Mechanical deflection compensation for a capacitive touch input device
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 monitoring mechanical deflection of a contact layer of a touch sensitive device, the method comprising:
measuring output signals associated with a multi-layer electrode pattern of the touch sensitive device generated in response to contact on the contact layer;
identifying at least a first electrode, of a first electrode layer of the multi-layer electrode pattern, positioned at an approximate location of contact on the contact layer;
selecting an output signal from the measured output signals, wherein the output signal is associated with at least one other electrode of the first electrode layer that is separated from the first electrode by a distance, and wherein the output signal corresponds to a deflection capacitance; and
determining a mechanical deflection of the contact layer caused by the contact, based on the deflection capacitance.
2. The method according to claim 1 , wherein the identifying at least a first electrode comprises determining which electrode of the first electrode layer includes a capacitance greater than a given threshold.
3. The method according to claim 1 , wherein each of the measured output signals includes a deflection capacitance component between a given electrode and a ground plane that is common to each electrode of the first electrode layer.
4. The method according to claim 1 , wherein the deflection capacitance is determined as follows:
Δ
C
i
=
1
N
[
(
N
-
i
)
m
o
+
i
m
N
]
where ΔC i is the capacitance associated with mechanical deflection of an i th electrode, N+1 is a number of electrodes of the first electrode layer, i=0, . . . , N, and m o and m N correspond to deflection capacitance components of a first and an Nth electrode, respectively.
5. The method according to claim 1 , wherein the deflection capacitance 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 of the first electrode layer, i=0, . . . , N−1, where the value of S x is determined from a measurement of ΔC i for at least one electrode of the first electrode layer remote from the approximate location of the contact.
6. The method according to claim 1 , wherein the contact layer comprises a transparent surface and the first electrode layer and a second electrode layer of the multi-layer electrode pattern are arranged orthogonally on the transparent surface, and the transparent surface is positioned over a display surface.
7. The method according to claim 1 , wherein electrodes of the first electrode layer terminate along a peripheral edge of the touch sensitive device.
8. The method according to claim 1 , wherein the distance corresponds to a distance between two or more electrodes of the first electrode layer.
9. A system for monitoring mechanical deflection of a contact layer on a touch sensitive device, the system comprising:
one or more analog-to-digital converters configured to measure output signals associated with a multi-layer electrode pattern, wherein the output signals occur in response to contact on the contact layer, and a first electrode layer of the multi-layer electrode pattern includes 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 contact layer approximately at the first electrode;
select an output signal from the measured output signals, wherein the output signal is associated with the at least one other electrode of the first electrode layer, and wherein the output signal corresponds to a deflection capacitance; and
determine a mechanical deflection of the contact layer caused by the contact, based on the deflection capacitance.
10. The system according to claim 9 , wherein the processor is further configured to identify the relative location of the first electrode by determining which electrode of the first electrode layer includes a capacitance greater than a given threshold.
11. The system according to claim 9 , wherein each of the measured output signals includes a deflection capacitance component between a given electrode and a ground plane that is common to each electrode of the first electrode layer.
12. The system according to claim 9 , wherein the processor is further configured to determine the deflection capacitance as follows:
Δ
C
i
=
1
N
[
(
N
-
i
)
m
o
+
i
m
N
]
where ΔC i is the capacitance associated with mechanical deflection of an i th electrode, N+1 is a number of electrodes of the first electrode layer, i=0, . . . , N, and m o and m N correspond to deflection capacitance components of a first and an Nth electrode, respectively.
13. The system according to claim 9 , wherein the processor is further configured to determine the deflection capacitance 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 of the first electrode layer, i=0, . . . , N−1, where the value of S x is determined from a measurement of ΔC i for at least one electrode of the first electrode layer remote from an approximate location of the contact.
14. The system according to claim 9 , wherein the contact layer comprises a transparent surface and the first electrode layer and a second electrode layer of the multi-layer electrode pattern are arranged orthogonally on the transparent surface, and the transparent surface is positioned over a display surface.
15. The system according to claim 9 , wherein electrodes of the first electrode layer terminate along a peripheral edge of the touch sensitive device.
16. The system according to claim 9 , wherein the distance corresponds to a distance between two or more electrodes of the first electrode layer.
17. A non-transitory computer readable storage medium having stored therein data representing instructions executable by a programmed processor for monitoring mechanical deflection of a contact layer on a touch sensitive device, the instructions comprising:
measuring output signals associated with a multi-layer electrode pattern of the touch sensitive device generated in response to contact on the contact layer;
identifying at least a first electrode of a first electrode layer of the multi-layer electrode pattern, positioned at an approximate location of contact on the contact layer;
selecting an output signal from the measured output signals, wherein the output signal is associated with at least one other electrode of the first electrode layer that is separated from the first electrode by a distance, and wherein the output signal corresponds to a deflection capacitance;
determining a mechanical deflection of the contact layer caused by the contact, based on the deflection capacitance.
18. The non-transitory computer readable storage medium of claim 17 , wherein the deflection capacitance 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 of the first layer, 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 first electrode.
19. The non-transitory computer readable storage medium of claim 17 , wherein the deflection capacitance is determined as follows:
Δ
C
i
=
1
N
[
(
N
-
i
)
m
o
+
i
m
N
]
where ΔC i is the capacitance associated with mechanical deflection of an i th electrode, N+1 is a number of electrodes of the first electrode layer, i=0, . . . , N, and m o and m N correspond to capacitance measurements of a first and an Nth electrode of the first electrode layer, respectively.
20. The non-transitory computer readable storage medium of claim 17 , wherein the contact layer comprises a transparent surface and the first electrode layer and a second electrode layer of the multi-layer electrode pattern are arranged orthogonally on the transparent surface, and the transparent surface is positioned over a display surface.