Method for controlling a capacitive touch pad

• US 9,542,035 B2
• Filed: 01/08/2015
• Issued: 01/10/2017
• 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): Hollington, Jermele M
• Assistant Examiner(s): DICKINSON, DUSTIN R
• Application Number:
  US14/592,194
• Publication Number:
  US 20150123943A1
• Time in Patent Office: 733 Days
• US Class Current: 1/1
• 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 device, comprising:

a capacitive touch pad proximity sensor having a first and a second sensor terminal;

a sampling capacitor having a first and a second sampling capacitor terminal, the first and second sampling capacitor terminals selectively coupled to the first and second sensor terminals, respectively;

a charge transfer circuit that includes;

a first voltage source;

a second voltage source at a lower voltage than the first voltage source, both the first and second voltage source at voltages greater than a ground voltage;

a first transistor coupled between the first voltage source and the first sampling capacitor terminal;

a second transistor coupled between the second voltage source and the second sampling capacitor terminal, the first and second transistor configured to pre-charge the sampling capacitor before the sampling capacitor is selectively coupled to the capacitive touch pad proximity sensor; and

a comparator coupled to the first sampling capacitor terminal and configured to compare a voltage on the first sampling capacitor terminal with a reference voltage.

2. The device of claim 1 wherein the first and second transistor are configured to pre-charge the capacitive touch pad proximity sensor before the sampling capacitor is selectively coupled to the capacitive touch pad proximity sensor.

3. The device of claim 1 wherein the capacitive touch pad proximity sensor includes a plurality of electrode rows and a plurality of electrode columns transverse to the plurality of electrode rows, the plurality of electrode rows and plurality of electrode columns creating a plurality of intersections that form a plurality of touch screen capacitors, a number of the touch screen capacitors of the plurality of touch screen capacitors being selectively coupled in turn to the sampling capacitor.

4. The device of claim 1 wherein the capacitive touch pad proximity sensor includes a plurality of triangular electrodes.

5. The device of claim 4 wherein the plurality of triangular electrodes are arranged in groups of four, the groups of four being arranged in rows and columns.

6. The device of claim 4 wherein the plurality of triangular electrodes are arranged in groups of four triangular electrodes where a point of each of the four triangular electrodes is facing a center of the respective group.

7. The device of claim 1 wherein the capacitive touch pad proximity sensor includes a first elongated electrode having a plurality of openings and a plurality of second electrodes, each second electrode positioned in one of the plurality of openings of the first elongated electrode.

8. A system, comprising:

a plurality of first electrodes;

a plurality of second electrodes;

a first electrode terminal coupled to at least one of the first electrodes;

a second electrode terminal coupled to at least one of the second electrodes;

a sampling capacitor having a first and a second sampling capacitor terminal, the first and second sampling capacitor terminals selectively coupled to the first and second electrode terminals, respectively;

a charge transfer circuit that includes;

a first voltage source;

a second voltage;

a first transistor coupled between the first voltage source and the first sampling capacitor terminal;

a second transistor coupled between the second voltage source and the second sampling capacitor terminal; and

a comparator coupled to the first sampling capacitor terminal and configured to compare a voltage on the first sampling capacitor terminal with a reference voltage.

9. The system of claim 8 wherein the second voltage source is at a lower voltage than the first voltage source and both the first and second voltage source are at voltages greater than a ground voltage.

10. The system of claim 8 wherein the first and second transistor are configured to pre-charge the sampling capacitor before the sampling capacitor is selectively coupled to the capacitive touch pad proximity sensor.

11. The system of claim 8 wherein the first and second transistor are configured to pre-charge the capacitive touch pad proximity sensor before the sampling capacitor is selectively coupled to the capacitive touch pad proximity sensor.

12. The system of claim 8 wherein the capacitive touch pad proximity sensor includes a plurality of electrode rows and a plurality of electrode columns transverse to the plurality of electrode rows, the plurality of electrode rows and plurality of electrode columns creating a plurality of intersections that form a plurality of touch screen capacitors, a number of the touch screen capacitors of the plurality of touch screen capacitors being selectively coupled in turn to the sampling capacitor.

13. The system of claim 8 wherein the capacitive touch pad proximity sensor includes a plurality of triangular electrodes arranged in groups of four, the groups of four being arranged in rows and columns.

14. The system of claim 8 wherein the capacitive touch pad proximity sensor includes a first elongated electrode having a plurality of openings and a plurality of second electrodes, each second electrode positioned in one of the plurality of openings of the first elongated electrode.

15. A device, comprising:

a plurality of pair of electrodes, each pair of electrodes having a first electrode terminal and a second electrode terminal;

a charge-transfer circuit, that includes;

a first voltage source;

a second voltage source at a lower voltage than the first voltage source, both the first and second voltage source at voltages greater than or equal to a ground voltage;

a sampling capacitor that is coupled between the first voltage source and the second voltage source and is configured to be charged by the first and second voltage sources, the sampling capacitor being configured to transfer charge from each pair of electrodes, the sampling capacitor having a first and a second sampling capacitor terminal, the first and second sampling capacitor terminals selectively coupled to ones of the first and second electrode terminals, respectively; and

a comparator coupled to the first sampling capacitor terminal and configured to compare a voltage on the first sampling capacitor terminal with a reference voltage.

16. The device of claim 15, further comprising a location detector configured to determine a position of an object on with respect to the plurality of pairs of electrodes according to an output of the comparator.

17. The device of claim 15 wherein the charge transfer circuit that includes a first transistor coupled between the first voltage source and the first sampling capacitor terminal and a second transistor coupled between the second voltage source and the second sampling capacitor terminal, the first and second transistor configured to pre-charge the sampling capacitor before the sampling capacitor is selectively coupled to the capacitive touch pad proximity sensor.