REDUCTION OF NOISE AND DE-GHOSTING IN A MUTUAL CAPACITANCE MULTI-TOUCH TOUCHPAD

• US 20120206407A1
• Filed: 02/15/2012
• Published: 08/16/2012
• Est. Priority Date: 02/15/2011
• Status: Active Grant

• Current Assignee: Cirque Corporation (Alps Alpine Co., Ltd.)
• Original Assignee: Cirque Corporation (Alps Alpine Co., Ltd.)
• Inventors: Vincent, Paul, Bytheway, Jared G., Taylor, David C.
• Granted Patent: US 8,976,145 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• 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 3/04186 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

Decreasing the cost of a touchpad by avoiding the cost of simultaneously measuring all signals from sense electrodes by using a limited number of measuring circuits to accomplish noise reduction and de-ghosting of signal data to thereby obtain the precise location of multiple fingers on a touchpad, wherein the touchpad separates the drive electrodes into groups to thereby provide a means for obtaining granular location information for de-ghosting the touchpad, and wherein overlapping measurements are made of groups of sense electrodes to obtain data that is separated in time to thereby obtain an averaged signal for each electrode and thereby reduce sensitivity to noise.

Claims

1. A method for determining the location of at least two objects on a touch sensor when there is a ghost effect, said method comprising of the steps of:

1) providing a touch sensor having a first electrode axis which is orthogonal to but co-planar with a second electrode axis, wherein each of the electrode axes are comprised of a plurality of parallel electrodes, wherein one axis functions as drive electrodes while the other axis functions as sense electrodes, and wherein these functions are interchangeable;

2) dividing the drive electrodes into approximately equal groups and driving each drive electrode group separately to thereby create one profile image for each drive electrode group from the sense electrodes that indicate what is present when each of the drive electrode groups is stimulated;

3) switching the functions of the first and second electrode axes;

4) repeating step

     2) for the switched axes; and

5) correlating data from the profile images to determine which objects are actually present on the touchpad, and which are ghost images.

2. The method as defined in claim 1 wherein the method further comprises the step of determining a granular location of the at least two objects on the touch sensor.

3. The method as defined in claim 2 wherein the method further comprises the step correlating data from the profile images by determining where drive electrode groups physically overlap each other when the profile image for that drive electrode group indicates that a finger is present somewhere along a corresponding drive electrode group.

4. The method as defined in claim 1 wherein the method further comprises the step of selecting the number of electrodes for each drive electrode group such that the physical width of the drive electrode group is approximately equal to a human finger.

5. The method as defined in claim 4 wherein the method further comprises the step of adjusting the number of electrodes in each drive electrode group if more than one detectable object can be disposed within a width of the drive electrode group.

13. The method as defined in claim 9 wherein the method further comprises the steps of:

1) selecting a new first set of contiguous sense electrodes that includes at least one sense electrode from the previous second set of contiguous sense electrodes;

2) selecting a new second set of contiguous sense electrodes that includes at least one sense electrode from the new first set of contiguous sense electrodes;

3) without selecting sense electrodes, perform steps

     2) through

     5) of claim 5 using the new sets of electrodes above; and

4) continue the selection of new sets of contiguous sense electrodes until a corrected sense measurement is obtained for each of the sense electrodes.

6. A touch sensor capable of determining the location of at least two objects on the touch sensor when there is a ghost effect, said method comprising of the steps of:

a first electrode axis which is orthogonal to but co-planar with a second electrode axis, wherein each of the electrode axes are comprised of a plurality of parallel electrodes, wherein one axis functions as drive electrodes while the other axis functions as sense electrodes, and wherein these functions are interchangeable;

drive circuitry that transmits drive signals to the drive electrodes;

sensor circuitry which receives sense signals from the sense electrodes, wherein the sensor circuitry generates a profile image that indicates the presence of an object on the touch sensor;

touch sensor circuitry for dividing the drive electrodes into approximately equal groups and driving each drive electrode group separately to thereby create one profile image for each drive electrode group from the sense electrodes that indicate what is present when each of the drive electrode groups is stimulated; and

a processor for correlating data from the profile images to determine which objects are actually present on the touchpad, and which are ghost images.

7. The touch sensor as defined in claim 6 wherein the touch sensor further comprises a plurality of Analog-to-Digital Converters (ADC channels) for receiving sense signals from whichever of the first or second axes is functioning as the sense electrodes.

8. The touch sensor as defined in claim 6 wherein the touch sensor is a mutual capacitance sensitive touch sensor.

9. A method for reducing noise in measurements used to determine a location of at least one finger on a touch sensor, said method comprised of the steps of:

1) providing a touch sensor having a first electrode axis which is orthogonal to hut co-planar with a second electrode axis, wherein each of the electrode axes are comprised of a plurality of parallel electrodes, wherein the touch sensor receives sense signals on the axis that is selected to function as sense electrodes;

2) selecting a first set of contiguous sense electrodes and measuring a first set sense signal from each of the electrodes in the first set;

3) selecting a second set of contiguous sense electrodes and measuring a second set sense signal from each of the electrodes in the second set, wherein there is at least one overlapping sense electrode that belongs to the first set and the second set;

4) calculating a corrected sense measurement for the at least one overlapping sense electrode that compensates for noise by using the sense signal from the first and second set sense signals; and

5) using the corrected sense measurements to determine a location of the at least one finger on the touch sensor.

10. The method as defined in claim 9 wherein the method further comprises the step of averaging the first set sense signal and the second set sense signal to obtain the corrected sense measurement for the at least one overlapping sense electrode.

11. The method as defined in claim 9 wherein the method further comprises the steps of:

1) subtracting the first set sense signal from the second set sense signal to create an offset; and

2) subtracting the offset from the second set sense signal for each electrode in the second set.

12. The method as defined in claim 9 wherein the method further comprises the steps of:

1) overlapping at least two sense electrodes in the first and second sets;

2) subtracting the first set sense signal from the second set sense signal to create an offset for each of the at least two sense electrodes;

3) averaging all of the offsets; and

4) subtracting the average offset from the second set sense signal for each electrode in the second set.

14. A system for reducing noise in measurements used to determine a location of at least one finger on a touch sensor, said system comprised of:

a first electrode axis which is orthogonal to but co-planar with a second electrode axis, wherein each of the electrode axes are comprised of a plurality of parallel electrodes, wherein the touch sensor receives sense signals on the axis that is selected to function as sense electrodes;

at least two Analog-to-Digital Converters (ADC channels) for receiving sense signals from whichever of the first or second electrode axes is functioning as the sense electrodes;

a switch for coupling a first set of contiguous sense electrodes to the ADC channels, one electrode for each ADC channel, and measuring a first set sense signal from each of the electrodes in the first set;

the switch for coupling a second set of contiguous sense electrodes and measuring a second set sense signal from each of the electrodes in the second set, wherein there is at least one overlapping sense electrode that belongs to the first set and the second set; and

a processor for calculating a corrected sense measurement for the at least one overlapping sense electrode that compensates for noise by using the sense signal from the first and second set sense signals and using the corrected sense measurements to determine a location of the at least two fingers on the touch sensor.