HK1132063B

HK1132063B - A multimode rfid tag and its operation method

Info

Publication number: HK1132063B
Application number: HK09109848.6A
Authority: HK
Inventors: 阿玛德雷兹．雷泽．罗弗戈兰; 玛雅姆．罗弗戈兰; 阿米．沙梅莉
Original assignee: Nxp Usa, Inc.
Priority date: 2007-10-30
Filing date: 2009-10-23
Publication date: 2011-12-23

Description

Multi-mode RFID tag and method of operating the same

Technical Field

The present invention relates to wireless communications, and more particularly to RFID systems.

Background

Radio Frequency Identification (RFID) systems typically include a reader, also known as an interrogator, and a remote tag, also known as a transponder. Each tag holds identification data or other data used to identify a person, item, tray or other object or data relating to characteristics of a person, item, tray or other object. Rfid systems may use active tags that have an internal power source, such as a battery, and/or passive tags that are remotely powered by a reader without an internal power source.

Communication between the reader and the remote tag is accomplished by Radio Frequency (RF) signals. Typically, to access identification data stored within an RFID tag, an RFID reader generates a modulated RF interrogation signal that evokes a modulated RF response signal from a certain tag. The RF response signal from the tag includes encoded data stored in the RFID tag. The RFID reader decodes the encoded data to identify or determine characteristics of the person, item, pallet or other object associated with the RFID tag. For passive tags without a battery or other power source, the RFID reader may generate an unmodulated continuous wave signal to deactivate and power the tag during data transmission. Thus, the passive tag derives power from the signal transmission of the RFID reader. Active tags have their own power source and have powerful capabilities to power transceivers, processors, memory and other devices located on the tag.

RFID systems typically utilize far field or near field technology. In far field technology, the distance between the reader and the tag is large compared to the wavelength of the carrier signal. Generally, far field techniques use carrier signals in the ultra-high frequency or microwave range. In remote applications, an RFID reader generates and transmits RF signals through an antenna to all tags within the coverage of the antenna. One or more tags respond to the reader after receiving the RF signal using a backscatter technique, using which the tag modulates and reflects the received RF signal.

In near field technology, the travel distance is typically less than one wavelength of the carrier signal. Therefore, the reading distance is limited to about 20cm or less depending on the frequency. In near field applications, the RFID reader and tag communicate through electromagnetic or inductive coupling between the reader coil and the tag. Generally, the near-field technology uses a carrier signal in a low frequency range. With respect to the tag coil antenna, the RFID tag is wound around a metal core using a multi-layer coil (e.g., 3 layers of coils of 100-. Sometimes, at high frequencies of 13.56MHz, RFID tags use a flat spiral coil inductor wound 5-7 turns in a credit card sized shape. These tag coil antennas are very large compared to other modules of the RFID tag and cannot be integrated on one chip with other modules of the RFID tag, such as Complementary Metal Oxide Semiconductor (CMOS), bipolar complementary metal oxide semiconductor (BiCOS), gallium arsenide (GaAs) integrated circuits, etc.

The international standards organization developed an RFID standard known as the ISO18000 series. The ISO18000 series of standards describes an air interface protocol for RFID systems in applications that track items in the supply chain, among other things. The ISO18000 series has seven parts covering the major frequencies used by RFID systems in the world. The seven parts are as follows:

18000-1: air interface generic parameters for globally accepted frequencies;

18000-2: an air interface below 135 KHz;

18000-3: a 13.56MHz air interface;

18000-4: 2.45GHz air interface;

18000-5: a 5.8GHz air interface;

18000-6: an 860MHz-930MHz air interface;

18000-7: 433.92MHz air interface.

The near field technology using magnetic/inductive coupling has an air interface protocol at a Low Frequency (LF) of 135KHz or lower or at a high frequency of 13.56MHz according to ISO18000-2 and 18000-3 parts of the ISO18000 series. ISO18000-3 defines two modes. In mode 1, the data rate from the tag to the reader is 26.48kbps, while mode 2 is a 105.9375 high speed interface on each of the 8 channels. The communication protocol used by the reader and the tag is a typical load modulation technique.

There are three ISO-defined air interfaces for far-field technology using RF backscatter coupling, which are the air interface at 2.49GHz microwave frequency defined according to ISO18000-5, the air interface in the 860MHz to 930MHz Ultra High Frequency (UHF) range defined according to ISO18000-6, and the 433.95MHz UHF air interface defined according to ISO 18000-7. For UHF at the 860-930MHz band, ISO18000-6 defines two tag types, type A and B, with a link defined from the tag to the reader having a data rate of 40kbps, Amplitude Shift Keying (ASK) modulation, and biphase space or FM0 encoding of the data.

Additionally, the EPCglobal Class1, second Generation (Class1, Generation2) standard defines a tag standard using ultra high frequencies, which possesses a tag-to-reader link of 40-640kbps, ASK or phase shift keying modulation (PSK), and FM0 or Miller modulated sub-carriers data encoding techniques.

Generally, tags operating at low or high frequencies using near field technology have two applications: one is item level labeling for inventory control in supply chain management, and the other is short-range reading, such as smart cards or proximity credit cards for access control, currency use, passports, currency bill validation, bank documents, and the like. These applications do not require reading the tag from a distance, but require more security than near field technology provides. In addition, near field technology has better performance in close range flow tags, such as drug flows, where far field RF coupling tends to create interference in the flow.

Tags that are RF coupled using far field technology in the microwave or ultra-high frequency range are often used for transportation units, such as tray or carton level tracking, or other applications requiring remote reading.

These different types of technologies and different RFID standards each define different protocols for enabling communication between the reader and the tag, which inhibits widespread use of RFID in a variety of applications. Therefore, there is a need for highly integrated, low cost RFID tags. Further, there is a need for multi-standard, multi-technology RFID tags.

Disclosure of Invention

The apparatus and method of operation of the present invention are further described in the following brief description of the drawings, detailed description of the invention, and claims. The features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

According to one aspect of the present invention, a multimode Radio Frequency Identification (RFID) tag includes:

configurable coupling circuitry to provide electromagnetic coupling to an RFID reader when the multi-mode RFID tag is in a near-field mode and to provide radio frequency coupling to the RFID reader when the multi-mode RFID tag is in a far-field mode;

a power generation and signal detection module connected to the configurable coupling circuit, the power generation and signal detection module converting an inbound receive signal to a supply voltage and recovering encoded data from the inbound receive signal;

a baseband processing module to:

decoding the encoded data to produce a decoded signal;

processing the decoded signal;

generating a response signal when the processing of the decoded signal indicates generation of the response signal;

encoding the response signal to produce outbound encoded data;

and the transmitting part is connected with the coding coupling circuit and converts the outbound coded data into an outbound transmitting signal.

In the multi-mode RFID tag of the present invention, the configurable coupling circuit comprises:

a first capacitor connected to the antenna in a far field mode and disconnected or connected to ground in a near field mode;

an inductor providing electromagnetic coupling in a near-field mode and an inductance value for impedance matching in a far-field mode;

a second capacitor connected to the inductor, the second capacitor providing a capacitance value for adjusting impedance matching in a far-field mode or adjusting at least one of the following of the configurable coupling circuit in a near-field mode: bandwidth, quality factor, gain and roll-off.

In the multi-mode RFID tag of the present invention, the second capacitor is adjustable.

In the multi-mode RFID tag of the present invention, the antenna transmits and receives a radio frequency signal in an ultra high frequency range in a far field mode.

In the multi-mode RFID tag of the present invention, the inductor providing electromagnetic coupling in the near-field mode includes an inductance coil providing electromagnetic coupling in the ultra-high frequency range in the near-field mode.

In the multi-mode RFID tag of the present invention, the inductor coil is integrated on a chip.

In the multi-mode RFID tag of the present invention, the inductor coil is integrated on a CMOS chip.

In the multi-mode RFID tag of the present invention, the baseband processing module for decoding the encoded data to generate a decoded signal is further configured to:

utilizing a first encoding/decoding protocol in near field mode;

a second encoding/decoding protocol is utilized in the far-field mode.

In the multi-mode RFID tag of the present invention, the baseband processing module for encoding the response signal to generate the encoded data includes:

at least a first encoding processing module that encodes the response signal according to a first encoding protocol in a near-field mode and encodes the response signal according to a second encoding protocol in a far-field mode.

In the multi-mode RFID tag of the present invention, the inductor providing electromagnetic coupling in a near field mode includes an inductance coil providing electromagnetic coupling in a Low Frequency (LF) range in the near field mode.

In the multi-mode RFID tag of the present invention, the configurable coupling circuit converts to a near field mode and provides electromagnetic coupling to the RFID reader in response to a command from the RFID reader.

In the multi-mode RFID tag of the present invention, the configurable coupling circuit switches to a far field mode and provides electromagnetic coupling to the RFID reader in response to a command from the RFID reader.

In the multi-mode RFID tag of the present invention, the configurable coupling circuit is configured to operate in a far-field mode and provide radio frequency coupling to the RFID reader until the configurable coupling circuit receives an instruction from the RFID reader to convert to a near-field mode and provide electromagnetic coupling to the RFID reader.

According to one aspect of the invention, a method of operating a multi-mode RFID tag includes:

configuring a coupling circuit of the multi-mode RFID tag to provide radio frequency coupling to an RFID reader in a far-field mode and to provide inductive coupling to the RFID reader in a near-field mode;

communicating with an RFID reader in one of a far field mode or a near field mode;

configuring the coupling circuit to provide the other of the far field mode and the near field mode upon receiving an instruction from an RFID reader;

and communicate with the RFID reader in the other mode.

In the method of the present invention, communicating with the RFID reader further comprises:

receiving an inbound signal from the RFID reader, recovering an encoded data signal from the inbound signal;

decoding the recovered encoded data signal, wherein the encoded data signal is encoded according to a first encoding protocol;

processing the decoded data signal;

generating a response signal for the decoded data signal according to an instruction which requires a response to an RFID reader in the decoded data signal;

encoding the response signal using the first encoding protocol.

The method of the invention further comprises the following steps:

modulating a response signal encoded according to the first encoding protocol to a carrier signal, wherein the carrier signal is located in the Ultra High Frequency (UHF) range;

transmitting the modulated carrier signal to an RFID reader using Radio Frequency (RF) coupling.

In a preferred embodiment, the method of the present invention further comprises:

modulating a response signal encoded according to a second encoding protocol to a carrier signal, wherein the carrier signal is located in the Ultra High Frequency (UHF) range;

the modulated carrier signal is transmitted to an RFID reader using inductive coupling.

a power source to operate the multi-mode RFID tag is generated from an inbound signal from an RFID reader in a near-field mode and a far-field mode.

According to an aspect of the present invention, a Radio Frequency Identification (RFID) tag includes:

a configurable coupling circuit that provides electromagnetic coupling to an RFID reader in a near-field mode and radio frequency coupling to the RFID reader in a far-field mode;

a power generation and signal detection module connected to the configurable coupling circuit, wherein the power generation and signal detection module converts an inbound receive signal from an RFID reader to a supply voltage and recovers encoded data from the inbound receive signal in a near-field mode and produces an encoded data signal that is also recovered in a far-field mode;

a baseband processing module to:

decoding the recovered encoded data signal using a first protocol in far field mode and a second protocol in near field mode, resulting in a decoded data signal;

processing the decoded data signal;

generating a response signal to the decoded data signal according to an instruction in the decoded data signal;

encoding the response signal using a first protocol in a far-field mode and a second protocol in a near-field mode, producing outbound encoded data;

a transmit section connected to the configurable coupling circuit, wherein the transmit section converts the outbound encoded data into an outbound transmit signal.

In the RFID tag of the present invention, the outbound transmitted signal is located in an Ultra High Frequency (UHF) range in both a near field mode and a far field mode.

In the RFID tag of the present invention, the configurable coupling circuit includes:

a radio frequency antenna providing radio frequency coupling in a far field mode;

a coil antenna providing electromagnetic coupling in a near field mode;

a signal detection module connected to the radio frequency antenna or coil antenna, the signal detection module recovering encoded data from the inbound receive signal to produce a recovered encoded data signal;

a baseband processing module to:

processing the decoded data signal;

a transmitting component coupled to the radio frequency antenna or the coil antenna, wherein the transmitting component converts the outbound encoded data into an outbound transmit signal.

In a preferred embodiment of the invention, the RFID tag further comprises a configurable coupling circuit coupling the radio frequency antenna to the signal detection module and the transmission means in a far field mode and coupling the coil antenna to the signal detection module and the transmission means in a near field mode.

In a preferred embodiment of the invention, the RFID tag is pre-configured to couple a radio frequency antenna to the signal detection module and the transmission means for operation in a far field mode and a coil antenna to the signal detection module and the transmission means for operation in a near field mode.

Drawings

Fig. 1 is a schematic block diagram of an embodiment of an RFID system according to the present invention.

FIG. 2 is a schematic block diagram of a multi-mode RFID tag embodiment according to the present invention.

Fig. 3 is a schematic block diagram of a configurable coupling circuit in an embodiment of an RFID tag according to the present invention.

FIG. 4 is a schematic block diagram of another embodiment of an RFID tag in accordance with the present invention

FIG. 5 is a schematic diagram of a coil antenna in a multi-mode RFID tag and RFID reader according to an embodiment of the present invention.

FIG. 6 is a schematic illustration of electromagnetic coupling between a multi-mode RFID tag and an RFID reader according to an embodiment of the present invention.

Detailed Description

FIG. 1 is a schematic block diagram of one embodiment of an RFID (radio frequency identification) system including a computer/server 12, a plurality of RFID readers 14-18, and a plurality of RFID tags 20-30. Each RFID tag 20-30 may be associated with a particular object for a variety of purposes including, but not limited to, tracking inventory, tracking status, locating, assembly progress, etc. The RFID tags may be active devices that include an internal power source or passive devices that draw power from the RFID readers 14-18.

Each RFID reader 14-18 wirelessly communicates with one or more RFID tags 20-30 within its coverage area. For example, RFID tags 20, 22 are within the coverage of RFID reader 14, RFID tags 24, 26 are within the coverage of RFID reader 16, and RFID tags 28, 30 are within the coverage of reader 18. In one mode of operation, the RF communication scheme between the RFID reader 14-18 and the RFID tags 20-30 is a backscatter coupling method using far field technology, where the RFID reader 14-18 requests data from the RFID tags 20-30 via RF signals and the RF tags 20-30 respond to the requested data by modulating and backscattering the RF signals provided by the RFID reader 14-18. In another mode of operation, the RF communication scheme between the RFID reader 14-18 and the RFID tag 20-30 is an electromagnetic or inductive coupling method using near field technology, where the RFID reader 14-18 electromagnetically or inductively couples to the RFID tag 20-30 to access data on the RFID tag 20-30. Thus, in one embodiment of the present invention, RFID tags 20-30 communicate with RFID reader 14-18 using this capability in the far field mode, and RFID tags 20-30 communicate with RFID reader 14-18 using this capability in the near field mode.

The RFID readers 14-18 collect data requested by the computer/server 12 from each RFID tag 20-30 within its coverage area. The collected data is then transmitted to the computer/server 12 via a wired or wireless connection 32 and/or peer-to-peer communication 34. In addition, the computer/server 12 may provide data to one or more RFID tags 20-30 via associated RFID readers 14-18. The information so downloaded depends on different applications and varies widely. Upon receiving the downloaded data, the RFID tag 20-30 can store the data in non-volatile memory.

As indicated above, the RFID readers 14-18 may communicate on a peer-to-peer basis, such that each RFID reader does not require a separate wired or wireless connection 32 to the computer/server 12. For example, RFID reader 14 and RFID reader 16 may communicate on a peer-to-peer network basis using backscatter technology, wireless local area network technology, and/or any other wireless communication technology. In this example, the RFID reader 16 may not include a wired or wireless connection 32 to the computer/server 12. In embodiments where communications between the RFID reader 16 and the computer/server 12 are communicated over a wired or wireless connection 32, the wired or wireless connection 32 may use any of a number of wired standards (e.g., Ethernet, firewire, etc.) and/or wireless communication standards (e.g., IEEE802.11x, Bluetooth, etc.).

As is well known to those of ordinary skill in the art, the RFID system of FIG. 1 may be expanded to include a plurality of RFID readers 14-18 distributed at desired locations (e.g., buildings, offices, etc.) where RFID tags may be associated with: access control cards, smart cards, mobile phones, personal digital assistants, laptops, personal computers, inventory items, trays, cartons, devices, individuals, and the like. Additionally, it should be noted that computer/server 12 may be connected to another server and/or network connection to provide wider area network coverage.

FIG. 2 is a schematic diagram of one embodiment of a multi-mode RFID tag 38 that may be used as one of the RFID tags 20-30 in FIG. 1. The multi-mode RFID tag 38 may communicate with the RFID readers 14-18 in a far-field mode and may communicate with the RFID readers 14-18 in a near-field mode. The multi-mode RFID tag 38 includes a power generation and signal detection module 40, a baseband processing module 42, a transmit section 44, configurable coupling circuitry 46, and an antenna section 48. The multi-mode RFID tag 38 may be an active tag that includes a battery 41. If it is an active tag, the battery 41 may replace or assist the power generation function of the power generation and signal detection module 40 to power the baseband processing module 42, the transmit section 44, and the configurable coupling circuit. If the multi-mode RFID tag 38 is a passive tag, there is no battery 41 in the figure.

The power generation and detection module 40, the baseband processing module 42, and the transmit section 44 may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, microcontroller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that processes signals (analog and/or digital) based on hard coding of circuitry and/or operational instructions. One or more of the modules may have an associated memory device, which may be a single memory, a plurality of memories, and/or embedded circuitry of the module. The memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that when the aforementioned means performs one or more functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory device storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. It is further noted that the hard-coded and/or operational instructions stored by the memory and executed by the aforementioned modules correspond to at least some of the steps and/or functions illustrated in fig. 1-7.

In one embodiment of the present invention, antenna element 48 is a dipole-type antenna operating in the microwave or UHF range. For compact applications, a folded dipole or half-wave dipole antenna, or other type of dipole antenna that can be bent or meandered, with capacitive tip loading or bowtie broadband structures, may be used. In general, the antenna component 48 may be one of several types of antennas that is optimized for the desired operating frequency and application.

During operation, when in far field mode, the configurable coupling circuit 46 couples the power generation and signal detection module 40 to the antenna assembly 48; when in near field mode, the power generation and signal detection module 40 is coupled to an inductor or coil antenna within the configurable coupling circuit 46, as will be explained in more detail below. In either mode, the configurable coupling circuit 46 may transmit the inbound receive signal 50 to the power generation and signal detection module 40. In the passive multi-mode RFID tag 38 embodiment, the RFID reader 14-18 first generates an unmodulated Continuous Wave (CW) signal to deactivate and power the tag. The power generation and signal detection module 40 converts such CW unmodulated inbound receive signals 50 to a supply voltage. The power generation and signal detection module 40 stores the power supply voltage and provides it to other modules for operation.

The RFID reader 14-18 then transmits a modulated encoded interrogation inbound receive signal 50. The power generation and signal detection module 40 receives the inbound receive signal 50 from the configurable coupling circuit 46. The power generation and detection module 40 demodulates the inbound receive signal 50 to recover encoded data 52. Depending on the RFID reader 14-18 and the mode of operation, the inbound receive signal 50 may be modulated using Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), or other types of modulation methods. In one embodiment, the power generation and signal detection module 40 demodulates the inbound receive signal 50 using one or more types of demodulation techniques to recover the encoded data 52 from the inbound receive signal 50. The power generation and signal detection module 40 transmits the recovered encoded data 52 to the baseband processing module 40.

The baseband processing module 42 receives the encoded data 52 and decodes the encoded data 52 using one or more protocols. Different data encoding protocols may be defined for the near field mode signal and the far field mode signal. For example, in near field mode, data may be decoded by the baseband processing module 42 using a first data encoding protocol, while in far field mode, data may be decoded by the baseband processing module 42 using a second data encoding protocol. For example, in the near-field mode, a Manchester encoding method may be used, and in the far-field mode, a Miller modulated subcarrier encoding method and/or a biphase spatial encoding method may be used. Alternatively, the baseband processing module 42 may use the same data encoding protocol in both the near field and far field modes.

In one embodiment of the invention, the baseband processing module 42 is programmed with multiple encoding protocols, and is capable of decoding the encoded data 52 according to different protocols. Thus, the baseband processing module 42 may use different encoding protocols to decode the encoded data 52, if necessary, whether in near-field mode or far-field mode. For example, when operating in near field mode, the baseband processing module 42 may attempt to decode the encoded data 52 using a first protocol that is common in near field mode, such as Manchester encoding. If such decoding is unsuccessful, the baseband processing module may attempt to decode the encoded data 52 using the next protocol until the encoded data 52 is decoded. Similarly, when operating in far-field mode, the baseband processing module 42 may attempt to decode the encoded data 52 using a second protocol that is common in far-field mode, such as Miller modulated subcarrier encoding and biphase spatial encoding. If this decoding operation is unsuccessful, the baseband processing module may attempt to decode the encoded data 52 using the next protocol until the encoded data 52 is decoded.

Once the decoding is complete, the baseband processing module 42 processes the decoded data and then determines the one or more instructions contained therein. The command may be to store data, update data, respond to stored data, verify command compliance, respond, change mode of operation, etc. If the instruction(s) request a response, the baseband processing module 42 determines the response data and encodes the response data into outbound encoded data 54. More suitably, the baseband processing module 42 encodes the data for the response using the same encoding protocol used to decode the inbound encoded data 52. Once encoded, the baseband processing module 42 provides the outbound encoded data 54 to the transmit section 44. The transmit section 44 receives the outbound encoded data 54 and converts the outbound encoded data 54 into an outbound transmit signal 56.

The outbound transmit signal 56 is a carrier signal for which amplitude modulation, such as ASK, or phase modulation, such as PSK, or load modulation may be used. In one embodiment of the invention, in the near field mode, the frequency of the carrier signal is in the Low Frequency (LF) or High Frequency (HF) range. The near field frequency range is a low frequency of about 135KHz or less, and a high frequency of about 13.56MHz, in accordance with the ISO series standard. In far field mode, according to one embodiment, the carrier signal frequency is in the ultra high frequency range or microwave range. The far field frequency range is a frequency of about 2.45GHz, an Ultra High Frequency (UHF) range of about 860MGHz to 930MHz, or a UHF of about 433.92MHz, according to the ISO series of standards.

In the near field mode, the configurable coupling circuit 46 couples the transmit component 44 with an inductor within the configurable coupling circuit 46 to transmit the outbound transmit signal 56 to the RFID readers 16-18 using electromagnetic or inductive coupling. In the far field mode, the configurable coupling circuit 46 couples the transmit section 44 to the antenna section 48, and the multi-mode RFID tag 38 then transmits the outbound transmit signal 56 to the RFID readers 16-18 using backscatter techniques.

Fig. 3 is a schematic diagram of one embodiment of configurable coupling circuit 46. The configurable coupling circuit 46 includes a capacitor C160, an inductor L162, and a second capacitor C266. In one embodiment, the configurable coupling circuit includes a converter 64. In this embodiment, in the first position, the switch 64 connects the antenna element 48 and the capacitor 66 to the inductor L1 and the capacitor C1. In the second position, switch 64 connects antenna element 48 and capacitor 66 to ground or disconnects the antenna from inductor L1 and capacitor C1. The transducer 64 may be an actuator, a transistor circuit, or other equivalent device. For active tags, a battery 41 powers the converter 64. For passive tags, the RFID readers 16-18 emit a continuous wave unmodulated signal to power the multi-mode RFID tag 38. The multi-mode RFID tag 38 may then power the converter 64 using the voltage from the power generation and signal detection module 40 to change position. In another embodiment, the multi-mode RFID tag 38 is preconfigured to operate only in the near-field and far-field modes. For example, the multi-mode RFID tag 38 may be hard-wired at the time of manufacture to couple only to the antenna assembly 48 for operation in far-field mode, or to couple only to the coil antenna 62 for operation in near-field mode. In another example, prior to provisioning, the RFID tag 38 is preprogrammed to operate only in near field or far field mode.

In far field mode, the antenna 48, capacitor C2 and inductor L1, capacitor C1 are connected. The inductor L1 and the capacitor C1 function as an impedance matching circuit for the antenna 48. Inductor L1 provides an impedance value for impedance matching of antenna 48 and inductor C1 provides a capacitance value for impedance matching of antenna 48. In one embodiment of the present invention, inductor C1 is adjustable or variable, such as a digital switched capacitor, and may be adjusted to provide a desired capacitance value for impedance matching in the far field mode. Thus, in far field mode, the antenna 48 and the configurable coupling circuit 46 receive the inbound receive signal 50 and provide the inbound receive signal 50 to the power generation and signal detection module 40.

In near field mode, the transducer 64 is off, and thus the capacitor C2 is floating or connected to ground. In another embodiment of the present invention, the multi-mode RFID tag 38 is not provided with the transducer 64, but is hard-wired at the time of manufacture to isolate the antenna 48 and/or the capacitor C2 from the inductor L1. In another embodiment of the present invention, other devices besides transducer 64 may be used to isolate antenna 48 and/or capacitor C2 from inductor L1 when the multi-mode RFID tag 38 is in near field mode.

The inductor L1 functions as a coil antenna providing electromagnetic or inductive coupling with the coil of the RFID reader 14-18. Inductor L1 and capacitor C1 form a resonant circuit for adjusting the transmission frequency of RFID reader 14-18. In response to the magnetic field generated by the coil antenna of the RFID reader 14-18, the voltage of the inductor L1 reaches a maximum due to the resonant rise in the parallel resonant circuit. In one embodiment, the capacitor C1 is adjustable or variable and can be adjusted to provide optimization of the parallel resonant circuit. For example, in near field mode, capacitor C1 may be adjusted to provide optimization of at least one of the following for configurable coupling circuit 46: bandwidth, quality factor, gain, and roll-off. Generally, when operating in the near field mode, the distance between inductor L1 of RFID tag 38 and the coil antenna of RFID reader 14-18 must not exceed λ/2 π so that inductor L1 is within the magnetic field generated by the coil antenna of RFID reader 14-18. In near field mode, the configurable coupling circuit 46 provides an inbound receive signal 50 to the power generation and signal detection module 40.

During transmission, inductor L1 acts as a coil antenna that generates a magnetic field from the current flowing through inductor L1 using the electrical energy supplied to the transmitting component 44 by the power generation and signal detection module 40. Again, to receive the outbound transmitted signal 56 in near field mode, the distance between the inductor L1 of the RFID tag 38 and the coil antenna of the RFID reader 14-18 should be equal to or less than λ/2 π so that the coil antenna of the RFID reader 14-18 is within the magnetic field generated by the inductor L1.

In one embodiment of the present invention, the baseband processing module 42 processes commands from the RFID readers 14-18 as explained above in connection with FIG. 2. For example, one command from the RFID reader 14-18 may be a mode command to operate the multi-mode RFID tag 38 in either a near-field or a far-field mode. Once such a mode command is processed, the baseband processing module 42 configures the multi-mode RFID tag 38 to operate in either a near-field or a far-field mode. In another embodiment, the multi-mode RFID tag may have a preset input set by the user to determine the mode of operation. Thus, once the multi-mode RFID tag is installed in a particular application, the RFID tag may be preset to the mode best suited for that application.

FIG. 4 is another embodiment of a multi-mode RFID tag 68 according to the present invention. Similar to fig. 2 and 3, the multi-mode RFID tag 68 of the present embodiment includes a power generation and signal detection module 40, a baseband processing module 42, a transmit section 44, a configurable coupling coil 46, and an antenna section 48. In addition, a converter 70 and a load resistor Zm are connected between the transmit section and the configurable coupling circuit. In operation, the turning on and off of the load resistance Zm at the inductor L1 (e.g., the coil antenna in near field mode) may affect a change in the voltage of the coil antenna of the RFID reader and thus have the effect that the multi-mode RFID tag 38 amplitude modulates the RFID reader antenna voltage. The transmitting component 44 may transmit data with load modulation from the RFID tag to the RFID reader by switching the load resistance Zm on and off in response to the outbound encoded data 54. Similarly, the switch 70 and the load resistance Zm can modulate the RF backscatter signal from the transmit section 44, thereby modulating the reflected RF outbound transmit signal 56 in far field mode. Thus, the switch 70 and the load resistance Zm provide the multimode RFID tag 38 with efficient modulation of the outbound transmit signal 56.

Embodiment 4 shows a passive RFID multimode tag 38. In another embodiment shown in fig. 2, the multi-mode tag 38 may be designed as an active tag that includes a battery 41 to provide power to the RFID tag 38. For active tag designs, a power generation circuit may not be necessary, and the RFID readers 14-18 need not transmit CW unmodulated signals to power the RFID tag 38 prior to communicating with the RFID tag 38. In addition, the battery 41 enables the RFID tag 38 to switch between the near field and the far field to detect signals from the RFID reader 14-18 without waiting for power signals and commands from the RFID reader 14-18. A disadvantage of active tags with a battery is the short lifetime of such tags. When the battery is exhausted, the tag will become inoperable. However, active multi-mode RFID tags 38 are optimal for certain higher processing applications or applications that require only a certain lifetime (e.g., tags for perishable items).

FIG. 5 illustrates a block diagram of the inductor L162 in an embodiment of a multi-mode RFID tag 38 according to the present invention. In this embodiment, inductor L1 within configurable coupling circuit 46 operates in the high frequency (UHF) range in the near field mode. The coil of inductor L1 is a very small size coil due to the high frequency and can be integrated with other modules of the multi-mode RFID tag 38 in one chip. As shown in FIG. 5, inductor L162 has a radius r₂(ii) a The coil antenna 80 of the RFID reader 14-18 has a radius r₁(ii) a The distance between inductor L1 and coil antenna 80 is equal to distance d. In this embodiment, referring to FIG. 5, the magnetic field M between the coil antenna 80 of the RFID reader 14-18 and the inductor L1 of the RFID tag 38₁₂This can be obtained from the following equation:

wherein mu₀Is the spatial permeability. Inductance L_tagAnd a label Q_tagThe Q factor of (a) can be determined by the following equation:

for example, for one embodiment of the multi-mode RFID tag 38 operating in near field mode in the UHF range of 900MHz, L_tagApproximately equal to 56.6nH, Q_tagEqual to about 4.9.

FIG. 6 illustrates the range between the RFID tag 38 and the RFID reader 14-18 in the UHF near field mode in the embodiment of FIG. 5. As can be seen in fig. 6, this range is limited by the tag's transmit power. For example:

assuming that the maximum transmit current of the tag is 500mA, the range is approximately 5mm for a minimum received signal of-55 dBV, and the minimum voltage of the tag is 0.25 volts, a blocker signal ratio (60 dB). Note that the input voltage of the tag is I₁*Z₁₁(ii) a Minimum RX signal of reader 0.5 ═ I (I)₁*ΔZ₁₁) 2; retardation signal ratio of Z₁₁/ΔZ₁₁. In this example, Manchester encoding with a data rate of 50kbps was used.

Although the communication range in the high frequency (UHF) near field mode is shorter than the low frequency (e.g., HF and LF), such short range UHF near field RFID communication is well suited for near field reading applications such as inventory checking, surveillance and analysis authentication, passports, credit cards, and the like. Near field high frequency (UHF) operation of the RFID tag 38 also provides more efficient handling of near field flowability, such as flowable medicine bottles. In addition, inductor L1 or coil antenna 62 may be designed to be very small for integration into the chip. If the RFID tag 38 is integrated onto a single integrated circuit, the cost of the RFID tag 38 can be greatly reduced.

The multi-mode RFID tag 38 thus provides near field and far field mode operation. In one embodiment, the multi-mode RFID tag operates in the UHF band of the near field mode using an inductor or coil antenna integrated into the chip. By operating in both near field and far field modes, RFID tags can offer a variety of standard, multi-technology options for a variety of applications. As above, the RFID tag is not limited to applications that only read at a short distance or a long distance, but can be used for both types of applications, and can be switched from a near field mode to a far field mode or from a far field mode to a near field mode to accommodate different types of RFID readers and different distances between the multi-mode RFID tag and the RFID reader.

It will be understood by those within the art that the term "substantially" or "about," as may be used herein, provides an industry-accepted tolerance to the corresponding term. Such an industry-accepted tolerance ranges from less than 1% to 20% and corresponds to, but is not limited to, component values, integrated circuit process fluctuations, temperature fluctuations, rise and fall times, and/or thermal noise. It will be further understood by those within the art that the term "operably coupled", as may be used herein, includes direct coupling and indirect coupling via another component, element, circuit, or module where, for indirect coupling, the intervening component, element, circuit, or module does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As one of ordinary skill in the art will appreciate, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two elements in the same manner as "operably coupled". One of ordinary skill in the art will also recognize that the term "compares favorably", as may be used herein, indicates that a comparison between two or more elements, items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater amplitude than signal 2, favorable comparison results may be obtained when the amplitude of signal 1 is greater than the amplitude of signal 2 or the amplitude of signal 2 is less than the amplitude of signal 1.

The present invention demonstrates the specific functionality and relationship thereof through the use of method steps. The scope and order of the method steps have been arbitrarily defined for convenience of description. Other boundaries and sequences may be applicable as long as the specified functions and sequences are performed. Any such stated or selected limits or sequences therefore fall within the scope and spirit of the invention.

The invention has also been described with the aid of functional blocks illustrating some of the important functions. The boundaries of the functional blocks and the relationships of the various functional blocks have been arbitrarily defined for the convenience of the description. Other boundaries or relationships may be applicable so long as the specified functions are performed. Such other limits or relationships are therefore within the scope and spirit of the invention. It will also be appreciated by those of ordinary skill in the art that the functional blocks and other illustrative blocks and components herein may be implemented as discrete components, application specific integrated circuits, processors executing appropriate software, and any combination of the foregoing.

Claims

1. A multi-mode RFID tag, comprising:

a configurable coupling circuit that provides electromagnetic coupling to an RFID reader when a multi-mode RFID tag is in a near-field mode, the coupling circuit providing radio frequency coupling to the RFID reader when the multi-mode RFID tag is in a far-field mode, the configurable coupling circuit comprising a converter that cooperatively implements the far-field mode and the near-field mode, a first capacitor connected to an antenna in the far-field mode and disconnected or connected to ground in the near-field mode, an inductor that provides electromagnetic coupling in the near-field mode and an inductance value for impedance matching in the far-field mode, and a second capacitor connected to the inductor, the second capacitor providing a capacitance value for adjusting impedance matching in the far-field mode or adjusting the configurable coupling circuit in the near-field mode at least one of: bandwidth, quality factor, gain and roll-off;

a baseband processing module to:

decoding the encoded data to produce a decoded signal;

processing the decoded signal;

encoding the response signal to produce outbound encoded data;

a transmit section coupled to the configurable coupling circuit, the transmit section converting the outbound encoded data into an outbound transmit signal.

2. The multi-mode RFID tag of claim 1, wherein the baseband processing module is further configured to:

utilizing a first encoding/decoding protocol in near field mode;

a second encoding/decoding protocol is utilized in the far-field mode.

3. The multi-mode RFID tag of claim 1, wherein the second capacitor is adjustable.

4. The multi-mode RFID tag of claim 3, wherein the antenna transmits and receives radio frequency signals in the ultra-high frequency range in the far field mode.

5. The multi-mode RFID tag of claim 4, wherein the inductor providing electromagnetic coupling in near field mode comprises an inductive coil providing electromagnetic coupling in the ultra high frequency range in near field mode.

6. The multi-mode RFID tag of claim 5, wherein the inductive coil is integrated on a chip.

7. A method of operating a multi-mode RFID tag, the method comprising:

configuring a coupling circuit of the multi-mode RFID tag to provide radio frequency coupling to an RFID reader in a far-field mode and inductive coupling to the RFID reader in a near-field mode, the coupling circuit including a transducer that cooperates to implement the far-field mode and the near-field mode, a first capacitor connected to an antenna in the far-field mode and disconnected or connected to ground in the near-field mode, an inductor that provides electromagnetic coupling in the near-field mode and an inductance value for impedance matching in the far-field mode, and a second capacitor connected to the inductor, the second capacitor providing a capacitance value for adjusting impedance matching in the far-field mode or adjusting the configurable coupling circuit in the near-field mode at least one of: bandwidth, quality factor, gain and roll-off;

communicating with an RFID reader in one of a far field mode or a near field mode; communicating with the RFID reader further comprises:

decoding the recovered encoded data signal to produce a decoded data signal, wherein the encoded data signal is encoded according to a first encoding protocol;

processing the decoded data signal;

encoding the response signal using the first encoding protocol;

and communicate with the RFID reader in the other mode.

8. The method of claim 7, further comprising:

modulating a response signal encoded according to the first encoding protocol to a carrier signal, wherein the carrier signal is located in an ultra-high frequency range;

the modulated carrier signal is transmitted to an RFID reader using radio frequency coupling.

9. An RFID tag, comprising:

a configurable coupling circuit that provides electromagnetic coupling to an RFID reader in a near-field mode and radio-frequency coupling to the RFID reader in a far-field mode, the configurable coupling circuit comprising a transducer that cooperatively implements the far-field mode and the near-field mode, a first capacitor connected to an antenna in the far-field mode and disconnected or connected to ground in the near-field mode, an inductor that provides electromagnetic coupling in the near-field mode and an inductance value for impedance matching in the far-field mode, and a second capacitor connected to the inductor, the second capacitor providing a capacitance value for adjusting impedance matching in the far-field mode, or adjusting at least one of the following of the configurable coupling circuit in the near-field mode: bandwidth, quality factor, gain and roll-off;

a power generation and signal detection module coupled to the configurable coupling circuit, wherein the power generation and signal detection module converts an inbound receive signal from an RFID reader to a supply voltage and recovers encoded data from the inbound receive signal in a near-field mode and generates a recovered encoded data signal in a far-field mode;

a baseband processing module to:

processing the decoded data signal;

10. An RFID tag, comprising:

a coil antenna providing electromagnetic coupling in a near field mode;

a baseband processing module to:

processing the decoded data signal;