JP2011028380A - Rfid communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate impedance mismatching while preventing a structure from being enlarged. <P>SOLUTION: An RFID communication device includes an antenna for radio communication with an IC tag, and an internal circuit for processing a signal transmitted or received through the antenna. The RFID communication device further includes, between the antenna and the internal circuit, a first conversion unit for performing impedance conversion at a first conversion rate, a second conversion unit for performing impedance conversion at a second conversion rate, and a switching unit for switching between the first and second conversion units for impedance conversion. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an RFID communication apparatus.

  2. Description of the Related Art Conventionally, an RFID system that transmits and receives data without contact using a radio signal has been proposed. FIG. 8 is a schematic block diagram showing the configuration of a conventional RFID system. When an instruction is sent from the host control unit P10 to the control unit P301 to read the data recorded in the IC tag P20, the control unit P301 generates the contents of the question to the IC tag P20. The transmission unit P302 generates a request signal corresponding to the contents of the question, the directional coupling unit P307 passes the request signal to the antenna P304 side, and the antenna P304 radiates the request signal to the space as a radio wave. The IC tag P20 uses the load modulation to record information on the radio wave and transmits it as a response signal to the antenna P304. The response signal returned to the antenna P304 passes through the directional coupler P307 and enters the receiver P305 and is demodulated. The control unit P301 receives the demodulated data from the reception unit P305, and generates response data to be transmitted to the host control unit P10.

  The matching circuit P303 is a circuit for impedance matching between the antenna P304 and the internal circuits (the transmission unit P302 and the reception unit P305). If impedance matching is not achieved, the request signal output from the transmission unit P302 is not radiated sufficiently from the antenna P304 and is reflected by the antenna P304. In a general wireless device, in order to sufficiently radiate the power of a signal generated in an internal circuit from an antenna, it is generally performed to adjust the impedance value to an optimum value to obtain impedance matching.

  However, when a metal body or dielectric (such as plastic or human body) approaches the antenna P304, impedance matching that has been achieved until then is shifted. If the impedance matching is shifted, the request signal output from the transmission unit P302 is reflected by the antenna P304 and enters the reception unit P305 as described above. If the level of the request signal entering the receiving unit P305 exceeds the allowable input level of the receiving unit P305, the receiving unit P305 cannot normally receive the response signal from the IC tag P20 that should be received. Further, since the impedance matching is deviated, the antenna P304 cannot sufficiently receive the radio wave of the response signal from the IC tag P20. Furthermore, if the impedance matching is shifted, the request signal output from the transmission unit P302 is not sufficiently radiated from the antenna P304, so that sufficient power is not supplied to the IC tag P20 and the IC tag P20 does not operate. sell. In an RFID system that transmits and receives data without contact, the IC tag P20 varies depending on the user, such as when it is extremely close to the antenna P304 or when it is held at a certain distance from the antenna P304. The deviation in impedance matching becomes a factor that increases the reading error of the IC tag P20.

  For such problems, the intensity of the signal reflected from the antenna P304 is measured, the impedance matching deviation is detected based on the measured signal intensity, and the impedance matching is adjusted according to the detection result. The technique to do is proposed (refer patent document 1).

JP 2001-060841 A

  However, the conventional technique described in Patent Document 1 requires a configuration for detecting a signal reflected from the antenna P304 and a configuration for feeding back the detection result to impedance adjustment. The overall configuration is increased in size and cost. There was a problem of increasing.

  In view of the above circumstances, an object of the present invention is to provide an RFID communication apparatus that can eliminate the mismatch of impedance matching while suppressing an increase in size of the configuration.

  One embodiment of the present invention is an RFID communication device including an antenna for performing wireless communication with an IC tag, and an internal circuit that processes a signal transmitted through the antenna or a signal received through the antenna. A first converter that performs impedance conversion at a first conversion ratio, a second converter that performs impedance conversion at a second conversion ratio, and the first converter between the antenna and the internal circuit. And a switching unit that switches between impedance conversion by the second conversion unit and impedance conversion by the second conversion unit.

  One aspect of the present invention is the above-described RFID communication device, wherein the switching unit performs switching every time an instruction for wireless communication is received from another device.

  One aspect of the present invention is the above-described RFID communication apparatus, further comprising a determination unit that determines whether or not wireless communication by the internal circuit and the antenna is successful, and the switching unit performs wireless communication in the determination unit. The switching is performed when it is determined that the above has not been successful.

  According to the present invention, it is possible to eliminate an impedance matching shift while suppressing an increase in size of the configuration.

1 is a system configuration diagram showing a system configuration of an RFID system. It is a circuit diagram showing the specific example of a switching circuit. It is a circuit diagram showing the equivalent circuit of the ON state and OFF state of a switching circuit. It is a flowchart showing operation | movement of the RFID communication apparatus by which the 1st control method was mounted. It is a flowchart showing operation | movement of the RFID communication apparatus by which the 2nd control method was mounted. It is a circuit diagram of the modification of a switching circuit. It is a schematic block diagram showing the modification of an RFID communication apparatus. It is a schematic block diagram showing the structure of the conventional RFID system.

FIG. 1 is a system configuration diagram showing a system configuration of an RFID (Radio Frequency IDentification) system 1. The RFID system 1 includes a host control unit 10, an IC (Integrated Circuit) tag 20, and an RFID communication device 30.
The host control unit 10 transmits a read command to the RFID communication apparatus 30 and receives response data including data recorded in the IC tag 20 from the RFID communication apparatus 30 as a response. The host control unit 10 may be provided in a general-purpose information processing device such as a personal computer connected to the RFID communication device 30, or may be used for a specific purpose such as a cash register, a vending machine, an automatic ticket gate device, or a mobile phone. It may be provided in the apparatus for. Specifically, the host control unit 10 may be realized by executing a host control program by a CPU (Central Processing Unit) provided in each of the above devices, or may be realized as dedicated hardware. good.

The IC tag 20 receives radio waves (request signals) radiated from the RFID communication device 30 and puts data (hereinafter referred to as “IC tag data”) recorded in a recording device provided in the IC tag 20. Transmitting radio waves (response signals). The response signal is a high-frequency analog signal and includes encoded IC tag data.
The RFID communication device 30 includes a control unit 301, a transmission unit 302, a matching circuit 303, an antenna 304, a reception unit 305, a switching circuit 306, and a directional coupling unit 307. Hereinafter, each functional unit included in the RFID communication device 30 will be described.

  When receiving a read command from the host control unit 10, the control unit 301 generates predetermined data (request data) for receiving data recorded on the IC tag 20 from the IC tag 20 and supplies the data to the transmission unit 302. In addition, when the control unit 301 receives the data received from the IC tag 20 from the reception unit 305, the control unit 301 generates response data for notifying the host control unit 10 of the received data, and sends the response data to the host control unit 10. Send to. In addition, the control unit 301 performs control processing for the switching circuit 306. Details of the control processing of the switching circuit 306 will be described later.

  When receiving the request data from the control unit 301, the transmission unit 302 generates a signal (request signal) to be transmitted to the IC tag 20 based on the request data. Then, the transmission unit 302 supplies the request signal to the antenna 304 via the directional coupling unit 307, the matching circuit 303, and the switching circuit 306.

  The matching circuit 303 (first conversion unit) is a circuit that performs impedance conversion in order to achieve impedance matching between the antenna 304 and the internal circuits (the transmission unit 302 and the reception unit 305). The conversion ratio n1 (first conversion ratio) of the impedance conversion in the matching circuit 303 is the RFID communication apparatus in the state where there is no dielectric such as plastic or human body, the IC tag 20, or metal near the RFID communication apparatus 30. 30 is designed to be in a state where impedance matching is achieved.

  The antenna 304 radiates a signal received from the transmission unit 302 via the directional coupling unit 307, the matching circuit 303, and the switching circuit 306. The antenna 304 receives the response signal radiated from the IC tag 20 and supplies the received response signal to the reception unit 305 via the switching circuit 306, the matching circuit 303, and the directional coupling unit 307.

When receiving the response signal from the antenna 304, the receiving unit 305 demodulates the response signal and supplies the demodulated data to the control unit 301. The demodulated data is a digitized signal and includes encoded IC tag data.
The switching circuit 306 includes a circuit that performs impedance conversion in order to achieve impedance matching between the antenna 304 and the internal circuit, and a switch that switches whether to perform impedance conversion according to a control signal received from the control unit 301. When the switching circuit 306 performs impedance conversion (in an ON state described later), impedance matching between the internal circuit and the antenna 304 is realized by impedance conversion by the switching circuit 306 and the matching circuit 303 (second conversion unit). The In this case, the conversion ratio n2 (second conversion ratio) of the impedance conversion is the RFID communication apparatus 30 in a state where a dielectric such as plastic or a human body, the IC tag 20, metal, or the like exists in the vicinity of the RFID communication apparatus 30. It is designed to be in a state where impedance matching is taken.
The directional coupling unit 307 is configured using a circulator, a directional coupler, or the like, and passes a signal output from the transmission unit 302 to the matching circuit 303 and passes a signal output from the matching circuit 303 to the reception unit 305.

  FIG. 2 is a circuit diagram illustrating a specific example of the switching circuit 306. FIG. 3 is a circuit diagram illustrating an equivalent circuit of the switching circuit 306 in the on state and the off state. FIG. 3A shows an equivalent circuit when the switching circuit 306 is in an on state. FIG. 3B illustrates an equivalent circuit when the switching circuit 306 is in an off state.

  The switching circuit 306 includes an antenna side connector 311, an internal circuit side connector 312, a control unit side connector 313, a diode 314, an inductor 315, and a resistor 316. When supplying an ON signal to the control unit side connector 313, the control unit 301 applies a predetermined voltage to the control unit side connector 313. In this case, as shown in FIG. 3A, a forward bias is applied to the diode 314, a current flows through the diode 314, and the switch is closed. Then, the inductor 315 enters between the antenna 304 and GND, the impedance changes, and impedance conversion with the conversion ratio n2 occurs.

  On the other hand, when the control unit 301 does not supply an ON signal to the control side connector 313, no voltage is applied to the control unit side connector 313. In this case, as shown in FIG. 3B, no current flows through the diode 314, which is equivalent to a state where the switch is open. Further, a transmission signal flows between the antenna-side connector 311 and the internal circuit-side connector 312 and is AC-coupled because of AC coupling. Therefore, direct current from the control unit side connector 313 does not flow. Therefore, the inductor 315 does not enter between the antenna 304 and GND, the impedance does not change, and impedance conversion by the conversion ratio n2 does not occur. As described above, whether the control unit 301 performs impedance conversion with the conversion ratio n1 or impedance conversion with the conversion ratio n2 depending on whether or not the ON signal is supplied to the control unit side connector 313 of the switching circuit 306. Switch.

  FIG. 4 is a flowchart showing the operation of the RFID communication apparatus 30 in which the first control method is implemented. FIG. 5 is a flowchart showing the operation of the RFID communication device 30 in which the second control method is implemented. The RFID communication device 30 may be implemented with a first control method or a second control method. Hereinafter, the processing flow of each of the first control method and the second control method will be described.

  First, the operation of the RFID communication apparatus 30 in which the first control method is implemented will be described using FIG. When the control unit 301 receives a read command from the host control unit 10 (step S101), the control unit 301 switches the switch of the switching circuit 306 (step S102). In step S102, the control unit 301 switches to the off state when the current switching circuit 306 is in the on state, and switches to the on state when it is in the off state.

  Next, the control unit 301 executes the reading process by supplying the request data to the transmission unit 302 (step S103). In the reading process, the transmission unit 302 that has received the request data generates a request signal and causes the antenna 304 to emit the request signal. The receiving unit 305 demodulates the response signal received from the antenna 304 and supplies the demodulated data to the control unit 301. Next, the control unit 301 receives the demodulated data, generates response data, and transmits the response data to the host control unit 10 as a read result (step S104). The response data includes the decrypted IC tag data.

  In the first control method, the impedance matching may not be achieved in the process of step S103, and reading may fail. In that case, in the process of step S104, the control unit 301 transmits error data indicating that the reading has failed to the host control unit 10. When the host control unit 10 receives the error data, the host control unit 10 transmits the read command again. Therefore, the control unit 301 receives the reading command (step S101), and the state of the switching circuit 306 is switched to a state different from the previous time in the process of step S102. Then, impedance conversion is performed at a conversion ratio different from the previous time, and reading processing (step S103) is performed.

  Next, operation | movement of the RFID communication apparatus 30 by which the 2nd control method was mounted is demonstrated using FIG. In the second control method, when the control unit 301 receives a read command from the host control unit 10 (step S101), the control unit 301 executes the reading process by supplying request data to the transmission unit 302 (step S201). In the reading process, the transmission unit 302 that has received the request data generates a request signal and causes the antenna 304 to emit the request signal. The receiving unit 305 demodulates the response signal received from the antenna 304 and supplies the demodulated data to the control unit 301.

  Next, the control unit 301 determines whether the reading process has been successful and the demodulated data has been normally received (step S202). When the reading process is successful and the data after normal demodulation is received (step S202-YES), the control unit 301 receives the demodulated data, generates response data, and uses the response data as a read result as the host control unit 10 (Step S104).

  On the other hand, when the reading process is not successful in step S202 and the demodulated data has not been received normally (NO in step S202), the control unit 301 switches the state of the switching circuit 306 (step S102). At this time, the control unit 301 switches to the off state when the current switching circuit 306 is in the on state, and switches to the on state when it is in the off state. Next, the control unit 301 executes the reading process by supplying the request data to the transmission unit 302 (step S103). Next, the control unit 301 receives the demodulated data, generates response data, and transmits the response data as a read result to the host control unit 10 (step S104).

  In the second control method, when the impedance matching is not achieved in the process of step S201 and the reading fails, the switching circuit 306 is set to the previous state in the process of step S102 without transmitting error data to the host controller 10. Can be switched to different states. Then, impedance conversion is performed at a conversion ratio different from the previous time, and reading processing (step S103) is performed.

  In the RFID communication device 30 configured as described above, the configuration (mainly the control unit 301 in the above case) that mainly controls the switching circuit 306 and the switching circuit 306 is increased as compared with the configuration of the conventional RFID communication device. As is apparent from FIGS. 2 and 3, these configurations can be easily made smaller than the configuration for detecting the signal reflected from the antenna and the configuration for feeding back the detection result to the impedance adjustment. it can. Therefore, it is possible to eliminate the impedance matching shift while suppressing an increase in the size of the configuration. As the impedance matching shift is eliminated as described above, the RFID communication device 30 can stably perform the reading process on the IC tag 20 in a wide range.

  In addition, when the first control method is adopted, the configuration for determining whether or not the reading is successful in the RFID communication apparatus 30 is not required, and therefore the configuration of the control unit 301 is compared with the second control method. It becomes simpler and can be made smaller. Further, in this case, since it is not necessary to determine whether or not the reading is successful, the response data can be transmitted to the host control unit 10 quickly when the first reading is successful.

  Further, when the second control method is adopted, it is determined whether or not the reading is successful in the RFID communication apparatus 30. If the reading is unsuccessful, the switching circuit 306 is switched based on the determination of the control unit 301. For this reason, when the reading fails, the switching of the switching circuit 306 is executed without sending another read command from the host control unit 10 botheringly. Accordingly, the types of conversion ratios of the impedance conversion of the reading process performed in response to one reading command increase, and the reading range of the IC tag becomes wide.

<Modification>
In the switching circuit 306, the portion of the inductor 315 may be configured by replacing with a capacitor, or may be configured by a combination of an inductor and a capacitor.
In step S104 of the first control method in FIG. 4, the demodulated data recognized by the control unit 301 may be generated as response data as it is and transmitted to the host control unit 10. In this case, the host control unit 10 determines whether the response data has failed to be read. If the host control unit 10 determines that the read has failed, the host control unit 10 transmits the read command again.

  The impedance conversion conversion ratio n1 in the matching circuit 303 is such that impedance matching in the RFID communication device 30 can be achieved in the presence of a dielectric such as plastic or a human body, the IC tag 20, or metal in the vicinity of the RFID communication device 30. It may be designed to be in a state of being. In this case, the conversion ratio n2 of impedance conversion by the switching circuit 306 and the matching circuit 303 when the switching circuit 306 is in the ON state is a dielectric such as plastic or a human body near the RFID communication device 30, the IC tag 20, The RFID communication device 30 is designed so that impedance matching is achieved in the absence of metal or the like.

  FIG. 6 is a circuit diagram of a modification of the switching circuit 306. The switching circuit 306 may be configured to include a plurality of sets of the control unit side connector 313, the diode 314, the inductor 315, and the resistor 316 between the antenna side connector 311 and the internal circuit side connector 312. In the case of FIG. 6, between the antenna side connector 311 and the internal circuit side connector 312, a set of a control unit side connector 313a, a diode 314a, an inductor 315a, and a resistor 316a, a control unit side connector 313b, a diode 314b, and an inductor 315b. And a set of resistors 316b and a total of two sets. With this configuration, by turning on or off the diodes 314 in each set, the conversion ratio of the impedance conversion in the switching circuit 306 can be selected and switched from more values. In this case, the value of the inductor 315 in each set may be configured to be different or may be configured to the same value.

  FIG. 7 is a schematic block diagram illustrating a modified example of the RFID communication device 30. The RFID communication apparatus 30 includes a matching circuit 303a connected to the transmission unit 302, a switching circuit 306a, an antenna 304a (hereinafter collectively referred to as “transmission side circuit”), and a matching circuit 303b connected to the reception unit 305. The switching circuit 306b and the antenna 304b (hereinafter collectively referred to as “reception side circuit”) may be configured as separate circuits. When the physical distance between the antenna 304a of the transmitting circuit and the antenna 304b of the receiving circuit is short, an impedance matching shift occurs in both the transmitting circuit and the receiving circuit by approaching the IC tag. . Therefore, when the physical distance between the antennas 304a and 304b is close as described above, the control unit 301 switches both switches of the switching circuit 306a and the switching circuit 306b. On the other hand, if the physical distance between the antenna 304a of the transmitting circuit and the antenna 304b of the receiving circuit is long, the IC tag approaches either the antenna 304a of the transmitting circuit or the antenna 304b of the receiving circuit. The impedance matching shift differs between the transmission side circuit and the reception side circuit. For this reason, when the physical distance between the two antennas 304a and 304b is long as described above, the control unit 301 switches either the switch circuit 306a or the switch circuit 306b. Alternatively, the switching circuit 306a may be provided only in the transmission side circuit, and the switching circuit 306b may not be provided in the reception side circuit. The switching circuit 306b may be provided only in the reception side circuit, and the switching circuit 306a may not be provided in the transmission side circuit.

  In addition, the antenna side connector 311, the internal circuit side connector 312, and the control unit side connector 313 shown in FIGS. 2, 3, and 6 are configurations for the case where the switching circuit 306 is configured independently. Not a required configuration. For example, when the switching circuit 306 is configured to be connected to an antenna, an internal circuit, or a control unit without using a connector, each of the connectors is not necessary.

The RFID communication device 30 in the above description is a specific example of a device having a control unit 301 that controls the switching circuit 306 and the switching circuit 306. Therefore, the control unit 301 and the switching circuit 306 that control the switching circuit 306 may be provided in another wireless communication device.
The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Host control part (other apparatus), 20 ... IC tag, 30 ... RFID communication apparatus, 301 ... Control part (switching part, determination part), 302 ... Transmission part (internal circuit), 303 ... Matching circuit (1st) Conversion unit, second conversion unit), 304 ... antenna, 305 ... receiving unit (internal circuit), 306 ... switching circuit (second conversion unit, switching unit), 307 ... directional coupling unit, 311 ... antenna side connector, 312 ... Internal circuit side connector, 313 ... Control unit side connector, 314 ... Diode, 315 ... Inductor, 316 ... Resistance

Claims (3)

An RFID communication device comprising an antenna for wireless communication with an IC tag, and an internal circuit for processing a signal transmitted via the antenna or a signal received via the antenna,
Between the antenna and the internal circuit,
A first conversion unit that performs impedance conversion at a first conversion ratio;
A second conversion unit that performs impedance conversion at a second conversion ratio;
A switching unit that switches between impedance conversion by the first conversion unit or impedance conversion by the second conversion unit;
An RFID communication device comprising:   The RFID communication apparatus according to claim 1, wherein the switching unit performs switching every time a wireless communication instruction is received from another apparatus. A determination unit for determining whether or not wireless communication by the internal circuit and the antenna is successful;
The RFID communication apparatus according to claim 1, wherein the switching unit performs switching when the determination unit determines that wireless communication has not been successful.

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