JP2021043663A - RFID reader device and RFID tag - Google Patents

Abstract

To response to a question wave with a simple configuration while avoiding collision.SOLUTION: An RFID reader device according to an embodiment comprises a transmission unit and a receiving unit. The transmission unit transmits a question wave obtained by modulating a carrier wave by a periodic signal, and the receiving unit receives a response wave from an RFID tag that responses with back-scatter modulation when a signal within a specific frequency range is detected from a demodulated signal of the question wave.SELECTED DRAWING: Figure 8

Description

The present invention relates to an RFID reader device and an RFID tag using RFID (Radio Frequency Identification) technology.

Send at least three commands, Select, Query, and Ack, from the RFID reader device to the RFID tag. Then, each RFID tag recognizes these commands and responds to the RFID reader device. This avoids the situation where the responses of the RFID tags collide with each other, and the RFID reader device can respond and recognize them individually. In order to avoid such response collisions, RFID tags required a semiconductor chip on which a processor and firmware were mounted.

Japanese Unexamined Patent Publication No. 2012-068769

By the way, recently, printed electronics (PE) technology has been attracting attention. With the PE technology, it is difficult to achieve high integration, and it is difficult to mount the semiconductor chip as described above. For this reason, it has been difficult for RFID tags that employ PE technology to individually respond to questions from reader devices while avoiding collisions.

An object of the present invention is to provide an RFID reader device and an RFID tag capable of suppressing response collision between RFID tags without using a command between the RFID reader device and the RFID tag.

The RFID reader device according to the embodiment includes a transmitting unit and a receiving unit. The transmitter transmits an interrogation wave in which the carrier wave is modulated by a periodic signal, and the receiver responds by backscatter modulation when a signal in a specific frequency range is detected from the demodulated signal of the interrogation wave. Receive waves.

It is a figure which shows an example of the schematic structure of the RFID reader device which concerns on embodiment. It is a figure which shows an example of the schematic structure of the RFID tag which concerns on embodiment. It is a figure which shows an example of the ID signal transmitted by the RFID tag which concerns on embodiment. It is a sequence diagram for demonstrating the operation of the RFID system which concerns on embodiment. It is a figure for demonstrating the modulation of the carrier wave performed by the RFID reader apparatus which concerns on embodiment. It is a figure for demonstrating the example of the sweep performed by the RFID reader device which concerns on embodiment. It is a figure for demonstrating the detection operation of the periodic signal performed by the RFID tag which concerns on embodiment. It is a figure for demonstrating the operation of the RFID system which concerns on embodiment.

Hereinafter, the RFID system according to the embodiment will be described with reference to the drawings. This RFID system includes an RFID reader device and an RFID tag.

(Configuration of RFID reader device)
FIG. 1 is a circuit block diagram showing a configuration example of an RFID reader device according to an embodiment. This RFID reader device includes a control unit 1, a baseband signal processing unit 2, a D / A converter (D / A) 3, an orthogonal modulator 4, a local oscillator 5, a transmission amplifier 6, a circulator 7, an antenna 8, and a low noise amplifier. (LNA) 9, an orthogonal detector 10, an A / D converter (A / D) 11, and an external interface circuit 12 are provided. With these configurations, a control system, a transmission system (transmission unit), a reception system (reception unit), and the like are configured respectively.

Specifically, the transmission system is mainly composed of a baseband signal processing unit 2, a D / A converter 3, a quadrature modulator 4, a local oscillator 5, a transmission amplifier 6, a circulator 7, and an antenna 8. The receiving system is mainly composed of an antenna 8, a circulator 7, a low noise amplifier 9, an orthogonal detector 10, a local oscillator 5, an A / D converter 11, and a baseband signal processing unit 2.

The control unit 1 includes a CPU and a memory (storage unit), and controls the transmission system and the reception system in an integrated manner. Therefore, the control unit 1 is included in the transmission system and the reception system. Specifically, the control unit 1 controls transmission of a question wave addressed to the RFID tag, reception control of a response wave transmitted from the RFID tag, and the like in response to an instruction through the external interface circuit 12, for example.

The control unit 1 controls the baseband signal processing unit 2 so that the baseband signal output by the D / A converter 3 described later becomes a signal having periodicity (hereinafter, referred to as a periodicity signal). However, the details will be described later (see question wave transmission processing RT1 and the like).

The baseband signal processing unit 2 can be configured by, for example, a DSP (Digital Signal Processor). Then, the baseband signal processing unit 2 generates a digital baseband signal (hereinafter, referred to as a transmission digital baseband signal) corresponding to the transmission data given from the control unit 1 in accordance with the instruction from the control unit 1. , The received digital baseband signal, which will be described later, is decoded to acquire the received data.

The D / A converter 3 converts the transmission digital baseband signal into an analog baseband signal (hereinafter, referred to as a transmission analog baseband signal). This transmission analog baseband signal is the periodic signal described above. As described above, the details will be described in the description of the transmission operation of the RFID reader device.

The quadrature modulator 4 modulates the carrier wave generated by the local oscillator 5 with the transmission analog baseband signal to generate an amplitude modulated wave. The frequency of the carrier wave generated by the local oscillator 5 is, for example, the 900 MHz band. This frequency is controlled by a frequency control signal given from the control unit 1.

The transmission amplifier 6 RF-amplifies the amplitude-modulated wave. This RF amplified signal is radiated into space from the antenna 8 via the circulator 7 as a question wave for the RFID tag.
On the other hand, the antenna 8 receives the response wave (response signal to the question wave) transmitted from the RFID tag described later, and outputs the response wave to the low noise amplifier 9 via the circulator 7.

The low noise amplifier 9 amplifies the response signal with low noise and outputs it to the orthogonal detector 10.
The orthogonal detector 10 directly converts the low noise amplified response signal into an analog baseband signal using the local oscillation signal generated by the local oscillator 5.

The A / D converter 11 A / D-converts the analog baseband signal demodulated by the direct conversion to obtain the received digital baseband signal. The received digital baseband signal is decoded into the information sent from the RFID tag by the baseband signal processing unit 2 and output to the control unit 1.

Various devices can be connected to the external interface circuit 12, and the external interface circuit 12 serves as an interface between these devices and the control unit 1. For example, the information input by the operator through the device or the instruction signal emitted from the device is given to the control unit 1, or the information given by the control unit 1 is output to the outside.

Here, as an example of the modulation method, the orthogonal type is taken as an example, but the present invention is not limited to this. Other modulation methods may be used as long as communication is possible between the RFID reader device and the RFID tag. For example, it is also possible to apply a single mixer type.

(Structure of RFID tag)
FIG. 2 is a circuit block diagram showing a configuration example of an RFID tag according to an embodiment. This RFID tag includes an antenna 21, a detector 22, a low-pass filter (LPF1) 23, a PLL circuit 24, an ID transmission circuit 29, a high frequency switch (SW) 30, and a smoothing circuit (LPF2) 31. With these configurations, a radio rectification type power supply unit, a periodic signal detection unit, a backscatter transmission unit, and the like are respectively configured.

Specifically, the radio wave rectification type power supply unit is mainly composed of an antenna 21, a detector 22, and a smoothing circuit 31. The periodic signal detection unit is mainly composed of a detector 22, a low-pass filter 23, and a PLL circuit 24. The backscatter transmitter is mainly composed of an ID transmission circuit 29, a high frequency switch 30, and an antenna 21.

The antenna 21 is for exchanging a radio signal with the antenna 8 of the RFID reader device. An example of the configuration is, for example, a dipole antenna having two elements. The length of each element of the dipole antenna corresponds to approximately 1/4 wavelength of the radio signal (question wave) transmitted by the RFID reader device, and corresponds to 1/2 wavelength as a whole.
The detector 22 detects a desired radio signal, that is, a question wave transmitted from the RFID reader device, demodulates the signal wave, and extracts the signal wave.

The smoothing circuit 31 is, for example, a low-pass filter, which converts the signal wave into a DC signal. This DC signal is used as the operating current of each part of the RFID tag such as the PLL circuit 24, the ID transmission circuit 29, and the high frequency switch 30, which will be described later.
The low-pass filter 23 filters the high-frequency component of the signal wave and outputs a periodic signal used for modulation in the RFID reader device.

The PLL circuit 24 monitors that the frequency of the periodic signal enters the capture range. Then, when the frequency of the periodic signal enters the capture range, the PLL circuit 24 draws in and locks the oscillation frequency of the locally oscillated signal that is oscillated internally, and outputs a Lock signal. The capture range is set in a narrow specific range centered on the self-propelled frequency of the built-in VCO (voltage controlled oscillator). This specific range is set in consideration of the manufacturing accuracy of the RFID tag, the operating environment, and the like.

As a specific configuration example of the PLL circuit 24, for example, a phase comparator 25, a VCO 26, a loop filter 27, and a lock determination circuit 28 are mainly provided. In the following description, the VCO 26 will be described as including a frequency divider.

The phase comparator 25 compares the phase of the periodic signal with the frequency-divided locally oscillated signal given from the VCO 26, and outputs the comparison result to the loop filter 27.

The VCO 26 oscillates a local oscillation signal having a frequency corresponding to the voltage of the VCO control signal given from the loop filter 27 described later. The VCO 26 also includes a frequency divider (not shown). This frequency divider divides the local oscillation signal and then outputs the frequency divider to the phase comparator 25.

The loop filter 27 generates a VCO control signal having a voltage value corresponding to the comparison result of the phase comparator 25. Then, the loop filter 27 controls the frequency of the local oscillation signal of the VCO 26 with this VCO control signal.
The lock determination circuit 28 observes the voltage value of the VCO control signal. Then, when the voltage value in the preset range is reached, the lock determination circuit 28 determines that the comparison result of the phase comparator 25 is in the phase lock state and outputs the Lock signal.

The ID transmission circuit 29 includes a shift register that stores ID information and the like uniquely set for the RFID tag. Then, the ID transmission circuit 29 enters an enable state when the Lock signal is given, uses the output of the VCO 26 as a Clock signal for driving the shift register, and uses the ID information, for example, the FM0 method or the mirror subcarrier method. Encode with. The result of this coding is output as an ID signal. FIG. 3 shows an example of the ID signal, which includes, for example, a synchronization signal, an identification code, and an error detection code.
The high-frequency switch 30 uses the ID signal to control the antenna 21 ON / OFF, and transmits a response wave addressed to the RFID reader device by backscatter modulation by the ON / OFF control.

(Explanation of operation)
Next, the operation of the RFID system having the above configuration will be described.
In actual operation, it is common that a plurality of RFID tags are present for one RFID reader device. In the following description, in order to simplify the operation, a case where two RFID tags Ta and Tb are present will be described as an example.

The RFID tags Ta and Tb may or may not be manufactured on the same production line. Further, it may or may not be manufactured based on the same standard. Even if both are manufactured on the same production line and based on the same standard, it is very difficult to completely match the reception characteristics of both, and the manufacturing time, difference in raw materials, manufacturing accuracy, and aging Due to various conditions such as changes, errors may occur in the reception characteristics.

Further, for example, the power supply voltage of the VCO 26 changes depending on the reception level of the carrier wave from the RFID reader device and the antenna posture of the RFID tag. Therefore, the probability that the self-propelled frequencies of the VCO 26 match between the RFID tags is low, and when the above-mentioned conditions are added, the probability that the self-propelled frequencies match is actually low.

FIG. 4 is a sequence diagram for explaining the operation from the RFID reader device transmitting the question wave to the two RFID tags Ta and Tb transmitting the response wave. Hereinafter, the operation of the RFID system will be described with reference to this figure.

(Transmission of question wave by RFID reader device)
First, the question wave transmission process RT1 by the RFID reader device will be described. The interrogation wave transmission process RT1 is started when the control unit 1 recognizes a transmission instruction through the external interface circuit 12 in, for example, an RFID reader device.

In the interrogation wave transmission process RT1, the RFID reader device transmits an interrogation wave whose carrier wave is amplitude-modulated using a periodic signal. Further, when transmitting this question wave, the frequency of the periodic signal is changed so as to sweep a predetermined range. As a result, the RFID reader device transmits a question wave whose envelope changes in response to the sweep to the RFID tags Ta and Tb. The RFID reader device transmits the question wave in the question wave transmission process RT1 while monitoring the arrival of the response wave from the RFID tag. The operation of receiving the response wave will be described later.

Hereinafter, the operation of each part in the RFID reader device will be described.
The control unit 1 controls the baseband signal processing unit 2 so that the transmission analog baseband signal output by the D / A converter 3 becomes, for example, a sine wave periodic signal as shown in FIG. 5 (c). To do. The sine wave is an example, and may be another waveform such as a rectangular wave as long as it has periodicity, and is not limited to the sine wave.

On the other hand, the carrier wave generated by the local oscillator 5 is as shown in FIG. 5A, for example. When the quadrature modulator 4 modulates this carrier wave with the periodic signal, an amplitude-modulated interrogation wave as shown in FIG. 5B can be obtained. The degree of modulation is preferably about 30% or less.

Further, the control unit 1 controls the baseband signal processing unit 2 to change the frequency of the periodic signal so as to sweep a predetermined range (hereinafter, referred to as a sweep process). This sweeping process changes the envelope of the interrogation wave output by the quadrature modulator 4.

Here, as the sweep process by the control unit 1, for example, as shown in FIG. 6A, continuous sweeping may be performed so that the frequency changes linearly with time, or is shown in FIG. 6B. As described above, the stepwise sweep may be performed so that the frequency changes stepwise with respect to time. In the case of this step sweep, for example, the range from 5 kHz to 6 kHz is changed in 2 Hz steps.

Further, for example, as shown in FIG. 6C, sweeping may be performed by excluding a specific frequency (hereinafter, referred to as exclusion sweeping). The specific frequency referred to here is a frequency obtained by obtaining a response wave from the RFID tag. Sweeps with such exclusions are not limited to continuous sweeps and may be applied to stepped sweeps. In the following description, the case of performing exclusion sweep will be described as an example.

(Reception of question wave and transmission of response wave by RFID tag)
Next, the inquiry wave reception processing T-Ra and T-Rb by the RFID tags Ta and Tb and the response wave reception processing T-Ta and T-Tb will be described.

First, the question wave reception processing T-Ra and T-Rb are started when the RFID tags Ta and Tb receive a radio signal from the RFID reader device, respectively. Specifically, in response to the supply of a direct current for driving each part from the smoothing circuit 31 by the reception of the radio signal, the reception is started respectively, and the above-mentioned question wave is received.

The operation of each part in the RFID tags Ta and Tb in this reception is as follows.
The PLL circuit 24 monitors whether or not the frequency of the signal output from the low-pass filter 23 is within the capture range. The sensitivities of the loop filter 27 and the VCO 26 are set so as to have a capture range having a width of about 2 Hz centered on the frequency obtained by dividing the self-propelled frequency of the VCO 26 by the frequency divider.

When the signal output from the low-pass filter 23 is a periodic signal transmitted from the RFID reader device, the frequency of the periodic signal is changed by the above-mentioned sweep process as shown in FIG. 7A, and in the process. Eventually it will enter the capture range. It is preferable that this capture range is set as narrow as possible in order to make the difference in response timing from other RFID tags remarkable.

Here, it is assumed that the RFID tag Ta detects the interrogation wave before the RFID tag Tb due to the difference in the VCO self-propelled frequency and the difference in the reception conditions of the RFID tags Ta and Tb.
In the RFID tag Ta, when the signal enters the capture range, that is, when the interrogation wave from the RFID reader device is detected, the interrogation wave reception process T-Ra is continued, while the response wave transmission process T-Ta is started. ..

In the response wave transmission process T-Ta, the PLL circuit 24 (lock determination circuit 28) outputs the Lock signal to the ID transmission circuit 29 when the signal enters the capture range. As a result, the ID transmission circuit 29 in the enabled state transmits an ID signal including its own ID as a response wave addressed to the RFID reader device by backscatter modulation.

At this time, the RFID tag Tb that has not detected the question wave from the RFID reader device continues the question wave reception process T-Rb. Later, when the RFID tag Tb detects the question wave, the response wave transmission process T-Tb is started. The response wave transmission process T-Tb is the same transmission process as the response wave transmission process T-Ta, but the response wave transmission process is due to the difference in the VCO self-propelled frequency and the difference in the reception conditions of the RFID tags Ta and Tb. It starts at a timing different from T-Ta, and it is rare that the timings match.

(Reception of response wave by RFID reader device)
Next, the operation of receiving the response wave by the RFID reader device will be described.
The received signal is orthogonally detected by the orthogonal detector 10. This detection result is converted into a received digital baseband signal by the A / D converter 11. This received digital baseband signal is decoded by the baseband signal processing unit 2. When the control unit 1 detects the response wave (ID signal) from the RFID tag Ta from this decoding result, the control unit 1 temporarily stops sweeping the periodic signal as shown in FIG. 7B. At this time, the sweep is stopped, but the transmission is performed, so that the operating current of the RFID tag is secured.

At this time, the RFID tag Ta that transmitted the response wave is in a state where the phase is locked by the PLL circuit 24. Then, the control unit 1 specifies the frequency of the periodic signal when the response wave is obtained, and records this frequency in the memory as the specific frequency. After that, when the control unit 1 determines from the decoding result that the reception of the response wave is completed, the control unit 1 restarts the stopped sweep in order to search for the RFID tag other than the RFID tag Ta, and the question wave transmission process R -Start T2.

The question wave transmission process R-T2 is almost the same as the question wave transmission process R-T1, except that exclusion sweep is performed. That is, the difference is that the baseband signal processing unit 2 is controlled so that the control unit 1 refers to the specific frequency recorded in the memory and performs sweeping except for the specific frequency. As a result, in the RFID reader device, for example, as shown in FIG. 6C, sweeping is performed excluding a specific frequency. In this figure, a case where a plurality of specific frequencies are excluded is illustrated.

On the other hand, at this time, the RFID tag Tb continues to perform the question wave reception process T-Rb. Eventually, when the exclusion sweep is started and the interrogation wave is received, the response wave transmission process T-Tb is started and the response wave (ID signal) is transmitted. Since the operation is the same as that of the response wave transmission process T-Ta, detailed description of the operation of each part will be omitted.

On the other hand, in the RFID reader device, when the response wave (ID signal) from the RFID tag Tb is received, the control unit 1 temporarily stops the sweep (exclusion sweep) as in the case of the RFID tag Ta described above (as in the case of the RFID tag Ta described above). (Transmission continues), the frequency of the periodic signal when the response wave is obtained is specified, and this frequency is recorded in the memory as a specific frequency. After that, when the reception of the response wave is completed, the control unit 1 restarts the stopped sweep in order to search for RFID tags other than the RFID tags Ta and Tb, and starts the interrogation wave transmission process RT3. ..
After that, in the same manner, the sweep excluding the specific frequency is performed, and the search for other RFID tags is continued.

(Summary)
As described above, in the RFID system having the above configuration, as shown in FIG. 8, the RFID reader device transmits a question wave in which the carrier wave is modulated by a periodic signal to the RFID tag, and the RFID tag responds to the question wave. When the question wave is demoted and a periodic signal is detected, the response wave (ID signal) is transmitted by backscatter modulation. Since there are differences in reception performance and reception environment between a plurality of RFID tags that are actually operated, for example, there is a difference in the self-propelled frequency of the VCO 26, the detection timing of the periodic signal among the plurality of RFID tags It is extremely rare that (the transmission timing of the response wave) is exactly the same.

Therefore, according to the RFID system having the above configuration, even if the RFID reader device sends a command to the RFID tag or the RFID tag does not interpret the command, the plurality of RFID tags send response waves at different timings to the RFID reader. Can be sent to the device. That is, even if the RFID tag is configured by a relatively simple circuit that does not have a CPU, for example, by adopting printed electronics technology, it is possible to operate a system that suppresses collision of response waves of a plurality of RFID tags.

Further, in the RFID system having the above configuration, when the RFID reader device sweeps the frequency of the periodic signal to detect the RFID tag, transmits a question wave, and starts receiving a response wave, the sweep is temporarily stopped. To do. Then, when the reception of the response wave is completed, the RFID reader device transmits the question wave by sweeping excluding the frequency from which the response wave was obtained. Since the question wave excluding the frequency from which the response wave was obtained is transmitted in this way, the search excluding the RFID tag that has already transmitted the response wave can be performed, and the RFID tag that has not yet transmitted the response wave can be efficiently searched. You can search.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

Further, for example, in the above embodiment, when the response wave is received and then the transmission of the interrogation wave is restarted, the sweep is performed by excluding a specific frequency, but the present invention is not limited to this. Absent. For example, when the response wave is received and then the transmission of the interrogation wave is resumed, the sweep may be performed by excluding a predetermined band including a specific frequency.

1 ... Control unit 2 ... Baseband signal processing unit 3 ... D / A converter 4 ... Orthogonal modulator 5 ... Local oscillator 6 ... Transmission amplifier 7 ... Circulator 8 ... Antenna 10 ... Orthogonal detector 11 ... A / D converter 12 ... External interface circuit 21 ... Antenna 22 ... Detector 23 ... Low-pass filter 24 ... PLL circuit 25 ... Phase-locked loop 27 ... Loop filter 28 ... Lock determination circuit 29 ... ID transmission circuit 30 ... High frequency switch 31 ... Smoothing circuit

Claims (5)

A transmitter that transmits a question wave whose carrier wave is modulated by a periodic signal,
A receiver that receives a response wave from an RFID tag that responds by backscatter modulation when a signal in a specific frequency range is detected from the demodulated signal of the interrogation wave.
An RFID reader device comprising. The RFID reader device according to claim 1, wherein the transmitter transmits a question wave while sweeping the frequency of the periodic signal stepwise or continuously. 2. The transmitting unit stops sweeping the frequency of the periodic signal when the receiving unit starts receiving the response wave, and then restarts the sweeping when the receiving unit finishes receiving the response wave. The RFID reader device described. It also has a storage unit that stores the frequency at which the sweeping of the periodic signal is stopped.
The RFID reader device according to claim 2 or 3, wherein when the sweep is restarted, the transmission unit performs the sweep excluding the frequency stored in the storage unit. An RFID tag that transmits a response wave when a question wave whose carrier wave is modulated by a periodic signal is received from an RFID reader device.
A detector that demodulates the received signal and
A detector that detects a signal in a specific frequency range from the signal demodulated by this detector,
An RFID tag including a transmitter that backscatter-modulates a question wave and transmits a response wave when the detector detects a signal.

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