Proximity sensing based on antenna impedance variation

• US 7,113,087 B1
• Filed: 04/08/2003
• Issued: 09/26/2006
• Est. Priority Date: 04/08/2003
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Casebolt, Mark W., Ranta, Craig S.
• Primary Examiner(s): Mullen, Thomas
• Assistant Examiner(s): BLOUNT, ERIC
• Application Number:
  US10/408,125
• Time in Patent Office: 1,267 Days
• Field of Search: 340/539.1
• US Class Current: 340/539.1
• CPC Class Codes: G01V 3/101 by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil measuring impedance or characteristics derived therefrom G01R27/00, e.g. quality factor G01R27/26
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: G06F 1/3215 Monitoring of peripheral devices
• CPC Class Codes: G06F 1/3231 Monitoring the presence, absence or movement of users
• CPC Class Codes: G06F 1/3259 Power saving in cursor control device, e.g. mouse, joystick, trackball
• CPC Class Codes: G06F 3/03543 Mice or pucks G06F3/03541 takes precedence
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

Proximity of a user body part can be detected by measuring the effects such proximity has on antenna impedance mismatches. The amount of mismatch affects the amount of RF signal energy reflected back into a transmission line connecting the antenna to a RF signal source. A directional coupler has a main line electrically connected to the transmission line, as well as a coupled line. The directional coupler produces a signal on its coupled line in relation to the magnitude of reflected energy on the transmission line; the amount of reflected energy varies in response to how well the antenna impedance matches the transmission line impedance. A signal detector is electrically connected to the coupled line, and responds to signals produced in the coupled line by the main line. The signal detector output is then used to determine whether a body part is in proximity. Other aspects the invention include an adaptive algorithm to adjust a threshold for proximity determination.

Claims

1. A proximity detection system for sensing the presence of an object or body portion in contact with or close proximity to another object, comprising:

a radio frequency (RF) signal source providing RF signals;

a transmission pathway connected to the RF source;

an antenna connected to the transmission pathway;

a directional coupler having a main line in electrical communication with the transmission pathway and a coupled line, the directional coupler producing a signal on the coupled line which varies in response to changes in antenna and transmission line impedance matching caused by presence of an object or body portion;

a signal detector in electrical communication with the coupled line and responsive to signals produced in the coupled line by the main line, wherein the signal detector produces an output signal that is within an output range, the output range corresponding to a range of antenna-transmission line impedance mismatch; and

a controller in communication with the signal detector, the controller configured to provide, in relation to the output signal, a state signal indicative of the presence or absence of an object or body portion in contact with or close proximity to another object.

2. The proximity detection system of claim 1, wherein the RF signal source provides RF signals at frequencies above 850 MHz.

3. The proximity detection system of claim 1, wherein the RF signal source provides RF signals at frequencies between 2.4 GHz and 2.483 GHz.

4. The proximity detection system of claim 1, wherein the RF signal source provides RF signals at frequencies between 5.725 GHz and 5.850 GHz.

5. The proximity detection system of claim 1, wherein the RF signal source provides RF signals of a power not exceeding approximately 10 mW.

6. The proximity detector of claim 1, wherein the controller is further configured to adjust one or more criteria by which the state signal is determined.

7. The proximity detector of claim 1, further comprising an Analog to Digital Converter (ADC) for converting the output signal to a digital value, and wherein the controller receives the digital value of the output signal.

8. The proximity detector of claim 1, wherein the controller is further configured to determine the state signal based upon multiple recent indications of output signal value.

9. The proximity sensor of claim 8, wherein the controller averages multiple recent indications of output signal value and determines the state signal based on the average of the multiple recent values.

10. The proximity detector of claim 1, wherein the controller is further configured to:

determine a value (TouchVal) relating to the output signal, and

generate, based upon TouchVal, a signal indicative of an ON state wherein an object or body portion is in contact with or close proximity to another object, and an OFF state wherein the object or body portion is not in contact with or close proximity to the other object.

11. The proximity detector of claim 10, wherein TouchVal is a moving average value.

12. The proximity detector of claim 10, wherein the controller is further configured to:

compare TouchVal, or a number derived from TouchVal, with a predetermined threshold value (TouchOff), or a number derived from TouchOff, and

generate the ON and OFF state indicating signals based upon the comparison.

13. The proximity detector of claim 12, wherein the controller is further configured to dynamically adjust the value of TouchOff.

14. The proximity detector of claim 13, wherein the controller is configured to dynamically adjust the value of TouchOff to adapt to fluctuations in the RF absorption characteristics of the environment or among different users.

15. The proximity detector of claim 13, wherein the controller is further configured to derive a value (TouchAvg) from TouchVal, and wherein the controller compares TouchAvg with TouchOff while in a state in which an ON state indicating signal is generated.

16. The proximity detector of claim 15, wherein the controller is further configured to:

initially set TouchAvg equal to TouchVal upon a transition from a state in which an OFF state indicating signal is generated to a state in which an ON state indicating signal is generated, and

increment the value of TouchAvg upon TouchVal exceeding TouchAvg for a predetermined interval.

17. The proximity detector of claim 16, wherein the controller is further configured to adapt to fluctuations in the RF absorption characteristics of the environment or among different users based upon an increase in TouchVal while in a state in which an OFF state indicating signal is generated.

18. The proximity detector of claim 17, wherein the controller adapts to fluctuations in RF absorption characteristics based upon TouchVal remaining above TouchOff for a predetermined interval.

19. The proximity detector of claim 12, wherein the controller is configured to transition, upon TouchVal decreasing below TouchOff by a predetermined amount, from a state in which an OFF state indicating signal is generated to a state in which an ON state indicating signal is generated.

20. The proximity detector of claim 12, wherein the controller is configured to decrement TouchOff upon TouchVal remaining below TouchOff for a predetermined interval.

21. The proximity detector of claim 12, wherein the controller is further configured to derive a value (TouchAvg) from TouchVal, and wherein the controller compares TouchAvg with TouchOff while in a state in which an ON state indicating signal is generated.

22. The proximity detector of claim 1, wherein the signal detector comprises a RF envelope detector and an amplifier.

23. A user input device, comprising

a controller for generating data in response to manipulation of the input device by a human user;

a radio frequency (RF) signal source providing modulated RF signals for transmission of the data to another device;

a transmission pathway connected to the RF source;

an antenna connected to the transmission pathway;

a directional coupler having a main line in electrical communication with the transmission pathway and a coupled line, the directional coupler producing a signal on the coupled line which varies in relation to an amount of modulated RF signal energy reflected back to the transmission line from the antenna because of mismatches in antenna and transmission line impedances; and

a signal detector in electrical communication with the coupled line and responsive to signals produced in the coupled line by the main line, the signal detector producing a detection signal having a value that varies in relation to the signal produced on the coupled line.

24. The user input device of claim 23, further comprising a power supply, and wherein the controller is configured to place the input device in a power conserving state based upon detection signal values.

25. The user input device of claim 23, further comprising a housing and a button located on the housing, and wherein manipulation of the input device by a human user includes actuation of the button.

26. The user input device of claim 23, wherein the RF signal source provides RF signals at frequencies above 850 MHz.

27. The user input device of claim 23, wherein the RF signal source provides RF signals at frequencies between 2.4 GHz and 2.483 GHz.

28. The user input device of claim 23, wherein the RF signal source provides RF signals at frequencies between 5.725 GHz and 5.850 GHz.

29. The user input device of claim 23, wherein the controller is further configured to provide, in relation to the detection signal, a state signal indicative of the presence or absence of an object or body portion in contact with or close proximity to the input device, and wherein the controller is further configured to adjust one or more criteria by which the state signal is determined.

30. The user input device of claim 29, wherein the controller is further configured to determine the state signal based upon multiple recent indications of detection signal value.

31. The user input device of claim 23, further comprising an analog-to-digital converter for converting the detection signal to a digital value, and wherein the controller receives the digital value of the detection signal.

32. The user input device of claim 23, wherein the controller is further configured to:

determine a value (TouchVal) relating to the detection signal value, and

generate, based upon TouchVal, a signal indicative of an ON state wherein a user body portion is in contact with or close proximity to the input device, and a power-conserving OFF state wherein a user body portion is not in contact with or close proximity to the input device.

33. The user input device of claim 32, wherein TouchVal is a moving average value.

34. The user input device of claim 32, wherein the controller is further configured to:

compare TouchVal, or a number derived from TouchVal, with a predetermined threshold value (TouchOff), or a number derived from TouchOff, and

generate the ON and OFF state indicating signals based upon the comparison.

35. The user input device of claim 34, wherein the controller is further configured to dynamically adjust the value of TouchOff.

36. The user input device of claim of claim 35, wherein the controller is configured to dynamically adjust the value of TouchOff to adapt to fluctuations in the RF absorption characteristics of the environment or among different users.

37. The user input device of claim 34, wherein the controller is further configured to derive a value (TouchAvg) from TouchVal, and wherein the controller compares TouchAvg with TouchOff while in a state in which an ON state indicating signal is generated.

38. The user input device of claim 37, wherein the controller is further configured to:

initially set TouchAvg equal to TouchVal upon a transition from a state in which an OFF state indicating signal is generated to a state in which an ON state indicating signal is generated, and

increment the value of TouchAvg upon TouchVal exceeding TouchAvg for a predetermined interval.

39. The user input device of claim 38, wherein the controller is further configured to adapt to a change in the RF absorption characteristics of the environment or among different users based an increase in TouchVal while in a state in which an OFF state indicating signal is generated.

40. The user input device of claim 39, wherein the controller adapts to change in RF absorption characteristics based upon TouchVal remaining above TouchOff for a predetermined interval.

41. The user input device of claim 34, wherein the controller is configured to transition, upon TouchVal decreasing below TouchOff by a predetermined amount, from a state in which an OFF state indicating signal is generated to a state in which an ON state indicating signal is generated.

42. The user input device of claim 34, wherein the controller is configured to decrement TouchOff upon TouchVal remaining below TouchOff for a predetermined interval.

43. The user input device of claim 34, wherein the controller is further configured to derive a value (TouchAvg) from TouchVal, and wherein the controller compares TouchAvg with TouchOff while in a state in which an ON state indicating signal is generated.