EP-4742093-A2 - DETUNING DETECTION AND COMPENSATION FOR INDUCTIVE COUPLING SYSTEMS

EP4742093A2EP 4742093 A2EP4742093 A2EP 4742093A2EP-4742093-A2

Abstract

This disclosure describes techniques for operating an inductive coupling reader. The techniques include operations comprising: detecting a change in a resonance frequency of the inductive coupling reader; comparing the change in the resonance frequency to a threshold; determining that the change in the resonance frequency falls outside the threshold; and activating a compensation circuit to offset the change in the resonance frequency of the inductive coupling reader in response to determining that the change in the resonance frequency falls outside the threshold.

Inventors

PIRCH, HANS-JUERGEN

Assignees

ASSA ABLOY AB

Dates

Publication Date: 20260513
Application Date: 20201125

Claims (15)

A system comprising: an inductive coupling reader positioned to interrogate a coverage region of the reader for the presence of one or more RF tags in the coverage region comprising a resonance circuit comprising a receiver for receiving, demodulating, and decoding identification signals from the one or more RF tags in the coverage region, a compensation circuit, one or more processors configured to perform operations comprising: detecting a change in a resonance frequency of the resonance circuit; comparing the change in the resonance frequency to a threshold based on comparing an amount of current being driven to the resonance circuit to an expected amount of current; determining that the change in the resonance frequency falls outside the threshold based on determining that the amount of current being driven to the resonance circuit is greater or less than the expected amount by a given amount; in response to determining that the change in the resonance frequency falls outside the threshold, activating the compensation circuit to offset the change in the resonance frequency of the inductive coupling reader in response to detecting the change in the resonance frequency; and receiving from the receiver the one or more identification signals corresponding to the one or more RF tags in the coverage region.
The system of claim 1, wherein the change in the resonance frequency is caused by an external metal material in close proximity to the inductive coupling reader, and wherein a range of the inductive coupling reader is reduced as a result of the change in the resonance frequency.
The system of claims 1 or 2, wherein the compensation circuit comprises: a switch; and one or more capacitors having a first terminal coupled to first terminals of capacitors of a resonance circuit of the inductive coupling reader and having a second terminal coupled to the switch.
The system of claim 3, wherein the compensation circuit comprises a first compensation subcircuit, and wherein the one or more processors are further configured to perform operations comprising: activating the first compensation subcircuit in response to determining that the change in the resonance frequency falls outside the threshold and falls within a second threshold; and activating a second compensation subcircuit in response to determining that the change in the resonance frequency falls outside the threshold and the second threshold, wherein the second compensation subcircuit provides a greater offset to the resonance frequency than the first compensation subcircuit.
The system of claim 4, wherein activation of the first compensation subcircuit couples a first capacitor in parallel with the resonance circuit, and wherein activation of the second compensation subcircuit couples a second capacitor in parallel with the resonance circuit, the second capacitor being greater than the first capacitor.
The system of claim 5, wherein the second capacitor includes the first capacitor and at least one more capacitor.
The system of any one of claims 1 to 6, further comprising a current sensor coupled to the resonance circuit and for measuring an amount of current driven to the resonance circuit, a comparator for determining whether the measured amount of current driven to the resonance circuit exceeds a stored threshold value, optionally, wherein the stored threshold value is stored in a programmed look-up table, optionally, wherein the processor is further configured to dynamically update the stored threshold.
The system of any one of claims 1 to 7, wherein the stored threshold value comprises a lower threshold value and an upper threshold value, and wherein the processor is further configured to detect the change in resonance frequency by determining if the current driven to the resonance circuit either fails to exceed the lower threshold value or exceeds the upper threshold value.
The system of claims of any one of 1 to 8, wherein the compensation circuit comprises a first compensation subcircuit comprising a first capacitor and a second compensation circuit comprising a second capacitor, and wherein the one or more processors is further configured to perform operations comprising: re-determining the current driven to the resonance circuit after activation of the first compensation subcircuit and activating the second compensation subcircuit in response to determining that the re-determined current driven to the resonance circuit still exceeds the threshold wherein activation of the first compensation subcircuit couples the first capacitor in parallel with the resonance circuit, and wherein activation of the second compensation subcircuit couples the second capacitor in parallel with the resonance circuit.
The system of claims of any one of 1 to 9, wherein the resonance circuit comprises a transmitter and wherein the one or more processors is further configured to perform operations comprising: generating interrogation signals using the transmitter, and/or generating acknowledgement signals using the transmitter.
A method for operating an inductive coupling reader, the method comprising: detecting a change in a resonance frequency of the inductive coupling reader; comparing the change in the resonance frequency to a threshold based on comparing an amount of current being driven to the inductive coupling reader to an expected amount of current; determining that the change in the resonance frequency falls outside the threshold based on determining that the amount of current being driven to the inductive coupling reader is greater or less than the expected amount by a given amount; and in response to determining that the change in the resonance frequency falls outside the threshold, adjusting capacitance of a switchable tuning capacitor based on the amount of additional parallel capacitance needed to offset the change in resonance frequency and coupling the switchable tuning capacitor to offset the change in the resonance frequency of the inductive coupling reader.
The method of claim 11, further comprising: re-detecting the change in the resonance frequency of the inductive coupling reader by re-determining that the amount of current being driven to the inductive coupling reader after coupling the switchable tuning capacitor, re-determining that the re-determined current driven to the inductive coupling reader still exceeds the threshold, and in response to re-determining that the change in the resonance frequency still falls outside the threshold, re-adjusting the capacitance of the switchable tuning capacitor based on an additional amount of parallel capacitance needed to further mitigate and compensate for the change in resonance frequency of the inductive coupling reader.
The method of claims 11 or 12, further comprising retrieving the threshold from memory or a lookup table.
The method of any one of claims 11 to 13, wherein the retrieval of the threshold is performed periodically or continually.
The method of any one of claims 11 to 14, further comprising dynamically updating the threshold based on one or more operating conditions.

Description

PRIORITY APPLICATION This application claims priority to U. S. Patent Application Serial Number 16/704,252, filed December 5, 2019, the disclosure of which is incorporated herein in its entirety by reference. 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 that 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. 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: detecting a change in a resonance frequency of the inductive coupling reader; comparing the change in the resonance frequency to a threshold; determining that the change in the resonance frequency exceeds the threshold; and activating a compensation circuit to offset the change in the resonance frequency of the inductive coupling reader in response to determining that the change in the resonance frequency exceeds the threshold. 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 in the resonance frequency comprises measuring an amount of current being driven to the inductive coupling reader using a current sensor. In some embodiments, the amount of current being driven to the inductive coupling reader is compared to the expected amount of current. In such cases, the change in the resonance frequency is determined to exceed the threshold when the amount of current is less than the expected amount of current by a given amount. In some embodiments, the amount of current being driven to the inductive coupling reader comprises the current being driven to an antenna of the inductive coupling reader, and the given amount comprises ten percent of the expected amount of current. In some embodiments, the expected amount of current is retrieved from a look-up table. In some embodiments, the compensation circuit comprises one or more capacitors coupled in parallel to a resonance circuit of the inductive coupling reader. In some embodiments, proper operation of the inductive coupling reader is verified after activating the compensation circuit by comparing a current amount of current being driven to the inductive coupling reader to an expected amount of current. In some embodiments, the threshold comprises a first threshold, and the compensation circuit comprises a first compensation circuit. In such cases, the operations further comprise: determining that the change in the resonance frequency exceeds the first threshold and is less than a second threshold; activating the first compensation circuit in response to determining that the change in the resonance frequency exceeds the first threshold and is less than the second threshold; determining that the change in the resonance frequency exceeds the first threshold and the second threshold; and activating a second compensation circuit in response to determining that the change in the resonance frequency exceeds the first threshold and the second threshold, wherein the second compensation circuit provides a greater offset to the resonance frequency than the first compensation circuit. In some embodiments, activation of the first compensation circuit couples a first capacitor in parallel with a resonance circuit of the inductive coupling reader, and activation of the second compensation circuit couples a second capacitor in parallel with the resonance circuit of the inductive coupling reader, the second capacitor being greater than the first capacitor. In some embodiments, the second capacitor includes the first capacitor and at least one more capacitor. In some embodiments, the operations further comprise computing the offset provided by the compensation circuit by: mounting the inductive coupling reader on a metal surface; measuring a detuning effect of the metal surface on the induct