Directional capacitive proximity sensor

• US 9,118,330 B2
• Filed: 12/01/2011
• Issued: 08/25/2015
• 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, Troise, Cyril, Teissier, Maxime
• Primary Examiner(s): NATALINI, JEFF WILLIAM
• Application Number:
  US13/309,411
• Publication Number:
  US 20120139562A1
• Time in Patent Office: 1,363 Days
• Field of Search: 324/679
• US Class Current: 1/1
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• 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 3/0443 using a single layer of sensing 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 2017/9604 characterised by the number of electrodes
• CPC Class Codes: H03K 2217/960725 Charge-transfer
• CPC Class Codes: H03K 2217/960765 Details of shielding arrangements
• CPC Class Codes: H03K 2217/96078 Sensor being a wire or a strip, e.g. used in automobile door handles or bumpers

Abstract

The present disclosure relates to a method for detecting an object near an electronic system, comprising steps of: forming electrodes around a central area, on an electrically insulating medium, determining measurements representative of the capacitance of the electrodes, and comparing the measurements with a detection threshold, and deducing whether or not an object is near the central area in a detection, the electrically insulating medium on which the electrodes are formed being deposited on an electrically conductive medium forming a shield, the capacitance measurements being taken by simultaneously activating all the electrodes.

Claims

1. A method, comprising:

detecting an object near an electronic system that includes an electrically conductive medium forming a shield, an electrically insulating medium on the electrically conductive medium, and electrodes around a central area and on the electrically insulating medium, the detecting including;

determining measurements representative of a capacitance on the electrodes, the determining for each measurement representative of capacitance including;

executing a number of charge and transfer cycles of charging the electrodes and of transferring the charge between the electrodes and a sampling capacitor, and

monitoring the number of charge and transfer cycles and a voltage across terminals of the sampling capacitor;

comparing the measurements representative of capacitance with a detection threshold; and

deducing whether an object is near the central area in a detection field based on the comparing,

wherein the determining includes simultaneously activating all the electrodes.

2. The method according to claim 1, further comprising defining the detection threshold so as to detect an object at a distance of at least several centimeters along an axis perpendicular to the central area and passing through a point of the central area, located at an equal distance from opposite pairs of electrodes of the electrodes.

3. The method according to claim 1, comprising generating a voltage greater than a supply voltage of the electronic system, wherein the determining includes using the voltage generated to determine the measurements representative of the capacitance on the electrodes.

4. The method according to claim 1, wherein the determining includes, for each measurement representative of the capacitance of the electrodes:

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

applying a third voltage to a first group of the electrodes, and the second voltage to a second group of the electrodes, not comprising the electrodes of the first group, wherein the second voltage is between the first and third voltages and the third voltage is greater than or equal to a ground voltage;

transferring electric charges between the electrodes and the sampling capacitor by linking the electrodes of the first group to the first terminal of the sampling capacitor and applying the second voltage to the electrodes of the second group and to the second terminal of the sampling capacitor;

executing a fixed number of cycles of the applying the third voltage and transferring the electric charges; and

determining the measurement representative of the capacitance of the electrodes as a function of a voltage of the sampling capacitor after executing the fixed number of cycles.

5. The method according to claim 1, wherein the determining includes, for each measurement representative of the capacitance of the electrodes:

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

applying a third voltage to a first group of the electrodes, and the second voltage to a second group of the electrodes, not comprising the electrodes of the first group, wherein the second voltage is between the first and third voltages and the third voltage is greater than or equal to a ground voltage;

transferring electric charges between the electrodes and the sampling capacitor by linking the electrodes of the first group to the first terminal of the sampling capacitor and applying the second voltage to the electrodes of the second group and to the second terminal of the sampling capacitor;

executing a plural number of cycles of the applying the third voltage and transferring the electric charges; and

determining the measurement representative of the capacitance of the electrodes as a function of the number of cycles executed until a voltage of the sampling capacitor reaches a threshold voltage.

6. A method, comprising:

detecting an object near an electronic system that includes an electrically conductive medium forming a shield, an electrically insulating medium on the electrically conductive medium, and electrodes around a central area and on the electrically insulating medium, the detecting including;

determining measurements representative of a capacitance on the electrodes, the determining for each measurement representative of capacitance including;

executing a fixed number of charge and transfer cycles of charging the electrodes and of transferring the charge between the electrodes and a sampling capacitor, and

determining the measurement representative of the capacitance on the electrodes according to the voltage at terminals of the sampling capacitor after the fixed number of the charge and transfer cycles;

comparing the measurements representative of capacitance with a detection threshold; and

deducing whether an object is near the central area in a detection field based on the comparing, the determining includes simultaneously activating all the electrodes.

7. The method of claim 6, further comprising:

precharging the sampling capacitor with a source voltage before executing a fixed number of charge and transfer cycles.

8. The method of claim 7, further comprising:

generating the source voltage from a supply voltage with a buffer circuit, the source voltage greater than the supply voltage.

9. A proximity detection device, comprising:

a central structure;

an electrically insulating medium having a first surface facing a detection field, a second surface opposite the first surface, and an outer side surface extending between the first surface and the second surface and being transverse to the first and second surfaces, the electrically insulating medium laterally surrounding the central structure;

electrode positioned laterally around and spaced from the central structure, the electrodes being positioned in the electrically insulating medium;

an electrically conductive shield laterally surrounding the central structure and the insulating medium, the electrically conductive shield having a first portion and a second portion that is transverse to the first portion, the second portion being on the second surface of the electrically insulating medium and the first portion being on the outer side surface of the electrically insulating medium, the first portion of the shield being separated from the central structure by the insulating medium;

a control circuit configured to control the electrodes, determine measurements representative of a capacitance on the electrodes, compare the measurements with a detection threshold, and deduce whether an object is near the central area in a detection field based on comparing the measurements with the detection threshold.

10. The device according to claim 9, wherein the control circuit is configured to determine the capacitance measurements by simultaneously activating all the electrodes.

11. The device according to claim 9, wherein the detection threshold is such that the control device is configured to detect an object at a distance of at least several centimeters along an axis perpendicular to the central structure and passing through a point of the central structure, located at an equal distance from opposite pairs of electrodes of the electrodes.

12. The device according to claim 9, wherein the first portion of the electrically conductive shield extends past the first surface of the electrically insulating medium towards the detection field.

13. The device according to claim 9, further comprising:

a second electrically insulating medium between the electrodes and the electrically conductive shield.

14. The device according to claim 9, comprising a buffer circuit configured to generate, from a supply voltage, a boosted voltage greater than the supply voltage, the control circuit being configured to use the boosted voltage to determine at least one of the measurements representative of the capacitance on the electrodes.

15. The device according to claim 9, wherein the shield is connected to a ground voltage.

16. The device according to claim 9, further comprising a sampling capacitor, wherein the control circuit is configured to:

execute several cycles of charging the electrodes and of transferring charge between the electrodes and the sampling capacitor, and

determine one of the measurements representative of the capacitance on the electrodes according to how many of the cycles are used to obtain a voltage at terminals of the sampling capacitor that reaches a threshold voltage.

17. The device according to claim 9, further comprising a sampling capacitor, wherein the control circuit is configured to:

apply a first voltage to a first terminal of the sampling capacitor and a second voltage to a second terminal of the sampling capacitor,

apply a third voltage to a first group of the electrodes, and the second voltage to a second group of the electrodes, not comprising the electrodes of the first group, wherein the second voltage is between the first and third voltages and the third voltage is greater than or equal to a ground voltage;

link the electrodes of the first group to the first terminal of the sampling capacitor and applying the second voltage to the electrodes of the second group and to the second terminal of the sampling capacitor, to transfer electric charges between the electrodes and the sampling capacitor,

execute a fixed number cycles of the applying the third voltage and linking the electrodes; and

determine one of the measurements representative of the capacitance on the electrodes as a function of a voltage of the sampling capacitor after executing the fixed number of cycles.

18. The device according to claim 9, wherein the electrodes include first and second electrodes extending longitudinally along opposite first and second sides of the central structure and third and fourth electrodes extending longitudinally along opposite third and fourth sides of the central structure, the first and second sides of the central structure being transverse with respect to the third and fourth sides of the central structure.

19. An electronic system comprising:

system electronics; and

a proximity detection device coupled to the system electronics and including;

a central structure;

an electrically insulating medium having a first surface facing a detection field, a second surface opposite the first surface, and an outer side surface extending between the first surface and the second surface and being transverse to the first and second surfaces, the electrically insulating medium laterally surrounding the central structure;

electrodes positioned laterally around and spaced from the central structure, the electrodes being positioned in the electrically insulating medium;

an electrically conductive shield laterally surrounding the central structure and the insulating medium, the electrically conductive shield having a first portion and a second portion that is transverse to the first portion, the second portion being on the second surface of the electrically insulating medium and the first portion being on the outer side surface of the electrically insulating medium, the first portion of the shield being separated from the central structure by the insulating medium;

a control circuit configured to control the electrodes, determine measurements representative of a capacitance on the electrodes, compare the measurements with a detection threshold, and deduce whether an object is near the central area in a detection field based on comparing the measurements with the detection threshold.

20. The system according to claim 19, wherein the control circuit is configured to determine the capacitance measurements by simultaneously activating all the electrodes.

21. The system according to claim 19, wherein the first portion of the electrically conductive shield extends past the first surface of the electrically insulating medium towards the detection field.

22. The system according to claim 19, further comprising:

a second electrically insulating medium between the electrodes and the electrically conductive shield.

23. The system according to claim 19, wherein the detection device is configured to generate, from a supply voltage, a boosted voltage greater than the supply voltage, and the control circuit is configured to use the boosted voltage to determine at least one of the measurements representative of the capacitance on the electrodes.

24. The system according to claim 19, wherein the detection device includes a sampling capacitor, wherein the control circuit is configured to:

execute a fixed number of cycles of charging the electrodes and of transferring charge between the electrodes and the sampling capacitor, and

determine one of the measurements representative of the capacitance on the electrodes according to a voltage at terminals of the sampling capacitor after the fixed number of cycles.

25. The system according to claim 19, wherein the detection device includes a sampling capacitor, wherein the control circuit is configured to:

apply a first voltage to a first terminal of a sampling capacitor and a second voltage to the second terminal of the sampling capacitor;

apply a third voltage to a first group of the electrodes, and the second voltage to a second group of the electrodes, not comprising the electrodes of the first group, wherein the second voltage is between the first and third voltages and the third voltage is greater than or equal to a ground voltage;

link the electrodes of the first group to the first terminal of the sampling capacitor and applying the second voltage to the electrodes of the second group and to the second terminal of the sampling capacitor, to transfer electric charges between the electrodes and the sampling capacitor,

execute several cycles of the applying the third voltage and linking the electrodes; and

determine one of the measurements representative of the capacitance on the electrodes as a function of how many of the cycles are used to obtain a voltage at a terminal of the sampling capacitor reaches a threshold voltage.

26. The system according to claim 19, wherein the electrodes include first and second electrodes extending longitudinally along opposite first and second sides of the central structure and third and fourth electrodes extending longitudinally along opposite third and fourth sides of the central structure, the first and second sides of the central structure being transverse with respect to the third and fourth sides of the central structure.

27. A proximity detection device comprising:

a central structure;

a plurality of electrodes laterally surrounding the central structure;

an electrically conductive shield that includes a conductive frame completely laterally surrounding the plurality of electrodes and the central structure;

an insulating medium that insulates the electrodes from the shield, the insulating medium including a first surface facing a detection field, a second surface opposite to the first surface, and an outer side surface between the first surface and the second surface and being transverse to the first and second surfaces, the shield being on the second surface and on the outer side surface of the insulating medium; and

a controller configured to make measurements representative of a capacitance on the electrodes and determine whether an object is within the detection field based on the measurements.

28. The device according to claim 27, wherein the electrodes include first and second electrodes extending longitudinally along opposite first and second sides of the central structure and third and fourth electrodes extending longitudinally along opposite third and fourth sides of the central structure, the first and second sides of the central structure being transverse with respect to the third and fourth sides of the central structure.

29. The device according to claim 27, wherein the electrodes are completely enclosed within the insulating medium.

30. The device according to claim 27, wherein the frame of the shield includes a lower portion on which the insulating medium and electrodes are positioned and an outer portion that completely laterally surrounds the electrodes.