Capacitive sensor filtering apparatus, method, and system

• US 9,569,054 B2
• Filed: 08/20/2015
• Issued: 02/14/2017
• Est. Priority Date: 08/19/2013
• Status: Active Grant

• Current Assignee: Touchsensor Technologies LLC (Methode Electronics Incorporated)
• Original Assignee: Touchsensor Technologies LLC (Methode Electronics Incorporated)
• Inventors: Citta, James W.
• Primary Examiner(s): Zhou, Hong
• Application Number:
  US14/831,501
• Publication Number:
  US 20150355756A1
• Time in Patent Office: 544 Days
• Field of Search: 345/174, 178/18.06
• US Class Current: 1/1
• CPC Class Codes: G06F 2203/04101 2.5D-digitiser, i.e. digitiser detecting the X/Y position of the input means, finger or stylus, also when it does not touch, but is proximate to the digitiser's interaction surface and also measures the distance of the input means within a short range in the Z direction, possibly with a separate measurement setup
• 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 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/96066 Thumbwheel, potentiometer, scrollbar or slider simulation by touch switch
• CPC Class Codes: H03K 2217/96071 characterised by the detection principle

Abstract

A transform is used to transform raw sensor data from the time domain to the frequency or sequency domain. The transformed data falls into several signal bins. The transformed data in at least one of the signal bins is analyzed to determine whether a touch event or release event has occurred.

Claims

1. A method for operating a touch screen having at least one first electrode and at least one second electrode, each said at least one first electrode intersecting said at least one second electrode, wherein each intersection of said at least one first electrode and said at least one second electrode defines a touch detection node, the method comprising:

selectively exciting each said at least one first electrode and thereby selectively generating an electric field about ones of said touch detection nodes corresponding to each said at least one first electrode;

periodically determining the capacitance about each of said touch detection nodes;

transforming a rolling sample of said capacitance data for each said node from the time domain to the sequency domain using a Walsh-Hadamard Transform, said transformation yielding data in at least a sequency bin 0;

determining for each said node, with all of said nodes in an untouched state and no stimulus proximate said touch screen, a reference value in said sequency bin 0;

determining for each said node a current value in said sequency bin 0;

determining for each said node a delta value by subtracting said current sequency bin 0 value of said node from said reference value of said node;

analyzing the data in at least one of the sequency bins resulting from the transformation; and

entering said delta values into a matrix;

applying a two-dimensional centroiding technique to said delta values in said matrix; and

determining a touch location with respect to one of an x coordinate and a y coordinate of said touch screen.

2. The method of claim 1 further comprising determining said touch location with respect to the other of said x coordinate and said y coordinate of said touch screen.

3. The method of claim 1 wherein said nodes may be deemed to be in said untouched state and no stimulus may be deemed proximate said touch screen when a noise level for each said node is below a predetermined threshold, said current sequency bin 0 value for each of said nodes is near zero, and a previous sequency bin zero value for each of said nodes is near zero.

4. The method of claim 1 wherein said at least one first electrode is a drive line and said at least one second electrode is a sense line.

5. A method of operating a slider comprising a plurality of keys, each key comprising a sensor electrode, the method comprising:

selectively exciting each said sensor electrode and thereby generating an electric field about the sensor electrode;

periodically determining the capacitance from each said sensor electrode to a reference potential;

transforming a rolling sample of capacitance data for each said sensor electrode from the time domain to the sequency domain using a Walsh-Hadamard Transform, said transformation yielding data in a plurality of sequency bins including a sequency bin 1;

analyzing the data in at least one of the sequency bins resulting from the transformation;

determining whether a touch event has occurred proximate a first of said keys based on the analysis;

deeming said first key to be a current key;

monitoring data values in said sequency bin 1 for each of said sensor electrodes;

comparing said sequency bin 1 value for each of said electrodes with the sequency bin 1 values of the others of said sensor electrodes and to a predetermined threshold; and

deeming a second of said keys to be the current key when the sequency bin 1 value for the sensor electrode of said second of said keys is greater than the sequency bin 1 values of the sensor electrodes of the others of said keys and greater than the predetermined threshold.

6. The method of claim 5 wherein the keys are arranged in a linear orientation.

7. The method of claim 5 wherein the keys are arranged in a rotary orientation.

8. The method of claim 5 wherein said sensor electrodes comprising said first and second keys are spatially-interpolated and wherein the capacitance from each said sensor electrode varies in response to introduction of a stimulus proximate each said sensor electrode, said method further comprising using interpolation techniques to determine a location of said stimulus proximate said first and second keys relative to locations of said first and second keys.

9. A method of determining proximity to a panel comprising a plurality of touch detection nodes, comprising:

determining a baseline capacitance for each of said touch detection nodes;

determining a change in capacitance for each of said touch detection nodes compared to said baseline capacitance for each of said touch detection nodes;

summing said changes in capacitance;

transforming a rolling sample of said summed changes in capacitance data from the time domain to the sequency domain using a Walsh-Hadamard Transform;

analyzing the data in at least one of the sequency bins resulting from the transformation; and

determining whether a proximity event has occurred based on the analysis.

10. The method of claim 9 further comprising offsetting the summed changes in capacitance prior to performing said step of transforming.

11. The method of claim 10 wherein said step of offsetting comprises offsetting the summed changes in capacitance to a 16 bit number.

12. A method for operating a sensor, comprising:

obtaining in the time domain data from said sensor indicative of a disturbance to said sensor;

continuously transforming a rolling sample of said data from the time domain to a plurality of data signals in the sequency domain using a Walsh-Hadamard Transform, each of the data signals in a corresponding sequency bin resulting from the Walsh-Hadamard Transform and each of the data signals comprising values related to the disturbance for corresponding samples of the rolling sample, wherein the rolling sample is an n-point rolling sample including a current sample and n−

1 samples immediately preceding the current sample, one of the n−

1 samples being a last sample, and n is an integer equal to or greater than 2 corresponding to a size of a Walsh matrix used in performance of the Walsh-Hadamard Transform;

analyzing in the sequency domain at least one of the plurality of data signals in the corresponding sequency bin resulting from the transformation; and

determining whether a threshold disturbance has occurred based on the analysis of the at least one of the plurality of data signals in the corresponding sequency bin.

13. The method of claim 12 wherein the threshold disturbance is deemed to have occurred when the difference between a baseline and the value of the current sample in a sequency bin 0 exceeds a predetermined threshold.

14. The method of claim 12 wherein the threshold disturbance is deemed to have occurred when the value of the last sample in a sequency bin 1 is greater than the value of the current sample in the sequency bin 1.

15. The method of claim 14 wherein the threshold disturbance is deemed to have terminated when the value of the current sample in the sequency bin 1 reaches a minimum.

16. The method of claim 12 wherein the threshold disturbance is deemed to have occurred when the difference between the value of the current sample in the sequency bin 1 and the value of the immediately previous sample in the sequency bin 1 exceeds a predetermined threshold.

17. The method of claim 12 wherein n=8 and the threshold disturbance is deemed to have occurred when the data signals in sequency bins 1, 2, 3, 6 and 7 are greater than zero and the data signals in sequency bins 4 and 5 are less than zero.

18. The method of claim 12 wherein the threshold disturbance is deemed to have occurred when the data signal in a sequency bin 1 crosses zero in the positive direction and then crosses zero in the negative direction.

19. The method of claim 12 wherein the threshold disturbance is deemed to have occurred when integration of successive non-negative transformed values of the samples in a sequency bin 1 yields a value that meets or exceeds a predetermined threshold.

20. The method of claim 12 wherein the threshold disturbance is deemed to have terminated when the absolute value of the value yielded by integration of successive non-positive transformed values of the samples in a sequency bin 1 meets or exceeds a predetermined threshold.

21. The method of claim 12 wherein the threshold disturbance is deemed to have occurred when the sum of the values of the samples in a sequency bin 1 exceeds a system noise level by a predetermined multiplier.

22. The method of claim 21 wherein the multiplier is less than one.

23. The method of claim 21 wherein n=8 and the system noise level is determined by summing the absolute values of the samples in sequency bins 4, 5, 6, and 7.

24. The method of claim 12 wherein the threshold disturbance is deemed to have occurred when the absolute value of the value yielded by integration of successive non-positive transformed values of the samples in a sequency bin 1 meets or exceeds a predetermined threshold that is a function of a system noise level.

25. The method of claim 12 wherein the threshold disturbance is deemed to have occurred when a system noise level increases above a predetermined threshold.

26. The method of claim 12 wherein the sensor is one of an infrared sensor, an ultrasonic sensor, and an accelerometer.