermined percentage; and

adjusting the stored threshold value based on the determined strength of the charge return path comprises storing the calculated new threshold value as the stored threshold value.

17. The touch-sensitive device of claim 13, the controller further operable to, after adjusting the stored threshold value based on the determined strength of the charge return path:

determine that the external object has not touched the touch sensor within a predetermined amount of time; and

periodically drift, at a predetermined rate, the stored threshold value back to an original value, the original value comprising a value of the stored threshold value before it was adjusted based on the determined strength of the charge return path.

18. The touch-sensitive device of claim 13, wherein:

adjusting the stored threshold value based on the determined strength of the charge return path comprises replacing the stored threshold value with a new threshold value; and

the stored threshold value is adjusted at a predetermined rate.

19. The touch-sensitive device of claim 13, wherein determining the strength of the charge return path between the touch sensor and ground comprises analyzing shapes of one or more capacitance graphs.

20. The touch-sensitive device of claim 19, wherein analyzing shapes of one or more capacitance graphs comprises:

comparing a capacitance graph derived from plurality of signals indicative of an amount of capacitance between the touch-sensitive device and an external object with a plurality of stored capacitance graphs, the stored capacitance graphs comprising;

a grounded capacitance graph indicative of a typical touch when the touch-sensitive device is grounded; and

a floating capacitance graph indicative of a typical touch when the touch-sensitive device is floating;

determining, based on the comparison, that the touch-sensitive device is grounded if the capacitance graph matches the grounded capacitance graph; and

determining, based on the comparison, that the touch-sensitive device is floating if the capacitance graph matches the floating capacitance graph.