Proximity Sensor

• US 20090027068A1
• Filed: 07/25/2008
• Published: 01/29/2009
• Est. Priority Date: 07/26/2007
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: QRG Limited
• Inventors: Philipp, Harald, Snoad, Kevin
• Granted Patent: US 7,952,366 B2
• Time in Patent Office: Days
• US Class Current: 324/678
• CPC Class Codes: G01R 27/26 Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: G06F 1/3231 Monitoring the presence, absence or movement of users
• CPC Class Codes: G06F 1/3262 Power saving in digitizer or tablet
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G08B 13/08 by opening, e.g. of door, of window, of drawer, of shutter, of curtain, of blind
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
• CPC Class Codes: H03K 2217/960725 Charge-transfer

Abstract

A capacitive touch sensor providing an automatic switch-off function for an apparatus in which the sensor is incorporated is provided. The sensor comprises a sensing element coupled to a capacitance measurement circuit for measuring the capacitance of the sensing element. A control circuit is operable to determine from the capacitance measurement whether an object is in proximity with the sensor. The determined presence of an object may be used to toggle a function of the apparatus. Furthermore, when it is determined that an object has not been in proximity with the sensor for a predetermined time duration, an output signal for switching off the apparatus is provided. The predetermined time duration may be selected from a number of predefined time durations, or may be programmed using an resistor-capacitor network. Pulses may be applied to the control circuit to override features of the automatic switch-off functionality.

Claims

1. A sensor for determining the presence of an object comprising:

a sensing element;

a capacitance measurement circuit operable to measure the capacitance of the sensing element; and

a control circuit operable to determine whether an object is in proximity with the sensor based on a measurement of the capacitance of the sensing element, the control circuit further being operable to provide an output signal to control a function of an apparatus when it is determined that an object has not been in proximity with the sensor for a predetermined time duration.

2. The sensor of claim 1, wherein the control circuit is configured so that the predetermined time duration is selectable from a number of different predefined time durations.

3. The sensor of claim 2, wherein the control circuit includes a time input terminal and the predetermined time duration is selectable from the number of different predefined time durations according to a voltage applied to the time input terminal.

4. The sensor of claim 2, wherein the control circuit includes a delay multiplier terminal and is configured so that a selected one of the number of different predefined time durations is multiplied by a multiplication factor according to a voltage applied to the delay multiplier terminal to provide the predetermined time duration.

5. The sensor of claim 1, wherein the control circuit is configured so that the predetermined time duration is programmable by a user to provide a user-selected time duration.

6. The sensor of claim 5, further comprising a resistor-capacitor (RC) network coupled to the control circuit and wherein the predetermined time duration depends on a time constant of the RC network.

7. The sensor of claim 5, wherein the control circuit includes a delay multiplier terminal and is configured so that the user-selected time duration is multiplied by a multiplication factor according to a voltage applied to the delay multiplier terminal to provide the predetermined time duration.

8. The sensor of claim 1, wherein the control circuit is configured such that the provision of the output signal to control a function of an apparatus after the predetermined time duration may be overridden so the output signal is not provided when it is determined that an object has not been in proximity with the sensor for a predetermined time duration.

9. The sensor of claim 8, wherein the control circuit is operable to receive an override pulse and on receipt of the override pulse to retrigger the predetermined time duration to so as to extend the time before the output signal to control a function of an apparatus is provided.

10. The sensor of claim 1, wherein the control circuit is configured such that the provision of the output signal to control a function of an apparatus after the predetermined time duration may be overridden so the output signal is provided before it is determined that an object has not been in proximity with the sensor for a predetermined time duration.

11. The sensor of claim 10, wherein the control circuit is operable to receive an override pulse and on receipt of the override pulse to provide the output signal to control a function of an apparatus.

12. The sensor of claim 1, wherein the sensor is configured to perform a recalibration when the sensor is powered up, when an object is determined to be in proximity with the sensor for more than a timer setting, and/or when an override is released.

13. The sensor of claim 1, wherein the control circuit is configured such that the output signal is toggled between a high state and a low state when an object is determined to be in proximity with the sensor.

14. The sensor of claim 1, wherein the function of an apparatus controlled by the output signal is a switch-off function.

15. The sensor of claim 1, wherein the capacitance measurement circuit employs bursts of charge-transfer cycles to acquire measurements.

16. The sensor of claim 1, wherein the capacitance measurement circuit is configured to operate in one of more than one acquisition modes depending on the output signal.

17. The sensor of claim 16, wherein a one of the more than one acquisition modes is a low-power mode.

18. The sensor of claim 16, wherein a one of the more than one acquisition modes is a fast mode.

19. The sensor of claim 1, wherein the capacitance measurement circuit and the control circuit are comprised in a general purpose microcontroller under firmware control.

20. The sensor of claim 1, wherein the capacitance measurement circuit and the control circuit are comprised within a six-pin integrated circuit chip package.

21. An apparatus comprising a sensor according to claim 1.

22. A method for controlling a function of an apparatus comprising:

determining whether an object is in proximity with a sensor based on a measurement of the capacitance of a sensing element and providing an output signal to control the function of the apparatus when it is determined that an object has not been in proximity with the sensor for a predetermined time duration.

23. The method of claim 22, wherein the function of the apparatus controlled by the output signal is a switch-off function.