News Column

Patent Issued for NFC Device for Contactless Communication

September 10, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- A patent by the inventor Merlin, Erich (Gratkorn, AT), filed on September 16, 2013, was published online on August 26, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8818297 is assigned to NXP, B.V. (Eindhoven, NL).

The following quote was obtained by the news editors from the background information supplied by the inventors: "FIG. 1 shows a prior art implementation of a transceiving circuit for contactless communication. This transceiving circuit employs an integrated near field communication transmission module 2, type no. PNSxx, e.g. type no. PN511 or PN512 prior art matching is also valid for the Micore family (MF RCSxx, MF RC632, SL RC400), manufactured by NXP Semiconductors and external passive electronic components. The transmission module 2 is integrally equipped with transmitter means 3 being adapted to generate an electromagnetic carrier signal, to modulate the carrier signal according to transmitting data and to drive an antenna 5 with the modulated carrier signal, and with receiver means 4 being adapted to sense response signals being received at the antenna 5 and to demodulate the response signals. The transmission module 2 has output terminals TX1, TX2 being connectable to first and second transmitting paths wherein the transmitting paths are connected to the antenna 5, being represented in FIG. 1 by its equivalent circuit components capacitance Cant and inductance Lant. Between the output terminals TX1, TX2 of the transmission module 2 and the external antenna 5 the following devices are switched into the transmitting paths: an electromagnetic compatibility (EMC) filter comprising two inductors L0 and two capacitors C0; and an impedance matching network comprising ohmic resistors RQ and capacitors (not shown). It should be noted that during manufacturing of the transceiving circuits the antenna 5 is 'tuned' by means of the impedance matching network.

"Further, the receiver means 4 of the transmission module 2 comprise an input terminal RX that is connected to a receiving path that branches off from the first transmitting path. A phase adjusting capacitor C13 is switched into the receiving path in order to enable adjusting of the phase angle of signals between the first transmission path and the receiving path. By adjusting the phase angle an optimal demodulation can be achieved. Further, an ohmic resistor R1 is serially switched into the receiving path. With this resistor R1 the voltage level appearing at the input terminal RX of the receiver means 4 can be adjusted. Numeral VMID depicts an analog reference voltage input of the receiver means 4. A capacitor C14 is switched between the analog reference voltage input VMID and ground potential. An ohmic resistor R2 connects the input terminal RX and the analog reference voltage input VMID.

"For a better understanding of the function of the RFID transmission module 2, a block diagram of the near field communication (NFC) transmission module type no. PN511 is shown in FIG. 2. The NFC transmission module 2 comprises analog circuitry which can be roughly divided into transmitter means 3 and receiver means 4. Although not shown, the analog circuitry comprises output drivers, an integrated demodulator, a bit decoder, a mode detector and an RF-level detector. A contactless UART communicates with the analog circuitry via a bus. The contactless UART comprises data processing means, CRC/Parity generation and checking means, frame generation and checking means, and bit coding and decoding means. The UART further communicates with a microprocessor, comprising a 80C51 core, ROM and RAM. A host interface enables to connect the transmission module to external devices. The host interface may comprise I2C, serial UART, SPI and/or USB interfaces. Further details of the transmission module can be looked up in the respective data sheets which are publicly available.

"One of the most important field of application of near field communication (NFC) transmission modules are mobile phones. Mobile phones equipped with NFC transmission modules can be used for ticketing, access control systems, payment services, etc. Usually, the NFC transmission modules are powered by the hosting mobile phone. Nevertheless, specifically for ticketing applications, there is a strong demand that the NFC transmission module must still be operable when the battery of the mobile phone has been exhausted in order to keep the tickets managed by the NFC transmission modules available. This demand has resulted in considerations of using electric energy that is provided by an electromagnetic field generated by an external reading device. This so called 'powered by the field mode' has already been implemented in standard NFC cards and standard cards where a powered by the field circuitry is directly connected with the antenna. This approach, however, has the inherent disadvantage that such a card cannot be operated in a so called 'reader mode' where the NFC card plays the role of a reading device that initiates communication with target NFC devices. Operating an NFC device in the reader mode requires an external voltage supply since the NFC device itself has to generate an electromagnetic field. In order to enable the reader mode for such a card the powered by the field circuitry has to be physically removed because it interferes with the reader mode circuitry. This removing in turn renders the powered by the field mode impossible. Therefore, there is still a strong need for a transceiving circuit for contactless communication that allows the circuit to be operated in a reader mode, a powered by the field card mode, and a battery supplied card mode without requiring to physically add or remove any hardware parts."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "It is an object of the invention to provide a transceiving circuit for contactless communication of the type defined in the opening paragraph and an NFC device in which the disadvantages defined above are avoided. Particularly, the transceiving circuit for contactless communication according to the present invention has to be operable in a reader mode, a powered by the field card mode, and a battery supplied card mode without requiring to physically add or remove any hardware parts.

"In order to achieve the object defined above, with a transceiving circuit according to the invention characteristic features are provided so that a transceiving circuit according to the invention can be characterized in the way defined below, that is:

"A transceiving circuit for contactless communication comprising:

"transmitter means being adapted to generate an electromagnetic carrier signal and to modulate the carrier signal according to transmitting data,

"an antenna having an inductor, which antenna is connected to and driven by the transmitter means with the modulated carrier signal,

"wherein AC coupling capacitors are coupled to the inductor of the antenna, wherein the AC coupling capacitors are further connected to inputs of switches the outputs of these switches being switchable between ground potential and inputs of rectifier means, the outputs of the rectifying means being fed to power supply rails of the transceiving circuit.

"The characteristic features according to the invention provide the advantage that the circuit can be operated in all NFC modes, i.e. a reader mode, a powered by the field card mode and a battery supplied card mode without the necessity to physically add or remove any hardware parts. Particularly, the transceiving circuit according to the present invention can safely be operated within the limits of the NFC standards.

"Switching among the various NFC modes can be done automatically by providing mode selection means that control the switches such that the outputs of the switches are switched to ground in a reader mode and optionally in a card mode, and are switched to the inputs of the rectifier means in a powered by the field mode.

"By arranging a capacitor in series between partial inductors of the inductor of the antenna and coupling each of the AC coupling capacitors with one of its terminals to a respective connection point of the serial capacitor and one of the partial inductors, the antenna can be tuned so that all three NFC modes can be operated within the required electrical boundaries.

"In order to achieve symmetric operation of the transceiver circuit it is preferred to divide the inductors of the antenna into two partial inductors having about the same inductance values.

"In another embodiment of the transceiver circuit according to the invention the AC coupling capacitors are inductively coupled to the inductor of the antenna by means of a coupling inductor, which together with the inductor of the antenna constitutes a transformer. This embodiment of the invention avoids direct coupling of the AC coupling capacitors to the antenna.

"In order to transform the AC electromagnetic signals received by the antenna to appropriate values it is preferred to choose the inductance of the inductor of the antenna to be smaller than the inductance of the coupling inductor.

"Further, in order to smooth the received AC electromagnetic signals, it is preferred to connect a smoothing capacitor in parallel to the coupling inductor.

"In yet another embodiment of the invention, the transceiver circuit the AC coupling capacitors are galvanic-coupled to the inductor of the antenna, preferably via ohmic resistors. This embodiment enables exact antenna tuning. In order to enhance the antenna tuning, it is preferred to couple resonance frequency setting capacitors with first terminals to the AC coupling capacitors and with second terminals to ground.

"In order to minimize variation of the resonance frequency of the antenna it is preferred that the capacitances of the resonance frequency setting capacitors are higher than the capacitances of the AC coupling capacitors, preferably at least by a factor of four.

"The transceiving circuit according to the invention can be incorporated in an NFC device.

"The aspects defined above and further aspects of the invention are apparent from the exemplary embodiments to be described hereinafter and are explained with reference to these exemplary embodiments."

URL and more information on this patent, see: Merlin, Erich. NFC Device for Contactless Communication. U.S. Patent Number 8818297, filed September 16, 2013, and published online on August 26, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8818297.PN.&OS=PN/8818297RS=PN/8818297

Keywords for this news article include: B.V., NXP, NXP B.V.

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Source: Journal of Engineering


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