TOUCH SENSE INTERFACE CIRCUIT

• US 20130154992A1
• Filed: 12/14/2011
• Published: 06/20/2013
• Est. Priority Date: 12/14/2011
• Status: Active Grant

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: NASCIMENTO, Ivan Carlos Ribeiro
• Granted Patent: US 8,599,169 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

A touch sensing interface (101) includes a noise touch sensing circuit (110) that utilizes electromagnetic (EM) noise in a touch panel (102) to determine whether a pad of the touch panel is touched, such as by a finger of a user. The noise touch sensing circuit detects noise in a first pad (104) and in a second pad (105) of the touch panel, compares power of the noise in the first pad to power of noise in the second pad, and outputs a signal (132) indicative of the first pad being touched when power of noise in the first pad exceeds power of noise in the second pad by a pre-selected amount. The touch sensing interface may include a capacitive touch sensing circuit (120) and a controller (130) that selectively actuates the noise touch sensing circuit and the capacitive touch sensing circuit.

Claims

1. A touch sense interface, comprising:

a noise touch sensing circuit, the noise touch sensing circuit including;

first circuitry for detecting electromagnetic (EM) noise at a first pad of a touch panel,

second circuitry for detecting EM noise at a second pad of the touch panel, and

a noise power comparator for comparing amplitude of EM noise detected by the first circuitry and amplitude of EM noise detected by the second circuitry, wherein the noise power comparator produces a signal based upon result of the comparing,

wherein the touch sense interface produces a touch indication indicative of a touch occurring at the first pad.

2. The touch sense interface of claim 1, wherein the first circuitry measures magnitude of power of the EM noise at the first pad, and wherein the second circuitry measures magnitude of power of the EM noise at the second pad.

3. The touch sense interface of claim 2, wherein the noise touch sensing circuit outputs the signal when the magnitude of the power of the EM noise at the first pad is a pre-selected amount greater than the magnitude of the power of the EM noise at the second pad.

4. The touch sense interface of claim 1, including:

a controller, the noise touch sensing circuit selectively actuated by the controller; and

a capacitive touch sensing circuit, selectively actuated by the controller, coupled to the first pad and to the second pad, the capacitive touch sensing circuit for determining whether a touch is occurring at the first pad,

wherein the capacitive touch sensing circuit outputs a signal based upon result of determining, and

wherein the controller produces the touch indication based upon one of or both;

the signal outputted by the noise touch sensing circuit and the signal outputted by the capacitive touch sensing circuit.

5. The touch sense interface of claim 4, wherein, when the EM noise at the second pad is above a pre-determined level, the controller produces the touch indication based solely upon the signal outputted by the noise touch sensing circuit.

6. The touch sense interface of claim 4, including a clock coupled to the controller, to the noise touch sensing circuit and to the capacitive touch sensing circuit, wherein the controller actuates the noise touch sensing circuit during a noise sensing interval and actuates the capacitive touch sensing circuit during a capacitive sensing interval, and wherein the noise touch sensing circuit determines during the noise sensing interval whether a touch is occurring at the first pad of the touch panel, and wherein the capacitive touch sensing circuit determines during the capacitive sensing interval whether a touch is occurring at the first pad.

7. A noise touch sensing circuit for detecting electromagnetic (EM) noise at pads of a touch panel, the noise touch sensing circuit comprising:

a first comparator with hysteresis having an input node coupled to a first pad of a touch panel, the first comparator with hysteresis outputting a first signal responsive to magnitude of EM noise at the first pad;

a second comparator with hysteresis having an input node coupled to a second pad of the touch panel, the second comparator with hysteresis outputting a second signal responsive to magnitude of EM noise at the second pad;

a first counter for counting toggling of the first signal;

a second counter for counting toggling of the second signal; and

a threshold controller, coupled to the first comparator with hysteresis and to the second comparator with hysteresis, wherein the threshold controller;

sets a positive threshold (V_p1) and a negative threshold (V_m1) of the first comparator in response to a count outputted by the first counter,

sets a positive threshold (V_p2) and a negative threshold (V_m2) of the second comparator in response to a count outputted by the second counter, and

outputs a noise touch sensing signal in response to a difference between the count of the first counter and the count of the second counter.

8. The noise touch sensing circuit of claim 7, wherein the threshold controller outputs a noise touch sensing signal when the count outputted by the first counter is greater than the count outputted by the second counter by a pre-selected amount.

9. The noise touch sensing circuit of claim 7, wherein the first comparator with hysteresis includes a first Schmitt trigger and wherein the second comparator with hysteresis includes a second Schmitt trigger.

10. The noise touch sensing circuit of claim 9, wherein the first comparator with hysteresis detects magnitude of a voltage attributable to EM noise at the first pad, and wherein the second comparator with hysteresis detects magnitude of a voltage attributable to EM noise at the second pad.

11. The noise touch sensing circuit of claim 10, including:

circuitry for maintaining a constant DC voltage at the input node of the first comparator with hysteresis; and

circuitry for maintaining a constant DC voltage at the input node of the second comparator with hysteresis.

12. The noise touch sensing circuit of claim 7, wherein the threshold controller:

increases the positive threshold (V_p1) and decreases the negative threshold (V_m1) of the first comparator in response to an increase in the count outputted by the first counter, and

increases the positive threshold (V_p2) and decreases the negative threshold (V_m2) of the second comparator in response to an increase in the count outputted by the second counter.

13. The noise touch sensing circuit of claim 12, wherein the threshold controller:

increases the positive threshold (V_p1) and decreases the negative threshold (V_m1) by a same factor over a previous setting of the respective threshold, and

increases the positive threshold (V_p2) and decreases the negative threshold (V_m2) by a same factor over a previous setting of the respective threshold.

14. The noise touch sensing circuit of claim 13, wherein the threshold controller outputs a noise touch sensing signal when the count of the first counter is greater than the count of the second counter by at least 3.

15. A method with a touch panel, the touch panel including a plurality of pads, comprising:

measuring power of electromagnetic (EM) noise in a first pad and measuring power of EM noise in a second pad;

comparing the power of EM noise measured in the first pad to the power of EM noise measured in the second pad; and

providing an indication of a touch occurring at the first pad when the power of the EM noise measured in the first pad is a pre-selected amount greater than the power of the EM noise measured in the second pad.

16. The method of claim 15, wherein the step of determining power of EM noise in a first pad includes:

setting a positive threshold of a first comparator with hysteresis, coupled to the first pad, to a low setting and a negative threshold of a comparator with hysteresis to a high setting;

changing the setting of the thresholds by increasing the positive threshold and decreasing the negative threshold in response to an output signal of the first comparator with hysteresis;

for each change of setting of the thresholds, calculating a difference between the setting of the positive threshold and the setting of the negative threshold; and

storing, as pad1V_pm, a maximum difference between the setting of the positive threshold and the setting of the negative threshold that resulted in toggling of the output signal of the first comparator with hysteresis.

17. The method of claim 16, wherein the step of determining power of EM noise in a second pad includes:

setting a positive threshold of the second comparator with hysteresis, coupled to the second pad, to a low setting and a negative threshold of the second comparator with hysteresis to a high setting;

changing the setting of the thresholds by increasing the positive threshold and simultaneously decreasing the negative threshold in response to an output signal of the second comparator with hysteresis;

for each change of setting of the thresholds, calculating a difference between the setting of the positive threshold and the setting of the negative threshold; and

storing, as pad2V_pm, a maximum difference between the setting of the positive threshold and the setting of the negative threshold that resulted in toggling of the output signal of the second comparator with hysteresis.

18. The method of claim 17, in which the step of determining power of EM noise in a first pad and the step of determining power of EM noise in a second pad are performed during a same time interval, and in which the step of comparing the power of EM noise in the first pad to the power of EM noise in the second pad includes calculating pad1V_pm minus pad2V_pm.

19. The method of claim 18, in which the step of outputting a signal indicative of a touch occurring at the first pad includes determining whether pad1V_pm is a pre-selected amount greater than pad2V_pm.

20. The method of claim 15, in which

the step of measuring includes measuring power of EM noise in the first pad and measuring power of EM noise in a plurality of neighboring pads;

the step of comparing includes comparing the power of EM noise measured in the first pad to an average of power of EM noise measured in each of the plurality of neighboring pads; and

the step of providing includes providing an indication of a touch occurring at the first pad when the power of the EM noise measured in the first pad is a pre-selected amount greater than the average of the power of the EM noise measured in each of the plurality of neighboring pads.