Controlling an RFID reader by observing a change in inductance

• US 20060170553A1
• Filed: 01/14/2005
• Published: 08/03/2006
• Est. Priority Date: 01/14/2005
• Status: Active Grant

• Current Assignee: Farpointe Data Incorporated (dormakaba Holding AG)
• Original Assignee: Farpointe Data Incorporated (dormakaba Holding AG)
• Inventors: Bierach, Kirk B.
• Granted Patent: US 7,245,222 B2
• Time in Patent Office: Days
• US Class Current: 340/572.400
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10128 the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device
• CPC Class Codes: H04B 5/24 Inductive coupling
• CPC Class Codes: H04B 5/45 Transponders
• CPC Class Codes: H04B 5/77 for interrogation
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer
• CPC Class Codes: H04W 52/0225 using monitoring of external events, e.g. the presence of a signal
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A method and apparatus for controlling a radio frequency identification (RFID) reader to detect the proximity of an RFID device based on observing a change in effective inductance. The RFID reader includes an excitation signal generator and a resonant filter that combined are capable of generating and transmitting a detection signal, an RFID device detector for measuring a detector parameter indicative of the change in effective inductance, and a detection signal receiver for determining whether an RFID device is present. The method includes awakening from a detection sleep state at a preselected time, generating and transmitting a detection signal, measuring at least one detector parameter indicative of the change in effective inductance, and determining whether the RFID device is present. When the RFID device is not present, the method returns to the detection sleep state and, when the RFID device is present, the method exits the detection sleep state.

Claims

1. A radio frequency identification (RFID) reader comprising:

an excitation signal generator and a resonant filter that combined are capable of generating and transmitting a detection signal;

an RFID device detector for measuring a detector parameter indicative of a change in effective inductance of the resonant filter; and

a detection signal receiver for determining whether an RFID device is in proximity of the RFID reader based on observing the change in effective inductance.

2. The RFID reader as defined in claim 1, wherein the resonant filter has an input and an output and comprises:

an inductor having a first node and a second node wherein the first node is connected to the input and the second node is connected to the output; and

a capacitor having a first node and a second node wherein the first node is connected to the output and the second node is connected to a constant voltage potential.

3. The RFID reader as defined in claim 1, wherein the resonant filter has an input and an output and comprises:

a resistor having a first node and a second node wherein the first node is connected to the input;

a first capacitor having a first node and a second node wherein the first node is connected to the second node of the resistor and the second node is connected to a constant voltage potential;

a second capacitor having a first node and a second node wherein the first node is connected to the second node of the resistor and the second node is connected to the output;

an inductor having a first node and a second node wherein the first node is connected to the output and the second node is connected to the constant voltage potential.

4. The RFID reader as defined in claim 3, wherein the RFID device detector has an input and an output and comprises:

a first capacitor having a first node and a second node wherein the first node is connected to the input;

a diode having an anode and a cathode wherein the anode is connected to the second node of the first capacitor and the cathode is connected to a constant voltage potential;

a resistor having a first node and a second node wherein the first node is connected to the second node of the first capacitor and the second node is connected to the output; and

a second capacitor having a first node and a second node wherein the first node is connected to the output and the second node is connected to the constant voltage potential.

5. The RFID reader as defined in claim 3, wherein the RFID device detector comprises a peak detector.

6. The RFID reader as defined in claim 3, wherein the RFID device detector comprises a slope detector.

7. The RFID reader as defined in claim 3, wherein the RFID device detector comprises a comparator.

8. The RFID reader as defined in claim 3, wherein the RFID device detector comprises an Analog-to-Digital converter.

9. The RFID reader as defined in claim 1, wherein the RFID device detector has an input and an output and comprises:

a first capacitor having a first node and a second node wherein the first node is connected to the input;

a diode having an anode and a cathode wherein the anode is connected to the second node of the first capacitor and the cathode is connected to a constant voltage potential;

a resistor having a first node and a second node wherein the first node is connected to the second node of the first capacitor and the second node is connected to the output; and

a second capacitor having a first node and a second node wherein the first node is connected to the output and the second node is connected to the constant voltage potential.

10. The RFID reader as defined in claim 1, wherein the RFID device detector comprises a peak detector.

11. The RFID reader as defined in claim 1, wherein the RFID device detector comprises a slope detector.

12. The RFID reader as defined in claim 1, wherein the RFID device detector comprises a comparator.

13. The RFID reader as defined in claim 1, wherein the RFID device detector comprises an Analog-to-Digital converter.

14. The RFID reader as defined in claim 1, wherein the excitation signal generator and the detection signal receiver are included among the elements of an RFID controller.

15. The RFID reader as defined in claim 14, wherein the RFID controller further comprises a response signal demodulator for extracting data from a response signal received from the RFID device.

16. The RFID reader as defined in claim 15, further comprising a response signal receiver for receiving the response signal.

17. A method for detecting the presence of a radio frequency identification (RFID) device in the proximity of an RFID reader by observing a change in effective inductance of a resonant filter of the RFID reader, the method comprising:

generating and transmitting a detection signal;

measuring at least one detector parameter indicative of the change in effective inductance; and

determining whether the RFID device is present.

18. The method as defined in claim 17, wherein prior to generating and transmitting the method is in a detection sleep state and the method further comprises:

awakening from the detection sleep state at a preselected time;

when the RFID device has been determined not to be present, returning to the detection sleep state; and

when the RFID device has been determined to be present, exiting the detection sleep state.

19. The method as defined in claim 18, wherein the detection sleep state enables energy savings by the RFID reader.

20. The method as defined in claim 17, wherein the detection signal is such that the resonant filter may not achieve steady state during the time period of generation and transmission.

21. The method as defined in claim 17, wherein the at least one detector parameter comprises a voltage.

22. The method as defined in claim 17, wherein the at least one detector parameter comprises a current.

23. The method as defined in claim 17, wherein determining whether the RFID device is present comprises comparing the at least one detector parameter to a threshold.

24. The method as defined in claim 17, wherein determining whether the RFID device is present comprises comparing the at least one detector parameter to an average of a set of previous detector parameter measurements.

25. The method as defined in claim 17, wherein determining whether the RFID device is present comprises comparing the at least one detector parameter to a majority vote based on a set of previous detector parameter measurements.

26. The method as defined in claim 17, wherein determining whether the RFID device is present comprises decision criteria that are static.

27. The method as defined in claim 17, wherein determining whether the RFID device is present comprises decision criteria that are dynamic.

28. The method as defined in claim 27, wherein the decision criteria are self calibrating.

29. An apparatus for detecting the presence of a radio frequency identification (RFID) device in the proximity of an RFID reader by observing a change in effective inductance of a resonant filter of the RFID reader, the apparatus comprising:

means for generating and transmitting a detection signal;

means for measuring at least one detector parameter indicative of the change in effective inductance; and

means for determining whether the RFID device is present.

30. The apparatus as defined in claim 29, wherein, prior to generating and transmitting a detection signal, the apparatus is in a detection sleep state and the apparatus further comprises:

means for awakening from the detection sleep state at a preselected time;

means for, when the RFID device has been determined not to be present, returning to the detection sleep state; and

means for, when the RFID device has been determined to be present, exiting the detection sleep state.

31. The apparatus as defined in claim 30, wherein the detection sleep state enables energy savings by the RFID reader.

32. The apparatus as defined in claim 29, wherein the detection signal is such that the resonant filter may not achieve steady state during the time period of generation and transmission.

33. The apparatus as defined in claim 29, wherein the at least one detector parameter comprises a voltage.

34. The apparatus as defined in claim 29, wherein the at least one detector parameter comprises a current.

35. The apparatus as defined in claim 29, wherein the means for determining whether the RFID device is present comprises means for comparing the at least one detector parameter to a threshold.

36. The apparatus as defined in claim 29, wherein the means for determining whether the RFID device is present comprises means for comparing the at least one detector parameter to an average of a set of previous detector parameter measurements.

37. The apparatus as defined in claim 29, wherein the means for determining whether the RFID device is present comprises means for comparing the at least one detector parameter to a majority vote based on a set of previous detector parameter measurements.

38. The apparatus as defined in claim 29, wherein the means for determining whether the RFID device is present comprises decision criteria that are static.

39. The apparatus as defined in claim 29, wherein the means for determining whether the RFID device is present comprises decision criteria that are dynamic.

40. The apparatus as defined in claim 39, wherein the decision criteria are self calibrating.