Noise Reduction in Capacitive Touch Sensors

• US 20100139991A1
• Filed: 10/21/2008
• Published: 06/10/2010
• 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: Philipp, Harald, Yilmaz, Esat
• Granted Patent: US 8,605,037 B2
• Time in Patent Office: Days
• US Class Current: 178/18.60
• 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 capacitive touch sensor for detecting proximity and location of a body, the sensor comprising:

one or multiple X lines;

a plurality of Y lines each arranged to have a portion thereof adjacent to a portion of each of the X lines to form a plurality of sensing capacitors;

a charge measurement capacitor connected to each Y line;

one or more drive circuits arranged to drive respective ones of the X lines to enable charge transfer from the sensing capacitors associated with that X line to the respective measurement capacitors connected to the Y lines; and

a controller operable to actuate respective ones of the X lines via their respective drive circuits, and to measure a signal value from each of the measurement capacitors indicative of the amount of charge transferred, the controller being configured such that, when seeking to measure a set of Y signal values from a particular X line, a test is applied to at least the first Y signal value measured which tests if the Y signal value has a magnitude lying outside an acceptable range, wherein responsive to said test, if the Y signal value lies outside the acceptable range, then the same X line is re-actuated to initiate another charge transfer into the measurement capacitors for that X line.

2. The sensor of claim 1, wherein said test is applied only to the first Y signal value measured.

3. The sensor of claim 1, wherein the acceptable range has an upper limit, so that any signal value above the upper limit is deemed to be unacceptable.

4. The sensor of claim 1, wherein the acceptable range has a lower limit, so that any signal value below the lower limit is deemed to be unacceptable.

5. The sensor of claim 1, wherein the acceptable range has a lower limit and an upper limit, so that any signal value below the lower limit or above the upper limit is deemed to be unacceptable.

6. The sensor of claim 1, wherein, if the test establishes that the Y signal value lies outside the acceptable range, then the controller does not measure any other as-yet unmeasured Y signal values from the same set.

7. The sensor of claim 1, wherein, if the test establishes that the Y signal value lies outside the acceptable range, then the controller discharges all the measurement capacitors in preparation for a new charge transfer.

8. A method of detecting proximity and location of a body to a touch panel with a capacitive touch sensor comprising:

one or multiple X lines and a plurality of Y lines, each Y line being arranged to have a portion thereof adjacent to a portion of each of the X lines to form a plurality of sensing capacitors;

a charge measurement capacitor connected to each Y line;

one or more drive circuits arranged to drive respective ones of the X lines; and

a controller operable to measure signal values from the charge measurement capacitors, the method comprising;

a) driving one of the X lines to enable charge transfer from the sensing capacitors associated with that X line to the respective measurement capacitors connected to the Y lines;

b) measuring a signal value from one of the measurement capacitors; and

c) testing if the Y signal value has a magnitude lying within an acceptable range, and if not re-driving the same X line to initiate another charge transfer into the measurement capacitors for that X line.

9. The method of claim 8, wherein step b) is applied only to the first Y signal value measured from a given X line.