Capacitive touch pad configured for proximity detection

• US 8,704,797 B2
• Filed: 12/01/2011
• Issued: 04/22/2014
• Est. Priority Date: 12/01/2010
• Status: Active Grant

• Current Assignee: Stmicroelectronics Rousset SAS (STMicroelectronics NV)
• Original Assignee: Stmicroelectronics Rousset SAS (STMicroelectronics NV)
• Inventors: Beyly, Laurent, Teissier, Maxime, Troise, Cyril
• Primary Examiner(s): Boddie, William
• Assistant Examiner(s): ONYEKABA, AMY
• Application Number:
  US13/309,284
• Publication Number:
  US 20120139870A1
• Time in Patent Office: 873 Days
• Field of Search: 345/173, 345/174, 178/18.01, 178/18.03, 178/18.04, 178/18.06
• US Class Current: 345/174
• CPC Class Codes: G06F 2203/04101 2.5D-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 and also measures the distance of the input means within a short range in the Z direction, possibly with a separate measurement setup
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• 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 controlling a touch pad, comprising an object locate mode for locating an object on the touch pad comprising steps of: determining a measurement of capacitance of each of the pairs of electrodes of the touch pad, each pair comprising a row electrode and a column electrode transverse to the row electrode, comparing each measurement with a first detection threshold, and if the comparison of at least one measurement with the first threshold reveals the presence of an object on the touch pad, locating the object on the touch pad according to the capacitance measurements, the method comprising a proximity detection mode comprising steps of: determining a measurement representative of the capacitance between one or two electrodes and one or two other electrodes of the touch pad, and comparing a measurement obtained with a second detection threshold different from the first threshold.

Claims

1. A method, comprising:

controlling a touch pad having a plurality of row electrodes transverse to a plurality of column electrodes, the controlling including;

executing an object locate mode, the executing of the object locate mode including;

determining a plurality of first capacitances between a plurality of pairs of electrodes, each pair of electrodes including one of the row electrodes that overlaps one of the column electrodes;

determining a presence of an object within a first distance of the touch pad by comparing each of the first capacitances with a first detection threshold; and

determining a position of the object with respect to the touch pad by analyzing the first capacitances;

executing a proximity detection mode, the executing of the proximity detection mode including;

determining a second capacitance between a first electrode and a second electrode of the touch pad, the first electrode being one of the row electrodes positioned at an edge of the touch pad and the second electrode being one of the column electrodes positioned at the edge of the touch pad;

determining a third capacitance between the second electrode and a third electrode that is one of the row electrodes at opposite edge of the touch pad from the first electrode and a fourth capacitance between the third electrode and a fourth electrode that is one of the column electrodes at an opposite edge of the touch pad from the second electrode, and a fifth capacitance between the first electrode and the fourth electrode; and

determining the presence of the object within a second distance of the touch pad by comparing the second capacitance with a second detection threshold, the second threshold being different from the first detection threshold.

2. The method according to claim 1 wherein the second detection threshold is larger than the first detection threshold.

3. The method according to claim 1, wherein the determining of the second, third, fourth, and fifth capacitance is performed concurrently.

4. The method according to claim 1, wherein the determining the second, third, fourth, and fifth capacitance is performed sequentially.

5. The method according to claim 1, wherein the determining of the first capacitances of the pairs of electrodes of the touch pad includes:

executing a first number of cycles of charging the capacitances on the pairs of electrodes and transferring the charge from the capacitances on the pairs of electrodes to a sampling capacitor; and

determining the first capacitances on the pairs of electrodes by analyzing the first number of cycles of charging and transferring so that a voltage at a terminal of the sampling capacitor exceeds a threshold voltage.

6. The method according to claim 1, wherein the determining of the first capacitances of the pairs of electrodes of the touch pad includes:

executing a first number of cycles of charging the capacitances on the pairs of electrodes and transferring the charge from the capacitances on the pairs of electrodes to a sampling capacitor;

determining the first capacitances on the pairs of electrodes by analyzing a voltage at a terminal of the sampling capacitor, after the first number of cycles of charging and transferring.

7. The method according to claim 1, wherein the determining of the first capacitances on the plurality of pairs of electrodes of the touch pad includes:

applying a first voltage to a first terminal of a sampling capacitor and a second voltage to a second terminal of the sampling capacitor, the second voltage being in between the first voltage and a third voltage that is greater than or equal to a ground voltage;

applying the third voltage to a first electrode of the pairs of electrodes, and the second voltage to the second electrode of the pairs of electrodes;

transferring electric charges between the first and second electrodes of the pairs of electrodes and the sampling capacitor by coupling the first electrode to the first terminal of the sampling capacitor and coupling the second voltage to the second electrode and to the second terminal of the sampling capacitor;

executing a first number of cycles of the applying and transferring; and

after executing the first number of cycles determining the first capacitances between the first and the second electrode of the pairs of electrodes as a function of the voltage at the first terminal of the sampling capacitor, the second terminal receiving the third voltage.

8. The method according to claim 7, wherein the first voltage is equal to a supply voltage and the second voltage is in the order of the first voltage divided by two, and the third voltage is equal to the ground voltage.

9. The method according to claim 7, wherein the proximity detection mode uses a sampling capacitor having a higher capacitance than that of the sampling capacitor used in the object locate mode.

10. The method according to claim 1, wherein the determining the first capacitances on the plurality of pairs of electrodes of the touch pad includes:

applying a first voltage to a first terminal of a sampling capacitor and a second intermediate voltage to a second terminal of the sampling capacitor, the second intermediate voltage being in between the first voltage and a third voltage that is greater than or equal to a ground voltage;

applying the third voltage to a first electrode of the pairs of electrodes, and the second voltage to the second electrode of the pairs of electrodes;

transferring electric charges between the first and second electrodes of the pairs of electrodes and the sampling capacitor by coupling the first electrode to the first terminal of the sampling capacitor and coupling the second voltage to the second electrode and to the second terminal of the sampling capacitor;

executing a first number of cycles of the applying and transferring; and

determining the first capacitances on the pairs of electrodes by determining the first number of cycles executed so that a voltage at the first terminal of the sampling capacitor reaches a threshold voltage.

11. A device, comprising:

a touch pad, having a plurality of electrodes disposed in rows and in columns that are transverse to the rows;

an object detection circuit configured to manage the touch pad, the detection circuit being configured to operate in an object locate mode and a proximity detection mode, wherein;

the object detection circuit is configured in the object locate mode to;

determine a plurality of first capacitances on each of a plurality of pairs of electrodes of the touch pad, each pair of electrodes having a row electrode and a column electrode;

compare the first capacitances with a first detection threshold, the first detection threshold configured to detect a presence of an object within a first distance of the touch pad; and

determine a position of the object with respect to the touch pad based on the first capacitances that detected the presence of the object;

the object detection circuit is configured in the proximity detection mode to;

determine a second capacitance between a first electrode and a second electrode of the touch pad, the first electrode being one of the row electrodes positioned at an edge of the touch pad and the second electrode being one of the column electrodes positioned at the edge of the touch pad;

determine a third capacitance between the second electrode and a third electrode that is one of the row electrodes at opposite edge of the touch pad from the first electrode and a fourth capacitance between the third electrode and a fourth electrode that is one of the column electrodes at an opposite edge of the touch pad from the second electrode, and a fifth capacitance between the first electrode and the fourth electrode; and

compare the second capacitance with a second detection threshold, the second detection threshold configured to detect the presence of the object within a second distance of the touch pad the second detection threshold being different from the first detection threshold.

12. The device according to claim 11, wherein the detection circuit in the proximity detection mode is configured to determine the second, third, fourth, and fifth capacitances sequentially.

13. The device according to claim 11, wherein the detection circuit in the object locate mode is configured to:

generate a charge on the pairs of electrodes and transfer the charge from the pairs of electrodes to a sampling capacitor for a first number of cycles; and

determine the first capacitances of the pairs of electrodes to determine the presence of the object based on a first terminal of the sampling capacitor reaching the first detection threshold.

14. The device according to claim 13, wherein the detection circuit in the object locate mode is configured to:

apply a first voltage to the first terminal of the sampling capacitor and a second voltage to a second terminal of the sampling capacitor, the second voltage being in between the first voltage and a third voltage greater than or equal to a ground voltage;

apply the third voltage to a first electrode of one of the pairs of electrodes and the second voltage to a second electrode of one of the pairs of electrodes;

couple the first electrode of one of the pairs of electrodes to the first terminal of the sampling capacitor and couple the second electrode of one of the pairs of electrodes to the second terminal of the sampling capacitor, to transfer the charges between the first and second electrodes and the sampling capacitor;

execute the first number of cycles that apply and couple; and

after the first number of cycles, determine the first capacitances between the first electrode and the second electrode as a function of the voltage at the first terminal of the sampling capacitor and the second terminal.

15. The device according to claim 14, wherein the first voltage is equal to a supply voltage and the second voltage is in the order of the first voltage divided by two, and the third voltage is equal to the ground voltage.

16. The device according to claim 14, wherein the proximity detection mode is configured to use a second sampling capacitor having a higher capacitance than that of the sampling capacitor used in the object locate mode.

17. The device according to claim 11, further comprising:

a sampling capacitor having a first terminal and a second terminal;

a power port;

a first switch unit;

a second switch unit;

a third switch unit;

an input/output circuit that includes;

a first port coupled to the first terminal of the sampling capacitor, the second terminal of the sampling capacitor being coupled ground;

a first group of ports each coupled to one of the row electrodes of the touch pad, coupled to the first port through the first switch unit, and coupled to the ground through the second switch unit;

a second group of ports each coupled to one of the column electrodes of the touch pad and each coupled to the power port through the third switch unit; and

a control circuit configured to control the first, second and third switch units and to determine from a voltage at the first terminal of the sampling capacitor, the first capacitances of the pairs of electrodes a first electrode of the pair coupled to one of the ports of the first group of ports and a second electrode of the pair coupled to one of the ports of the second group of ports.

18. The device according to claim 11, further comprising:

a power port;

an input/output circuit that includes;

a plurality of switch units;

a sampling capacitor;

a control circuit configured to control the switch units and to determine, with voltage measurements at a first terminal of the sampling capacitor, the first capacitances of the pairs of electrodes;

a first group of ports that include;

a first port configured to receive a voltage lower than a supply voltage;

a plurality of second ports each coupled to one of the electrodes of the touch pad; and

a third port coupled to the first terminal of the sampling capacitor and coupled to the ground through one of the switch units;

a second group of ports that include;

a first port coupled to a second terminal of the sampling capacitor and coupled to the power port through one of the switch units;

a plurality of second ports each coupled to one of the electrodes of the touch pad and each coupled to the ground through one of the switch units; and

a node common coupled to the first and second groups of ports through respective ones of the switch units and the control circuit, a first electrode of the pair of electrodes being coupled to one of the ports of the first group of ports and the second electrode being coupled to one of the ports of the second group of ports.

19. The device according to claim 18, further comprising:

a second sampling capacitor;

wherein the input/output circuit includes at least three groups of ports each coupled to the common node through a respective one of the switch units controlled by the control circuit, one port of one of the groups of ports being coupled to a first terminal of the second sampling capacitor, a second terminal of the second sampling capacitor being coupled to a port of another respective group of ports.

20. The device according to claim 19, wherein the control circuit is configured to control the switch units so as to execute the first number of cycles to generate a charge between the pairs of electrodes and to transfer the charge between the pairs of electrodes and the sampling capacitor, and to compare with a threshold the voltage at the first terminal of the sampling capacitor until the compared voltage reaches the threshold, the first capacitances to be measured being determined according to the first number of cycles executed.

21. The device according to claim 19, wherein the control circuit is configured to control the switch units so as to execute the first number of cycles to generate a charge on the pairs of electrodes and to transfer the charge between the pairs of electrodes and the sampling capacitor, and to measure the voltage at a terminal of the sampling capacitor, the first capacitances being determined according to the voltage measured.

22. A processor, comprising:

a device configured to manage a touch pad that has a plurality of electrodes disposed in rows and in columns transverse to the rows, the device being configured to operate in an object locate mode and a proximity detection mode, wherein;

the device is configured in the object locate mode to;

determine a plurality of first capacitances of each of a plurality of pairs of electrodes of the touch pad, each pair of electrodes having a row electrode and a column electrode;

compare each first capacitance with a first detection threshold configured to detect a presence of an object within a first distance of the touch pad; and

determine position of the object with respect to the touch pad from the first capacitances;

the device is configured in the proximity detection mode to;

determine a second capacitance between a first electrode and a second electrode of the touch pad; and

compare the second capacitance with a second detection threshold that is different from the first detection threshold to determine a presence of the object within a second distance of the touch pad; and

wherein the device is further configured in the object locate mode to;

apply a first voltage to a first terminal of a sampling capacitor and a second intermediate voltage to a second terminal of the sampling capacitor, the second voltage being in between the first voltage and a third voltage greater than or equal to a ground voltage;

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

couple the first electrode to the first terminal of the sampling capacitor and couple the second voltage to the second electrode and to the second terminal of the sampling capacitor, to transfer charges between the first and second electrodes and the sampling capacitor; and

execute a first number of cycles to apply and coupler and

after the first number of cycles, determine the first capacitance between the first and the second electrode as a function of a voltage at the first terminal of the sampling capacitor and the second terminal of which receives the third voltage.

23. The processor according to claim 22, wherein the first electrode is one of the row electrodes and the second electrode is one of the column electrodes.

24. The processor according to claim 22, wherein the first and second electrodes are parallel electrodes at opposite edges of the touch pad.

25. The processor according to claim 22, wherein the device is configured in the object locate mode to:

execute the first number of cycles generate a charge on the pairs of electrodes and transfer the charge from the pairs of electrodes to the sampling capacitor; and

determine the first capacitances on the pairs of electrodes according to the first number of cycles, so that a voltage at the first terminal of the sampling capacitor reaches a threshold voltage.

26. The processor according to claim 22, further comprising:

a power port;

an input/output circuit, that includes;

a first switch unit;

a second switch unit;

a third switch unit;

a first port coupled to the first terminal of the sampling capacitor, the second terminal of which is coupled to the ground voltage;

a first group of ports each coupled to a respective one of the electrodes of the touch pad, coupled to the first port through the first switch unit and coupled to the ground voltage through the second switch unit;

a second group of ports each coupled to a respective one of the electrodes of the touch pad and each coupled to the power port of the input/output circuit through the third switch unit, and

a control circuit configured to control the first, second, and third switch units and to determine, with voltage measurements at the first terminal of the sampling capacitor, the first capacitances on the pairs of electrodes wherein a first electrode of the pairs of electrodes is coupled to a port of the first group of ports and a second electrode of the pairs of electrodes is coupled to a port of the second group of ports.

27. The processor according to claim 26, wherein the control circuit is configured to control the switch units so as to execute the first number of cycles to generate the charge on the pairs of electrodes and transfer the charge between the pairs of electrodes to the sampling capacitor, and of compare with a threshold the voltage at a terminal of the sampling capacitor until the compared voltage reaches the threshold, the first capacitance to be measured being determined according to the first number of cycles executed.

28. The processor according to claim 26, wherein the control circuit is configured to control the switch units so as to execute the first number of cycles to generate the charge on the pairs of electrodes, and transfer the charge between the pairs of electrodes to the sampling capacitor, and to measure the voltage at a terminal of the sampling capacitor, the first capacitance to be measured being determined according to the voltage measured.

29. The processor according to claim 22, further comprising:

a power port;

an input/output circuit that includes;

a first switch unit;

a second switch unit;

a third switch unit;

a fourth switch unit;

a control circuit configured to control the switch units and to determine, using voltage measurements at the first terminal of the sampling capacitor, the first capacitance of the pairs of electrodes;

a first group of ports that include;

a first port configured to receive a voltage lower than a supply voltage;

a plurality of second ports each coupled to one of the electrodes of the touch pad; and

a third port coupled to the first terminal of the sampling capacitor and coupled to the ground through the first switch unit;

a second group of ports that include;

a first port connected to the second terminal of the sampling capacitor and coupled to the power port through the second switch unit;

a plurality of second ports each coupled to one of the electrodes of the touch pad and each coupled to the ground through the third switch unit; and

a node common to the first and second group of ports through the fourth switch unit, and the control circuit; and

wherein

a first electrode of the pairs of electrodes being coupled to a port of the first group of ports and a second electrode of the pairs of electrodes being coupled to a port of the second group of ports.

30. The processor according to claim 29, wherein the input/output circuit comprises third group of ports coupled to the common node through a fifth switch unit controlled by the control circuit, one port from the first, second, and third group of ports being coupled to a terminal of several sampling capacitors, another terminal of each sampling capacitor being coupled to a port from one of the other groups of ports.

31. A method, comprising:

controlling a touch pad having a plurality of row electrodes transverse to a plurality of column electrodes, the controlling including;

executing an object locate mode, the executing of the object locate mode including;

determining a plurality of first capacitances between a plurality of pairs of electrodes, each pair of electrodes including one of the row electrodes that overlaps one of the column electrodes;

determining a presence of an object within a first distance of the touch pad by comparing each of the first capacitances with a first detection threshold; and

determining a position of the object with respect to the touch pad by analyzing the first capacitances;

executing a proximity detection mode, the executing of the proximity detection mode including;

determining a second capacitance using only a first one of the row electrodes and a second one of the row electrodes of the touch pad, the first one of the row electrodes being at an edge of the touch pad, the second one of the row electrodes being at a center of the touch pad wherein the first one of the row electrodes is not adjacent to the second one of the row electrodes; and

determining the presence of the object within a second distance of the touch pad by comparing the second capacitance with a second detection threshold, the second threshold being different from the first detection threshold.

32. The method of claim 31, further comprising a third electrode that is one of the row electrodes at an opposite edge of the touch pad from the first electrode and the executing of the proximity detection mode includes determining a third capacitance between the second electrode and a third electrode.