JP2007104092A - Rfid device and reader/writer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems due to the temperature characteristics or variation when noncontact wireless communication is performed between a reader/writer and an RFID. <P>SOLUTION: The RFID device comprises a temperature detecting section 34, and sections 31 and 32 for shifting the frequency tuned at a tuning section 12 depending on the temperature detected at the temperature detecting section 34. Similarly, the reader/writer comprises a temperature detecting section, and a section for shifting the frequency tuned at the tuning section depending on the temperature detected at its temperature detecting section. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an RFID device having a short-range wireless communication function called a non-contact type IC card, and a reader / writer device that performs wireless communication with the RFID device.

  In recent years, the use of non-contact type IC cards is rapidly spreading as transportation tickets, membership cards, employee cards, cards for payment methods at stores, and the like. Non-contact type IC card performs authentication processing by performing wireless communication with a nearby reader / writer, so it can be used in a wallet, pass case, etc., and is easier to use than a magnetic card. Is good.

  In addition, such a non-contact type IC card (or a circuit component having a function equivalent to that of an IC card) is built in a portable electronic device such as a mobile phone terminal, and these devices are used in the same manner. It has been put into practical use to enable authentication and settlement. When the IC card function unit is incorporated into the mobile terminal, the IC card function unit is not necessarily in the shape of a card. However, in the following description, the IC card function unit is particularly described when referred to as an IC card. Unless otherwise specified, it includes a portion having an IC card function. In addition, this type of non-contact type IC card is also referred to as RFID (Radio Frequency Identification) or a wireless IC tag. Even when used alone, there are various types such as a label type, a coin type, and a stick type in addition to the card type. Here, it is referred to as an IC card for convenience.

  When the IC card function unit performs wireless communication with the reader / writer, the IC card function unit is activated by electromagnetic induction from the reader / writer. That is, on the IC card side, a process of tuning to a carrier wave of a predetermined frequency output from the reader / writer is performed, and the detected carrier wave is modulated by ASK (Amplitude shift keying) modulation or the like, and the reader / writer side is modulated. I am trying to send data.

  FIG. 9 is a diagram showing a configuration example of a conventional IC card function unit. One end a and the other end b of the loop antenna 11 are connected to an RFID circuit block 14 made of LSI, and wireless communication processing is performed in the RFID circuit block 14. Here, a tuning capacitor 12 is connected between one end a and the other end b of the loop antenna 11, and the tuning frequency is determined by the characteristics of the loop antenna 11 and the tuning capacitor 12. Further, a rectifying diode 13 is connected to the other end b side. When the IC card function unit is built in the mobile phone terminal, the RFID circuit block 14 is connected to the radio telephone circuit block 15.

  FIG. 10 is a diagram showing a configuration example of a conventional reader / writer. A transmission block 22 and a reception block 27 are connected to an RFID communication circuit block 21 constituted by an LSI that performs transmission processing and reception processing as a reader / writer, and an output terminal and a reception block of the transmission block 22 are connected to each other. 27 is connected to the antenna 26 via the tuning circuit 25. The transmission signal supplied to the transmission block 22 is modulated by the modulation circuit 23, amplified to a predetermined transmission output by the drive circuit 24, and then supplied to the tuning circuit 25 side. The reception block 27 includes a filter 28 and an amplifier 29. The reception block 27 extracts a reception signal in the vicinity of the tuning frequency and supplies the reception signal to the demodulation unit in the RFID communication circuit block 21.

Patent Document 1 discloses a tuning circuit included in a non-contact type IC card.
Japanese Patent Laying-Open No. 2003-67693 (FIG. 2)

  As shown in FIG. 9, the IC card function unit requires a loop antenna for performing wireless communication by electromagnetic induction. Wireless communication is performed between this loop antenna and a dedicated antenna installed in the reader / writer. Both antennas are tuned according to the carrier frequency, and are assembled to optimize transmission characteristics. Yes.

  However, since the tuning frequency of both antennas has temperature characteristics, there is a problem that the communication performance is affected by temperature changes. In other words, it has been impossible to prevent deterioration in communication performance due to a shift in the tuning frequency optimized at room temperature due to a temperature change.

  In addition, individual variations in the tuning frequency of both antennas are not processed so as to eliminate the conventional variation, but only work such as selecting parts within a certain standard range when manufacturing an IC card. There were many cases that caused problems in communication performance.

  Referring to FIG. 11, the problem of temperature characteristics and individual variations will be described. The horizontal axis of FIG. 11 represents the tuning frequency, and it is assumed that the approximate midpoint in the figure is an appropriate tuning frequency. The communication distance L at which communication is possible has a characteristic that changes like a bow that becomes shorter as it deviates from the appropriate tuning frequency. In FIG. 11, three temperature characteristics a, b, and c are shown, and the tuning frequency changes in proportion to the change in temperature. If the communicable distance is determined according to the standard as shown in FIG. 11, in the case of the characteristic b, the almost maximum communication distance can be obtained at a certain temperature. In the case of the characteristic c having a high tuning frequency, there is a possibility that the communicable distance defined by the standard may not be satisfied depending on the temperature. There was a problem due to such unfavorable variation in characteristics.

  In the description so far, the problem mainly on the IC card side (RFID side) has been described. However, the tuning frequency shift due to the temperature characteristic has the same problem in the tuning circuit on the reader / writer side.

  SUMMARY An advantage of some aspects of the invention is that it solves a problem due to temperature characteristics and variations in wireless communication between a reader / writer and an RFID device.

  According to the present invention, an RFID device or a reader / writer includes a temperature detection unit and a frequency shift unit that shifts the frequency to be tuned by the tuning unit according to the temperature detected by the temperature detection unit.

  By doing so, the tuning frequency is shifted according to the temperature of the environment in which it is used. However, the frequency shift is corrected by the action of the frequency shift unit, and the tuning frequency does not vary.

  According to the present invention, the frequency shift is corrected by the action of the frequency shift unit so that the tuning frequency does not vary, and short-range wireless communication can be performed between the RFID device and the reader / writer at the specified tuning frequency. It becomes like this. Since this tuning frequency correction process is performed as a circuit measure, there is no restriction on the antenna shape or the device shape, and the design freedom of the device is improved. In addition, since almost complete temperature compensation can be performed, the communication state becomes stable as a result, and there are no restrictions on actual use, improving the usability for the user. Furthermore, it is possible to prevent deterioration in communication performance due to manufacturing variations of the RFID device or the reader / writer.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

  In this example, an RFID device that is a non-contact type IC card is used. The RFID device may be either a single IC card or an IC card function unit built in the mobile phone terminal device.

  FIG. 1 is a diagram showing a configuration example of the RFID device of this example. One end a and the other end b of the loop antenna 11 are connected to an RFID circuit block 14 made of LSI, and wireless communication processing is performed in the RFID circuit block 14. Here, a tuning capacitor 12 is connected between one end a and the other end b of the loop antenna 11, and the tuning frequency is determined by the characteristics of the loop antenna 11 and the tuning capacitor 12. The tuning frequency is set to 13.56 MHz in order to receive, for example, a 13.56 MHz carrier wave transmitted from the reader / writer. Further, a rectifying diode 13 is connected to the other end b side.

  The RFID circuit block 14 includes a demodulation circuit for taking out data subjected to ASK modulation at 212 kHz from a carrier wave from a reader / writer, a switch circuit for load switching, a clock extraction circuit, and a communication control unit for realizing a higher layer of a wireless communication protocol Built-in memory. When the IC card function unit is built in the mobile phone terminal, the RFID circuit block 14 is connected to the radio telephone circuit block 15.

  Up to this point, the configuration is the same as that shown in FIG. In this example, a series circuit of a capacitor 31 and a variable capacitance diode 32 is connected in parallel with the tuning capacitor 12 between one end a and the other end b of the loop antenna 11. The connection point between the capacitor 31 and the variable capacitance diode 32 is configured to be supplied with a voltage for controlling the capacitor capacity from a control unit 33 described later.

  The control unit 33 controls a process for compensating the temperature characteristic, and the temperature detection unit 34 and the memory 35 are connected to each other. As for the temperature detection unit 34, for example, as shown in FIG. 2, a series circuit of a resistor 36 and a thermistor 37 is connected between a terminal from which a power supply voltage Vcc is obtained and a ground potential unit. And the thermistor 37 are supplied to the analog / digital converter 37 to convert them into digital data, and the converted data is supplied to the control unit 33. With this configuration, the resistance value of the thermistor 37 changes according to the ambient temperature, the voltage data supplied to the control unit 33 changes, and the control unit 33 can determine the ambient temperature from the voltage data.

  The memory 35 connected to the control unit 33 stores the correspondence between the temperature and the correction value of the tuning frequency as a conversion data table, and the correction voltage value corresponding to the detected temperature (voltage data) is The voltage supplied to the connection point between the capacitor 31 and the variable capacitance diode 32 is set. In this embodiment, the analog / digital converter 37 takes in the temperature detection data only when the RFID device detects the carrier wave from the reader / writer.

  The correction value stored in the memory 35 is measured (stored) by measuring the communication characteristics of the RFID device when the RFID device is manufactured.

  The flowchart of FIG. 3 shows an example of the correction value recording process. Hereinafter, the processing will be described based on the flowchart of FIG. 3. When the initial value measurement processing for storing the characteristics in the memory 35 is started (step S11), the RFID device for measuring the characteristics is set to a certain temperature (for example, 25). ) And measure the tuning frequency in that state. It should be noted that after determining that the temperature is constant from the output of the temperature detector 34, the tuning frequency may be measured. In the measurement at this time, measurement is performed in a state where the correction is not performed by the series circuit of the capacitor 31 and the variable capacitance diode 32 (or the correction state is the initial state). Then, it is determined whether or not the measured tuning frequency is within the standard range of the specified tuning frequency (step S12). Here, if the value is within the specified range, the value stored in the memory 35 is left as the initial value, and the process is terminated (step S13).

  If it is determined in step S12 that it is not within the standard range, a correction value for correcting the tuning frequency is calculated using a series circuit of the capacitor 31 and the variable capacitance diode 32 (step S14), and the calculation is performed. The corrected value is stored in the memory 35. After the storage, the stored correction value voltage is applied to the connection point between the capacitor 31 and the variable capacitance diode 32 (step S15), and the tuning frequency is measured again (step S16). Then, it is determined whether or not the measured tuning frequency is within the specified range of the specified tuning frequency (step S17). If it is within the specified range, the process proceeds to step S13 and the adjustment process is terminated. If it is determined that the value is not within the specified range, the process returns to step S11, the initial value measurement process is re-executed, and the process of the flowchart of FIG. Note that the tuning frequency measurement and correction value calculation processing may be performed by a separate adjustment device (not shown) connected to the RFID device. The correction data calculated in step S14 is correction data at a constant temperature. As correction data stored in the memory 35, correction at each temperature within a temperature range in which the RFID device is used. Data is stored.

  When using the RFID device that has been adjusted in this way, the processing shown in the flowchart of FIG. 4 is executed. First, the control unit 33 detects a carrier wave from the reader / writer and determines whether or not the reader / writer has approached (step S21). When the carrier wave from the reader / writer is not detected, the process waits as it is. When the carrier wave from the reader / writer is detected on the RFID circuit block 14 side and it is determined that the reader / writer is approaching, the processing in the analog / digital converter 38 (FIG. 2) is started to detect the temperature. Data capture is turned on (step S22). The supply of the power supply voltage to the thermistor 37 side may also be turned off at the normal time and turned on at this time.

  And the correction data according to the temperature detected by the control part 33 is judged from the memory | storage data of the memory 35 (step S23). Using the determined correction data, the voltage value supplied to the connection point between the capacitor 31 and the variable capacitance diode 32 is set, and the tuning frequency is corrected (step S24). After the tuning frequency is corrected in this way, it is determined whether or not the carrier wave from the reader / writer is not detected (that is, whether the carrier wave is separated from the reader / writer) (step S25). If the state in which the carrier wave from the reader / writer is detected continues, the processes in steps S23 and S24 are repeated.

  If it is determined that the reader / writer is away from the reader / writer, the processing in the analog / digital converter 38 is stopped, the temperature detection data capturing is turned off (step S26), and the process returns to the determination in step S21.

  In this way, the tuning frequency is corrected in accordance with the temperature of the environment in which the RFID device is used, so that fluctuations due to the temperature of the tuning frequency can be removed. Wireless communication. FIG. 5 is a diagram showing the relationship between the ambient temperature and the tuning frequency. In the characteristic without correction indicated by the solid line in the figure, the tuning frequency changes linearly in proportion to the change in temperature. On the other hand, in the case of this example, by performing a correction process corresponding to the detected temperature, as shown by the broken line, any temperature is corrected to a substantially constant tuning frequency, and even if there is a change in the ambient temperature. Communication can be performed at a constant tuning frequency.

  FIG. 6 is an example in which the relationship between the tuning frequency and the communication distance is applied when the tuning frequency correction of this example is performed. As described above, the relationship between the tuning frequency of the RFID device and the communication distance is such that the communication distance L capable of wireless communication with the reader / writer changes in a bow shape that becomes shorter as it deviates up and down from the appropriate tuning frequency. It is. Here, in the case of this example, a tuning frequency characteristic x that maintains a constant appropriate tuning frequency is obtained regardless of which temperature is used, and the distance that enables wireless communication with the reader / writer is maintained at the longest distance. Good wireless communication characteristics can always be obtained. Variations in the tuning frequency of each RFID device are also corrected at the same time, so that any RFID device has the tuning frequency characteristic x, and the communicable distance determined by the standard is always maintained.

  As a configuration for changing the tuning frequency, the configuration of FIG. 1 uses a variable capacitance diode, but a configuration for changing the tuning frequency may be used in another configuration. For example, as shown in FIG. 7, in parallel with the tuning capacitor 12, a series circuit of a switch 41 and a capacitor 51, a series circuit of a switch 42 and a capacitor 53, and a series circuit 53 of a switch 43 and a capacitor 53 A configuration in which three capacitors are connected and a capacitance of a capacitor connected in parallel with the tuning capacitor 12 is variably set in a plurality of stages. And opening / closing of each switch 41-43 is controlled according to the temperature detected by the control part 33. FIG. Other parts have the same configuration as that of the RFID device shown in FIG. With this configuration, the tuning frequency can be corrected by appropriately performing the open / close control of the switches 41 to 43 in accordance with the detected temperature. Although the three correction capacitors 51 to 53 are provided in FIG. 7, the number of capacitors and switches is not limited to this. The capacitance value of each capacitor need not be the same value.

  Furthermore, the tuning frequency may be corrected according to the temperature with another configuration.

  In the above example, the data conversion table is stored in the memory 35. However, for example, an arithmetic expression for obtaining a correction voltage value from the temperature data and a constant necessary for the expression are stored in the memory 35. A correction voltage value (a switch open / closed state value in the case of FIG. 7) necessary for calculation of the calculation formula may be obtained.

  Further, the temperature detection configuration using the thermistor shown in FIG. 2 is an example, and temperature detection may be performed with other configurations. The control unit 33 and the memory 35 shown in FIG. 1 are also separate circuits from the RFID circuit block 14, but may be incorporated in the RFID circuit block 14.

  In the configuration of FIG. 1, as an example in which the RFID device is incorporated in another device, an example in which a non-contact IC card function as a wireless IC tag is incorporated in a mobile phone terminal device is shown. The present invention is also applicable to a case where an IC card or IC tag corresponding to an RFID device is built in or attached to a portable terminal device (for example, a portable information processing terminal such as PDA: Personal Digital Assistance).

  Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the present invention is applied to a reader / writer that performs near field communication with an RFID device (IC card). In this example, the reader / writer is subjected to the tuning frequency correction process according to the temperature described in the first embodiment.

  FIG. 8 shows a configuration example of the reader / writer of this example. A transmission block 22 and a reception block 27 are connected to an RFID communication circuit block 21 constituted by an LSI that performs transmission processing and reception processing as a reader / writer, and an output terminal and a reception block of the transmission block 22 are connected to each other. 27 is connected to the antenna 26 via the tuning circuit 61. The transmission signal supplied to the transmission block 22 is modulated by the modulation circuit 23, amplified to a predetermined transmission output by the drive circuit 24, and then supplied to the tuning circuit 25 side. The reception block 27 includes a filter 28 and an amplifier 29. The reception block 27 extracts a reception signal in the vicinity of the tuning frequency and supplies the reception signal to the demodulation unit in the RFID communication circuit block 21.

  Up to this point, the configuration is the same as the configuration described as the conventional example, but in this example, the tuning frequency determined by the characteristics of the tuning circuit 61 and the antenna 26 can be adjusted by a variable capacitance process in the tuning circuit 61 or the like. As a configuration. For the variable capacitance processing, for example, the variable capacitance diode already described in the first embodiment can be applied.

  The control of the tuning frequency in the tuning circuit 61 is controlled by the control unit 62. A temperature detection unit 63 and a memory 64 are connected to the control unit 62, and the temperature data detected by the temperature detection unit 63 is used to correct the tuning frequency by using the conversion table data stored in the memory 64. The necessary data is obtained and the correction data is supplied to the tuning circuit 61 to correct the tuning frequency shift due to temperature. Variations in the tuning frequency of each reader / writer device are also corrected at the same time.

  With such a configuration, the tuning frequency of the reader / writer can be kept constant regardless of the temperature change, and short-distance wireless communication with the RFID device can always be performed satisfactorily.

It is a block diagram which shows the example of the RFID apparatus by the 1st Embodiment of this invention. It is a block diagram which shows the example of the temperature detection part of the 1st Embodiment of this invention. It is a flowchart which shows the example of a recording of the correction value by the 1st Embodiment of this invention. It is a flowchart which shows the example of a correction process by the 1st Embodiment of this invention. It is a characteristic view which shows the temperature correction characteristic example by the 1st Embodiment of this invention. It is a characteristic view which shows the example of the characteristic corrected by the 1st Embodiment of this invention. It is a block diagram which shows the modification of the 1st Embodiment of this invention. It is a block diagram which shows the example of the reader / writer by the 2nd Embodiment of this invention. It is a block diagram which shows an example of the conventional RFID apparatus. It is a block diagram which shows an example of the conventional reader / writer. It is a characteristic view which shows the example of the relationship between a tuning frequency in the case of having the conventional temperature characteristic, and a communicable distance.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Loop antenna part, 12 ... Tuning capacitor, 13 ... Rectifier diode, 14 ... RFID circuit block, 15 ... Radio telephone circuit block, 21 ... RFID communication circuit block, 22 ... Transmission block, 23 ... Modulation circuit, 24 DESCRIPTION OF SYMBOLS ... Drive circuit, 25 ... Tuning part, 26 ... Antenna, 27 ... Reception block, 28 ... Filter, 29 ... Amplifier, 31 ... Capacitor, 32 ... Variable capacitance diode, 33 ... Control part, 34 ... Temperature detection part, 35 ... Memory 36, resistor, 37, thermistor, 38, analog / digital converter, 41, 42, 43 ... switch, 51, 52, 53 ... capacitor, 61 ... tuning unit, 62 ... control unit, 63 ... temperature detection unit, 64 ... Memory

Claims (5)

In an RFID device that detects a carrier wave of a predetermined frequency output from a reader / writer and performs short-range wireless communication,
An antenna for wireless communication with the reader / writer;
A tuning unit connected to the antenna;
A communication processing unit for processing a signal tuned by the tuning unit;
A temperature detector;
An RFID device comprising: a frequency shift unit that shifts a frequency to be tuned by the tuning unit according to a temperature detected by the temperature detection unit. The RFID device according to claim 1, wherein
The frequency shift unit is composed of a variable capacitance diode connected in parallel with a capacitor constituting the tuning means,
An RFID apparatus, wherein a capacitance value of the variable capacitance diode is controlled according to a temperature detected by the temperature detection unit. The RFID device according to claim 1, wherein
A first capacitor and a second capacitor connected in parallel to the antenna;
The first capacitor is the tuning unit, the second capacitor is the frequency shift unit,
An RFID device characterized in that the second capacitor is selectively connected in accordance with the temperature detected by the temperature detector. The RFID device according to claim 1, wherein
An RFID apparatus comprising: a storage unit that stores data corresponding to the temperature detection unit and a frequency shift amount in the frequency shift unit. In a reader / writer device that transmits a carrier wave of a predetermined frequency, detects a response wave from the RFID device, and performs short-range wireless communication,
An antenna for wireless communication with the RFID device;
A tuning unit connected to the antenna;
A transmission signal processing unit for transmitting the carrier wave from the antenna;
A reception processing unit for processing a reception signal tuned by the tuning means;
A temperature detector;
A reader / writer device comprising: a frequency shift unit that shifts a frequency to be tuned by the tuning unit according to the temperature detected by the temperature detecting hand unit.

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