JP2011066760A - Antenna device and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device which can improve communication characteristics while made thin on the whole. <P>SOLUTION: The antenna device includes a first resonance circuit 111 which is constituted by winding a conductor 101 and inductively coupled to a reader writer 2 transmitting a magnetic field to communicate, and a second resonance circuit 112 having a booster coil 11c constituted by winding a conductor 102, wherein one of the conductors 101 and 102 is wound with the other winding therein with insulating layers 103 interposed, and the resonance circuits 111 and 112 have a resonance frequency equal to an oscillation frequency of the reader writer 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an antenna device capable of receiving a magnetic field transmitted from a transmitter, inductively coupled with the transmitter, and enabling communication, and a communication device incorporating the antenna device.

  An RFID (Radio Frequency Identification) antenna module incorporated in a portable electronic device such as a cellular phone communicates with a reader / writer using inductive coupling as a transformer. In other words, the antenna module receives the magnetic field from the reader / writer by the antenna coil and converts it into electric power, and moves the communication processing circuit using the electric power. At this time, the antenna module needs to have strong inductive coupling with the reader / writer antenna in order to maximize the power received by the antenna coil and efficiently return the load modulation processed in the module to the reader / writer. Furthermore, power is efficiently received by resonating with the frequency of the signal transmitted from the reader / writer. In order to maximize the power reception, it is necessary that the magnetic coupling between the coils is strong and the resistance of the antenna is low, that is, the Q value of the antenna coil is high.

  For the purpose of extending the communication distance, an invention has been proposed in which a coil resonating at the frequency of a carrier wave is incorporated in an antenna module.

  For example, in the invention described in Patent Document 1, it is assumed that the booster coil is arranged between the reader / writer and the card antenna or on the same plane, and the booster coil is larger than the antenna coil.

JP 2005-323019 A

  Although the invention described in Patent Document 1 described above can be expected to greatly increase the communication distance, particularly when mounted in a portable electronic device that is required to be downsized, a large booster antenna coil is used. Not suitable. Certainly, a booster coil is effective to improve communication characteristics, but it is necessary to use a booster coil that is larger than the antenna coil, and its use is limited when it is mounted inside a portable electronic device. come.

  In order to increase the communication sensitivity between the antennas, attempts have been made to increase the mutual inductance by increasing the number of turns of the coil and using a magnetic sheet that serves to draw a magnetic field into the antenna coil.

  However, when the number of turns of the coil is increased for the purpose of strengthening the magnetic coupling, the resistance of the coil increases, and it is difficult to increase the efficiency beyond the optimum number of turns for the following reason.

  First, increasing the number of turns of the coil to increase the self-inductance increases the magnetic coupling. Therefore, as the number of turns of the antenna coil is increased, this coupling increases, but the coil resistance increases. In a radio communication system for RFID, for example, power is efficiently received by resonating a coil on the card side in accordance with 13.56 MHz of a carrier wave generated by a reader / writer. At a frequency of 13.56 MHz, current flows only in a portion corresponding to 17 microns on the surface of the conductor forming the coil due to the skin effect. Therefore, in order to reduce the coil resistance that increases by increasing the number of turns, there is a limit even if the cross-sectional area of the coil is widened. Further, due to the proximity effect, the skin is further thinned by the magnetic field leaking from the adjacent coil, and it is substantially difficult to reduce the coil resistance even if the coil cross-sectional area and spacing are designed with allowable dimensions. Therefore, the number of turns of the coil must be designed with a certain optimum value. As a result, it is difficult to improve the communication distance simply by increasing the number of turns of the coil.

  Incorporation of a magnetic sheet into an antenna module is also a situation in which improvement of the magnetic properties of the magnetic material cannot be expected to meet future demands for thinner antennas.

  For example, a problem occurs when an antenna module is mounted on a mobile phone. There are metals and substrates that carry electricity in the mobile phone. When a high frequency signal of 13.56 MHz from the reader / writer enters the mobile phone, an eddy current is generated in the metal part, thereby repelling the magnetic field, and the communication distance is significantly shortened. In order to prevent this, a magnetic sheet is used between the antenna module and the metal. This magnetic sheet blocks the metal eddy current and serves to guide the signal to the antenna coil without repelling the signal from the reader / writer. If the magnetic sheet has a high magnetic permeability, the magnetic coupling between the reader / writer and the antenna coil becomes strong, so that the communication distance can be increased. However, the space between the reader / writer and the antenna coil is mostly air, and even if there is a sheet with high magnetic permeability in a part thereof, a great effect cannot be expected. Furthermore, mobile phones have recently been in the trend of thinning, and this magnetic sheet is also required to be thin. Even if the magnetic properties of the magnetic sheet are increased, it is quite difficult to increase the communication distance. As described above, it is very difficult to cope with future demands for antenna miniaturization.

  Therefore, the present invention has been proposed in view of such circumstances, and provides an antenna device capable of improving communication characteristics while achieving a reduction in thickness as a whole, and a communication device incorporating this antenna device. For the purpose.

  In order to solve the above-described problem, an antenna device according to the present invention includes a first coil that is configured by winding a first conductive wire and is inductively coupled to a transmitter that transmits a magnetic field to enable communication. And a second resonant circuit having a second coil configured by winding the second conductive wire, the first conductive wire and the second conductive wire being insulated from each other The other conducting wire is wound between one conducting wire through the layer, and the first resonant circuit and the second resonant circuit have a resonance frequency that matches the oscillation frequency of the oscillator.

  In addition, the communication device according to the present invention includes a first resonance circuit including a first coil that is configured by winding the first conductor and is inductively coupled to a transmitter that transmits a magnetic field. And a second resonant circuit having a second coil configured by winding the second conductive wire, and a communication that is driven by a current flowing in the first resonant circuit and communicates with a transmitter A first conductive wire and a second conductive wire, each of the first conductive wire and the second conductive wire is wound around one conductive wire through an insulating layer, and the first resonant circuit and the second resonant circuit are The resonance frequency coincides with the oscillation frequency of the magnetic field transmitted from the transmitter.

  In the present invention, the first conductive wire and the second conductive wire are wound with each other between the first conductive wire and the second coil through the insulating layer. By forming and using the mutual inductance acting between these coils, the communication characteristics of the first coil constituted by the first conductive wire are improved, thereby achieving good communication while reducing the overall thickness. Characteristics can be realized.

It is a figure which shows the structure of the radio | wireless communications system incorporating the antenna module to which this invention was applied. It is a figure for demonstrating the laminated structure of an antenna board | substrate. It is a figure for demonstrating the change of the communication characteristic at the time of changing the number of turns of the booster coil boost in the state which fixed the number of turns of the antenna coil ant to 4. It is a figure which shows the change of Q value according to the number of turns of booster coil boost. It is a figure which shows the antenna module in which only the antenna coil ant was mounted in the antenna board | substrate. It is a figure for demonstrating the structure of each antenna board | substrate in the antenna module A which concerns on this embodiment, and antenna module BD which concerns on a comparative example. It is a figure for demonstrating the communication characteristic which concerns on each antenna module AD when changing the winding number of the antenna coil ant.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the present invention.

  An antenna module to which the present invention is applied is an antenna device that is in a communicable state by electromagnetic induction generated with a transmitter that transmits electromagnetic waves. For example, for an RFID (Radio Frequency Identification) as shown in FIG. The wireless communication system 100 is used by being incorporated.

  The wireless communication system 100 includes an antenna module 1 to which the present invention is applied, and a reader / writer 2 that accesses the antenna module 1.

  The reader / writer 2 functions as a transmitter that transmits a magnetic field to the antenna module 1, and specifically, an antenna 2a that transmits a magnetic field toward the antenna module 1, and an antenna that is inductively coupled via the antenna 2a. A control board 2b that communicates with the module 1 is provided.

  That is, the reader / writer 2 is provided with a control board 2b electrically connected to the antenna 2a. A control circuit composed of electronic components such as one or a plurality of integrated circuit chips is mounted on the control board 2b. The control circuit executes various processes based on the data received from the antenna module 1. For example, when writing data to the antenna module 1, the control circuit encodes the data, modulates a carrier wave of a predetermined frequency (for example, 13.56 MHz) based on the encoded data, and amplifies the modulated modulation signal Then, the antenna 2a is driven by the amplified modulation signal. Further, when reading data from the antenna module 1, the control circuit amplifies the modulation signal of the data received by the antenna 2a, demodulates the modulation signal of the amplified data, and decodes the demodulated data. In the control circuit, an encoding method and a modulation method used in a general reader / writer are used. For example, a Manchester encoding method or an ASK (Amplitude Shift Keying) modulation method is used.

  The antenna module 1 incorporated in the housing 3a of the electronic device draws a magnetic field into the antenna coil 11a and the antenna substrate 11 on which the antenna coil 11a that can communicate with the reader / writer 2 that is inductively coupled is mounted. The magnetic sheet 12 formed in the position which overlaps with the antenna coil 11a, and the communication processing part 13 which drives with the electric current which flows through the antenna coil 11a, and communicates with the reader / writer 2 are provided.

  The antenna substrate 11 includes an antenna coil 11a disposed on a two-dimensional orthogonal plane XY orthogonal to the direction Z of the magnetic field transmitted from the reader / writer 2, and a capacitor 11b electrically connected to the antenna coil 11a. A first resonance circuit 111 made of is mounted.

  When the first resonant circuit 111 receives the magnetic field transmitted from the reader / writer 2 by the antenna coil 11a, the first resonant circuit 111 is magnetically coupled to the reader / writer 2 by inductive coupling, receives the modulated electromagnetic wave, and communicates the received signal. This is supplied to the processing unit 13. Here, in order to make the signal level of the received signal as high as possible, the first resonance circuit 111 is configured by an element having an electric characteristic such that the resonance frequency matches the oscillation frequency of the reader / writer 2.

  The antenna substrate 11 has a booster coil 11c disposed on a two-dimensional orthogonal plane XY orthogonal to the direction Z of the magnetic field transmitted from the reader / writer 2, and a capacitor electrically connected to the booster coil 11c. A second resonance circuit 112 consisting of 11d is mounted.

  The second resonance circuit 112 is a circuit that is magnetically coupled to the reader / writer 2 by inductive coupling when a magnetic field transmitted from the reader / writer 2 is received by the booster coil 11c. Here, in order to strengthen the inductive coupling with the reader / writer 2 as much as possible, the second resonance circuit 112 is configured by an element having an electrical characteristic such that the resonance frequency matches the oscillation frequency of the reader / writer 2. .

  As shown in FIG. 2, the antenna substrate 11 having such a configuration includes a first conductive wire 101 that forms the antenna coil 11 a and a conductive wire 102 that forms the booster coil 11 c with an insulating layer 103 therebetween. Thus, the other conductor is wound between one conductor. In this manner, the antenna coil 11a and the booster coil 11c are mounted on the antenna substrate 11 on the same plane while being electrically insulated from each other.

  Further, in the antenna substrate 11, by making the line width of the conducting wire 102 constituting the booster coil 11c substantially the same as the line width of the conducting wire 101 constituting the antenna coil 11a, the electrical characteristics of each coil and the number of turns are parameters. From the viewpoint of adjusting circuit characteristics.

  The magnetic sheet 12 is formed at a position overlapping the antenna coil 11a in order to draw the magnetic field transmitted from the reader / writer 2 into the antenna coil 11a. The magnetic sheet 12 suppresses a metal component provided inside the SUS plate 3b of the portable electronic device from rebounding a magnetic field transmitted from the reader / writer 2 and generating an eddy current. In order to fulfill such a function, the magnetic sheet 12 has a structure in which the magnetic sheet 12 is bonded to the antenna substrate 11 via the adhesive layer 114 on the side opposite to the direction in which the magnetic field is radiated.

  The communication processing unit 13 is driven by a current flowing through the first resonance circuit 111 that is electrically connected, and communicates with the reader / writer 2. Specifically, the communication processing unit 13 demodulates the received modulation signal, decodes the demodulated data, and writes the decoded data to the memory. The communication processing unit 13 reads data to be transmitted to the reader / writer 2 from the memory, encodes the read data, modulates the carrier wave based on the encoded data, and is magnetically coupled by inductive coupling. The modulated radio wave is transmitted to the reader / writer 2 via the resonance circuit 111.

  Next, specific communication characteristics of the antenna module 1 will be described.

  In the antenna module 1 according to the present embodiment, with the number of turns of the antenna coil ant fixed to 4, the number of turns of the booster coil boost as shown in FIGS. 3 (A), 3 (B), and 3 (C). Table 1 below shows communication characteristics when the value is changed to 4, 3, and 2.

  In Table 1, from the left end to the right end, the number of turns of the booster coil boost, the resistance value of each element, the inductance of each element, the coupling coefficient of each element, and the Q value as an evaluation index of communication characteristics are shown. Here, the resistance value and the inductance of each element are values at 13.56 MHz, which is the oscillation frequency of the magnetic field transmitted from the reader / writer.

  That is, “4T” to “2T” indicate that the number of turns of the booster coil boost is “4” to “2”, respectively.

  Rant indicates the resistance value of the antenna coil ant. Rboost indicates the resistance value of the booster coil boost. Rrw indicates the resistance value of the antenna coil on the reader / writer side.

  Lant represents the self-inductance value of the antenna coil ant. Mant-boost indicates a mutual inductance value between the antenna coil ant and the booster coil boost. Lboost represents the self-inductance value of the booster coil boost. Mant-rw represents a mutual inductance value between the antenna coil ant and the antenna coil on the reader / writer side. Mboost-rw represents a mutual inductance value between the booster coil boost and the antenna coil on the reader / writer side. Lrw represents the self-inductance value of the antenna coil on the reader / writer side. Kant-boost indicates a coupling coefficient between the antenna coil ant and the booster coil boost. Kant-rw represents a coupling coefficient between the antenna coil ant and the antenna coil on the reader / writer side. Kboost-rw represents a coupling coefficient between the booster coil and the antenna coil on the reader / writer side.

  The Q value is a value calculated by the following equation (1) as an evaluation index of communication characteristics, and the larger the value, the better the communication characteristics.

Q = ω × (Lant + Lboost) / Rant (1)
Here, ω is the angular frequency of the magnetic field transmitted from the reader / writer.

  FIG. 4A is a diagram showing a change in the Q value of each antenna module when the number of turns of the booster coil boost is changed in a state where the number of turns of the antenna coil ant is fixed to 4. FIG.

  FIG. 4B shows an antenna disposed at a predetermined separation distance as communication characteristics of each antenna module when the number of turns of the booster coil boost is changed with the number of turns of the antenna coil ant being fixed to 4. It is a figure which shows the change of the signal level Vrw returned to the reader / writer 2 from a module. The signal level Vrw according to the “comparative example” in FIG. 4B is a value obtained using an antenna module in which only the antenna coil ant is mounted on the antenna substrate as shown in FIG.

  As is clear from the results of FIG. 4, the antenna module 1 according to the present embodiment has a larger Q value than the antenna module according to the comparative example in which the booster coil boost is not mounted, and can realize better communication characteristics. .

  4A, the antenna module 1 according to the present embodiment can maintain good communication characteristics even when the number of turns of the booster coil boost is equal to or less than the number of turns of the antenna coil ant. it can. In particular, the antenna module 1 according to the present embodiment can reduce the weight and maintain the cost while maintaining good communication characteristics by making the number of turns of the booster coil boost smaller than the number of turns of the antenna coil ant. .

  Next, as an example of the antenna module 1 according to the present embodiment, as shown in FIG. 6A, the communication characteristics of the antenna module A in which the number of turns of the antenna coil ant and the number of turns of the booster coil boost are the same. Next, it evaluates compared with the antenna module which concerns on three types of comparative examples. In the antenna module B according to the first comparative example, only the antenna coil ant as shown in FIG. 6B is mounted on the antenna substrate. In addition, as shown in FIG. 6C, the antenna module C according to the second comparative example includes an antenna module ant having 4 turns and one booster coil boost having 4 turns. It is formed on the same plane of the substrate. Further, the antenna module D according to the third comparative example has a booster coil boost having the same number of turns as that of the antenna coil ant on the inner periphery of the antenna coil ant having 4 turns as shown in FIG. Are formed on the same plane of the antenna substrate.

  Here, the antenna modules A to D described above are assumed to have the same outer shape determined by the outer periphery of the antenna coil ant. In addition, each antenna module has a magnetic sheet attached to the antenna substrate, and is assumed to be incorporated in a mobile phone or the like, with the surface of the antenna substrate to which the magnetic sheet is bonded as a reference. An SUS plate was placed at a position 2 mm apart, and the communication characteristics were evaluated based on the Q value.

  FIG. 7A is a diagram illustrating changes in the Q values of the antenna modules A to D when the number of turns of the antenna coil ant is changed. FIG. 7B shows the signal level Vrw returned to the reader / writer 2 from the antenna module arranged at a predetermined separation distance as the communication characteristics of the antenna modules A to D when the number of turns of the antenna coil ant is changed. It is a figure which shows a change.

  As is clear from the results of FIG. 7, the antenna module A according to the example has a larger Q value than the antenna modules B, C, and D according to the comparative example, and can realize better communication characteristics.

  As is apparent from the above results, in the antenna module 1 according to the present embodiment, the conducting wire 101 and the conducting wire 102 are wound around one conducting wire with the other conducting wire interposed between the conducting wires. By forming the antenna coil 11a and the booster coil 11c by using the mutual inductance acting between these coils, the communication characteristics of the antenna coil 11a constituted by the conducting wire 101 are improved, so that the booster coil Compared to an antenna module that is not mounted, it is possible to realize better communication characteristics. Further, the antenna module 1 according to the present embodiment can maintain good communication characteristics even when the number of turns of the booster coil boost is equal to or less than the number of turns of the antenna coil ant. In particular, the antenna module 1 according to the present embodiment can reduce weight and cost while maintaining good communication characteristics by making the number of turns of the booster coil boost smaller than the number of turns of the antenna coil ant.

  Here, it is desirable that the opening area of the booster coil is larger than the opening area of the antenna coil from the viewpoint of simply realizing good communication characteristics, but the booster coil is not mounted from the viewpoint of reducing the size of the antenna module. There is a physical restriction that it is preferable that the outer shape of the antenna substrate does not increase compared to the case.

  Under such restrictions, the antenna module 1 according to the present embodiment is configured such that the conducting wire 101 and the conducting wire 102 are wound by winding the other conducting wire between the conducting wires via the insulating layer 103. By forming the coil 11a and the booster coil 11c and utilizing the mutual inductance acting between these coils, the communication characteristic of the antenna coil 11a constituted by the conducting wire 101 is improved, thereby providing good communication characteristics. Can be realized.

  1 antenna module, 2 reader / writer, 2a antenna, 2b control board, 3a housing, 3b SUS board, 11 antenna board, 11a antenna coil, 11b capacitor, 11c booster coil, 11d capacitor, 12 magnetic sheet, 13 communication processing unit, 100 wireless communication system 101 conductive wire 102 conductive wire 103 insulating layer 111 resonant circuit 112 resonant circuit 114 adhesive layer

Claims (5)

A first resonance circuit having a first coil that is configured by winding a first conductive wire and is inductively coupled to a transmitter that transmits a magnetic field to enable communication;
A second resonant circuit having a second coil configured by winding a second conducting wire;
The first conducting wire and the second conducting wire are wound with each other between one conducting wire and the other conducting wire through an insulating layer.
The antenna device, wherein the first resonance circuit and the second resonance circuit have a resonance frequency that matches an oscillation frequency of the transmitter.   The antenna device according to claim 1, wherein the number of turns of the second coil is equal to or less than the number of turns of the first coil.   The antenna device according to claim 2, wherein the number of turns of the second coil is smaller than the number of turns of the first coil.   The antenna according to any one of claims 1 to 3, wherein a line width of the conducting wire constituting the second coil is substantially the same as a line width of the conducting wire constituting the first coil. apparatus. A first resonance circuit having a first coil that is configured by winding a first conductive wire and is inductively coupled to a transmitter that transmits a magnetic field to enable communication;
A second resonant circuit having a second coil configured by winding a second conductor;
A communication processing unit that is driven by a current flowing through the first resonance circuit and performs communication with the transmitter;
The first conducting wire and the second conducting wire are wound with each other between one conducting wire and the other conducting wire through an insulating layer.
The communication device, wherein the first resonance circuit and the second resonance circuit have a resonance frequency that matches an oscillation frequency of a magnetic field transmitted from a transmitter.

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