JP2011205632A - Radio tag apparatus, power reception circuit, and radio tag reading method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To read a radio tag apparatus, which is installed around a running path such as a road, from a remote site.SOLUTION: The invention relates to a radio tag apparatus having a power reception circuit for obtaining a boosted and rectified DC power supply voltage and an RF signal at a connecting point D between a capacitor 1 and a rectifying element D3 from an RF input signal supplied from a feed point C of a radio tag antenna and obtaining a boosted RF signal at a connecting point E between the rectifying element D3 and a short stub L7, a microprocessor U3, a data input circuit related thereto and a power supply control circuit. The radio tag apparatus further has a microstrip reflector L1, bisected microstrip power feeding elements L2 and L3 and microstrip waveguides L4-L6 as the radio tag antenna. A GND plate is disposed at an interval of about λ40 (λ is a wavelength of an electromagnetic wave) from L1 to L6, a structure tilting directivity from a front direction toward L4-L6 is provided. A reflection coefficient of the antenna is efficiently changed by variable impedance elements D1 and D2, and a tag response signal is redirected with a high gain.

Description

  The present invention relates to a passive or semi-passive type RFID tag device that does not require a battery, and in particular, an antenna structure having a beam tilted directivity, and an RF (Radio Frequency) signal received by the antenna is efficient. The present invention relates to a power receiving circuit that boosts and rectifies the signal, and a wireless tag reading technology that can be read from several tens of meters away.

  In ITS (Intelligent Transport Systems), the realization of an Advanced Cruise-Assist Highway Systems (AHS) for safe driving of vehicles is a particularly important issue. Warnings such as road freezing, lane sticking out, approaching guardrails, crosswinds, etc. need to be given to the driver in advance, and infrastructure maintenance and maintenance costs need not be huge. On the other hand, it is very effective if a passive wireless tag device that can be used by being embedded in a road or attached to a guardrail and can be read from a remote location (about 100 m) can be used.

  FIG. 1 shows a temperature recording device (Patent Document 1) which is a conventionally known technique. In this sensor tag device, electromagnetic induction is used for power supply to the tag and communication with the reader (501 is the reader side coil, 502 is the tag side coil, and the electromagnetic induction between 501 and 502 is used for power supply and communication. Only a communication distance of about several tens of centimeters. If you try to read temperature information from a car that runs with this tag embedded in the road, you will receive a road surface temperature (freezing warning) when the car comes directly above the tag sensor. It is difficult to take appropriate measures.

  Therefore, Patent Document 2 has developed a technology for a passive wireless tag with a sensor that can be read from a distance of several tens of meters. In this passive RFID tag device, a stub resonator and ladder boost rectifier circuit are used in the power receiving circuit, so that a high voltage can be supplied based on a weak signal received from the antenna, and power supply to the microprocessor can be achieved. The sensor device can detect power even when it does not receive radio waves from the reader, and can extend the wireless communication distance (about 30 m in the 2.45 GHz band).

JP 2000-258254 "Temperature recording device" Japanese Patent Application No. 2005-207464 “Sensor Tag, Sensor Tag Device, Power Receiving Circuit, Power Supply Method of Sensor Tag Device”

  However, in Patent Document 2, since the directivity of the tag antenna faces the front direction of the tag surface, it is difficult to read from the vehicle when embedded in a road surface or when used on a guard rail. FIG. 7 shows the installation status of the wireless tag device used in the driving support road system. When the RFID tag device is attached to the license plate and read from the following car, the RFID tag antenna may be in the front direction, but when it is attached to the road surface or guardrail and read from the car. Is preferably a tilted direction (an oblique direction) rather than a front direction of the RFID tag antenna (see FIG. 2). In addition, when making a RFID tag device in the 2.45GHz band (assigned frequency for RFID tags), it is necessary to use a high-Q capacitor of about 0.15pF for the boost rectifier circuit, which increases the cost of the RFID tag device. It made circuit implementation difficult.

  In order to solve the above problem, the present invention uses an antenna structure having a beam tilted directivity with high reading performance from an oblique direction, and a power receiving circuit that efficiently boosts and rectifies an RF signal received by the antenna. Makes it easy to read from the diagonal direction of the tag, and enables about 20 times step-up rectification operation without using a capacitor with a high Q value (less than 1 pF in the 2.45 GHz band). Provided is a technique for realizing a possible wireless tag device.

In order to achieve the above object, the power receiving circuit according to claim 1 is a power receiving circuit that boosts and rectifies an RF signal received by a radio tag antenna,
A capacitor C1, a rectifying element D3, and a short stub L7 are connected in series from an antenna feed point C provided on the feed element of the RFID tag antenna, and from an RF input signal supplied from the antenna feed point C, a capacitor C1 And a boosted rectified DC power supply voltage and an RF signal are obtained at a connection point D between the rectifier element D3 and a boosted RF signal is obtained at a connection point E between the rectifier element D3 and the short stub L7.

  The power receiving circuit according to claim 2 is the power receiving circuit according to claim 1, wherein the first boosted rectified DC power supply voltage is supplied from the connection point E between the rectifying element D3 and the short stub L7 via the rectifying element D4. By charging the capacitor C3 and charging the capacitor C2 with the second boosted rectified DC power supply voltage from the connection point D between the capacitor C1 and the rectifying element D3 via the resistor R3, two types of voltage sources are obtained, that is, D4 A positive voltage is obtained at a connection point G between C3 and C3, and a negative voltage is obtained at a connection point F between R3 and C2.

  The power receiving circuit according to claim 3 is the power receiving circuit according to claim 2, wherein the inversion logic circuit U1 detects a potential difference between the first power supply point G and the second power supply point F as a received signal, and is connected. The DC voltage boosted and rectified from the point G via the rectifying element D5 is charged into the capacitor C4 to be used as a power supply voltage for a circuit that performs data input and power supply control of the microprocessors U3 and U3.

  A power receiving circuit according to a fourth aspect is the power receiving circuit according to the first to third aspects, wherein the rectifying elements D3, D4, and D5 are Schottky barrier diodes.

  A radio tag device according to a fifth aspect includes the radio tag antenna and the power receiving circuit according to any one of the first to fourth aspects.

  The wireless tag device according to claim 6 is the wireless tag device according to claim 5, wherein the antenna for the wireless tag includes a microstrip reflector L1, two-divided microstrip feed elements L2 and L3, and a microstrip conductor. It has corrugators L4 to L6, and a GND plate is arranged at an interval of about λ / 40 from λ1 to L6 (λ is the wavelength of the electromagnetic wave), and the reflector L1 is about 3 to 5% than the feed element L2 + L3 The directors L4 to L6 are the same length and 3 to 5% shorter than the feeding elements L2 + L3, the strip conductor width of L1 to L6 is about λ / 10, and the arrangement interval of L1 to L6 is λ. The directivity is tilted from the front direction to the L4 to L6 direction by setting it to about / 5, and variable impedance elements D1 and D2 such as varactor diodes are connected between the feeding elements L2 and L3, and D1 and Return the response signal by changing the bias voltage of D2. And features.

  The wireless tag device according to claim 7 is the wireless tag device according to claim 6, wherein the wireless tag antenna, the power receiving circuit, and a circuit for performing data input and power control of the microprocessors U3 and U3 are provided. The RFID tag device has a second power supply F point connected to the antenna strip conductor L3 via a resistor R2, and a microprocessor U3 data output terminal Dout connected to the antenna strip conductor L2 via a resistor R1. , By efficiently changing the bias voltage of the variable impedance elements D1 and D2 in accordance with the output from the data output terminal Dout, the information output from the microprocessor U3 is returned to the reader on radio waves .

  The RFID tag device according to claim 8 is the RFID tag device according to claim 7, wherein the power of the microprocessor U3 is supplied from the OR circuit U2, and one input of the OR circuit U2 is supplied to the inverting logic circuit U1. Controlled by the output, the other input of the OR circuit U2 is connected to be controlled by the output of the microprocessor U3, shortening the rise time of the power supply voltage, ensuring the startup of the microprocessor U3, and It is characterized by holding it when it is activated.

  The wireless tag device according to claim 9 is the wireless tag device according to claims 5 to 8, wherein the microprocessor U3 includes a comparator function, an analog / digital conversion function, etc. It is characterized in that various sensor information can be taken in and returned as a response signal. Here, as the microprocessor U3, for example, a general-purpose microprocessor such as PIC16F684 manufactured by Microchip can be used.

  The wireless tag device according to claim 10 is the wireless tag device according to claims 5 to 9, wherein a rectifier element D7 is inserted between the power source of the inverting logic circuit U1 and the power source of the logical sum circuit U2, and A semi-passive RFID tag device that operates the microprocessor U3 with battery power by inserting a battery between power supplies A and F. When receiving a signal from the reader, the battery is charged based on the received signal When there is no reception from the reader, the output of the inverting logic circuit U1 becomes Low, and U3 monitors the input state of the data input terminal DIN to turn the power-on output terminal Pon low and turn off its power supply. This reduces battery consumption.

  The wireless tag device according to claim 11 is the wireless tag device according to claim 10, wherein the rectifying element D7 is a Schottky barrier diode.

According to a radio tag reading method of a twelfth aspect, the radio tag device according to the fifth to eleventh aspects is installed around a road such as a road, and a carrier signal is transmitted from an in-vehicle reader to the radio tag device. A wireless tag reading method for reading a response signal from the wireless tag device,
When a query carrier signal is continuously transmitted from a reader, a reset synchronization carrier non-transmission section of about 1 ms is inserted every T seconds for a predetermined period, and the reset synchronization has a role of waking up a sleeping RFID tag device. It is also used for synchronization of the return timing from the RFID tag device, and the return timing from the RFID tag device is a tag response time slot in which the delay time from the reset synchronization determined for each RFID tag device is recorded. By using the same tag response time slot between neighboring RFID tag devices in the RFID tag devices installed in the same location, and repeatedly using the same tag response time slot between remote RFID tag devices, The received tag response signal is characterized in that there is no overlap.

  According to the first and second aspects of the invention, it is possible to obtain a negative voltage output and a positive voltage output at the same time, thereby enabling an efficient step-up rectification operation and verifying that the step-up rectification factor is about 20 times. It was done. It was also verified that the RF input signal received by the antenna was efficiently converted to DC power near the stub resonance frequency. Furthermore, in the conventional method (Patent Document 2), in order to resonate C1 and L7 with a high Q value, a small capacitance of about 0.15 pF is required as C1 in the 2.45 GHz band, whereas the capacitance of C1 is the resonance frequency. It is possible to use several tens of pF that is easy to handle. That is, it is possible to realize a low-cost power receiving circuit without using a relatively expensive capacitor having a very small capacity.

  According to the third and fourth aspects of the present invention, the RF input signal received by the antenna is boosted and rectified to obtain a power supply voltage for a circuit that performs data input and power control of the microprocessors U3 and U3. It becomes possible to operate with a battery.

  According to the fifth aspect of the present invention, it is possible to provide a passive RFID tag device that does not require a battery by a power receiving circuit that efficiently boosts and rectifies an RF (Radio Frequency) signal received by an antenna.

  According to the invention of claim 6, the antenna structure having a beam tilted directivity with high reading performance in an oblique direction is used, so that the road surface direction is −90 ° to −135 compared with the conventional tag antenna. It was verified that the reading gain (directivity gain) from the vehicle over several degrees was several dB higher. Furthermore, since the current concentrates at both ends in the width direction of the two-divided microstrip conductors L2 and L3, it is possible to efficiently change the reflection coefficient of the antenna with a small number of variable impedance elements D1 and D2 and return the tag response signal with a high gain. It becomes.

  According to the invention of claim 7, the information output from the microprocessor U3 is obtained by efficiently changing the bias voltages of the variable impedance elements D1 and D2 in accordance with the output from the data output terminal Dout of the microprocessor U3. It can be sent back to the reader on radio waves. This RFID tag device facilitates reading from an oblique direction of the tag and can be read from several tens of meters from a distance. By embedding this RFID tag device on a road or the like or installing it on a guardrail or the like, it can be remotely read by an in-vehicle reader. It becomes possible to read. In addition, by adding sensor functions, it is possible to relatively easily supply social infrastructure that can warn drivers from a distance of several tens of meters, such as road freezing, crosswinds, lane protrusions and access to guardrails. It becomes possible. In addition, the passive sensor tag device can operate without a battery and has an advantage that no operation maintenance is required.

  According to the eighth aspect of the invention, the normal power on reset operation of the microprocessor U3 can be performed by using the output of the logical sum circuit U2 to supply power to the microprocessor U3. That is, if the reader transmits a carrier off signal of about 1 ms by ASK modulation at regular intervals, the microprocessor U3 can reliably perform the power on reset operation. Furthermore, while the microprocessor U3 is operating, the power-on output terminal Pon output is fixed to the high state, and even if the inverting logic circuit U1 output becomes low, the output of the logical sum circuit U2 remains high, thereby temporarily If activated, it can be held.

  According to the ninth aspect of the invention, since the microprocessor U3 has a built-in analog / digital conversion function, various information such as temperature and pressure detected by the sensor device can be captured and returned as a response signal. It becomes.

  According to the invention of claim 10-11, in the semi-passive type wireless tag device that operates the microprocessor U3 with the power of the battery, when there is reception from the reader, the battery is charged based on the received signal. When there is no reception from the reader, it is possible to save battery consumption by turning off its own power supply.

  According to the twelfth aspect of the present invention, in a method of transmitting a carrier signal from an in-vehicle reader and reading a response signal from a radio tag device installed around a road such as a road, a tag response received by the in-vehicle reader By ensuring that the signals do not overlap, it is possible to reliably read from a vehicle traveling at high speed. It is estimated that the response signal from the wireless tag device can be read within 0.1 seconds.

It is a block diagram which shows the structure of the conventional non-contact reading sensor tag apparatus. It is a figure which shows the directivity concept of the radio | wireless tag antenna embedded in the road surface. It is a figure which shows the structure and circuit diagram of the wireless tag apparatus which concern on embodiment of this invention. (a) RFID tag device with passive sensor (b) RFID tag device with semi-passive sensor It is a figure which shows the operation experiment type | system | group of the standing wave step-up rectifier circuit which concerns on embodiment of this invention. Here, HSMS-2865 (Co = 0.3 pF, Rs = 6Ω, Ir = 10 μA, Bv = 7 V) is used for the Schottky barrier diodes D3 and D4. DS-8882 is used for digital oscilloscopes, and HP83620A is used for synthesized sweepers. It is a figure which shows the experimental result which evaluates the standing wave step-up rectifier circuit which concerns on embodiment of this invention. The graph shows the frequency response of the standing wave boost rectifier (input 0dB, short stub length 6cm, load resistance 47kΩ). It is a figure which shows the experimental result which evaluates the directivity of the microstrip antenna which concerns on embodiment of this invention. The graph shows the H-plane directivity of the microstrip antenna (strip conductor width 10 mm, element spacing 20 mm, evaluation frequency 2.45 GHz). It is a figure which shows the application example at the time of applying the radio | wireless tag apparatus which concerns on embodiment of this invention to a driving assistance road system (AHS). (Part of the figure is reprinted from the ITS website of the Ministry of Land, Infrastructure, Transport and Tourism) It is the figure which showed the example which installed the radio | wireless tag apparatus which concerns on embodiment of this invention on a road, a guardrail, etc., and the timing and the intensity | strength which an in-vehicle reader reads these tags for every position of a vehicle.

  Next, a wireless tag device according to an embodiment of the present invention will be described with reference to the drawings. In addition, this invention is not limited by this embodiment.

  FIG. 3 is a diagram showing a configuration and a circuit diagram of the wireless tag device according to the embodiment of the present invention. FIG. 3A is a configuration and circuit diagram of a passive RFID tag device, and FIG. 3B is a configuration and circuit diagram of a semi-passive RFID tag device.

  The wireless tag device includes a wireless tag antenna, a power receiving circuit that efficiently boosts and rectifies an RF signal received by the wireless tag antenna, and a circuit that performs data input and power control of the microprocessors U3 and U3.

  The wireless tag antenna is a rectenna having a microstrip reflector L1, two-divided microstrip feed elements L2 and L3, and microstrip directors L4 to L6, and is about λ / 40 from L1 to L6 (λ The GND plate is arranged at intervals of the electromagnetic wave), the reflector L1 is about 3 to 5% longer than the feeding element L2 + L3, and the directors L4 to L6 are the same length and longer than the feeding element L2 + L3. Is 3 to 5% shorter, the strip conductor width of L1 to L6 is about λ / 10, and the arrangement interval of L1 to L6 is about λ / 5, so that the directivity is tilted from the front direction to the L4 to L6 direction. It has a structure.

  Furthermore, the RFID tag antenna periodically changes the resonance frequency of the antenna by connecting variable impedance elements D1 and D2 between the feeding elements L2 and L3 and periodically changing the bias voltage of D1 and D2. The response signal is returned, and for example, varactor diodes are used as the variable impedance elements D1 and D2.

  L1, L4, L5, and L6 in FIG. 3 are reflectors and directors for tilting the directivity of the RFID tag antenna and operate as the well-known Yagi-Uda array. However, the antenna of the present invention is a microstrip type, and does not constitute a beam in the direction of the waveguide, but tilts the beam in the direction of the waveguide (L4, L5, L6) from the front direction of the GND plate. At this time, the wavelength is λ, the strip conductor width W of L1 to L6 is about λ / 10, and the element interval is about λ / 5. Further, it is desirable that the length of the reflector L1 is about 3 to 5% longer and the length of the directors L4 to L6 is about 3 to 5% shorter than the feed element length (L2 + L3).

  The conventional Yagi-Uda array antenna has a structure in which the GND plate of the RFID tag antenna in FIG. 3 is removed and balanced power is fed between L2 and L3 without the variable impedance elements D1 and D2. In the antenna of the present invention, a GND plate is arranged in the very vicinity of L1 to L6 (about λ / 40), variable impedance elements D1 and D2 are loaded or short-circuited between L2 and L3, and between L2 or L3 and the GND plate. The antenna has an unbalanced feed structure, and is an antenna characterized in that beam tilt is performed not in the waveguide direction but in an intermediate direction between the waveguide direction and the antenna surface direction.

  The conventional microstrip antenna (patch antenna) uses a patch conductor having a size of about λ / 2 × λ / 2 as an antenna, whereas the antenna of the present invention is an elongated shape of about λ / 2 × λ / 10. By using a combination of patch conductors, not only a tilt beam can be obtained with an antenna of about λ / 2 × λ size, but also the current concentrates at both ends in the width direction of the feed elements L2 and L3, so there are few variable impedance elements D1 and D2 can efficiently change the reflection coefficient of the antenna and return the tag response signal with a high gain.

  Further, the antenna of the present invention can also insert the circuit shown in FIG. 3 into the gap between the GND plate and the strip conductors L1 to L6. In particular, the short stag L7 can be easily realized between the antenna GND plates. is there.

  FIG. 6 shows the experimental results for evaluating the directivity of the microstrip antenna. From the experimental results shown in FIG. 6, the antenna (5 elements) of the present invention is compared with the conventional microstrip antenna (1 element), and the reading gain (directional gain) from the vehicle from −90 ° to −135 ° on the road surface direction. Was found to be several dB higher.

  Next, FIG. 4 shows an operation experiment system of the standing wave boost rectifier circuit. It is a feature of the present invention that this circuit does not require a minute capacitor in C1 of the power feeding system. In the conventional method (Patent Document 2), in order to resonate C1 and L7 with a high Q value, it is necessary to use a minute capacitance of about 0.15 pF as C1 in the 2.45 GHz band. Microcapacitors are relatively expensive, and have the drawback that the effect of characteristic changes due to mounting conditions is large. In the power receiving circuit of the present invention, since the capacitance of C1 does not affect the resonance frequency, it is possible to use several tens of pF that is easy to handle.

  The stub boosting operation of the present invention is performed by the rectifying element D3, and a V1 minus voltage output and a V2 plus voltage output can be obtained at the same time as the experimental result shown in FIG. The step-up rectification ratio of this circuit is ± 20 VDC output voltage of about 4 to 5 V for 0 dB input (0.22 Vms). As can be seen from the frequency characteristics of the input reflection coefficient S11 in FIG. 5, when the DC load resistance is set to 5 kΩ, especially in the vicinity of the stub resonance frequency, the RF input signal is efficiently converted into DC power. It can be seen that it has been converted into (less RF reflection).

Next, the operation of the circuit diagram shown in FIG. The power receiving circuit is connected to the antenna feed point C provided in the feed element L2 or L3 via the capacitor C1, and boosts and rectifies the RF input signal supplied from the antenna feed point C to supply power to the external load. To do. Furthermore, a capacitor having a capacity of about several tens of pF (pico farad: 10 ⁻¹² F) can be used as the capacitor C1.

  Capacitor C1, rectifier element D3, and short stub L7 are connected in series from antenna feed point C. Capacitor C1 supplies the antenna reception RF signal to rectifier element D3 and charges a DC voltage, and rectifier element D3 is an RF signal. To the short stub L7, and the standing wave boost signal generated in L7 is rectified and charged to C1. Here, for example, a Schottky barrier diode is used as the rectifying element D3.

  Further, the first step-up rectified DC power supply voltage is charged to the capacitor C3 from the connection point E between the rectifier element D3 and the short stub L7 through the rectifier element D4, and the resistor R3 is connected from the connection point D between the capacitor C1 and the rectifier element D3. Then, the second boosted rectified DC power supply voltage is charged to the capacitor C2 through two types of voltage sources. That is, a positive voltage is obtained at the connection point G between D4 and C3, and a negative voltage is obtained at the connection point F between R3 and C2. Here, for example, a Schottky barrier diode is used as the rectifying element D4.

That is, the resistor R3 charges the capacitor C2 only with the DC component of the capacitor C1 to obtain a minus DC voltage. The rectifying element D4 rectifies the standing wave boost RF signal generated in the short stub L7, charges the capacitor C3, and obtains a positive DC voltage. Here, the time constant composed of C1, C2, C3 and R3 and R4 is 1ms or less, and the ASK output from the tag reader
(Amplitude shift keying) Demodulate the modulated carrier signal.

  Further, the power receiving circuit detects the potential difference between the first power supply G point and the second power supply F point as a received signal by the inverting logic circuit U1, and also receives the DC voltage boosted and rectified from the connection point G via the rectifying element D5. The capacitor C4 is charged and used as a power supply voltage for a circuit that performs data input and power control of the microprocessors U3 and U3.

  That is, the rectifying element D5 is used to charge the boosted rectified DC voltage to the capacitor C4 having a relatively large capacity, and the voltage charged to C4 serves as a power source for the inverting logic circuit U1 and the OR circuit U2. The capacity of C4 is set to have a time constant sufficiently larger than 1 ms with respect to the loads of U1 and U2 (not affected by ASK modulation from the tag reader). D6 is a Zener diode that protects the circuit so that the received voltage does not exceed a certain level even if the RFID tag device gets too close to the tag reader. Here, for example, a Schottky barrier diode is used as the rectifying element D5.

  The resistor R4 is used to adjust the time constant of the ASK demodulation operation and absorb the reverse leakage current of the rectifying element D5. The inverting logic circuit U1 performs waveform shaping and logic inverting operation of the ASK demodulated signal. When the input of U1 is Low, the output of U1 is High and the output of the OR circuit U2 is High. The output of U2 supplies power to the microprocessor U3. C5 is a bypass capacitor for stabilizing the power supply voltage of the microprocessor.

  The reason why the output of the logical sum circuit U2 is used to supply power to the microprocessor U3 is that there is a limit condition on the rise time of the power supply voltage in devices such as microprocessors. Because there are things that do not. That is, if a carrier off signal of about 1 ms is transmitted at regular intervals from the tag reader by the ASK modulation operation, the microprocessor U3 in the wireless tag device can surely perform the power on reset operation. Further, during the operation of the microprocessor U3, the Pon output is fixed to the high state, and the output of the logical sum circuit U2 can be kept high even if the output of the inverting logic circuit U1 becomes low. Since the carrier off signal from the tag reader gives the reference timing of the response operation from the wireless tag device as well as the start-up of the microprocessor U3, the DIN input is monitored and the response operation timing is adjusted at the time of Pon output.

  Microprocessor U3's C1 +, C1-, C2 +, and C2- are comparator input terminals, respectively, that compare the U3 power supply voltage divided by resistors R5, R6, and R7 with the voltages divided by resistors R8 and RS. . Here, if RS is an element whose resistance value changes with temperature, such as a thermistor, U3 detects temperature information of the RFID tag device. Further, if RS is an element whose resistance value is changed by pressure such as a piezoresistive element, U3 detects wind pressure information applied to the RFID tag device. The sensor information thus detected and the tag ID code (corresponding to the position and the like) are output from the data output terminal Dout in accordance with the synchronization signal from the reader. When Dout is a low output, the variable impedance elements D1 and D2 are in a zero bias state through the resistors R1 and R2, and when Dout is a high output, the variable impedance elements D1 and D2 are in a reverse bias state. When this bias state is repeatedly changed, the reflection coefficient of the RFID tag antenna periodically changes, and a part of the radio wave incident on the RFID tag antenna is modulated and reflected, and the information output from the microprocessor U3 is reflected in the radio wave. Can be sent back to the reader.

  Here, the microprocessor U3 has a built-in comparator function, an analog / digital conversion function, and the like, and can receive various sensor information such as temperature and pressure and return it as a response signal. For example, a general-purpose microprocessor such as PIC16F684 manufactured by Microchip can be used.

  Next, the operation of the circuit diagram shown in FIG. The circuit shown in FIG. 3B is the same as that shown in FIG. 3A except that the microprocessor U3 is operated by battery power.

  In FIG. 3 (b), the rectifier D7 is inserted between the power supply of the inverting logic circuit U1 and the power supply of the logical sum circuit U2, and the battery is inserted between the power supplies A and F of the U2, so that the microprocessor uses the power of the battery. In the semi-passive type RFID tag device that operates U3, when there is reception from the reader, the battery is charged based on the received signal, and when there is no reception from the reader, the output of the inverting logic circuit U1 becomes Low, U3 is characterized by reducing battery consumption by monitoring the input state of the data input terminal DIN and turning the power-on output terminal Pon as a low output to turn off its own power supply. Here, for example, a Schottky barrier diode is used as the rectifying element D7.

  Next, FIG. 8 shows an example in which the RFID tag device is installed on a road, a guardrail, etc., and the timing at which the in-vehicle reader reads the RFID tag device (tag response delay time from the reader synchronous output) and its strength. It is the figure represented for every position. Based on the tag response signal received by the in-vehicle reader, the relative speed and distance between the reader and the tag can be estimated from the frequency difference and the intensity difference from the interrogation carrier signal transmitted from the reader.

  The wireless tag reading method of FIG. 8 transmits a carrier signal from an in-vehicle reader and reads a response signal from a wireless tag device installed around a road such as a road. In this reading method, when the interrogation carrier signal is continuously transmitted from the reader, a carrier non-transmission section for reset synchronization of about 1 ms is inserted every fixed period T seconds, and the reset synchronization wakes up the sleeping RFID tag device. It is also used for the synchronization of the return timing from the RFID tag device together with the role, and the return timing from the RFID tag device is a tag response that records the delay time from reset synchronization determined for each RFID tag device. As a time slot, by not using the same tag response time slot between adjacent RFID tag devices in a RFID tag device installed on a road or the like, and repeatedly using the same tag response time slot between remote RFID tag devices Make sure that tag response signals received by the on-vehicle reader do not overlap. It is characterized in.

  In FIG. 8, the response timings (tag response time slots) of the wireless tag devices A to R are set to t1 to t6. As can be seen from the table of FIG. 8, it is possible to determine the traveling lane position of the vehicle by looking at the time change of the strong received signal. In addition, when the vehicle position is (3), the response signal from tag J (response timing t4) and tag K (response timing t5) contains information on the approach of the curve. Can inform the driver. In addition, when the vehicle position is (4), the received signal at response timing t4 is subject to strong Doppler frequency shift due to the presence of the tag in the direction of moving front, so the received signal strength is strong (distance is close) or Doppler frequency If the shift amount is large (relative speed is large), the driver can be warned that there is a risk of collision. In the case of tag J in FIG. 8 (attached to the curve / guard rail), tag antennas L1 and L4 to L6 in FIG. 3 are removed, and the directivity in the front direction as in the case of one element in FIG. A suitable configuration can also be provided.

  Further, as an application example of FIG. 8, it can be applied to a highway or the like, and it is possible to supply a social infrastructure that performs automatic driving using these tag response signals.

500 LSI
501 High-frequency coil belonging to reader / writer 502 High-frequency coil 503 Temperature sensing element 504 Battery 505 Crystal resonator 510 Bridge 511 AD converter 512 Memory 513 Rectification, modulation, demodulation circuit 514 Power supply circuit 515 Microcomputer 516 Oscillation circuit 517 First power supply Path 518 Second power supply path 519 Information flow L1 Microstrip reflector L2, L3 Two-divided microstrip antenna (feeding element)
L4, L5, L6 Microstrip director L7 Microstrip short stub D1, D2 Varactor diode D3, D4, D5, D7 Schottky barrier diode D6 Zener diode E1 Battery U1 Inverting logic circuit U2 OR circuit U3 Microprocessor C1 C5 Capacitor R1-R8 Resistor RS Thermistor λ Wavelength of electromagnetic wave used

Claims (12)

A power receiving circuit that boosts and rectifies an RF signal received by a radio tag antenna,
A capacitor C1, a rectifying element D3, and a short stub L7 are connected in series from an antenna feed point C provided on the feed element of the RFID tag antenna, and from an RF input signal supplied from the antenna feed point C, a capacitor C1 A booster DC power supply voltage and an RF signal are obtained at a connection point D between the rectifier element D3 and the rectifier element D3, and a boosted RF signal is obtained at a connection point E between the rectifier element D3 and the short stub L7.   The first step-up rectified DC power supply voltage is charged to the capacitor C3 from the connection point E between the rectifier element D3 and the short stub L7 via the rectifier element D4, and the resistance point R3 is connected from the connection point D between the capacitor C1 and the rectifier element D3. By charging the second step-up rectified DC power supply voltage to the capacitor C2, two types of voltage sources are obtained, that is, a positive voltage at the connection point G between D4 and C3, and a negative voltage at the connection point F between R3 and C2. The power receiving circuit according to claim 1, wherein a voltage is obtained.   A potential difference between the first power supply point G and the second power supply point F is detected as a received signal by the inverting logic circuit U1, and a DC voltage boosted and rectified from the connection point G through the rectifier D5 is charged to the capacitor C4. 3. The power receiving circuit according to claim 2, wherein the power supply voltage is a power supply voltage of a circuit for performing data input and power supply control of the microprocessors U3 and U3.   4. The power receiving circuit according to claim 1, wherein the rectifying elements D3, D4, and D5 are Schottky barrier diodes.   A wireless tag device comprising the wireless tag antenna and the power receiving circuit according to claim 1.   The RFID tag antenna includes a microstrip reflector L1, two-divided microstrip feed elements L2 and L3, and microstrip directors L4 to L6, and about λ / 40 from L1 to L6 (λ is an electromagnetic wave). The reflector L1 is 3 to 5% longer than the feed element L2 + L3, and the directors L4 to L6 are the same length and 3 than the feed element L2 + L3. A structure in which the directivity is tilted from the front direction to the L4 to L6 direction by shortening the strip conductor width of L1 to L6 to about λ / 10 and the arrangement interval of L1 to L6 to about λ / 5. The variable impedance elements D1 and D2 such as varactor diodes are connected between the feeding elements L2 and L3, and the response signal is returned by changing the bias voltage of D1 and D2. 5. The wireless tag device according to 5.   The wireless tag device according to claim 6, wherein the wireless tag device includes the antenna for the wireless tag, the power receiving circuit, and a circuit for performing data input and power control of the microprocessors U3 and U3, and a second power supply. Connected to the antenna strip conductor L3 through the resistor R2 from the point F, connected to the antenna strip conductor L2 through the resistor R1 from the data output terminal Dout of the microprocessor U3, and according to the output from the data output terminal Dout 7. The RFID tag device according to claim 6, wherein the information output from the microprocessor U3 is returned to the reader on radio waves by efficiently changing the bias voltages of the variable impedance elements D1 and D2.   The power supply of the microprocessor U3 is supplied from the logical sum circuit U2, one input of the logical sum circuit U2 is controlled by the output of the inverting logic circuit U1, and the other input of the logical sum circuit U2 is controlled by the output of the microprocessor U3. The wireless tag device according to claim 7, wherein the RFID tag device is connected in such a manner that the rise time of the power supply voltage is shortened, the startup of the microprocessor U3 is ensured, and the startup is held once started.   9. The microprocessor U3 includes a comparator function, an analog / digital conversion function, and the like, and can capture various sensor information such as temperature and pressure and return it as a response signal. Wireless tag device.   A semi-passive type that operates the microprocessor U3 with battery power by inserting a rectifier element D7 between the power supply of the inverting logic circuit U1 and the power supply of the logical sum circuit U2 and inserting a battery between the power supplies A and F of the U2. In the RFID tag device, when there is reception from the reader, the battery is charged based on the received signal, and when there is no reception from the reader, the output of the inverting logic circuit U1 becomes Low, and U3 is a data input terminal 10. The wireless tag device according to claim 5, wherein the power consumption of the battery is reduced by monitoring the DIN input state to turn the power-on output terminal Pon as a low output and turning off its own power supply. .   11. The RFID tag device according to claim 10, wherein the rectifying element D7 is a Schottky barrier diode. A radio tag device according to claim 5 is installed around a road such as a road, and a radio signal is transmitted to the radio tag device from a vehicle-mounted reader and a response signal is read from the radio tag device. A tag reading method,
When a query carrier signal is continuously transmitted from a reader, a reset synchronization carrier non-transmission section of about 1 ms is inserted every T seconds for a predetermined period, and the reset synchronization has a role of waking up a sleeping RFID tag device. It is also used for synchronization of the return timing from the RFID tag device, and the return timing from the RFID tag device is a tag response time slot in which the delay time from the reset synchronization determined for each RFID tag device is recorded. By using the same tag response time slot between neighboring RFID tag devices in the RFID tag devices installed in the same location, and repeatedly using the same tag response time slot between remote RFID tag devices, Radio characterized by no overlap in received tag response signals Grayed reading method.

Images