JP4449770B2 - Wireless tag communication device - Google Patents

Description

  The present invention relates to an improvement in a wireless tag communication device that performs communication with a wireless tag capable of wirelessly writing and reading information.

  2. Description of the Related Art An RFID (Radio Frequency Identification) system is known in which information is read out in a non-contact manner by a predetermined wireless tag communication device (interrogator) from a small wireless tag (responder) in which predetermined information is stored. This RFID system is capable of reading information stored in a wireless tag by communication with the wireless tag communication device even when the wireless tag is dirty or disposed at an invisible position. Therefore, practical use is expected in various fields such as merchandise management and inspection processes.

  By the way, normally, the wireless tag communication apparatus transmits a predetermined transmission signal from the antenna toward the wireless tag, and receives a reply signal returned from the wireless tag that has received the transmission signal by the antenna. Although information is communicated with the wireless tag, a strong sneak signal from the transmission side may be mixed in the received reply signal to increase the overall received signal strength. As a result, the allowable input intensity of the amplifier is exceeded, so that the received signal cannot be sufficiently amplified, and as a result, the return signal component cannot be sufficiently amplified, resulting in a decrease in the signal-to-noise ratio. was there. Therefore, a technique for removing such a sneak signal from the transmission side has been proposed. For example, this is an interference compensation device for a mobile object identification device described in Patent Document 1.

JP-A-8-122429

  However, the removal of the sneak signal from the transmission side in the above-mentioned conventional technique is such that the control of the amplitude and phase of the cancel signal (compensation signal) for removing the sneak signal is performed exclusively by analog processing. In addition to the need for an expensive and large phase shifter, there is a negative effect that it is difficult to control. The applicant of the present invention has applied for a wireless tag communication device that outputs the cancel signal as a digital signal in order to eliminate this problem. This is the wireless tag communication device described in Patent Document 2.

Japanese Patent Application No. 2004-28013

  By the way, when the cancel signal is output as a digital signal, a D / A converter for converting the output digital signal into an analog signal is required, and a predetermined attenuation is given according to a sneak signal from the transmission side. Therefore, a high-resolution D / A converter is required. However, in general, a high-resolution D / A converter is slow and expensive, and a high-speed D / A converter is inexpensive but has low and low resolution. Depending on the case, there is a possibility that sufficient removal cannot be performed. In particular, when the amplitude of the sneak signal is considerably smaller than the maximum output amplitude of the D / A converter, even if a high-resolution D / A converter is used, only a part of the output range is used, and the effective resolution is reduced. It will decline. Further, the error due to the nonlinear distortion of the D / A converter becomes relatively large with a decrease in effective resolution, and sufficient phase and amplitude control cannot be performed. For this reason, there has been a demand for the development of a wireless tag communication device having a simple configuration that can suitably remove the sneak signal from the transmission side regardless of the signal level.

  The present invention has been made against the background of the above circumstances, and the object of the present invention is to provide a wireless tag communication device having a simple configuration capable of suitably removing a sneak signal from the transmission side regardless of the signal level. It is to provide.

In order to achieve such an object, the gist of the present invention is that a predetermined transmission signal is transmitted from an antenna toward a wireless tag, and a reply signal returned from the wireless tag according to the transmission signal is transmitted. A wireless tag communication device that communicates information with the wireless tag by receiving it through an antenna, and a cancel signal for removing a sneak signal from the transmission side included in the received signal received by the antenna A cancel signal output unit that outputs a digital signal, a cancel signal D / A conversion unit that performs analog conversion of the cancel signal output from the cancel signal output unit, and reception that detects the amplitude of the received signal received by the antenna Based on the amplitude of the received signal detected by the signal amplitude detector and the received signal amplitude detector, the The output from the Le signal D / A conversion unit to within a predetermined range based on the maximum amplitude, a control signal for controlling at least one of the canceling signal amplitude and phase output from the cancellation signal output portion The cancel signal control unit for outputting the signal, and the amplitude corresponding to the sneak signal from the transmission side of the cancel signal analog-converted by the cancel signal D / A conversion unit based on the control signal output from the cancel signal control unit An attenuating unit for attenuating the signal and a canceling signal attenuated by the attenuating unit and a signal combining unit for combining the received signal.

With this configuration, the cancel signal output unit that outputs a cancel signal for removing the sneak signal from the transmission side included in the reception signal received by the antenna as a digital signal, and the cancel signal output unit outputs the cancel signal. A cancel signal D / A converter for analog conversion of the cancel signal, a received signal amplitude detector for detecting the amplitude of the received signal received by the antenna , and the received signal detected by the received signal amplitude detector Based on the amplitude , at least one of the amplitude and phase of the cancellation signal output from the cancellation signal output unit is set so that the output from the cancellation signal D / A conversion unit is within a predetermined range based on the maximum amplitude. From the cancel signal control unit that outputs a control signal for control and the cancel signal control unit An attenuation unit for attenuating the cancellation signal analog-converted by the cancellation signal D / A conversion unit based on a control signal input to an amplitude corresponding to a sneak signal from the transmission side, and attenuated by the attenuation unit And a signal synthesizer that synthesizes the cancel signal and the received signal. Therefore, by changing the setting of the attenuation unit according to the signal level of the sneak signal, the sneak signal is relatively small. Can also be suitably removed. That is, it is possible to provide a wireless tag communication device having a simple configuration that can suitably remove a sneak signal from the transmission side regardless of the signal level.

  Here, it is preferable that the attenuation unit sets the attenuation amount so that the amplitude of the cancellation signal in a predetermined input signal is a value closest to the amplitude within a limit that does not exceed the amplitude of the sneak signal from the transmission side. It is to set. In this way, since the control signal can be generated so that the maximum output amplitude of the cancel signal D / A conversion unit or a value close to half of the maximum output amplitude, the phase and amplitude of the cancel signal can be controlled with high accuracy. And the sneak signal from the transmission side can be sufficiently removed.

  Preferably, the attenuation unit sets the attenuation amount so that the amplitude of the cancel signal in a predetermined input signal exceeds the amplitude of the sneak signal from the transmission side and is a value closest to the amplitude. It is to set. In this way, the sneak signal from the transmission side can be sufficiently removed.

  Preferably, the control signal is a value that makes the amplitude of the cancel signal output from the cancel signal D / A converter close to half of the maximum amplitude that can be output from the cancel signal D / A converter. It is. In this way, it is possible to suitably remove the sneak signal from the transmission side with high accuracy by making use of the resolution of the D / A converter.

Preferably, a second cancel signal output unit that outputs, as a digital signal, a second cancel signal for removing a sneak signal from the transmission side included in the received signal, and the second cancel signal output A second cancel signal D / A converter that converts the second cancel signal output from the analog to analog, a combined signal amplitude detector that detects the amplitude of the combined signal output from the signal combiner, and a combination thereof Based on the amplitude of the combined signal detected by the signal amplitude detector, the second cancel signal D / A converter is configured to output the second cancel signal within a predetermined range with reference to the maximum amplitude . the second cancellation signal control for outputting a second control signal for controlling at least one of the amplitude and phase of the second canceling signal output from the cancellation signal output portion And a second cancel signal that has been analog-converted by the second cancel signal D / A converter based on the second control signal output from the second cancel signal control unit, wraps around from the transmission side. A second attenuating unit for attenuating to an amplitude corresponding to the signal, a second canceling signal that is attenuated by the second attenuating unit, and a synthesized signal output from the signal synthesizing unit. Part. In this way, the sneak signal from the transmission side can be removed twice, and the signal-to-interference ratio can be further increased.

  Preferably, the cancel signal includes an up-converter that increases a frequency of the cancel signal analog-converted by the cancel signal D / A converter by a predetermined value, and the attenuator has a cancel signal whose frequency is increased by a predetermined value by the up-converter. Is attenuated to an amplitude corresponding to the sneak signal from the transmission side. In this way, the sneak signal from the transmission side can be removed in a practical manner.

  Preferably, the attenuation section discretely changes the attenuation amount of the cancellation signal. In this way, the configuration of the attenuation unit can be simplified. In addition, the control of the input signal when the attenuation is changed can be simplified.

  Preferably, the attenuation unit sets the attenuation amount of the cancel signal to an integer power of 1/2. In this way, the configuration of the attenuation unit can be made as simple as possible. Further, since the input signal is controlled in binary numbers when the attenuation is changed, it can be simplified by a bit shift operation or the like.

  Preferably, the attenuation section includes a plurality of resistors constituting a plurality of voltage dividers and a plurality of switches for selectively operating the plurality of voltage dividers. In this way, the structure of the attenuation part can be made simple and inexpensive.

  Preferably, the attenuation unit has a buffer device. In this way, the operation of the attenuation unit can be stabilized.

  Preferably, the number of samples of the cancel signal D / A converter is 4 samples per period of the output period function. In this way, the noise floor can be kept low, the processing speed can be increased, and a sufficient signal-to-interference wave ratio can be obtained even if the signal is attenuated by the attenuation unit.

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

FIG. 1 is a diagram illustrating a configuration of a communication system 10 to which the present invention is preferably applied. The communication system 10 is a so-called RFID (Radio Frequency Identification) system, which is a wireless tag communication device 12 according to an embodiment of the present invention and a plurality (four in FIG. 1) of wireless tags 14a, 14b, 14c, 14d. (Hereinafter, simply referred to as a wireless tag 14 unless otherwise distinguished). The RFID tag communication device 12 functions as an interrogator of the communication system 10, and the RFID tag 14 functions as a responder of the communication system 10. That is, when a carrier wave F _c1 that is a transmission signal is transmitted from the wireless tag communication device 12, the carrier waves F _c1 are received based on predetermined information in the wireless tags 14a, 14b, 14c, and 14d that have received the carrier wave F _{c1. Are} reflected as reflected signals F _r1 , F _r2 , F _r3 , F _r4 (hereinafter simply referred to as reflected waves F _rf unless otherwise distinguished), and are returned by the RFID tag communication device 12. The reflected wave _rf is received and demodulated, whereby information is communicated with the wireless tag 14.

FIG. 2 is a diagram for explaining the electrical configuration of the RFID tag communication apparatus 12. The wireless tag communication device 12 communicates information with the wireless tag 14 to execute at least one of reading and writing of information with respect to the wireless tag 14, and outputs a transmission signal as a digital signal. A DSP (Digital Signal Processor) 16 for executing digital signal processing such as demodulating a return signal from the wireless tag 14, or controlling attenuation amounts in attenuators 55 and 65, which will be described later, The transmission signal output from the DSP 16 is converted into an analog signal and transmitted as a carrier wave F _c1 , or the reflected wave F _rf from the wireless tag 14 is received and converted into a digital signal and supplied to the DSP 16. The transmission / reception circuit 18 is configured.

  The DSP 16 is a so-called microcomputer system that includes a CPU, a ROM, a RAM, and the like, and performs signal processing according to a program stored in advance in the ROM while using a temporary storage function of the RAM. A transmission digital signal output unit 20 that outputs a digital signal as a digital signal, a modulation unit 22 that modulates the transmission digital signal output from the transmission digital signal output unit 20 based on a predetermined information signal (command), and the transmission signal The first cancel signal output unit 24 that outputs the first cancel signal based on the digital signal as a digital signal, the signal output from the first cancel signal output unit 24, and the attenuation amount in a first cancel signal attenuator 55 described later By controlling the amplitude A1 and / or phase of the first cancel signal. A first cancel signal control unit 26 that outputs a first control signal for controlling C1, a second cancel signal output unit 28 that outputs a second cancel signal based on the transmission signal as a digital signal, and a second For controlling a signal output from the cancel signal output unit 28 and controlling an amplitude A2 and / or a phase φC2 of the second cancel signal by controlling an attenuation amount in a second cancel signal attenuator 65 described later. A second cancellation signal control unit 30 that outputs a second control signal, a demodulation unit 32 that demodulates a reception signal received by a transmission / reception antenna 52 described later, and a DC component ( DC component detector 34 for detecting the DC component), received signal amplitude detector 36 for detecting the amplitude AR of the received signal, and a first described later. The first synthesized signal amplitude detector 38 that detects the amplitude AM1 of the first synthesized signal output from the signal synthesizer 58 and the function table 40 in which sampling values corresponding to the respective phases are stored in advance at predetermined sampling points Is prepared. Here, preferably, the control signal output from the first cancel signal control unit 26 preferably has an amplitude of the first cancel signal output from the first cancel signal D / A conversion unit 54. This is a value that is about ½ of the maximum amplitude that can be output from the first cancel signal D / A converter.

  The function table 40 is preferably a sine wave or cosine wave table in which sampling values corresponding to respective phases are stored in advance at predetermined sampling points, and FIG. 5 shows an example of the sine wave table. . In this function table 40, two values of “sinφ” and “sin (φ + 0.5π)” are stored in advance with respect to the initial phase “φ”. For example, “sinφ = “0” and “sin (φ + 0.5π) = 1” are stored, and “sinφ = 0.58779” and “sin (φ + 0.5π) = 0.80902” are stored for “φ = 0.2π”, respectively. Since “sin (φ + π) = − sinφ”, “sin (φ + π)” and “sin (φ + 1.5π)” can be read out from these two values, and “φ = 0”. For "0,1,0, -1,0,1,0, -1,0,1,0, -1, ...", the continuous value for "φ = 0.2π" is "0.58779, 0.80902, -0.58779, -0.80902, 0.58779, 0.80902, -0.58779, -0.80902, 0.58779, 0.80902, -0.58779, -0.80902, ... "are read out. These continuous values generate a predetermined sine wave signal. In order to change the phase of the sine wave signal, the read position in the function table 40 may be changed. To change the amplitude, the read sine wave signal is multiplied by a predetermined control value. Therefore, the transmission digital signal output unit 20, the first cancel signal output unit 24, and the second cancel signal output unit 28 can output an arbitrary sine wave signal based on the function table 40.

The transmission / reception circuit 18 includes a transmission signal D / A conversion unit 42 that converts a transmission digital signal output from the modulation unit 22 into an analog signal, a local oscillation signal output unit 44 that outputs a predetermined local oscillation signal, A first up-converter 46 that increases the frequency of the transmission signal converted into an analog signal by the transmission signal D / A converter 42 by the frequency of the local oscillation signal output from the local oscillation signal output unit 44; A first amplifying unit 48 that amplifies the transmission signal output from the converter 46 and changes its amplitude, and a transmission signal output from the first amplifying unit 48 via a filter 51 for removing harmonic components. In addition to being supplied to the transmission / reception antenna 52, a reply signal (including a sneak signal from the transmission side) from the wireless tag 14 received by the transmission / reception antenna 52 is also received. A transceiver separator 50 and supplies the received signal) to the first signal combining unit 58 and the second down-converter 74 via the filter 51, transmitting a transmission signal supplied through the transmission and reception separator 50 as the carrier wave F _c1 In addition, the transmission / reception antenna 52 that receives the reflected wave F _rf from the wireless tag 14 and supplies it to the transmission / reception separator 50, and the first cancellation signal output from the first cancellation signal output unit 24 as an analog signal. Based on the first cancel signal D / A converter 54 to be converted and the first control signal output from the first cancel signal controller 26, the first cancel signal D / A converter 54 performs analog conversion. A first cancel signal attenuator 55 for attenuating the first cancel signal to an amplitude corresponding to a sneak signal from the transmission side, and the first cancel signal A second up-converter 56 that increases the frequency of the first cancellation signal attenuated by the local signal attenuator 55 by the frequency of the local oscillation signal output from the local oscillation signal output unit 44; A first signal combining unit 58 that combines the output first cancel signal and the reception signal supplied from the transmission / reception antenna 52 via the transmission / reception separator 50, and a first combination output from the first signal combining unit 58. A second amplifying unit 60 that amplifies the signal and changes its amplitude AM1, and the frequency of the first synthesized signal output from the second amplifying unit 60 is the frequency of the local oscillating signal output from the local oscillating signal output unit 44. The first down converter 62 that lowers the frequency only, and the second cancel signal output from the second cancel signal output unit 28 is converted into an analog signal. The second cancel signal D / A converter 64 and the second cancel signal D / A converter 64 analog-converted based on the second control signal output from the second cancel signal controller 30. 2 from the second cancel signal attenuator 65 for attenuating the cancel signal to the amplitude corresponding to the sneak signal from the transmission side, the second cancel signal attenuated by the second cancel signal attenuator 65 and the first down converter 62 A second signal synthesis unit 66 that synthesizes the first synthesized signal that is output (which may also be amplified if necessary), and amplifies the first synthesized signal that is output from the first down-converter 62 to obtain its amplitude AM1. The third amplifying unit 68 to be changed and the first synthesized signal output from the third amplifying unit 68 are digitally converted and supplied to the first synthesized signal amplitude detecting unit 38. A first synthesized signal A / D converter 70; a second synthesized signal A / D converter 72 that digitally converts the second synthesized signal output from the second signal synthesizer 66 and supplies it to the demodulator 32; A second down converter 74 that lowers the frequency of the reception signal supplied via the transmission / reception separator 50 by the frequency of the local oscillation signal output from the local oscillation signal output unit 44, and the second down converter 74 A reception signal A / D conversion unit 76 that converts the reception signal output from the digital signal and supplies the digital signal to the reception signal amplitude detection unit 36, and a clock signal output unit 78 that outputs a predetermined clock signal. The clock signal output unit 78 preferably supplies a clock signal to the transmission signal D / A conversion unit 42, and also includes the first cancellation signal D / A conversion unit 54 and the second cancellation signal D / A conversion unit. 64, at least one of the first combined signal A / D converter 70, the second combined signal A / D converter 72, and the received signal A / D converter 76, and more preferably, the transmission signal D A clock signal common to the / A converter 42 is supplied. The received signal A / D converter 76 is preferably a converter having a smaller number of bits than the converter used in the first combined signal A / D converter 70 and the like. According to such a converter, there is an advantage that components relating to modulation by the wireless tag 14 can be ignored. As the local oscillation signal output unit 44, an oscillator that oscillates in the vicinity of 900 MHz or 2.4 GHz is preferably used. As the transmission / reception separator 50, a circulator or a directional coupler is generally used.

  FIG. 3 is a diagram for explaining the configuration of the first cancel signal attenuator 55. The second cancel signal attenuator 65 has the same configuration as that of the first cancel signal attenuator 55. Therefore, in the following description, the first cancel signal attenuator 55 will be described, and the second cancel signal attenuator 55 will be described. A description of the attenuator 65 is omitted. As shown in FIG. 3, the first cancel signal attenuator 55 includes resistors R1 and R2 and a plurality of resistors constituting a plurality (three in FIG. 3) of voltage dividers 55a, 55b, 55c, 55d, and 55e. Ra, Rb, Rc, Rd, Re, an analog switch SW having a plurality of switches Sa, Sb, Sc, Sd, Se for selectively operating the plurality of voltage dividers, and an amplifier having a buffer function A buffer amplifier BA is provided. Here, although the resistor R2 is grounded, a mode in which the resistor R2 is grounded via a predetermined switch is also conceivable. The opening / closing device SW preferably connects the plurality of resistors Ra, Rb, Rc, Rd, Re selectively, and in this way, the first cancel signal attenuator 55 is The attenuation amount of the input signal is discretely changed and output. More preferably, the attenuation amount of the input signal is set to an integer power of 1/2.

FIG. 4 is a diagram for explaining the relationship between the leaked carrier wave level and the suppression amount. Unnecessary signals mixed in the received signal include sneak due to leakage from the transmission / reception separator 50, sneak due to the fact that the transmitted radio wave is reflected by an external reflector and received. In addition, when the transmission antenna and the reception antenna are provided separately, direct or indirect wraparound from the transmission antenna to the reception antenna is included. Here, as shown in FIG. 4, when a 14-bit D / A converter is used, a maximum suppression amount of 50 dB can be obtained. However, when the leakage carrier amplitude becomes 1/4, that is, the leakage carrier level is D / A. When the A converter input bit number converted value is reduced from 12 bits to about 10 bits, the suppression amount also deteriorates by about 10 dB. Further, when the leaked carrier wave level is about 6 bits in terms of the D / A converter input bit number converted value, the suppression amount is reduced by about 15 dB. In particular, since a high-resolution D / A converter has a large conversion error per LSB due to nonlinear distortion, the error increases as a small signal is generated (the amplitude shifts from the value in FIG. 5, resulting in a phase error). There is a risk that sufficient suppression will not be performed. In the RFID tag communication apparatus 12 of the present embodiment, as described above with reference to FIG. 3, the attenuation amount is 2 ^−N (ie 1/2, 1/1 /) on the output side of the first cancel signal D / A conversion unit 54. 4, 1/8,...), And an attenuator 55 that can be switched as shown in FIG. As a result, the amplitude of the first cancel signal output from the first cancel signal D / A converter 54 can be adjusted by the attenuator 55 according to the signal level of the leaked carrier wave. The output of the first cancel signal D / A converter 54 is generated between the number -2 and the full-scale bit number -3. Therefore, if it is a 14-bit D / A converter, a suppression amount of about 45 to 51 dB is always obtained regardless of the leaked carrier wave level, and unnecessary signals can be suitably removed. The phase adjustment and the fine adjustment of the amplitude of the first cancel signal can also be performed by inputting a control signal to the first cancel signal D / A converter 54. Further, as described above with reference to FIG. 5, the number of samples in the function table 40 is 4 samples per period, and thereby sufficient phase accuracy can be obtained and the processing speed can be increased. Furthermore, since the quantization error becomes a harmonic component, it can be removed by the filter 51 provided between the transmission / reception separator 50 and the transmission / reception antenna 52, and the signal to interference ratio (S / N) is high. A signal can be transmitted. Further, since the noise floor can be prevented from rising, a sufficient signal-to-interference ratio can be ensured even if the signal is attenuated by the attenuator 55.

FIG. 6A is a block diagram illustrating a configuration of a wireless tag circuit 14 a provided in the wireless tag 14. The wireless tag circuit 14a receives a carrier wave F _c1 that is a transmission signal from the wireless tag communication device 12, and also returns an antenna 80 that _returns a reflected wave F _rf that is a return signal, and a signal connected to the antenna 80. A modulation / demodulation unit 82 that performs modulation and demodulation of the digital signal, and a digital circuit unit 84 that performs digital signal processing. The digital circuit unit 84 includes a control unit 86 that controls the operation of the RFID circuit 14a using the carrier wave _Fc1 received by the antenna 80 as an energy source, a subcarrier oscillation unit 88 that generates a subcarrier, and a subcarrier oscillation unit 88 that generates the subcarrier. A subcarrier modulation unit 90 that modulates the subcarrier generated by the carrier oscillation unit 88 based on a predetermined information signal input via the control unit 86.

Next, the communication operation of the communication system 10 configured as described above will be described. First, the transmission digital signal output unit 20 of the RFID tag communication apparatus 12 outputs a transmission signal that is a digital signal based on the function table 40. This transmission signal is, for example, a signal obtained by sampling a sine wave. Next, the transmission digital signal output from the transmission digital signal output unit 20 is modulated by the modulation unit 22. Next, the transmission digital signal modulated by the modulation unit 22 is converted into an analog signal by the transmission signal D / A conversion unit 42. Next, the frequency of the transmission signal converted into an analog signal by the transmission signal D / A converter 42 is increased by the frequency of the local oscillation signal output from the local oscillation signal output unit 44 by the first up-converter 46. . Next, the amplitude of the transmission signal output from the first up-converter 46 is increased in the first amplifying unit 48. Next, the transmission signal output from the first amplifying unit 48 is supplied to the transmission / reception antenna 52 via the transmission / reception separator 50 and the filter 51, and is transmitted from the transmission / reception antenna 52 to the wireless tag 14 as a carrier wave _Fc1. Sent.

When the carrier wave F _c1 from the transmission / reception antenna 52 is received by the antenna 80 of the wireless tag 14, the carrier wave F _c1 is supplied to the modulation / demodulation unit 82 and demodulated. A part of the carrier wave F _c1 is rectified by a rectification unit (not shown), and the sub-carrier wave is output from the sub-carrier oscillation unit 88 using the carrier wave F _c1 as an energy source. Next, the subcarrier output from the subcarrier oscillating unit 88 is primarily modulated by the subcarrier modulating unit 90 based on a predetermined information signal input via the control unit 86. Next, the modulation / demodulation unit 82 secondarily modulates the carrier wave F _c1 by the primary modulated subcarrier output from the subcarrier modulation unit 90, and the reflected signal F _rf is transmitted from the antenna 80 as the reflected wave F _rf. Reply to 12 The wireless tag 14 may be configured as a wireless tag circuit 14b that does not use a subcarrier as shown in FIG. 4B. In this case, a signal passed from the control unit 86b to the modulation / demodulation unit 82b as a return signal from the wireless tag 14 needs to be modulated by ASK or PSK.

When the reflected wave F _rf from the wireless tag 14 is received by the transmission / reception antenna 52 of the wireless tag communication device 12, the reflected wave F _rf is received as the received signal through the filter 51 and the transmission / reception separator 50. The signal is supplied to the signal synthesis unit 58 and the second down converter 74. At this time, the transmission signal that wraps around to the reception side via the transmission / reception separator 50 is also supplied to the first signal synthesis unit 58 and the second down converter 74 simultaneously with the reception signal. FIG. 7A shows the waveform of the reception signal supplied to the first signal synthesis unit 58. Here, since the sneak signal is much larger than the reflected wave (reply signal), it can be seen in FIG. 7A that the amplitude modulation component is very small. The frequency of the received signal supplied to the second down converter 74 is lowered by the frequency of the local oscillation signal output from the local oscillation signal output unit 44. FIG. 7B shows the waveform of the down-converted received signal output from the second down converter 74. Next, the down-converted received signal output from the second down converter 74 is digitally converted by the received signal A / D converter 76 and supplied to the received signal amplitude detector 36. Next, the reception signal amplitude detection unit 36 detects the amplitude AR of the reception signal, and the detection result is supplied to the first cancel signal control unit 26.

  Before and after the processing, the first cancel signal control unit 26 determines the phase φC1 and the amplitude A1 of the first cancel signal, and the first cancel signal output unit 24 is a digital signal based on the function table 40. A first cancel signal is output and converted to an analog signal by the first cancel signal D / A converter 54 and attenuated by the first cancel signal attenuator 55. This attenuation amount is preferably determined based on the amplitude AR of the received signal supplied from the received signal amplitude detector 36. For example, the amplitude A1 of the first cancel signal in a predetermined input signal is set to a value closest to the amplitude within a limit that does not exceed the amplitude of the sneak signal from the transmission side. Alternatively, the amplitude A1 of the first cancel signal in a predetermined input signal is set to a value that exceeds the amplitude of the sneak signal from the transmission side and is closest to the amplitude. Next, the frequency of the first cancel signal attenuated by the first cancel signal attenuator 55 is increased by the frequency of the local oscillation signal output from the local oscillation signal output unit 44 by the second up-converter 56. FIG. 7C shows the waveform of the up-converted first cancel signal output from the second up-converter 56. Next, the first cancellation signal output from the second up-converter 56 and the reception signal supplied via the filter 51 and the transmission / reception separator 50 are combined by the first signal combining unit 58 and the received signal is combined. The sneak signal from the included transmission side is removed. FIG. 7D shows the waveform of the first combined signal output from the first signal combining unit 58. However, the amplitude is shown enlarged here. Actually, the amplitude is smaller than that in FIG. 7A from which the sneak signal from the transmission side is removed, but the amplitude modulation component does not change. Therefore, when this signal is amplified by the second amplifying unit 60, FIG. The waveform of (d) is obtained. In this first synthesized signal, the amplitude modulation component is relatively large, and it can be seen that the sneak signal from the transmission side is removed as compared with the reception signal of FIG. Since the strength of the sneak signal from the transmission side is larger than the response signal strength of 14, the sneak signal still has a size that cannot be ignored. The amplitude of the first synthesized signal output from the first signal synthesizing unit 58 is changed by the gain G1 in the second amplifying unit 60. When the amplitude A1 and the phase φC1 of the first cancel signal are suitably determined, the signal strength is relatively lowered and the input signal to the first down converter 62 is reduced. The gain G1 is increased as appropriate. Here, the gain G2 of the third amplifying unit 68 is set to a predetermined initial value. Next, the frequency of the first synthesized signal output from the second amplifying unit 60 is decreased by the frequency of the local oscillation signal output from the local oscillation signal output unit 44 by the first down converter 62, and the first The signal is supplied to the two-signal synthesis unit 66 and the third amplification unit 68.

  FIG. 8A shows the waveform of the down-converted first composite signal output from the first down converter 62. The frequency of the clock signal output from the clock signal output unit 78 is preferably four times or an integer multiple of the frequency of the down-converted first synthesized signal (intermediate frequency signal). The amplitude of the first combined signal supplied to the third amplifying unit 68 is changed by the gain G2 in the third amplifying unit 68. Since the first synthesized signal output from the first down converter 62 becomes smaller as the removal of the sneak signal from the transmission side in the first signal synthesizing unit 58 proceeds, preferably, the third amplifying unit The gain G2 at 68 is sequentially increased accordingly. Next, the first synthesized signal output from the third amplifier 68 is digitally converted by the first synthesized signal A / D converter 70 and supplied to the first synthesized signal amplitude detector 38. Next, the first composite signal amplitude detector 38 detects the amplitude AM1 of the first composite signal, and the detection result is supplied to the first cancel signal controller 26 and the second cancel signal controller 30. Preferably, based on the amplitude AM1 of the first composite signal, the first cancel signal control unit 26 controls the phase φC1 of the first cancel signal so that the amplitude AM1 becomes as small as possible. . Preferably, the average value of the amplitude AM1 of the first composite signal is determined to be as small as possible.

  Before and after the processing, the second cancellation signal control unit 30 determines the phase φC2 and the amplitude A2 of the second cancellation signal, and the second cancellation signal output unit 28 is a digital signal based on the function table 40. A second cancel signal is output and converted to an analog signal by the second cancel signal D / A converter 64 and attenuated by the second cancel signal attenuator 65. The amplitude A2 of the second cancel signal is preferably determined based on the amplitude AM1 of the first composite signal supplied from the first composite signal amplitude detector 38. Preferably, the amplitude of the down-converted first combined signal input to the second signal combining unit 66 is equal to the amplitude of the second cancel signal output from the second cancel signal attenuator 65. It is determined. FIG. 8B shows the waveform of the second cancel signal output from the second cancel signal attenuator 65. Next, the second cancellation signal attenuated by the second cancellation signal attenuation unit 65 and the down-converted first combined signal supplied from the first down converter 62 are combined by the second signal combining unit 66. The sneak signal from the transmission side included in the first composite signal is removed. FIG. 8C shows the waveform of the second synthesized signal output from the second signal synthesizer 66. In this second synthesized signal, the amplitude modulation component is relatively larger than the received signal in FIG. 7A and the first synthesized signal in FIG. 7D, and the sneak signal from the transmission side is removed. You can see that. The second synthesized signal output from the second signal synthesizer 66 is digitally converted by the second synthesized signal A / D converter 72 and then supplied to the first cancel signal controller 26 and the demodulator 32. The Then, the demodulator 32 demodulates the second combined signal and reads the information signal of the wireless tag 14. Preferably, the first cancel signal control unit 26 controls the phase φC1 of the first cancel signal based on the second composite signal. Preferably, the second signal synthesis unit 66 also functions as a differential amplifier, and the input voltage to the second synthesis signal A / D conversion unit 72 is set to a suitable value. The gain G3 in the second signal combining unit 66 is changed.

  FIG. 8D shows the waveform of the demodulated signal output from the demodulator 32. The DC component detector 34 detects the DC component of the demodulated signal shown in FIG. 8D, and the detection result is supplied to the second cancel signal controller 30. This DC component corresponds to a sneak signal from the transmission side, and preferably, the second cancellation signal control unit 30 makes the second cancellation signal so that the amplitude D2 of the DC component is as small as possible. The phase φC2 of the signal is controlled. By the above communication operation, a sneak signal from the transmission side included in the received signal is preferably removed, and highly sensitive communication is realized.

  FIG. 9 to FIG. 14 are flowcharts for explaining a main part of the sneak signal removal control operation from the transmission side by the DSP 16 of the RFID tag communication apparatus 12, which is repeatedly executed with an extremely short cycle time of about several milliseconds to several tens of milliseconds. It is what is done.

First, in step S1 of FIG. 9 (hereinafter, step is omitted), the phase φC1 of the first cancel signal and the phase φC2 of the second cancel signal are both set to zero. Next, in S <b> 2, it is determined whether or not command transmission is performed toward the wireless tag 14. An instruction as to whether or not to transmit a command is appropriately switched by an upper routine (not shown). If the determination in S2 is affirmative, the process from S5 onward is executed after the transmission signal is modulated with a predetermined command in S3 corresponding to the modulation unit 22, but the determination in S2 is negative. In S4, the transmission signal is not modulated in S4, and the reception signal AD1 digitally converted by the reception signal A / D converter 76 is read in S5. Next, in S6 corresponding to the received signal amplitude detector 36, the amplitude AR of the received signal AD1 read in S5 is detected. Next, in S7, the amplitude A1 of the first cancel signal is determined. Next, in S8, N is set to 0. Next, in S9, it is determined whether 2- ^{(N + 1)} is smaller than A1 / A1F. Here, A1F represents the full scale value of the first cancel signal D / A converter 54 in terms of the number of input bits. If the determination in S9 is negative, 1 is added to N in S12, and then the processing from S9 is executed again. However, if the determination in S9 is affirmative, in S10, attenuation of the first cancellation signal attenuator 55 is set to ^{2 -N,} in S11, thereby being made a A1D ^{= 2} N · A1, S13 and thereafter in Figure 10 is executed.

  In S13 of FIG. 10, the variables i, k, and X are all set to 0. Next, in S14, the function values stored in the function table 40 are read out. Next, in S15, the function value read in S14 is multiplied by the amplitude A1D determined in S11. Next, in S16, the first combined signal AD2 digitally converted by the first combined signal A / D conversion unit 70 is read out. Next, in S17, the amplitude AM1 of the first composite signal AD2 read in S16 is detected. Next, in S18, it is determined whether or not the amplitude AM1 of the first composite signal detected in S17 is equal to or smaller than a first predetermined value. If the determination in S18 is negative, the processing from S23 onward is executed. If the determination in S18 is positive, in S19, is the gain G2 of the third amplification unit 68 maximum? It is determined whether or not. If the determination in S19 is affirmative, that is, if it is determined that the gain G2 of the third amplifying unit 68 is maximum, the processing from S27 in FIG. 11 is executed, but the determination in S19 is denied. If it is determined that the gain G2 of the third amplifying unit 68 is not maximum, the variable X is divided by the gain G2 of the third amplifying unit 68 in S20. Next, in S21, a predetermined value dG is added to the gain G2 of the third amplifying unit 68. Next, in S22, after the variable G is multiplied by the gain G2 of the third amplifying unit 68, the processing from S16 onward is executed again. In S23, it is determined whether or not the amplitude AM1 of the first composite signal detected in S17 is greater than or equal to a second predetermined value. That is, the range in which the input voltage to the first combined signal A / D converter 70 is determined to be at an appropriate level is set to be within the range of the first predetermined value or more and the second predetermined value or less. If the input voltage is initially too low, it is necessary to amplify. Therefore, if the determination in S18 is affirmative, it is determined in S19 whether the gain G2 of the third amplifying unit 68 is maximum. However, if the determination in S18 is negative, the determination in S23 is made. If the determination in S23 is negative, it is determined that the input voltage to the first combined signal A / D conversion unit 70 is at an appropriate level, so the processing from S27 onward in FIG. 11 is executed. If the determination is affirmative, that is, if the input voltage to the first combined signal A / D converter 72 is too large, whether or not the gain G2 of the third amplifying unit 68 is minimum in S24. Is judged. If the determination in S24 is affirmative, the processing from S27 onward in FIG. 11 is executed. If the determination in S24 is negative, the variable X is set to the gain of the third amplifying unit 68 in S25. Divide by G2. Next, in S26, after a predetermined value dG is subtracted from the gain G2 of the third amplifying unit 68, the processes in S22 and subsequent steps are executed. Accordingly, the gain of the third amplifying unit 68 can be controlled so that the input signal amplitude (voltage) to the reception signal A / D conversion unit 76 is always an appropriate value. Even if the amplitude of the first synthesized signal output from 58 decreases due to the removal of the sneak signal, control can be performed with high sensitivity.

  In S27 of FIG. 11, it is determined whether or not the variable i is 0. If the determination in S27 is affirmative, in S28, variables X = AM1 and i = 1 are set, and in S29, after a predetermined value dφ is added to the phase φC1 of the first cancel signal, FIG. The processing from S14 onward is executed again, but if the determination in S27 is negative, it is determined in S30 whether the variable X is larger than the amplitude AM1 of the first composite signal. If the determination in S30 is affirmative, the variable X = AM1 is set in S31, and then the processing from S29 is executed. However, if the determination in S30 is negative, the variable k is determined in S32. It is determined whether = 0. If the determination in S32 is affirmative, in S33, after the variable k = 1 and the predetermined value dφ = −dφ, the processing from S29 is executed, but the determination in S32 is denied. In S34, the gain G2 of the third amplifying unit 68 is set to 1. After the phase φC1 of the first cancel signal is determined in S35, the processing from S36 onward in FIG. 12 is executed. By this series of processing, the phase φC1 of the first cancel signal can be controlled so that the amplitude AM1 of the first composite signal is minimized.

In S36 of FIG. 12, a predetermined value dG is added to the gain G1 of the second amplifying unit 60. Next, in S37, the first composite signal digitally converted by the first composite signal A / D converter 70 is read out. Next, in S38, the amplitude AM1 of the first composite signal read in S31 is detected. Next, in S39, it is determined whether or not the amplitude AM1 of the first composite signal detected in S38 has reached a predetermined value. If the determination in S39 is affirmative, the processing from S41 is executed. If the determination in S39 is negative, in S40, whether the gain G1 of the second amplifying unit is maximum. Is judged. If the determination in S40 is negative, the processing from S36 is executed again, but if the determination in S40 is affirmative, the amplitude A2 of the second cancel signal is determined in S41. Next, in S42, N is set to 0. Next, in S43, it is determined whether 2- ^{(N + 1)} is smaller than A2 / A2F. Here, A2F is obtained by converting the full scale value of the second cancel signal D / A converter 64 into the number of input bits. If the determination at S43 is negative, after S is incremented by 1 at S46, the processing after S43 is executed again. However, when the determination at S43 is affirmative, at S44, attenuation amount of the second cancellation signal attenuator 65 is set to ^{2 -N,} in S45, after it is with A2D ^{= 2} N · A2, S47 and thereafter in Figure 13 is executed. By this series of processing, the reception signal from which the sneak signal is removed and the amplitude modulation component is relatively increased can be amplified at a high frequency by the second amplifying unit 60, so that it is possible to suppress the generation of noise and detect a highly sensitive reply signal. It becomes possible.

In S47 of FIG. 13, the variables i, k, and Y are all set to 0. Next, in S48, the function values stored in the function table 40 are read out. Next, in S49, the function value read in S48 is multiplied by the amplitude A2D determined in S45. Next, in S50, it is determined whether or not there is a demodulated signal output from the demodulator 32. If the determination in S50 is negative, it is determined in S51 whether a predetermined time has elapsed. If the determination in S51 is affirmative, it is determined that the wireless tag 14 has not transmitted a reply signal, so the processing from S2 in FIG. 9 is executed again, but the determination in S51 is denied. In the case where it is determined, the processing after S50 is executed again. If the determination in S50 is affirmative, that is, if it is determined that there is a demodulated signal output from the demodulator 32, the second combined signal is demodulated and demodulated in S52 corresponding to the demodulator 32. The signal is read out. Next, in S53 corresponding to the DC component detector 34, the amplitude D2 of the DC component of the demodulated signal is detected. Next, after the maximum amplitude AB _max of the demodulated signal is detected in S54, in S55, the maximum amplitude AB _max of the demodulated signal detected in S54 is a first predetermined value (the first described in the control of FIG. 10). It is determined whether the value is equal to or less than a predetermined value. That is, a range in which the input voltage to the second combined signal A / D converter 72 is determined to be at an appropriate level is set to be within a range not less than the first predetermined value and not more than the second predetermined value. If the input voltage is initially too low, it is necessary to amplify. Therefore, if the determination in S55 is affirmative, whether or not the gain G3 of the second signal combining unit 66 is maximum in S56. However, if the determination in S55 is negative, in S60, the maximum amplitude AB _max of the demodulated signal detected in S54 is a second predetermined value (the second predetermined value described in the control of FIG. 10). It is determined whether the value is equal to or greater than (a value different from the above). If the determination in S60 is negative, the processing of S64 and subsequent steps in FIG. 14 is executed. If the determination in S60 is positive, that is, the input voltage to the second combined signal A / D converter 72. If is too large, it is determined in S61 whether or not the gain G3 of the second signal synthesis unit 66 is minimum. If the determination in S56 is affirmative, that is, if it is determined that the gain G3 of the second signal synthesis unit 66 is the maximum, the processing from S64 onward in FIG. 14 is executed, but the determination in S56 is negative. If it is determined that the gain G3 of the second signal synthesis unit 66 is not the maximum, the variable Y is divided by the gain G3 of the second signal synthesis unit 66 in S57. Next, in S58, a predetermined value dG is added to the gain G3 of the second signal synthesis unit 66 to increase the amplification factor. Next, in S59, after the variable G is multiplied by the gain G3 of the second signal synthesizer 66, the processing from S50 onward is executed again. If the determination in S61 is affirmative, that is, the input voltage to the second combined signal A / D converter 72 is outside the proper range, and the gain G3 of the second signal combiner 66 is minimum. When the determination is made, the processing from S64 onward in FIG. 14 is executed, but when the determination at S61 is negative, that is, when the gain G3 of the second signal combining unit 66 is determined not to be minimum. In S62, the variable Y is divided by the gain G3 of the second signal synthesizer 66. In S63, the predetermined value dG is subtracted from the gain G3 of the second signal synthesizer 66 (the amplification factor has been lowered). ) After that, the processing from S59 is executed.

  In S64 of FIG. 14, it is determined whether or not the variable i = 0. If the determination in S64 is affirmative, in S65, the variables Y = D2 and i = 1 are set, and in S66, after a predetermined value dφ is added to the phase φC2 of the second cancel signal, FIG. The processing from S48 onward is executed again. If the determination in S64 is negative, it is determined in S67 whether the variable Y is larger than the amplitude D2 of the DC component of the demodulated signal. If the determination in S67 is affirmative, the variable Y = D2 is set in S68, and then the processing in S66 and subsequent steps is executed. However, if the determination in S67 is negative, the variable k is determined in S69. It is determined whether = 0. If the determination in S69 is affirmative, in S70, after the variable k = 1 and the predetermined value dφ = −dφ, the processing from S66 onward is executed, but the determination in S69 is negative. In S71, the gain G3 of the second signal synthesizer 66 is set to 1. After the phase φC2 of the second cancel signal is determined in S72, the processing from S2 onward in FIG. 9 is executed again. Through this series of processing, the phase φC2 of the second cancel signal can be controlled so that the DC component D2 of the demodulated signal is minimized. In the above control, S7, S11, and S35 are the operations of the first cancel signal control unit 26, S41, S45, and S72 are the operations of the second cancel signal control unit 30, and S17 and S38 are the first operations. This corresponds to the operation of the combined signal amplitude detector 38, respectively.

  Here, in addition to the above-described configuration, correction means for correcting the phase change in the first signal synthesizing unit 58 and the second signal synthesizing unit 66 and the influence of the gain of the amplifying unit, particularly the amplitude, may be provided. Preferably, the correction amount is obtained in advance and stored in the storage device of the DSP 16. Further, after determining the amplitude and phase of the first cancellation signal and the second cancellation signal so that the amplitude of the sneak signal from the transmission side is minimized, the first cancellation signal is further reduced so that the amplitude of the sneak signal is further reduced. The amplitude A1 of the signal and the amplitude A2 of the second cancellation signal may be corrected. FIG. 15 is a flowchart showing a control operation executed in place of a part of the control operation shown in the flowcharts of FIGS. In this control, initial setting is executed in S73 corresponding to the processing of S1 in FIG. Next, in S74 corresponding to the processes of S2 to S7, the amplitude A1 of the first cancel signal is determined. Next, in S75 corresponding to S13 to S35 of FIGS. 10 and 11, the phase φC1 of the first cancel signal is determined. Next, in S76, the amplitude A1 of the first cancel signal that may have changed based on the phase change in the first signal synthesis unit 58, the gain G1 of the second amplification unit 60, or the like is corrected. In this case, correction may be performed so that the amplitude AM1 of the first combined signal is minimized. Next, in S77 corresponding to S36 to S41 in FIG. 12, the amplitude A2 of the second cancel signal is determined. Next, in S78 corresponding to S37 to S63 in FIG. 13, the phase φC2 of the second cancel signal is determined. Next, in S79, the amplitude A2 of the second cancellation signal that may have changed based on the phase change in the second signal synthesis unit 66, the gain G3 of the second signal synthesis unit 66, etc. Correction is made so that the DC component D2 is minimized. That is, in addition to the process described above, the processes of S76 and S79 are newly performed. In the above control, S74 to S76 correspond to the operation of the first cancel signal control unit 26, and S77 to S79 correspond to the operation of the second cancel signal control unit 30, respectively.

  Thus, according to the present embodiment, the first cancel signal output for outputting the first cancel signal for removing the sneak signal from the transmission side included in the reception signal received by the transmission / reception antenna 52 as a digital signal. Unit 24, a first cancel signal D / A converter 54 for analog conversion of the first cancel signal output from the first cancel signal output unit 24, and a first output from the first cancel signal output unit 24. A first cancel signal control unit 26 that outputs a first control signal for controlling the amplitude A1 and / or the phase φC1 of the cancel signal, and a first control signal output from the first cancel signal control unit 26 Based on the first cancel signal, the first cancel signal D / A converter 54 analog-converts the first cancel signal from the transmission side. A first cancel signal attenuator 55 that attenuates to an amplitude corresponding to the signal, and a first signal combiner 58 that combines the first cancel signal attenuated by the first cancel signal attenuator 55 and the received signal, Therefore, by changing the setting of the first cancel signal attenuator 55 in accordance with the signal level of the sneak signal, it can be suitably removed even when the sneak signal is relatively small. That is, it is possible to provide the wireless tag communication device 12 having a simple configuration capable of suitably removing the sneak signal from the transmission side regardless of the signal level.

  Further, the first cancel signal attenuator 55 is set so that the amplitude A1 of the first cancel signal in a predetermined input signal becomes a value closest to the amplitude as long as it does not exceed the amplitude of the sneak signal from the transmission side. Since the amount of attenuation is set, the control signal can be generated so as to have a maximum output amplitude of the first cancel signal D / A converter 54 or a value close to half of the maximum output amplitude. Amplitude A1 and phase φC1 can be controlled with high accuracy, and the sneak signal from the transmission side can be sufficiently removed.

  The first cancel signal attenuator 55 is configured such that the amplitude A1 of the first cancel signal in a predetermined input signal is a value that exceeds the amplitude of the sneak signal from the transmission side and is the closest to the amplitude. Therefore, the sneak signal from the transmission side can be sufficiently removed.

  The first control signal has a maximum amplitude at which the first cancel signal D / A converter 54 can output the amplitude of the first cancel signal output from the first cancel signal D / A converter 54. Therefore, the sneak signal from the transmission side can be suitably removed.

  The second cancel signal output unit 28 outputs a second cancel signal for removing a sneak signal from the transmission side included in the received signal as a digital signal, and the second cancel signal output unit 28 outputs the second cancel signal. A second cancel signal D / A converter 64 for analog conversion of the second cancel signal, and a second cancel signal for controlling the amplitude A2 and / or phase φC2 of the second cancel signal output from the second cancel signal output unit 28. The second cancel signal control unit 30 that outputs the control signal 2 and analog conversion by the second cancel signal D / A conversion unit 64 based on the second control signal output from the second cancel signal control unit 30 A second cancel signal attenuator 65 for attenuating the second cancel signal thus made to an amplitude corresponding to a sneak signal from the transmission side; A second signal combining unit 66 that combines the second cancel signal attenuated by the second cancel signal attenuator 65 and the first combined signal output from the first signal combining unit 58. The sneak signal from the transmission side can be removed twice, and the signal-to-interference ratio can be further increased.

  In addition, since the attenuators 55 and 65 change the attenuation amount of the cancel signal in a discrete manner, the configuration of the attenuation units 55 and 65 can be simplified. In addition, the control of the input signal when the attenuation is changed can be simplified.

  Further, since the attenuators 55 and 65 make the attenuation amount of the cancel signal be an integral power of 1/2, the configuration of the attenuation units 55 and 65 may be as simple as possible. it can. Further, since the input signal is controlled in binary numbers when the attenuation is changed, it can be simplified by a bit shift operation or the like.

  The attenuators 55 and 65 include a plurality of resistors Ra to Re constituting a plurality of voltage dividers 55a to 55e, and a plurality of switches Sa to selectively operating the plurality of voltage dividers 55a to 55e. Since it consists of Se, the structure of the said attenuation | damping parts 55 and 65 can be made simple and cheap.

  Further, since the attenuators 55 and 65 have a buffer amplifier BA that functions as a buffer device, the operations of the attenuators 55 and 65 can be stabilized.

  In addition, since the number of samples of the cancel signal D / A converters 54 and 64 is 4 samples per cycle of the output periodic function, the noise floor can be suppressed low, the processing can be speeded up, and the attenuator Even if the signal is attenuated by 55 and 65, a sufficient signal-to-interference ratio can be obtained.

  Next, another embodiment of the present invention will be described in detail with reference to the drawings. In the drawings used for the following description, the same reference numerals are given to the portions common to the first embodiment, and the description thereof is omitted.

  FIG. 16 is a diagram for explaining the configuration of the RFID tag communication apparatus 92 according to the second embodiment of the present invention. As shown in FIG. 16, in the RFID tag communication apparatus 92 of the present embodiment, the first cancel signal attenuator 55 is provided on the output side of the second up-converter 56, and the frequency is increased by the up-converter 56. The first cancellation signal increased by a predetermined value is attenuated to an amplitude corresponding to the wraparound signal from the transmission side. Also with such a configuration, a sneak signal from the transmission side can be removed in a practical manner, similar to the wireless tag communication device 12 described above.

  FIG. 17 is a diagram for explaining the configuration of an RFID tag communication apparatus 94 according to the third embodiment of the present invention. As shown in FIG. 17, in the RFID tag communication apparatus 94 of this embodiment, a transmission signal register 96 is provided between the modulation unit 22 and the transmission signal D / A conversion unit 42 of the DSP 16. A first cancel signal register 98 is provided between the first cancel signal output unit 24 and the first cancel signal D / A converter 54 of the DSP 16. In addition, a high-speed clock signal output unit 100 that supplies a clock signal to the transmission signal D / A conversion unit 42 and the first cancel signal D / A conversion unit 54, and a clock signal output from the high-speed clock signal output unit 100 The frequency is divided to be supplied to the second cancel signal D / A converter 64, the first combined signal A / D converter 70, the second combined signal A / D converter 72, and the received signal A / D converter 76. The first frequency divider 102, the second frequency divider 104 that divides the clock signal output from the high-speed clock signal output unit 100 to supply the PLL 116, and the second frequency divider 104. And a PLL 106 that generates a local oscillation signal having a predetermined frequency based on a clock signal and supplies the local oscillation signal to the first down converter 62 and the second down converter 74. It has been. As shown in FIG. 4 described above, an 8-bit D / A converter can be used to obtain a suppression amount of 20 dB or more, but if it is 8 bits, a relatively high-speed D / A converter can be used. Therefore, a mode in which the RF signal is directly generated in the D / A converters 42 and 54 as in the RFID tag communication apparatus 94 of the present embodiment is also conceivable. Further, it is preferable that the input data is temporarily stored in the registers 96 and 98 that can be accessed at high speed. Thus, according to the present embodiment, the processing speed can be increased while ensuring a sufficient signal-to-interference ratio.

  The preferred embodiments of the present invention have been described in detail with reference to the drawings. However, the present invention is not limited to these embodiments, and may be implemented in other modes.

  For example, in the above-described embodiment, the first cancel signal output unit 24, the first cancel signal control unit 26, the second cancel signal output unit 28, the second cancel signal control unit 30 and the like are all provided in the DSP 16. However, they may be a control device provided separately from the DSP 16.

  In the above embodiment, the first cancel signal attenuator 55 corresponding to the first cancel signal and the second cancel signal attenuator 65 corresponding to the second cancel signal are provided. As long as it can be sufficiently removed, only one of them may be provided.

  In the above-described embodiment, the second signal synthesis unit 66 also functions as an amplifier that amplifies the second synthesis signal output from the second signal synthesis unit 66, but the second signal A second synthesized signal amplification unit that is a separate body from the synthesis unit 66 may be provided between the second signal synthesis unit 66 and the second synthesized signal A / D conversion unit 72. The first signal synthesis unit 58 may also function as an amplifier that amplifies the first synthesis signal output from the first signal synthesis unit 58. In this case, the second amplifying unit 60 is unnecessary.

In the above-described embodiment, the radio tag communication device 12 transmits the carrier wave F _c1 toward the radio tag 14 and receives the reflected wave F _rf returned from the radio tag 14. However, a transmitting antenna that transmits the carrier wave F _c1 toward the wireless tag 14 and a receiving antenna that receives the reflected wave F _rf returned from the wireless tag 14 are provided separately. Also good.

  Further, in the above-described embodiment, the RFID tag communication apparatus 12 is provided with the first down converter 62 that downconverts the first combined signal into an intermediate frequency signal. A mode in which the signal is not down-converted is also conceivable. By doing so, the first down converter 62 is not required, and thus there is an advantage that the configuration of the transmission / reception circuit 18 is simplified.

  In the above-described embodiment, the first cancel signal attenuator 55 is composed of a plurality of resistors and switches. However, the structure is a combination of a D / A conversion means and a bridge T-type variable attenuator using a PIN diode. May be used.

  In the above-described embodiment, the wireless tag communication device 12 is mainly used as an interrogator in the communication system 10 of FIG. 1, but the present invention is for writing predetermined information in the wireless tag 14. The present invention is also suitably applied to a wireless tag creation device and a wireless tag reader / writer that reads and writes information.

  In addition, although not illustrated one by one, the present invention is implemented with various modifications within a range not departing from the gist thereof.

It is a figure explaining the structure of the communication system with which the RFID tag communication apparatus of this invention is applied suitably. It is a figure explaining the electrical structure of the RFID tag communication apparatus of FIG. It is a figure explaining the structure of the attenuator with which the RFID tag communication apparatus of FIG. 2 was equipped. It is a figure explaining the relationship between a leaking carrier wave level and the amount of suppression. 3 shows a sine wave table which is an example of a function table provided in the RFID tag communication apparatus of FIG. 2A and 2B are block diagrams illustrating a configuration of a wireless tag circuit provided in the wireless tag in FIG. 1, in which FIG. 1A illustrates a configuration using subcarriers, and FIG. 2B illustrates a configuration using no subcarriers. FIGS. 3A and 3B are diagrams illustrating waveforms of signals of respective units in the RFID tag communication apparatus of FIG. 2, where FIG. 3A is a waveform of a reception signal supplied from a transmission / reception antenna, and FIG. (C) shows the waveform of the up-converted first cancel signal output from the second up converter, and (d) shows the waveform of the first composite signal output from the first signal synthesis unit. Each waveform is shown. FIGS. 3A and 3B are diagrams illustrating examples of signal waveforms of respective units in the RFID tag communication apparatus of FIG. 2, wherein FIG. 3A is a waveform of a down-converted first composite signal output from the first down converter, and FIG. The waveform of the second cancel signal output from the cancel signal D / A converter, (c) is the waveform of the second composite signal output from the second signal combiner, and (d) is output from the demodulator. The waveforms of the demodulated signals are shown. 3 is a part of a flowchart for explaining a main part of a wraparound signal removal control operation from a transmission side by a DSP of the RFID tag communication apparatus of FIG. 2. 3 is a part of a flowchart for explaining a main part of a wraparound signal removal control operation from a transmission side by a DSP of the RFID tag communication apparatus of FIG. 2. 3 is a part of a flowchart for explaining a main part of a wraparound signal removal control operation from a transmission side by a DSP of the RFID tag communication apparatus of FIG. 2. 3 is a part of a flowchart for explaining a main part of a wraparound signal removal control operation from a transmission side by a DSP of the RFID tag communication apparatus of FIG. 2. 3 is a part of a flowchart for explaining a main part of a wraparound signal removal control operation from a transmission side by a DSP of the RFID tag communication apparatus of FIG. 2. 3 is a part of a flowchart for explaining a main part of a wraparound signal removal control operation from a transmission side by a DSP of the RFID tag communication apparatus of FIG. 2. 3 is a part of a flowchart for explaining a main part of a wraparound signal removal control operation from a transmission side by a DSP of the RFID tag communication apparatus of FIG. 2. It is a figure explaining the electrical constitution of the radio | wireless tag communication apparatus which is 2nd Example of this invention. It is a figure explaining the electrical constitution of the RFID tag communication apparatus which is 3rd Example of this invention.

Explanation of symbols

12, 92, 94: RFID tag communication device 14: RFID tag 24: first cancel signal output unit 26: first cancel signal control unit 28: second cancel signal output unit 30: second cancel signal control unit 52: transmission / reception antenna 54: first cancel signal D / A converter 55: first cancel signal attenuator 56: second up converter 58: first signal combiner 64: second cancel signal D / A converter 65: second cancel signal attenuation 66: second signal synthesis unit A1: first cancel signal amplitude A2: second cancel signal amplitude BA: buffer amplifier (buffer device)
R1, R2, Ra, Rb, Rc, Rd, Re: resistors Sa, Sb, Sc, Sd, Se: switch φC1: phase shift of the first cancel signal φC2: phase of the second cancel signal

Claims (11)

A predetermined transmission signal is transmitted from the antenna toward the wireless tag, and information is communicated with the wireless tag by receiving a return signal returned from the wireless tag according to the transmission signal by the antenna. A wireless tag communication device,
A cancellation signal output unit for outputting a cancellation signal as a digital signal for removing a sneak signal from the transmission side included in the reception signal received by the antenna;
A cancel signal D / A converter for analog conversion of the cancel signal output from the cancel signal output unit;
A received signal amplitude detector for detecting the amplitude of the received signal received by the antenna;
Based on the amplitude of the received signal detected by the received signal amplitude detector, the cancel signal output unit is configured so that the output from the cancel signal D / A converter is within a predetermined range with reference to the maximum amplitude. A cancel signal control unit that outputs a control signal for controlling at least one of the amplitude and phase of the cancel signal output from
An attenuation unit that attenuates the cancellation signal analog-converted by the cancellation signal D / A conversion unit based on a control signal output from the cancellation signal control unit to an amplitude corresponding to a sneak signal from the transmission side;
A wireless tag communication apparatus, comprising: a cancel signal attenuated by the attenuation unit; and a signal synthesis unit that synthesizes the reception signal. The wireless tag communication device according to claim 1 , wherein the attenuation unit discretely changes an attenuation amount of the cancel signal.   The attenuation unit sets an attenuation amount so that an amplitude of the cancel signal in a predetermined input signal becomes a value closest to the amplitude within a limit not exceeding an amplitude of a sneak signal from the transmission side. 1 or 2 RFID tag communication apparatus;   The attenuation unit sets an attenuation amount so that an amplitude of the cancel signal in a predetermined input signal is a value that exceeds an amplitude of a sneak signal from the transmission side and is a value closest to the amplitude. Item 3. The wireless tag communication device according to Item 1 or 2.   The predetermined control signal is a value that makes an amplitude of a cancel signal output from the cancel signal D / A converter close to a half of a maximum amplitude that can be output from the cancel signal D / A converter. 3 or 4 RFID tag communication devices. A second cancel signal output unit that outputs a second cancel signal for removing a sneak signal from the transmission side included in the received signal as a digital signal;
A second cancel signal D / A converter for analog conversion of the second cancel signal output from the second cancel signal output unit;
A combined signal amplitude detecting unit for detecting the amplitude of the combined signal output from the signal combining unit;
Based on the amplitude of the combined signal detected by the combined signal amplitude detector, the output from the second cancel signal D / A converter is set within a predetermined range based on the maximum amplitude . A second cancel signal control unit that outputs a second control signal for controlling at least one of the amplitude and phase of the second cancel signal output from the two cancel signal output units;
Based on the second control signal output from the second cancellation signal control unit, the second cancellation signal analog-converted by the second cancellation signal D / A conversion unit is used as a wraparound signal from the transmission side. A second attenuation section for attenuating to a corresponding amplitude;
The second signal combining unit that combines the second cancel signal attenuated by the second attenuation unit and the combined signal output from the signal combining unit. Wireless tag communication device.   An up-converter that increases the frequency of the cancellation signal analog-converted by the cancellation signal D / A conversion unit by a predetermined value; and the attenuating unit receives a cancellation signal whose frequency is increased by a predetermined value by the up-converter from the transmission side The RFID tag communication apparatus according to claim 1, wherein the apparatus is attenuated to an amplitude corresponding to a wraparound signal.   The wireless tag communication device according to claim 7, wherein the attenuation unit sets the attenuation amount of the cancellation signal to an integer power of ½.   9. The wireless tag according to claim 1, wherein the attenuating unit comprises a plurality of resistors constituting a plurality of voltage dividers and a plurality of switches for selectively operating the plurality of voltage dividers. Communication device.   The wireless tag communication device according to claim 9, wherein the attenuation unit includes a buffer device.   11. The RFID tag communication apparatus according to claim 1, wherein the number of samples of the cancel signal D / A conversion unit is 4 samples per cycle of the output periodic function.

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