CAPACITIVE PROXIMITY SENSOR WITH ENABLED TOUCH DETECTION

• US 20140002108A1
• Filed: 07/02/2012
• Published: 01/02/2014
• Est. Priority Date: 07/02/2012
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Inventors: Tan, Kien Beng, Soo, Jenn Woei
• Granted Patent: US 9,236,861 B2
• Time in Patent Office: Days
• US Class Current: 324/647
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2217/96074 Switched capacitor
• CPC Class Codes: H03K 2217/960765 Details of shielding arrangements

Abstract

A capacitive proximity sensor circuit capable of distinguishing between instances of detected user proximity includes one or more guard electrodes, a first sensor, and a second sensor. The capacitive proximity sensor is installed in a device such that a first sensor faces a first component of the device, and the second sensor faces a second component of the device. The first and second sensors measure a capacitance to detect proximity of a user relative to the respective sensor. The guard electrode is provided to mitigate stray capacitance to reduce error in the capacitance measurements obtained by the first and second sensors.

Claims

1. A capacitive proximity sensing circuit comprising:

one or more guard electrodes;

first capacitive sensor circuitry operable to sense a first capacitance and produce a first capacitive sensor reading indicative of the sensed first capacitance, wherein the first capacitive sensor circuitry includes a first capacitive sensor coupled to a first side of at least one of the one or more guard electrodes; and

second capacitive sensor circuitry operable to sense a second capacitance and produce a second capacitive sensor reading indicative of the sensed second capacitance, wherein the second capacitive sensor circuitry includes a second capacitive sensor coupled to a second side of at least one of the one or more guard electrodes.

2. The capacitive proximity sensing circuit as set forth in claim 1, wherein the first capacitive sensor circuitry further comprises a first switched integrator circuit operable during a first phase to apply a voltage to the first capacitive sensor, and operable during a second phase to transfer the first capacitance to a first capacitor and generate the first capacitive sensor reading.

3. The capacitive proximity sensing circuit as set forth in claim 1, wherein the second capacitive sensor circuitry further comprises a second switched integrator circuit operable during a first phase to apply a voltage to the second capacitive sensor, and operable during a second phase to transfer the second capacitance to a second capacitor and generate the second capacitive sensor reading.

4. The capacitive proximity sensing circuit as set forth in claim 1, further comprising output circuitry operable to produce an output signal to indicate detection of a user proximity to at least one of the first capacitive sensor and the second capacitive sensor.

5. The capacitive proximity sensing circuit as set forth in claim 4, wherein the output signal indicates detection of user proximity to the first capacitive sensor when the first capacitive sensor reading is greater than a threshold.

6. The capacitive proximity sensing circuit as set forth in claim 5, wherein the threshold is the second capacitive sensor reading.

7. The capacitive proximity sensing circuit as set forth in claim 1, wherein the first capacitance is indicative of a proximity of a user with respect to the first capacitive sensor.

8. The capacitive proximity sensing circuit as set forth in claim 1, wherein the second capacitance is indicative of a proximity of a user with respect to the second capacitive sensor.

9. The capacitive proximity sensing circuit as set forth in claim 1, wherein the one or more guard electrodes are controlled with a low impedance output to one or more voltages.

10. The capacitive proximity sensing circuit as set forth in claim 9, wherein the one or more guard electrodes are coupled to a first voltage in a first phase, and are coupled to a second voltage in a second phase.

11. The capacitive proximity sensing circuit as set forth in claim 1, wherein the one or more guard electrodes comprises a first guard electrode having the first capacitive sensor coupled to a first side of the first guard electrode, and the second capacitive sensor coupled to a second side of the first guard electrode.

12. The capacitive proximity sensing circuit as set forth in claim 1, wherein the one or more guard electrodes comprises a first guard electrode having the first capacitive sensor coupled to a first side of the first guard electrode, and a second guard electrode having the second capacitive sensor coupled to a second side of the second guard electrode.

13. The capacitive proximity sensing circuit as set forth in claim 12, wherein the first guard electrode is disposed in a device at a first location, and the second guard electrode is disposed in the device at a second location.

14. The capacitive proximity sensing circuit as set forth in claim 1, wherein the first side of the at least one of the one or more guard electrodes is disposed towards a first component of a device and the second side of the at least one of the one or more guard electrodes is disposed towards a second component of the device.

15. The capacitive proximity sensing circuit as set forth in claim 14, wherein the device comprises a mobile phone, the first component comprises a screen, and the second component comprises an external casing.

16. A capacitive proximity sensing circuit comprising:

one or more guard electrodes;

a first sensor coupled to a first side of at least one of the one or more guard electrodes;

a second sensor coupled to a second side of at least one of the one or more guard electrodes;

first capacitive sensor circuitry coupled to the first sensor, the first capacitive sensor circuitry operable to sense user proximity with respect to the first sensor and to produce a first capacitive sensor reading indicative of the sensed user proximity with respect to the first sensor; and

second capacitive sensor circuitry coupled to the second sensor, the second capacitive sensor circuitry operable to sense user proximity with respect to the second sensor and to produce a second capacitive sensor reading indicative of the sensed user proximity with respect to the second sensor.

17. The capacitive proximity sensing circuit as set forth in claim 16, further comprising output circuitry operable to produce an output signal to indicate detection of user proximity to at least one of the first sensor and the second sensor.

18. The capacitive proximity sensing circuit as set forth in claim 17, wherein the output signal indicates detection of user proximity to the first sensor when the first capacitive sensor reading is greater than a threshold.

19. The capacitive proximity sensing circuit as set forth in claim 18, wherein the threshold is the second capacitive sensor reading.

20. The capacitive proximity sensing circuit as set forth in claim 16, wherein sensing user proximity with respect to the first sensor includes the first capacitive sensor circuitry sensing a first capacitance between the user and the first sensor.

21. The capacitive proximity sensing circuit as set forth in claim 20, wherein the first capacitive sensor circuitry comprises a first switched integrator circuit operable during a first phase to apply a voltage to the first sensor, and operable during a second phase to transfer the first capacitance to a first capacitor and generate the first capacitive sensor reading.

22. The capacitive proximity sensing circuit as set forth in claim 20, wherein the first capacitive sensor reading is indicative of the sensed first capacitance.

23. The capacitive proximity sensing circuit as set forth in claim 16, wherein sensing user proximity with respect to the second sensor includes the second capacitive sensor circuitry sensing a second capacitance between the user and the second sensor.

24. The capacitive proximity sensing circuit as set forth in claim 23, wherein the second capacitive sensor circuitry comprises a second switched integrator circuit operable during a first phase to apply a voltage to the second sensor, and operable during a second phase to transfer the second capacitance to a second capacitor and generate the second capacitive sensor reading.

25. The capacitive proximity sensing circuit as set forth in claim 23, wherein the second capacitive sensor reading is indicative of the sensed second capacitance.

26. The capacitive proximity sensing circuit as set forth in claim 16, wherein the one or more guard electrodes are controlled with a low impedance output to one or more voltages.

27. The capacitive proximity sensing circuit as set forth in claim 26, wherein the one or more guard electrodes are coupled to a first voltage in a first phase, and are coupled to a second voltage in a second phase.

28. The capacitive proximity sensing circuit as set forth in claim 16, wherein the one or more guard electrodes comprises a first guard electrode having the first sensor coupled to a first side of the first guard electrode, and the second sensor coupled to a second side of the first guard electrode.

29. The capacitive proximity sensing circuit as set forth in claim 16, wherein the one or more guard electrodes comprises a first guard electrode having the first sensor coupled to a first side of the first guard electrode, and a second guard electrode having the second sensor coupled to a second side of the second guard electrode.

30. The capacitive proximity sensing circuit as set forth in claim 29, wherein the first guard electrode is disposed in a device at a first location, and the second guard electrode is disposed in the device at a second location.

31. The capacitive proximity sensing circuit as set forth in claim 16, wherein the first side of the at least one of the one or more guard electrodes is disposed towards a first component of a device.

32. The capacitive proximity sensing circuit as set forth in claim 31, wherein the first component comprises a screen.

33. The capacitive proximity sensing circuit as set forth in claim 16, wherein the second side of the at least one of the one or more guard electrodes is disposed towards a second component of a device.

34. The capacitive proximity sensing circuit as set forth in claim 33, wherein the second component of the device comprises an external casing.

35. An integrated circuit operable to detect user proximity with respect to a first component of a device and user proximity with respect to a second component of the device, the integrated circuit comprising:

a first switched capacitive integrator circuit coupled towards the first component of the device, the first switched capacitive integrator circuit operable to sense a first capacitance and produce a first output signal in response to the sensed first capacitance;

a second switched capacitive integrator circuit coupled towards the second component of the device, the second switched capacitive integrator circuit operable to sense a second capacitance and produce a second output signal in response to the sensed second capacitance;

one or more capacitive plates, wherein at least one of the one or more capacitive plates is coupled on a first side to the first switched capacitive integrator circuit, and at least one of the one or more capacitive plates is coupled on a second side to the second switched capacitive integrator circuit; and

output circuitry operable to receive the first output signal and second output signal, and to produce a third output signal operable to indicate detection of the user proximity with respect to one of the first switched capacitive integrator circuit or the second switched capacitive integrator circuit.

36. The integrated circuit as set forth in claim 35, wherein the first switched capacitive integrator circuit includes a first sensor plate coupled to the first side of the at least one of the one or more capacitive plates.

37. The integrated circuit as set forth in claim 36, wherein the first capacitance is generated by the user proximate the first sensor plate.

38. The integrated circuit as set forth in claim 37, wherein the first output signal is indicative of the user proximity to the first sensor plate.

39. The integrated circuit as set forth in claim 36, wherein the first switched capacitive integrator circuit is operable during a first phase to apply a voltage to the first sensor plate, and operable during a second phase to transfer the first capacitance to a first capacitor and generate the first output signal.

40. The integrated circuit as set forth in claim 35, wherein the second switched capacitive integrator circuit includes a second sensor plate coupled to the second side of the at least one of the one or more capacitive plates.

41. The integrated circuit as set forth in claim 40, wherein the second capacitance is generated by the user proximate the second sensor plate.

42. The integrated circuit as set forth in claim 41, wherein the second output signal is indicative of the user proximity to the second sensor plate.

43. The integrated circuit as set forth in claim 40, wherein the second switched capacitive integrator circuit is operable during a first phase to apply a voltage to the second sensor plate, and operable during a second phase to transfer the second capacitance to a second capacitor and generate the second output signal.

44. The integrated circuit as set forth in claim 35, wherein the one or more capacitive plates comprises a first capacitive plate having the first switched capacitive integrator circuit coupled to a first side of the first capacitive plate, and the second switched capacitive integrator circuit coupled to a second side of the first capacitive plate.

45. The integrated circuit as set forth in claim 35, wherein the one or more capacitive plates comprises a first capacitive plate having the first switched capacitive integrator circuit coupled to a first side of the first capacitive plate, and a second capacitive plate having the second switched capacitive integrator circuit coupled to a second side of the second capacitive plate.

46. The integrated circuit as set forth in claim 45, wherein the first capacitive plate is disposed in the device at a first location, and the second capacitive plate is disposed in the device at a second location.