JP2011066627A - Nfc sensor antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an NFC sensor antenna having an NFC antenna matching box for improving data communication performance with an IC card using 13.56 MHz, by improving the matching characteristics of the NFC sensor antenna of an IC card reader/writer available in the market. <P>SOLUTION: The NFC sensor antenna, which is used for the IC card using the frequency band of 13.56 MHz, a tag and the IC card reader/writer, includes: an NFC antenna unit obtained by laminating a printed circuit board with an antenna coil wired, a magnetic sheet and a metal plate; and a communication part comprising an IC element for transmission and reception and a peripheral circuit element on the printed circuit board. In an impedance value of an antenna coil in which the resonance frequency of the NFC antenna matching box for performing impedance matching with the antenna coil is 13.56 MHz, a resistance component is 5 to 20 Ω, and a reactance component is 200 to 300 Ω. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is an NFC antenna matching which improves the impedance matching characteristics of an NFC antenna of an IC card, a tag and an IC card reading / writing device using a frequency of 13.56 MHz conforming to the RFID standard (ISO / IEC 14443, 15693, 18092). The present invention relates to an NFC sensor antenna having a device.

  Proximity-type communication interface implementation that ensures compatibility with RFID tags when performing data communications between IC cards and RFID tags that use a commercially available frequency of 13.56 MHz and an IC card reader / writer Are disclosed in Non-Patent Document 1, and a compatibility evaluation test method and the like are introduced therein. Products that have achieved compatibility in this evaluation test are available.

  FIG. 6 is an operation principle diagram of data communication between the IC card and the IC card reading / writing device. The IC card performs power supply and data communication by electromagnetic induction of an antenna coil of the IC card reading / writing device.

  FIG. 7 shows frequency bands of data communication of Type A and Type B of the IC card of the RFID standard (ISO / IEC14443). By setting the resonance frequency from the IC card reading / writing device to the carrier frequency of 13.56 MHz via the NFC antenna, a voltage due to electromagnetic induction is generated and power is supplied to the IC card and the RFID tag.

  The data signals read / written from the Type A, Type B, and Type C IC cars are first ASK modulated (Amplitude Shift Keying), and then further subjected to load modulation to be synthesized to a carrier frequency of 13.56 MHz to 13.56 MHz. Data communication is performed by transmitting and receiving a signal wave in which data is carried on a subcarrier of ± 340 KHz. However, in the case of a Type B IC card, data communication is performed using a BPSK modulation method (Binary Phase Shift Keying) in the uplink, and data communication is performed using a 13.56 MHz ± 106 KHz subcarrier.

  A commercially available NFC antenna has a resonance characteristic (Q coefficient) so as to cover the subcarrier frequency band of 13.56 MHz ± 340 KHz including the carrier frequency of 13.56 MHz and the data signal. For example, a method for coupling an NFC element and an antenna disclosed in Patent Document 1 is introduced.

JP 2008-259200 A

Proximity Communication Interface Implementation Agreement, New Media Development Association, March 2004

  However, after evaluating the communication distance of an existing IC card using 13.56 MHz using a commercially available IC card reader / writer, a commercially available general-purpose IC card reader / writer Then, we could not read the Type B ELWISE card. As shown in FIG. 8, when the IC card is held over the NFC sensor antenna of the IC card reader / writer, the impedance of the NFC sensor antenna fluctuates due to the influence of the metal plate of the IC card, and the carrier frequency is 13.56 MHz. Deviation occurs in the direction in which the peak frequency value increases. For this reason, the IC card having high Q characteristics has a problem that data communication cannot be performed because the power supply is lowered and a necessary electromotive force cannot be obtained due to fluctuation of the resonance frequency.

  The present invention has been made in order to solve the above-mentioned problems, and improves the matching characteristics of NFC sensor antennas of IC cards and IC card reading / writing devices that are generally available on the market, and uses existing 13.56 MHz ICs. An object of the present invention is to provide an NFC sensor antenna having an NFC antenna matching unit that improves data communication performance with a card.

  In order to achieve the above-mentioned object, the present invention comprises the following configurations (1) to (7).

  (1) An NFC antenna unit configured by integrally bonding a magnetic sheet between a printed board on which a plurality of turns of the antenna coil are wired and a metal plate, and mounted on the printed board An NFC sensor antenna of an IC card, a tag, and an IC card reading / writing device using a frequency band of 13.56 MHz. The NFC sensor antenna has an NFC antenna matching unit comprising a plurality of matching circuit constants for impedance matching with the antenna coil, and the impedance value of the antenna coil at which the resonance frequency of the NFC antenna matching unit is the frequency of 13.56 MHz However, the resistance component including the insertion resistance is 5 to 20Ω, and the reactance component is 200 to 30 NFC sensor antenna, characterized in that in the range of Omega.

  (2) By graphing impedance values obtained by calculating a plurality of matching circuit constants of the NFC antenna matching unit over the use range of impedance values of the antenna coil, the matching circuit constants determined from the graph The NFC sensor antenna according to (1), wherein an impedance value of the antenna coil is measured on the condition that the matching circuit constant is determined by applying the measured value to the graph.

  (3) The NFC sensor according to (1) or (2), wherein the insertion resistance is in the range of 1 to 5Ω when the resonance frequency of the antenna coil on the printed circuit board is 13.56 MHz. antenna.

  (4) The metal plate of the NFC antenna unit, the transmission / reception IC element mounted on the printed circuit board, and the communication unit including its peripheral circuit elements are connected by a common ground so as to have the same potential. The NFC sensor antenna according to any one of (1) to (3), wherein:

  (5) In the NFC antenna section, the transmitting / receiving IC element and its peripheral circuit elements are not mounted on the printed circuit board on which the antenna coil is formed, and these components are mounted on a separate board. The NFC sensor antenna as described in any one of (1) to (4) above, wherein the substrate is connected by an antenna feed line, and the thickness of the entire antenna including the magnetic sheet and the metal plate is reduced.

  (6) A notch such as a window is formed in a central portion of the magnetic sheet, and the communication unit including the transmitting / receiving IC element mounted on the printed circuit board and its peripheral elements is notched in the magnetic sheet. The NFC sensor antenna as described in any one of (1) to (4) above, wherein the thickness is further relaxed by being accommodated in the antenna, and the entire antenna is further thinned.

  (7) When the impedance value of the antenna coil is measured and applied to the graph to determine the matching circuit constant, it is necessary to provide a metal plate by adjusting in advance on the metal plate and considering the influence of the metal surface in advance. The NFC sensor antenna according to any one of (1) to (6) above, wherein the thickness of the metal plate can be reduced.

  According to the present invention, the data communication performance with the IC card is improved by improving the impedance matching characteristics of the NFC sensor antenna of the IC card and IC card reader / writer using the frequency of 13.56 MHz. Can provide an NFC sensor antenna having an NFC antenna matching device.

NFC sensor antenna diagram according to the present embodiment, (a) NFC sensor antenna external view, (b) NFC sensor antenna circuit diagram Matching circuit constant of the NFC sensor antenna according to the present embodiment, (a) matching circuit constant (1), (b) matching circuit constant (2) Comparison diagram of communication distance between NFC sensor antenna of this embodiment and commercial product Thin configuration example of NFC sensor antenna according to this embodiment Another thin configuration example of the NFC sensor antenna according to this embodiment Basic operation circuit diagram of IC card and IC card reader / writer Frequency characteristics of RFID standard IC cards Graph showing the change in impedance due to the influence of a metal plate

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to examples.

  The present invention will be described with reference to the drawings.

  FIG. 1 shows an NFC sensor antenna according to this embodiment. FIG. 1A is an external view of an NFC sensor antenna. FIG. 1B is a circuit diagram of the NFC sensor antenna. In the figure, 1 is a square or rectangular printed circuit board. The printed circuit board 1 has a length of about 25 to 70 mm on a side (about 40 to 50 mm square for a personal computer, about 25 to 30 mm square for a mobile phone), and a thickness of about 0.4 mm or less and about 0.1 mm. Is used. An NFC antenna coil 1a is formed by wiring a plurality of turns around the printed circuit board 1. Reference numeral 1 b denotes an NFC peripheral circuit element mounted on the printed circuit board 1. Reference numeral 8 denotes an NFC transmission / reception IC (for example, PN531, PN532, PN533, etc.) mounted on the printed circuit board 1. The mounting position of the peripheral circuit element 1b including the matching circuit is performed around the IC, and the area 7 of the printed board is indicated by 7a and 7b. Reference numeral 1c denotes a signal line for connecting to a USB of a device such as a personal computer. Reference numeral 2 denotes a magnetic sheet, which is approximately the same size as the printed circuit board 1. The magnetic sheet 2 has a thickness of about 0.5 mm or less and a relative permeability of 100 or more. Reference numeral 3 denotes a metal plate, which is approximately the same size as the printed circuit board 1, has a thickness of about 0.1 mm, and is made of aluminum or stainless steel. Copper foil or aluminum foil may be used. The printed circuit board 1, the magnetic sheet 2, and the metal plate 3 are bonded and integrated with each other with an adhesive. Reference numeral 4 denotes a main body of the NFC sensor antenna according to the present embodiment.

  The RFID standard (ISO / IEC 14443, 15693, 18092) type A and type C IC cards transmit and receive data by transmitting signal waves with load modulation on subcarriers with resonance frequencies of 13.56 MHz and 13.56 MHz ± 340 KHz. In the Type B IC card, data communication is performed using the BPSK modulation method, and data communication is performed using a 13.56 MHz ± 106 KHz subcarrier. By holding the IC card over the NFC sensor antenna 4 attached to the IC card reading / writing device, power is supplied to the IC card by electromagnetic induction at a resonance frequency of 13.56 MHz.

  However, actually, as shown in FIG. 8, when the IC card is held over the NFC sensor antenna 4 of the IC card reading / writing device, the impedance of the NFC sensor antenna 4 fluctuates due to the influence of the metal plate 3, and the carrier frequency It is known that deviation occurs in the direction in which the frequency value of 13.56 MHz increases. Therefore, in a Type B IC card with high Q characteristics, an electromotive force due to electromagnetic induction cannot be obtained due to a shift in resonance frequency, or even if an electromotive force is obtained, the effective power is greatly reduced. An error occurs in the data communication because the interval with the apparatus is limited to a narrow range or the frequency band of the data communication is out of range.

  Further, when the metal plate 3 bonded to the antenna of the IC card or IC card reading / writing device and the ground of the printed board 1 are not connected, stray capacitance is generated between the printed board 1 and the metal plate 3. Therefore, grounding that makes the potential of the metal plate 3 and the ground of the printed circuit board 1 common is necessary. However, since the common ground is not set in the commercially available NFC sensor antenna 4, the impedance changes to cause a deviation of the resonance frequency. Therefore, in the NFC sensor antenna 4 according to the present embodiment, as shown in the circuit diagram of FIG. 1B, the common potential is provided between the metal plate 3 and the ground of the printed circuit board 1 by providing the metal plate 3 with a common ground. Grounding.

  Next, the matching circuit constant of the NFC sensor antenna 4 is changed to verify the matching of the antenna impedance. Changing the matching circuit constants (Cs, Cp) of the NFC antenna matching unit included in the peripheral circuit element 1b between the transmitting / receiving IC element 8 and the NFC antenna coil 1a on the printed circuit board 1 in FIG. It verified by.

  2A and 2B are graphs of antenna impedance matching circuit constants. In the circuit diagram of the NFC sensor antenna 4 in FIG. 1B, the matching circuit constant for matching the antenna impedance Za within a predetermined range (Zo = 50Ω) in consideration of the circuit constant of the EMC filter unit. (Cs, Cp) is calculated and graphed. If this graph is used, the matching circuit constant can be easily obtained by actually measuring the antenna impedance Za, so there is no need to calculate by substituting a value into a complicated calculation formula.

  Further, matching cannot be achieved unless the matching circuit is assembled so that the values of the matching circuit constants (Cs, Cp) shown in the graph fall within this range. Better transmission and reception by performing impedance matching of the NFC sensor antenna 4 by setting the resistance of the antenna impedance Za to 5Ω to 20Ω (including Ra) and reactance to 200Ω to 300Ω at a frequency of 13.56 MHz. Performance is obtained.

  The insertion resistance Ra shown in the circuit diagram of FIG. 1B is for suppressing the Q characteristic of the NFC antenna coil 1a to 30 or less and should be about 1 to 5Ω (actually about 3Ω). The function of the resistor Ra suppresses the Q characteristic of the resonance frequency of the NFC antenna coil 1a to 30 or less, and has a Q characteristic that allows a wide resonance frequency band in which effective power can be supplied without reducing the electric field strength. As a result, by setting the matching circuit constants (Cs, Cp) shown in FIG. 2 to the optimum settings, the shift width of the carrier frequency due to the influence of the respective metal plates 3 on a wide variety of existing IC cards and IC tags. Can be covered.

  From the comparison table of the communication distance with the commercially available NFC sensor antenna shown in FIG. 3, the NFC sensor antenna 4 of the present embodiment greatly extends the communication distance of data communication by the NFC antenna matching unit that improves the NFC antenna matching characteristics. In addition, the data communication of the reading / writing of the Type B ELWISE card, which could not be performed, is now possible.

  Next, a setting method for thinning the NFC sensor antenna 4 will be described. In the case of a commercially available NFC sensor antenna 4, the shape shown in the external view of FIG.

  An antenna including a printed circuit board 1, a transmitting / receiving IC element 8, a peripheral circuit element 1 b, a magnetic sheet 2, and a metal plate 3 of a communication unit on the substrate from a side view of the antenna section shown in FIG. The total thickness is 2 mm or less (about 1.7 mm). However, when the matching circuit constants (Cs, Cp) of the NFC sensor antenna 4 are adjusted to the optimum settings on the metal surface in advance, the antenna portion of the IC card or the IC card reading / writing device is affected by the metal surface. Therefore, it is not necessary to apply the metal plate 3, and the thickness of the metal plate 3 can be reduced.

  FIG. 4 shows a configuration for thinning the antenna portion of the NFC sensor antenna 4. In FIG. 4A, the printed circuit board 1 is not mounted with the transmitting / receiving IC element 8 and its peripheral circuit element 1b, and these components are provided with a separate printed circuit board area 7 to form a main body board of a device such as a personal computer. The main body substrate composed of the printed circuit board region 7 on which the communication part of the transmission / reception IC element 8 and its peripheral circuit element 1b is mounted and the antenna coil printed circuit board 1 are connected by the antenna feeding line 1d. I made it. FIG. 4B is a view of the antenna portion of FIG. 4A viewed from the side, and the thickness of the entire antenna can be reduced to 1 mm or less (about 0.65 to 0.7 mm). Moreover, when it adjusts on a metal surface as mentioned above, it will be about 0.55-0.6 mm and can be made still thinner.

  FIG. 5 shows another configuration example of the NFC sensor antenna 4 configuration. The difference from the commercially available NFC sensor antenna 4 shown in FIG. 1A is that a notch is formed in the central portion of the magnetic sheet 2 as shown in FIG. The IC element 8 and the peripheral circuit element 1b) are mounted on the substrate surface on the side where the magnetic sheet 2 is present, and are configured to fit within the cutout of the magnetic sheet 2a. When the thickness of the magnetic sheet 2 shown in FIG. 5B is as thin as about 0.38 mm, and the thickness of the IC element is about 0.8 mm, a space of about 0.42 mm as shown in FIG. A plastic frame 12 having a thickness of about 0.4 mm may be applied. The thickness of the magnetic sheet 2 may be increased instead of using the plastic frame 12. However, since the magnetic body is expensive, it is covered with the minimum thickness of the magnetic body, and this magnetic path allows the magnetic field to pass through and avoids the influence of the metal surface. For the extra thickness, it is more economical to use cheap plastic.

  As described above, the thickness of the entire antenna can be reduced by reducing the protrusion of the mounted component and the thickness of the magnetic material. Furthermore, if a notch is also provided in the metal plate (thickness of about 0.1 mm) so that the protrusions of the mounting portion can be accommodated in the thickness of this portion, the thickness can be reduced by about 0.48 to 0.5 mm as a whole.

  As an example of thinning the magnetic sheet 2, one or two 0.19 mm thick magnetic sheets 2 that are sintered with a magnetic green sheet and fixed with a plastic laminate can be used. In the case of one sheet, the magnetic path is narrow and sufficient characteristics cannot be obtained, but in the case where the thickness is 0.38 mm using two sheets, sufficient characteristics are obtained. Even with a single 0.19 mm magnetic body, the characteristics are inferior, but can be used if the communication distance is about 10 to 20 mm. When one sheet of 0.3 mm thick magnetic material sheet 2 is used, a value close to the characteristics of the two 0.19 mm magnetic material layers is obtained.

  As described above, the present invention improves the matching characteristics of an NFC sensor antenna of a generally available IC card reader / writer and improves the data communication performance with an existing IC card using an existing 13.56 MHz. A highly sensitive NFC sensor antenna having a matching unit can be provided.

Cs Matching circuit constant Cp Matching circuit constant Ra Resistance Za Antenna impedance 1 Printed circuit board 1a NFC antenna coil 1b Peripheral circuit element 1c Signal line 2 Magnetic sheet 3 Metal plate 4 NFC sensor antenna 7 IC peripheral circuit area 8 NFC transmission / reception IC element 12 Plastic frame

Claims (7)

An NFC antenna unit formed by laminating and integrating a magnetic sheet between a printed board on which a plurality of turns of the antenna coil are arranged in a circular pattern and a metal plate, and a transmitter / receiver mounted on the printed board An NFC sensor antenna of an IC card, a tag, and an IC card reading / writing device that includes an IC element and a communication unit including peripheral circuit elements and uses a 13.56 MHz frequency band,
The NFC sensor antenna has an NFC antenna matching unit comprising a plurality of matching circuit constants for impedance matching with the antenna coil;
The impedance value of the antenna coil at which the resonance frequency of the NFC antenna matching unit becomes the frequency of 13.56 MHz is such that the resistance component including the insertion resistance is in the range of 5 to 20Ω and the reactance component is in the range of 200 to 300Ω. NFC sensor antenna.   By graphing the impedance values obtained by calculating a plurality of matching circuit constants of the NFC antenna matching unit over the use range of the impedance value of the antenna coil, the matching circuit constants determined from the graph are obtained. 2. The NFC sensor antenna according to claim 1, wherein an impedance value of the antenna coil is measured as a condition, and is applied to the graph to determine a matching circuit constant.   3. The NFC sensor antenna according to claim 1, wherein the insertion resistance is in a range of 1 to 5Ω when the resonance frequency of the antenna coil on the printed circuit board is 13.56 MHz. The metal plate of the NFC antenna unit, the transmission / reception IC element mounted on the printed circuit board, and the communication unit including its peripheral circuit elements are connected by a common ground so as to have the same potential. The NFC sensor antenna according to claim 1, wherein the antenna is an NFC sensor antenna.   In the NFC antenna section, the IC element for transmission and reception and its peripheral circuit elements are not mounted on the printed circuit board on which the antenna coil is formed, and these components are mounted on separate substrates. The NFC sensor antenna according to any one of claims 1 to 4, wherein the antenna feeding line is connected, and the thickness of the entire antenna including the magnetic sheet and the metal plate is reduced.   A notch such as a window is formed in a central portion of the magnetic sheet, and the communication unit including the transmission / reception IC element and its peripheral elements mounted on the printed board is in the notch of the magnetic sheet. 5. The NFC sensor antenna according to claim 1, wherein the NFC antenna portion is further reduced in thickness by being mounted on the printed circuit board so that the NFC antenna portion can be accommodated.   When the impedance value of the antenna coil is measured and applied to the graph to determine the matching circuit constant, it is not necessary to provide a metal plate by adjusting in advance on the metal plate and considering the influence of the metal surface in advance. The NFC sensor antenna according to claim 1, wherein the thickness of the plate can be reduced.

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