JP2005063123A - Non-contact type IC card reader / writer device, automatic adjustment method of antenna natural frequency, program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically adjust even when a deviation from an optimum natural frequency for communication occurs due to various factors during manufacture, installation, and operation.
An antenna coil (loop antenna) of a transmission / reception antenna 1, a resonance antenna 5, and a resonance monitor antenna 11 is disposed at a position where they are electromagnetically coupled to each other. The resonant frequency adjustment circuit 6 connected to the resonant antenna 5 is composed of a variable capacitance element (varicap or the like) whose capacitance changes depending on the applied voltage, and the control microcomputer 16 determines the output voltage value from the D / A converter 14. Change sequentially. That is, the resonant frequency of all the antennas is changed by changing the capacitance by sequentially changing the voltage applied to the varicap. Then, the voltage induced in the resonance monitor antenna 11 is measured, and for example, the voltage applied to the varicap is adjusted so that the induced voltage value becomes maximum.
[Selection] Figure 1

Description

  The present invention relates to a reader / writer device for a non-contact IC card, and more particularly to a device, a method, and the like for realizing stabilization of communication performance.

  In recent years, for example, a system using a non-contact type IC card such as a ticket gate of a station or a gate of a ski resort has been built. Such a system is provided with a reader / writer device for performing wireless communication with a non-contact type IC card to read or write data.

  The reader / writer device mainly includes a transmission unit, a reception unit, a signal control unit, a transmission / reception antenna, and the like. In communication with a conventional non-contact type IC card (hereinafter abbreviated as IC card), in order to communicate from the reader / writer device to the IC card, first, a carrier wave is transmitted from the reader / writer device, and the IC card At the same time as power is supplied to the transmitter, a transmission signal in which the carrier wave is amplitude-modulated with a modulation factor of about 10% is transmitted from the transmission / reception antenna. During reception, which is communication from the IC card to the reader / writer device, power is supplied to the IC card, and at the same time, an unmodulated carrier wave is transmitted from the transmission / reception antenna through the transmission unit for signal transmission from the IC card. doing.

  The signal from the IC card is sent to the reader / writer device by the load switching method on the IC card side. The load switching method is a state in which the transmission / reception antenna of the reader / writer device and the antenna of the IC card are electromagnetically coupled, and the electric load on the IC card side is changed according to the transmission data, thereby changing the reader / writer device's electrical load. In this method, the antenna current is changed and a signal is transmitted from the IC card to the reader / writer device.

  In order to perform stable communication between the reader / writer device and the IC card, it is necessary to increase the magnetic field generated from the transmission antenna of the reader / writer device. Since the strength of the magnetic field radiated from the antenna is determined by the magnitude of the current flowing through the transmitting antenna, it is necessary to maintain the antenna in a resonance state (for example, by matching the resonance (inherent) frequency of the antenna with the carrier frequency). If the design is to increase the strength of the magnetic field, this natural frequency should not fluctuate) is an indispensable requirement for stable communication.

  On the other hand, there are many cases where the resonance frequency has already shifted at the time of manufacture due to, for example, variations in inductance of the antenna coil, variations in capacitor capacity, variations due to mounting errors of the housing, or the like.

  For this reason, conventionally, for example, at the time of inspection before shipment, the resonance of the antenna is taken by adjusting the value of the resonance capacitor connected to the antenna coil of the reader / writer device. Adjustment is required, and normally, when adjustment is performed for resonance at the time of shipment or the like, readjustment is not performed after that (re-adjustment step by step is very troublesome).

  For example, when a reader / writer device is used for a ski gate, the capacity of the resonance capacitor changes due to low air temperature, and communication performance may deteriorate. However, as described above, the readjustment of the resonance frequency of the transmission antenna cannot be performed in practice.

  The reader / writer device is used not only in the ski area gate system but also in various places such as entrance / exit gates of various entertainment facilities, station ticket gates, entrance / exit management systems, etc. In the installation environment of the apparatus, the antenna may be installed near a metal or a dielectric material without giving consideration to the electromagnetic field related to the antenna. In such a case, the antenna of the reader / writer device is generally a loop antenna that is resonated with a resonance capacitor. Therefore, if a metal or dielectric approaches the back of the antenna, the antenna coil When the inductance changes, the resonance shifts and the antenna performance deteriorates. As described above, since readjustment cannot be performed practically, the antenna will continue to deteriorate until the installation environment changes.

  Conventionally, as a method for reducing the influence of such an installation environment, for example, a metal is previously attached to the back surface of the antenna coil, and adjustment is performed so that resonance occurs at the time of shipment in this state. . However, in this method, for example, when a metal or a dielectric material is present beside the antenna in the installation environment, the influence cannot be reduced. Moreover, since an eddy current flows through the metal plate on the back surface, a problem of energy loss occurs.

  Also, conventionally, when an IC card is brought close to a reader / writer device in actual use, mutual induction between the transmission / reception antenna of the reader / writer device and the antenna of the IC card (because of the influence of the electrical impedance of the IC card) ), The resonance frequency fluctuates and the resonance frequency deviates from the carrier frequency.

In contrast, conventionally, for example, by reducing the sharpness of resonance of the transmission / reception antenna, the degree of influence received by mutual induction with the antenna of the IC card has been reduced.
Heretofore, for example, the invention described in Patent Document 1 has been proposed.

  The invention described in Patent Document 1 extends the communication distance between the IC card and the reader / writer, and further reduces the strength of the magnetic field generated by the reader / writer by mutual induction that occurs when the IC card is brought close to the reader / writer. This is to reduce (prevent) the decrease in the strength of the magnetic field.

  The invention described in Patent Document 1 has a plurality of loop coils arranged on the same plane, and the plurality of loop coils is a rectangle which is a cross section of a conventional loop coil, and is divided into two halves. It is a coil having a cross section of four rectangles obtained in this way. Since the cross-sectional area of each of the plurality of loop coils is smaller than that of a conventional loop coil having the same cross-sectional area as the whole area, even if the IC card approaches, the loop coil of the IC card and the plurality of loop coils Since the coupling with each of the resonance circuits configured by the above is weak, the amount of change in the resonance frequency of the resonance circuit is suppressed, and as a result, it is possible to prevent the magnetic field strength from being lowered due to the IC card approaching.

JP-A-8-194785

  The invention described in Patent Document 1 suppresses the amount of change in the resonance frequency of the resonance circuit due to the approach of the IC card. As described above, for example, variations in parts at the time of manufacture, the ambient environment of the installation location, after installation The resonance frequency of the antenna resonance circuit may deviate from the optimum value due to a temperature change during operation. The invention described in Patent Document 1 is not performed until automatic adjustment is performed in such a case. Even if the amount of change in the resonance frequency of the resonance circuit is suppressed, it is meaningless if the resonance frequency is originally shifted. In the invention described in Patent Document 1, the resonance frequency of the resonance circuit constituted by each of the loop coils increased to four is adjusted to the same value by operating the variable resistors by the configuration shown in FIG. However, it has to be adjusted manually, and there is no idea until it automatically adjusts as needed in response to the ambient environment around the installation location, temperature changes during operation after installation, etc. Further, regarding the prevention of a decrease in the strength of the magnetic field due to the approach of the IC card, the invention described in Patent Document 1 connects the loop circuit of the IC card and each of the resonance circuits configured by a plurality of loop coils. Since it corresponds by making weak, there exists a possibility that the data from an IC card may be obtained, that is, the change of the amplitude and phase of the carrier cannot be detected accurately. For this reason, in the invention described in Patent Document 1, for example, the circuit configuration shown in FIG. 6 addresses this problem and the circuit configuration becomes more complicated.

  The problem of the present invention is that this deviation is automatically detected even when it deviates from the optimum natural frequency for communication due to various factors such as variations in parts during production, installation and operation, installation environment and temperature change. By providing a reader / writer device that can be adjusted automatically, thus preventing deterioration in communication performance, and also suppressing a decrease in magnetic field strength due to the proximity of an IC card, an automatic adjustment method thereof, etc. is there.

  The reader / writer device of the present invention is a reader / writer device having a transmission / reception antenna used for wireless communication with a non-contact type IC card, and includes a resonance antenna having an antenna coil and a resonance capacitor, and a resonance monitor antenna. Is provided at a position where each of the antennas including the transmission / reception antenna can be electromagnetically coupled to each other, and a resonance frequency adjusting circuit having a variable capacitance element connected in parallel or in series with the resonance capacitor of the resonance antenna And, at any time or when a change in the surrounding environment is detected, the applied voltage to the variable capacitance element is sequentially changed, and each time the applied voltage is changed, the voltage value induced in the resonance monitor antenna is measured, Based on the measurement result, the voltage applied to the variable capacitance element when the voltage value induced in the resonance monitoring antenna is maximized. The calculated, constitutes a voltage determined on the basis of the results of obtaining the to have a control means to be applied to the variable capacitance element.

  As described above, each antenna can be in an electromagnetically coupled state (this state is obtained when magnetic flux is generated from the transmitting antenna). Antenna). The resonance monitor antenna is provided to monitor the strength of the magnetic field radiated from all the antennas, and the voltage value induced therein increases as the strength of the magnetic field increases. When the resonance frequency of the antenna is changed by changing the capacitance by changing the voltage applied to the variable capacitance element of the resonance antenna, the strength of the magnetic field changes. In this way, by measuring the intensity of the magnetic field actually radiated from the antenna, the natural (resonant) frequency of the antenna is set to the initial set value due to component variations, the influence of the surrounding environment of the installation location, temperature change, etc. Even if it deviates from (a value optimal for communication), it can be restored to the original state based on the actual measurement result (first adjustment function).

  The reader / writer device of the present invention further receives, for example, a voltage induced in the resonance monitoring antenna, and when the voltage drops due to the approach of the non-contact type IC card, A voltage inverting circuit for raising the output voltage, a peak hold circuit for maintaining the peak voltage value of the output voltage of the voltage inverting circuit, and adding the output voltage value of the peak hold circuit to the applied voltage value by the control means. And an addition circuit for applying a voltage having a voltage value after the addition to the variable capacitance element.

  During actual operation, the user brings his / her IC card close to the reader / writer device during use. At this time, it has been confirmed by experiments that the resonant frequency of the antenna shifts to a lower side as the IC card approaches. Therefore, in the adder circuit 7, the correction voltage corresponding to the voltage drop of the voltage induced in the resonance monitor antenna is added to the voltage output from the control means by the first adjustment function, so that the IC card Control is performed so that the voltage applied to the variable capacitance element increases in accordance with the approach. As the voltage applied to the variable capacitance element increases, the capacitance decreases, and therefore the resonance frequency shifts higher. That is, the resonance frequency shifted to the lower side operates so as to approach the original state.

  Further, for example, the resonance frequency adjusting circuit has a pair of variable capacitance elements in which the cathodes are connected to each other, and a connection point of the cathode is grounded through a resistor, and a choke coil is interposed between the grounding point and the cathode. The applied voltage may be applied, and the antenna coil of the resonance antenna may be configured to be grounded at an intermediate point where the turns ratio is 1: 1.

  With the above configuration, resonance voltages having opposite phases to each other are applied to the anode side of the pair of variable capacitance elements, and a voltage is applied to the anode side so that the resonance voltage is just canceled. Therefore, it is possible to suppress the applied voltage on the cathode side from fluctuating due to the resonance voltage.

  As described above in detail, according to the reader / writer device of the present invention, its automatic adjustment method, etc., there are various factors such as variations in parts at the time of manufacture, installation, operation, installation environment, and temperature change. Therefore, even when the frequency deviates from the optimum natural frequency for communication, this deviation can be automatically adjusted, thereby preventing the deterioration of communication performance, and further the strength of the magnetic field caused by the approach of the IC card. Can also be prevented. Further, it is possible to suppress the applied voltage on the cathode side of the variable capacitance element from fluctuating due to the resonance voltage.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the reader / writer device according to the present embodiment.
The reader / writer device of this example is roughly divided into an antenna unit shown in the figure and another configuration (referred to as an antenna control unit).

  The antenna unit includes four types of antennas, that is, a transmission / reception antenna 1 (two types of transmission antenna and reception antenna), a resonance antenna 5 and a resonance monitor antenna 11 as shown in the figure. The transmission / reception antenna 1 is a transmission antenna and a reception antenna for exchanging data with the IC card. As shown in FIG. 2, the resonant antenna 5 includes an antenna coil 21, a resonant capacitor 22, a resistor 23, and the like, to which a resonant frequency adjusting circuit 6 is connected.

  As shown in FIG. 2, the resonance frequency adjusting circuit 6 includes a varicap 25 (variable capacitance diode) that is a variable capacitance element, a capacitor 24, a resistor 26, and the like. The varicap 25 and the capacitor 24 are connected in series, and these are connected in parallel to the resonance capacitor 22 of the resonant antenna 5 (may be configured to be connected in series). The cathode side of the varicap 25 is connected to the capacitor 24, and a resistor 26 is inserted between this connection point and the external adder circuit 7. With this configuration, a voltage is applied from the adder circuit 7 to the varicap 25, and when this applied voltage changes, the capacitance of the varicap 25 changes (the varicap 25 (variable capacitance diode) is applied as shown in FIG. 6). When the voltage increases, the capacity decreases.)

The resonance monitor antenna 11 has a configuration for monitoring the resonance state.
The resonance monitor antenna 11 is connected to a full-wave rectifier circuit 12 for converting an AC voltage generated in the resonance monitor antenna 11 into a DC voltage. The resonance monitor antenna 11 is an antenna coil 31 as shown in FIG. As shown in FIG. 3, the full-wave rectifier circuit 12 is a general bridge rectifier circuit (a full-wave rectifier circuit having a diode bridge), and is not particularly described.

  The configuration other than the antenna unit includes a crystal oscillation unit 4, an RF unit 2, a control unit 3, a control microcomputer 16, an addition circuit 7, a peak hold circuit 9, a switch 8, a voltage inverting circuit 10, a temperature sensor 13, and the like. is there.

The crystal oscillation unit 4 generates a carrier having a frequency of 13.56 (MHz), for example.
Although not shown in particular, the RF unit 2 includes a transmission unit and a reception unit. The transmission unit includes a modulator for obtaining ASK modulation, a detector, and a power amplifier for obtaining sufficient power for communication. The receiving unit includes a detector for detecting the received signal, an amplifier for amplifying the detected signal, and a binarization circuit for converting the amplified signal into a digital signal.

The control unit 3 is configured to perform communication control between the IC card and the reader / writer device and communication with the host control microcomputer 16.
The control microcomputer 16 includes a D / A converter 14 and an A / D converter 15, and includes a memory for storing voltage values and various calculation functions.

  The adder circuit 7, the peak hold circuit 9 and the voltage inverting circuit 10 are for controlling (changing) the DC voltage applied to the varicap 25 in the resonance frequency adjusting circuit 6 during operation (when the IC card approaches). It is a configuration.

  The switch 8 is configured to switch between two types of adjustment functions (functions for adjusting the resonance frequency deviation) of the reader / writer device of this example. That is, when the switch 8 is OFF, the first adjustment function for adjusting the resonance frequency shift due to the change in the surrounding environment and the variation of the components operates using the control microcomputer 16. The ambient environment change is determined by measuring the ambient temperature change at any time using, for example, the temperature sensor 13 and comparing it with, for example, a predetermined threshold.

  On the other hand, when the adder circuit 7 and the peak hold circuit 9 are connected by turning on the switch 8, the DC voltage applied to the varicap 25 in accordance with the output change of the full-wave rectifier circuit 12 without using the control microcomputer 16. The second adjustment function that controls the shift of the resonance frequency when the IC card is held over is operated. That is, during actual operation, the switch 8 is turned on, and the switch 8 is turned off only when the first adjustment function is operated.

FIG. 4 shows an example in which the antenna coils of the various antennas (the transmission / reception antenna 1, the resonance antenna 5, and the resonance monitor antenna 11) are actually arranged on a printed board.
In the illustrated example, the antenna coils (loop antennas) of the transmission / reception antenna 1, the resonance antenna 5, and the resonance monitor antenna 11 are arranged on the same printed circuit board. In order to realize this method, the antennas must be arranged at positions where they are electromagnetically coupled to each other. For example, here, all the antennas are arranged on the same substrate or the same plane. However, since the antennas may be arranged at positions where they are electromagnetically coupled to each other, the antennas need only be in a positional relationship that satisfies this condition. For example, it may be arranged three-dimensionally before and after, and is not particularly limited to the configuration of being arranged on the same substrate or the same plane.

The transmitting / receiving antenna 1 includes a transmitting antenna 1a and a receiving antenna 1b as shown in the figure.
FIG. 5 shows a general configuration of an IC card. As shown in the figure, the IC card 40 includes a resonance capacitor 42 for resonating with a loop antenna 43 wound around the card, and an IC chip 41, and has an electrical impedance. Further, since the power is supplied from the reader / writer device side, there is no power in the IC card 40 itself. Although not particularly shown, the IC chip 41 includes, for example, a transmission / reception circuit, a memory, a control circuit, and the like.

  In the configuration described above, for example, when the reader / writer device is shipped, installed at an arbitrary installation location, or when the surrounding environment changes, the control microcomputer 16 performs the processing shown in FIG. The first adjustment function is executed.

  In this method, as will be described below with reference to FIGS. 7 to 11, the actual output state of the antenna is monitored by the resonance monitor antenna 11, for example, so that the antenna output becomes maximum, that is, the antenna output. The capacity of the varicap 25 is adjusted (the applied voltage is changed) so that the resonance frequency matches the carrier frequency. However, this is only an example, and as will be described later, the optimum state for communication is not always obtained when the strength of the magnetic field is maximized. Therefore, the purpose of adjustment is not necessarily limited to matching the resonance (natural) frequency of the antenna with the carrier frequency. From the above, the purpose of the adjustment of the first and second adjustment functions by this method is to “adjust the deviation from the resonance (natural) frequency of the antenna optimum for communication”. However, in the following description, a case where adjustment is performed so that the intensity of the magnetic field becomes maximum is taken as an example.

Hereinafter, first, the first adjustment function will be described with reference to FIG.
In FIG. 7, the control microcomputer 16 is instructed by the user to execute automatic adjustment at the time of shipment of the reader / writer device, installation at an arbitrary installation location, or the like, or by the temperature sensor 13 as shown in the figure. In order to start the automatic adjustment process when the sensed temperature change is equal to or greater than a predetermined amount, first, a signal to perform automatic adjustment is sent to the control unit 3 (step S1). On the other hand, the control unit 3 notifies the control microcomputer 16 that transmission is started (step S21), and controls the RF unit 2 to generate a magnetic field from the transmission antenna 1a (step S22).

  When receiving the notification in step S21 (step S2), the control microcomputer 16 starts the automatic adjustment process (step S3). First, the switch 8 is turned off (step S4) to enter the first adjustment function mode. enter.

  Then, the control microcomputer 16 sequentially changes the output voltage from the D / A converter 14 at a predetermined interval within a predetermined voltage range set in advance. That is, the voltage applied to the varicap 25 is sequentially changed (step S5). Each time this output voltage is changed, the input voltage input to the A / D converter 15, that is, the voltage induced in the resonance monitor antenna 11 by the magnetic field generated from the antenna is rectified by the full-wave rectifier circuit 12. The voltage is acquired, and this input voltage value is stored in a memory or the like in association with the output voltage value from the D / A converter 14 at that time (step S6).

  A correlation table (not shown) showing the correlation between the output voltage from the D / A converter 14 and the input voltage from the A / D converter 15 by repeatedly executing the processes in steps S5 and S6. ) Is created (step S7).

Here, FIGS. 8A to 8C show examples of signal states of the respective units related to the creation of the correlation table.
FIG. 8A shows an example of the relationship between the output voltage (horizontal axis) from the D / A converter 14 and the antenna natural frequency (vertical axis). As shown in the figure, when the output voltage from the D / A conversion unit 14 changes, the capacitance of the varicap 25 changes, so that the antenna natural frequency changes.

  Here, assuming that the carrier frequency is 13.56 (MHz), the antenna natural frequency is set to 13.56 (MHz) when the output of the D / A converter 14 is 10 (V) as in the illustrated example. In this case, as shown in FIG. 8B, the voltage induced in the resonance monitor antenna 11 has a peak (33 V in this example) when the output of the D / A converter 14 is 10 (V). .

  Therefore, as a matter of course, the input voltage to the A / D converter 15 formed by rectifying the voltage induced in the resonance monitor antenna 11 by the full-wave rectifier circuit 12 is also D / A as shown in FIG. When the output of the conversion unit 14 is 10 (V), a peak is obtained (16 V in this example). The correlation table is a table showing the relationship shown in FIG.

  The control microcomputer 16 obtains the output voltage from the D / A converter 14 when the input voltage from the A / D converter 15 becomes maximum based on this correlation table (step S8). Thereafter, the output voltage from the D / A converter 14 is fixed to the output voltage obtained in step S8 (step S9).

  With the above processing, adjustment can be made so that the input voltage from the A / D converter 15 becomes maximum, that is, adjustment can be made so that the intensity of the magnetic field generated from the antenna becomes maximum. In other words, the resonance frequency of the antenna can be adjusted to an optimum state. Finally, the switch 8 is switched (turned on) (step S10), the control unit 3 is notified of the completion of the correction process (step S11), and the process by the first adjustment function is completed. Upon receiving the notification in step S11, the control unit 3 ends transmission from the transmission antenna 1a.

  Here, in this method, the reason why the resonant antenna 5 is used, that is, the reason that the varicap is not provided and adjusted on the transmission / reception antenna 1 side is that the varicap is connected to the transmission antenna 1a. In this case, when the transmission output becomes large, the withstand voltage of the varicap becomes a problem, and the second is that when the varicap is connected to the receiving antenna 1b, the receiving sensitivity is not constant. is there.

  In addition, the term “antenna” in the above description means all four of the transmission antenna 1a, the reception antenna 1b, the resonance antenna 5, and the resonance monitor antenna 11. Therefore, “adjusting the resonant frequency of the antenna to the optimum state” described above is a form that takes into account all the self-inductance, mutual inductance, line-to-line capacitance, and elements connected to each antenna. This means that the capacity of the varicap 25 is determined so that the resonance frequencies of all the antennas are optimum values for communication (not only the transmission / reception antenna is resonated).

  Where the input voltage of the A / D converter 15 is maximum, the voltage induced in the resonance monitor antenna 11 is maximum. This is because the magnetic flux is maximum. It can be considered that the resonance frequencies of all the antennas are in an optimal state (not the resonance frequency of the transmission / reception antenna but the resonance frequency of the antenna at this time, as described above, all the antennas and the elements connected thereto) Is the resonant frequency of the combined inductance L and capacitance C). In other words, considering the self-inductance and mutual inductance of all the antennas, the influence on the capacitance between the lines and the housing, etc., the varicap 25 is set so that the magnetic flux of the antenna is maximized on the combined inductance and capacitance. The capacity (that is, the applied voltage) is determined.

  More specifically, first, the resonant antenna 5 is a configuration for determining a frequency unique to all antennas by combining all the antennas of the transmitting antenna 1a, the receiving antenna 1b, the resonant monitor antenna 11, and itself (the resonant antenna 5). It is. When magnetic flux is generated from the transmitting antenna 1a, each antenna is electromagnetically coupled. The term “all antennas” means that when a magnetic field is generated from the transmission antenna 1a, the reception antenna 1b, the resonance monitor antenna 11, the resonance antenna 5, and itself (the transmission antenna 1a) are electromagnetically coupled. This is because these can be viewed as one antenna (all antennas). In an electromagnetically coupled state, each antenna has mutual inductance, self-inductance, and line-to-line capacitance. If these are considered as antenna elements (L and C), the combined antenna L can be regarded as a combined inductance L and a combined capacitance C. Here, in order to determine the natural frequency of the entire antenna, a certain inductance L value is determined for the combined capacitance C, or a certain capacitance C value is determined for the combined inductance L. . Here, since there is a purpose to adjust the resonance (inherent) frequency of the antenna to an optimum frequency for communication, the combined inductance L is considered to be the inductance of the resonant antenna 5 + other L, and the resonant antenna 5 Take a method of adding capacity to. This is the role of the resonant antenna 5.

  In general, the resonance frequency of the antenna is expressed by the following equation (1), where L is the combined inductance of the antenna and C is the combined capacitance.

The combined capacitance is determined by a capacitance obtained by combining a resonance capacitor, a varicap connected in parallel with the resonance capacitor, and a stray capacitance or a parasitic capacitance between the antennas.
The resonance monitor antenna 11 is provided to monitor the intensity of the magnetic field radiated from all antennas. This is possible because the four antennas are electromagnetically coupled as described above. At the time of adjustment, a current is applied to the transmitting antenna 1a by the RF unit 2 in step S22, thereby maintaining a state where magnetic flux is generated. This amount of current varies depending on the state of the natural frequency of all antennas. By changing the variable capacitance of the resonant antenna 5, the resonance monitor antenna 11 captures that the natural frequency of all the antennas changes and the magnetic flux changes.

  Here, adjustment of the resonance (inherent) frequency of the antenna to a frequency optimal for communication will be described. The natural frequency that is optimal for communication is generally a frequency that matches the carrier frequency, as described in Patent Document 1, for example. That is, the resonance frequency of the antenna that maximizes the intensity of the magnetic field radiated from the transmitting antenna 1a is a frequency that matches the carrier frequency. In this case, the power supply and signal transmission to the IC card are most efficient. It is considered a thing. However, in view of obtaining optimum communication performance for data transmission / reception with an IC card, the present invention is not necessarily limited to this example.

  That is, considering the receiving antenna 1b, in order to efficiently receive a signal from the IC card, it is necessary to close electromagnetic coupling between the receiving antenna 1b and the IC card antenna. This is almost determined by the shape of each antenna, and the greater the mutual inductance, the greater the degree of coupling. When it is desired to obtain the optimum received signal strength, the mutual inductance received from the IC card also increases. When the natural frequency of the antenna is set in consideration of this, the set frequency of the receiving antenna 1b does not necessarily match the carrier frequency. become. As for the antenna of this apparatus, although the transmitting antenna 1a, the receiving antenna 1b, and the resonant antenna 5 are separate, they are electromagnetically coupled as described above, and all the antennas are set to frequencies set by the resonant antenna 5. A natural frequency is set. Therefore, even if the transmission output is somewhat reduced, the total communication distance may be longer if adjustment is made to increase the received signal strength. That is, a place where the transmission output and the received signal strength are well balanced is the most optimal frequency for communication, and in this setting, the natural frequency of the antenna does not match the carrier frequency. Therefore, as described above, it is not necessarily the optimum setting that “the natural frequency of the antenna” = “the carrier frequency”.

  Various factors such as manufacturing variations of antennas, variations of varicap characteristics and capacitor capacities of components during manufacturing, variations due to component mounting, and variations in antenna characteristics due to mounting to the chassis are considered. It is done. According to the first adjustment function, the deviation of the resonance frequency caused by these various factors can be corrected by adjusting the capacity of the varicap. For example, by performing the first adjustment function at the time of shipment, installation, or periodically after installation, it is possible to cope with a resonance frequency shift caused by these various factors.

  However, even if such a correction is performed, the resonance frequency of the antenna shifts due to the impedance of the IC card when the user brings his IC card closer to the reader / writer device during actual operation. Communication performance deteriorates as the IC card approaches. In general, even if the communication performance is deteriorated, the IC card is approaching, so it is considered that communication is not often interrupted. However, it has actually been confirmed that there is a place where communication becomes unstable such that communication cannot be performed under the condition that the impedance of the antenna is relative to the impedance of the IC card. Therefore, when trying to perform stable communication with various types of IC cards, it is necessary to adjust the resonance frequency deviation of the antenna due to the approach of the IC card.

On the other hand, by setting the switch 8 to the ON state in step S10 at the end of the correction process, the second adjustment function described below operates during the subsequent operation.
The second adjustment function is realized by the operation of the peak hold circuit 9, the voltage inverting circuit 10, and the adder circuit 7 without the control microcomputer 16 by turning the switch 8 ON (however, The output voltage determined by the adjustment function 1 continues to be output from the D / A conversion unit 14).

  Note that the second adjustment function does not cope with strictly adjusting the resonance frequency optimally. This is because the IC card is held over the antenna for only a short time (about 0.1 to 0.5 seconds), and strictly controlling it will be costly. Therefore, the second adjustment function is not strict, but if the adjustment direction (addition or subtraction of voltage applied to the varicap when the IC card is held over the antenna) is matched, the IC card is held over. The voltage applied to the varicap is changed almost automatically so that the resonance frequency is roughly corrected.

Hereinafter, the operation relating to the second adjustment function will be described with reference to FIG.
First, when receiving an operation start command, the control microcomputer 16 issues a communication start request to the control unit 3 (step S31) and outputs a reset signal to the peak hold circuit 9 to clear the hold voltage. (Step S32).

The control unit 3 that has received the communication start request passes a polling signal to the RF unit 2, and the polling signal is transmitted from the transmission antenna 1a (step S41).
Thereafter, the system enters a state of waiting for use, and communicates with the IC card each time the user brings the IC card closer to the reader / writer device (step S42). When communication is completed, a communication end notification is issued (step S42). S43), the next use waiting state is entered, but when the IC card is brought closer to the antenna of the reader / writer device, as described above, the resonance frequency of the antenna deviates from the optimum value set by the first adjustment function. As a result, the voltage induced in the resonance monitor antenna 11 decreases, and the output voltage from the full-wave rectifier circuit 12 also decreases (A in FIG. 9).

  In the second adjustment function, this voltage is controlled to be close to the original voltage. Here, it has been confirmed by experiments that the resonant frequency of the antenna shifts to a lower side as the IC card approaches. Therefore, in the second adjustment function, by adding the necessary correction voltage to the voltage output by the first adjustment function in the adder circuit 7, the applied voltage to the varicap when the IC card approaches Control is performed so as to increase (the voltage applied to the varicap increases, so the capacitance decreases and the resonance frequency shifts higher). That is, when the voltage from the resonance monitor antenna 11 decreases, the voltage inverting circuit 10 and the peak hold circuit 9 increase the output voltage value from the peak hold circuit 9 (B in FIG. 9). By adding to the output voltage from the A converter 14 (C in FIG. 9), the voltage applied to the varicap 25 is increased. Therefore, as described above, the resonance frequency shifts higher and approaches the original resonance frequency (D in FIG. 9). The peak hold circuit 9 is controlled so that the voltage applied to the varicap 25 returns to the voltage in the original state based on the principle of this circuit, that is, the voltage induced in the resonance monitor antenna 11 is changed. Since it works to return to the original state, the voltage applied to the varicap decreases as it is, so that the peak voltage value is maintained by the peak hold circuit 9.

Specific examples of the adder circuit 7, the voltage inverting circuit 10, and the peak hold circuit 9 are shown in FIGS. Since both are general circuit configurations, they will not be described in detail. For example, in the adder circuit 7 shown in FIG. 10A, the voltage output Vout from the operational amplifier is
_{Vout = -R 3 / R 1 ·} Vin1-R 3 / R 2 · Vin2
The following relational expression holds. (Vin1 and Vin2 are output voltages from the D / A converter 14 and the peak hold circuit 9).

Further, for example, in the voltage inverting circuit 10 shown in FIG.
_{Vout = -R 6 / R 5 ·} Vin
The following relational expression holds.

  For example, in the peak hold circuit 9 shown in FIG.

The following relational expression holds.
Further, the specific example of the peak hold circuit 9 shown in FIG. 10C is merely an example, and is not limited to this example, and other generally well-known peak hold circuits ( For example, a circuit configuration using two operational amplifiers described in “Transistor Technology SPECIAL, NO.71” or the like may be used.

FIGS. 11A to 11D show examples of changes in the antenna natural frequency and the voltage value of each part when the IC card is brought close to each other.
FIG. 11A is a diagram illustrating an example of the relationship between the antenna natural frequency and the distance (horizontal axis) between the antenna of the reader / writer device and the IC card. In this example, it is assumed that the antenna natural frequency is adjusted to the optimum frequency for communication (here, 13.56 MHz) by the first adjustment function. In this state, when the IC card is gradually approached, there is no change up to 10 (cm), but when the distance is closer than 10 (cm), the antenna natural frequency becomes lower as the distance is closer.

The output voltage of the resonance monitor antenna 11 at this time is shown in FIG.
As described above, since the antenna natural frequency decreases as the IC card approaches, the antenna natural frequency deviates from the optimum frequency for communication. As described above, since the resonance monitor antenna 11 monitors the strength of the magnetic field radiated from all antennas, the strength of the magnetic field radiated from all antennas decreases as the IC card approaches, so that FIG. As shown in b), the voltage induced in the resonance monitor antenna 11 decreases. At this time, the output voltage value of the voltage inverting circuit 10 increases as the voltage of the resonance monitor antenna 11 decreases as shown in FIG. Therefore, the output voltage value of the adder circuit 7 also rises as shown in FIG.

The first and second adjustment functions according to the present method described above will be collectively described below again.
The transmission antenna 1a used in the reader / writer device of this example does not have a resonance capacitor as a single transmission antenna. The receiving antenna 1b alone does not have a resonance capacitor. In this state, the burden on the transmitter becomes large. Therefore, the resonance antenna 5 is arranged around the transmission / reception antenna 1, the resonance capacitor 22, the varicap 25, and the like are connected to the resonance antenna 5, By controlling the applied voltage, the natural (resonant) frequency of all antennas can be changed / adjusted. The set value (optimum value) of the resonance frequency of the antenna is determined by the degree of coupling between the card and the antenna depending on the antenna structure. That is, it may be better to match the carrier frequency, or it may be better to be the frequency before and after that. However, the optimum frequency for the communication can be determined as one point (frequency). The communication performance deteriorates when this point fluctuates due to fluctuations in the surrounding environment, various places, etc. Therefore, automatically returning this fluctuating point to the original point is characterized by the first and second adjustment functions. Become.

  In order to realize this, it is necessary to know how much the current frequency deviates from that point. In order to know this, the resonance monitor antenna 11 is arranged. Since the resonance monitor antenna 11 is electromagnetically coupled to other antennas, a voltage corresponding to the resonance state of all the antennas is induced in the resonance monitor antenna 11, and the current antenna is monitored by monitoring this voltage. Output (magnetic field strength) can be known.

  Thus, in the first adjustment function, the control microcomputer 16 sequentially changes the voltage applied to the varicap 25 in the resonant antenna 5 through the D / A converter 14, and the resonance monitor antenna 11 at that time is changed. The induced voltage is taken into the microcomputer 16 through the A / D converter 15 and a correlation table is created. Since the list of input voltages to the A / D converter 15 for each output voltage of the D / A converter 14 is recorded in the correlation table, the input voltage has a peak somewhere in the correlation table. Can be found. The output voltage of the D / A converter 14, or match the output voltage to the input voltage to a peak, then is either matched to some distance point, as described above, it means that different by the antenna, what to do in advance antenna A designer or the like decides it and stores it in a memory or the like in the control microcomputer 16. In any case, it is possible to find a point having an optimum frequency for communication.

  On the other hand, the second adjustment function is provided in order to reduce the influence on the antenna due to the approach of the IC card, which simply adjusts the antenna without using the control microcomputer 16. There is a method in which the variation of the induced voltage of the resonance monitor antenna 11 is applied to the varicap of the resonance antenna 5 as it is. In order to realize this, the voltage change of the resonance monitor antenna 11 is inverted by the voltage inverting circuit 10 so as to match the characteristics of the varicap (variable capacitance diode).

Next, a second embodiment will be described below.
In the second embodiment, the resonant antenna 5 and the resonant frequency adjusting circuit 6 use the configuration shown in FIG. 9 instead of the configuration shown in FIG.

  In the reader / writer device of this example described above, the resonance voltage and the output (control voltage; DC) of the D / A converter 14 are applied to the applied voltage applied to the cathode of the varicap 25 in FIG. Voltage) is applied simultaneously, and the control voltage changes due to the swing of the resonance voltage, and as a result, the phenomenon that the capacitance of the variable capacitance element (varicap) fluctuates may occur. For this reason, there is a possibility that a sufficient amount of change in capacity cannot be obtained.

In contrast, in the second embodiment, the configuration shown in FIG. 9 is used.
In FIG. 9, first, the resonance frequency adjustment circuit 6 is provided with two varicaps 53 and 54 in parallel with the resonance capacitor 52 of the resonance antenna 5. The two varicaps 53 and 54 are connected in series and the cathodes are connected to each other. Further, a resistor 55 is inserted between the connection point of the cathodes and the ground point. The control voltage is applied between the ground point and the cathode via the choke coil 56. The antenna coil 51 of the resonant antenna 5 is grounded at an intermediate point where the turns ratio is 1: 1.

  With the configuration described above, resonance voltages having opposite phases are applied to the anode side of the varicaps 53 and 54, and a voltage is applied to the anode side so that the resonance voltage is just canceled. Therefore, it is possible to prevent the applied voltage on the cathode side from fluctuating due to the resonance voltage.

  That is, by taking out an intermediate tap from the resonant antenna 5 and fixing it to a certain potential (here, ground), the alternating voltage (alternating current) induced in this antenna is reversed with reference to the fixed potential. Phase voltage is generated. By applying the reverse phase voltage to the anode side of the varicap, the voltage on the cathode side is almost constant and does not change, and behaves as if it is fixed at a certain potential. Therefore, by applying a DC control voltage via the choke coil, the voltage difference between the anode and the cathode changes only by the applied DC voltage, and thus the amount of change in capacity increases.

  In the configuration of FIG. 2, since the control DC voltage and the AC voltage of the resonance circuit are on the applied voltage of the cathode, the potential difference between the anode and the cathode is small, and the change in capacitance is small. The resistor had a high resistance value in order to stabilize the cathode potential.

  The choke coil 56 is inserted for the purpose of separating the high-frequency current (13.56 MHz) flowing through the antenna and the direct current, and is a configuration necessary to make the terminal to which the direct-current voltage of the control voltage is input high impedance. .

It is a block diagram of the configuration of a reader / writer device for a non-contact type IC card. It is a block diagram of a resonant antenna and a resonant frequency adjustment circuit. It is a block diagram of a resonance monitor antenna and a full-wave rectifier circuit. An example in which antenna coils of various antennas are actually arranged on a printed board is shown. It is a figure which shows the general structure of an IC card. It is a figure which shows the characteristic of a varicap. It is a process flowchart figure of a 1st adjustment function. (A)-(c) is a figure which shows an example of the signal state of each part regarding a correlation table preparation. It is a figure for demonstrating the circuit operation | movement regarding a 2nd adjustment function. (A) is an addition circuit, (b) is a voltage inversion circuit, (c) is a figure which shows the specific example of a peak hold circuit. (A)-(d) is a figure which shows an example of the change of the antenna natural frequency when the IC card is brought close, and the voltage value of each part. It is a block diagram of the resonant antenna by 2nd Example, and a resonant frequency adjustment circuit.

Explanation of symbols

1 transmit / receive antenna 1a transmit antenna 1b receive antenna,
2 RF unit 3 Control unit 4 Crystal oscillation unit 5 Resonance antenna 6 Resonance frequency adjustment circuit 7 Addition circuit 8 Switch 9 Peak hold circuit 10 Voltage inversion circuit 11 Resonance monitor antenna 12 Full wave rectification circuit 13 Temperature sensor 14 D / A conversion unit 15 A / D converter 16 Control microcomputer 21 Antenna coil 22 Resonant capacitor 23 Resistor 24 Capacitor 25 Varicap (variable capacitance diode)
26 resistor 40 IC card 41 IC chip 42 resonance capacitor 43 loop antenna 51 antenna coil 52 resonance capacitor 53 varicap 54 varicap 55 resistor 56 choke coil

Claims (5)

In a reader / writer device having a transmission / reception antenna used for wireless communication with a non-contact type IC card,
A resonance antenna having an antenna coil and a resonance capacitor, and a resonance monitoring antenna are provided at positions where each antenna including the transmission / reception antenna can be electromagnetically coupled to each other,
A resonance frequency adjusting circuit having a variable capacitance element connected in parallel or in series with a resonance capacitor of the resonance antenna;
At any time or when a change in the surrounding environment is detected, the voltage applied to the variable capacitance element is sequentially changed, and the voltage value induced in the resonance monitor antenna is measured each time the applied voltage is changed. Based on the result, the voltage applied to the variable capacitance element when the voltage value induced in the resonance monitoring antenna becomes maximum is obtained, and the voltage determined based on the obtained result is applied to the variable capacitance element. A reader / writer device comprising control means for performing A voltage inverting circuit that inputs a voltage induced in the resonance monitoring antenna and raises its output voltage in response to the voltage drop when the voltage drops due to the approach of the non-contact type IC card;
A peak hold circuit that maintains the peak voltage value of the output voltage of the voltage inverting circuit;
An addition circuit for adding an output voltage value of the peak hold circuit to an applied voltage value by the control means and applying a voltage of the voltage value after the addition to the variable capacitance element;
The reader / writer device according to claim 1, further comprising: The resonance frequency adjusting circuit has a pair of variable capacitance elements in which the cathodes are connected to each other, the connection point of the cathode is grounded via a resistor, and the applied voltage is connected between the ground point and the cathode via a choke coil. Is applied, and
3. The reader / writer device according to claim 1, wherein the antenna coil of the resonance antenna is grounded at an intermediate point where the turns ratio is 1: 1. A method for automatically adjusting an antenna natural frequency in a reader / writer device having a transmission / reception antenna used for wireless communication with a non-contact type IC card,
By providing a resonance antenna having an antenna coil and a resonance capacitor, and a resonance monitoring antenna at a position where the antennas including the transmission / reception antenna can be electromagnetically coupled to each other, one antenna is provided. When the resonance frequency of the antenna is regarded as a variable capacitance element connected in parallel or in series with the resonance capacitor of the resonance antenna at any time or when a change in the surrounding environment is detected, the variable capacitance element The voltage applied to the resonance monitor antenna is measured every time the applied voltage is changed, and the voltage value induced in the resonance monitor antenna is measured based on the measurement result. The voltage applied to the variable capacitance element when the voltage becomes maximum is obtained, and the voltage determined based on the obtained result is applied to the variable capacitance element. An automatic adjustment method for the natural frequency of an antenna, characterized in that adjustment is performed by On the computer,
In the reader / writer device having a transmission / reception antenna used for wireless communication with a non-contact type IC card, a resonance antenna having an antenna coil and a resonance capacitor, and a resonance monitoring antenna, including the transmission / reception antenna The resonance frequency of the antenna when the antennas are considered as one antenna by providing the antennas at positions where they can be electromagnetically coupled to each other,
With respect to the variable capacitance element connected in parallel or in series with the resonance capacitor of the resonance antenna, at any time or when a change in the surrounding environment is detected, the applied voltage to the variable capacitance element is sequentially changed, Each time the applied voltage is changed, the voltage value induced in the resonance monitor antenna is measured, and based on the measurement result, the voltage value induced in the resonance monitor antenna is maximized. A program for realizing a function of adjusting the voltage by applying the voltage determined based on the obtained result to the variable capacitance element.

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