JP4345567B2 - Wireless communication device - Google Patents

Description

  The present invention relates to a radio communication apparatus using a radio wave communication system using microwaves of a specific frequency band, and more particularly to a radio communication apparatus that realizes a communication operation with low power consumption between devices in a relatively short distance.

  More specifically, the present invention relates to wireless communication in which data communication is performed by a back scatter method using transmission of an unmodulated carrier wave from the reader side and absorption and reflection of received radio waves based on an antenna termination operation on the transmitter side. In particular, the present invention relates to a wireless communication apparatus that performs back-scatter data communication having a high transmission rate by incorporating modulation processing of a higher bit rate.

  As an example of wireless communication means that can be applied only locally, RFID can be cited. The RFID is a system composed of a tag and a reader, and is a system that reads information stored in the tag in a contactless manner with a reader. Other names include “ID system, data carrier system” and the like, but the RFID system is common worldwide. For short, it may be called RFID. Translated into Japanese, it becomes “a recognition system using high frequency (wireless)”. Examples of the communication method between the tag and the reader / writer include an electromagnetic coupling method, an electromagnetic induction method, and a radio wave communication method (for example, see Non-Patent Document 1).

The RFID system includes an RFID tag and a tag reader. Tag receives the radio wave f _o unmodulated transmitted from the tag reader is rectified, is converted to a DC power source, it is possible to use the DC power supply operating power. On the tag side, the termination of the antenna is performed according to the bit image of the transmission data, and the data is expressed using absorption and reflection of the received radio wave. That is, when the data is 1, the antenna is terminated with the antenna impedance, and the radio wave from the tag reader is absorbed. If the data is 0, the radio wave from the tag reader is reflected by opening the end of the antenna. From the tag, a signal having the same frequency as the transmission signal from the tag reader is returned by reflection of the received radio wave. A communication method that expresses data by a reflection or absorption pattern of an incoming radio wave is called a “back scatter method”. In this way, the tag can send internal information to the reader side with no power supply.

  FIG. 9 shows a configuration example of a conventional RFID system. Reference number 1 corresponds to the tag side of the RFID, and includes a tag chip 2 and an antenna 3. As the antenna 3, a half-wave dipole antenna or the like is used. The tag chip 2 includes a modulation unit 10, a rectification / demodulation unit 12, and a memory unit 13.

The radio wave f _o transmitted from the tag reader 21 is received by the antenna 3 and input to the rectifying / demodulating unit 10. Here, the received radio wave f _o is rectified, and at the same time is converted into a DC power source, the demodulation function by the DC power supply starts operating, that to the tag 1 is read signal is recognized. The power generated by receiving the radio wave f _o is also supplied to the memory unit 13 and the modulation unit 10.

  The memory unit 13 reads ID information stored therein in advance and sends it to the modulation unit 10 as transmission data. The modulation unit 10 includes a diode switch 11 and repeats the on / off operation of the diode switch 11 according to the bit image of the transmission data. That is, if the data is 1, the switch is turned on and the antenna is terminated with antenna impedance (eg, 50 ohms). At this time, radio waves from the tag reader 21 are absorbed. When the data is 0, the switch is turned off, the diode switch 11 is opened, and at the same time, the end of the antenna is opened. At this time, the radio wave from the tag reader 21 is reflected and returns to the transmission source. In this way, the tag 1 can send internal information to the reader side with no power supply.

  One tag reader 21 includes a host device 6 such as a portable information terminal, a tag reader module 4, and an antenna 5 connected to the tag reader module 4.

The host device 6 notifies the communication control unit 19 of the tag 1 read instruction via the host interface unit 20. Upon receiving the tag read command from the host interface unit 20, the communication control unit 19 performs a predetermined editing process on the transmission data, and further performs filtering, and then sends it to the ASK modulation unit 17 as a baseband signal. send. ASK modulating unit 17, ASK with frequency f _o of the frequency synthesizer 16: performing (Amplitude Shift Keying amplitude shift keying) modulation.

  The frequency setting of the frequency synthesizer 16 is performed by the communication control unit 20. In general, the transmission frequency to the tag is used by hopping in order to reduce the standing wave of the signal from the RF tag and multipath. This hopping instruction is also given by the communication control unit 20. The transmission signal subjected to ASK modulation is radiated from the antenna 5 toward the tag 1 via the circulator 14.

From the tag 1, a transmission signal having the same frequency as the transmission signal from the tag reader 21 is returned as a backscatter-modulated reflected wave (described above). This signal is received by the antenna 5 of the tag reader 21 and input to the mixer 15. Because the same local frequency f _o and sent to the mixer 15 is input, so that the signal subjected to modulation in the tag 1 side appears at the output of the mixer 15. The demodulator 18 demodulates 1/0 data from this signal and sends it to the communication controller 19. The communication control unit 19 decodes the data, takes out the data (ID) stored in the memory 13 in the tag 1, and transfers the data (ID) from the host interface unit 20 to the host device 6.

  The tag reader 21 can read information in the tag 1 by the mechanism as described above. In general, the tag reader can also be used as a tag writer, and can write specified data on the host device 6 side into the memory 13 in the tag 1.

  Conventionally, such a back-scatter wireless communication system is applied to identification and authentication of articles and people, as represented by RFID tags, because the communication range is limited to a relatively short distance. There were many things.

  For example, an IC chip having transmission / reception and memory functions, a driving source of the chip, and an antenna can be packaged to manufacture a wireless identification device in a small size (see, for example, Patent Document 1). According to this wireless identification device, various data relating to articles and the like are transmitted to the receiving means of the IC chip via the antenna, the output is stored in the memory, and the data in the memory is read as necessary, It can be supplied to the outside wirelessly through an antenna. Accordingly, it is possible to quickly and easily confirm or track the presence or position of an article or the like.

  On the other hand, RFID tags are generally non-powered and power is supplied by radio waves from a reader. By supplying this power from the battery in the device, wireless data transmission with low power consumption by the back scatter method can be realized. That is, back-scatter wireless communication has a feature that a wireless transmission path with extremely low power consumption can be established if the communication distance is limited. Recently, with the improvement of mounting technology, IC chips equipped with a memory function have appeared, and the memory capacity has further increased. Therefore, there is a demand not only to perform communication of relatively short data such as identification / authentication information but also to adopt back-scatter communication for general data transmission. For example, it is effective for image transmission from a digital camera or mobile phone to a PC, printer, TV, or the like.

  However, the conventional back scatter communication systems employ a modulation method with a relatively low bit rate, such as ASK (Amplitude Shift Keying) and BPSK (Binary Phase Shift Keying). There is a problem in terms.

JP-A-6-123773 Klaus Finkenzeller (Translated by Software Engineering Laboratory) "RFID Handbook Principles and Applications of Contactless IC Cards" (Nikkan Kogyo Shimbun)

  An object of the present invention is to suitably perform data communication by a back scatter method using transmission of an unmodulated carrier wave from the reader side and absorption and reflection of received radio waves based on an antenna termination operation on the transmitter side. An object of the present invention is to provide an excellent wireless communication device that can be used.

  It is a further object of the present invention to provide an excellent wireless communication apparatus capable of performing back scatter type data communication having a high transmission rate by incorporating modulation processing of a higher bit rate.

The present invention has been made in consideration of the above problems, and is a wireless communication apparatus that performs data communication by a back scatter method using absorption and reflection of received radio waves,
An antenna for receiving radio waves coming from the transfer destination;
First, second, and third phasers connected sequentially in series to the antenna;
A first switch connected between the antenna and the first phaser;
A second switch connected between the first phaser and the second phaser;
A third switch connected between the second phaser and the third phaser;
Back scatter type phase modulation means for obtaining four reflection points having different phase differences by a combination of on / off of the first to third switches,
The first to third phase shifters are adjusted in length so as to obtain a desired phase difference.
This is a wireless communication device.

  According to the present invention, in a back scatter system composed of an antenna and a high-frequency switch, first to third phase shifters that give a phase difference of λ / 8 in one way are connected in series to the antenna, A first signal path that obtains a first reflected wave that directly reflects the received radio wave without passing through the phase shifter, and a phase that is π / 2 compared with the first reflected wave that reciprocates only through the first phase shifter. And a second signal path for obtaining a second reflected wave shifted from the first and second phase shifters, and a third reflected wave having a phase shifted by π compared to the first reflected wave. A third signal path and a fourth signal path for obtaining a fourth reflected wave whose phase is shifted by 3π / 2 as compared with the first reflected wave by reciprocating between the first to third phase shifters. As a result, four values with different phase differences are obtained for each reflection point, so that QPSK modulation can be realized. .

  Here, the first to third phase shifters are constituted by strip lines or other lines. However, since the switch itself also functions as a delay element having a delay time, it is accurate for each reflection point. There is a problem that an accurate phase difference cannot be obtained and accurate mapping to each signal point in QPSK modulation cannot be performed.

  Therefore, in the present invention, the time difference between the case where the received radio wave is reflected without passing through any of the first to third phase shifters and the case where the received radio wave is reflected through only the first phase shifter, the first The time difference between the case of reflecting through only the first phase shifter and the case of reflecting through the first and second phase shifters, the case of reflecting through the first and second phase shifters, and the first Each strip line constituting the first to third phase shifters so that the time difference when reflected through the first to third phase shifters is T / 4 with respect to the period T of the incoming radio wave. The length is adjusted.

  As described above, the lengths of the first to third phase shifters are adjusted in consideration of the delay time of each switch element, so that back-scatter QPSK modulation capable of high-precision QPSK modulation is realized. can do.

  Further, because of the delay characteristics of the first to third switches, there is a problem that the received signal is deteriorated every time it passes through each phase shifter. The switch element is composed of, for example, a pin diode, and is a delay element that operates as an equivalent circuit (RL) of reactance and inductance when turned on and as an equivalent circuit (C) of capacitance when turned off.

  Therefore, in the present invention, when the first to third switches are grounded at one end to the corresponding phase shifter and the other end to the ground, the first to third switches are connected between the terminals when the first to third switches are off. By connecting an inductance element that resonates in parallel with the capacitor in parallel to each switch element, the attenuation of the reflected wave power may be reduced.

  Alternatively, when the first to third switches are connected in series between the corresponding phase shifters, a capacitor element that directly resonates with an inductance component that is regulated when the first to third switches are turned on is further provided. You may make it reduce attenuation | damping of the electric power of a reflected wave by connecting in series with each switch element.

  According to the present invention, data communication can be suitably performed by a back scatter method using transmission of an unmodulated carrier wave from the reader side and absorption and reflection of received radio waves based on an antenna termination operation on the transmitter side. It is possible to provide an excellent wireless communication device.

  Further, according to the present invention, it is possible to provide an excellent wireless communication apparatus that can perform back scatter type data communication having a high transmission rate by incorporating modulation processing of a higher bit rate.

  According to the present invention, in a backscatter system composed of an antenna and a high-frequency switch, first to third phase shifters that give a phase difference of λ / 8 in one way are connected in series to the antenna to transmit data. Accordingly, by selecting any one of the signal paths, four reflected waves having different phases are formed for each reflection point, so that QPSK modulation can be realized. Further, by adjusting the lengths of the first to third phase shifters in consideration of the delay time of each switch element, it is possible to realize back scatter QPSK modulation capable of highly accurate QPSK modulation. .

  That is, according to the present invention, it is possible to provide a back-scatter wireless communication apparatus capable of high-precision QPSK modulation by adjusting the length of each phase shifter in consideration of the delay time of the switch element. Can do. Further, by connecting the inductance element and the capacitor element so as to cancel the inductor component when the switch element is conductive or the capacitor component when the switch element is non-conductive, the attenuation of the power of the reflected wave can be reduced.

  Other objects, features, and advantages of the present invention will become apparent from more detailed description based on embodiments of the present invention described later and the accompanying drawings.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  An object of the present invention is to realize low power consumption in a communication mode in which a transmission ratio occupies most of communication between devices that are relatively limited to a short distance. -Wireless transmission using reflected waves based on the scatter method. The RFID system itself is widely known in the art as an example of locally applicable wireless communication means.

  The RFID is a system composed of a tag and a reader, and is a system that reads information stored in the tag in a contactless manner. An RFID tag has an operating characteristic that oscillates a radio wave of a modulation frequency corresponding to transmission information in response to reception of a radio wave of a specific frequency, and what is that based on the oscillation frequency of the RFID tag on the reading device side Can be specified. Examples of the communication method between the tag and the reader / writer include an electromagnetic coupling method, an electromagnetic induction method, and a radio wave communication method. The present invention relates to a radio wave communication system using a microwave such as a 2.4 GHz band.

  The present invention also relates to a wireless communication apparatus that performs data transmission with low power by a back scatter modulation method that uses reflection of an incoming radio wave. As one embodiment, the reflected wave of a wireless transmission module unit is provided. As a modulation method, a QPSK (Quadrature Phase Shift Keying) method is applied. The purpose of changing from PSK to QPSK is to speed up data. In the PSK modulation method, 0 and 1 are assigned to the phase shifts shifted by 180 degrees, respectively. On the other hand, in the QPSK modulation method, four types of values can be obtained by obtaining different phase differences for each reflection point, so that the 0 phase, π / 2 phase, π phase, 3π / 2 phase shifted by π / 2 are obtained. By assigning (0, 0), (0, 1), (1, 0), and (1, 1) respectively, back scatter QPSK modulation can be realized, and the bit rate can be improved.

  FIG. 1 schematically shows the configuration of a wireless communication apparatus according to an embodiment of the present invention. The illustrated wireless communication apparatus 109 includes an antenna 101, three phase shifters 102, 103, and 104 connected in series to the antenna 101, between the antenna 101 and the phase shifter 102, between the phase shifters 102 and 103, and the phase. The high-frequency switches 105, 106, and 107 are connected between the devices 103 and 104, respectively.

The phase shifters 102, 103, and 104 are constituted by lines such as strip lines that are λ / 8 with respect to the wavelength λ of the received radio wave 108. At this time, the length L of the strip line is determined in consideration of the dielectric constant ε of the substrate and is given by the following equation. Where ε _eff is the effective dielectric constant of the substrate.

The signal transmission speed on the substrate is as shown in the following equation. However, _C0 is the speed of light.

  The time required for the received radio wave to pass through each phase shifter is as shown in the following equation. Where T is the period of the received radio wave.

  Accordingly, the received radio wave 108 passes through each of the phase shifters 102, 103, and 104, so that the phase is rotated by 360 / T × T / 8, and a difference of 45 degrees in one way and 90 degrees in a round trip is obtained. Each phase shifter 102, 103, 104 is connected in series from the antenna 101, and a short-circuit point is provided by a combination of on / off of the high-frequency switches 105, 106, 107. The incoming received radio wave is reflected at the short-circuit point, however, a difference in signal path reciprocating depending on on / off of the switch is provided, and four kinds of phase differences can be given to the reflected wave.

  For example, when only the high frequency switch 105 is turned on, reflection of the received radio wave occurs at point 1a in the figure. When only the high-frequency switch 106 is turned on, reflection of the received radio wave occurs at the point 1b in the figure, but compared with the phase of the reflected wave at the point 1a, the phase is 90 because it passes through the phase shifter 102. Will shift. When only the high-frequency switch 107 is turned on, reflection occurs at the point 1c in the figure, but the phase is shifted by 180 degrees because it passes through the phase shifters 102 and 103 as compared with the phase of the reflected wave at the point 1a. Will do. In addition, when all the high frequency switches 105 to 107 are turned off, reflection occurs at the point 1d in the figure, but compared with the phase of the reflected wave at the point 1a, it passes through the phase shifters 102, 103, and 104. The phase will shift 270 degrees. Therefore, by selectively turning on the high-frequency switches 105, 106, and 107, reflected waves having four phases that are different from each other by 90 degrees can be created.

  When data transmission is performed, QPSK modulation is realized by dividing transmission data into two bits and assigning a phase corresponding to a combination of 0 and 1 of 2 bits. Specifically, the transmission data is divided into two bits. When 00, only the high frequency switch 105 is turned on, when 01, only the high frequency switch 106 is turned on, and when 11, only the high frequency switch 107 is turned on. When it is 10, it operates to turn off all the high-frequency switches 105 to 107.

  Here, when the data is 00, since only the high frequency switch 105 is turned on, reflection occurs at the point 1a.

  When the data is 01, only the high frequency switch 106 is turned on, and reflection occurs at the point 1b. Compared with the phase of the reflected wave at point 1a in the case of data 00, the phase of the reflected wave is shifted by 90 degrees because it passes through the phase shifter 102.

  When the data is 11, since only the high frequency switch 107 is turned on, reflection occurs at the point 1c. Compared with the phase of the reflected wave at point 1a in the case of data 00, the phase of the reflected wave is shifted by 180 degrees because it passes through the phase shifters 102 and 103.

  When the data is 10, since all the high frequency switches 105 to 107 are turned off, reflection occurs at the 1d point. Compared with the phase of the reflected wave at point 1a in the case of data 00, the phase of the reflected wave is shifted by 270 degrees because it passes through the phase shifters 102, 103 and 104.

  In this way, according to the 2-bit value of data, it is possible to create reflected waves having four phases that are 90 degrees apart from each other, and a QPSK-modulated reflected wave can be created.

  FIG. 2 shows the time until the received radio wave is reflected via the phase shifters 102, 103, and 104 when the radio wave 108 having the transmission frequency f “Hz” is incident on the wireless communication device 109.

  The point 2a in the figure is the time required for the received radio wave to be reflected at point 1a in FIG. 1, the point 2b is the time required for reflection at point 1b via the phase shifter 102, and the point 2c is The time required for reflection at the point 1c via the phase shifters 102 and 103, and the point 2d indicate the time required for reflection at the point 1d via the phase shifters 102, 103 and 104, respectively. From the figure, the time difference between 2a and 2b, the time difference between 2b and 2c, and the time difference between 2c and 2d are T · 4, respectively, and there is a difference of 90 degrees (360 / T × T / 4) as a phase difference.

  For example, when only the high frequency switch 105 is turned on, reflection of the received radio wave occurs at a point 1a in FIG. When only the high-frequency switch 106 is turned on, reflection of the received radio wave occurs at the point 1b in the figure, but compared with the phase of the reflected wave at the point 1a, the phase is 90 because it passes through the phase shifter 102. Shift degrees. When only the high-frequency switch 107 is turned on, reflection occurs at the point 1c in the figure, but the phase is shifted by 180 degrees because it passes through the phase shifters 102 and 103 as compared with the phase of the reflected wave at the point 1a. Will do. Further, when all of the high frequency switches 105, 106, and 107 are off, reflection occurs at the point 1d in the figure, but compared with the phase of the reflected wave at the point 1a, it passes through the phase shifters 102, 103, and 104. The phase will shift 270 degrees. Therefore, by selectively turning on / off the high frequency switches 105, 106, and 107, it is possible to create reflected waves having four phases different from each other by 90 degrees, and for the reflected waves of the received radio wave, QPSK Modulation can be applied.

  The wireless communication device 109 configured as shown in FIG. 1 is effective when the high-frequency switches 105, 106, and 107 can realize an ideal open / short, but actually operates ideally. There is nothing.

  The high-frequency switch for switching the reflection points 1a to 1c is usually realized by a diode or the like (for example, a pin diode) as shown in FIG. 3, and is switched by conduction / non-conduction of the diode. This type of switching element is a delay element that operates as an equivalent circuit (RL) of reactance and inductance when turned on and as an equivalent circuit (C) of capacitance when turned off.

  For simplification, a bias circuit for controlling conduction / non-conduction of the diodes 301, 302, and 303 is not shown in FIG. 3, but actually, the diodes 301, 302 are formed by a bias circuit (not shown). , 303 is controlled to switch the reflection point.

  FIG. 4 shows a circuit equivalently representing the case where only the diode 303 in FIG. 3 is conductive.

  In FIG. 4, the conductive diode 303 is equivalently indicated by an inductor component 403 and a resistance component 404, and the nonconductive diodes 302 and 303 are equivalently indicated by capacitor components 401 and 402. Normally, the capacitor components have very small values, but when they are connected in a plurality as shown in FIG. 4, the influence cannot be ignored. Specifically, there is a problem that mismatch occurs between the antenna 101 and the phase shifter 102 and between the phase shifter 102 and the phase shifter 103 in FIG. 1, and the power of the reflected wave is attenuated.

  The capacitor components 401 and 402 and the inductor component 403 operate as delay elements, respectively. FIG. 5 shows the time until the received radio wave is reflected via the phase shifters 304, 305, and 306 in FIG.

  In FIG. 3, point 5a is the time required for the received radio wave to be reflected at point 3a in FIG. 3, point 5b is the time required for reflection at point 3b via phaser 304, and point 5c is phaser 304. Time required for reflection at point 3c via 305, and point 5d indicate the time required for reflection at point 3d via phase shifters 304, 305 and 306, respectively.

  From the figure, the time difference between 5a and 5b, the time difference between 5b and 5c, and the time difference between 5c and 5d are different, so that any of the diodes 301, 302, and 303 is selectively turned on / off. It can be seen that the phase difference between the reflected waves passing through the phase shifters 304, 305, and 306 is not necessarily 90 degrees, and that the QPSK modulation accuracy is deteriorated.

  Therefore, in order to realize the back scatter type QPSK modulation method, it is necessary to reduce the attenuation of electric power in reflection and obtain a more accurate phase difference for each reflection point to improve the modulation accuracy.

  Therefore, in the following, by adjusting the length of each phase shifter in consideration of the delay time of the switch element, the time for the received radio wave to reciprocate through each phase shifter is T / 4, T / 2, 3 / 4T (T The second embodiment of the present invention, in which the circuit is configured so that the period of the received radio wave) is further described.

  In this embodiment, an inductance element that resonates in parallel with the inter-terminal capacitance of the switch element is connected in parallel with the switch element, so that mismatch due to the capacitor component when the switch element is off is suppressed, and the power of the reflected wave is reduced. Can be prevented.

  In this embodiment, the switch element is connected in series with each phase shifter. In this case, the capacitor element that is in series resonance with the parasitic inductor component when the switch element is turned on is connected in series with the switch element. As a result, mismatch due to the inductor component when the switch element is on can be suppressed, and a reduction in the power of the reflected wave can be prevented.

  FIG. 6 shows the configuration of a back scatter type wireless communication apparatus according to the second embodiment of the present invention. The wireless communication device 613 is built in a device serving as a transmission source of image data such as a digital camera or a camera-equipped mobile phone, and is driven using, for example, a battery (not shown) as a main power source.

  The QPSK modulator 612 includes an antenna 601 that receives a radio wave 615 coming from the reader 614, three phase shifters 602, 603, and 604 connected in series to the antenna 601, and a phase shifter between the antenna 601 and the phase shifter 602. It is comprised by the diodes 605, 606, and 607 as a high frequency switch connected between 602 and 603 and between the phase shifters 603 and 604, respectively.

  One of the diodes 605 is connected between the antenna 601 and the phase shifter 602, the other is connected to the ground, one of the diodes 606 is connected between the phase shifter 602 and the phase shifter 603, and the other is connected to the ground. One is connected between the phase shifter 603 and the phase shifter 604, and the other is grounded. Inductor elements 608, 609, and 610 that resonate in parallel with the inter-terminal capacitances of the diodes 605, 606, and 607 are connected in parallel to the diodes 605, 606, and 607, respectively.

  The phase shifters 602, 603, and 604 are configured by a line such as a strip line that has a wavelength of λ / 8 with respect to the wavelength λ of the received radio wave 615. Since the phase shifters 602, 603, and 604 are connected in series from the antenna 601, the four reflection points 6a, 6b, 6c, and 6d have different phase differences in the round trip path.

  When transmitting the data, the wireless communication device 613 converts the data to be transmitted into a bit image by the data decoding unit 611, and controls conduction / non-conduction of the diodes 604, 605, 606 according to the bit image. At this time, the incoming received radio wave 615 is reflected at any one of the short-circuit points 6a, 6b, 6c, and 6d formed by conduction / non-conduction of the diode, and is radiated from the antenna 601 as a reflected wave 616. Depending on the conduction / non-conduction state of the diodes 604, 605, and 606, the signal path along which the reflected wave reciprocates is determined, and four kinds of phase differences can be given to the reflected wave.

  Note that a bias circuit that controls conduction / non-conduction of the diodes 604, 605, and 606 is not shown, but actually, a bias circuit (not shown) that controls conduction / non-conduction of the diodes 604, 605, and 606 is illustrated. Is added.

  The phase shifters 602, 603, and 604 are configured by lines such as strip lines having lengths L1, L2, and L3, respectively. The lengths L1, L2, and L3 of the phase shifters 602, 603, and 604 are the required time t1 when the received radio wave is reflected at the point 6a, the required time t2 when the reflected wave is reflected at the point 6b via the phase shifter 602, It is determined in consideration of the required time t3 when reflecting at the point 6c via the phase shifters 602 and 603, and the required time t4 when reflecting at the point 6d via the phase shifters 604, 605 and 606, t2- t1, t3-t2, and t4-t3 are adjusted to be T / 4 (T: period of received radio wave).

  In FIG. 7, as a result of adjusting the lengths L1, L2, and L3 of the phase shifters 602, 603, and 604 as described above, the time until the received radio wave is reflected via the phase shifters 604, 605, and 606 is shown. An example is shown. However, in FIG. 6, when the frequency of the radio wave 615 coming from the reader is 2.5 G [Hz] in FIG. 6, the time until the received radio wave is reflected via the phase shifters 602, 603, and 604 is shown. ing.

In FIG. 7, point 7 a is the time required when the received radio wave is reflected at point 6 a in FIG. 6, point 7 b is the time required for reflection at point 6 b via phaser 602, and point 7 c is phaser 602. The time required for reflection at a point 6c via 603 and the point 7d indicate the time required for reflection at a point 6d via phase shifters 602, 603 and 604. The time difference between 7a-7b, the time difference between 7b-7c, and the time difference between 7c-7d is 100 picoseconds, and is T / 4 for the period of the incoming radio wave T = 1 / 2.5 GHz = 400 picoseconds. . That is, the reflected wave can obtain a phase difference of 360 / T × T / 4 = 90 degrees corresponding to T / 4 every time it passes through the phase shifters 602, 603, and 604.

  Therefore, by selectively making the diodes 605, 606, and 607 conductive / non-conductive, reflected waves having four phases different from each other by 90 degrees can be created. High-precision QPSK modulation can be applied.

  The data decoding unit 611 implements QPSK modulation by assigning a phase corresponding to a combination of 0 and 1 of 2 bits. Specifically, the data is divided into 2 bits. When 00, only the diode 605 is turned on. When 01, only the diode 606 is turned on. When 11 is set, only the diode 607 is turned on. Operates to turn off all diodes.

  Here, when the data is 00, since only the diode 605 is conductive, the received radio wave is reflected at the point 6a, is radiated from the antenna 601 as a reflected wave having a certain phase, and is received by the reader 614.

  When the data is 01, only the diode 606 becomes conductive, and reflection occurs at the point 6b. At this time, when compared with the phase of the reflected wave at point 6a in the case of data 00, the phase of the reflected wave is shifted by 90 degrees because it passes through the phase shifter 602. Further, the diode 605 is connected in parallel with an inductor element 608 that cancels the non-conducting capacitor component by parallel resonance, so that mismatch between the antenna 601 and the phase shifter 602 due to the non-conducting capacitor component is suppressed. Thus, the decrease in reflected wave power can be reduced.

  When the data is 11, only the diode 607 becomes conductive, and reflection occurs at the point 6c. Compared with the phase of the reflected wave at point 6a in the case of data 00, the phase of the reflected wave is shifted by 180 degrees because it passes through the phase shifters 602 and 603. Furthermore, since the diodes 605 and 606 are connected in parallel with the inductor elements 608 and 609 for canceling the capacitor component in the non-conducting state by parallel resonance, the antenna by the capacitor component in the non-conducting state of the diodes 605 and 606 is connected. The mismatch between 601 and the phase shifter 602 and the mismatch between the phase shifter 602 and the phase shifter 603 can be suppressed, and the decrease in the reflected wave power can be reduced.

  When the data is 10, since all the diodes 605, 606, and 607 are non-conductive, reflection occurs at the 6d point. Compared with the phase of the reflected wave at the point 6a in the case of data 00, the phase of the reflected wave is shifted by 270 degrees because it passes through the phase shifters 602, 603, and 604. Furthermore, the diodes 605, 606, and 607 are connected in parallel with the inductor elements 608, 609, and 610 that cancel the capacitor components at the time of non-conduction by parallel resonance. The mismatch between the antenna 601 and the phase shifter 602, the mismatch between the phase shifter 602 and the phase shifter 603, and the mismatch between the phase shifter 603 and the phase shifter 604 due to the capacitor component at the time can be suppressed, and the reduction in reflected wave power can be reduced. .

  In this way, according to the value of data 2 bits, it is possible to create reflected waves having four phases different from each other by 90 degrees, and a QPSK-modulated reflected wave can be created with high accuracy.

  FIG. 8 shows a modification of the QPSK modulator 612 shown in FIG.

  In the embodiment shown in FIG. 6, an inductance element that resonates in parallel with the inter-terminal capacitance of the switch element is connected in parallel with the switch element, thereby creating a reflection point by a short circuit due to conduction / non-conduction of the switch element. In this case, mismatch due to the capacitor component when the switch element is off can be suppressed, and a reduction in the power of the reflected wave can be prevented.

  On the other hand, in the embodiment shown in FIG. 8, the switch elements 805, 806, and 807 are connected in series to the phase shifters 802, 803, and 804, and are reflected when the switch elements are opened and closed by conduction / non-conduction. Configured to make dots. In this case as well, the diodes 805, 806, and 807 are selectively turned on / off, so that reflected waves having four phases different from each other by 90 degrees can be created. Highly accurate QPSK modulation can be applied.

  In the example shown in FIG. 8, capacitor elements 808, 809, and 810 for canceling the inductor component that is parasitic at the time of conduction by series resonance are connected in series to the diodes 805, 806, and 807, depending on the inductor component. Mismatch between the antenna 801 and the phase shifter 802, between the phase shifter 802 and the phase shifter 803, and between the phase shifter 803 and the phase shifter 804 can be suppressed, and a decrease in reflected wave power can be reduced.

  In each of the embodiments described above, a diode is used as the switching element. However, the gist of the present invention is not limited to this, and for example, a gallium arsenide IC may be used. Since the power consumption of a gallium arsenide IC is generally several tens of μW or less, in this case, QPSK modulation can be performed with extremely low consumption.

  The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiment without departing from the gist of the present invention. That is, the present invention has been disclosed in the form of exemplification, and the contents described in the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims section described at the beginning should be considered.

FIG. 1 is a diagram schematically showing a configuration of a wireless communication apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing the time until the received radio wave is reflected through the phase shifters 102, 103, and 104 when the radio wave 108 with the transmission frequency f [Hz] is incident on the wireless communication device 109. FIG. 3 is a diagram showing an actual circuit configuration of the QPSK modulator shown in FIG. FIG. 4 is a diagram showing an equivalent circuit in the case where only the diode 303 is conductive in the back scatter QPSK modulator shown in FIG. FIG. 5 is a diagram showing the time until the received radio wave is reflected via the phase shifters 304, 305, and 306 in the back scatter QPSK modulator shown in FIG. FIG. 6 is a diagram showing a configuration of a back-scatter wireless communication apparatus according to the second embodiment of the present invention. FIG. 7 is a diagram showing an example of the time until the received radio wave is reflected via the phase shifters 604, 605, and 606 as a result of adjusting the lengths L1, L2, and L3 of the phase shifters 602, 603, and 604. It is. FIG. 8 is a diagram showing a modification of the QPSK modulator 612 shown in FIG. FIG. 9 is a diagram illustrating a configuration example of a conventional RFID system.

Explanation of symbols

601... Antenna 602 603 604 Phase shifter 605 606 607 Diode 608 609 610 Inductor element 612 QPSK modulator 614 Reader

Claims (3)

A wireless communication device that performs data communication by a back scatter method using absorption and reflection of received radio waves,
An antenna for receiving radio waves coming from the transfer destination;
First, second, and third phase shifters configured with striplines or other lines and sequentially connected in series to the antenna;
A first diode that is connected between the antenna and the first phase shifter , the other is grounded, and switches between conduction and non-conduction ;
A second diode that is connected between the first phase shifter and the second phase shifter , the other is grounded, and switches between conduction and non-conduction ;
A third diode , one of which is connected to the second phaser and the third phaser, and the other is grounded, and switches between conduction and non-conduction ;
Back scatter type phase modulation means for obtaining four reflection points having different phase differences by combination of conduction / non-conduction of the first to third diodes ;
The time difference between the case where the received radio wave in the operating frequency band is reflected without passing through any of the first to third phase shifters and the case where the reception radio wave is reflected through only the first phase shifter, the first phase A time difference between the case where the light passes through the first and second phase shifters and the case where the light passes through the first and second phase shifters, and the case where the light passes through the first and second phase shifters. The length of each line constituting the first to third phase shifters so that the time difference when reflected through the third phase shifter is T / 4 with respect to the period T of the incoming radio wave. Phase difference adjusting means for adjusting
A wireless communication apparatus comprising: A wireless communication device that performs data communication by a back scatter method using absorption and reflection of received radio waves,
An antenna for receiving radio waves coming from the transfer destination;
First, second, and third phase shifters configured with striplines or other lines and sequentially connected in series to the antenna;
A first diode that is connected between the antenna and the first phase shifter, the other is grounded, and switches between conduction and non-conduction;
A second diode that is connected between the first phase shifter and the second phase shifter, the other is grounded, and switches between conduction and non-conduction;
A third diode that is connected to the second phase shifter and the third phase shifter, the other is grounded to ground, and switches between conduction and non-conduction;
First to third inductances respectively connected in parallel to the first, second, and third diodes that resonate in parallel with the inter-terminal capacitances of the first, second, and third diodes when not conducting. Elements,
Back scatter type phase modulation means for obtaining four reflection points having different phase differences by combination of conduction / non-conduction of the first to third diodes;
A wireless communication apparatus comprising: A wireless communication device that performs data communication by a back scatter method using absorption and reflection of received radio waves,
An antenna for receiving radio waves coming from the transfer destination;
A first diode connected to the antenna side and the other connected to the first phaser side to switch between conduction and non-conduction;
A second diode that is connected to the first phaser side, the other is connected to the second phaser side, and switches between conduction and non-conduction;
The third diode has one side connected to the second phaser side, the other connected to the third phaser side, and a third diode that switches between conduction and non-conduction,
The first diode and the first phase shifter are connected in series between the second diode and the second phase shifter, and between the third diode and the third phase shifter, respectively. First to third capacitor elements that respectively resonate in series with inductance components that are parasitic when the first, second, and third diodes are conductive;
Back scatter type phase modulation means for obtaining four reflection points having different phase differences by combination of conduction / non-conduction of the first to third diodes;
A wireless communication apparatus comprising:

Images