Noise reduction in capacitive touch sensors

• US 8,605,037 B2
• Filed: 10/21/2008
• Issued: 12/10/2013
• Est. Priority Date: 10/21/2008
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Yilmaz, Esat, Philipp, Harald
• Primary Examiner(s): Wang, Quan-Zhen
• Assistant Examiner(s): DAVIS, TONY O
• Application Number:
  US12/255,335
• Publication Number:
  US 20100139991A1
• Time in Patent Office: 1,876 Days
• Field of Search: 345/173
• US Class Current: 345/173
• 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
• 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 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
• CPC Class Codes: H03K 2217/960725 Charge-transfer

Abstract

Noise reduction in a one- or two-dimensional capacitive sensor array is achieved by rejecting and re-acquiring noisy signals. The sensor array is formed of crossed X and Y lines for drive and sense functions respectively, each of the X lines being driven in turn to acquire a full frame of data from the sensor array. A controller actuates the X lines in turn and, for each X line, charge is transferred to charge measurement capacitors connected to respective ones of the Y lines. The controller measures a signal value from a first one of the measurement capacitors, and then tests if that Y signal value has a magnitude lying within an acceptable range. If not, the measurement capacitors are all reset without their signal values being measured, and the controller re-drives the same X line to initiate another charge transfer into the measurement capacitors for that X line. It is then attempted once again to acquire Y signal values for that X line. Noisy signal values are thus rejected, and the sensor re-acquires substitute signal values. This is distinct from the approach of acquiring data and then reprocessing it to remove or suppress noisy data as in the prior art.

Claims

1. A touch sensor comprising:

a first set of electrodes, the first set of electrodes arranged in at least three groupings of electrodes, each grouping of the at least three groupings of electrodes of the first set of electrodes extending along a first axis;

a second set of electrodes, the second set of electrodes arranged in at least three groupings of electrodes, each grouping of the at least three groupings of electrodes of the second set of electrodes extending along a second axis different than the first axis, each electrode of the second set of electrodes arranged to have a portion thereof adjacent to a portion of each of the first set of electrodes such that the second set of electrodes is capacitively coupled to the first set of electrodes; and

one or more non-transitory electronic storage media comprising code that, when executed, is configured to;

cause a first drive signal to be sent to a first grouping of electrodes of the first set of electrodes;

determine a first measurement associated with a first grouping of electrodes of the second set of electrodes after causing the first drive signal to be sent to the first grouping of electrodes of the first set of electrodes, the first measurement related to the first drive signal;

compare the first measurement to a limit;

determine that the first measurement is within the limit;

in response to determining that the first measurement is within the limit, determine a second measurement associated with a second grouping of electrodes of the second set of electrodes;

compare the second measurement to the limit;

determine that the second measurement is outside the limit;

in response to determining that the second measurement is outside the limit, determine not to measure an effect of the first drive signal on a third grouping of electrodes of the second set of electrodes; and

in response to determining that the second measurement is outside the limit, cause a second drive signal to be sent to the first grouping of electrodes of the first set of electrodes.

2. The sensor of claim 1, wherein the code is configured to:

determine a set of measurements associated with the at least three groupings of electrodes of the second set of electrodes after causing the second drive signal to be sent to the first grouping of electrodes of the first set of electrodes;

determine that the first set of measurements are within the limit; and

in response to determining that the set of measurements are within the limit, determine a location of a touch using the set of measurements.

3. The sensor of claim 1, wherein:

the limit is an upper limit; and

the code is configured to determine that the second measurement is outside the limit by determining that the second measurement is above the upper limit.

4. The sensor of claim 1, wherein:

the limit is a lower limit; and

the code is configured to determine that the second measurement is outside the limit by determining that the second measurement is below the lower limit.

5. The sensor of claim 1, wherein the code is configured to determine that the second measurement is outside the limit by determining that the second measurement is outside a range.

6. The sensor of claim 1, wherein the code is further configured to:

determine a set of measurements associated with the at least three groupings of electrodes of the second set of electrodes after causing the second drive signal to be sent to the first grouping of electrodes of the first set of electrodes;

determine that the first set of measurements are within the limit; and

in response to determining that the set of measurements are within the limit, cause a third drive signal to be sent to a second grouping of electrodes of the first set of electrodes.

7. The sensor of claim 1, wherein the code is further configured to cause discharging of at least one capacitor associated with the second set of electrodes in response to determining that the second measurement is outside the limit.

8. A method comprising:

causing a first drive signal to be sent to a first grouping of electrodes of a first set of electrodes, the first set of electrodes arranged in at least three groupings of electrodes, each grouping of the at least three groupings of electrodes of the first set of electrodes extending along a first axis, the at least three groupings of electrodes of the first set of electrodes comprising the first grouping of electrodes of the first set of electrodes;

determining a first measurement associated with a first grouping of electrodes of a second set of electrodes after causing the first drive signal to be sent to the first grouping of electrodes of the first set of electrodes, the second set of electrodes arranged in at least three groupings of electrodes, the at least three groupings of electrodes of the second set of electrodes comprising the first grouping of electrodes of the second set of electrodes, each grouping of the at least three groupings of electrodes of the second set of electrodes extending along a second axis different than the first axis, each electrode of the second set of electrodes arranged to have a portion thereof adjacent to a portion of each of the first set of electrodes such that the second set of electrodes is capacitively coupled to the first set of electrodes, the first measurement related to the first drive signal;

comparing the first measurement to a limit;

determining that the first measurement is within the limit;

in response to determining that the first measurement is within the limit, determining a second measurement associated with a second grouping of electrodes of the second set of electrodes;

comparing the second measurement to the limit;

determining that the second measurement is outside the limit;

in response to determining that the second measurement is outside the limit, determining not to measure an effect of the first drive signal on a third grouping of electrodes of the second set of electrodes; and

in response to determining that the second measurement is outside the limit, causing a second drive signal to be sent to the first grouping of electrodes of the first set of electrodes.

9. The method of claim 8, further comprising:

determining a set of measurements associated with the at least three groupings of electrodes of the second set of electrodes after causing the second drive signal to be sent to the first grouping of electrodes of the first set of electrodes;

determining that the first set of measurements are within the limit; and

in response to determining that the set of measurements are within the limit, determining a location of a touch using the set of measurements.

10. The method of claim 8, wherein:

the limit is an upper limit; and

determining that the second measurement is outside the limit comprises determining that the second measurement is above the upper limit.

11. The method of claim 8, wherein:

the limit is a lower limit; and

determining that the second measurement is outside the limit comprises determining that the second measurement is below the lower limit.

12. The method of claim 8, wherein determining that the second measurement is outside the limit comprises determining that the second measurement is outside a range.

13. The method of claim 8, further comprising:

determining a set of measurements associated with the at least three groupings of electrodes of the second set of electrodes after causing the second drive signal to be sent to the first grouping of electrodes of the first set of electrodes;

determining that the first set of measurements are within the limit; and

in response to determining that the set of measurements are within the limit, causing a third drive signal to be sent to a second grouping of electrodes of the first set of electrodes.

14. The method of claim 8, further comprising causing the discharge of at least one capacitor associated with the second set of electrodes in response to determining that the second measurement is outside the limit.

15. One or more non-transitory electronic storage media comprising code that, when executed, is configured to:

cause a first drive signal to be sent to a first grouping of electrodes of a first set of electrodes, the first set of electrodes arranged in at least three groupings of electrodes, each grouping of the at least three groupings of electrodes of the first set of electrodes extending along a first axis, the at least three groupings of electrodes of the first set of electrodes comprising the first grouping of electrodes of the first set of electrodes;

determine a first measurement associated with a first grouping of electrodes of a second set of electrodes after causing the first drive signal to be sent to the first grouping of electrodes of the first set of electrodes, the second set of electrodes arranged in at least three groupings of electrodes, the at least three groupings of electrodes of the second set of electrodes comprising the first grouping of electrodes of the second set of electrodes, each grouping of the at least three groupings of electrodes of the second set of electrodes extending along a second axis different than the first axis, the first measurement related to the first drive signal, each electrode of the second set of electrodes arranged to have a portion thereof adjacent to a portion of each of the first set of electrodes such that the second set of electrodes is capacitively coupled to the first set of electrodes;

compare the first measurement to a limit;

determine that the first measurement is within the limit;

in response to determining that the first measurement is within the limit, determine a second measurement associated with a second grouping of electrodes of the second set of electrodes;

compare the second measurement to the limit;

determine that the second measurement is outside the limit;

in response to determining that the second measurement is outside the limit, determine not to measure an effect of the first drive signal on a third grouping of electrodes of the second set of electrodes; and

in response to determining that the second measurement is outside the limit, cause a second drive signal to be sent to the first grouping of electrodes of the first set of electrodes.

16. The media of claim 15, wherein the code is further configured to:

determine a set of measurements associated with the at least three groupings of electrodes of the second set of electrodes after causing the second drive signal to be sent to the first grouping of electrodes of the first set of electrodes;

determine that the first set of measurements are within the limit; and

in response to determining that the set of measurements are within the limit, determining a location of a touch using the set of measurements.

17. The media of claim 15, wherein:

the limit is an upper limit; and

the code is configured to determine that the second measurement is outside the limit by determining that the second measurement is above the upper limit.

18. The media of claim 15, wherein:

the limit is a lower limit; and

the code is configured to determine that the second measurement is outside the limit by determining that the second measurement is below the lower limit.

19. The media of claim 15, wherein the code is configured to determine that the second measurement is outside the limit by determining that the second measurement is outside a range.

20. The media of claim 15, wherein the code is further configured to:

determine a set of measurements associated with the at least three groupings of electrodes of the second set of electrodes after causing the second drive signal to be sent to the first grouping of electrodes of the first set of electrodes;

determine that the first set of measurements are within the limit; and

in response to determining that the set of measurements are within the limit, cause a third drive signal to be sent to a second grouping of electrodes of the first set of electrodes.

21. The media of claim 15, wherein the code is further configured to cause discharging at least one capacitor associated with the second set of electrodes in response to determining that the second measurement is outside the limit.