JP2008109200A - Communication device - Google Patents

Abstract

A communication device capable of writing and reading information to and from a UHF band RFID tag while being a 2.4 GHz band RFID reader / writer, for example.
In general, the impedance of a variable impedance unit 13 is maintained at an optimum value for communication with the 2.4 GHz band RFID tag 2, and the antenna 11 of the RFID reader / writer 1 is connected to the dipole antenna 25 a of the UHF band RFID tag 25. When the DC level signal Qi of the DC voltage detection circuit 32 becomes larger than the threshold value P, the impedance of the variable impedance unit 13 is adjusted, and the antenna 11 of the RFID reader / writer 1 and the dipole of the UHF band RFID tag 25 are adjusted. The antenna 25a is capacitively coupled to enable communication between the RFID reader / writer 1 and the UHF band RFID tag 25.
[Selection] Figure 1

Description

  The present invention relates to a communication device such as a reader / writer that performs wireless communication with a tag.

  Currently, reader / writers (RFID reader / writers) that perform wireless communication with tags (RFID tags) mainly have carrier frequencies of 13 MHz, 950 MHz, and 2.4 GHz.

  Among them, the one of 950 MHz is called a UHF band RFID reader / writer. Since this reader / writer has a long communicable distance of about 10 m, for example, it is suitable for RFID (Radio Frequency Identification) for merchandise and physical distribution management and has attracted attention. For example, it is possible to attach a tag to a product, distribute the product and the tag from the manufacturer to the consumer, and manage the product while writing and reading information on the tag in the distribution process. That is, products can be managed from the upstream to the downstream of the distribution process using the same tag.

  However, due to severe restrictions on the use of radio waves in the UHF band, UHF band RFID reader / writers are equipped with a crystal oscillator for accurately maintaining and stabilizing the carrier frequency, and for preventing spurious signals. Expensive parts are required, such as inserting a plurality of various filters such as SAW filters and dielectric filters, and it is difficult to reduce the size and cost.

  The frequency band near 2.4 GHz is used not only for communication but also in fields such as a microwave oven and medical equipment, and is used at a high output. For this reason, in this frequency band, compared to the UHF band, restrictions on the use of radio waves are not stricter, and the 2.4 GHz band RFID reader / writer can be configured with inexpensive parts, enabling downsizing and cost reduction. Therefore, it can be expected to spread to general users. However, since the restrictions on the use of radio waves are loose, the effective use area is specified for factories and warehouses, and it is not suitable for a wide range of products and logistics management like the UHF band.

On the other hand, Patent Document 1 discloses a technique in which a plurality of capacitances are selectively connected in parallel to an antenna on a tag to control and control a power supply voltage. The capacitance is not used for the purpose of communication control with an external device.
JP 2001-160122 A

  In this way, UHF band RFID reader / writers are suitable for merchandise and logistics management, but regulations on the use of radio waves in the UHF band are strict, expensive parts are required, and miniaturization and cost reduction are difficult. Therefore, it is unlikely that it will spread to general users.

  In addition, the 2.4 GHz band RFID reader / writer can be configured with inexpensive parts, and can be reduced in size and cost, and can be expected to spread to general users. It is specified and not suitable for a wide range of goods and logistics management such as UHF band.

  Furthermore, the conventional 2.4 GHz band RFID reader / writer is used in a completely different frequency band from the UHF band RFID reader / writer, and information cannot be written to or read from the UHF band RFID tag.

  Therefore, the present invention has been made in view of the above-described conventional problems, and provides a communication device capable of writing and reading information to and from a UHF band RFID tag, for example, while being a 2.4 GHz band RFID reader / writer. For the purpose.

  In order to solve the above problems, the present invention provides a carrier transmitting / receiving antenna in a communication device that transmits and receives a carrier wave to an external device, receives the carrier wave reflected by the external device, and transmits and receives signals. Means, a transmission / reception means for transmitting / receiving a carrier wave via the antenna means, a variable impedance means inserted between the antenna means and the transmission / reception means, and a reception level of the carrier wave received by the transmission / reception means, Control means for adjusting and controlling the impedance of the variable impedance means in accordance with the detected reception level of the carrier wave.

  For example, the control means adjusts and controls the impedance of the variable impedance means so that the reception level of the detected carrier wave becomes the lowest.

  Alternatively, the control means uses the carrier to change the variable so that the received level of the detected carrier becomes the lowest when communicating with an external device using a frequency of another carrier different from the frequency of the carrier. Adjust and control the impedance of the impedance means.

  The variable impedance means includes a variable capacitor, and the control means adjusts and controls the capacitance of the variable capacitor.

  Alternatively, the variable impedance means includes a variable inductor, and the control means adjusts and controls the inductance of the variable inductor.

  The antenna means is a dipole antenna.

  Alternatively, the antenna means is a meander antenna.

  In such a communication apparatus of the present invention, a carrier wave is transmitted to an external apparatus, and the carrier wave reflected by the external apparatus is received to transmit and receive signals. In this case, if the impedance of the variable impedance means inserted between the antenna means and the transmission / reception means is set to a specified value, a carrier wave can be transmitted / received to / from an external device.

  Also, if the reception level of the carrier wave received by the transmission / reception means is detected and the impedance of the variable impedance means is adjusted and controlled according to the detected reception level, the frequency of another carrier wave different from the frequency of the carrier wave is used. It is also possible to communicate with an external device. Therefore, communication is possible between any of the original external device and other external devices.

  For example, the impedance of the variable impedance means is adjusted and controlled so that the detected reception level of the carrier wave becomes the lowest. Alternatively, the impedance of the variable impedance means is adjusted and controlled so that the reception level of the detected carrier becomes the lowest when communicating with an external device using a frequency of another carrier different from the frequency of the carrier using the carrier. . However, it is assumed that the communication device and an external device using another carrier frequency are arranged close to each other. In the state where both devices are arranged close to each other, the reception level of the carrier wave is the lowest, the reflection level of the carrier wave from the antenna of the other external device is low, and the absorption level of the carrier wave in this other external device is high This means that the carrier wave is reliably received by the other external device. This enables communication with other external devices.

  More specifically, assuming that the communication device is a 2.4 GHz band RFID reader / writer and the external device is also a 2.4 GHz band RFID tag, when communicating with the RFID tag, the impedance of the variable impedance means is a specified value. And communication between the RFID reader / writer and the RFID tag is performed. In addition, when communicating with a 950 MHz UHF band RFID tag, the impedance of the variable impedance means is set so that the reception level of the detected carrier wave becomes the lowest with the 2.4 GHz band RFID reader / writer and the UHF band RFID tag placed close together. Adjust and control. As a result, the reflection level of the carrier wave from the antenna of the UHF band RFID tag is lowered, the absorption level of the carrier wave at the antenna of the UHF band RFID tag is increased, and communication with the UHF band RFID tag becomes possible. . When the 2.4 GHz band RFID reader / writer and UHF band RFID tag are placed close together, the antenna on the reader / writer side and the antenna on the tag side are capacitively coupled, so the impedance of the variable impedance means is adjusted and detected by the reader / writer. By making the received level of the received carrier wave the lowest, the absorption level of the carrier wave at the tag can be increased.

  As the variable impedance means, a variable capacitor such as a variable capacitance diode can be used. Alternatively, a variable inductor can be used as the variable impedance means.

  As the antenna means, a dipole antenna, a meander antenna, or the like employed in an RFID reader / writer or an RFID tag can be used. Other types of antennas may be used.

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

  FIG. 1 is a block diagram showing an embodiment of a communication apparatus of the present invention. The communication apparatus according to this embodiment is a 2.4 GHz band RFID reader / writer 1, and performs communication with the 2.4 GHz band RFID tag 2 to write and read information with respect to the RFID tag 2.

  The RFID reader / writer 1 includes an antenna 11, a transceiver 12, a variable impedance unit 13 inserted between the antenna 11 and the transceiver 12, and a control unit 14 that adjusts and controls the impedance of the variable impedance unit 13.

  The antenna 11 is a dipole antenna for transmitting and receiving a 2.4 GHz band carrier wave. The variable impedance unit 13 is formed by connecting a coil 13 a and a variable capacitance diode 13 b in series, and both ends of the series circuit are connected to respective lines from the transceiver 12 to each element of the antenna 11.

  The transceiver 12 includes a local oscillator 21 that oscillates and outputs a carrier signal in the 2.4 GHz band, a carrier circuit from the local oscillator 21, a transmission circuit 22 that generates a transmission signal and outputs the transmission signal to the antenna 11, and a local oscillator 21. Receiving circuit 23 that demodulates the received signal from antenna 11 using the carrier wave signal from, and transmits the transmission signal in the direction from transmitting circuit 22 to antenna 11 and receives the signal in the direction from antenna 11 to receiving circuit 23. Is provided.

  The transmission circuit 22 receives the carrier signal Sh from the local oscillator 21 as shown in FIG. 2B, for example, and also receives the information signal Si as shown in FIG. Sh is modulated to output a transmission signal St as shown in FIG. The transmission signal St is applied to the antenna 11 via the directional coupler 24, transmitted as an electromagnetic wave from the antenna 11, and received by the RFID tag 2.

  Further, the transmission circuit 22 outputs the transmission signal St as it is without modulating the carrier signal Sh of FIG. 2B during the response period of the RFID tag 2.

  As shown in FIG. 3, the reception circuit 23 includes a mixer 23 a and a low-pass filter 23 b, and receives a reception signal Sr from the RFID tag 2 through the antenna 11 and the directional coupler 24 during the response period of the RFID tag 2. Then, the mixer 23a mixes the received signal Sr and the carrier signal Sh from the local oscillator 21 to perform frequency selection, and the low-pass filter 23b removes unnecessary high-frequency components from the output of the mixer 23a, thereby obtaining the demodulated output Sk. Generate and output.

  Here, the RFID tag 2 includes a dipole antenna 2a and a tag IC 2b. The electromagnetic wave transmission signal St from the transmission circuit 22 is received by the dipole antenna 2a, and the reception signal Str is transmitted from the dipole antenna 2a to the tag IC 2b. input. In the tag IC 2b, a part of the reception signal Str is converted into operating power and consumed.

  Further, the tag IC 2b has an envelope detector composed of a diode D1 and a resistance element R1 as shown in FIG. 4, and when a reception signal Str as shown in FIG. 2C is inputted, this reception signal Str Is passed through the envelope detector to extract only the DC component of the received signal Str, and an information signal Si as shown in FIG. 2A is obtained, and information is written and read out based on the information signal Si. Etc.

  Further, the tag IC 2b has a response circuit formed by connecting a diode D2 and a resistance element R2 in series as shown in FIG. 5, and this response circuit is connected to the dipole antenna 2a. When the response period of the RFID tag 2 is reached, the carrier signal Sh of FIG. 2B is transmitted as it is as the electromagnetic wave transmission signal St from the transmission circuit 22, so that the tag IC 2b applies the response signal Sj to the response circuit, The impedance of the dipole antenna 2a is changed according to the signal Sj, and the level of the transmission signal St of the electromagnetic wave reflected by the dipole antenna 2a is changed as shown in FIG. The transmission signal St in FIG. 2C is received by the antenna 11 of the RFID reader / writer 1 as a reception signal Sr and input to the reception circuit 23.

  The control unit 14 of the RFID reader / writer 1 normally maintains the impedance of the variable impedance unit 13 at an optimum value for communication with the 2.4 GHz band RFID tag 2. That is, at the time of communication between the 2.4 GHz band RFID reader / writer 1 and the 2.4 GHz band RFID tag 2, the impedance of the variable impedance unit 13 is set so that electromagnetic waves are efficiently transmitted and received by the antenna 11 of the RFID reader / writer 1. Set.

  Further, when communicating with the UHF band RFID tag, the control unit 14 of the RFID reader / writer 1 extracts the DC component level of the demodulated output Sk of the receiving circuit 23, and based on the DC component level, the UHF band RFID is extracted. The impedance of the variable impedance unit 13 is adjusted so that communication with the tag is efficiently performed. When adjusting the impedance of the variable impedance unit 13, as in the response period of the RFID tag 2, the reception signal Sr is received in the state where the carrier signal Sh in FIG. Then, the demodulated output Sk of the receiving circuit 23 is added to the control unit 14.

  As shown in FIG. 6, in the state where the 2.4 GHz band RFID reader / writer 1 is disposed close to the UHF band RFID tag 25, the antenna 11 of the RFID reader / writer 1 and the dipole antenna 25a of the UHF band RFID tag 25 are capacitively coupled. Communication between the RFID reader / writer 1 and the UHF band RFID tag 25 becomes possible by adjusting the impedance of the variable impedance unit 13. The dipole antenna 25a of the UHF band RFID tag 25 is designed to resonate at around 950 MHz. However, when capacitively coupled to the antenna 11 of the RFID reader / writer 1, the dipole antenna 25a is affected by the impedance of the variable impedance unit 13 and thus has variable impedance. By adjusting the impedance of the unit 13, the resonance occurs in the 2.4 GHz band, and the 2.4 GHz band electromagnetic wave from the RFID reader / writer 1 can be transmitted and received.

  The distance between the RFID reader / writer 1 and the UHF band RFID tag 25 is preferably 3 cm or less (about ¼ of the 2.4 GHz wavelength). In addition, as UHF band RFID tag 25 capable of receiving and responding to a 2.4 GHz band carrier wave signal, there is UCODE HSL (trade name) manufactured by Philips, for example, and many UHF bands. Since the RFID tag is made by an IC process capable of processing a 2.4 GHz carrier wave signal for miniaturization and power saving, it can be used in most UHF band RFID tags.

  Next, the configuration and operation of the control unit 14 of the RFID reader / writer 1 will be described in detail. As shown in FIG. 7, the control unit 14 of the RFID reader / writer 1 includes a low-pass filter 31, a DC voltage detection circuit 32, a delay circuit 33, a comparison circuit 34, an addition / subtraction circuit 35, a delay circuit 36, and a DC voltage output circuit 37. I have.

  The DC voltage detection circuit 32 inputs the demodulated output Sk of the receiving circuit 23 via the low-pass filter 31, extracts the DC component of the demodulated output Sk, and outputs a DC level signal Qi indicating the level of the DC component. Since this DC level signal Qi indicates the level of the DC component of the demodulated output Sk of the receiving circuit 23, it indicates the level of the received signal Sr from the tag. Since the level of the reception signal Sr corresponds to the level of the electromagnetic wave of the carrier wave reflected by the tag antenna, the DC level signal Qi indicates the level of the electromagnetic wave of the carrier wave reflected by the tag antenna.

  This DC level signal Qi is applied to the comparator 34 and also to the delay circuit 33. The delay circuit 33 delays the DC level signal Qi for a predetermined time and then applies it to the comparison circuit 34. As a result, the DC level signal Qi1 detected this time and the DC level signal Qi0 detected last time are added to the comparison circuit 34. The comparison circuit 34 compares the DC level signal Qi1 detected this time with the DC level signal Qi0 detected last time, and adds the comparison result to the addition / subtraction circuit 35.

  Further, the delay circuit 36 delays the output level instruction signal Qc of the addition / subtraction circuit 35 for a predetermined time and then adds it to the addition / subtraction circuit 35. As a result, the previous output level instruction signal Qc0 is added to the addition / subtraction circuit 35.

  The addition / subtraction circuit 35 obtains the level of the current output voltage signal Qo by adding or subtracting the specified level to the level of the output voltage signal Qo indicated by the previous output level instruction signal Qc0, and obtains the current output voltage signal Qo. The current output level instruction signal Qc1 indicating the current level is applied to the DC voltage output circuit 37.

  When the current output level instruction signal Qc1 is input, the DC voltage output circuit 37 adjusts the output voltage signal Qo to a level indicated by the output level instruction signal Qc1, and the output voltage signal Qo is converted to the coil 13a of the variable impedance unit 13. And applied to a series circuit composed of the variable capacitance diode 13b. This output voltage signal Qo becomes a reverse bias of the variable capacitance diode 13b and changes the capacitance of the variable capacitance diode 13b. As a result, the impedance of the variable impedance unit 13 is adjusted. Specifically, when the level of the output voltage signal Qo increases, the capacitance of the variable capacitance diode 13b decreases, and when the level of the output voltage signal Qo decreases, the capacitance of the variable capacitance diode 13b increases.

  Here, if the comparison result of the comparison circuit 34 indicates that the current DC level signal Qi1 is less than the previous DC level signal Qi0, the addition / subtraction circuit 35, that is, the carrier wave reflected by the tag antenna. If the electromagnetic wave level is small, the previous addition or subtraction is maintained, and the level of the current output voltage signal Qo is derived from the previous output voltage signal Qo to indicate the level of the current output voltage signal Qo. The current output level instruction signal Qc1 is generated and output. For example, when the previous addition is performed by the addition / subtraction circuit 35, the level of the current output voltage signal Qo obtained by adding the specified level to the previous output voltage signal Qo is derived, and the level of the current output voltage signal Qo is determined. The current output level instruction signal Qc1 shown is output. If the previous subtraction is performed by the addition / subtraction circuit 35, the level of the current output voltage signal Qo obtained by subtracting the specified level from the previous output voltage signal Qo is derived, and the level of the current output voltage signal Qo is obtained. The current output level instruction signal Qc1 shown is output.

  If the comparison result of the comparison circuit 34 indicates that the current DC level signal Qi1 is larger than the previous DC level signal Qi0, that is, the level of the electromagnetic wave of the carrier wave reflected by the tag antenna is increased. Then, after changing the previous addition or subtraction, the level of the current output voltage signal Qo is derived from the previous output voltage signal Qo, and the current output level indicating the level of the current output voltage signal Qo. The instruction signal Qc1 is generated and output. For example, if the previous addition has been performed by the addition / subtraction circuit 35, switching from addition to subtraction, the level of the current output voltage signal Qo obtained by subtracting the specified level from the previous output voltage signal Qo, and the current output A level instruction signal Qc1 is output. When the previous subtraction is performed by the addition / subtraction circuit 35, the subtraction is switched to the addition, the level of the current output voltage signal Qo obtained by adding the specified level to the previous output voltage signal Qo, and the current output is derived. A level instruction signal Qc1 is output.

  As a result, the level of the output voltage signal Qo of the DC voltage output circuit 37 is changed so that the level of the electromagnetic wave of the carrier wave reflected by the tag antenna is always reduced, and the impedance of the variable impedance unit 13 is adjusted. .

  Thus, when the level of the carrier wave reflected by the tag antenna is reduced, the absorption level of the carrier wave at the tag antenna is high, and the carrier wave is reliably received by the tag antenna. Therefore, it is possible to reliably perform communication between the RFID reader / writer 1 and the tag.

  The graph of FIG. 8 shows an output voltage signal Qo and a DC level signal Qi (DC of the demodulated output Sk) applied to the variable impedance unit 13 in communication between the 2.4 GHz band RFID reader / writer 1 and the 2.4 GHz band RFID tag 2. The characteristic of the component level is indicated by a dotted line H.

  As is apparent from the characteristics of the dotted line H, when the output voltage signal Qo applied to the variable impedance unit 13 is at a specified level, that is, when the impedance of the variable impedance unit 13 is at a specified value, the DC level signal Qi (demodulated output) It can be seen that the level of the DC component of Sk) is the lowest value, and the level of the electromagnetic wave of the carrier wave reflected by the antenna 2a of the 2.4 GHz band RFID tag 2 is the lowest. At this time, communication between the RFID reader / writer 1 and the RFID tag 2 can be reliably performed.

  However, in the actual communication between the 2.4 GHz band RFID reader / writer 1 and the 2.4 GHz band RFID tag 2, consideration is given to variations in the resonance frequency of the antenna 2 a of the RFID tag 2 and impedance adjustment errors of the variable impedance unit 13. However, it is not necessary to adjust the impedance of the variable impedance unit 13 one by one. For this reason, the control unit 14 normally sets and fixes the output voltage signal Qo of the DC voltage output circuit 37 at a specified level, and the impedance of the variable impedance unit 13 is optimal for communication with the 2.4 GHz band RFID tag 2. This impedance adjustment is not performed while keeping the value fixed.

  Further, in the graph of FIG. 8, the output voltage signal Qo and the DC level signal Qi (DC of the demodulated output Sk) applied to the variable impedance unit 13 in the communication between the 2.4 GHz band RFID reader / writer 1 and the UHF band RFID tag 25 are shown. The characteristic of the component level is indicated by a solid line I.

As is clear from the characteristics of this solid line I, when communicating with the UHF band RFID tag 25,
By adjusting the output voltage signal Qo applied to the variable impedance unit 13, that is, by adjusting the impedance of the variable impedance unit 13, the DC level signal Qi (the level of the DC component of the demodulated output Sk) is adjusted to the minimum value. can do. At this time, the level of the electromagnetic wave of the carrier wave reflected by the dipole antenna 25a of the UHF band RFID tag 25 is the lowest and the absorption level of the carrier wave by the dipole antenna 25a is high, so the RFID reader / writer 1 and the UHF band RFID tag Communication with 25 can be performed reliably.

  As shown in FIG. 6, the communication with the UHF band RFID tag 25 is performed in a state where the 2.4 GHz band RFID reader / writer 1 is disposed close to the UHF band RFID tag 25 and the antenna 11 of the RFID reader / writer 1 and the UHF band RFID tag. This is performed when 25 dipole antennas 25a are capacitively coupled, and the proximity arrangement and capacitive coupling state are not specified. For example, the distance between the RFID reader / writer 1 and the UHF band RFID tag 25 may be about 3 cm, but a good communication state should be set even if it is several mm or about 5 to 6 cm. It is.

  Therefore, when communicating with the UHF band RFID tag 25, the level of the output voltage signal Qo of the DC voltage output circuit 37 is changed by the control unit 14 of the RFID reader / writer 1 as described above, so that the variable impedance unit 13 As shown in the characteristic of solid line I in FIG. 8, the direct current level signal Qi (the level of the direct current component of the demodulated output Sk) is set to the lowest value and reflected by the dipole antenna 25a of the UHF band RFID tag 25. It is necessary to make the level of the electromagnetic wave of the carrier wave the lowest so that the communication between the RFID reader / writer 1 and the UHF band RFID tag 25 is reliably performed.

  Therefore, in the RFID reader / writer 1 of the present embodiment, a threshold P higher than the minimum value of the DC level signal Qi on the dotted line H in FIG. 8 is obtained and set in advance, and the DC level signal Qi of the DC voltage detection circuit 32 is obtained. Is less than the threshold value P, it is assumed that communication with the 2.4 GHz band RFID tag 2 is being performed, the output voltage signal Qo of the DC voltage output circuit 37 is fixed to a specified level, and the impedance of the variable impedance unit 13 is set. When the DC level signal Qi of the DC voltage detection circuit 32 becomes larger than the threshold value P, the communication with the UHF band RFID tag 25 is maintained. The communication between the RFID reader / writer 1 and the UHF band RFID tag 25 is performed by adjusting the impedance of the variable impedance unit 13 as if it is being performed. And in the manner it is really done.

  As apparent from the graph of FIG. 8, when the DC level signal Qi of the DC voltage detection circuit 32 becomes larger than the threshold value P, the RFID reader / writer 1 is disposed close to the UHF band RFID tag 25, and the UHF band RFID tag 25 It can be assumed that the carrier wave reflected by the dipole antenna 25a is received. Conversely, when the DC level signal Qi of the DC voltage detection circuit 32 is less than the threshold value P, it can be assumed that there is no UHF band RFID tag 25 in the vicinity of the RFID reader / writer 1 and the 2.4 GHz band RFID tag 2 exists.

  The control unit 14 of the RFID reader / writer 1 usually fixes the output voltage signal Qo of the DC voltage output circuit 37 to a specified level, and the impedance of the variable impedance unit 13 is optimal for communication with the 2.4 GHz band RFID tag 2. In this state, if the DC level signal Qi becomes larger than the threshold value P while monitoring the DC level signal Qi of the DC voltage detection circuit 32, the RFID reader / writer 1 is connected to the UHF band RFID tag 25. Assuming that they are arranged close to each other, the adjustment control of the impedance of the variable impedance unit 13 is started to enable communication between the RFID reader / writer 1 and the UHF band RFID tag 25.

  9A and 9B show the DC level signal Qi of the DC voltage detection circuit 32 and the DC voltage output circuit 37 when the separation distance between the 2.4 GHz band RFID reader / writer 1 and the UHF band RFID tag 25 is changed. Shows the characteristics of the output voltage signal Qo. FIG. 9C shows the characteristics of the DC level signal Qi of the DC voltage detection circuit 32 when the impedance of the variable impedance unit 13 is not adjusted and controlled as a comparative example.

  As is apparent from FIGS. 9A and 9B, from time t 0 to time t 1, the DC level signal Qi of the DC voltage detection circuit 32 is less than the threshold value P, and the output voltage signal Qo of the DC voltage output circuit 37. Is fixed at a specified level, and the impedance of the variable impedance unit 13 is maintained at an optimum value for communication with the 2.4 GHz band RFID tag 2.

  During the period from time t1 to time t2, the 2.4 GHz band RFID reader / writer 1 is approaching the UHF band RFID tag 25, and the DC level signal Qi of the DC voltage detection circuit 32 increases.

  Since the 2.4 GHz band RFID reader / writer 1 is placed close to the UHF band RFID tag 25 during the period from the time point t2 to the time point t3, the direct current level signal Qi of the direct current voltage detection circuit 32 becomes larger than the threshold value P. The output voltage signal Qo of the voltage output circuit 37 is changed, the impedance of the variable impedance unit 13 is adjusted, and the DC level signal Qi (DC component of the demodulated output Sk) of the DC voltage detection circuit 32 is set to a minimum value and held. . At this time, communication between the RFID reader / writer 1 and the UHF band RFID tag 25 is performed.

  If the impedance of the variable impedance unit 13 is not adjusted during this period, the level of the carrier wave reflected by the antenna 25a of the UHF band RFID tag 25 becomes high, and a DC voltage detection circuit as shown in FIG. 9C. The 32 DC level signal Qi becomes high. In this state, communication between the RFID reader / writer 1 and the UHF band RFID tag 25 is impossible.

  In the period after time t3, the 2.4 GHz band RFID reader / writer 1 is moving away from the UHF band RFID tag 25, and the direct current level signal Qi of the direct current voltage detection circuit 32 rises and falls once. When Qi becomes less than the threshold value P, the output voltage signal Qo of the DC voltage output circuit 37 is fixed to a specified level, and the impedance of the variable impedance unit 13 is adjusted to an optimum value for communication with the 2.4 GHz band RFID tag 2. The

  Next, the process of controlling the impedance of the variable impedance unit 13 by the control unit 14 of the RFID reader / writer 1 will be described with reference to the flowchart of FIG.

  In the control unit 14 of the RFID reader / writer 1, the DC level signal Qi of the DC voltage detection circuit 32 is usually less than the threshold value P, and the output voltage signal Qo of the DC voltage output circuit 37 is fixed to a specified level and is variable. The impedance of the impedance unit 13 is maintained at an optimum value for communication with the 2.4 GHz band RFID tag 2.

  When communication with the UHF band RFID tag 25 is started, the user places the antenna 11 of the RFID reader / writer 1 close to the dipole antenna 25 a of the UHF band RFID tag 25. For this reason, the level of the electromagnetic wave of the carrier wave reflected by the dipole antenna 25a of the UHF band RFID tag 25 becomes high, and the DC level signal Qi of the DC voltage detection circuit 32 exceeds the threshold value P.

  When the DC level signal Qi of the DC voltage detection circuit 32 becomes larger than the threshold value P, the output level instruction signal Qc of the addition / subtraction circuit 35 is initialized (step S101), and the output voltage signal Qo of the DC voltage output circuit 37 is also initialized. It is set (step S102).

  Further, the flag flag is initialized to “+1” instructing addition (step S103). This flag flag is for instructing one of addition and subtraction by the addition / subtraction circuit 35.

  Further, the DC level signal Qi of the DC voltage detection circuit 32 is taken into the delay circuit 33 and the comparison circuit 34 (step S104).

  After the initial setting is performed in this way, the processes of steps S105 to S111 are repeated, and the impedance of the variable impedance unit 13 is adjusted. At the beginning of the processing of steps S105 to S111, the initial value of the output level instruction signal Qc, the initial value of the output voltage signal Qo of the DC voltage output circuit 37, and the initial value of the DC level signal Qi of the DC voltage detection circuit 32 are set. In response, a transitional control state is entered, but a transition is immediately made to the following control state.

  That is, the delay circuit 33 delays the DC level signal Qi for a predetermined time and then applies it to the comparison circuit 34. As a result, the DC level signal Qi1 detected this time and the DC level signal Qi0 detected last time are added to the comparison circuit 34. The comparison circuit 34 compares the DC level signal Qi1 detected this time with the DC level signal Qi0 detected last time, and adds the comparison result to the addition / subtraction circuit 35. Further, the delay circuit 36 delays the output level instruction signal Qc of the addition / subtraction circuit 35 for a predetermined time and then adds it to the addition / subtraction circuit 35. Thereby, the previous output level instruction signal Qc0 is added to the addition / subtraction circuit 35 (step S105).

  The addition / subtraction circuit 35 updates the output voltage signal Qo by adding a certain level α to the output voltage signal Qo indicated by the previous output level instruction signal Qc0 because the flag flag is “+1” instructing addition. Then, the current output level instruction signal Qc1 indicating the level of the updated output voltage signal Qo is applied to the DC voltage output circuit 37 (step S106).

  The DC voltage output circuit 37 applies the output voltage signal Qo indicated by the current output level instruction signal Qc1 to the variable capacitance diode 13b of the variable impedance unit 13 to reduce the capacitance of the variable capacitance diode 13b, thereby changing the variable impedance. The impedance of the unit 13 is adjusted (step S107).

  As a result, the level of the electromagnetic wave of the carrier wave reflected by the dipole antenna 25a of the UHF band RFID tag 25 changes, and the level of the DC component of the demodulated output Sk of the receiving circuit 23 changes.

  Thereafter, the comparison circuit 34 takes in the DC level signal Qi1 detected this time from the DC voltage detection circuit 32 (step S108).

  If the DC level signal Qi of the DC voltage detection circuit 32 is not less than the threshold value P (“No” in step S109), that is, if the RFID reader / writer 1 is not separated from the UHF band RFID tag 25, the comparison circuit. 34 compares the DC level signal Qi1 detected this time with the DC level signal Qi0 detected last time (step S110).

  At this time, if the comparison result indicates that the DC level signal Qi1 detected this time is less than the DC level signal Qi0 detected last time (“Qi1 <Qi0” in step S110), the flag flag remains “+1”. The process returns to the process from step S105 until the previous DC level signal Qi0 is updated, the constant level α is added again to the output voltage signal Qo, and the updated output voltage signal Qo is changed to the variable capacitance of the variable impedance unit 13. When applied to the diode 13b, the capacitance of the variable capacitance diode 13b decreases, the level of the DC component of the demodulated output Sk of the receiving circuit 23 changes, and this DC level signal Qi1 is captured.

  Therefore, as long as the DC level signal Qi1 detected this time is less than the DC level signal Qi0 detected last time and the DC level signal Qi1 detected this time is smaller, the flag flag is maintained at “+1”. Then, a constant level α is repeatedly added to the output voltage signal Qo, the output voltage signal Qo is gradually increased, and this output voltage signal Qo is applied to the variable capacitance diode 13b, and its electrostatic capacity is gradually reduced. The level of the DC component of the demodulated output Sk of the receiving circuit 23 changes.

  If the comparison result indicates that the DC level signal Qi1 detected this time is larger than the DC level signal Qi0 detected last time (“Qi1 <Qi0” in step S110), the flag flag is switched to “−1”. (Step S111), the process returns to Step S105.

  Also in this case, the comparison result between the DC level signal Qi1 detected this time by the comparison circuit 34 and the DC level signal Qi0 detected last time is added to the addition / subtraction circuit 35, and the previous output level instruction signal Qc0 is added to the addition / subtraction circuit. 35 (step S105), the addition / subtraction circuit 35 subtracts a constant level α from the output voltage signal Qo of the DC voltage output circuit 37 because the flag flag is “−1” instructing subtraction. Then, the output level instruction signal Qc indicating the level of the updated output voltage signal Qo is applied to the DC voltage output circuit 37 (step S106).

  The DC voltage output circuit 37 applies the output voltage signal Qo to the variable capacitance diode 13b of the variable impedance unit 13, thereby increasing the capacitance of the variable capacitance diode 13b and adjusting the impedance of the variable impedance unit 13 (step S107). ).

  As a result, the level of the electromagnetic wave of the carrier wave reflected by the dipole antenna 25a of the UHF band RFID tag 25 changes, and the level of the DC component of the demodulated output Sk of the receiving circuit 23 changes.

  Thereafter, the comparison circuit 34 takes in the DC level signal Qi1 detected this time from the DC voltage detection circuit 32 (step S108).

  Further, if the comparison result indicates that the DC level signal Qi1 detected this time is smaller than the DC level signal Qi0 detected last time (“Qi1 <Qi0” in step S110), the flag flag remains “−1”. The process returns to the process from step S105 until the previous DC level signal Qi0 is updated, the constant level α is subtracted again from the output voltage signal Qo, and the updated output voltage signal Qo is changed to the variable capacitance of the variable impedance unit 13. When applied to the diode 13b, the capacitance of the variable capacitance diode 13b increases, the level of the DC component of the demodulated output Sk of the receiving circuit 23 changes, and this DC level signal Qi1 is captured.

  Therefore, as long as the DC level signal Qi1 detected this time is smaller, the flag flag is maintained at “−1”, the constant level α is repeatedly subtracted from the output voltage signal Qo, and the output voltage signal Qo is The output voltage signal Qo is gradually decreased, and the output voltage signal Qo is applied to the variable-capacitance diode 13b so that the capacitance is gradually increased, and the level of the DC component of the demodulated output Sk of the receiving circuit 23 is sequentially changed.

  Thus, as long as the DC level signal Qi1 detected this time becomes smaller, the output voltage signal Qo increases or decreases by a certain level α. When the detected DC level signal Qi1 becomes larger, the addition and subtraction of the constant level α with respect to the output voltage signal Qo is switched to make the DC level signal Qi smaller. Accordingly, the output voltage signal Qo is gradually changed until the DC level signal Qi1 detected this time is minimized, and the capacitance of the variable capacitance diode 13b is adjusted.

  When the DC level signal Qi1 detected this time becomes the smallest, the update of the output voltage signal Qo is stopped, the level of the output voltage signal Qo is maintained, and the capacitance of the variable capacitance diode 13b is constant. Maintained. Thereby, the electromagnetic wave level of the carrier wave reflected by the dipole antenna 25a of the UHF band RFID tag 25 becomes the lowest, and the state where the communication between the RFID reader / writer 1 and the UHF band RFID tag 25 is reliably performed is maintained. .

  When the level of the output voltage signal Qo is maintained so that the DC level signal Qi1 of the DC voltage detection circuit 32 is minimized, the DC level signal Qi further decreases and becomes less than the threshold value P (in step S109). “Yes”), it is considered that the RFID reader / writer 1 is separated from the UHF band RFID tag 25, and the control process of FIG. 10 ends. If the threshold value P is exceeded even if the DC level signal Qi1 changes, the control process of FIG. 10 is restarted from step S110.

  Next, a modification of the impedance control process of the variable impedance unit 13 will be described with reference to the flowchart of FIG. In FIG. 11, the steps having the same functions as those in FIG.

  In this control process, in order to shorten the adjustment time of the capacitance of the variable-capacitance diode 13b, the update width of the output voltage signal Qo is increased at the beginning of the adjustment, and the adjustment of the capacitance is performed roughly. As the value proceeds, the update width of the output voltage signal Qo is reduced, and the capacitance is finely adjusted. Therefore, in FIG. 11, step S103A is inserted and step S112 is added instead of step S103 in FIG.

  Now, when the antenna 11 of the RFID reader / writer 1 is placed close to the dipole antenna 25a of the UHF band RFID tag 25, the level of the electromagnetic wave of the carrier wave reflected by the dipole antenna 25a of the UHF band RFID tag 25 increases, and the DC voltage detection is performed. When the DC level signal Qi of the circuit 32 becomes larger than the threshold value P, the output level instruction signal Qc of the addition / subtraction circuit 35 and the output voltage signal Qo of the DC voltage output circuit 37 are initialized (steps S101 and S102).

  The flag flag is initialized to “+100” instructing addition (step S103). This flag flag “+100” changes the DC level signal Qi of the DC voltage detection circuit 32 at an update level (100 × α) that is 100 times larger than the constant level α when the flag flag “+1” in the control process of FIG. It shows that

  Further, the DC level signal Qi of the DC voltage detection circuit 32 is taken into the delay circuit 33 and the comparison circuit 34 (step S104).

  After the initial setting is performed in this way, the processes in steps S105 to S112 are repeated to enter the following control state.

  The comparison circuit 34 compares the DC level signal Qi1 detected this time with the DC level signal Qi0 detected last time, and adds the comparison result to the addition / subtraction circuit 35. The previous output level instruction signal Qc0 is added to the addition / subtraction circuit 35 (step S105).

  The addition / subtraction circuit 35 adds the update level (100 × α) to the output voltage signal Qo of the DC voltage output circuit 37 and greatly increases the output voltage signal Qo because the flag flag is “+100” instructing addition. And the current output level instruction signal Qc1 indicating the level of the updated output voltage signal Qo is added to the DC voltage output circuit 37 (step S106).

  The DC voltage output circuit 37 applies the output voltage signal Qo indicated by the current output level instruction signal Qc1 to the variable capacitance diode 13b of the variable impedance unit 13, thereby greatly reducing the capacitance of the variable capacitance diode 13b. The impedance of the variable impedance unit 13 is greatly adjusted (step S107).

  As a result, the level of the electromagnetic wave of the carrier wave reflected by the dipole antenna 25a of the UHF band RFID tag 25 changes, and the level of the DC component of the demodulated output Sk of the receiving circuit 23 changes.

  Thereafter, the comparison circuit 34 takes in the DC level signal Qi1 detected this time from the DC voltage detection circuit 32 (step S108).

  If the DC level signal Qi of the DC voltage detection circuit 32 is not less than the threshold value P (“No” in step S109), the DC level signal Qi1 detected this time by the comparison circuit 34 and the DC level signal detected last time are compared. Qi0 is compared (step S110).

  At this time, if the DC level signal Qi1 detected this time is less than the DC level signal Qi0 detected last time (“Qi1 <Qi0” in step S110), the flag flag “+100” is ½. It is updated to “+50”, that is, the update level of the output voltage signal Qo is updated from (100 × α) to (50 × α) which is ½ (step S112). Thereafter, the processing returns to step S105, and the previous time The DC level signal Qi0 is updated, the update level (50 × α) is added to the output voltage signal Qo, and the updated output voltage signal Qo is applied to the variable capacitance diode 13b of the variable impedance unit 13 to be variable. The capacitance of the capacitive diode 13b decreases, the level of the DC component of the demodulated output Sk of the receiving circuit 23 changes, and this DC level signal Qi1 is taken. It is inserted.

  Similarly, as long as the DC level signal Qi1 detected this time is less than the DC level signal Qi0 detected last time and the DC level signal Qi1 detected this time is smaller, the output voltage signal Qo is every time. The update level is halved, and the ½ update level is added to the output voltage signal Qo. As a result, the update width of the output voltage signal Qo is initially greatly increased and gradually decreased, and accordingly, the electrostatic capacitance of the variable capacitance diode 13b is also largely changed initially and gradually changed to a smaller width. The level of the direct current component of the demodulated output Sk of 23 decreases rapidly.

  If the comparison result indicates that the DC level signal Qi1 detected this time is larger than the DC level signal Qi0 detected last time (“Qi1 <Qi0” in step S110), the addition / subtraction circuit 35 switches the flag flag between positive and negative. Change (step S111) and return to the processing from step S105.

  Also in this case, as long as the DC level signal Qi1 detected this time is less than the DC level signal Qi0 detected last time and the DC level signal Qi1 detected this time is smaller, the output voltage signal Qo each time. The update level is halved, and the ½ update level is subtracted from the output voltage signal Qo, so that the update width of the output voltage signal Qo initially becomes large and gradually smaller. As a result, the capacitance of the variable capacitance diode 13b is also significantly changed only at the beginning and gradually changed to a small width, and the level of the DC component of the demodulated output Sk of the receiving circuit 23 is rapidly lowered.

  As a result, the output voltage signal Qo is quickly changed until the DC level signal Qi1 detected this time is minimized, and the capacitance of the variable capacitance diode 13b is also quickly adjusted.

  When the DC level signal Qi1 detected this time becomes the smallest, the update of the output voltage signal Qo is stopped, the level of the output voltage signal Qo is maintained, and the capacitance of the variable capacitance diode 13b is constant. Maintained. Thereby, the level of the electromagnetic wave of the carrier wave reflected by the dipole antenna 25a of the UHF band RFID tag 25 becomes the lowest, and the state where the communication between the RFID reader / writer 1 and the UHF band RFID tag 25 is reliably performed is maintained. The

  When the level of the output voltage signal Qo is maintained so that the DC level signal Qi1 of the DC voltage detection circuit 32 is minimized, the DC level signal Qi further decreases and becomes less than the threshold value P (in step S109). “Yes”), the RFID reader / writer 1 is regarded as being separated from the UHF band RFID tag 25, and the control process of FIG. 11 is terminated. If the threshold level P is exceeded even if the DC level signal Qi1 changes, the control process of FIG. 11 is restarted from step S110.

  As described above, in this embodiment, the impedance of the variable impedance unit 13 is normally maintained at an optimum value for communication with the 2.4 GHz band RFID tag 2, and the antenna 11 of the RFID reader / writer 1 is connected to the UHF band RFID tag 25. When the DC level signal Qi of the DC voltage detection circuit 32 becomes larger than the threshold value P, the impedance of the variable impedance unit 13 is adjusted, and the antenna 11 of the RFID reader / writer 1 and the UHF band RFID are arranged. The dipole antenna 25a of the tag 25 is capacitively coupled to enable communication between the RFID reader / writer 1 and the UHF band RFID tag 25.

  Therefore, although it is the 2.4 GHz band RFID reader / writer 1, it can communicate with both the 2.4 GHz band RFID tag 2 and the UHF band RFID tag 25.

  Moreover, the 2.4 GHz band RFID reader / writer 1 does not require expensive parts such as a crystal oscillator, a SAW filter, and a dielectric filter unlike the UHF band RFID reader / writer, and can be configured with inexpensive parts. Therefore, it can be reduced in size and cost, and can be expected to spread to general users. For example, the RFID reader / writer 1 can be integrated on a 5 mm to 10 mm square chip, and can be mounted on a mobile device such as a mobile phone. In this case, the antenna of the mobile device may be used as the antenna 11 of the RFID reader / writer 1.

  It is also possible to mount the 2.4 GHz band RFID reader / writer 1 on an electronic shelf label having a 2.4 GHz band communication function. In this case, the UHF band RFID tag 25 is attached to the product, the product UHF band RFID tag 25 is brought close to the RFID reader / writer 1 mounted on the electronic shelf label, and the product is read by the RFID reader / writer 1 of the electronic shelf label. It is possible to read / write information from / to the UHF band RFID tag 25. For example, when a customer inadvertently moves a product to another shelf, information is read from the UHF band RFID tag 25 of the product by the RFID reader / writer 1 of the electronic shelf label, and the product is based on this information. Can be returned to the original shelf.

  Or when many electronic shelf labels are used, it is not easy to manage the identification and arrangement of these electronic shelf labels. Therefore, the UHF band RFID tag 25 is mounted on the electronic shelf label, and a handy terminal is separately prepared. The 2.4 GHz band RFID reader / writer 1 is mounted on the handy terminal, and the RFID reader / writer 1 of the handy terminal is used. Information is read from the UHF band RFID tag 25 of the electronic shelf label, and this information is used for management of the electronic shelf label.

  Further, in the production process of the UHF band RFID tag, the 2.4 GHz band RFID reader / writer 1 can be used for inspection of the tag. In particular, in overseas production factories and the like, the UHF band near 950 MHz may be assigned to another communication system and the UHF band may not be used. In such a situation, if the 2.4 GHz band RFID reader / writer 1 is placed close to the UHF band RFID tag, and the RFID reader / writer 1 reads / writes information from / to the UHF band RFID tag, it can be used in other communication systems in the UHF band. The UHF band RFID tag can be inspected without any influence.

  In addition, this invention is not limited to the said embodiment, It can deform | transform variously. For example, although a dipole antenna is illustrated as an antenna for an RFID reader / writer and an RFID tag, a meander antenna 41 as shown in FIG. 12 or another type of antenna may be applied.

  As the variable impedance unit 13, not only a series circuit of the coil 13a and the variable capacitance diode 13b but also a circuit combining a capacitor 13c, a coil 13d and the like as shown in FIGS. 13A to 13H, FIG. A circuit combining the coil 13a and the switch 13e as shown in i), a circuit combining the coil 13a and the high frequency PIN diode 13f as shown in FIG. 13J, and the like can be applied. Alternatively, a known variable inductance element may be used. Further, a variable capacitance diode or a variable inductance element may be used in combination.

  Furthermore, in the above embodiment, the 2.4 GHz band RFID reader / writer is exemplified, but the 2.4 GHz band RFID tag and the UHF band RFID tag are exemplified, but even with other types of communication devices, communication systems, and communication methods, The present invention can be applied.

1 is a block diagram showing a 2.4 GHz band RFID reader / writer which is an embodiment of a communication apparatus of the present invention. FIG. (A), (b), and (c) are waveform diagrams showing an information signal, a carrier wave signal, and a transmission signal input to and output from the transmission circuit in the RFID reader / writer of FIG. FIG. 2 is a block diagram illustrating a configuration of a receiving circuit in the RFID reader / writer of FIG. 1. It is a block diagram which shows the structure of the detector of the RFID tag which communicates with the RFID reader / writer of FIG. It is a block diagram which shows the structure of the response circuit of the RFID tag which communicates with the RFID reader / writer of FIG. FIG. 2 is a diagram conceptually showing a state in which UHF band RFID tags are arranged close to the RFID reader / writer of FIG. 1. It is a block diagram which shows the structure of the control part in the RFID reader / writer of FIG. 2 is a graph showing characteristics of DC component levels of an output voltage signal Qo and a demodulated output Sk applied to a variable impedance unit in the RFID reader / writer of FIG. 1. (A)-(c) is a timing chart which shows the change of the direct-current component level of the output voltage signal Qo applied to the variable impedance part in a RFID reader-writer, and the demodulation output Sk. 3 is a flowchart illustrating a process of controlling impedance of a variable impedance unit in the RFID reader / writer of FIG. 1. 6 is a flowchart illustrating a modification of the impedance control process of the variable impedance unit in the RFID reader / writer of FIG. 1. It is a figure which illustrates the meander antenna applicable to the RFID reader-writer of FIG. (A)-(h) is a figure which shows the modification of the variable impedance part in the RFID reader-writer of FIG. (A), (b) is a figure which shows the other modification of the variable impedance part in the RFID reader-writer of FIG.

Explanation of symbols

1 2.4 GHz band RFID reader / writer 2 2.4 GHz band RFID tag 11 Antenna 12 Transceiver 13 Variable impedance unit 14 Control unit 21 Local oscillator 22 Transmission circuit 23 Reception circuit 24 Directional coupler 25 UHF band RFID tag 31 Low pass filter 32 DC voltage detection circuit 33 delay circuit 34 comparison circuit 35 addition subtraction circuit 36 delay circuit 37 DC voltage output circuit

Claims (7)

In a communication device that transmits a carrier wave to an external device, receives the carrier wave reflected by the external device, and transmits and receives signals.
Antenna means for carrier transmission and reception;
Transmitting and receiving means for transmitting and receiving a carrier wave via the antenna means;
Variable impedance means inserted between the antenna means and the transceiver means;
And a control unit that detects a reception level of the carrier wave received by the transmission / reception unit and adjusts and controls the impedance of the variable impedance unit according to the detected reception level of the carrier wave.   2. The communication apparatus according to claim 1, wherein the control means adjusts and controls the impedance of the variable impedance means so that the reception level of the detected carrier wave becomes the lowest.   When the control means communicates with an external device using a frequency of another carrier different from the frequency of the carrier using the carrier, the variable impedance means so that the received level of the detected carrier becomes the lowest. The communication apparatus according to claim 1, wherein the impedance of the communication apparatus is adjusted and controlled. The variable impedance means includes a variable capacitor,
The communication apparatus according to claim 1, wherein the control unit adjusts and controls a capacitance of the variable capacitor. The variable impedance means includes a variable inductor,
The communication device according to claim 1, wherein the control unit adjusts and controls an inductance of the variable inductor.   The communication apparatus according to claim 1, wherein the antenna unit is a dipole antenna.   The communication apparatus according to claim 1, wherein the antenna unit is a meander antenna.

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