JP2001238372A - Power transmission system, electromagnetic field generator and electromagnetic field receiver - Google Patents

Abstract

(57) [Summary] In a contactless IC card system, it is an important issue to efficiently supply power from a reader / writer to an IC card. Therefore, it is necessary to perform impedance matching on the transmitting and receiving sides of the power and the signal. However, power can be supplied efficiently only within the range where impedance matching is achieved, and the effective operation range is limited. Therefore, it is necessary to realize a non-contact IC card system with a wide operation range. It had been. In the present invention, an impedance matching circuit is connected to an antenna coil on a transmission side or a reception side,
At the same time, the power transmission / reception state is detected, it is determined whether or not the impedance matching condition is satisfied, and the matching condition is automatically switched according to the result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IC card system of a non-contact type IC card which not only exchanges data between a reader / writer and an IC card but also supplies power for operating the IC card. In particular, the present invention relates to impedance matching means for efficiently supplying power over a wide operating range.

[0002]

2. Description of the Related Art Non-contact type IC cards are being standardized in ISO / IEC, and are classified into close-contact type, close-up type, close-up type, and microwave type according to the non-contact interface used. Among these, especially 13.56
2. Description of the Related Art An electromagnetic induction type proximity IC card using a carrier frequency of MHz has attracted attention in applications such as electronic tickets, electronic money, access management, amusement, and government / public cards. In addition, the proximity type, which is an electromagnetic induction system using the same frequency, has also attracted attention in entry / exit management, amusement, and the like.

[0003] These proximity-type and proximity-type non-contact IC cards do not have a built-in battery, but use an electric power supplied from a reader / writer by electromagnetic induction to operate an IC inside the card and to respond. How to efficiently receive power is important for improving the processing performance of the IC card and for expanding the operating range in the communication distance between the reader / writer and the IC card. It is a well-known fact that in power transmission from a reader / writer to a contactless IC card, it is well known that impedance matching between the two is effective in terms of power transmission efficiency, but impedance matching also depends on the distance between the two. Nevertheless, in the conventional IC card, as shown in FIG. 10, a tuning capacitor 65 is inserted between an antenna coil 62 and an internal circuit 63 on an IC card 61 on the receiving side, and a reader on the transmitting side is inserted. On the writer 66, the transmission circuit 67 and the antenna coil 68
Since the impedance matching circuit 69 was inserted between them and impedance matching was performed for a specific distance, the IC card operated effectively only within a narrow operating range. That is, for example, in the case of a proximity IC card using a modulation method of ASK 10%, the upper limit of the communication distance between the reader / writer and the IC card is about 10 cm, but the circuit constant is fixed so that the IC card can operate at 10 cm. Then, only a width of about 2 or 3 cm before and after the distance can actually be operated. Outside the range, the impedance matching is lost, the power that can be received becomes insufficient, and the IC card does not operate. In the proximity type, the upper limit of the communication distance is about 70 cm, which can reach a far greater distance than the proximity type, and the width of the operation range is expanded accordingly, but the situation is the same,
Again, with fixed impedance matching, the width over which communication is possible is not very large.

Japanese Patent Laid-Open No. 10-145987 describes that an IC card has an impedance control circuit to control received power. According to this conventional technique, as shown in FIG. 11, the characteristic value of an impedance variable circuit 53 composed of a variable resistor or a variable capacitor inserted in parallel with an antenna coil 52 on the IC card side is changed. This technology reduces the excessive input at close distances by equivalently controlling the inductance of the device and removing impedance matching. However, since there is only one variable impedance circuit 53 to be controlled in parallel with the antenna coil 52, even if the impedance matching can be removed, the impedance matching cannot be adjusted, and the distance from the reader / writer is large. There was no effect of improving the power supply efficiency in a place where the matching greatly deviated, and expanding the range of the communicable distance. One of the features of the non-contact IC card is that it can be operated away from the reader / writer, so if the width in which the IC card can operate is narrow,
This was inconvenient for the card user and caused a malfunction.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention relates to a non-contact IC card system for performing power transmission and signal transmission and reception using electromagnetic induction in a power transmission efficiency over a wide range of communicable distance. The purpose of the present invention is to increase the operating range of the non-contact IC card, thereby realizing an excellent practical system.

[0006]

In order to achieve the above object, the present invention provides at least one of an electromagnetic field generating device serving as a reader / writer of a non-contact IC card system and an electromagnetic field receiving device serving as a non-contact IC card. The variable impedance matching means is inserted between one antenna coil and the internal circuit, and at the same time, the matching condition of the variable impedance matching means is switched as necessary according to the power transmission state detecting means and the power transmission state obtained thereby. The system is provided with control means including power transmission state determination means for determining the necessity of the system, whereby the distance range between the non-contact IC card operable by the system and the reader / writer is expanded.

Here, the electromagnetic field generating device and the electromagnetic field receiving device are provided between the respective antenna coils and the internal circuit to correct the impedance change caused by the change of the coupling state of the two antenna coils due to the change of the distance between them. The variable impedance matching means includes a power transmission state detecting means for examining a power transmission state by detecting, for example, an induced electromotive voltage generated in an antenna coil, and an induced electromotive voltage which is a result of the detection. It is controlled by a control circuit that includes a power transmission state determination unit that determines whether to switch the matching condition of the variable impedance matching unit by comparing with a set reference voltage.

Therefore, as the variable impedance matching means, a variable capacitor circuit, a variable inductor circuit or a variable resistance circuit is connected in parallel and in series with the antenna coil, and the characteristic values of these variable elements are determined by a signal from the control means. And a switch for controlling the switch. Further, as the above-mentioned variable impedance matching means, by connecting a plurality of capacitor circuits, inductor circuits or resistance circuits through switches in parallel and in series with the antenna coil, and controlling the switches by a signal from the control means, A configuration for equivalently controlling the characteristic value of an element is also defined.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a basic configuration of a contactless IC card system according to an embodiment of the present invention. That is, as shown in FIG. 1, the non-contact type IC card system includes a set of a reader / writer 30 for performing power transmission and signal transmission / reception using electromagnetic induction, a control terminal 31 such as a PC for controlling the reader / writer 30 and a non-contact type. And a contact IC card 32.

FIG. 2 illustrates a basic configuration of a power transmission / signal transmission / reception system according to the present invention. That is, in a set of an electromagnetic field generating device 1 and an electromagnetic field receiving device 2 that perform power transmission and signal transmission and reception using electromagnetic induction, the electromagnetic field generating device 1 forms a reader / writer of a non-contact type IC card. An oscillation circuit 6 for generating an electromagnetic wave necessary for communication and power supply, a signal modulating means 7 for modulating a carrier of the electromagnetic wave, and a signal load-modulated by the electromagnetic field receiving device 2 which is a non-contact type IC card An internal circuit 3 including signal demodulating means 8 for demodulating
An antenna coil 4 for generating an electromagnetic field based on an output signal of the internal circuit 3 and a matching circuit 5 for impedance matching are provided. In addition, the electromagnetic field receiving device 2
Includes an antenna coil 9 for receiving an electromagnetic field generated from the electromagnetic field generating device 1,
An impedance variable matching means 10 capable of variably controlling the input / output impedance of the electromagnetic field receiving apparatus 2, a power transmission state detecting means 18 for detecting a power transmission state between the electromagnetic field generating apparatus 1 and the electromagnetic field receiving apparatus 2, and The control circuit 11 includes a power transmission state determination unit 19 that determines the power transmission state based on the result detected by the power transmission state detection unit 18 and controls the impedance variable matching unit 10.
And a rectifier circuit 12 for rectifying the received AC wave, and an internal circuit 13 operated by the signal rectified by the rectifier circuit.
have. Here, the power transmission state detecting means 18
Is for detecting an induced electromotive voltage induced in the antenna coil 9, for example. The power transmission state determining means 19 compares the induced electromotive voltage with a reference voltage corresponding to the received power at which the IC card can operate. The switching of the matching condition of the variable impedance matching means 10 is controlled based on the result. Further, the internal circuit 13 includes a constant voltage generation unit 14 that generates a DC voltage used for a power supply such as a CPU, a signal demodulation unit 15 that demodulates a modulated carrier wave, and a load impedance of the internal circuit. It comprises a signal modulating means 16 for performing load modulation on a carrier wave, and a digital circuit 17 such as a CPU for actually performing operations. In addition, the digital circuit 17 such as a CPU usually includes
Communication means with the host computer, reference frequency generation means for generating a clock, buffer memory, control means for a communication protocol such as initial response and collision prevention, clock recovery circuit, CPU, RAM, ROM, electrically rewritable / erasable Non-volatile memory (EEPROM, flash memory, ferroelectric memory, etc.) is included.

The variable impedance matching means 10 comprises:
Although it may be inserted after the antenna coil 9 or after the rectifier circuit 12, it is more effective to operate on the signal before rectification because the effect of the variable impedance matching is greater. It is good to insert in. The variable impedance matching means 10
Is characterized in that in order to arbitrarily control the input / output impedance, the characteristic values of two elements connected in series and in parallel are equivalently controlled. By using two elements connected in series and in parallel, it is possible to control so that reflection due to impedance mismatch is minimized and power supply efficiency is increased. Here, capacitors, inductors, and resistors can be used as the elements inserted in series and in parallel.The resistors have the characteristic that their characteristic values can be controlled continuously with a simple configuration, but power loss is avoided. Absent. In addition, although the inductor has less power loss than the resistor, it has a large shape, is difficult to mount on an integrated circuit, and is not easy to control. Therefore, if only the variable capacitors 20 and 21 shown in FIG. 3 are used from the viewpoints of power loss, easy control of characteristic values, and the like, impedance matching can be performed continuously, and the configuration or the trouble of adjustment can be improved. Is also suitable. Note that FIG.
The capacitance range of the variable capacitors 20 and 21 shown in (1) may be varied in a range of about 1 pF to about 200 pF, and mounting on an integrated circuit is possible.

The element used for the variable impedance matching means 10 does not need to be constituted by one element.
Since it is sufficient that the characteristic value of each one element connected in series and in parallel can be controlled equivalently, as shown in FIG. 4, instead of one variable capacitor in FIG. A plurality of sets each including a fixed capacitor and a switch group inserted in series with this capacitor are inserted in parallel,
By controlling these switches by the control circuit 11, one or a plurality of capacitors are respectively selected and connected in parallel and in series from the antenna coil 9 in advance, and the characteristic values of the elements are equivalently controlled. It does not matter. Here, since the switch operates at high speed and is easily controlled by the control circuit 11, an electronic switch formed of a transistor such as a CMOS is preferable. With such a configuration, the characteristic value of the element is changed discontinuously and discretely. However, in normal use, even when the distance changes, the power supply efficiency is about 50%.
% Or more, and by using more sets of these capacitors and switches, it is possible to control the characteristic values continuously and closely. In FIG. 3, the elements used for the variable impedance matching means 10 are all capacitors. However, it is a matter of course that some or all of these elements may be inductors or resistors or a combination of a plurality of these. .

FIG. 3 shows an example in which the variable impedance matching means 10 is inserted after the antenna 9. However, as shown in FIG. A changeover switch that selects and switches any of the middle taps,
It is possible to use a variable capacitor inserted in parallel with the antenna coil 9 and control them by the control circuit 11. In this case, since the midpoint tap of the antenna 9 is used, the characteristic value cannot be controlled continuously, and the characteristic value is changed discontinuously and discretely. By taking them out and switching them, it is possible to control the inductance of the antenna 9 almost continuously. At this time, the variable range of the inductance may be changed in a range of approximately 0.5 μH to 3 μH. For example, even in a limited range such as a card shape, the number of turns of the antenna coil 9 is set to approximately 10 turns and the midpoint is set. By taking out the tap, it is possible to change the inductance value in the above range.

The control circuit 11 includes a power transmission state detecting means 18 for detecting one or both of the power transmission efficiency and the derivative thereof between the electromagnetic field transmitting apparatus 1 and the electromagnetic field receiving apparatus 2, and determining the power transmission state. Controlling the variable impedance matching means 10 so that the electromagnetic field transmitting device 1 and the electromagnetic field receiving device 2
To maximize the power transmission efficiency between the two.

The input of the control circuit 11 may detect the voltage at both ends of the antenna 9 as indicated by the broken line in FIG. 2, but the DC voltage is easier to detect than the AC voltage. Preferably, as shown by the solid line in FIG. The control by the control circuit 11 is desirably controlled by having a CPU or a dedicated control circuit therein. However, the control circuit 11 is a simple determination circuit that performs a control operation provided in advance according to the magnitude of the input voltage. No problem. The power transmission state determination means 19 included in the control circuit 11 is a digital circuit 17 such as a CPU.
The determination may be made by the CPU within. In this case, the power transmission efficiency detected by the power transmission state detecting means 18 is input to the digital circuit 17 such as a CPU, the power transmission state is determined by the internal CPU, and a control signal based on the determination result is output to the control circuit 11. Control.

In FIG. 2, the variable impedance matching means 10 is provided in the electromagnetic field receiving device 2, but may be provided in the electromagnetic field transmitting device 1 as shown in FIG.
The variable impedance matching means 10 includes the electromagnetic field transmitter 1
, Between the internal circuit 3 and the antenna coil 4.
Further, the matching circuit 5 is inserted between the antenna coil 9 and the rectifier circuit 12 in the electromagnetic field receiver 2. Similarly, a control circuit 11 for controlling the variable impedance matching means 10 is also configured in the electromagnetic field generator 1, and its input uses a voltage detected at both ends of the antenna coil 4. Even with such a configuration, the effect is the same as when the variable impedance matching means is configured in the electromagnetic field receiving device 2 described above.

Normally, in a power transmission / communication system using the electromagnetic field generating device 1 and the electromagnetic field receiving device 2, the electromagnetic field generating device 1 is in the form of a terminal whose position is fixed, whereas the electromagnetic field receiving device 2 is small and compact. Portable and used by users. Therefore, in the above power transmission / communication system, the number of the electromagnetic field generators 1 is much smaller than the number of the electromagnetic field receivers 2, and when the variable impedance matching means 10 is configured in the electromagnetic field generator 1,
There is an industrial advantage that the cost of the configuration is low. Further, when the variable impedance matching means 10 is configured in the electromagnetic field receiving apparatus 2, the communication distance can be extended even with the general-purpose electromagnetic field generating apparatus 1, so that the conventional electromagnetic field generating apparatus can be used. This has the advantage of ensuring compatibility with existing infrastructure.

The frequency of the transmitting circuit 6 can be arbitrarily used. However, since the power transmission between the electromagnetic field generating device 1 and the electromagnetic field receiving device 2 is performed by an induction electromagnetic field, if the frequency is high, the distance over which the power can be transmitted can be obtained. Is desirably shorter than about 100 MHz. In addition, approximately 100kHz
When it is below, the number of turns of the antenna coil for generating and receiving the electromagnetic field needs to be approximately 100 turns or more, and when the electromagnetic field receiving device 2 is limited to a card shape,
There is a problem that implementation becomes difficult. Among them, 13.
The frequency of 56 MHz is used for a non-contact IC card which is a typical application example of a power transmission / communication system using the electromagnetic field generating device 1 and the electromagnetic field receiving device 2.
This is a frequency standardized in the above, and the band around this frequency has an industrial advantage that a large output can be used even under the Radio Law. Further, as a system using the above-mentioned non-contact IC card, there is a system such as a general-purpose ticket whose convenience is improved by an increase in communication distance. Therefore, the effect of expanding the operable range according to the present invention is great. In view of the above, the frequency of the transmitting circuit 6 is desirably 13.56 MHz.

As described above, according to the above configuration,
Even when the distance between the electromagnetic field generating device 1 and the electromagnetic field receiving device 2 fluctuates and the degree of electromagnetic induction coupling between the two antenna coils fluctuates, the impedance variable matching means in the electromagnetic field generating device 1 or the electromagnetic field receiving device 2 always makes it possible. Impedance matching is achieved, and high power supply efficiency is always obtained. Thereby, the operable range of the electromagnetic field receiver 2 is expanded, and a stable communication operation can be realized.

FIG. 7 is a circuit diagram more specifically showing a circuit near the antenna matching means in the present invention described above. Here, the reader / writer 30 is 13.56 MHz.
Oscillating circuit 40, a signal modulating circuit 41 for modulating the signal of the oscillating circuit 40 at about 106 kbps by about 10%, and a matching circuit composed of two capacitors inserted in series and in parallel at the preceding stage of the antenna coil 42 43 and an antenna coil 42 formed in a spiral shape. The output is such that a maximum power of about 1 W can be supplied from the normal antenna coil 42 to the non-contact IC card 32. Further, the non-contact IC force 32 is an antenna coil 44 which is printed and formed in a planar spiral shape by copper etching.
In addition, although an internal circuit is not shown, an IC chip formed in one chip by CMOS is sealed and formed inside a card base material by PET.

The signal induced by the antenna coil 44 of the non-contact IC card 32 by the electromagnetic field output by the reader / writer 30 is input to the IC chip. The internal circuit of this IC chip is input to the variable impedance matching means 45 at the first stage. The variable impedance matching means 45 includes capacitors (a to
h) are arranged in parallel, and the electronic switches SW1 and S
Depending on W2, one or a plurality of capacitors to be connected are selected from these capacitors and connected. This is placed in parallel with the antenna 44 at a subsequent stage of the antenna 44.
And one set is inserted in series at the subsequent stage. The electronic switches SW1 and SW2 are controlled by a signal from the control circuit 46. Variable impedance matching means 45
At the subsequent stage, a full-wave rectifier circuit 47 composed of four diodes is inserted. A capacitor 48 for smoothing the rectified waveform is inserted in parallel at the subsequent stage of the full-wave rectifier circuit 47, and a constant voltage circuit 49 for generating an operating voltage of a digital circuit such as a CPU is provided at the subsequent stage. It is constituted by a shunt regulator using a diode or the like. A signal demodulation circuit 50 for extracting a signal from a voltage signal induced by the antenna coil 44 of the non-contact IC card 32
Then, a signal modulation circuit 51 for performing communication by load modulation by changing the load impedance inserted in parallel with the antenna coil 44 is inserted. The outputs of the constant voltage circuit 49 constituted by the above-described shunt regulator and the output of the signal demodulation circuit 50 are input to the inputs of the digital circuit 52 such as the CPU. The output of the digital circuit 52 such as the CPU is input to the signal modulation circuit 51. Is done.

In the configuration described above, the electronic switches SW1, SW2 of the variable impedance matching
The four different states S1 to S4 are set by combining the capacitors a to h having different capacities by SW2. FIG. 8 shows four types of states obtained by this combination of capacitances.
FIG. 9 illustrates an example of a change in the received power with respect to the distance between the non-contact IC card 32 and the reader / writer 30 obtained thereby. In FIG. 9, the horizontal axis is the non-contact IC card 3
This is the distance (cm) between 2 and the reader / writer 30, and the vertical axis indicates that the power transmission efficiency of 100% is 1. In FIG. 9, each state of S1 to S4 is equal to the reception power characteristic of the conventional non-contact IC card having no variable impedance matching means, and in the conventional non-contact IC card, any one of S1 to S4 of FIG. As shown in the state, the peak position of the received power differs depending on the different impedance matching conditions, so that the distance over which a certain power required for card operation can be obtained is limited to a narrow range. According to the present embodiment, the electronic switches SW1 and SW2 of the variable impedance matching means 45 are sequentially turned on / off in accordance with the distance, so that a certain power or more (for example, FIG.
, The range in which the received power P) can be obtained can be expanded. That is, in FIG. 9, when the distance between the non-contact IC card 32 and the writer writer 30 of the present embodiment changes, for example, when the received power decreases to P, the operation is performed by switching the electronic switches SW1 to SW2. The possible range can be expanded to the range of the distances d1 to d2 in FIG.

[0023]

According to the present invention, at least one of the electromagnetic field generating device and the electromagnetic field receiving device in a set of an electromagnetic field generating device and an electromagnetic field receiving device for performing power transmission and signal transmission / reception using electromagnetic induction. By providing variable impedance matching means for variably controlling the input and output impedance, even if the distance between the electromagnetic field generating device and the electromagnetic field receiving device fluctuates, the reception power sufficient for the electromagnetic field receiving device to operate is ensured and stable. It becomes possible to perform power supply and communication, and by expanding the operating range of the electromagnetic field receiver,
It is possible to construct a power transmission / signal transmission / reception system that allows a user to use a contactless IC card more comfortably.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a contactless IC card system to which the present invention is applied.

FIG. 2 is a block diagram showing a basic configuration of a contactless IC card system according to the present invention.

FIG. 3 is a circuit diagram of an impedance variable matching unit using a variable capacitance capacitor.

FIG. 4 is a circuit diagram showing a configuration example of an impedance variable matching unit using a capacitor and a changeover switch.

FIG. 5 is a circuit diagram showing a configuration example of an impedance variable matching unit using an inductance having a center tap.

FIG. 6 is a block diagram showing a system configuration when the variable impedance matching means is configured in the electromagnetic field transmission device.

FIG. 7 is a circuit diagram of a main part of a system to which the present invention is applied.

FIG. 8 is a combination diagram schematically showing impedance matching by switching a switch.

FIG. 9 is a view showing a change in received electric field strength according to a distance between an IC card and a reader / writer with respect to each impedance in FIG. 8;

FIG. 10 is a block diagram showing a configuration of a conventional contactless IC card system.

FIG. 11 shows a conventional non-contact IC card system.
FIG. 4 is a circuit configuration diagram when a variable impedance circuit is provided in the C card.

[Explanation of symbols]

1: Electromagnetic field generator 2: Electromagnetic field receiver 3: Internal circuit 4: Antenna coil 5: Matching circuit 9: Antenna coil 10: Variable impedance matching means 11: Control circuit 12: Rectifier circuit 13: Internal circuit 14: Constant voltage generating means 15: Signal demodulation means 16: Signal modulation means 17: CP
U and other digital circuits 18: power transmission state detection means 19: power transmission state determination means 20: variable capacitor 21: variable capacitor 30: reader / writer 31: PC
Host terminal 32: non-contact type IC card 40: oscillation circuit 41: signal modulation circuit 42: antenna coil 44: antenna coil 45: variable impedance matching means 46: control circuit 47: rectifier circuit 48: capacitor 49: constant voltage circuit 50 : Signal demodulation circuit 51: Signal modulation circuit 52: Digital circuit such as CPU

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tadao Takeda 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 2C005 MA40 NA08 TA22 5B035 CA23 5B058 CA17

Claims (9)

[Claims] 1. An electromagnetic coil for transmitting a signal and transmitting and receiving a signal using electromagnetic induction, comprising a pair of electromagnetic field generators and an electromagnetic field receiver, wherein the electromagnetic field generator includes at least an antenna coil for generating a signal by an electromagnetic field. , A signal modulation means for modulating a generated signal, and a signal demodulation means for demodulating a load modulation signal of the electromagnetic field reception device, wherein the electromagnetic field reception device has at least an antenna coil for receiving an electromagnetic field Electromagnetic field receiving means including, DC voltage generating means for rectifying the received AC signal and making it a constant voltage,
A power transmission system comprising: signal demodulation means for demodulating a modulated signal; and signal modulation means for performing load modulation on an electromagnetic field generated by the electromagnetic field generator by changing a load of an internal circuit. And / or at least one of the electromagnetic field generating means and the electromagnetic field receiving means of the electromagnetic field receiving apparatus, the variable impedance matching means for variably controlling the input / output impedance; and the electromagnetic field generating apparatus and the electromagnetic field for controlling the variable impedance matching means. Control means comprising power transmission efficiency detecting means for detecting one or both of the power transmission efficiency and its derivative with the receiving apparatus, and power transmission state determining means for determining the power transmission state. The input / output impedance of the variable impedance matching means is controlled by the control means. Controls, by matching the impedance between the electric field generator and the electric field receiving apparatus, power transmission system, characterized in that to improve the reception power in the electric field receiving apparatus. 2. The variable impedance matching means according to claim 1, wherein said variable impedance matching means includes at least a variable capacitor circuit, a variable inductor circuit, or a variable resistance circuit connected in parallel and series to said antenna coil. A power transmission system, wherein a characteristic value of the variable capacitor circuit, the variable inductor circuit, or the variable resistance circuit is controlled by an output. 3. A variable circuit according to claim 2, wherein the variable circuit constituting the variable impedance matching means includes at least a capacitor element, an inductor element, or a resistance element;
A power transmission system including a disconnection switch connected to each of them in series, wherein the disconnection switch is controlled by an output from the control means. 4. The variable circuit according to claim 2, wherein the variable circuit constituting the variable impedance matching means includes at least a variable capacitor element, a variable inductor element, or a variable resistance element, and the variable circuit is controlled by an output from the control means. A power transmission system wherein a characteristic value is continuously controlled within a variable range of a capacitor element, the variable inductor element, or the variable resistance element. 5. The antenna coil according to claim 2, wherein said antenna coil is formed by connecting a plurality of antenna coils in series, and said variable impedance matching means connects at least one of two connection points with said antenna coil to said antenna coil. Means for selecting and switching from both ends and a series connection point, and a variable capacitance element connected in parallel to the antenna coil, and a connection point between the antenna coil and the connection point based on an output from the control means. A power transmission system characterized by controlling a characteristic value of a variable element. 6. The method according to claim 1, wherein the electromagnetic wave receiving device is an IC.
A power transmission system characterized by being a card. 7. The method according to claim 1, wherein the carrier frequency is 1
A power transmission system having a frequency of 3.56 MHz. 8. An electromagnetic field generator for use in a power transmission system according to claim 1, wherein said variable impedance matching means is provided between a transmission antenna and an internal circuit. An electromagnetic field generator, comprising: a control circuit including a power transmission state detection unit and a power transmission state determination unit for controlling a variable matching unit. 9. An electromagnetic field receiving apparatus used in the power transmission system according to claim 1, wherein said impedance variable matching means is provided between a receiving antenna and an internal circuit. An electromagnetic field receiving apparatus, comprising: a control circuit including a power transmission state detection unit for controlling a variable matching unit and a power transmission state determination unit.