Dynamic frequency tuning in inductively coupled systems.

Abstract

To improve the overall power efficiency and range of an inductively coupled reader.SOLUTION: The present disclosure describes techniques for operating an inductively coupled reader. The technique includes the operations of: applying an excitation frequency to a resonant circuit of the inductively coupled reader; detecting a change in a resonant frequency of the resonant circuit of the inductively coupled reader; and adjusting the excitation frequency applied to the resonant circuit in response to detection of a change in the resonant frequency of the inductively coupled reader.SELECTED DRAWING: Figure 2A

Description

[Technical field]

[0001] This specification relates generally, but not limited to, to radio frequency identification (RFID) systems, and specifically to techniques for reducing harmful interference effects in RFID systems. This application claims priority to U.S. Provisional Application No. 16 / 705,574, filed December 6, 2019, the disclosure of which is incorporated herein by reference in its entirety. [Background technology]

[0002] 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 contains information that identifies that item. When identification is required, a radio frequency reader unit (e.g., an interrogator) is used to excite (e.g., interrogate) the transponder on the item, which transmits an identifying signal (containing the item's identifying information) back to the reader unit. The reader unit uses the identifying information received from the transponder to perform any of a variety of RFID applications. For example, the identifying information may be used to perform functions such as asset management, inventory tracking, access control, etc. Summary of the Invention

[0003] In some specific embodiments, systems and methods are provided for operating an inductively coupled reader that perform operations including applying an excitation frequency to a resonant circuit of an inductively coupled reader, detecting a change in the resonant frequency of the resonant circuit of the inductively coupled reader, and adjusting the excitation frequency applied to the resonant circuit in response to detecting the change in the resonant frequency of the inductively coupled reader.

[0004] In some embodiments, the change in resonant frequency is caused by an external metallic material in proximity to the inductively coupled reader, such that the range of the inductively coupled reader is reduced in response to the change in resonant frequency.

[0005] In some embodiments, detecting the change includes accessing configuration information of the inductive coupling reader that is indicative of the inductive coupling reader being in proximity to an external metallic material.

[0006] In some embodiments, the resonant circuit comprises a tuned resonant circuit configured to generate a constant resonant frequency of 125 kHz or 134 kHz. In some embodiments, the operations include applying a first excitation frequency to the resonant circuit of the inductively coupled reader, measuring a first amplitude of a first voltage developed across the resonant circuit of the inductively coupled reader by applying the first excitation frequency, and determining that the first amplitude of the first voltage does not meet a criterion.

[0007] In some embodiments, the reference comprises a predetermined voltage level. In some embodiments, the criterion includes exceeding a voltage level produced by application of a second excitation frequency.

[0008] In some embodiments, the operations include applying a second excitation frequency to the resonant circuit of the inductively coupled reader, measuring a second amplitude of a second voltage developed across the resonant circuit of the inductively coupled reader by 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.

[0009] In some embodiments, adjusting the excitation frequency applied to the resonant circuit includes 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.

[0010] In some embodiments, the operations include operating an inductive coupling device inductively coupled to the inductively coupled reader at the adjusted excitation frequency, the inductive coupling device deriving a clock frequency from the adjusted excitation frequency such that data transfer between the inductive coupling device and the inductively coupled reader is synchronized to the adjusted excitation frequency.

[0011] In some embodiments, the inductive coupling device includes a radio frequency identification (RFID) authentication device. In some embodiments, the inductive coupling reader comprises a radio frequency identification (RFID) reader.

[0012] In some embodiments, the excitation frequency adjustment is determined by applying a range of frequencies to the resonant circuit and identifying the frequency at which a maximum voltage amplitude occurs at the output of the inductively coupled reader.

[0013] The range of a conventional RFID reader is typically reduced by metallic materials when in close proximity to the reader because the metallic materials change the resonant frequency of the RFID reader's resonant circuit. The disclosed embodiments detect such interference caused by metallic materials and, in response, adjust the excitation (drive) frequency applied to the resonant circuit. This improves the overall power efficiency and range of the disclosed RFID reader over conventional RFID readers.

[0014] 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 further information regarding this patent application. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram illustrating an RFID system in accordance with various embodiments. [Figure 2A] FIG. 2A is a block diagram illustrating a reader unit used in an RFID system according to various embodiments. [Figure 2B] FIG. 2B illustrates waveforms of drive frequency versus resonant frequency for an exemplary RFID system in accordance with various embodiments. [Diagram 3] FIG. 3 is a flow diagram illustrating an exemplary process for operating an inductive coupling reader according to various embodiments. [Figure 4] FIG. 4 is a block diagram illustrating an example of a machine capable of implementing one or more embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The drawings are not necessarily drawn to scale, and in the drawings like reference numbers may represent like components in different views. Like reference numbers with different suffixes may represent different instances of like components. The drawings illustrate generally, by way of example, and not by way of limitation, various embodiments discussed in the present document.

[0017] This disclosure describes techniques, among others, for operating inductively coupled readers. Specifically, the techniques of this disclosure detect interference and detuning of the resonant circuit of the inductively coupled reader and adjust the excitation (drive) frequency being applied to the resonant circuit accordingly. This improves the overall power efficiency and range of the inductively coupled reader, such as an RFID reader, thereby improving the overall efficiency and functionality of the computer.

[0018] Problems arise in RFID systems when one or more external interfering signals are present within the frequency band of the system during an interrogation operation. Such interference can lead to misidentification and misreporting of items of interest in the RFID system. Such interference is more likely to be caused by metallic materials located in the vicinity of the system of interest. Such metallic materials significantly reduce the range of the RFID interrogator, especially since they change the resonant frequency of the RFID interrogator's resonant circuit. For example, when an inductively coupled reader (e.g., a 13.56 MHz RFID reader) is mounted on a metallic surface, the apparent inductance of the antenna changes. Because the antenna is part of a parallel resonant circuit used to communicate with RFID transponders (e.g., certificates such as RFID tags), detuning this circuit reduces the actual performance (e.g., read range), especially because the drive frequency does not match the resonant frequency of the antenna. This causes the RFID reader to consume more power to read a given RFID tag, thereby wasting system resources.

[0019] To address the challenges of such typical situations, the disclosed technique detects when the resonant circuit of an inductively coupled reader is detuned and compensates for such detuning by modifying the excitation (drive) frequency applied to the resonant circuit, thereby restoring and improving the performance of the inductively coupled reader, thereby increasing the power efficiency and range of the inductively coupled reader, thereby improving the overall efficiency and functionality of the computer.

[0020] 1 is a block diagram illustrating an RFID system according to some embodiments. As illustrated, the RFID system 8 includes an RF reader unit 12 (an inductively coupled reader) and a number 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, 44 and used to identify that item of interest. The items of interest 34, 36, 38, 40, 42, 44 may include, for example, pieces of inventory, people, capital assets, animals, or any other object that may be desired to be tracked or monitored within a particular area. The number of items a particular reader is capable of tracking is typically a matter of design choice.

[0021] The RF reader unit 12 may be a fixed unit, such as, for example, a wall-mounted proximity reader, or a portable unit that can be easily relocated. In general, the coverage area served by an RF reader unit may depend on the transmit power level of that reader, the antenna pattern of the reader transmitting antenna, and the location and orientation of that reader at any particular time.

[0022] During normal operation of the exemplary system of FIG. 1, the RF reader unit 12 periodically interrogates its coverage area 52 to identify items of interest currently located therein. That is, the reader unit 12 periodically transmits an RF interrogation signal within the coverage area 52, which acts as a "request" for each of the RF identification tags 16-26 within the area 52 to transmit an identification signal identifying the associated item of interest. The RF interrogation signal drives the resonant circuit at a specific frequency that matches the resonant frequency of the resonant circuit. Upon receiving the RF interrogation signal, the RF tag derives a local clock frequency based on the RF interrogation signal. The RF tag synchronizes the transmission and reception of data to and from the reader unit 12 according to the local clock frequency and thus the driving frequency of the RF interrogation signal. Upon receiving the interrogation signal, each RF tag within the coverage area 52 responds by transmitting its identification signal back to the interrogating reader. After receiving identification information from all RF tags within the coverage area 52, the RF reader unit reports the collected information to the appropriate entity.

[0023] With reference to FIG. 1, it can be seen that interference is likely to occur between the RF reader unit 12 and metallic materials. For example, the RF reader unit 12 may be mounted on a wall that includes metallic materials. Such metallic materials may affect the resonant circuit of the RF reader unit 12, changing the resonant frequency of the resonant circuit. This may reduce the range of the RF reader unit 12 and cause the RF reader unit 12 to misidentify or fail to identify items in the area 52 that are farther away from the RF reader unit 12. In particular, the resonant frequency of the resonant circuit may change, while the drive frequency of the interrogation signal may correspond to the expected resonant frequency under conditions in which no interference is present. Due to the mismatch between the drive frequency and the resonant frequency, the overall power consumed by the system increases and the range of the RF reader unit 12 decreases. That is, the size of the area 52 may decrease when metallic materials are present near the RF reader unit 12. Also, 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 properly may increase.

[0024] In accordance with the present disclosure, methods and apparatus are provided for reducing the adverse effects of interference in an RFID system by modifying the excitation (drive) frequency applied to the resonant circuit to compensate when metallic materials are determined to cause a change in the resonant frequency of the RF reader unit 12.

[0025] 2A is a block diagram illustrating an RF reader unit 200 according to one embodiment of the present disclosure. The RF reader unit 200 may be an example of the RF reader unit 12 (FIG. 1). As shown, the reader unit 200 may include a tuning circuit 210, a driver circuit 230, a receiver circuit 240, an antenna voltage detection circuit 250, and a microcontroller 220. In some implementations, the antenna voltage detection circuit 250 may be excluded or deactivated from the RF reader unit 200.

[0026] The microcontroller 220 is operable to control the operation of the RF reader unit 200 to interrogate, track, and report on items of interest within the coverage area 52 of the RF reader unit 200. The microcontroller 220 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. Additionally, one or more of the other functional blocks shown in FIG. 2A may also be implemented digitally in the same (or different) digital processor as the microcontroller 220. The microcontroller 220 may include an adjustable frequency timer and volatile and non-volatile memory.

[0027] The tuning circuit 210 includes an inductive loop antenna and a tuning capacitance. The tuning circuit 210 is used to generate and transmit (under the control of the microcontroller 220 and the driver circuit 230) an interrogation signal for transmission into the coverage area 52 via the inductive loop antenna during an interrogation operation. The receiver circuit 240 operates, among other things, to receive identification signals from RF tags located within the coverage area 52, demodulate and decode the received identification signals, and provide the resulting identification information to the microcontroller 220.

[0028] In some embodiments, the microcontroller 220 detects a change in the resonant frequency of the RF reader unit 200. Specifically, the microcontroller 220 detects a change in the resonant frequency of the tuning circuit 210. In some implementations, the microcontroller 220 detects a change in the resonant frequency based on a preset setting of the microcontroller 220 stored in the non-volatile memory of the microcontroller 220. For example, a configuration bit stored in the non-volatile memory of the microcontroller 220 during operation or manufacturing of the RF reader unit 200 may indicate the presence or absence of an interference source, such as a metallic material. The microcontroller 220 may access the configuration bit during operation to determine whether the configuration bit is asserted or de-asserted. If the configuration bit is asserted, the microcontroller 220 determines that an interference source, such as a metallic material, is present or in close proximity to the RF reader unit 200. In such a case, the microcontroller 220 detects a change in the resonant frequency of the RF reader unit 200. If the configuration bit is de-asserted, the microcontroller 220 determines that an interference source is not present.

[0029] In some embodiments, the microcontroller 220 communicates with the antenna voltage detection circuit 250 to determine and detect changes in the resonant frequency of the RF reader unit 200. Specifically, the microcontroller 220 may use the antenna voltage detection circuit 250 to measure the value of the voltage consumed by the tuning circuit 210 when an interrogation signal having a given excitation frequency is applied to the tuning circuit 210. The given excitation frequency applied is a frequency that matches the expected resonant frequency of the tuning circuit 210 (e.g., the resonant frequency at which the tuning circuit 210 normally operates when no interference source is present). For example, the tuning circuit 210 may be configured to operate at a resonant frequency of 125 kHz or 134 kHz or any other suitable value. In such a case, the excitation frequency of the interrogation signal is also set to 125 kHz or 134 kHz to match the resonant frequency. If the voltage value does not meet the threshold or falls below a certain threshold (e.g., because the resonant frequency does not match the excitation frequency), the microcontroller 220 detects a change in the resonant frequency.

[0030] Upon determining that the resonant frequency of the tuned circuit 210 has changed, the microcontroller 220 adjusts the excitation frequency of the interrogation signal using an adjustable frequency timer to offset the change in resonant frequency. For example, if the resonant frequency is 10% higher than the expected resonant frequency, the microcontroller 220 increases the excitation frequency by 10%.

[0031] The preset threshold to which the voltage measured by the antenna voltage detection circuit 250 is compared may be set to a value 10% (or any other suitable percentage or value) higher or lower than the value of the voltage consumed by the tuning circuit 210 when no metallic material is in proximity to the RF reader unit 200. The preset threshold may be programmed into a look-up table or memory during manufacture of the RF reader unit 200 and / or may be dynamically updated based on different operating conditions. In some cases, the preset threshold may be a specific value or may be a range of values. If the measured voltage is outside the range of values, the microcontroller 220 detects a change in the resonant frequency and adjusts the excitation frequency of the interrogation circuit by a specific value.

[0032] In some cases, the microcontroller 220 instructs the driver circuit 230 to operate at a first frequency or a second frequency. The first frequency may correspond to a resonant frequency of the tuned circuit 210 under normal conditions in the absence of an interference source. In response to detecting a change in the resonant frequency (e.g., based on a configuration bit value or a measured voltage), the microcontroller 220 instructs the driver circuit 230 to operate at a second frequency that is higher or lower than the first frequency.

[0033] In some embodiments, the microcontroller 220 searches for an optimal excitation frequency of the interrogation signal based on the voltage value measured by the antenna voltage detection circuit 250. For example, the microcontroller 220 may first drive the tuning circuit 210 at a first frequency corresponding to the resonant frequency of the tuning circuit 210 under normal conditions in the absence of an interference source. The microcontroller 220 receives a first voltage measurement from the antenna voltage detection circuit 250. The microcontroller 220 stores this first voltage measurement in a volatile memory of the microcontroller 220. The microcontroller 220 then increases the excitation frequency to drive the tuning circuit 210 at a second frequency that is higher than the first frequency. The microcontroller 220 receives a second voltage measurement from the antenna voltage detection circuit 250. The microcontroller 220 compares the second voltage measurement with the first voltage measurement. In response to determining that the second voltage measurement is greater than the first voltage measurement, the microcontroller 220 may increase the excitation frequency to drive the tuned circuit 210 at a third frequency that is greater than the second frequency. Alternatively, in response to determining that the second voltage measurement is greater than the first voltage measurement, the microcontroller 220 may set the excitation frequency to drive the tuned circuit 210 at the second frequency. In response to determining that the second voltage measurement is less than the first voltage measurement, the microcontroller 220 may decrease the excitation frequency to drive the tuned circuit 210 at a third frequency that is less than the first frequency. Alternatively, in response to determining that the second voltage measurement is less than the first voltage measurement, the microcontroller 220 may set the excitation frequency to drive the tuned circuit 210 at the first frequency.

[0034] The microcontroller 220 again compares the resulting voltage measured by the antenna voltage detection circuit 250 when driving the tuning circuit 210 at the third frequency with the voltage obtained when driving the tuning circuit 210 at the previous frequency. If the third frequency corresponds to a frequency higher than the previously applied frequency, the microcontroller 220 may continue to gradually increase the drive frequency by a particular value until the resulting voltage is lower than the previously measured voltage. If the third frequency corresponds to a frequency lower than the previously applied frequency, the microcontroller 220 may continue to gradually decrease the drive frequency by a particular value until the resulting voltage is lower than the previously measured voltage. At that point, the microcontroller 220 sets the drive frequency to the frequency that resulted in the previously measured voltage. That is, the microcontroller 220 searches (by gradually increasing or decreasing the drive frequency) for the frequency that results in the maximum voltage measurement output by the antenna voltage detection circuit 250.

[0035] FIG. 2B is a waveform of drive frequency versus resonant frequency of an exemplary RFID system according to various embodiments. As shown in FIG. 2B, when the drive frequency of the interrogation signal applied to the resonant circuit does not match the resonant frequency of the resonant circuit, the antenna voltage (and therefore the range of the RFID system) is reduced. As shown in FIG. 2B, the antenna voltage is at a maximum value when the drive frequency matches the resonant or resonant frequency of the resonant circuit. Specifically, under normal operating conditions where no interference source, such as a metallic material, is present or is not in close proximity to the RF reader unit 200, the resonant frequency of the resonant circuit is at a preset value of 125 kHz or 134 kHz. The excitation frequency of the interrogation signal applied to the resonant circuit is also 125 kHz or 134 kHz, and the excitation frequency is set to be equal to or match the value of the resonant frequency. The resulting voltage measured by the antenna voltage detection circuit 250 is close to or at a maximum value. At a later point in time, when the RF reader unit 200 is placed in close proximity to an interference source, such as a metallic material, the resonant frequency of the resonant circuit changes (e.g., from 125 kHz to 135 kHz). When the resonant circuit is driven with the currently set excitation frequency (e.g., 125 kHz), the voltage measurement provided by the antenna voltage detection circuit 250 drops compared to the previously measured maximum voltage value. In response, the excitation frequency is increased or decreased by a certain value that may coincide with the modified resonant frequency of the resonant circuit. As a result, when the resonant circuit is driven with the adjusted excitation frequency (e.g., 135 kHz), the voltage measurement provided by the antenna voltage detection circuit 250 is close to or equal to the maximum value.

[0036] In this case, the inductive coupling device (e.g., an RF tag) receives an RF interrogation signal at the adjusted excitation frequency and derives a local clock frequency based on the RF interrogation signal (e.g., 135 kHz). The inductive coupling device synchronizes data transmission and reception with the reader unit 12 according to the local clock frequency and thus the adjusted excitation (drive) frequency of the RF interrogation signal.

[0037] FIG. 3 is a flow diagram illustrating an example process 300 for operating an inductive coupling reader according to various embodiments. In operation 310, the inductively coupled reader applies an excitation frequency to a resonant circuit of the inductively coupled reader.

[0038] In operation 320, the inductively coupled reader detects a change in the resonant frequency of the resonant circuit of the inductively coupled reader. At operation 330, the inductively coupled reader adjusts the excitation frequency applied to the resonant circuit in response to detecting a change in the resonant frequency of the inductively coupled reader.

[0039] FIG. 4 is a block diagram of an example machine 400 on which any one or more of the techniques (e.g., methods) described herein may be performed and / or may be included as part of an inductive coupling reader. In alternative embodiments, the machine 400 may operate as a standalone device or may be connected (e.g., networked) with other machines. In a network deployment, the machine 400 may operate in the functions of a server machine, a client machine, or both, in a server-client network environment. In one example, the machine 400 may function as a peer machine in a peer-to-peer (P2P) (or other distributed) network environment. The machine 400 may be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile phone, a web appliance, an IoT device, an automotive system, an aerospace system, or any machine capable of executing instructions (sequential or otherwise) that specify operations to be performed by the machine. Moreover, although only a single machine is illustrated, the term "machine" should be interpreted to include any collection of machines that individually or collectively execute a set (or sets) of instructions to perform any one or more of the methods described herein, such as via cloud computing, software as a service (SaaS), or other computer cluster configurations.

[0040] The examples described herein may include or operate by logic, components, devices, packages, or mechanisms. A circuit configuration is a group (e.g., a set) of circuits implemented in a tangible entity that includes hardware (e.g., simple circuits, gates, logic, etc.). Circuit components may flexibly respond to the passage of time and variations in the underlying hardware. A circuit includes elements that may, when operating, work alone or in concert to perform a specific task. In one example, the hardware of a circuit configuration may be immutably designed to perform a specific operation (e.g., hardwired). In one example, the hardware of a circuit configuration may include variably connected physical components (e.g., execution units, transistors, simple circuits, etc.) that include computer-readable media that have been physically altered (e.g., magnetically, electrically, or by movable arrangements of immutable mass particles) to encode instructions for a specific operation. In connecting the physical components, the underlying electrical properties of the hardware components are altered (e.g., from an insulator to a conductor, or vice versa). The instructions cause the configuring hardware (e.g., execution unit or loading mechanism) to form elements of the circuitry within the hardware via variable connections to perform some of the specific tasks during operation. Thus, the computer-readable medium is communicatively coupled to other components of the circuitry when the device is operating. In one example, any of the physical components may be used in multiple elements of multiple circuitry. For example, during operation, an execution unit may be used in a first circuit in a first circuitry at one time and may be reused by a second circuit in the first circuitry or by a third circuit in the second circuitry at another time.

[0041] The machine (e.g., computer system) 400 may include a hardware processor 402 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof, such as, for example, a memory controller), a main memory 404, and a static memory 406, some or all of which may be in communication with each other via an interlink (e.g., a bus) 408. The machine 400 may further include a display device 410, an alphanumeric input device 412 (e.g., a keyboard), and a user interface (UI) navigation device 414 (e.g., a mouse). In one example, the display device 410, the alphanumeric input device 412, and the UI navigation device 414 may be touch screen displays. The machine 400 may further include a storage device 422 (e.g., a drive unit), a signal generating device 418 (e.g., a speaker), a network interface device 420, and one or more sensors 416 (e.g., 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, etc.). The machine 400 may include an output controller 428 (e.g., a serial connection (e.g., a universal serial bus (USB)), a parallel connection, or other wired or wireless (e.g., infrared (IR)) connection, a near field communication (NFC) connection, etc.) for communicating with or controlling one or more peripheral devices (e.g., a printer, a card reader, etc.).

[0042] Storage device 422 may include a machine-readable medium having stored thereon one or more sets of data structures or instructions 424 (e.g., software) that embody or utilize any one or more of the techniques or functions described herein. Also, instructions 424 may reside, completely or at least partially, within main memory 404, static memory 406, or within hardware processor 402 during execution of instructions 424 by machine 400. In one example, one or any combination of hardware processor 402, main memory 404, static memory 406, and storage device 421 may constitute a machine-readable medium.

[0043] Although the machine-readable medium is illustrated as a single medium, the term "machine-readable medium" may include a single medium or multiple media (e.g., a centralized or distributed database, or associated caches and servers) configured to store one or more instructions 424.

[0044] The term "machine-readable medium" may include any temporary or non-transient medium capable of storing, encoding, or carrying temporary or non-transient instructions for execution by the machine 400, and capable of storing, encoding, or carrying data structures used by or associated with instructions that cause the machine 400 to execute any one or more of the techniques of this disclosure. Non-limiting examples of machine-readable media include solid-state memory, optical media, and magnetic media. In one example, a massive machine-readable medium includes a machine-readable medium having a plurality of particles having an unchanging (e.g., stationary) mass. Thus, a massive machine-readable medium is not a transient propagating signal. Particular examples of massive 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, CD-ROM disks, and DVD-ROM disks.

[0045] Instructions 424 (e.g., software, programs, operating system (OS), etc.) or other data stored in storage device 421 may be accessed by main memory 404 for use by hardware processor 402. Main memory 404 (e.g., DRAM) is a different type of storage than storage device 421 (e.g., SSD), which is typically fast but volatile and therefore suitable for long-term storage, including periods of "off" states. Instructions 424 or data are typically loaded into main memory 404 for use by hardware processor 402 upon use by a user or machine 400. When main memory 404 becomes full, virtual space from storage device 421 can be allocated to supplement main memory 404, but because storage device 421 is typically slower than main memory 404 and write speeds are typically at least twice as slow as read speeds, using virtual memory (as opposed to main memory 404, e.g., DRAM) can significantly reduce the user experience due to the latency of the storage device. Furthermore, the use of storage device 421 for virtual memory can significantly reduce the usable life of storage device 421.

[0046] The instructions 424 may further be transmitted or received over a communications network 426 using a transmission medium via the network interface device 420 utilizing any one of a number of transport protocols (e.g., Frame Relay, Internet Protocol (IP), Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Hypertext Transfer Protocol (HTTP), etc.). Examples of communications networks may include, among others, local area networks (LANs), wide area networks (WANs), packet data networks (e.g., the Internet), mobile telephone networks (e.g., cellular networks), Plain Old Telephone Service (POTS), and wireless data networks (e.g., the Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards known as Wi-Fi®, the IEEE 802.16 family of standards known as WiMax®, the IEEE 802.15.4 family of standards for peer-to-peer (P2P) networks, etc.). In one example, the network interface device 420 may include one or more physical jacks (e.g., Ethernet, coaxial cable, or telephone jacks) or one or more antennas for connecting to the communications network 426. In one example, network interface device 420 may include multiple antennas for wireless communication using at least one of single-input multiple-output (SIMO), multiple-input multiple-output (MIMO), or multiple-input single-output (MISO) technologies. The term "transmission medium" is intended to include any tangible or intangible medium capable of storing, encoding, or carrying instructions executed by machine 400, including digital or analog communications signals or other tangible or intangible media to facilitate communication of such software.

[0047] Each of the non-limiting aspects or embodiments described herein may stand on its own or may be implemented in various permutations or combinations with one or more of the other embodiments. The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the subject matter of the present invention may be practiced. These embodiments are also referred to herein as "examples." Such examples may include other elements in addition to those shown or described. However, the inventors also contemplate examples in which only the elements shown or described are provided. Moreover, the inventors also contemplate examples using any combination or permutation of these elements (or one or more aspects thereof) as shown or described, with respect to the particular example (or one or more aspects thereof) or with respect to the other example (or one or more aspects thereof) shown or described.

[0048] In the event of inconsistent usage between this specification and a document incorporated by reference, the usage in this specification takes precedence. The term "a" is used herein as is common in patent literature to include one or more, independent of other instances and the use of "at least one" or "one or more." In this specification, the term "or" refers to non-exclusiveness, unless otherwise specified, and "A or B" includes "A but not B," "B but not A," and "A and B." In this specification, the term "comprises" is used synonymously with the term "comprises." Also, in the following claims, the terms "comprises" and "comprises" are considered to be open-ended, i.e., systems, devices, articles, compositions, methods, or processes that include elements other than those recited following such terms are still considered to be within the scope of the claims. Moreover, in the following claims, the terms "first," "second," "third," etc. are used merely as labels and are not intended to impose numerical requirements on their objects.

[0049] Examples of the methods described herein may be at least partially implemented on a machine or computer. Some examples may include computer-readable or machine-readable media encoded with temporary or non-transient instructions operable to configure an electronic device to perform the methods described in the above examples. Implementations of such methods may include code, such as microcode, assembly language code, high-level language code, etc. Such code may include temporary or non-transient computer-readable instructions for performing various methods. The code may form part of a computer program product. Further, in one example, the code may be tangibly stored in 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 magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memory (RAM), read-only memory (ROM), etc.

[0050] The above description is illustrative and not restrictive. For example, the above examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments may be used by those skilled in the art upon review of the above description. The Abstract is provided to enable the reader to quickly ascertain the nature of the technical disclosure. As such, it is not intended to interpret or limit the scope or meaning of the claims. Also, in the above detailed description, various features may be grouped together to simplify the disclosure. This should not be construed as intending that any disclosed feature not recited in a claim is essential to any claim. Rather, the subject matter of the invention may include less than all features of a particular disclosed embodiment. Thus, the following claims are incorporated into the detailed description as examples or embodiments, with each claim standing on its own as a separate embodiment, and such embodiments can be implemented with each other in various combinations or permutations. The scope of the subject matter of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. 1. A method for operating an inductively coupled reader, comprising: applying an excitation frequency to a resonant circuit of the inductively coupled reader; detecting a change in a resonant frequency of the resonant circuit of the inductively coupled reader; adjusting the excitation frequency applied to the resonant circuit in response to detecting a change in the resonant frequency of the inductively coupled reader; Equipped with the change in resonant frequency is caused by an external interference source in proximity to the inductively coupled reader; The method, wherein detecting the change includes obtaining a configuration bit from a non-volatile memory of the inductive coupling reader that indicates the presence or absence of the external interference inducing source.

2. The method of claim 1 , wherein the resonant circuit comprises a tuned oscillator circuit configured to generate an initial resonant frequency of 125 kHz or 134 kHz.

3. applying a first excitation frequency to the resonant circuit of the inductively coupled reader; measuring a first amplitude of a first voltage developed across the resonant circuit of the inductively coupled reader by applying the first excitation frequency; determining that the first amplitude of the first voltage does not meet a predetermined voltage level; The method of claim 1 or 2, further comprising:

4. determining whether the configuration bit is asserted or deasserted during operation of the inductive coupling reader; detecting a change in the resonant frequency if the configuration bit is determined to be asserted; determining that the external interference inducing source is not present if the configuration bit is determined to be deasserted; The method of any one of claims 1 to 3, further comprising:

5. applying a second excitation frequency to the resonant circuit of the inductively coupled reader; measuring a second amplitude of a second voltage developed across the resonant circuit of the inductively coupled reader by applying the second excitation frequency; determining that the first amplitude of the first voltage is less than the second amplitude of the second voltage; The method of claim 3 further comprising:

6. The method of claim 5 , wherein adjusting the first excitation frequency applied to the resonant circuit comprises setting the first excitation frequency to the second excitation frequency.

7. The method of claim 5 , wherein the second excitation frequency is higher or lower than the first excitation frequency by a predetermined amount.

8. 10. The method of claim 1, further comprising operating an inductively coupled device inductively coupled to the inductively coupled reader at the adjusted excitation frequency, the inductively coupled device deriving a clock frequency from the adjusted excitation frequency such that data transfer between the inductively coupled device and the inductively coupled reader is synchronized with the adjusted excitation frequency.

9. The method of claim 8 , wherein the inductive coupling device comprises a radio frequency identification (RFID) authentication device.

10. The method of any one of claims 1 to 9, wherein the inductive coupling reader comprises a radio frequency identification (RFID) reader.

11. applying a range of frequencies to the resonant circuit; identifying a frequency at which a maximum voltage amplitude occurs at the output of said inductively coupled reader; The method of claim 1 , further comprising determining the excitation frequency adjustment by:

12. an inductive coupling reader including one or more processors, the one or more processors comprising: applying an excitation frequency to a resonant circuit of the inductively coupled reader; detecting a change in a resonant frequency of the resonant circuit of the inductively coupled reader; adjusting the excitation frequency applied to the resonant circuit in response to detecting a change in the resonant frequency of the inductively coupled reader; configured to perform operations including: the change in resonant frequency is caused by an external interference source in proximity to the inductively coupled reader; The system, wherein detecting the change includes obtaining a configuration bit from a non-volatile memory of the inductive coupling reader that indicates the presence or absence of the external interference inducing source.

13. an inductive coupling reader including a microcontroller, an antenna voltage detection circuit, and an adjustable frequency timer, implemented by one or more processors, the one or more processors: applying an excitation frequency to a resonant circuit of the inductive coupling reader by the microcontroller; measuring a value of a voltage consumed by the resonant circuit by the antenna voltage detection circuit; detecting a change in the resonant frequency of the resonant circuit by the microcontroller when the measured voltage value does not meet a threshold or falls below a certain threshold; adjusting, by the microcontroller, the excitation frequency applied to the resonant circuit in response to detecting a change in the resonant frequency; configured to perform operations including: The system, wherein adjusting the excitation frequency includes using the adjustable frequency timer to offset changes in the resonant frequency.

14. applying the excitation frequency includes applying a first excitation frequency to the resonant circuit; adjusting the excitation frequency includes applying a second excitation frequency to the resonant circuit, the second excitation frequency being higher than the first excitation frequency; The one or more processors further comprise: receiving a first voltage measurement from the antenna voltage detection circuit, the first voltage measurement being measured upon application of the first excitation frequency to the resonant circuit; receiving a second voltage measurement from the antenna voltage detection circuit, the second voltage measurement being measured upon application of the second excitation frequency to the resonant circuit; comparing, by the microcontroller, the first voltage measurement and the second voltage measurement; applying, by the microcontroller, a third excitation frequency to the resonant circuit, the third excitation frequency being different from the first and second excitation frequencies based on a comparison of the first voltage measurement and the second voltage measurement; The system of claim 13 configured to perform operations including:

15. applying the third excitation frequency to the resonant circuit applying the third excitation frequency, which is greater than the second excitation frequency, to the resonant circuit when the second voltage measurement is greater than the first voltage measurement; The system of claim 14 including applying an excitation frequency to the resonant circuit that is less than the first excitation frequency when the second voltage measurement is less than the first voltage measurement.

16. A system according to any one of claims 13 to 15, wherein the resonant circuit comprises a tuned oscillator circuit configured to generate an initial resonant frequency of 125 kHz or 134 kHz.

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