Proximity detection

• US 8,400,209 B2
• Filed: 10/22/2010
• Issued: 03/19/2013
• Est. Priority Date: 10/22/2010
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Ujvari, Daniel Arthur
• Primary Examiner(s): Donovan, Lincoln
• Assistant Examiner(s): ENGLUND, TERRY LEE
• Application Number:
  US12/910,484
• Publication Number:
  US 20120098588A1
• Time in Patent Office: 879 Days
• Field of Search: 327/517
• US Class Current: 327/517
• CPC Class Codes: G01B 7/14 for measuring distance or clearance between spaced objects or spaced apertures G01B7/30 takes precedence
• CPC Class Codes: G01N 22/00 Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more G01N3/00 - G01N17/00, G01N24/00 take precedence
• CPC Class Codes: G01R 21/00 Arrangements for measuring electric power or power factor G01R7/12 takes precedence
• CPC Class Codes: G01R 23/00 Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
• CPC Class Codes: G01R 27/00 Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00
• CPC Class Codes: G01R 27/04 in circuits having distributed constants , e.g. having very long conductors or involving high frequencies
• CPC Class Codes: G01R 27/06 Measuring reflection coefficients; Measuring standing-wave ratio
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G01R 27/32 in circuits having distributed constants , e.g. having very long conductors or involving high frequencies
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2017/9606 using one electrode only per touch switch

Abstract

For proximity detection, capacitance of a sensing element to ground is measured as one or more objects move into or out of proximity to the sensing element.

Claims

1. A proximity sensor comprising:

an antenna, wherein the antenna has a capacitance to ground that is variable as a function of the proximity of an object to the antenna;

a sample capacitor connected to the antenna; and

control circuitry connected to the sample capacitor, the control circuitry configured to;

supply a charge to the sample capacitor and the antenna;

discharge the antenna;

in response to the discharge of the antenna, provide a signal indicative of the capacitance to ground of the antenna; and

process the signal to detect a change in the capacitance to ground as indicative of the proximity of the object to the antenna; and

the control circuitry comprising three switching elements and an analog comparator, each switching element having a respective open state and a respective closed state, wherein;

a first of the switching elements is configured to connect the sample capacitor to ground in the closed state;

a second of the switching elements is configured in the closed state to connect a voltage source to the sample capacitor to supply the charge to the sample capacitor and the antenna, the voltage source connected to the sample capacitor at a polarity opposite a polarity of the connection of the first switch element to the sample capacitor and to the comparator;

a third of the switching elements is configured in the closed state to connect the comparator and sample capacitor to ground; and

the comparator is configured to receive a reference voltage and to compare the reference voltage to the voltage on the sample capacitor; and

the control circuitry further comprising a pulse width modulation circuit configured to receive on a clock input an output of the comparator.

2. The proximity sensor of claim 1, wherein the control circuitry is configured to discharge the antenna and the sample capacitor when the first and third switching elements are in the closed state and the second switching element is in the open state.

3. The proximity sensor of claim 1, wherein the control circuitry is configured to cause the voltage on the sample capacitor to float when the first, second, and third switching elements are in the open state.

4. The proximity sensor of claim 1, wherein, to supply the charge to the sample capacitor and the antenna, the control circuitry is configured to transfer charge to the sample capacitor and the antenna when the first and third switching elements are in the open state and the second switching element is in the closed state.

5. The proximity sensor of claim 1, wherein the control circuitry is configured to discharge the antenna and the sample capacitor and compare the voltage across the sample capacitor and the reference voltage when the first switching element is in the closed state and the second and third switching elements are in the open state.

6. The proximity sensor of claim 1, further comprising a counter configured to produce an output signal gated by an output of the pulse width modulation circuit.

7. The proximity sensor of claim 1, wherein the antenna comprises a loop antenna.

8. The proximity sensor of claim 1, wherein the control circuitry is configured to dynamically vary the detection range of the proximity sensor.

9. A proximity sensor controller, comprising:

control circuitry including a processor, wherein the control circuitry is connected to a sample capacitor and an antenna, wherein the antenna has a capacitance to ground that is variable as a function of proximity of an object to the antenna, the processor configured to execute instructions that cause the processor to perform operations to measure the antenna capacitance to ground, comprising operations to;

supply a charge to the sample capacitor and the antenna;

discharge the antenna;

in response to the discharge of the antenna, provide a signal indicative of the capacitance to ground of the antenna; and

process the signal to detect a change in the capacitance to ground as indicative of the proximity of the object to the antenna; and

the control circuitry comprising three switching elements and an analog comparator, each switching element having a respective open state and a respective closed state, wherein;

a first switching element is configured to connect the sample capacitor to ground in the closed state;

a second switching element is configured in the closed state to connect a voltage source to the sample capacitor to supply the charge to the sample capacitor and the antenna, the voltage source connected to the sample capacitor at a polarity opposite a polarity of the connection of the first switch element to the sample capacitor and to the comparator; and

a third switching element configured in the closed state to connect the comparator and sample capacitor to ground; and

the comparator is configured to receive a reference voltage and to compare the reference voltage to the voltage on the sample capacitor; and

the control circuitry further comprising a pulse width modulation circuit configured to receive on a clock input an output of the comparator.

10. The proximity sensor controller of claim 9, wherein the processor is further configured to perform operations to:

dynamically varying the detection range of the proximity sensor.

11. The proximity sensor controller of claim 9, wherein the control circuitry is configured to discharge the antenna and the sample capacitor when the first and third switching elements are in the closed state and the second switching element is in the open state.

12. The proximity sensor controller of claim 9, wherein, to supply the charge to the sample capacitor and the antenna, the control circuitry is configured to transfer charge to the sample capacitor and the antenna when the first and third switching elements are in the open state and the second switching element is in the closed state.

13. The proximity sensor controller of claim 9, wherein the control circuitry is configured to discharge the antenna and the sample capacitor and compare the voltage across the sample capacitor and the reference voltage when the first switching element is in the closed state and the second and third switching elements are in the open state.

14. The proximity sensor controller of claim 9, further comprising a counter configured to produce an output signal gated by an output of the pulse width modulation circuit.

15. An article of manufacture comprising:

a non-transitory machine readable storage medium; and

executable program instructions embodied in the machine readable storage medium that when executed by a processor of a programmable computing device configures the programmable computing device to control a proximity sensor having control circuitry connected to a sample capacitor and an antenna, wherein the antenna has a capacitance to ground that is variable as a function of the proximity of a person or object to the antenna, to perform operations to measure the antenna capacitance to ground, including operations to;

supply a charge to the sample capacitor and the antenna;

discharge the antenna; and

provide a signal indicative of the capacitance to ground of the antenna; and

the control circuitry comprising three switching elements and an analog comparator, each switching element having a respective open state and a respective closed state, wherein;

a first switching element is configured to connect the sample capacitor to ground in the closed state;

a second switching element is configured in the closed state to connect a voltage source to the sample capacitor to supply the charge to the sample capacitor and the antenna, the voltage source connected to the sample capacitor at a polarity opposite a polarity of the connection of the first switch element to the sample capacitor and to the comparator; and

a third switching element configured in the closed state to connect the comparator and sample capacitor to ground; and

the comparator is configured to receive a reference voltage and to compare the reference voltage to the voltage on the sample capacitor; and

the control circuitry further comprising a pulse width modulation circuit configured to receive on a clock input an output of the comparator.