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EP-4404099-B1 - DYNAMIC FREQUENCY TUNING FOR INDUCTIVE COUPLING SYSTEMS

EP4404099B1EP 4404099 B1EP4404099 B1EP 4404099B1EP-4404099-B1

Inventors

  • CABBLE, Paul
  • EDMONDS, PETER

Dates

Publication Date
20260506
Application Date
20201125

Claims (15)

  1. A method for operating an inductive coupling reader (12), the method comprising: - applying an excitation frequency to a resonance circuit of the inductive coupling reader (12); - detecting a change to the resonance frequency of the resonance circuit of the inductive coupling reader (12), the change in the resonance frequency being caused by an external interference-causing material in close proximity to the inductive coupling reader (12), wherein detecting the change comprises retrieving, from a non-volatile memory of the inductive coupling reader (12), a configuration bit that indicates presence or lack of presence of the external interference-causing source; and - in response to detecting the change to the resonance frequency of the inductive coupling reader (12), adjusting the excitation frequency being applied to the resonance circuit.
  2. The method of claim 1, wherein a range of the inductive coupling reader (12) is reduced as a result of the change in the resonance frequency.
  3. The method of any one of claims 1-2, wherein detecting the change comprises accessing configuration information for the inductive coupling reader (12), the configuration information indicating that the inductive coupling reader (12) is in close proximity to an external interference-causing material.
  4. The method of any one of claims 1-3, wherein the resonance circuit comprises a tuned oscillating circuity configured to generate a default resonance frequency at 125kHz or 134kHz.
  5. The method of any one of claims 1-4, further comprising: - applying a first excitation frequency to the resonance circuit of the inductive coupling reader (12); - measuring a first amplitude of a first voltage across the resonance circuit of the inductive coupling reader (12) resulting from applying the first excitation frequency; and - determining that the first amplitude of the first voltage fails to satisfy a criterion.
  6. The method of claim 5, wherein the criterion comprises a predetermined voltage level.
  7. The method of claim 5, wherein the criterion comprises exceeding a voltage level resulting from application of a second excitation frequency.
  8. The method of claim 5, further comprising: - applying a second excitation frequency to the resonance circuit of the inductive coupling reader (12); - measuring a second amplitude of a second voltage across the resonance circuit of the inductive coupling reader (12) resulting from applying the second excitation frequency; and - determining that the first amplitude of the first voltage is less than the second amplitude of the second voltage.
  9. The method of claim 8, wherein adjusting the excitation frequency being applied to the resonance circuit comprises setting the excitation frequency to the second excitation frequency.
  10. A system comprising: an inductive coupling reader (12) comprising: a driver circuit (230); a receiver circuit (240); an antenna voltage detection circuit (250); a resonance circuit; a microcontroller (220) being operative for controlling the operation of the inductive coupling reader (12) in order to interrogate, track, and report on items-of-interest within a coverage region (52) of the inductive coupling reader (12); a tuned circuit (210) being used to generate and transmit interrogation signals under the control of the microcontroller (220) and driver circuit (230) for transmission into the coverage region (52) via the inductive loop antenna during an interrogation operation; one or more processors configured to perform operations comprising: - applying an excitation frequency to the resonance circuit of the inductive coupling reader (12); - detecting a change to a resonance frequency of the resonance circuit of the inductive coupling reader (12), the change in the resonance frequency being caused by an external interference-causing material in close proximity to the inductive coupling reader (12), wherein detecting the change comprises retrieving, from a non-volatile memory of the inductive coupling reader (12), a configuration bit that indicates presence or lack of presence of the external interference-causing source; and - in response to detecting the change to the resonance frequency of the inductive coupling reader (12), adjusting the excitation frequency being applied to the resonance circuit.
  11. The system of claim 10, further comprising: applying a first excitation frequency to the resonance circuit of the inductive coupling reader; measuring a first amplitude of a first voltage across the resonance circuit of the inductive coupling reader resulting from applying the first excitation frequency; and determining that the first amplitude of the first voltage fails to satisfy a criterion.
  12. The system of claim 10, wherein adjusting the excitation frequency being applied to the resonance circuit comprises setting the excitation frequency to a second excitation frequency.
  13. The system of claim 12, wherein the second excitation frequency is higher or lower than the first excitation frequency by a predetermined amount.
  14. The system of claim 13, wherein: the microcontroller (220) receives a second voltage measurement from the antenna voltage detection circuit (250); the microcontroller 220 compares the second voltage measurement to the first voltage measurement; and in response to determining that the second voltage measurement is greater than the first voltage measurement, the microcontroller (220) increases the excitation frequency to drive the tuned circuit (210) at a third frequency that is higher than the second frequency.
  15. The system of claim 10, wherein the microcontroller (220) searches for the frequency that results in the maximum voltage measurement output by the antenna voltage detection circuit (250) by gradually increasing or decreasing the drive frequency.

Description

FIELD OF THE DISCLOSURE This document pertains generally, but not by way of limitation, to Radio Frequency Identification (RFID) systems and, more particularly, to techniques for reducing harmful interference effects in RFID systems. BACKGROUND An RFID system is a system that uses radio frequency transponders (e.g., tags) to identify items-of-interest. Each radio frequency transponder is attached to or near a corresponding item and includes information identifying that item. When an identification needs to be made, a radio frequency reader unit (e.g., an interrogator) is used to excite (e.g., interrogate) the transponder on the item, which then transmits an identification signal (including the identification information for the item) back to the reader unit. The reader unit then uses the identification information received from the transponder to perform any of a number of different RFID applications. For example, the identification information can be used to perform functions such as asset management, inventory tracking, access control, and others. An auto-tuning scanning proximity reader is known from EP 1 770 665 A1. EP 2 693 407 A1 describes a method and device for optimizing the RFID field of an access control device. SUMMARY OF THE DISCLOSURE In some certain embodiments, a system and method are provided for operating an inductive coupling reader. The disclosed system and method perform operations comprising: applying an excitation frequency to a resonance circuit of the inductive coupling reader; detecting a change to a resonance frequency of the resonance circuit of the inductive coupling reader, wherein detecting the change comprises retrieving, from a non-volatile memory of the inductive coupling reader (12), a configuration bit that indicates presence or lack of presence of the external interference-causing source; and in response to detecting the change to the resonance frequency of the inductive coupling reader, adjusting the excitation frequency being applied to the resonance circuit. In some embodiments, the change in the resonance frequency is caused by an external metal material in close proximity to the inductive coupling reader, and a range of the inductive coupling reader is reduced as a result of the change in the resonance frequency. In some embodiments, detecting the change comprises accessing configuration information for the inductive coupling reader, the configuration information indicating that the inductive coupling reader is in close proximity to external metal material. In some embodiments, the resonance circuit comprises a tuned oscillating circuity configured to generate a fixed resonance frequency at 125kHz or 134kHz. In some embodiments, the operations comprise: applying a first excitation frequency to the resonance circuit of the inductive coupling reader; measuring a first amplitude of a first voltage across the resonance circuit of the inductive coupling reader resulting from applying the first excitation frequency; and determining that the first amplitude of the first voltage fails to satisfy a criterion. In some embodiments, the criterion comprises a predetermined voltage level. In some embodiments, the criterion comprises exceeding a voltage level resulting from application of a second excitation frequency. In some embodiments, the operations comprise: applying a second excitation frequency to the resonance circuit of the inductive coupling reader; measuring a second amplitude of a second voltage across the resonance circuit of the inductive coupling reader resulting from applying the second excitation frequency; and determining that the first amplitude of the first voltage is less than the second amplitude of the second voltage. In some embodiments, adjusting the excitation frequency being applied to the resonance circuit comprises setting the excitation frequency to the second excitation frequency. In some embodiments, the second excitation frequency is higher or lower than the first excitation frequency by a predetermined amount. In some embodiments, the operations comprise causing an inductive coupling device, inductively coupled to the inductive coupling reader, to operate at the adjusted excitation frequency, where the inductive coupling device derives a clock frequency from the adjusted excitation frequency such that data transfer between the inductive coupling device and the inductive coupling reader is synchronous with the adjusted excitation frequency. In some embodiments, the inductive coupling device comprises a Radio Frequency Identification (RFID) credential device. In some embodiments, the inductive coupling reader comprises a Radio Frequency Identification (RFID) reader. In some embodiments, the adjustment to the excitation frequency is determined by: applying a range of frequencies to the resonance circuit; and identifying a frequency that causes a maximum voltage amplitude to be generated at an output of the inductive coupling reader. Metal material i