JP2008099007A - Rfid reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a RFID reader which transmits a question radio wave, receives a response radio wave from a contactless identification tag and reads individual identification information, and whose amplification circuit is comprised of the amplification circuit having a few number of elements. <P>SOLUTION: The RFID reader 10 includes a detection circuit 12 to detect the response radio wave from the contactless identification tag received through an antenna 11 and to output a RF baseband signal, the amplification circuit 13 to amplify the RF baseband signal output from the detection circuit 12 and to output a RF output signal of a logic level, and an operation processing circuit 14 to extract the individual identification information recorded in the contactless identification tag from the RF output signal output from the amplification circuit 13. The amplification circuit 13 is constituted of an amplification stage 301 consisting of a transistor whose base is an input terminal of the RF baseband signal and whose emitter is grounded and whose collector is connected to a parallel resonance circuit 302 consisting of parallel circuits of an inductance and a capacitor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an RFID reader that reads identification information recorded on a contactless identification tag, and more particularly to an RFID reader that simplifies the configuration of an amplifier circuit that amplifies a signal obtained by removing a carrier wave from a received radio wave. It is.

  In recent years, in the field of logistics and goods management, it is possible to communicate wirelessly, record more information, and record more information, instead of using barcodes and barcode readers for individual identification of products and packages. The use of RFID (Radio Frequency Identification) systems using non-contact type identification tags (non-contact IC tags) that can be rewritten is expanding.

  An RFID element forms a resonance circuit by an antenna pattern provided on a base material such as paper, plastic, or an article body, and a capacitive element built in the antenna pattern and an IC chip, and through the antenna pattern, Operates at a specific resonant frequency. The RFID element is represented by a name such as a non-contact IC tag or a wireless IC tag depending on the shape or application of the base material. In the present specification, these are referred to as RFID elements.

  An RFID system for individual identification using an RFID element is disclosed in, for example, the following Patent Document 1 (Japanese Patent Laid-Open No. 2003-226434). In the system disclosed in Patent Document 1, an active RFID element is attached to a luggage transport box configured to be loaded on a transport vehicle in a state in which the luggage is placed. Information unique to the RFID element is written. The unique information is, for example, a manufacturing serial number. A reader is provided for reading unique information from an RFID element attached to the package carrying box, and the number of package carrying boxes is managed based on the unique information read by the reader. is there.

  An RFID element and an RFID reader used in such an RFID system are disclosed as an RFID system in, for example, the following Patent Document 2 (Japanese Patent Laid-Open No. 2000-49654). The RFID system disclosed in Patent Document 2 relates to a passive RFID system, and the antenna output power of the interrogation radio wave of the reader is reduced according to whether or not a response radio wave is received from the contactless identification tag. The control circuit is set as follows.

  The block diagram shown in FIG. 6 is a block diagram showing the configuration of a conventional RFID system disclosed in Patent Document 2. This RFID system includes a reader 100 that transmits an interrogation radio wave, and a contactless identification tag 200 that returns a response radio wave including identification information for individual identification when the interrogation radio wave is received from the reader 100. The reading apparatus 100 includes a transmission circuit 101 that generates a carrier wave, a transmission / reception antenna 102 that transmits the carrier wave as an interrogation radio wave and receives a response radio wave, and a reception circuit 103 that extracts identification information from the response radio wave received by the transmission / reception antenna 102.

  The non-contact identification tag 200 includes a transmission / reception antenna 201 that receives an interrogation radio wave and transmits a response radio wave, a reception circuit 202 that generates a clock signal CLK from the interrogation radio wave received by the transmission / reception antenna 201, and a rectifier circuit that converts the interrogation radio wave into electric power. 203, a control processing circuit 204 that outputs identification information when a clock signal CLK is input, and a transmission circuit 205 that multiplexes the identification information on the interrogation radio wave received by the transmission / reception antenna 201.

The transmission circuit 101 in the reading apparatus 100 outputs a carrier wave to the transmission / reception antenna 102, and the transmission / reception antenna 102 transmits this as an interrogation radio wave of frequency f1. The rectifier circuit 203 in the contactless identification tag 200 converts the interrogation radio wave received by the transmission / reception antenna 201 into electric power. When this power is supplied, the control processing circuit 204 starts operation. On the other hand, the reception circuit 202 generates a clock signal CLK from the interrogation radio wave received by the transmission / reception antenna 201.

  Then, when the clock signal CLK is input from the receiving circuit 202, the control processing circuit 204 reads identification information from an internal storage circuit (not shown). Subsequently, the transmission circuit 205 uses the interrogation radio wave received by the transmission / reception antenna 201 as a carrier wave, multiplexes the identification information thereon, and outputs the multiplexed information to the transmission / reception antenna 201. As described above, when the transmission circuit 205 performs FSK modulation of the carrier wave with the identification information, the frequency becomes f1 ± f2. In this way, the response radio wave having the frequency f1 ± f2 is transmitted from the transmission / reception antenna 201. Next, the receiving circuit 103 in the reading apparatus 100 extracts identification information from the response radio wave received by the transmission / reception antenna 102.

  Thus, by obtaining the identification information from the non-contact identification tag 200, it is possible to identify the non-contact identification tag 200 (or the object to which the non-contact identification tag 200 is attached). In such an RFID system, the interrogation radio wave transmitted from the reading device 100 is used as a carrier wave of identification information transmitted from the non-contact identification tag 200 to the reading device 100 and supplies driving power to the control processing circuit 204. It is also used as a feeding wave. A system in which the non-contact identification tag 200 does not have power supply means such as a battery is called a passive RFID system.

  In RFID readers that transmit interrogation radio waves to non-contact identification tags and read response radio waves from non-contact identification tags, the received radio waves received by the transmitting and receiving antennas are input to the detection circuit, and the carrier (carrier wave) is removed by the detection circuit. The amplified signal is amplified and identification information is extracted from the response radio wave. As this amplifier circuit, a common-emitter transistor amplifier circuit as shown in FIG. 7 is generally used for the reasons of easy adjustment, operational stability, and high amplification factor.

  The received radio wave (RF signal) received by the transmission / reception antenna is input to the amplification circuit 400 after the carrier wave is removed by the detection circuit 300 as shown in FIG. In order to obtain a required amplification factor, the amplifier circuit is amplified through multiple transistor amplification stages 401 to 403 in FIG. The signal amplified by the amplifier circuit is converted to a logic level signal by the comparator 500 and processed by an arithmetic control circuit such as a CPU at the subsequent stage. The amplification factor of each amplification stage is determined by the resistors R1 / R2 in FIG. 7, and theoretically, a target amplification factor can be obtained with one transistor amplification stage. However, in the case of a high-frequency signal such as an RF signal, In this case, a negative feedback is applied to the signal due to the feedback capacitance generated in the structure of the transistor, and a theoretical amplification factor cannot be obtained.

  For this reason, as shown in FIG. 7, it is set as the structure using the multistage transistor amplification stages 401-403. In order to amplify a weak signal without distortion, the amplifier circuit 400 is configured to perform a class A amplification operation by biasing the output point (OUT) of the transistor amplification stage at the midpoint of the power supply VCC, but processes the identification signal. In order to transmit a signal to an arithmetic control circuit such as a CPU in the subsequent stage, it is necessary to convert the amplified signal to a logic level, and the output of the final transistor amplification stage 403 is input to a high-frequency comparator 500 to obtain a logic level signal. It is configured to output as a signal.

JP 2003-226434 A (FIGS. 1 and 2) JP 2000-49654 A (FIGS. 1 and 2)

As described in the above prior art, the RFID reader in the RFID system has the following problems. That is,
(1) In order to amplify a high-frequency RF signal with a target amplification factor, an amplifier circuit using a multi-stage transistor amplification stage is required, and the number of elements increases.
(2) The influence of the coupling capacitor due to multi-stage amplification is increased, resulting in signal distortion.
(3) In order to amplify signals other than the RF signal, it is necessary to provide a separate pan-pass filter circuit in order to increase the signal-to-noise ratio (S / N ratio).
(4) The operating point of the amplification stage transistor changes depending on the ambient temperature and becomes unstable, and is easily affected by changes in the constants of the components.
(5) Since the operating point of the transistor in the amplification stage changes under the influence of a constant change due to aging of parts, the performance deteriorates with the passage of time.
(6) It is necessary to place the transistor in the amplification stage at the class A operating point, and an idle current is always required, resulting in power consumption.
(7) A high-frequency comparator circuit is required to make a weak signal after amplification a logic level signal, which increases the number of components and the circuit configuration.
There are problems as described above, and there arises a problem that the downsizing of the RFID reader is hindered and the cost is increased.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an RFID reader including an amplifier circuit with a small number of elements.

In order to solve the above-mentioned problem, the invention according to claim 1 of the present application is
In the RFID reader that transmits the interrogation radio wave to the non-contact identification tag, receives the response radio wave from the non-contact identification tag, and reads the individual identification information recorded on the non-contact identification tag,
A detection circuit that detects a response radio wave from a contactless identification tag received via an antenna and outputs an RF baseband signal; amplifies the RF baseband signal output from the detection circuit; and outputs a logic level RF output signal. An amplification circuit for outputting, and an arithmetic processing circuit for extracting individual identification information recorded in the non-contact identification tag from an RF output signal outputted from the amplification circuit, wherein the amplification circuit uses an RF baseband signal as a base And an amplifier output terminal and an emitter connected to the ground, and a parallel resonance circuit comprising a parallel circuit of an inductance and a capacitor connected to the collector. To do.

The invention according to claim 2 of the present invention is the RFID reader according to claim 1, wherein the RFID reader further modulates a resonator that generates a carrier wave and a carrier wave that is input from the resonator. A transmission driver / modulation circuit; and a resonance circuit that transmits an RF signal output from the transmission driver / modulation circuit to an antenna;
The arithmetic processing circuit inputs a carrier on / off control signal for controlling on / off of a carrier wave and a modulation signal to the transmission driver / modulation circuit, and the transmission driver / modulation circuit transmits an RF modulation signal for the contactless identification tag. The resonance circuit transmits the RF modulation signal to an antenna, and the antenna transmits an interrogation radio wave to the contactless identification tag.

  In the invention according to claim 1, the RFID reader detects a response radio wave from the non-contact identification tag received via the antenna and outputs an RF baseband signal, and an RF output from the detection circuit An amplifying circuit for amplifying a baseband signal and outputting a logic level RF output signal; an arithmetic processing circuit for extracting individual identification information recorded in the non-contact identification tag from the RF output signal output from the amplifying circuit; The amplifier circuit has a base as an input terminal for an RF baseband signal, a collector as an amplifier output terminal, an emitter stage installed transistor circuit, and a parallel circuit of an inductance and a capacitor connected to the collector And a parallel resonant circuit.

  By providing the amplifier circuit having such a configuration, the parallel resonant circuit resonates at the frequency of the RF baseband input, and the impedance at the time of resonance is ideally almost infinite, so that a very large amplification factor can be obtained. become able to. An amplified output that is twice the amplified output obtained by a normal transistor can be obtained by the counter electromotive force of the inductance. Accordingly, a logic level amplified output having a sufficient amplitude required by the subsequent arithmetic processing circuit (CPU) can be obtained, so that a conversion circuit such as a comparator circuit can be omitted.

  In the invention according to claim 2, in the RFID reader according to claim 1, the RFID reader further includes a resonator that generates a carrier wave and a transmission driver that modulates the carrier wave input from the resonator. A modulation circuit and a resonance circuit that transmits an RF signal output from the transmission driver and modulation circuit to an antenna, and the arithmetic processing circuit modulates a carrier on / off control signal for on / off control of the carrier wave A signal is input to the transmission driver / modulation circuit, the transmission driver / modulation circuit generates an RF modulation signal for the contactless identification tag, the resonance circuit transmits the RF modulation signal to an antenna, and the antenna An interrogation radio wave for the contactless identification tag is transmitted.

  According to such a configuration, the RFID reader transmits an interrogation radio wave to a non-contact identification tag present in the vicinity, receives a response radio wave from the non-contact identification tag, and is recorded on the non-contact identification tag The identification information can be read.

  Hereinafter, specific examples of the present invention will be described in detail with reference to examples and drawings. However, the embodiment shown below exemplifies an RFID reader for embodying the technical idea of the present invention, and is not intended to specify the present invention as the RFID reader of this embodiment. However, it is equally applicable to the RFID readers of other embodiments within the scope of the claims.

  FIG. 1 is a block diagram showing a configuration of an RFID reader 10 according to an embodiment of the present invention. As shown in FIG. 1, the RFID reader 10 includes an antenna 11, a detector circuit 12, an amplifier circuit 13, a CPU (arithmetic processing unit) 14, a resonator 15, a transmission driver / modulation circuit 16, and a resonance circuit 17. ing.

  The antenna 11 receives a transmission radio wave from a non-contact identification tag (not shown). The radio wave received by the antenna 11 is input to the detection circuit 12 and the carrier wave is removed. The RF baseband signal from which the carrier wave has been removed by the detection circuit 12 is input to the amplifier circuit 13 and amplified. As will be described later, this amplifier circuit has a circuit configuration capable of obtaining a predetermined amplification factor with a small number of elements and obtaining an amplified signal having an amplitude that does not require a high-frequency comparator for conversion to a logic level.

  Since the RF signal amplified by the amplifier circuit 13 is output as a signal having sufficient amplitude, it can be input to the arithmetic processing circuit (CPU) 14, and the arithmetic processing circuit 14 processes the input RF signal. Thus, the individual identification information recorded on the non-contact identification tag can be obtained. Therefore, unlike the conventional RF reader 10, there is no need for a high-frequency comparator circuit for converting an output signal amplified in the subsequent stage of the amplifier circuit into a logic level signal that can be processed by the arithmetic processing circuit.

  On the other hand, the transmission driver / modulation circuit 16 generates an inquiry signal for reading the individual identification information recorded in the non-contact identification tag (not shown). The arithmetic processing circuit (CPU) 14 supplies a modulation signal to the transmission driver / modulation circuit 16, and the transmission driver / modulation circuit 16 modulates the carrier wave supplied from the resonator 15 to generate an RF interrogation signal. The RF interrogation signal generated by the transmission driver / modulation circuit 16 is input to the resonance circuit 17 connected to the input winding of the antenna 11 and transmitted to the non-contact identification tag (not shown) via the antenna 11.

  Next, the configuration of each circuit in FIG. 1 will be described. 2 is a diagram showing a configuration of the detection circuit 12 in FIG. 1. FIG. 2 (a) is a detailed circuit configuration diagram of the detection circuit 12, FIG. 2 (b) is an RF input waveform, and FIG. Each of the RF baseband output waveforms is shown. The detection circuit 12 includes capacitors C1 and C2, diodes D1 and D2, and a resistor R1, and an RF response radio wave received by the antenna 11 is applied to the RF input terminal 21 and detected by the diodes D1 and D2, and the capacitor C2 and the resistor A carrier wave (13.56 MHz) is removed by an integrating circuit composed of R1, and an RF baseband signal is output to the RF baseband output terminal 22.

  FIG. 3 is a circuit configuration diagram showing a detailed configuration of the amplifier circuit 13 in FIG. The amplifying circuit 13 includes a transistor amplifying stage 301 having an amplifying output terminal 32 as a collector of the amplifying transistor Q1. A parallel resonant circuit 302 including a capacitor C2 and an inductance L1 is connected to the collector of the amplifying transistor Q1. The amplifier stage 301 is a grounded-emitter amplifier circuit in which the emitter of the transistor Q1 is grounded (connected to GND) via a resistor R3. A power supply voltage Vcc is applied to the power supply terminal 33. The base of the transistor Q1 is connected to the connection point of the resistors R1 and R2 connected in series, and is connected to the input terminal 31 via the capacitor C1. Both ends of the series circuit of the resistors R1 and R2 are connected to the power sources Vcc and GND.

  The RF baseband signal output from the detection circuit 12 is input to the input terminal 31 and amplified by the transistor Q1. An input waveform and an output waveform after amplification are shown at the input terminal 31 and the output terminal 32. At the time of amplification by the transistor Q1, the parallel resonant circuit 302 composed of C2 and L1 resonates at the frequency of the RF baseband input, and the impedance at the time of resonance is ideally almost infinite, so that a very large amplification factor can be obtained. . Then, by the back electromotive force of the inductance L1, it is possible to obtain an amplified output (see the waveform of the output terminal 32) that is twice the amplified output obtained by the normal transistor Q1. Therefore, since a logic level amplified output having a sufficient amplitude required by the subsequent arithmetic processing circuit (CPU) 14 can be obtained, a conversion circuit such as a comparator circuit is not required.

Since the amplifier circuit 13 is a circuit as described above, it has the following advantages. That is,
(1) In order to amplify a high-frequency RF signal with a target amplification factor, it is only necessary to use a single transistor amplification stage 301 having a parallel resonant circuit 302 by LC, no special elements are required, and component accuracy There is little influence by.
(2) Since there are few coupling capacitors by multi-stage amplification, signal distortion is small.
(3) Since the configuration of the amplifier circuit itself is a band-pass filter, the signal-to-noise ratio (S / N ratio) is good, and there is no need to provide a separate pan-pass filter circuit.
(4) Since the operation of the transistor Q1 in the amplification stage is similar to the ON-OFF operation, it is not affected by changes in the ambient temperature. In addition, the allowable range for the component constant is wide and hardly affected by the change in the constant.
(5) In addition, since it is not affected by changes in the constants of the components, the performance does not deteriorate even if the constants of the components change due to aging.
(6) Since the operation of the transistor Q1 in the amplification stage is close to the ON-OFF operation as in (4) above, no idle current is required and power consumption is small.
(7) An amplified output that is twice the amplified output obtained by the normal transistor Q1 can be obtained by the back electromotive force of the inductance L1. Accordingly, since a logic level amplified output having sufficient amplitude required by the subsequent stage arithmetic processing circuit (CPU) 14 can be obtained, a conversion circuit such as a comparator circuit is not required.

  The amplified output output from the collector (output terminal 32) of the amplification transistor Q1 is processed by the arithmetic processing circuit (CPU) 14, reads the individual identification information recorded in the non-contact identification tag, and is provided to an external utilization device. The At this time, since the amplified output is a logic level signal having sufficient amplitude as described above, it can be directly processed by the arithmetic processing circuit (CPU) 14.

  The transmission driver / modulation circuit 16 and the resonance circuit 17 are circuits for transmitting interrogation radio waves for reading the individual identification information recorded on the non-contact identification tag from the RFID reader 10. As these transmission driver / modulation circuit 16 and resonance circuit 17, circuits used in a conventional RFID system reader as shown in FIGS. 4 and 5, respectively, can be applied.

  As shown in FIG. 4, the transmission driver / modulation circuit 16 has an amplifier IC1 for amplifying a 13.56 MHz carrier current and an input terminal 41 to which a modulation signal is input from an arithmetic processing circuit (CPU) 14. Transistor Q1. The carrier wave output (RF output) amplified by the amplifier unit IC1 is input to the modulation transistor Q1 via the inductance L1 and the resistor R1, and an RF modulation signal is output from the connection point (output terminal 42) between the inductance L1 and the resistor R1. Is done.

  A carrier wave of 13.56 MHz is input from the resonator 15 to the input terminal 43 of the amplification unit IC1, and a carrier on / off control signal for controlling ON / OFF of the carrier wave from the arithmetic processing means (CPU) 14 is input to the input terminal 44. Entered. The carrier wave is current-amplified by the amplifier IC1, and at this time, an output twice as large as the power supply voltage (Vcc) is obtained as an RF output by the counter electromotive force of the inductance L1. When a modulation signal is input to the modulation transistor Q1 (input terminal 41), the signal is modulated with a modulation factor corresponding to the resistance value of the resistor R1, and an RF modulation output is output to the output terminal.

  The RF output output from the transmission driver / modulation circuit 16 is transmitted to the antenna 11 by the resonance circuit 17 shown in FIG. 5 and is used as an interrogation radio wave for reading the individual identification information recorded on the non-contact identification tag from the antenna 11. Sent to the contactless identification tag. As shown in FIG. 5, the resonance circuit 17 includes an antenna winding ANT and capacitors C 1 and C 2, and an RF output output from the transmission driver / modulation circuit 16 is input to an input terminal of the resonance circuit 17. The resonance circuit 17 is set to match the inductance component of the antenna winding ANT and the constants of the capacitors C1 and C2 so as to be a resonance point most suitable for 13.56 MHz.

As described above in detail, the RFID reader 10 according to the present invention uses the amplification circuit that amplifies the RF signal after the carrier wave is removed by the detection circuit as the input terminal for the RF baseband signal and amplifies the collector. The amplifier comprises an amplifying stage comprising an output terminal and a grounded emitter, and a parallel resonant circuit comprising a parallel circuit of an inductance and a capacitor connected to the collector.
Accordingly, the parallel resonant circuit resonates at the frequency of the RF baseband input, and the impedance at the time of resonance is ideally almost infinite, so that a very large amplification factor can be obtained. An amplified output that is twice the amplified output obtained by a normal transistor can be obtained by the counter electromotive force of the inductance. As a result, a logic level amplified output having a sufficient amplitude required by the subsequent arithmetic processing circuit (CPU) can be obtained, so that a conversion circuit such as a comparator circuit can be omitted.

It is a block diagram which shows the structure of the RFID reader concerning the Example of this invention. 2A and 2B are diagrams showing a configuration and waveforms of a detection circuit of the RFID reader shown in FIG. 1, FIG. 2A is a detailed circuit configuration diagram of the detection circuit, FIG. 2B is a diagram showing an RF input waveform, and FIG. (C) is a figure which shows RF baseband output waveform. It is a circuit block diagram which shows the structure of the amplifier circuit of the RFID reader shown in FIG. FIG. 2 is a circuit configuration diagram illustrating a configuration of a transmission driver / modulation circuit of the RFID reader illustrated in FIG. 1. It is a circuit block diagram which shows the structure of the resonance circuit of the RFID reader shown in FIG. It is a block diagram which shows the structure of the conventional RFID system. It is a circuit block diagram which shows the structure of the amplifier circuit generally conventionally used for the RFID reader.

Explanation of symbols

10. RFID reader 11 ... Antenna 12 ... Detection circuit 13 ... Amplification circuit 14 ... CPU (arithmetic processing unit)
15... Resonator 16... Transmission driver and modulation circuit 17... Resonance circuit 301... Transistor amplification stage Q 1. C2 ... Capacitor 31 ... Input terminal 32 ... Output terminal

Claims (2)

In the RFID reader that transmits the interrogation radio wave to the non-contact identification tag, receives the response radio wave from the non-contact identification tag, and reads the individual identification information recorded on the non-contact identification tag,
A detection circuit that detects a response radio wave from a contactless identification tag received via an antenna and outputs an RF baseband signal; amplifies the RF baseband signal output from the detection circuit; and outputs a logic level RF output signal. An amplification circuit for outputting, and an arithmetic processing circuit for extracting individual identification information recorded in the non-contact identification tag from an RF output signal outputted from the amplification circuit, wherein the amplification circuit uses an RF baseband signal as a base And an amplifier output terminal and an emitter connected to the ground, and a parallel resonance circuit comprising a parallel circuit of an inductance and a capacitor connected to the collector. RFID reader. The RFID reader further includes a resonator that generates a carrier wave, a transmission driver / modulation circuit that modulates the carrier wave input from the resonator, and an RF signal output from the transmission driver / modulation circuit to the antenna. And a resonant circuit that
The arithmetic processing circuit inputs a carrier on / off control signal for controlling on / off of a carrier wave and a modulation signal to the transmission driver / modulation circuit, and the transmission driver / modulation circuit transmits an RF modulation signal for the contactless identification tag. The RFID reader according to claim 1, wherein the resonance circuit transmits the RF modulation signal to an antenna, and the antenna transmits an interrogation radio wave to the contactless identification tag.

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