Method for controlling a capacitive touch pad

• US 8,952,709 B2
• Filed: 12/01/2011
• Issued: 02/10/2015
• Est. Priority Date: 12/01/2010
• Status: Active Grant

• Current Assignee: STMicroelectronics SAS (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SAS (STMicroelectronics NV)
• Inventors: Teissier, Maxime, Beyly, Laurent, Troise, Cyril
• Primary Examiner(s): Natalini, Jeff
• Assistant Examiner(s): DICKINSON, DUSTIN R
• Application Number:
  US13/309,413
• Publication Number:
  US 20120139563A1
• Time in Patent Office: 1,167 Days
• Field of Search: 324/658, 324/663, 324/672, 324/674, 324/676, 324/678, 324/679, 324/681, 324/684, 324/686
• US Class Current: 324/678
• CPC Class Codes: G06F 2203/04108 Touchless 2D- digitiser, i.e. digitiser detecting the X/Y position of the input means, finger or stylus, also when it does not touch, but is proximate to the digitiser's interaction surface without distance measurement in the Z direction
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers
• 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 17/955 using a capacitive detector
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2217/960725 Charge-transfer

Abstract

The present disclosure relates to a method for measuring a capacitance of a pair of electrodes including charging the pair of electrodes and transferring the charge between the pair of electrodes and a sampling capacitor, and a measuring step representative of the capacitance of the pair of electrodes according to the voltage at the terminals of the sampling capacitor according to the number of cycles executed so that the voltage at the terminals of the sampling capacitor reaches a threshold voltage. According to the present disclosure, the method comprises an initial step of charging the sampling capacitor between a first voltage and a second intermediate voltage in between the first voltage and a third voltage greater than or equal to a ground voltage, the pair of electrodes being charged between the second voltage and the third voltage. The present disclosure applies in particular to the control of a touch pad.

Claims

1. A method, comprising:

measuring a capacitance on a pair of electrodes, the measuring including;

performing plural cycles of charging the pair of electrodes and transferring charge between the pair of electrodes and a sampling capacitor;

measuring a quantity representative of the capacitance on the pair of electrodes, the measuring including;

measuring a voltage at terminals of the sampling capacitor after executing a fixed number of cycles, or

determining the quantity as a function of the number of cycles performed until the voltage at the terminals of the sampling capacitor reaches a threshold voltage;

prior to the performing, charging the sampling capacitor coupled between a first voltage and a second voltage, the second voltage being less than the first voltage and being greater than a third voltage, the third voltage being greater than or equal to a ground voltage; and

the charging the pair of electrodes including charging the pair of electrodes coupled between the second voltage and the third voltage.

2. The method according to claim 1, wherein:

charging the sampling capacitor includes applying the first voltage to a first terminal of the sampling capacitor, and the second voltage to a second terminal of the sampling capacitor;

charging the pair of electrodes includes applying the third voltage to a first electrode of the pair of electrodes, and the second voltage to a second electrode of the pair of electrodes; and

transferring the charge between the pair of electrodes and the sampling capacitor including establishing an electrical coupling between the first electrode and the first terminal of the sampling capacitor and applying the second voltage to the second electrode and to the second terminal of the sampling capacitor.

3. The method according to claim 1, wherein the first voltage is equal to a supply voltage, the second voltage is approximately equal to half of the first voltage, and the third voltage is equal to the ground voltage.

4. A method, comprising:

controlling a touch pad that includes row electrodes and column electrodes transverse to the row electrodes, the row and column electrodes being arranged in electrode pairs, each electrode pair including a corresponding one of the row electrodes and a corresponding one of the column electrodes, the controlling including;

determining measurements representative of respective capacitances of the electrode pairs of the touch pad, respectively; and

determining a position of an object on the touch pad according to the measurements representative of the capacitances of the electrode pairs of the touch pad, the determining measurements for each electrode pair including;

performing plural cycles of charging the electrode pair and transferring charge between the electrode pair and a sampling capacitor,

measuring a quantity representative of the capacitance on the electrode pair, the measuring including;

measuring a voltage at terminals of the sampling capacitor after executing a fixed number of cycles, or

determining the quantity as a function of the number of cycles executed until the voltage at the terminals of the sampling capacitor reaches a threshold voltage;

prior to performing the plural cycles, charging the sampling capacitor coupled between a first voltage and a second voltage, the second voltage being less than the first voltage and being greater than a third voltage the third voltage being greater than or equal to a ground voltage; and

the charging of the electrode pair includes charging the electrode pair coupled between the second voltage and the third voltage.

5. The method according to claim 4, wherein:

charging the sampling capacitor includes applying the first voltage to a first terminal of the sampling capacitor, and the second voltage to a second terminal of the sampling capacitor;

charging the electrode pair includes applying the third voltage to a first electrode of the electrode pair, and the second voltage to a second electrode of the electrode pair; and

transferring the charge includes establishing an electrical coupling between the first electrode and the first terminal of the sampling capacitor and applying the second voltage to the second electrode and to the second terminal of the sampling capacitor.

6. The method according to claim 4, wherein the first voltage is equal to a supply voltage, the second voltage is approximately equal to half of the first voltage, and the third voltage is equal to the ground voltage.

7. The method according to claim 4, wherein determining the position of the object includes:

comparing each measurement representative of capacitance with a first detection thresholds; and

if the comparison of at least one measurement with the first detection threshold reveals the presence of the object on the touch pad, determining the position of the object on the touch pad as a function of the measurements representative of the capacitances on the electrode pairs of the touch pad.

8. The method according to claim 4, further comprising a proximity detection mode that includes determining measurements of the capacitance on the electrode pairs of electrodes of a group including one to four electrode pairs of the touch pad, and determining an object proximity detection status based on the measurements representative of the capacitance of the electrode pairs of the group.

9. The method according to claim 8, further comprising, in proximity detection mode, detecting the object near the touch pad using the measurement representative of the capacitance on a single one of the electrode pairs.

10. The method according to claim 8, further comprising, in proximity detection mode, detecting the object near the touch pad is detected using the measurements representative of the capacitance on four electrode pairs of the electrode pairs, each of the four electrode pairs being located on an edge of the touch pad.

11. The method according to claim 10, wherein the measurement representative of the capacitance on the four electrode pairs of electrodes is taken in one measurement, or in two or four successive measurements.

12. The method according to claim 8, further comprising, in proximity detection mode, detecting the object near the touch pad using the measurement representative of the capacitance of a single pair of parallel electrodes each located on an edge of the touch pad.

13. The method according to claim 8, wherein, in proximity detection mode, detecting the object near the touch pad using the measurement representative of the capacitance between a central electrode of the touch pad and two other electrodes parallel to the first electrode and each located on an edge of the touch pad.

14. The method according to claim 13, wherein the measurement representative of the capacitance between the central electrode of the touch pad and the two other electrodes is taken in one or in two successive measurements.

15. A device to manage a touch pad that includes row electrodes and column electrodes transverse to the row electrodes, the row and column electrodes being arranged in electrode pairs, each electrode pair including a corresponding one of the row electrodes and a corresponding one of the column electrodes, the device comprising:

a charge-transfer circuit configured to;

charge at least one sampling capacitor that is coupled between a first voltage and a second voltage, the second voltage being less than the first voltage and being greater than a third voltage, the third voltage being greater than or equal to a ground voltage;

perform plural cycles that charge each pair of electrodes coupled between the second voltage and the third voltage and transfer charge between each pair of electrodes and the at least one sampling capacitors; and

measure a quantity representative of a capacitance on each pair of electrodes as a function of a voltage at the at least one sampling capacitor; and

a location detector configured to determine a position of an object on the touch pad according to the measurements representative of the capacitances on the pairs of electrodes of the touch pad.

16. The device according to claim 15, wherein the charge-transfer circuit is configured to:

apply the first voltage to a first terminal of the at least one sampling capacitor, and the second voltage to a second terminal of the at least one sampling capacitor;

apply the third voltage to a first electrode of the pair of electrodes, and the second voltage to a second electrode of the pair of electrodes to charge the pair of electrodes; and

establish an electrical coupling between the first electrode and the first terminal of the at least one sampling capacitor and apply the second voltage to the second electrode and to the second terminal of the at least one sampling capacitor to transfer the charge between the pair of electrodes and the at least one sampling capacitor.

17. The device according to claim 15, wherein the first voltage is equal to a supply voltage, the second voltage is approximately equal to half the first voltage, and the third voltage is equal to the ground voltage.

18. The device according to claim 15, wherein the location detector is configured to compare each measurement representative of capacitance with a detection threshold, and if the comparison of at least one measurement with the first detection threshold reveals the presence of the object on the touch pad, determine a position of the object on the touch pad as a function of the measurements representative of the capacitance on the pairs of electrodes of the touch pad.

19. The device according to claim 15, wherein the charge-transfer circuit is configured, in a proximity detection mode, to determine measurements of the capacitance of pairs of electrodes of a group that includes one to four pairs of electrodes of the touch pad, and the location detector is configured to determine an object proximity detection status as a function of the measurements representative of the capacitance of the pairs of electrodes of the group.

20. The device according to claim 19, wherein the location detector is configured in the proximity detection mode to detect the presence of the object near the touch pad by using the measurement representative of the capacitance on a single one of the electrode pairs.

21. The device according to claim 19, wherein the location detector is configured in the proximity detection mode to detect the presence of the object near the touch pad by using the measurement representative of the capacitance on four pairs of electrodes each located on an edge of the touch pad.

22. The device according to claim 21, wherein the charge-transfer circuit is configured to perform the measurement representative of the capacitance on the four pairs of electrodes in one, or in two or four successive measurements.

23. The device according to claim 19, wherein the location detector is configured in proximity detection mode to detect the presence of the object near the touch pad by using the measurement representative of the capacitance on a single pair of parallel electrodes each located on an edge of the touch pad.

24. The device according to claim 19, wherein the location detector is configured in proximity detection mode to detect the presence of the object near the touch pad by using the measurement representative of the capacitance between a first central electrode of the touch pad and two other electrodes parallel to the first electrode and each located on an edge of the touch pad.

25. The device according to claim 15, wherein the charge-transfer circuit includes:

a first port configured to be coupled to a first terminal of the sampling capacitor, the sampling capacitor having a second terminal coupled to ground;

a first group of ports configured to be coupled to respective first electrodes of the touch pad;

a first plurality of switch units respectively coupled to the ports of the first group to the first port;

a second plurality of switch units respectively coupled between the first port and ground;

a second group of ports configured to be coupled to respective second electrodes of the touch pad;

a third plurality of switch units respectively coupled to the ports of the second group and configured to couple the second group of ports to a supply voltage source; and

a control circuit configured to control the switch units and supply from voltage measurements at the at least one sampling capacitor, the measurements corresponding to the capacitance on pairs of electrodes that include one electrode configured to be coupled to a port of the first group of ports and one electrode configured to be coupled to a port of the second group of ports.

26. The device according to claim 15, wherein the charge-transfer circuit includes:

a first group of ports that include a first port, configured to receive a reference voltage that is coupled between a supply voltage and ground, plural ports configured to be coupled to respective first electrodes of the touch pad, and a second port configured to be coupled to a first terminal of a first sampling capacitor;

a plurality of first switch units configured to respectively couple the ports of the first group to a first common node;

a second group of ports that include a third port, configured to be coupled to a second terminal of the first sampling capacitor, and plural ports configured to be coupled to respective second electrodes of the touch pad;

a plurality of second switch units configured to respectively couple the ports of the second group to a second common node; and

a control circuit configured to control the switch units and supply from voltage measurements at one of the terminals of the sampling capacitor, the measurements corresponding to the capacitance of pairs of electrodes that each include one electrode configured to be coupled to a port of the first group of ports and one electrode configured to be coupled to a port of the second group of ports.

27. The device according to claim 26, further comprising:

a third groups of ports that include a fourth port, configured to be coupled to a second terminal of the second sampling capacitor, and plural ports configured to be coupled to respective third electrodes of the touch pad; and

a plurality of third switch units configured to respectively couple the ports of the third group to a third common node.

28. The device according to claim 15, wherein the charge-transfer circuit is configured to compare the charge between the pair of electrodes and the at least one sampling capacitor with a threshold a voltage until the compared voltage reaches the threshold voltage, and measure the quantity representative of the capacitance according to the number of cycles executed.

29. The device according to claim 15, wherein the charge-transfer circuit is configured to execute a fixed number of cycles that charge each pair of electrodes, transfer charge between the pair of electrodes and the at least one sampling capacitor, and measure the voltage at the at least one sampling capacitor to measure the quantity representative of the capacitance according to the voltage measured.