Dynamic frequency tuning for inductively coupled systems

Abstract

This disclosure describes techniques for operating an inductively coupled reader. The techniques include operations 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, 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.

Description

[0001] Priority Application

[0002] This application claims priority to U.S. Provisional Application Serial No. 16 / 705,574, filed December 6, 2019, the disclosure of which is incorporated by reference herein in its entirety. TECHNICAL FIELD

[0003] The present 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

[0004] RFID systems are systems that use radio frequency transponders (e.g., tags) to identify items of interest. Each radio frequency transponder is attached to or near a respective item and includes information that identifies the item. When identification is needed, a radio frequency reader unit (e.g., interrogator) is used to energize (e.g., interrogate) the transponder on the item, which then sends an identification signal (including the item’s identification information) back to the reader unit. The reader unit then uses the identification information received from the transponder to perform any of a number of different RFID applications. For example, the identification information can be used to perform functions such as asset management, inventory tracking, access control, and the like. SUMMARY

[0005] In some particular embodiments, a system and method for operating an inductively coupled reader are provided. The disclosed system and method perform operations including 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 detecting the change in the resonant frequency of the inductively coupled reader.

[0006] In some embodiments, the change in the resonant frequency is caused by an external metallic material being in close proximity to the inductively coupled reader, and a range of the inductively coupled reader is reduced due to the change in the resonant frequency.

[0007] In some embodiments, detecting the change includes accessing configuration information for the inductively coupled reader, the configuration information indicating that the inductively coupled reader is in close proximity to the external metallic material.

[0008] In some embodiments, the resonant circuit includes tuned oscillator circuitry configured to generate a fixed resonant frequency of 125 kHz or 134 kHz.

[0009] 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 across the resonant circuit of the inductively coupled reader resulting from applying the first excitation frequency; and determining that the first amplitude of the first voltage fails to satisfy a criterion.

[0010] In some embodiments, the criterion includes a predetermined voltage level.

[0011] In some embodiments, the criterion includes exceeding a voltage level resulting from applying the second excitation frequency.

[0012] 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 across the resonant circuit of the inductively coupled reader resulting from applying the second excitation frequency; and determining that the first amplitude of the first voltage is less than the second amplitude of the second voltage.

[0013] In some embodiments, adjusting the excitation frequency applied to the resonant circuit includes setting the excitation frequency to the second excitation frequency.

[0014] In some embodiments, the second excitation frequency is higher or lower than the first excitation frequency by a predetermined amount.

[0015] In some embodiments, the operations include causing an inductively coupled device inductively coupled to the inductively coupled reader to operate at the adjusted excitation frequency, wherein the inductively coupled device derives a clock frequency from the adjusted excitation frequency such that data transmission between the inductively coupled device and the inductively coupled reader is synchronized with the adjusted excitation frequency.

[0016] In some embodiments, the inductively coupled device includes a radio frequency identification (RFID) credential device.

[0017] In some embodiments, the inductively coupled reader includes a radio frequency identification (RFID) reader.

[0018] In some embodiments, the adjustment to the excitation frequency is determined by: applying a range of frequencies to the resonant circuit; and identifying a frequency that causes a maximum voltage amplitude to be produced at an output of the inductively coupled reader.

[0019] Metallic materials in close proximity to a conventional RFID reader typically reduce the range of the conventional RFID reader because the metallic materials change the resonant frequency of the resonant circuit of the RFID reader. The disclosed embodiments detect interference, such as that caused by metallic materials, and in response, adjust the excitation (drive) frequency applied to the resonant circuit. In this manner, the overall power efficiency and range of the disclosed RFID reader is improved compared to conventional RFID readers.

[0020] This Summary is intended to provide an overview of the subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the inventive subject matter. The Detailed Description is included to provide further information about the present patent application. BRIEF DESCRIPTION OF DRAWINGS

[0021] In the drawings, which are not necessarily drawn to scale, like numerals can describe similar components in different views. Like numerals having different letter suffixes can represent different instances of similar components. The drawings illustrate generally, by way of example, various embodiments discussed in the present document.

[0022] Figure 1 is a block diagram illustrating an RFID system, in accordance with various embodiments.

[0023] Figure 2A is a block diagram illustrating a reader unit for use in an RFID system, in accordance with various embodiments.

[0024] Figure 2B is an illustrative RFID system drive and resonant frequency waveform, in accordance with various embodiments.

[0025] Figure 3 is a flow diagram depicting an example process for operating an inductively coupled reader, in accordance with various embodiments.

[0026] Figure 4 is a block diagram illustrating an example of a machine upon which one or more embodiments can be implemented. DETAILED DESCRIPTION

[0027] The present disclosure describes, among other things, techniques for operating an inductively coupled reader. In particular, the disclosed techniques detect disturbances and detuning of a resonant circuit of an inductively coupled reader, and in response, adjust an excitation (drive) frequency applied to the resonant circuit. In this way, the overall power efficiency and range of the inductively coupled reader, e.g., an RFID reader, is improved, which improves the overall efficiency and functionality of the computer.

[0028] In an RFID system, problems arise when one or more external interference signals are present in the frequency band of the system during an interrogation operation. Such interference will typically result in false identification of items of interest and false reporting in the RFID system. Increasingly, such interference is caused by metallic materials located in the vicinity of the system of interest. Such metallic materials significantly reduce the range of the RFID interrogator, in particular 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 metallic surface, the apparent inductance of its antenna will change. Since the antenna is part of a parallel resonant circuit used to communicate with RFID transponders (e.g., credentials such as RFID tags), the actual performance (e.g., read range) will deteriorate due to the detuning of this circuit, in particular because the drive frequency will not match the resonant frequency of the antenna. This will also cause the RFID reader to consume more power to read a given RFID tag, which wastes system resources.

[0029] To address the shortcomings of such typical scenarios, the disclosed technology detects instances of detuning of the resonant circuit of an inductively coupled reader and compensates for such detuning by modifying the excitation (drive) frequency applied to the resonant circuit. This enables the performance of the inductively coupled reader to be restored and improved, which improves the power efficiency and range of the inductively coupled reader. As a result, the overall efficiency and functionality of the computer is improved.

[0030] Figure 1 is 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 plurality of RF identification tags 16, 18, 20, 22, 24, 26, each attached to a respective 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 can include, for example, inventory items, personnel, capital assets, animals, or any other objects that it can be desirable to track or monitor within a particular area. The number of items that a particular reader is able to track is typically a matter of design choice.

[0031] The RF reader unit 12 can be a fixed unit, such as a wall-mounted proximity reader, or can be a portable unit that can be easily repositioned. Typically, the coverage area served by the RF reader unit will be a function of the transmission power level of the reader, the antenna pattern of the reader's transmission antenna, and the location and orientation of the reader at any particular time.

[0032] In Figure 1During normal operation of the example system, 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 its identification signal identifying the associated item of interest. The RF interrogation signal drives the resonant circuit at a particular frequency that matches the resonant frequency of the resonant circuit. The RF tag receives the RF interrogation signal and derives a local clock frequency based on the RF interrogation signal. The RF tag synchronizes the exchange of data with the reader unit 12 according to the local clock frequency and, in turn, according to the driving frequency of the RF interrogation signal. 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. After receiving the identification information from all of the RF tags within its coverage area 52, the RF reader unit reports the collected information to the appropriate entity.

[0033] Referring to Figure 1 It can be appreciated that some interference between the RF reader unit 12 and metallic materials can occur. For example, the RF reader unit 12 can be wall-mounted on a wall that includes metallic materials. Such metallic materials can affect the resonant circuit of the RF reader unit 12 and change the resonant frequency of the resonant circuit. This can reduce the range of the RF reader unit 12, resulting in the RF reader unit 12 incorrectly identifying or failing to identify items within the area 52 that are further away from the RF reader unit 12. In particular, when the resonant frequency of the resonant circuit changes, the driving frequency of the interrogation signal can correspond to the expected resonant frequency in the absence of the interference. Because the driving frequency and the resonant frequency do not match, the total power consumed by the system increases and the range of the RF reader unit 12 decreases. That is, the size of the area 52 can be reduced when metallic materials are present near the RF reader unit 12. Furthermore, the amount of power required for the RF reader unit 12 to operate normally can increase because the resonant frequency RF of the RF reader unit 12 changes.

[0034] In accordance with the present disclosure, a method and apparatus are provided for reducing the negative effects of interference within an RFID system by modifying the excitation (driving) frequency applied to the resonant circuit to compensate for metallic materials determined to cause a change in the resonant frequency of the RF reader unit 12.

[0035] Figure 2A is a block diagram illustrating an RF reader unit 200 in accordance with one embodiment of the present disclosure. The RF reader unit 200 can be illustrative of the RF reader unit 12 Figure 1). As shown, the reader unit 200 can include a tuning circuit 210, a drive 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 can be excluded or disabled from the RF reader unit 200.

[0036] The microcontroller 220 is operable to control the operation of the RF reader unit 200 in order 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. In addition, Figure 2A One or more of the other functional blocks shown in FIG. 2 can also be implemented digitally within the same (or a different) digital processor as the microcontroller 220. The microcontroller 220 can include adjustable frequency timers as well as volatile and non-volatile memory.

[0037] The tuning circuit 210 includes an inductive loop antenna and a tuning capacitor. The tuning circuit 210 is used to generate and transmit an interrogation signal (under the control of the microcontroller 220 and the drive circuit 230) via the inductive loop antenna into the coverage area 52 during an interrogation operation. The receiver circuit 240 is operable, inter alia, to receive, demodulate, and decode identification signals received from RF tags located within the coverage area 52, and is operable to deliver the resulting identification information to the microcontroller 220.

[0038] In some implementations, the microcontroller 220 detects a change in the resonant frequency of the RF reader unit 200. In particular, the microcontroller 220 detects a change in the resonant frequency of the tuning circuit 210. In some implementations, the microcontroller 220 detects the change in the resonant frequency based on a preconfigured setting stored in the non-volatile memory of the microcontroller 220. For example, during operation of the RF reader unit 200 or during manufacture of the RF reader unit 200, a configuration bit stored in the non-volatile memory of the microcontroller 220 can indicate the presence or absence of an interference source such as a metallic material. The microcontroller 220 can access this configuration bit during operation and determine whether the configuration bit is valid or invalid. If the configuration bit is invalid, 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 valid, the microcontroller 220 determines that an interference source is not present.

[0039] In some implementations, 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, when an interrogation signal having a given excitation frequency is applied to the tuning circuit 210, the microcontroller 220 can use the antenna voltage detection circuit 250 to measure the amount of voltage consumed by the tuning circuit 210. The given excitation frequency applied matches the expected resonant frequency of the tuning circuit 210 (e.g., the resonant frequency of the tuning circuit 210 when operating under normal conditions without the presence of an interference source). For example, the tuning circuit 210 can be configured to operate at a resonant frequency of 125 kHz or 134 kHz or any other suitable value. In such cases, the excitation frequency of the interrogation signal is also set to 125 kHz or 134 kHz to match the resonant frequency. If the amount of voltage fails to meet a threshold or falls below a specified threshold (e.g., because the resonant frequency does not match the excitation frequency), the microcontroller 220 detects a change in the resonant frequency.

[0040] In response to determining that the resonant frequency of the tuning circuit 210 has changed, the microcontroller 220 uses an adjustable frequency timer to adjust the excitation frequency of the interrogation signal to offset the change in the 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%.

[0041] When no metallic material is in close proximity to the RF reader unit 200, the preset threshold value compared to the voltage measured by the antenna voltage detection circuit 250 can be set to a value that is 10% (or any other suitable percentage or value) higher or 10% (or any other suitable percentage or value) lower than the value of voltage consumed by the tuning circuit 210. The preset threshold value can be programmed into a lookup table or memory during manufacturing of the RF reader unit 200 and / or can be dynamically updated based on different operating conditions. In some cases, the preset threshold value can be a specific value or can be a range of values. If the measured voltage falls 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 the specified amount.

[0042] In some cases, the microcontroller 220 instructs the driver circuit 230 to operate at a first frequency or a second frequency. The first frequency can correspond to the resonant frequency of the tuning circuit 210 when operating under normal conditions without the presence 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.

[0043] In some implementations, the microcontroller 220 searches for an optimal excitation frequency of the interrogation signal based on voltage values measured by the antenna voltage detection circuit 250. For example, the microcontroller 220 can initially drive the tuning circuit 210 at a first frequency that corresponds to a resonant frequency of the tuning circuit 210 in normal conditions without the presence of an interference source. The microcontroller 220 receives a first voltage measurement from the antenna voltage detection circuit 250. The microcontroller 220 stores the first voltage measurement in a volatile memory of the microcontroller 220. Next, the microcontroller 220 increases the excitation frequency so as 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 to the first voltage measurement. In response to determining that the second voltage measurement is greater than the first voltage measurement, the microcontroller 220 can increase the excitation frequency so as to drive the tuning circuit 210 at a third frequency that is higher than the second frequency. Alternatively, in response to determining that the second voltage measurement is greater than the first voltage measurement, the microcontroller 220 can set the excitation frequency so as to drive the tuning 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 can decrease the excitation frequency so as to drive the tuning circuit 210 at a third frequency that is lower than the first frequency. Alternatively, in response to determining that the second voltage measurement is less than the first voltage measurement, the microcontroller 220 can set the excitation frequency so as to drive the tuning circuit 210 at the first frequency.

[0044] The microcontroller 220 again compares the resulting voltage measured by the antenna voltage detection circuit 250 as a result of driving the tuning circuit 210 at the third frequency to the voltage resulting from driving the tuning circuit 210 at the previous frequency. In the case that the third frequency corresponds to a higher frequency than the previously applied frequency, the microcontroller 220 can continue to gradually increase the drive frequency by a specified amount until the resulting voltage is less than the previously measured voltage. In the case that the third frequency corresponds to a lower frequency than the previously applied frequency, the microcontroller 220 can continue to gradually decrease the drive frequency by a specified amount until the resulting voltage is less than the previously measured voltage. At this point, the microcontroller 220 sets the drive frequency to the frequency that produced the previously measured voltage. That is, the microcontroller 220 searches for the frequency that produces the largest voltage measurement output by the antenna voltage detection circuit 250 (by gradually increasing or decreasing the drive frequency).

[0045] Figure 2B is an illustrative RFID system drive frequency vs. resonant frequency waveform in accordance with various implementations. As shown in Figure 2B the antenna voltage (and thus the range of the RFID system) decreases as the drive frequency of the interrogation signal applied to the resonant circuit does not match the resonant frequency of the resonant circuit. As shown in Figure 2BAs shown, 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 in which no interfering sources, such as metallic materials, are present or in close proximity to the RF reader unit 200, the resonant frequency of the resonant circuit is a pre-set 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 is set to a value equal to or matching the resonant frequency. The resulting voltage measured by the antenna voltage detection circuit 250 is close to or at a maximum value. Later, the RF reader unit 200 is placed in close proximity to an interfering source, such as a metallic material, which changes the resonant frequency of the resonant circuit (e.g., from 125 kHz to 135 kHz). Driving the resonant circuit at the currently set excitation frequency (e.g., at 125 kHz) results in a reduced voltage measurement provided by the antenna voltage detection circuit 250 relative to the previously measured maximum voltage value. In response, the excitation frequency is increased or decreased by a specified amount that can match the changed resonant frequency of the resonant circuit. Driving the resonant circuit at the adjusted excitation frequency (e.g., at 135 kHz) results in a voltage measurement provided by the antenna voltage detection circuit 250 that is close to or equal to the maximum value.

[0046] In such a case, the inductively coupled device (e.g., RF tag) receives the RF interrogation signal at the adjusted excitation frequency and derives a local clock frequency based on the RF interrogation signal (e.g., at 135 kHz). The inductively coupled device synchronizes the exchange of data with the reader unit 12 in accordance with the local clock frequency and, in turn, the adjusted excitation (drive) frequency of the RF interrogation signal.

[0047] Figure 3 is a flowchart depicting an example process 300 for operating an inductively coupled reader in accordance with various embodiments.

[0048] At operation 310, the inductively coupled reader applies an excitation frequency to a resonant circuit of the inductively coupled reader.

[0049] At operation 320, the inductively coupled reader detects a change in a resonant frequency of the resonant circuit of the inductively coupled reader.

[0050] At operation 330, the inductively coupled reader adjusts the excitation frequency applied to the resonant circuit in response to detecting the change in the resonant frequency of the inductively coupled reader.

[0051] Figure 4is a block diagram of an example machine 400 upon which any one or more of the techniques (e.g., methodologies) discussed herein can perform and / or that can be included as part of an inductively coupled reader. In alternative embodiments, the machine 400 can operate as a standalone device or can be connected (e.g., networked) to other machines. In a networked deployment, the machine 400 can operate in the capacity of a server machine, a client machine, or both in server-client network environments. In an example, the machine 400 can act as a peer machine in peer-to-peer (P2P) (or other distributed) network environment. The machine 400 can be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile telephone, a web appliance, an internet appliance, an IoT device, an automotive system, an aerospace system, or any machine capable of executing instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only 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, e.g., via cloud computing, Software as a Service (SaaS), other computer cluster configurations.

[0052] 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 (e.g., set) of circuits implemented in a tangible entity including hardware (e.g., simple circuits, gates, logic, etc.). Circuit system components can be flexible over time and with potential hardware variability. A circuit system includes components that can perform specific tasks individually or in combination when operating. In an example, the hardware of the circuit system can be designed to perform specific operations (e.g., hardwired). 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, wherein the variably connected physical components include computer-readable media that are physically modified (e.g., magnetically, electrically, by the removable placement of constant mass particles, etc.). When the physical components are connected, the basic 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 variably connected components to perform a portion of a specific task when operating. Thus, when the device is operating, 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.

[0053] The machine (e.g., computer system) 400 can 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 a multi-core processor), a main memory 404 and a static memory 406, some or all of which can communicate with one another via an interlink (e.g., bus) 408. The machine 400 can 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 an example, the display device 410, alphanumeric input device 412, and UI navigation device 414 can be a touch screen display. The machine 400 can additionally include a storage device 422 (e.g., a drive unit), a signal generation device 418 (e.g., a speaker), a network interface device 420, one or more sensors 416, such as a global positioning system (GPS) sensor, an ICP sensor, a bridge sensor, an audio sensor, an industrial sensor, a compass, an accelerometer, or a

[0054] The storage device 422 can include a machine readable medium 422 on which is stored one or more sets of data structures or instructions 424 (e.g., software) embodying or utilized by any one or more of the technologies or functions described herein. The instructions 424 can also reside, completely or at least partially, within the main memory 404, within static memory 406, or within the hardware processor 402 during

[0055] While the machine -readable medium is illustrated as a single medium, the term "machine-readable medium" can include a single medium or multiple media (e.g., a centralized or distributed database, or associated caches and servers) configured to store the one or more instructions 424.

[0056] The term“machine-readable medium” can include any transitory or non-transitory medium that is capable of storing, encoding, or carrying instructions for execution by the machine 400 and that cause the machine 400 to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by such instructions. Non-limiting machine-readable medium examples can include solid-state memories, and optical and magnetic media. In examples, a massed machine-readable medium includes a machine-readable medium with a plurality of particles having invariant (e.g., rest) mass. Accordingly, massed machine-readable media are not transitory propagating signals. Specific examples of massed machine-readable media can 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.

[0057] Instructions 424 (e.g., software, programs, an operating system (OS), etc.) or other data stored on storage device 421 can be accessed by the main memory 404 for use by the hardware processor 402. The main memory 404 (e.g., DRAM) is typically fast, but volatile, and thus a different type of storage device (e.g., SSD) than storage device 421, which is suitable for long-term storage, including when in an“off’ condition. Instructions 424 or data being used by a user or machine 400 are typically loaded into main memory 404 for use by the hardware processor 402. When the main memory 404 is full, virtual space from the storage device 421 can be allocated to supplement the main memory 404; however, because the storage device 421 is typically slower than the main memory 404, and write speeds are typically at least twice as slow as read speeds, the use of virtual memory can greatly degrade user experience due to storage device latency (compared to main memory 404, e.g., DRAM). Moreover, using the storage device 421 as virtual memory can greatly degrade the useful life of the storage device 421.

[0058] The instructions 424 can be further 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 transfer protocols (e.g., frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks can include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g., cellular networks), Plain Old Telephone (POTS) networks, and wireless data networks (e.g., Wi-Fi networks, LTE networks, WiMAX networks, etc.). In examples, the network interface device 420 can include one or more physical network interface cards (NICs) to communicate over the one or more communication networks 426. Each NIC can include an appropriate physical interface to connect to the particular types of communication networks 426. Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards, the IEEE 802.16 family of standards, the IEEE 802.15.4 family of standards, peer-to-peer (P2P) networks, among others. In an example, network interface device 420 can include one or more physical jacks (e.g., Ethernet, coaxial, or phone jacks) or one or more antennas to connect to communication network 426. In an example, network interface device 420 can include a plurality of antennas to wirelessly communicate using at least one of Single-Input Multiple-Output (SIMO), Multiple-Input Multiple-Output (MIMO), or Multiple-Input Single-Output (MISO) techniques. The term“transmission medium” shall be taken to include any intangible medium that is capable of storing, encoding or carrying the instructions for execution by the machine 400, and includes digital or analog communications signals or other intangible media to facilitate communication of such software.

[0059] Each of the non-limiting aspects or examples described herein can exist independently of one another or can be combined in any permutation or combination of one or more of the other examples.

[0060] 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 inventive subject matter can be practiced. These embodiments are also referred to as“examples.” Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

[0061] In the event that the use of terms do not conform between this document and any document incorporated by reference, the use of the terms in this document shall control.

[0062] In the present document, the terms "a" or "an," are used, as is common in patent documents, to include one or more than one, unless otherwise indicated. In the present document, the term "or" is used to refer to a nonexclusive or, such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise indicated. In the present document, the terms "including" and "comprising" are used as synonymous for the respective terms "containing" and "comprising," in their broadest sense. Furthermore, in the appended claims, the terms "including" and "comprising" are open-ended; that is, a system, device, article, composition, formulation, or process that includes, or that comprises, elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. 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.

[0063] Method examples described herein can be machine or computer- implemented at least in part. Some examples can include a computer- readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level languages code, or the like. Such code can include computer readable instructions for performing various methods. The code can form portions of computer program products. Further, in an example, the code can be tangibly embodied on one or more volatile or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, volatile or non-volatile memory devices, such as a hard disk, a removable magnetic disk, a removable optical disk (e.g., a compact disk and a digital video disk), a magnetic cassette, memory cards or sticks, a random access memory (RAM), a read-only memory (ROM), and the like.

[0064] The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) can be used in combination with each other. For example, other embodiments utilizing such features can be employed without departing from the scope of the application. The Abstract is provided to allow a quick determination of the disclosure's purpose. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or the meaning of the claims. Also, in the above Detailed Description, various features can be grouped together or described in a single embodiment for the purposes of streamlining the disclosure. This should not be interpreted as intending that the disclosed features are necessarily related, or that the described implementation necessarily makes any or all of the disclosed features mandatory in any claims. Rather, the inventiveness can reside in less than all features of a particular disclosed implementation. The claims, therefore, should not be read to be limited only to the described implementation. Rather, the scope of the application is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

Claims

1. A method for operating an inductively coupled reader, the method comprising: applying a first excitation frequency to a resonant circuit of the inductively coupled reader; measuring a first magnitude of a first voltage across the resonant circuit of the inductively coupled reader resulting from application of the first excitation frequency; comparing the first magnitude of the first voltage to a specified threshold value, the specified threshold value being set to a value that differs by a specified amount from a value of a voltage consumed by the resonant circuit in the absence of an external interference inducing source; responsive to determining that the first magnitude of the first voltage fails to satisfy the specified threshold, detecting a change in a resonant frequency of the resonant circuit of the inductively coupled reader; and The first excitation frequency applied to the resonant circuit is adjusted in response to detecting 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 the external disturbance-inducing source being in close proximity to the inductively coupled reader, and wherein the 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 includes retrieving a configuration bit from a non-volatile memory of the inductively coupled reader, the configuration bit indicating the presence or absence of the external interference inducing source.

4. The method according to claim 3, further comprising: determining whether the configuration bit is valid or invalid during operation of the inductively coupled reader; detecting the change in the resonant frequency in response to determining that the configuration bit is valid during operation of the inductively coupled reader; as well as In response to determining that the configuration bit is invalid during operation of the inductively coupled reader, the interference-inducing source is determined to be absent.

5. The method according to claim 1, wherein The specified threshold is programmed into the memory of the inductively coupled reader during manufacturing.

6. The method according to claim 1, wherein The specified threshold is dynamically updated based on different operating conditions and includes a range of values.

7. The method according to claim 1, further comprising: applying a second excitation frequency to the resonant circuit of the inductively coupled reader; measuring a second magnitude of a second voltage across the resonant circuit of the inductively coupled reader resulting from application of the second excitation frequency; as well as It is determined that the first magnitude of the first voltage is less than the second magnitude of the second voltage.

8. The method according to claim 7, wherein: Adjusting the first excitation frequency applied to the resonant circuit includes setting the first excitation frequency to the second excitation frequency.

9. The method according to claim 7, wherein: The second excitation frequency is higher or lower than the first excitation frequency by a predetermined amount.

10. The method of claim 1, further comprising operating an inductively coupled device inductively coupled to the inductively coupled reader at the adjusted first excitation frequency, wherein The inductive coupling device derives a clock frequency from the adjusted first excitation frequency, so that data transmission between the inductive coupling device and the inductive coupling reader is synchronized with the adjusted first excitation frequency.

11. The method according to claim 10, wherein: The inductive coupling device includes a radio frequency identification (RFID) credential device.

12. The method according to claim 1, wherein The inductively coupled reader comprises a radio frequency identification (RFID) reader.

13. The method of claim 1 , further comprising determining an adjustment to the first excitation frequency by: applying a range of frequencies to the resonant circuit; and A frequency that causes a maximum voltage amplitude to be generated at an output of the inductively coupled reader is identified.

14. A system comprising: An inductively coupled reader comprising one or more processors configured to perform operations comprising: applying a first excitation frequency to a resonant circuit of the inductively coupled reader; measuring a first magnitude of a first voltage across the resonant circuit of the inductively coupled reader resulting from applying the first excitation frequency; comparing the first magnitude of the first voltage to a specified threshold value, the specified threshold value being set to a value that differs by a specified amount from a value of a voltage consumed by the resonant circuit in the absence of an external interference inducing source; responsive to determining that the first magnitude of the first voltage fails to satisfy the specified threshold, detecting a change in a resonant frequency of the resonant circuit of the inductively coupled reader; and The first excitation frequency applied to the resonant circuit is adjusted in response to detecting the change in the resonant frequency of the inductively coupled reader.

Images