Background capacitance compensation for a capacitive touch input device

• US 9,152,278 B2
• Filed: 01/25/2011
• Issued: 10/06/2015
• Est. Priority Date: 12/22/2010
• Status: Active Grant

• Current Assignee: Elo Touch Solutions, Inc.
• Original Assignee: Elo Touch Solutions, Inc.
• Inventors: Kent, Joel C., Li, Selina, Yi, Jong
• Primary Examiner(s): Ghebretinsae, Temesgh
• Assistant Examiner(s): Xie, Kwin
• Application Number:
  US13/013,613
• Publication Number:
  US 20120162123A1
• Time in Patent Office: 1,715 Days
• Field of Search: 345173-174
• US Class Current: 1/1
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes

Abstract

A location of contact with a touch sensitive device is determined. Values associated with each electrode of a plurality of electrodes formed on a single layer of the touch sensitive device are sampled. A determination is made as to whether a contact with the touch sensitive device has occurred. Values sampled subsequent to the contact are adjusted based on selected stored sampled values. A location of contact is then determined based on the adjusted values.

Claims

1. A method for determining a location of contact with a touch sensitive device, the method comprising:

sampling, on a periodic basis, a plurality of first values associated with each electrode of a plurality of electrodes of the touch sensitive device, the touch sensitive device comprising a single electrode layer device, wherein the sampling of the plurality of first values occurs during a first time period, the first time period comprising a plurality of sampling periods, a sampling period being a time difference between two consecutive samplings;

storing a subset of the plurality of first values for a second time period, the second time period being at least twice the sampling period and comprising at least two samplings;

determining whether a contact with the touch sensitive device has occurred, wherein the first time period ceases upon contact determination;

sampling, subsequent to the contact, a second value associated with at least one electrode of the plurality of electrodes;

adjusting one or more second values based on at least one of the stored subset of the plurality of first values while the contact is occurring, the at least one of the stored subset being sampled at least two sampling periods prior to the determination of the contact; and

determining a location of the contact based on the adjusted values.

2. The method according to claim 1, further comprising determining whether a rate of change of a value associated with one or more electrodes of the plurality of electrodes exceeds a threshold.

3. The method according to claim 1, further comprising:

determining a rate of change of a value associated with one or more electrodes of the plurality of electrodes; and

selecting one or more of the plurality of first values based on the determined rate of change.

4. The method according to claim 1, further comprising ceasing storing of the subset after determining the contact with the touch sensitive device has occurred.

5. The method according to claim 4, continuously determining the location of contact based on the subset until contact with the touch sensitive device has ceased.

6. The method according to claim 4, further comprising:

determining whether contact with the touch sensitive device has ceased, and resuming storing of samples after contact with the touch sensitive device has ceased.

7. The method according to claim 1, wherein the time period lasts a time limit based on one of a maximum sample count and a maximum second count.

8. The method according to claim 1, wherein the touch sensitive device comprises a transparent surface and the electrodes are arranged on the transparent surface, the touch sensitive device surface is positioned over a display surface, and the location of contact corresponds to a location where a user touches the touch sensitive device.

9. A system for determining a location of contact with a capacitive touch sensitive device, the system comprising:

one or more analog-to-digital converters configured to sample, on a periodic basis, signals at a plurality of electrodes; and

a processor configured to;

store a subset of a plurality of one or more first values associated with a plurality of the sampled signals, the signals sampled during a first time period, the first time period comprising a plurality of sampling periods, a sampling period being a time difference between two consecutive samplings, the subset stored for a second time period, the second time period being at least twice the sampling period and comprising at least two samplings;

determine whether a contact with the touch sensitive device has occurred, the sampling ceasing upon contact determination;

select a background value for each of the electrodes of the plurality based on at least one of the stored subset of the plurality of one or more first values, the at least one of the stored subset used in the selection of the background value for each of the electrodes being sampled at least two sample periods prior to the determination of the contact;

sample, subsequent to the contact, a second value associated with at least one electrode of the plurality of electrodes;

adjust one or more second values for each of the electrodes by the respective background values while the contact is occurring, the one or more first values being sampled prior to the determination of the contact; and

determine a location of the contact based on the adjusted values.

10. The system according to claim 9, wherein the processor is configured to determine whether a rate of change of a value associated with one or more electrodes of the plurality of electrodes exceeds a threshold.

11. The system according to claim 9, wherein the processor is configured to:

determine a rate of change of a value associated with one or more electrodes of the plurality of electrodes; and

select one or more first values based on the determined rate of change.

12. The system according to claim 9, wherein the processor is configured to cease storage of the plurality of one or more first values after contact with the touch sensitive device has occurred.

13. The system according to claim 12, wherein the processor is configured to continuously determine the location of contact based on the plurality of one or more first values until contact with the touch sensitive device has ceased.

14. The system according to claim 12, wherein the processor is configured to:

determine whether contact with the touch sensitive device has ceased, and resume storage of values after contact with the touch sensitive device has ceased.

15. The system according to claim 9, wherein the processor is configured to store a subset for a time period lasting a limited time based on one of a maximum sample count and a maximum second count.

16. The system according to claim 9, wherein the touch sensitive device comprises a transparent surface and the electrodes are arranged on the transparent surface, the touch sensitive device surface is positioned over a display surface, and the location of contact corresponds to a location where a user touches the touch sensitive device.

17. A non-transitory computer readable storage medium having stored therein data representing instructions executable by a programmed processor for determining a location of contact with a touch sensitive device, the storage medium comprising instructions for:

identifying background capacitance from prior to a contact with the touch sensitive device;

removing the background capacitance from measurements of a plurality of electrodes while the contact is occurring, the background capacitance being identified prior to the determination of the contact by sampling, on a periodic basis, a plurality of first values associated with each electrode of a plurality of electrodes of the touch sensitive device the sampling occurring during a first time period that ceases upon contact determination, the first time period comprising a plurality of sampling periods, a sampling period being a time difference between two consecutive samplings, and storing a subset of the plurality of first values associated with a plurality of the sampled signals for a second time period, the second time period being at least twice the sampling period and comprising at least two samplings,

at least one of the stored subset used in the identification of the background capacitance being sampled at least two sample periods prior to the determination of the contact; and

determining a location of the contact based on the measurements with the background capacitance removed.

18. The non-transitory computer readable storage medium according to claim 17, wherein identifying comprises:

determining a rate of change of values associated with one or more electrodes of the plurality of electrodes; and

selecting the background capacitance based on the determined rate of change.

19. The non-transitory computer readable storage medium according to claim 17, further comprising:

storing values sampled prior to the contact, the background capacitance based on the stored values; and

ceasing storing of the values after contact with the touch sensitive device has occurred.

20. The non-transitory computer readable storage medium according to claim 19, wherein the location of contact is continuously determined based on the removing of the background capacitance until contact with the touch sensitive device has ceased.