JP2003069336A - Antenna coil and read/write system for contactless ic card - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna coil with a wide tuning frequency band by eliminating a deviation in a tuning point. SOLUTION: The antenna coil 1 is provided with a plurality of tuning circuits comprising a feeding coil 2, tuning coils 31, 32, 33 coupled with the feeding coil 2 by mutual induction, and tuning capacitors 4 connected to the tuning coils 4 by which a plurality of tuning points appear. Further, the feeding coil 2 and the tuning circuits are placed coaxially. Moreover, the feeding coil 2 and the tuning circuits are placed on the same plane and the tuning circuits are placed at the inside of the feeding coil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna coil used in a reader / writer for a non-contact IC card and a reader / writer system for a non-contact IC card.

[0002]

2. Description of the Related Art Conventionally, it is known that electric power is supplied from an electric power supply side to an IC card by using light or a magnetic field in a non-contact manner. For example, cash cards, credit cards used at station ticket gates, buses, entrances and exits, etc.
When a passenger ticket, a commuter pass, etc. are made into an IC card and the user passes this IC card in a non-contact manner with a reader / writer provided at a ticket gate of a station, a bus, an entrance / exit, etc. It is a non-contact IC card that transfers power and / or signals by an electromagnetic induction method or the like between a reader / writer and a card.

By the way, in the conventional communication between a non-contact IC card and a reader / writer, when both antennas come close to each other, an induced current generated by electromagnetic induction causes impedance, and the tuning points of them are deviated from each other. There was a problem that it would end up. If the tuning point is deviated, the communication characteristic is deteriorated, and if the band of the tuning point is narrow, the communication characteristic is significantly deteriorated.

FIG. 1 shows a circuit diagram of such a conventional antenna coil, FIG. 1 (a) shows an equivalent circuit in the conventional antenna coil, and FIG. 1 (b) shows a conventional antenna characteristic. . Further, how many times the voltage of L or C at the time of tuning is higher than the power supply voltage can be expressed by a value Q, and Q is expressed by the following equation (1).

[0005]

[Equation 1] As shown in FIG. 1 (a), the conventional single coil has a high Q, so that it can be said that the efficiency is extremely high if the tuning points are matched, but the communication characteristics when the tuning points deviate from each other. There was a problem that was significantly reduced. Further, in the conventional antenna coil, since the impedance of the coil becomes high, it is difficult to match with the transmitter and the like, and it is necessary to design the peripheral circuit such as the matching circuit. For this reason, antennas have been created by predicting that the tuning points will shift in advance.

[0006]

However, in a system that communicates while changing the distance like a non-contact IC card, the expected effect cannot be obtained even if the shift of the tuning point is corrected. Further, it is possible to insert a resistor or the like into the coil to lower the Q, but since the output level is lowered, the application is limited, and it cannot be an essential countermeasure.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to solve the above-mentioned problems of the prior art, eliminate the deviation of the tuning point, and provide an antenna coil having a wide tuning frequency band.

[0008]

In order to achieve the above object, an antenna coil according to the present invention comprises a feeding coil, a tuning coil coupled to the feeding coil by mutual induction, and a tuning capacitor connected to the tuning coil. And a tuning circuit having the tuning circuit, and the tuning circuit is arranged so that a plurality of tuning points appear.

The antenna coil according to the present invention is characterized in that the feeding coil and the tuning circuit are arranged coaxially.

Further, the antenna coil according to the present invention is
The power feeding coil and the tuning circuit are arranged on the same plane, and the tuning circuit is arranged inside the power feeding coil.

According to the above antenna coil of the present invention, the tuning points of the tuning circuit are delicately shifted,
Can show the tuning points in each tuning circuit,
An antenna with low impedance and a wide tuning frequency band can be created.

Therefore, when the coils communicate with each other, it is possible to prevent the deterioration of the communication characteristics due to the shift of the tuning point. Further, by increasing the communication efficiency, it is possible to reduce the transmission power in the transmitter, which contributes to cost reduction and performance improvement. Further, since the tuning circuit is provided in the antenna, a tuning circuit, which has been separately required in the past, is not required, and the design of the entire device becomes easy.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, before describing the antenna coil according to the present invention, the configuration of a read / write system for a non-contact IC card using the antenna coil according to the present invention will be described with reference to FIG. FIG. 11 is a diagram showing a read / write system for a non-contact IC card using the antenna coil according to the present invention.

As shown in FIG. 11, the read-ride system 1 includes an antenna coil 1 for transmitting a high frequency power signal to an IC card (not shown) and receiving a high frequency signal from the IC card, and an antenna coil 1 for the IC card. A transmission circuit 5 for converting transmission data and electric power into a high frequency power signal, a reception circuit 6 for converting a high frequency signal from an IC card into reception data, and a synchronizing signal supplied is modulated according to data output from the IF. A modulation circuit 7, a demodulation circuit 8 for demodulating a received signal, a control microcomputer 9 for controlling IC card and reader / writer wireless communication, and an interface IF.

A command issued from the outside is received by the interface IF and the control microcomputer 9, converted into a modulation signal by the modulation circuit 7, and transmitted from the antenna coil 1 to the IC card via the transmission circuit 5. . Note that the configurations of the modulation circuit and the demodulation circuit are digital circuit, analog circuit,
Further, it may be either a digital or analog mixed circuit, and is not limited to the configuration shown in FIG.

Next, the antenna coil according to the present invention will be specifically described. FIG. 2 is a diagram showing an antenna coil according to the first embodiment of the present invention. As shown in FIG. 2, 1 is an antenna coil, 2 is a two-winding feed coil connected to the transmission circuit 5, 3 is a tuning coil that is coupled to the feed coil by mutual induction, and 4 is connected to the tuning coil 3. The capacitor as a resonance capacitor, the tuning coil 3 and the resonance capacitor 4 form a tuning circuit.

The tuning coil 31 and the tuning capacitor 4 form a first tuning circuit, and the tuning coil 32 and the tuning capacitor 4 form a second tuning circuit.
In the present embodiment, since the tuning coil 33 and the tuning capacitor 4 form a third tuning capacitor, the tuning circuit of
Two tuning circuits are formed. In the antenna coil 1, the feeding coil 2 and the first to third tuning circuits are arranged on the same plane so that three tuning points of the tuning circuit appear, and the first to third tuning circuits are provided. Are arranged inside the feeding coil 2.

Further, the antenna coil 1 is characterized in that the tuning circuit itself is provided in the antenna coil 1. In the conventional antenna coil, a tuning circuit is required separately from the antenna coil in order to tune with the antenna of the IC card, but as shown in FIG. 11, the antenna coil 1 according to the present invention is tuned in the antenna coil 1. Since the circuit itself is provided, it is not necessary to separately provide a tuning circuit as in the prior art, which contributes to cost reduction by deleting the circuit.
Further, in the present invention, since the principle of stagger tuning, which will be described later, is used, the tuning points of the first to third tuning circuits can be delicately shifted to reveal the tuning points of each tuning circuit. Therefore, an antenna with a low impedance and a wide tuning frequency band can be created.

Here, the principle of stagger tuning will be briefly described in order to facilitate understanding of the antenna coil in the present invention. FIG. 3 is a diagram for explaining the principle of stagger tuning. A tuning circuit using a plurality of resonance circuits is called a stagger tuning circuit. By using this principle, the tuning circuit can be arranged so that the individual tuning points are displaced, and the total antenna characteristics can be expanded.

In FIG. 3, FIG. 3A shows a power feeding circuit and a tuning circuit. In addition, FIG.
(A) shows the power supply circuit and one tuning circuit taken out, and the power supply circuit and the tuning circuit are coupled by a coupling coefficient M. Further, FIG. 3C shows an equivalent circuit of the circuit shown in FIG. 3B, where Z1 represents impedance on the power feeding side and Z2 represents impedance on the tuning side.

Here, Z, which is the impedance on the power feeding side,
Since 1 is much smaller than the impedance Z2 on the tuning side (Z2 << Z1), the impedance Z2 on the tuning side can be considered as the impedance of the entire antenna as shown in FIG. 3 (d). Moreover, since the impedance Z2 on the tuning side is also very small, the impedance of the antenna as a whole is also very low. Therefore, in the antenna coil 1 according to the present embodiment, the impedance of the outer feeding coil 2 is invisible,
Since only the impedance of the inner tuning circuit is visible, only the tuning points of the inner tuning circuit are visible from the outside of the antenna.

In the RF band, the feeding coil and the tuning circuit are coupled by the coupling coefficient M as described above. Then, if the coupling between the feeding coil and the tuning circuit becomes dense, that is, if the coupling coefficient becomes M≈1, the tuning circuits are coupled to each other and only the characteristic as one antenna is shown. It does not show the antenna characteristics in which multiple tuning points appear as shown. Therefore, in order to realize the antenna coil 1 of the present invention, the coupling between the feeding coil 1 and the first to third tuning circuits is made coarse (M << 1), and the first
Therefore, the individual tuning points in the third to third tuning circuits appear separately as shown in FIG. As a result, individual tuning points can be seen when viewed from the feeding coil.

As in the present invention, the tuning points of the tuning circuits can be expressed individually by subtly shifting the tuning points of the tuning circuits, and an antenna having a low impedance and a wide tuning frequency band can be produced. it can. Therefore, during communication, even if the tuning points of the antennas deviate from each other, the output level can be prevented from lowering, and the communication characteristics are not impaired.

Next, a specific configuration of the antenna coil 1 described with reference to FIG. 2 will be described with reference to FIG. 5 so that a plurality of tuning points appear in the tuning coil. As shown in FIG. 5, the power feeding coil 2, the tuning circuit including the tuning coils 31, 32 and 33, and the tuning capacitor 4 are arranged on the same plane, and are coaxially arranged. In this way, if the feeding coil 2 and the tuning circuit are arranged coaxially,
The inductances of the first to third tuning circuits gradually become smaller toward the inner side of the coaxial line, and the tuning points can be automatically made slightly different by using the same tuning capacitance 4.

As shown in FIG. 5, in the present embodiment,
The antenna coil 1 is a predetermined feeding coil 2, the tuning coil 31 is 0.22 [μH], and the tuning coil 32 is 0.20.
[H], the tuning coil 33 is 0.18 [H], and the resonance capacitance 4 is 410 [pF]. In this case, the tuning frequency is determined by the following equation (2).

Tuning frequency (fc) = 1 / 2π√LC (2) From the equation (2), the tuning frequency (fc of the first tuning circuit is
1) is 16.76 [MHz], the tuning frequency (fc2) of the second tuning circuit is 17.58 [MHz], and the tuning frequency (fc3) of the third tuning circuit is 18.53 [MHz]. As shown in FIG. 4, three tuning points appear in the coil 1 as a whole. Thereby, an antenna coil having a wide tuning frequency band as a whole, a low Q, and a low impedance can be easily manufactured.

Next, a second embodiment will be described with reference to FIG. FIG. 6 is a diagram showing an antenna coil according to the second embodiment of the present invention. In addition, hereinafter, the first of FIG.
The description of the parts described in detail in the embodiment will be omitted.

As shown in FIG. 6, the antenna coil 11
Is the feeding coil 12 and the tuning coils 131, 132, 13
3 and 134 and the tuning capacitor 4 are provided, and the tuning coil 131 and the tuning capacitor 4 tune the first tuning circuit, and the tuning coil 132 and the tuning capacitor 4 tune the second tuning circuit. Since the coil 132 and the tuning capacitor 4 form a third tuning circuit and the tuning coil 133 and the tuning capacitor 4 form a fourth tuning capacitor, four tuning circuits are formed in the present embodiment. .

In the antenna coil 11, the feed coil 12 and the first to fourth tuning circuits are arranged on the same plane so that three tuning points of the tuning circuit appear, and the first tuning circuit is provided.
The second and third tuning circuits are arranged inside the feeding coil 12, and the third and fourth tuning circuits are arranged outside the feeding coil 12. As a result, the antenna coil 12 can delicately shift the respective tuning points of the first to fourth tuning circuits, can show the tuning points in each tuning circuit, and have a low impedance and a tuning frequency. A wide band antenna can be created.

Next, a third embodiment will be described with reference to FIG. FIG. 7 is a diagram showing an antenna coil according to the third embodiment of the present invention. As shown in FIG. 7, the antenna coil 21 includes a feeding coil 22 and a tuning coil 23.
1, 232, 233 and a tuning capacitor 4 are provided, and the tuning coil 231 and the tuning capacitor 4 form a first tuning circuit, and the tuning coil 232 and the tuning capacitor 4 form a second tuning circuit. Since the tuning coil 233 and the tuning capacitor 4 form a third tuning circuit, in the present embodiment, 3
Two tuning circuits are formed.

Further, in the antenna coil 21, the feeding coil 22 and the first to third tuning circuits are arranged on the same plane so that three tuning points of the tuning circuit appear, and the first tuning circuit is used.
To the third tuning circuit are arranged outside the feeding coil 22. As a result, the antenna coil 22 can show the tuning points in each tuning circuit by subtly shifting the tuning points of the first to fourth tuning circuits, and the tuning frequency band is low with low impedance. You can create a wide antenna.

Next, a fourth embodiment will be described with reference to FIG. FIG. 8 is a diagram showing an antenna coil according to the fourth embodiment of the present invention.

FIG. 8 shows the antenna coil 31.
FIG. 8A shows a view of the substrate KB on the surface of which the power feeding coil 32 is mounted, and FIG. 8B shows the tuning coils 331, 332, 333 and the tuning capacitor 4. The figure which looked at the board | substrate KB which mounted the tuning circuit from the back surface is shown. The tuning coil 331 and the tuning capacitor 4 form a first tuning circuit, the tuning coil 332 and the tuning capacitor 4 form a second tuning circuit, and the tuning coil 333 and the tuning capacitor 4 form a third tuning circuit. Therefore, three tuning circuits are formed in the present embodiment.

The antenna coil 31 and the feeding coil 32 and the first to the third coils are arranged so that three tuning points of the tuning circuit appear.
The tuning circuit is arranged on a different plane, and the first to third tuning circuits are arranged so as to be overlapped with the feeding coil at a distance. When this embodiment is applied to a module, the feeding coil 32 is arranged on one surface of the substrate of the antenna coil 31, and the first to third tuning circuits are arranged on the other surface of the substrate.

As a result, the antenna coil 31 can have the feeding coil 32 and the first to third tuning circuits arranged in an overlapping manner, and the first to third tuning circuits can be arranged in the same manner as in the above-described embodiment. The tuning points of each tuning circuit can be revealed by subtly shifting the tuning points of the circuit, and an antenna with a low impedance and a wide tuning frequency band can be created.

Next, a fifth embodiment will be described with reference to FIG. FIG. 9 is a diagram showing an antenna coil according to the fifth embodiment of the present invention. As shown in FIG. 9, the antenna coil 41 includes a feeding coil 42 and a tuning coil 43.
1, 432, 433 and a tuning capacitor 4 are provided, the tuning coil 431 and the tuning capacitor 4 form a first tuning circuit, and the tuning coil 432 and the tuning capacitor 4 form a second tuning circuit. Since the tuning coil 433 and the tuning capacitor 4 form a third tuning circuit, in the present embodiment, 3
Two tuning circuits are formed.

In addition, the present embodiment is characterized in that the feeding coil and the tuning coil are formed in a circular shape. The antenna coil 41 includes a feeding coil 42 and first to third tuning circuits so that three tuning circuits appear.
The first to third tuning circuits arranged on the same plane are arranged inside the feeding coil 42.

As a result, the antenna coil 41 has the first coil
By slightly shifting the respective tuning points of the fourth tuning circuit, the tuning points in each tuning circuit can be expressed, and an antenna with low impedance and a wide tuning frequency band can be created.

Next, a sixth embodiment will be described with reference to FIG. FIG. 10 is a diagram showing an antenna coil according to the sixth embodiment of the present invention. As shown in FIG. 10, the antenna coil 51 includes a tuning circuit composed of a feeding coil 52, tuning coils 531, 532, 533 and a tuning capacitor 4, and the tuning coil 531 and the tuning capacitor 4 make a first tuning. Since the tuning coil 532 and the tuning capacitor 4 form a second tuning circuit and the tuning coil 533 and the tuning capacitor 4 form a third tuning circuit, in the present embodiment, three tuning circuits are provided. Has been formed.

The present embodiment is characterized in that the feeding coil and the tuning coil are formed in an octagon.
Further, in the antenna coil 41, the feeding coil 52 and the first to third tuning circuits are arranged on the same plane so that three tuning circuits appear, and the first to third tuning circuits feed the same. It is located inside the coil.

In the antenna coil according to the present invention, the number of turns of the feeding coil and the tuning coil, the number of windings, the material and shape of the coil, etc. are not limited to those in the above-described embodiment.

Next, a non-contact IC card read / write system using the antenna coil according to the present invention will be described. FIG. 12 is a diagram showing a configuration example of a non-contact IC card read / write system using the antenna coil according to the present invention. As shown in FIG. 12, the readride system 1 includes a mounting board A on which the antenna coil 1 according to the present invention is mounted, a transmitter circuit 5, a receiver circuit 6, a modulator circuit 7, a demodulator circuit 8, a control microcomputer 9, and a USB. US to connect
A mounting board B on which the B interface IF (USB) is mounted, and four spacers C inserted between the mounting board A and the mounting board B in order to prevent radio waves generated from the antenna coil 1 from being reflected by the mounting board B. It consists of and.

The antenna coil according to the present invention is provided with a non-contact IC
By applying it to the card reader / writer system, it is possible to improve the communication specification with the non-contact IC card by using the antenna having a wide frequency band.

The preferred embodiment of the present invention has been described above in detail. The antenna coil according to the present invention is a non-contact type I
The present invention is not limited to the one used for the C-card reader / writer system, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

[0045]

As is apparent from the above detailed description, according to the present invention, it is possible to prevent the deterioration of the communication characteristic due to the shift of the tuning point when the coils communicate with each other. Further, by increasing the communication efficiency, it is possible to reduce the transmission power in the transmitter, which contributes to cost reduction and performance improvement. Furthermore, since it is not necessary to separately provide a tuning circuit, the design of the entire device becomes easy.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a conventional antenna coil.

FIG. 2 is a diagram showing an antenna coil according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining the principle of a stagger tuning circuit.

FIG. 4 is a diagram showing antenna characteristics of an antenna coil according to the present invention.

FIG. 5 is a diagram for explaining the antenna coil according to the first embodiment.

FIG. 6 is a diagram showing an antenna coil according to a second embodiment of the present invention.

FIG. 7 is a diagram showing an antenna coil according to a third embodiment of the present invention.

FIG. 8 is a diagram showing an antenna coil according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing an antenna coil according to a fifth embodiment of the present invention.

FIG. 10 is a diagram showing an antenna coil according to a sixth embodiment of the present invention.

FIG. 11 is a view showing a non-contact IC card read / write system using the antenna coil according to the first embodiment.

FIG. 12 is a diagram showing a configuration example of a non-contact IC card read / write system using an antenna coil according to the present invention.

[Explanation of symbols]

1, 11, 21, 31, 41, 51 Antenna coil 2, 12, 22, 32, 42, 52 Feeding coil 3, 31, 32, 33, 131, 132, 133, 13
4, 231, 232, 233, 331, 332, 33
3, 431, 432, 433, 531, 532, 533
Tuning coil 4 Resonance capacitance 5 Transmission circuit, 6 Reception circuit 7 Modulation circuit 8 Demodulation circuit 9 Control microcomputer 10 IF

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01Q 21/30 H01Q 21/30 H04B 5/02 H04B 5/02 F term (reference) 2C005 MA40 NA08 5B058 CA15 KA24 5J021 AA01 AB04 CA05 DB07 JA02 5J046 AA03 AB11 PA07 5K012 AA04 AB02 AB05 AC06 AC08 AC10 AE13 BA02

Claims (8)

[Claims] 1. A tuning circuit having a feeding coil, a tuning coil coupled to the feeding coil by mutual induction, and a tuning capacitor connected to the tuning coil, wherein the tuning circuit has a plurality of tuning points. An antenna coil characterized by being arranged. 2. The antenna coil according to claim 1, wherein the feeding coil and the tuning circuit are coaxially arranged. 3. The antenna coil according to claim 1, wherein the feeding coil and the tuning circuit are arranged on the same plane, and the tuning circuit is arranged inside the feeding coil. Antenna coil to do. 4. The antenna coil according to claim 1, wherein the feeding coil and the tuning circuit are arranged on the same plane, and one tuning circuit is arranged inside the feeding coil. An antenna coil, wherein the tuning circuit of 1. is arranged outside the feeding coil. 5. The antenna coil according to claim 1, wherein the feeding coil and the tuning circuit are arranged on the same plane, and the tuning circuit is arranged outside the feeding coil. Antenna coil to do. 6. The antenna coil according to claim 1, wherein the feeding coil and the tuning circuit are arranged on different planes, and the tuning circuit is arranged so as to overlap the feeding coil with a space therebetween. An antenna coil characterized by being formed. 7. A read / write system for a non-contact IC card, which uses the antenna coil according to claim 1. Description: 8. A first mounting board on which an electronic component is mounted, and a second mounting board provided on a circuit board via a spacer, wherein the second mounting board is mounted on the second mounting board. Through 6
A read / write system for a non-contact IC card, characterized in that the antenna coil according to any one of 1 to 3 is formed.