Detuning detection and compensation for inductively coupled systems

Abstract

The present disclosure describes techniques for operating an inductively coupled reader. The techniques include operations including: detecting a change in a resonant frequency of the inductively coupled reader; comparing the change in the resonant frequency to a threshold; determining that the change in the resonant frequency falls outside the threshold; and in response to determining that the change in the resonant frequency falls outside the threshold, activating a compensation circuit to counteract the change in the resonant frequency of the inductively coupled reader.

Description

[0001] Priority application

[0002] This application claims priority to U.S. patent application serial number 16 / 704,252 filed on December 5, 2019, the disclosure of which is incorporated herein by reference in its entirety.

[0003] Public content area

[0004] This document relates 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 Art

[0005] 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 that identifies the item. When identification is required, a radio frequency reader unit (e.g., an interrogator) is used to excite (e.g., query) the transponder on the item and then send an identification signal (including the identification information of the item) back to the reader unit. The reader unit then uses the identification information received from the transponder to perform any of many different RFID applications. For example, the identification information can be used to perform functions such as asset management, inventory tracking, access control, and other functions. Summary of the invention

[0006] In certain embodiments, systems and methods for operating an inductively coupled reader are provided. The disclosed systems and methods perform operations including: detecting a change in a resonant frequency of the inductively coupled reader; comparing the change in the resonant frequency to a threshold; determining that the change in the resonant frequency exceeds the threshold; and in response to determining that the change in the resonant frequency exceeds the threshold, activating a compensation circuit to offset the change in the resonant frequency of the inductively coupled reader.

[0007] In some embodiments, a change in the resonant frequency is caused by an external metallic material in close proximity to the inductively coupled reader, and the range of the inductively coupled reader is reduced due to the change in the resonant frequency.

[0008] In some implementations, detecting the change in the resonant frequency includes measuring an amount of current driven to the inductively coupled reader using a current sensor.

[0009] In some embodiments, the amount of current driven to the inductively coupled reader is compared to an expected amount of current. In such a case, when the amount of current is less than the expected amount of current by a given amount, it is determined that the change in resonant frequency exceeds a threshold.

[0010] In some embodiments, the amount of current driven to the inductively coupled reader includes current driven to an antenna of the inductively coupled reader, and the given amount includes ten percent of the expected amount of current.

[0011] In some implementations, the expected amount of current is retrieved from a lookup table.

[0012] In some embodiments, the compensation circuit includes one or more capacitors in a resonant circuit with the inductively coupled reader.

[0013] In some implementations, correct operation of the inductively coupled reader is verified after activation of the compensation circuit by comparing the amount of present current driven to the inductively coupled reader to the expected amount of current.

[0014] In some embodiments, the threshold comprises a first threshold, and the compensation circuit comprises a first compensation circuit. In such a case, the operation further comprises: determining that the change in the resonant 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 resonant frequency exceeds the first threshold and is less than the second threshold; determining that the change in the resonant frequency exceeds the first threshold and the second threshold; and activating the second compensation circuit in response to determining that the change in the resonant frequency exceeds the first threshold and the second threshold, wherein the second compensation circuit provides a greater shift in the resonant frequency than the first compensation circuit.

[0015] In some embodiments, activation of the first compensation circuit couples a first capacitor in parallel with the resonant circuit of the inductively coupled reader, and activation of the second compensation circuit couples a second capacitor in parallel with the resonant circuit of the inductively coupled reader, the second capacitor being larger than the first capacitor.

[0016] In some embodiments, the second capacitor includes the first capacitor and at least one additional capacitor.

[0017] In some embodiments, the operations further include calculating an offset provided by the compensation circuit by: mounting the inductively coupled reader on a metal surface; measuring a detuning effect of the metal surface on the inductively coupled reader; and calculating an offset to compensate for the measured detuning effect.

[0018] In some embodiments, the compensation circuit includes: a switch; and one or more capacitors having a first terminal coupled to a first terminal of a capacitor of a resonant circuit of the inductively coupled reader and having a second terminal coupled to the switch.

[0019] In some implementations, one or more capacitors are coupled to the switch via a diode.

[0020] In some implementations, the compensation circuitry is activated by closing a switch to couple the second terminal of the one or more capacitors to ground.

[0021] In some implementations, the switch includes a transistor.

[0022] In some embodiments, the inductively coupled reader comprises an RFID reader.

[0023] Metallic materials in close proximity to conventional RFID readers typically reduce the range of conventional RFID readers because the metallic materials change the resonant frequency of the resonant circuit of the RFID reader. The disclosed embodiments detect disturbances and detuning of the resonant circuit of an inductively coupled reader and, in response, switch additional parallel capacitance to compensate for such detuning. In this manner, the overall power efficiency and range of an inductively coupled reader, such as an RFID reader, is improved, which improves the overall efficiency and functionality of a computer.

[0024] This summary is intended to provide an overview of the subject matter of this patent application. It is not intended to provide an exclusive or exhaustive description of the subject matter of the present invention. The detailed description is included to provide additional information about this patent application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In the accompanying drawings, which are not necessarily drawn to scale, similar reference numerals may describe similar components in different views. Similar reference numerals with different letter suffixes may represent different instances of similar components. The accompanying drawings generally illustrate various embodiments discussed in this document by way of example and not by way of limitation.

[0026] Figure 1 is a block diagram illustrating an RFID system according to various embodiments.

[0027] Figure 2 is a block diagram illustrating a reader unit used in an RFID system according to various embodiments.

[0028] Figure 3 is a block diagram illustrating a reader unit used in an RFID system according to various embodiments.

[0029] Figure 4 is a flow chart depicting an example process for operating an inductively coupled reader in accordance with various implementations.

[0030] Figure 5 is a block diagram illustrating an example of a machine upon which one or more embodiments may be implemented. DETAILED DESCRIPTION

[0031] The present disclosure further describes techniques for operating an inductively coupled reader. Specifically, the disclosed techniques detect disturbances and detuning of a resonant circuit of an inductively coupled reader, and in response, switch additional parallel capacitance to compensate for such detuning. In this manner, the overall power efficiency and range of an inductively coupled reader, such as an RFID reader, is improved, which improves the overall efficiency and functionality of a computer.

[0032] In RFID systems, problems arise when one or more external interference signals appear within the frequency band of the system during an interrogation operation. Such interference will typically result in misidentification of the item of interest and erroneous reporting in the RFID system. Increasingly, such interference is caused by metallic materials located near the system of interest. Such metallic materials significantly reduce the range of the RFID interrogator, particularly because such metallic materials change the resonant frequency of the resonant circuit of the RFID interrogator. For example, if an inductively coupled reader (e.g., a 13.56 MHz RFID reader) is mounted on a metal surface, the apparent inductance of its antenna will change. Since the antenna is part of a parallel resonant circuit used to communicate with an RFID transponder (e.g., a credential such as an RFID tag), the actual performance (e.g., read range) will be reduced due to the detuning of this circuit. This will also cause the RFID reader to consume more power to read a given RFID tag, which wastes system resources.

[0033] To address the shortcomings of such a typical scenario, the disclosed technology detects the detuning of the resonant circuit of the inductively coupled reader and compensates for such detuning. In particular, the disclosed technology uses a current sensor to measure the actual power consumption of the inductively coupled reader. If the power consumption fails to reach a predetermined threshold (e.g., exceeds the threshold, drops below the threshold, or falls outside the threshold range), the system determines that the resonant circuit has been detuned (e.g., due to the presence of metallic material adjacent to the inductively coupled reader). In such a case, the inductively coupled reader uses a switchable tuning capacitor that allows the inductively coupled reader to add additional parallel capacitance to mitigate and compensate for the detuning. This enables the performance of the inductively coupled reader to be restored and improved, which enhances the power efficiency and range of the inductively coupled reader. Therefore, the overall efficiency and functionality of the computer are improved.

[0034] Figure 1is a block diagram illustrating an RFID system according to some embodiments; as shown, the RFID system 8 includes: an RF reader unit 12 (inductively coupled reader) and a first plurality of RF identification tags 16, 18, 20, 22, 24, 26, each of which is attached to a corresponding item of interest 34, 36, 38, 40, 42 and 44 for identifying the item of interest. The items of interest 34, 36, 38, 40, 42 and 44 may include, for example, inventory items, personnel, capital assets, or any other object that may be desired to be tracked or monitored within a particular area. The number of items that a particular reader is capable of tracking is generally a matter of design choice.

[0035] The RF reader unit 12 may be a fixed unit such as a wall mounted proximity reader, or a portable unit that can be easily relocated. In general, the coverage area served by the RF reader unit will be a function of the reader's transmit power level, the antenna pattern of the reader's transmitting antenna, and the reader's location and direction at any particular time.

[0036] exist Figure 1 During normal operation of the example system, the RF reader unit 12 periodically interrogates its coverage area 52 to identify the items of interest currently located therein. That is, the reader unit 12 periodically transmits an RF interrogation signal within the coverage area 52, which serves as a "request" that each of the RF tags 16 to 26 within the area 52 transmits its identification signal identifying the associated items of interest. Each of the RF tags within the coverage area 52 receives the interrogation signal and responds by transmitting its identification signal back to the interrogating reader. In order to prevent signal collisions in the channel between the RF tags and the reader within a particular coverage area, the RF tags can each transmit their identification signals after different quasi-random delay periods. When the RF reader receives an identification signal from one of the RF tags, the RF reader transmits a confirmation signal to the RF tag, notifying the RF tag that its identity has been recorded. After receiving the confirmation signal, the identified RF tag will not resend its identification signal. If the RF tag does not receive a confirmation signal after transmitting its identification signal and waiting for a predetermined period of time, it can be assumed that a collision has occurred in the channel and its identification signal can be resent after another quasi-random delay period. This may continue until every RF tag in the coverage area receives an acknowledgement signal from the reader.After receiving identification information from all RF tags within its coverage area 52, the RF reader unit reports the collected information to the appropriate entities.

[0037] Reference Figure 1, it will be appreciated that some interference between the RF reader unit 12 and the metallic material may occur. For example, the RF reader unit 12 may be wall mounted on a wall that includes metallic material. Such metallic material may affect the resonant circuit of the RF reader unit 12 and change the resonant frequency of the resonant circuit. This may reduce the range of the RF reader unit 12, causing the RF reader unit 12 to misidentify or fail to identify items within the area 52 that are farther away from the RF reader unit 12. That is, when metallic material is present near the RF reader unit 12, the size of the area 52 may be reduced. In addition, due to the change in the resonant frequency of the RF reader unit 12, the amount of power required for the RF reader unit 12 to operate normally may increase.

[0038] In accordance with the present disclosure, a method and apparatus are provided for reducing the negative effects of interference within an RFID system by compensating for metallic materials that are determined to cause a change in the resonant frequency of the RF reader unit 12 .

[0039] Figure 2 1 is a block diagram illustrating an RF reader unit 12 according to one embodiment of the present disclosure. As shown, the reader unit 12 includes: an antenna 60, a matching and tuning circuit 62, a resonant circuit 210 including a transmitter 64 and a receiver 66, a controller 68, a current sensor 70, a comparator 72, a compensation circuit 220, and a user interface 74. Although the comparator 72 is Figure 2 Although the comparator 72 is drawn as a separate physical component in FIG. 6 , some or all of the functions of the comparator 72 may be implemented by the controller 68. That is, the functions of the comparator 72 may be implemented in software by the controller 68, rather than by hardware components. In such a case, the output of the current sensor 70 is provided directly to the controller 68.

[0040] The controller 68 is operable to control the operation of the reader unit 12 to interrogate, track, and report items of interest within the coverage area 52 of the reader unit 12. The controller 68 is implemented using a digital processing device such as a general purpose microprocessor, a digital signal processor, a reduced instruction set computer, a complex instruction set computer, or a field programmable gate array. Figure 2 One or more of the other functional blocks shown in FIG. 6A may also be digitally implemented within the same (or different) digital processor as controller 68 .

[0041] The transmitter 64 is used to generate an interrogation signal that is transmitted to the coverage area 52 via the antenna 60 during an interrogation operation (under the control of the controller 68). As described above, the transmitter 64 can also be used to generate an acknowledgment signal for transmission to a particular RF tag after receiving identification information from the tag. The receiver 66 is operable to, among other things, receive, demodulate and decode identification signals received from RF tags located within the coverage area 52, and to transmit the resulting identification information to the controller 68.

[0042] The matching and tuning circuit 62 is a device that improves the efficiency of transferring the power obtained from the driver to the antenna 60. The impedance at the antenna 60 may be too high for the low voltage driver to produce enough power directly, and in such a case, the matching network is used to compensate and match the impedance at the antenna 60. In addition to impedance matching in the case of an inductively coupled RFID system, the matching and tuning circuit 62 can also be used to correctly set the resonant frequency of the antenna 60.

[0043] When the controller 68 collects tag identification information from the corresponding coverage area 52, the controller 68 reports the data to the appropriate entity via the user interface 74. Alternatively, the controller 68 can wait until all tag information has been collected for the coverage area 52, and then the controller 68 reports the data. Depending on the type of reporting performed within the system, the user interface 74 can take many different forms. For example, the interface 74 can be coupled to a video display for displaying identification data to an operator. Alternatively, the interface 74 can include a modem for transmitting data to a remote computer for storage. In some embodiments, the reader unit in a large RFID system is connected to a central control processor via the interface 74, which collects, manages and analyzes the identification information to generate system-wide reports. The central control processor can also use the information to perform other system functions such as activating electric door locks, sending messages to user displays (including displays on the reader itself), sounding alarms, and activating recording devices (such as cameras). Other forms of user interfaces 74 can also be used.

[0044] In some embodiments, the controller 68 detects a change in the resonant frequency of the reader 12. Specifically, the controller 68 detects a change in the resonant frequency of the resonant circuit 210. In some embodiments, the controller 68 detects a change in the resonant frequency based on the amount of current driven to the reader 12 and, in particular, driven to the resonant circuit 210. In particular, the current sensor 70 is coupled to the resonant circuit 210 and measures the amount of current driven to the resonant circuit 210. The current sensor 70 provides the measured current value to the comparator 72. The comparator 72 accesses a preset threshold and determines whether the value of the measured current received from the current sensor 70 falls outside the threshold. In some cases, the comparator 72 determines whether the measured current falls below the threshold. In some cases, the comparator 72 determines whether the measured current exceeds the threshold. In some cases, the comparator 72 determines whether the measured current falls outside the threshold range. That is, the threshold may be a specific value such as a value 10% higher or 10% lower than the normal current, or the threshold may be a range such as within 10% of the normal current.

[0045] The preset threshold of comparator 72 represents the amount of current expected to be drawn by resonant circuit 210 under normal operation. When the current falls outside the preset threshold, comparator 72 provides an indication to controller 68. The indication can inform controller 68 that metal material is in close proximity to reader 12. In response to determining that the current is above a preset value, below a preset value, or outside a range of values, controller 68 can detect that the resonant frequency of the inductively coupled reader has changed by an amount that falls outside the threshold. In such a case, controller 68 activates compensation circuit 220 to couple one or more capacitors in parallel with resonant circuit 210 to offset the change in resonant frequency.

[0046] As an example, the preset threshold value may be set to a value 10% higher or lower than the value of the current drawn by the resonant circuit 210 (e.g., the antenna of the resonant circuit 210) when no metallic material is in close proximity to the reader 12. The preset threshold value may be programmed into a lookup table or memory during manufacture of the reader 12 and / or may be dynamically updated based on different operating conditions. The comparator 72 may periodically or continuously retrieve the preset threshold value from the lookup table or memory to compare with the current being measured by the current sensor 70.

[0047] In some embodiments, after the controller 68 activates the compensation circuit 220, the controller 68 may instruct the current sensor 70 to remeasure the current drawn by the resonant circuit 210. The remeasured current is compared to the preset threshold by the comparator 72 to determine whether the change in the resonant frequency of the resonant circuit 210 still falls outside the threshold. As an example, after activating the compensation circuit 220, the current measured by the current sensor 70 may now be within 5% of the normal operating current driven to the resonant circuit 210. The preset threshold may be set to a value that is 10% higher or lower than the normal operating current, and in such a case, the controller 68 may determine that the change in the resonant frequency of the resonant circuit 210 no longer falls outside the threshold (e.g., because the current measured by the current sensor 70 is not 10% more or less than the normal operating current of the resonant circuit 210).

[0048] In some embodiments, after the controller 68 activates the compensation circuit 220, the controller 68 may determine that the current measured by the current sensor 70 may now be 12% greater than the normal operating current driven to the resonant circuit 210. That is, even though the compensation circuit 220 is activated, the change in the resonant frequency of the resonant circuit 210 may still fall outside the threshold. In such a case, the controller 68 may instruct the compensation circuit 220 to couple one or more additional capacitors in parallel with the resonant circuit 210 (e.g., to increase the total parallel capacitance coupled to the resonant circuit 210).

[0049] As an example, the compensation circuit 220 may include a first compensation circuit and a second compensation circuit. The first compensation circuit may include a first capacitor, and the second compensation circuit may include a second capacitor. The first capacitor may have the same size and value as the second capacitor. In such a case, the controller 68 determines that the change in the resonant frequency of the resonant circuit 210 falls outside the first threshold but within the second threshold. For example, the first threshold may be set to a value that is 10% greater than the normal operating current drawn by the resonant circuit 210, and the second threshold may be set to a value that is 15% greater than the normal operating current drawn by the resonant circuit 210. The controller 68 may determine that the current drawn by the resonant circuit 210 is 12% greater than the normal operating current drawn by the resonant circuit 210. In such a case, the controller 68 determines that the change in the resonant frequency of the resonant circuit 210 (caused by the amount that the current drawn by the resonant circuit 210 is 12% greater than the normal operating current) falls outside the first threshold but within the second threshold. In response, the controller 68 activates the first compensation circuit. By activating the first compensation circuit, the controller 68 couples the first capacitor in parallel to the resonant circuit 210.

[0050] In some cases, after activating the first compensation circuit or at some other time before activating the first compensation circuit, the controller 68 measures the current driven to the resonant circuit 210. The controller 68 determines that the change in the resonant frequency falls outside the first threshold and the second threshold. For example, the controller 68 may determine that the current drawn by the resonant circuit 210 is 17% greater than the normal operating current drawn by the resonant circuit 210. In such a case, the controller 68 determines that the change in the resonant frequency of the resonant circuit 210 (caused by the current drawn by the resonant circuit 210 being 17% greater than the normal operating current) falls outside the first threshold (e.g., set to a value 10% greater than the normal operating current) and the second threshold (e.g., set to a value 15% greater than the normal operating current). In response, the controller 68 activates the second compensation circuit. By activating the second compensation circuit, the controller 68 couples the first capacitor and the second capacitor in parallel to the resonant circuit 210.

[0051] In some embodiments, the first capacitor can be smaller than the second capacitor. In such a case, activation of the second compensation circuit couples the larger capacitor in parallel with the resonant circuit 210 and decouples the smaller capacitor of the first compensation circuit from the resonant circuit 210. That is, when the respective compensation circuits implement capacitors of different sizes, only one of the first compensation circuit and the second compensation circuit is coupled to the resonant circuit 210.

[0052] In some embodiments, the first compensation circuit or the second compensation circuit is coupled in parallel with the resonant circuit 210 through a switch such as a transistor. For example, when the controller 68 activates (closes) the switch of the compensation circuit 220, one or more capacitors of the compensation circuit 220 can be coupled in parallel to the resonant circuit 210. When the switch is deactivated (opened), the one or more capacitors are decoupled from the resonant circuit 210.

[0053] In some embodiments, the value of the capacitor or capacitance in the compensation circuit 220 is determined when the reader 12 is manufactured. In one example, to this end, the reader 12 is mounted on a metal surface or material. The detuning effect of the resonant circuit 210 of the reader 12 is measured. As an example, the current sensor can output a first current value drawn by the resonant circuit 210 when the reader 12 is not mounted on a metal surface or material. The first current value can represent the expected current drawn by the resonant circuit 210 under normal operating conditions. In some cases, the threshold value can be calculated as a function or factor of the expected current (for example, the threshold value can be set to a value that is 10% greater than the first current value). In some cases, the current sensor can output a second current value drawn by the resonant circuit 210 after the reader 12 is mounted on a metal surface or material. In such an implementation, the threshold value can be set to a value of the second current value or to a value based on the second current value or a function of the second current value but higher or lower than the second current value. After the reader 12 is mounted on the metal surface, one or more capacitors may be coupled in parallel to the resonant circuit 210 until a capacitor value is determined that causes the current measured by the current sensor to be substantially close to the first current value. The capacitance value may be used to set the capacitance value of the compensation circuit 220. Thus, when the reader 12 is operated in close proximity to the metal surface (e.g., as determined by the current measured by the current sensor 70 exceeding a threshold), the controller 68 activates the compensation circuit 220 to couple the capacitor value in parallel to the resonant circuit 210 to offset the change in the resonant frequency of the resonant circuit 210.

[0054] In some implementations, the capacitor value may be determined mathematically (eg, without actually mounting reader 12 on a metal surface during manufacturing). In some cases, the capacitor value may be determined based on the expected metal material upon which reader 12 is disposed during operation.

[0055] Figure 3 is a block diagram showing a reader unit for use in an RFID system according to various embodiments. Figure 3As shown, the control circuit system 68 can be coupled to the resonant circuit and the compensation circuit. The control circuit system 68 can include and / or implement the functions of the controller 68. The control circuit 68 measures the current drawn by the resonant circuit. In response to determining that the current drawn by the resonant circuit exceeds the threshold, the controller 68 activates the switch 320. Therefore, the compensation capacitor 310 becomes coupled in parallel with the resonant circuit. That is, the first terminal of the compensation capacitor 310 is coupled to the ground via the diode 330 and the switch 320. When the switch is deactivated, the compensation capacitor 310 is not coupled to the ground, and therefore, is decoupled from the resonant circuit. When the switch 320 is closed, the first terminal of the compensation capacitor 310 is coupled to the ground via the diode 330 and the switch 320. The second terminal of the compensation capacitor 310 is coupled to the first terminal of one or more capacitors of the resonant circuit. The second terminal of the one or more capacitors of the resonant circuit is coupled to the ground. In this way, when the switch 320 is activated or closed, the compensation capacitor 310 can be coupled in parallel with the capacitor of the resonant circuit.

[0056] Figure 4 is a flow chart depicting an example process 400 for operating an inductively coupled reader in accordance with various implementations.

[0057] At operation 410, the inductively coupled reader detects a change in a resonant frequency of the inductively coupled reader.

[0058] At operation 420, the inductively coupled reader compares the change in resonant frequency to a threshold value.

[0059] At operation 430, the inductively coupled reader determines that the change in resonant frequency falls outside a threshold.

[0060] At operation 440 , in response to determining that the change in the resonant frequency falls outside of a threshold value, the inductively coupled reader activates a compensation circuit to counteract the change in the resonant frequency of the inductively coupled reader.

[0061] Figure 55 is a block diagram of an example machine 500, on which any one or more of the techniques (e.g., methods) discussed herein may be performed and / or may be included in the reader discussed above. In alternative embodiments, the machine 500 may operate as an independent device, or may be connected (e.g., networked) to other machines. In a networked deployment, the machine 500 may operate in a server-client network environment with the capabilities of a server machine, a client machine, or both. In an example, the machine 500 may act as a peer machine in a peer-to-peer (P2P) (or other distributed) network environment. The machine 500 may be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile phone, a web application, an IoT device, an automotive system, an aerospace system, or any machine capable of (sequentially or otherwise) executing instructions specifying an action to be taken by the machine. Further, while a single machine is illustrated, the term "machine" shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets of instructions) to perform any one or more of the methodologies discussed herein, such as via cloud computing, Software as a Service (SaaS) or other computer cluster configurations.

[0062] As described herein, examples may include logic, components, devices, packages, or mechanisms, or may be operated by logic, components, devices, packages, or mechanisms. A circuit system is a collection of circuits (e.g., a circuit set) implemented in a tangible entity including hardware (e.g., simple circuits, gates, logic, etc.). Circuit system components may be flexible over time and potential hardware variability. A circuit system includes components that can perform specific tasks individually or in combination when operating. In one example, the hardware of the circuit system may be designed to perform specific operations (e.g., hard wiring) invariably. In an example, the hardware of the circuit system may include variably connected physical components (e.g., execution units, transistors, simple circuits, etc.) to encode instructions for specific operations, and the variably connected physical components include computer-readable media that are physically modified (e.g., magnetically, electrically, by movable placement of constant mass particles, etc.). When the physical components are connected, the potential electrical properties of the hardware components are changed, for example, from an insulator to a conductor or from a conductor to an insulator. Instructions enable embedded hardware (e.g., execution units or loading mechanisms) to create components of the circuit system in hardware via variable connections to perform parts of specific tasks when operating. Thus, when the device operates, the computer-readable medium is communicatively coupled to other components of the circuit system. In examples, any physical component can be used in more than one component of more than one circuit system. For example, in operation, an execution unit can be used in a first circuit in a first circuit system at one point in time and reused by a second circuit in the first circuit system or by a third circuit in the second circuit system at a different time.

[0063] The machine (e.g., computer system) 500 may include a hardware processor 502 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof such as a memory controller, etc.), a main memory 504, and a static memory 506, some or all of which may communicate with each other via an interconnection link (e.g., a bus) 508. The machine 500 may also include a display device 510, an alphanumeric input device 512 (e.g., a keyboard), and a user interface (UI) navigation device 514 (e.g., a mouse). In an example, the display device 510, the alphanumeric input device 512, and the UI navigation device 514 may be a touch screen display. The machine 500 may additionally include a storage device 522 (e.g., a drive unit); a signal generating device 518 (e.g., a speaker); a network interface device 520; one or more sensors 516 such as a global positioning system (GPS) sensor, a wing sensor, a mechanical device sensor, a temperature sensor, an ICP sensor, a bridge sensor, an audio sensor, an industrial sensor, a compass, an accelerometer, or other sensors; and one or more system-in-package data acquisition devices 590. The system-in-package data acquisition device 590 may implement some or all of the functions of the offset calibration system 100. The machine 500 may include an output controller 528, such as a serial (e.g., universal serial bus (USB)), parallel or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection to communicate with or control one or more peripheral devices (e.g., printers, card readers, etc.).

[0064] The storage device 522 may include a machine-readable medium having stored thereon one or more data structures or sets of instructions 524 (e.g., software) implementing or utilized by any one or more of the techniques or functions described herein. The instructions 524 may also reside, in whole or in part, within the main memory 504, within the static memory 506, or within the hardware processor 502 during execution of the instructions 524 by the machine 500. In an example, one or any combination of the hardware processor 502, the main memory 504, the static memory 506, or the storage device 521 may constitute a machine-readable medium.

[0065] Although the machine-readable medium is illustrated as a single medium, the term “machine-readable medium” may include a single medium or multiple media (eg, a centralized or distributed database, or associated caches and servers) configured to store one or more instructions 524 .

[0066] The term "machine-readable medium" may include any transient or non-transient medium capable of storing, encoding or carrying transient or non-transient instructions for execution by the machine 500 and causing the machine 500 to perform any one or more of the techniques of the present disclosure, or any transient or non-transient medium capable of storing, encoding or carrying data structures used by such instructions or data structures associated with such instructions. Non-limiting examples of machine-readable media may include solid-state memory and optical and magnetic media. In an example, a large-capacity machine-readable medium includes a machine-readable medium having a plurality of particles, the particles having a constant (e.g., stationary) mass. Therefore, a large-capacity machine-readable medium is not a transient propagation signal. Specific examples of large-capacity machine-readable media may include: non-volatile memory, such as semiconductor memory devices (e.g., electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

[0067] Instructions 524 (e.g., software, programs, operating systems (OS), etc.) or other data stored on storage devices 521 can be accessed by main memory 504 for use by hardware processors 502. Main memory 504 (e.g., DRAM) is typically fast but volatile, and is therefore a different type of storage than storage devices 521 (e.g., SSD), which are suitable for long-term storage, including when in "off" conditions. Instructions 524 or data used by a user or machine 500 are typically loaded into main memory 504 for use by hardware processors 502. When main memory 504 is full, virtual space can be allocated from storage devices 521 to supplement main memory 504; however, because storage devices 521 are typically slower than main memory 504, and write speeds are typically at least twice as slow as read speeds, using virtual memory can greatly reduce the user experience due to storage device latency (compared to main memory 504, such as DRAM). In addition, using storage devices 521 as virtual memory can greatly reduce the useful life of storage devices 521.

[0068] Instructions 524 may also be sent or received over a communication network 526 using a transmission medium via the network interface device 520 using any of a number of transmission protocols (e.g., frame relay, Internet Protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks may include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), a mobile telephone network (e.g., a cellular network), a plain old telephone service (POTS) network, and a wireless data network (e.g., a wireless network known as a cellular network). The Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards, known as IEEE 802.16 family of standards), IEEE 802.15.4 family of standards, peer-to-peer (P2P) networks), etc. In an example, the network interface device 520 may include one or more physical jacks (e.g., Ethernet, coaxial, or telephone jacks) or one or more antennas to connect to the communication network 526. In an example, the network interface device 520 may include multiple antennas to communicate wirelessly using at least one of single-input multiple-output (SIMO) technology, multiple-input multiple-output (MIMO) technology, or multiple-input single-output (MISO) technology. The term "transmission medium" should be taken to include any tangible or intangible medium that can store, encode, or carry instructions for execution by the machine 500, and includes digital or analog communication signals or other tangible or intangible media to facilitate the communication of such software.

[0069] Each of the non-limiting aspects or examples described herein may stand alone or may be combined with one or more of the other examples in various permutations or combinations.

[0070] The above specific embodiments include reference to the accompanying drawings, which form a part of the specific embodiments. The accompanying drawings show the specific embodiments in which the subject matter of the present invention can be put into practice by way of illustration. These embodiments are also referred to as "examples" in this article. Such examples may include elements other than the elements shown or described. However, the inventors have also considered examples in which only the elements shown or described are provided. In addition, the inventors have also contemplated examples of any combination or permutation of those elements (or one or more aspects of those elements) shown or described with respect to a specific example (or one or more aspects of a specific example) or with respect to other examples (or one or more aspects of other examples) shown or described in this article.

[0071] In the event of an inconsistency in usage between this document and any document incorporated by reference, the usage in this document controls.

[0072] In this document, as is common in patent literature, the terms "a" or "an" are used to include one or more, regardless of any other instances or uses of "at least one of" or "one or more". In this document, unless otherwise indicated, the term "or" is used to represent a non-exclusive or, such that "A or B" includes "A but not B", "B but not A", and "A and B". In this document, the terms "including" and "in..." are used as the plain English equivalents of the corresponding terms "comprising" and "wherein". In addition, in the appended claims, the terms "including" and "comprising" are open-ended, that is, systems, devices, articles, compositions, formulas, or processes that include elements in addition to those listed after such terms in the claim are still considered to fall within the scope of the claim. In addition, in the following claims, the terms "first", "second", "third", etc. are used only as labels and are not intended to impose numerical requirements on their objects.

[0073] The method examples described herein may be implemented at least in part by a machine or computer. Some examples may include a computer-readable medium or machine-readable medium encoded with a transient or non-transient instruction, which may be operated to configure an electronic device to perform the method described in the above example. The implementation of such a method may include code such as microcode, assembly language code, high-level language code, etc. Such a code may include a transient or non-transient computer-readable instruction for performing various methods. The code may form a part of a computer program product. In addition, in an example, the code may be tangibly stored on one or more volatile non-transient or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media may include, but are not limited to, hard disks, removable disks, removable optical disks (e.g., compact disks and digital video disks), tapes, memory cards or sticks, random access memory (RAM), read-only memory (ROM), etc.

[0074] The above description is intended to be illustrative rather than restrictive. For example, the above examples (or one or more aspects of the above examples) can be used in combination with each other. For example, a person of ordinary skill in the art can use other embodiments after reading the above description. An abstract is provided to comply with 37C.FR§1.72(b) to allow readers to quickly determine the nature of the disclosure of the present technology. The abstract is submitted with the understanding that the abstract will not be used to interpret or limit the scope or meaning of the claims. In addition, in the above detailed description, various features can be grouped together to simplify the disclosure. This should not be interpreted as intended to be necessary for any claim to disclose features that are not required for protection. Instead, the subject matter of the invention may be less than all the features of a specific disclosed embodiment. Therefore, the attached claims are thus incorporated into the specific embodiments as examples or embodiments, wherein each claim exists independently as a separate embodiment, and it is expected that such embodiments can be combined with each other in various combinations or arrangements. The scope of the subject matter of the present invention should be determined with reference to the attached claims and the full scope of equivalents given by such claims.

Claims

1. A method for operating an inductively coupled reader, the method comprising: detecting a change in a resonant frequency of the inductively coupled reader; comparing the change in the resonant frequency to a threshold value based on a comparison of an amount of current driven to the inductively coupled reader to an expected amount of current; determining that the change in the resonant frequency falls outside the threshold based on a determination that the amount of the current driven to the inductively coupled reader is greater or less than the expected amount of current by a given amount; as well as In response to determining that the change in the resonant frequency falls outside the threshold, a compensation circuit is activated to counteract the change in the resonant frequency of the inductively coupled reader.

2. The method according to claim 1, wherein: The change in the resonant frequency is caused by an external metallic material in close proximity to the inductively coupled reader, and wherein a range of the inductively coupled reader is reduced due to the change in the resonant frequency.

3. The method according to claim 1, wherein: Detecting the change in the resonant frequency includes measuring an amount of the current driven to the inductively coupled reader using a current sensor.

4. The method according to claim 1, wherein: The amount of current driven to the inductively coupled reader comprises a current driven to an antenna of the inductively coupled reader, and wherein the given amount comprises ten percent of the expected amount of current. The method of claim 1 , further comprising retrieving the expected amount of current from a lookup table.

6. The method according to claim 1, wherein: The compensation circuit includes one or more capacitors coupled in parallel with a resonant circuit of the inductively coupled reader.

7. The method of claim 1, further comprising verifying proper operation of the inductively coupled reader after activating the compensation circuit by comparing an amount of present current driven to the inductively coupled reader to the expected amount of current.

8. The method according to claim 1, wherein: The compensation circuit includes a first compensation circuit, and the method further includes: In response to determining that the change in the resonant frequency falls outside the threshold and within a second threshold, activating the first compensation circuit; and In response to determining that the change in the resonant frequency falls outside the threshold and the second threshold, a second compensation circuit is activated, wherein the second compensation circuit provides a greater shift in the resonant frequency than the first compensation circuit.

9. The method according to claim 8, wherein: Activation of the first compensation circuit couples a first capacitor in parallel with a resonant circuit of the inductively coupled reader, and wherein activation of the second compensation circuit couples a second capacitor in parallel with the resonant circuit of the inductively coupled reader, the second capacitor being larger than the first capacitor.

10. The method according to claim 9, wherein: The second capacitor includes the first capacitor and at least one additional capacitor.

11. The method of claim 1 , further comprising calculating an offset provided by the compensation circuit by: mounting the inductively coupled reader on a metal surface; measuring the effect of detuning the metal surface on the inductively coupled reader; and The offset is calculated to compensate for the measured detuning effect.

12. The method according to claim 1, wherein: The compensation circuit comprises: Switches; and One or more capacitors having a first terminal coupled to a first terminal of a capacitor of a resonant circuit of the inductively coupled reader and having a second terminal coupled to the switch.

13. A system comprising: An inductively coupled reader comprising one or more processors configured to perform operations comprising: detecting a change in a resonant frequency of the inductively coupled reader; comparing the change in the resonant frequency to a threshold value based on a comparison of an amount of current driven to the inductively coupled reader to an expected amount of current; determining that the change in the resonant frequency falls outside the threshold based on a determination that the amount of the current driven to the inductively coupled reader is greater or less than the expected amount of current by a given amount; and In response to detecting the change in the resonant frequency, in response to determining that the change in the resonant frequency falls outside the threshold, activating a compensation circuit to counteract the change in the resonant frequency of the inductively coupled reader.

14. The system according to claim 13, wherein: The change in the resonant frequency is caused by an external metallic material in close proximity to the inductively coupled reader, and wherein a range of the inductively coupled reader is reduced due to the change in the resonant frequency.

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