Mechanical deflection compensation for a capacitive touch input device
View Patent ↗A location of contact with a touch sensitive device is determined. Output signals associated with a plurality of electrodes such as formed on a single layer of the touch sensitive device are measured to identify a first electrode positioned at an approximate location of contact with the touch sensor. An output signal associated with a different electrode that is separated from the first electrode is measured to determine an undesired signal amount, such as due to deflection. An undesired single amount associated with the first electrode may be estimated based on the undesired signal amount measured at the other electrode. The signal amount measured at the first electrode is then compensated by the estimated undesired signal amount. The location of contact with the touch sensor is then determined based on the compensated signal amount.
1. A method for determining a location of contact on a touch sensitive device, the method comprising:
measuring output signals associated with a plurality of electrodes of the touch sensitive device generated in response to contact on the touch sensitive device;
identifying at least a first electrode, from the plurality of electrodes, positioned at an approximate location of contact on the touch sensitive device;
selecting an output signal from the measured output signals, wherein the output signal is associated with at least one other electrode that is separated from the first electrode by a distance, and wherein the output signal corresponds to an undesired signal amount;
estimating an undesired signal amount associated with the first electrode based on the output signal in response to the contact with the touch sensitive device for which the location of the contact is being determined, wherein estimating the undesired signal amount comprises determining a capacitance associated with mechanical deflection of the touch sensitive device;
adjusting a signal amount of a second output signal from the measured output signals by the estimated undesired signal amount, wherein the signal amount is measured at the first electrode; and
determining the location of the contact that generated the measured output signals based on the adjusted signal amount.
2. The method according to claim 1 , further comprising measuring signal amounts at a first group of electrodes positioned at the approximate location of the contact and compensating signal amounts measured at the first group of electrodes.
3. The method according to claim 2 , further comprising measuring signal amounts at a second group of electrodes separated from the first group of electrodes to estimate undesired signal amounts associated with the first group of electrodes based on the measured signal amounts at the second group of electrodes.
4. The method according to claim 1 , wherein the capacitance associated with mechanical deflection is determined as follows:
Δ
C
i
=
1
N
[
(
N
-
i
)
m
o
+
im
N
]
where ΔC i is the capacitance associated with mechanical deflection of an i th electrode, N+1 is a number of electrodes, i=0, . . . , N, and m o and m N correspond to capacitance measurements of a first and an Nth electrode, respectively.
5. The method according to claim 1 , wherein the capacitance associated with mechanical deflection is determined as follows:
Δ
C
i
=
4
S
x
(
2
i
+
1
)
(
2
N
-
2
i
-
1
)
(
2
N
)
2
where ΔC i is the capacitance associated with mechanical deflection of an i th electrode, N is a number of electrodes, i=0, . . . , N−1, and where the value of S x is determined from a measurement of ΔC i for at least one electrode remote from the location of the contact.
6. The method according to claim 1 , wherein the touch sensitive device comprises a transparent surface and the plurality of electrodes are arranged on the transparent surface, the transparent surface is positioned over a display surface, and the location of the contact corresponds to a location associated with a touch on the touch sensitive device.
7. The method according to claim 1 , wherein the plurality of electrodes terminate along a peripheral edge of the touch sensitive device.
8. The method according to claim 1 , where the distance corresponds to a distance between two or more electrodes.
9. A system for determining a location of contact on a touch sensitive device, the system comprising:
one or more analog-to-digital converters configured to measure output signals associated with a plurality of electrodes, wherein the output signals occur in response to contact on the touch sensitive device, and the plurality of electrodes include a first electrode and at least one other electrode that is separated from the first electrode by a distance; and
a processor configured to:
identify a relative location of the first electrode in response to contact being made with the touch sensitive device approximately at the first electrode;
estimate an undesired signal amount associated with the first electrode based on an undesired signal amount measured at the at least one other electrode in response to the contact with the touch sensitive device for which the location of the contact is being determined, wherein the undesired signal amount associated with the at least one other electrode is generated by mechanical deflection of the touch sensitive device;
compensate for a signal amount measured at the first electrode in response to the contact on the touch sensitive device by adjusting the signal amount by the estimated undesired signal amount; and
determine the location of the contact that generated the output signals based on the compensated signal amount.
10. The system according to claim 9 , wherein the one or more analog-to-digital converters are further configured to measure signal amounts of a first group of electrodes positioned at an approximate location of the contact and the processor is further configured to compensate for signal amounts measured at the first group of electrodes.
11. The system according to claim 10 , wherein the one or more analog-to-digital converters are further configured to measure signal amounts at a second group of electrodes separated from the first group of electrodes, and the processor is further configured to estimate an undesired signal amount associated with the first group of electrodes based on the measured signal amounts at the second group of electrodes.
12. The system according to claim 9 , wherein a capacitance associated with mechanical deflection is determined as follows:
Δ
C
i
=
1
N
[
(
N
-
i
)
m
o
+
im
N
]
where ΔC i is the capacitance associated with mechanical deflection of an i th electrode, N+1 is a number of electrodes, i=0, . . . , N, and m o and m N correspond to capacitance measurements of a first and an Nth electrode, respectively.
13. The system according to claim 9 , wherein a capacitance associated with mechanical deflection is determined as follows:
Δ
C
i
=
4
S
x
(
2
i
+
1
)
(
2
N
-
2
i
-
1
)
(
2
N
)
2
where ΔC i is the capacitance associated with mechanical deflection of an i th electrode, N is a number of electrodes, i=0, . . . , N−1, and where the value of S x is determined from a measurement of ΔC i for at least one electrode remote from the location of the contact.
14. The system according to claim 9 , wherein the touch sensitive device comprises a transparent surface and the plurality of electrodes are arranged on the transparent surface, the transparent surface is positioned over a display surface, and the location of the contact corresponds to a location associated with a touch on the touch sensitive device.
15. The system according to claim 9 , wherein the plurality of electrodes terminate along a peripheral edge of the touch sensitive device.
16. The system according to claim 9 , where the distance corresponds to a distance between two or more electrodes.
17. A non-transitory computer readable storage medium having stored therein data representing instructions executable by a programmed processor for determining contact location on a touch sensitive device, the storage medium comprising instructions for:
measuring a plurality of capacitance measurements at a plurality of electrodes during contact with the touch sensitive device;
estimating an undesired amount of capacitance measurement at an area proximate to the contact location due to mechanical deflection based on at least one capacitance measurement from the plurality of capacitance measurements spaced away from the area proximate to the contact location, wherein the at least one capacitance measurement is obtained in response to the contact with the touch sensitive device for which the contact location is being determined; and
adjusting a capacitance measurement at the contact location by the estimated undesired amount of capacitance measurement; and
determining the contact location that generated the plurality of capacitance measurements based on the adjusted capacitance measurement.
18. The non-transitory computer readable storage medium of claim 17 , wherein the estimating comprises:
comparing the plurality of capacitance measurements to a threshold;
selecting one of the plurality of electrodes as near the contact location where the capacitance measurement of the one of the plurality of electrodes is above the threshold;
selecting another of the plurality of electrodes as spaced from the contact location where the capacitance measurement of another of the plurality of electrodes is below the threshold; and
determining the undesired amount based on the capacitance measurement below the threshold;
wherein the adjusting comprises subtracting the undesired amount from the capacitance measurement over the threshold.
19. The non-transitory computer readable storage medium of claim 17 , wherein a capacitance associated with mechanical deflection is determined as follows:
Δ
C
i
=
1
2
[
(
N
-
i
)
m
o
+
im
N
]
where ΔC i is the capacitance associated with mechanical deflection of an i th electrode, N+1 is a number of electrodes, i=0, . . . , N, and m o and m N correspond to capacitance measurements of a first and an Nth electrode, respectively.
20. The non-transitory computer readable storage medium of claim 17 , wherein the touch sensitive device comprises a transparent surface and the plurality of electrodes are arranged on the transparent surface, the touch sensitive device surface is positioned over a display surface, and the location of the contact corresponds to a location associated with a touch on the touch sensitive device.