JP2015230608A - Rfid reader writer device, rfid reader writer system, and rfid read method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize deviation in the carrier leak suppression characteristics of a coupler of an RFID reader writer device and prevent degradation of communication quality.SOLUTION: An RFID reader writer device comprises: a coupler; a termination circuit terminating one terminal of the coupler for impedance matching; a carrier leak monitor circuit measuring a carrier leak amount from a modulation/transmission unit to a reception/demodulation unit of the coupler; and impedance adjustment means adjusting an impedance of the termination circuit so as to minimize the carrier leak amount, the transmission/modulation unit performing modulation of an RFID read command on a carrier if the impedance adjustment means adjusts the impedance of the termination means so as to minimize the carrier leak amount. With this configuration, even if the impedance of an antenna changes, an increase in the carrier leak amount of the coupler of the RFID reader writer device can be minimized and it is, therefore, possible to prevent a degradation of a communication quality such as an RFID reading rate.

Description

  The present invention relates to a radio frequency identification (hereinafter referred to as “RFID”) reader / writer device, an RFID reader / writer system, and an RFID reading method.

  In recent years, RFID systems that identify and manage people and objects using RFID have been adopted for various purposes. In particular, the handy type RFID reader / writer device is easy to carry, and is operated in a wider variety of scenes and environments than the stationary type RFID reader / writer.

  In Patent Document 1, in an RFID system using an isolator to isolate a transmission signal and a reception signal, the function of removing the transmission leakage signal of the RFID system is controlled independently of the RFID reading function and mixed into the reception signal. It has been proposed to remove a transmission leak signal by detecting a transmission leak signal, generating a cancellation signal having the same magnitude as that of the transmission leak signal, but having the opposite phase, and adding it to the reception signal. Further, Patent Document 2 describes a coupler including a detection unit that detects reception characteristics, and a control unit that adjusts a phase and a gain so that the reception characteristics are improved, and a transmission / reception apparatus including the coupler. ing.

  Further, in Patent Document 3, the voltage level of the sneak signal that sneaks from the transmission unit to the reception unit is detected using the components of the reception unit, and the sneak signal level is transmitted from the transmission unit according to this sneak signal level. It has been proposed to automatically adjust the phase of the generated signal.

JP 2011-244457 A JP 2010-109462 A JP 2011-87137 A

  In the invention proposed in Patent Document 1, the process of generating the cancellation signal from the detected magnitude and phase of the transmission leakage signal is complicated, and it is necessary to use an expensive isolator. Moreover, although the transmission / reception apparatus described in patent document 2 can reduce the loss of a transmission signal with a directional coupler, it efficiently reduces the carrier leak that leaks from the transmitter to the receiver without going through the antenna. I can't do it.

  Furthermore, the technique proposed in Patent Document 3 does not consider carrier leakage that leaks from the transmitting unit to the receiving unit without passing through the antenna when the impedance of the antenna changes due to the environment around the antenna.

  The coupler is designed with the assumption that it is terminated with an impedance of 50Ω. Therefore, when the impedance of the antenna changes, the coupler cannot exhibit its original performance and the transmission power leaks from the transmitter to the receiver. A certain amount of carrier leak increases. As a result, the communication quality such as the probability of correctly reading the RFID (reading rate) is deteriorated.

  According to the present invention, even when the impedance of the antenna changes due to the environment around the antenna, the carrier leak amount of the coupler is adjusted to the minimum, and then RFID reading can be performed to prevent deterioration in communication quality such as the reading rate. An object of the present invention is to provide an RFID reader / writer device, an RFID reader / writer system, and an RFID reading method using the RFID reader / writer device.

  An RFID reader / writer device according to a first aspect of the present invention outputs a transmission power of an unmodulated carrier wave and performs modulation including an RFID read command on the carrier wave, and outputs from the transmission / modulation unit The transmission power to be transmitted to the antenna, the coupler for guiding the reflected power from the RFID tag (which is added in the same way) input from the antenna to the reception / demodulation unit, and one terminal of the coupler for impedance matching A termination circuit that terminates the transmission, a carrier leak monitor circuit that measures a carrier leak amount that is a transmission power amount leaking from the transmission / modulation unit to the reception / demodulation unit in the coupler, and an unmodulated carrier wave to the RFID. A control signal for adjusting impedance so that the amount of carrier leak is minimized while outputting transmission power. Impedance adjustment means for outputting to the path, and the transmission / modulation section adjusts the impedance of the termination circuit so that the amount of carrier leakage is minimized after the impedance adjustment means The read command is modulated.

  The RFID reader / writer system according to the second aspect is powered by the RFID reader / writer device and transmission power transmitted from the RFID reader / writer device, and receives the RFID read command, the RFID reader / writer device is reflected by reflected power. And an RFID for returning an identification code.

  An RFID reader / writer device having a coupler that guides transmission power output from a transmission unit of an RFID reader / writer device to an antenna and guides reflected power from the RFID input from the antenna to a reception unit. A first method for measuring a carrier leak amount, which is a transmission power amount leaking from a transmission unit to a reception unit, and outputting transmission power of an unmodulated carrier wave from the transmission unit to the RFID. The second process of adjusting the impedance of the termination circuit connected to one terminal of the coupler so that the carrier leak amount is minimized, and the carrier leak amount is minimized. And a third process for modulating the RFID read command to the carrier wave after adjusting the impedance of the termination circuit. And features.

  According to the present invention, the RFID reader / writer impedance-matches the coupler that guides the transmission power output from the transmitter to the antenna and the reflected power from the RFID input from the antenna to the receiver, and one terminal of the coupler. Termination circuit that terminates for the purpose, a carrier leak monitor circuit that measures the amount of carrier leak that is the amount of transmission power leaking from the transmitter to the receiver in the coupler, and the amount of carrier leak measured by the carrier leak monitor is minimized And an impedance adjusting means for adjusting the impedance of the termination circuit. Accordingly, even when the impedance of the antenna changes due to the environment around the antenna, the carrier leak amount of the coupler is adjusted to the minimum, so that it is possible to prevent deterioration in communication quality such as a reading rate.

1 is a system configuration diagram showing an outline of an RFID reader / writer system according to an embodiment of the present invention. It is a block diagram which shows the outline of the principal part of the RFID reader / writer apparatus in FIG. FIG. 2 is a circuit diagram illustrating a circuit example of the RFID reader / writer device in FIG. 1. It is a figure explaining the use environment of a handy type RFID reader / writer. It is a block diagram which shows the outline of the principal part of the conventional RFID reader / writer apparatus. FIG. 6 is a circuit diagram showing an example of a termination circuit 31A in FIG. It is a figure explaining the carrier leak of the coupler of RFID reader / writer apparatus. It is a figure which shows the relationship between the impedance (VSWR) of an antenna, and carrier leak amount. It is a figure which shows the relationship between the amount of carrier leaks, and the reading rate of RFID. It is a circuit diagram which shows an example of the termination circuit of embodiment of this invention. It is a circuit diagram which shows another example of the termination circuit of embodiment of this invention. It is a circuit diagram which shows another example of the termination circuit of embodiment of this invention. It is a flowchart which shows the process of the impedance adjustment means of Embodiment 1 of this invention. It is a figure which shows the relationship between the control value and carrier leak amount in FIG. It is a circuit diagram which shows the example of the impedance adjustment means of Embodiment 2 of this invention. It is a figure explaining operation | movement of the RFID reader-writer system of embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Configuration of the embodiment)
FIG. 1 is a system configuration diagram showing an outline of an RFID reader / writer system according to an embodiment of the present invention.

  The RFID reader / writer system according to the embodiment of the present invention includes an RFID reader / writer device 10 and a plurality of RFIDs 41 attached to a plurality of articles 40. The RFID reader / writer device 10 transmits a search button 11 to be pressed when reading the RFID 41, an antenna 12 that transmits transmission power toward the RFID 41, receives reflected power from the RFID 41, an identification code of the read RFID 41, and the like. And a display unit 13 for displaying.

  The RFID 41 is an identification tag affixed to the identification / management target article 40, and includes an antenna 41a and a load 41b. The antenna 41a is formed so as to be tuned to the frequency of the transmission power given from the RFID reader / writer device 10, and is, for example, a microstrip antenna made of a copper foil of a printed board. The load 41b is for impedance matching with the antenna 41a and is, for example, 50Ω. The RFID tag 41 receives radio waves continuously sent from the RFID reader / writer device 10 and returns them to the RFID reader / writer device 10 by a backscatter method.

  The RFID reader / writer device 10 receives the reflected wave from the RFID 41, demodulates the response data, and displays the read RFID identification code on the display unit 13.

FIG. 2 is a block diagram showing an outline of a main part of the RFID reader / writer device in FIG.
The RFID reader / writer device 10 includes a microprocessor unit (Micro-Processing Unit, hereinafter referred to as “MPU”) 20, a transmission / modulation unit 21, a first coupler 30, an antenna 12, and a termination. A circuit 31, a carrier leak monitor circuit 33, a reception / demodulation unit 34, and an impedance adjustment unit 35 are included.

  The transmission / modulation unit 21 transmits, amplifies and outputs a high-frequency carrier wave supplied to the RFID 41, and modulates a read command of the RFID 41 on the high-frequency carrier wave. The first coupler 30 guides a high-frequency carrier wave output from the transmission / modulation unit 21 to the antenna 12, and receives a reflected wave from the RFID 41 input from the antenna 12 via the carrier leak monitor circuit 33. 34.

  The termination circuit 31 is a circuit that guarantees the original performance of the coupler 30 by being connected between one terminal of the first coupler 30 and the ground, and is particularly a circuit configured to be capable of adjusting the impedance.

  The characteristics of the coupler 30 are, for example, that the attenuation of the terminal a → terminal b is 1.5 dB, the attenuation of the terminal b → terminal c is 10 dB, the attenuation of the terminal c → terminal d is 1.5 dB, and the terminal a → terminal d. Is 15 dB or more.

  The carrier leak monitor circuit 33 is a circuit that measures the amount of carrier leak, which is the amount of power that the transmission power output from the transmission / modulation unit 21 leaks from the terminal a to the terminal d of the coupler 30.

  The reception / demodulation unit 34 receives and demodulates the reflected wave from the RFID 41 by amplifying and converting it to an intermediate frequency.

  The impedance adjustment unit 35 generates a control signal for adjusting the impedance of the termination circuit 31 so that the monitor value of the carrier leak amount output from the carrier leak monitoring circuit 33 is minimized, and outputs the control signal to the termination circuit 31. is there. In FIG. 2, the impedance adjusting means 35 is built in the MPU 20. The impedance adjusting means 35 may be provided outside the MPU 20.

FIG. 3 is a circuit diagram showing an example of the RFID reader / writer device in FIG.
3, the transmission / modulation unit 21 in FIG. 2 is controlled by the MPU 20 and outputs a non-modulated intermediate frequency signal or an intermediate frequency signal subjected to RFID read command modulation, and an intermediate frequency signal. A filter 21b that removes unnecessary frequency components from the signal, a mixer 21c that mixes the intermediate frequency signal and the output signal of the local transmitter 23 to frequency-convert the carrier signal, and an amplifier 21d that amplifies the carrier signal to a predetermined transmission power. It consists of and. The configuration of the modulation unit 21a, the filter 21b, the mixer 21c, and the amplifier 21d illustrated in FIG. 3 is merely an example of the configuration of the transmission / modulation unit 21.

  In FIG. 3, a carrier leak monitor circuit 33 in FIG. 2 includes a second coupler 33a that extracts a part of the carrier leak power as monitor power, and a power detector 33b that converts the monitor power into a direct current (DC) voltage. And an analog-digital converter (hereinafter referred to as “ADC”) 33c for converting an analog DC voltage into a digital value. The reason why one terminal of the second coupler 33a is grounded is to increase the detection voltage extracted from the other end by grounding one end. The grounded terminal may be grounded via a 50Ω termination resistor, for example.

  The power detection unit 33b includes a detection diode (not shown), a smoothing capacitor, a resistor, and the like.

  In the example shown in FIG. 3, the carrier leak monitor circuit 33 is provided between the amplifier 32 and the mixer 34a, but may be provided between the mixer 34a and the filter 34b, or may be provided between the filter 34b and the demodulator 34c. You may provide between.

  The configuration of the carrier leak monitor circuit 33 shown in FIG. 3 is merely an example, and the configuration of the carrier leak monitor circuit 33 is not limited to the configuration of FIG.

  3, the reception / demodulation unit 34 in FIG. 2 includes a mixer 34a, a filter 34b, and a demodulation unit 34c. The configuration of the reception / demodulation unit 34 shown in FIG. 3 is merely an example, and is not limited to the configuration of FIG. Note that the demodulator 34c employs a synchronous detection method in which the demodulated signal is output after being separated into an in-phase channel (I channel) and a quadrature channel (Q channel).

  In FIG. 3, the impedance adjusting means 35 built in the MPU 20 outputs a control signal for changing the impedance of the termination circuit 31 so that the monitor value of the carrier leak amount output from the ADC 33c is minimized.

(Operation of the embodiment)
Regarding the operation of the RFID reader / writer device of the embodiment of the present invention,
(I) Operation of the conventional RFID reader / writer device, (II) Configuration example and operation of the termination circuit of the embodiment of the present invention, and (III) Impedance adjustment processing of the termination circuit of the present invention. To do.

(I) Operation of Conventional RFID Reader / Writer Device FIG. 4 is a diagram for explaining the usage environment of a handy type RFID reader / writer, and FIG. 4 (a) is attached to a container containing water or other liquid. FIG. 4B shows a case where an RFID is read, and FIG. 4B shows a case where there is a metal (such as a rocker) around the RFID to be read.

  In the conventional RFID reader / writer 10A, when the RFID 41 is read in the usage environment shown in FIGS. 4A and 4B, the impedance of the antenna 12 of the RFID reader / writer 10A is disturbed, and the coupler 30 is specified. There was a problem that the RFID could not be read correctly due to the deterioration and the amount of carrier leak.

  In order to solve this problem, the mechanism of degradation of the read rate of the analyzed RFID will be described below.

  FIG. 5 is a block diagram showing an outline of a main part of a conventional RFID reader / writer device. Elements common to FIG. 2 showing the outline of the main part of the present invention are denoted by common reference numerals.

  A conventional RFID reader / writer device 10A includes a transmission / modulation unit 21, a first coupler 30, an antenna 12, and a reception / demodulation unit 34 similar to those in FIG. 2, and an MPU 20A and a termination circuit 31A different from those in FIG. Have. The MPU 20A controls the entire RFID reader / writer device 10A in the same manner as the MPU 20 of FIG. 2, but has an impedance adjustment function for adjusting the impedance of the termination circuit 31A so that the amount of carrier leakage is minimized as in the present invention. Not done.

FIG. 6 shows a circuit diagram example of the termination circuit 31A in FIG.
As shown in FIG. 6, the termination circuit 31A includes, for example, a 50Ω termination resistor 51 having one terminal grounded, one terminal connected to one terminal of the coupler 30, and the other terminal to a termination resistor. 51, an inductor 52 connected to the other terminal of 51, one terminal of inductor 52, a first capacitor 53 connected to one terminal and the other terminal grounded, the other terminal of inductor 52, The second capacitor 54 has one terminal connected and the other terminal grounded. The value of each element of the termination circuit 31A is selected so that the impedance when the termination circuit 31A is viewed from the coupler 30 side appears to be 50Ω.

Here, the carrier leak of the coupler 30 will be described.
FIG. 7 is a diagram for explaining the carrier leak of the coupler of the RFID reader / writer device.

  Focusing on the coupler 30 in FIG. 7, the transmission / modulation unit 21 receives and demodulates a transmission signal from the terminal 30a of the coupler 30 through the terminal b to the antenna 12, and from the antenna 12 through the terminal b of the coupler 30 through the terminal d. A reception signal directed to the unit 34 and a carrier leak from the transmission / modulation unit 21 to the reception / demodulation unit 34 via the terminal a to the terminal d of the coupler 30 are shown.

Both the reception signal and the carrier leak are input to the reception / demodulation unit 34. The antenna impedance (input impedance) (S ₁₁ ) when the antenna 12 is viewed from the terminal b of the coupler 30 and the impedance when the termination circuit 31A is viewed from the terminal c of the coupler 30 are adjusted to 50Ω. In a state where impedance matching (matching) between the input impedance (S ₁₁ ) and the termination circuit 31A is achieved, the amount of carrier leak is less than −25 dB with respect to the amount of power of the transmission signal.

However, when the RFID 41 is read in the use environment as shown in FIGS. 4A and 4B, the input impedance (S ₁₁ ) when the antenna 12 is viewed from the terminal b of the coupler 30 is 50Ω. Therefore, the coupler 30 cannot exhibit its original performance.

8 is input Inpi - a diagram illustrating dance and (VSWR) the relationship of the carrier leakage quantity, FIG. 8 (a), an input on the Smith chart Inpi - Dance S ₁₁ and the voltage standing wave ratio (Voltage Standing Wave Ratio (hereinafter referred to as “VSWR”)), and FIG. 8B shows a characteristic example of the carrier leak amount of the coupler with respect to VSWR.

The FIG. 8 (a), the input Inpi the normalized antenna 12 with characteristic impedance 50Ω seen from the terminal b of the coupler 30 - Dance S ₁₁ is shown on the Smith chart. S ₁₁ = 1 on the Smith chart indicates that the input impedance of the antenna 12 is 50Ω (VSWR = 1.0). S ₁₁ = 1 + j1.25 indicates that the input impedance of the antenna 12 is 50 + j62.5Ω (VSWR≈1.5), and S ₁₁ = 1 + j1.7 indicates that the input impedance of the antenna 12 is 50 + j85Ω (VSWR≈2.0). Show.

Referring to FIG. 8B, when S ₁₁ = 1 (VSWR = 1.0), the carrier leak amount is about −15 dB with respect to the transmission power amount, and the carrier leak at VSWR = 1.5. The amount is about −10 dB with respect to the transmission power amount, and the carrier leak amount at VSWR = 2.0 is about −5 dB with respect to the transmission power amount. From FIG. 8B, it can be seen that the amount of carrier leak increases with an increase in the value of VSWR.

FIG. 9 is a diagram illustrating the relationship between the amount of carrier leak and the reading rate of RFID.
Referring to FIG. 9, when the carrier leak power amount is less than −10 dB with respect to the transmission power amount, the probability that the RFID identification code can be read correctly (hereinafter referred to as “read rate”) is 90% or more. However, it can be seen that when the amount of carrier leak power is −5 dB or more with respect to the amount of power of the transmission signal, the RFID reading rate rapidly decreases.

On the other hand, the conventional RFID reader / writer device 10A shown in FIGS. 5 and 6 is different from the RFID reader / writer device 10 of the embodiment of the present invention shown in FIG. The carrier leak monitor circuit 33 and the impedance adjusting means 35 are not provided. Therefore, a large amount of water in the vicinity of the antenna 12, there are metal, the input impedance S ₁₁ of the antenna 12 is offset from the center of the circle of the Smith chart, the value of VSWR is increased, the amount of carrier leakage is increased, RFID reader Even if the rate is reduced, the conventional RFID reader / writer device 10A can only isolate the antenna 12 from the affected one.

(II) Configuration Example and Operation of Termination Circuit of Embodiment of the Present Invention FIG. 10 is a circuit diagram showing an example of the termination circuit of the embodiment of the present invention, and FIG. 11 shows the termination circuit of the embodiment of the present invention. FIG. 12 is a circuit diagram showing another example, and FIG. 12 is a circuit diagram showing another example of the termination circuit according to the embodiment of the present invention.

  Termination circuits 31-1, 31-2 and 31-3 shown in FIGS. 10 to 12 are examples of termination circuits capable of adjusting impedance.

  In the termination circuit 31-1 shown in FIG. 10, one terminal is grounded, one terminal is connected to the terminal c of the coupler 30, and the other terminal is connected to the other terminal of the termination resistor 51. The connected inductor 52, one terminal of the inductor 52, one terminal is connected, the other terminal is grounded, and the first is capable of controlling the capacitance by a control signal output from the impedance adjusting means 35. The capacitor 53A, the other terminal of the inductor 52, one terminal is connected, the other terminal is grounded, and a second capacitor 54A capable of controlling the capacitance by a control signal output from the impedance adjusting means 35 ,have.

According to the termination circuit 31-1 shown in FIG. 10, when the input impedance S ₁₁ of the antenna 12 is shifted due to the environment in the vicinity of the antenna 12, the value of VSWR is increased, and the amount of power of carrier leak is increased. By varying the capacitances of the first and second capacitors 53A and 54A, the coupler 30 can be brought close to its original characteristics, the amount of carrier leakage can be reduced, and the RFID reading rate can be minimized.

  Also, the termination circuit 31-2 shown in FIG. 11 has one terminal grounded, a termination resistor 51A whose resistance value can be controlled by a control signal output from the impedance adjusting means 35, and one terminal a coupler 30. An inductor 52 having the other terminal connected to the other terminal of the termination resistor 51A, one terminal of the inductor 52, one terminal being connected, and the other terminal being grounded. Capacitor 53, the other terminal of inductor 52, and a second capacitor 54 having one terminal connected and the other terminal grounded.

According to the termination circuit 31-2 shown in FIG. 11, the environment in the vicinity of the antenna 12, the input impedance S ₁₁ Gazure antenna 12, the value of VSWR is increased, if the power amount of the carrier leak is increased, By varying the resistance value of the terminating resistor 51A, the VSWR is brought close to 1, whereby the coupler 30 can be brought close to its original characteristics, the amount of carrier leakage can be reduced, and the RFID reading rate can be minimized.

  Further, the termination circuit 31-3 shown in FIG. 12 includes a termination resistor 51 having one terminal grounded, one terminal connected to the terminal c of the coupler 30, and the other terminal connected to the other terminal of the termination resistor 51. An inductor 52A whose inductance value is changed by a control signal output from the impedance adjustment means 35, one terminal of the inductor 52A, one terminal connected to the other terminal, and the other terminal grounded. The capacitor 53, the other terminal of the inductor 52A, and a second capacitor 54 having one terminal connected and the other terminal grounded.

According to the termination circuit 31-3 shown in FIG. 12, the environment in the vicinity of the antenna 12, the input impedance S ₁₁ Gazure antenna 12, the value of VSWR is increased, if the power amount of the carrier leak is increased, By varying the inductance value of the inductor 52A, by bringing the VSWR closer to 1, the coupler 30 can be brought closer to its original characteristics, the amount of carrier leakage can be reduced, and the RFID reading rate can be minimized.

  The inductor 52A in FIG. 12 is configured to select one of a plurality of inductors L1, L2,..., Ln according to a control signal. The inductor 52A capable of controlling the inductance value is not limited to the configuration in which one inductor among the plurality of inductors is selected by the control signal, and the inductance value of the inductor itself may be variably controlled by the control signal.

(III) Impedance Adjustment Processing of Termination Circuit of Present Invention FIG. 13 is a flowchart showing processing of impedance adjustment means.

  The processing of the impedance adjusting means will be described along the flowchart of FIG. 13 with reference to FIGS.

  When the process is started, the process proceeds to step S1. In step S1, the MPU 20 performs initial setting of “monitor allowable maximum value” as the control value = 0 and the monitor minimum value in the impedance adjusting means 35, and then proceeds to step S2. move on. Here, the maximum allowable monitor value is the amount of carrier leakage that must be secured in order to secure an RFID reading rate that must be secured at a minimum, for example, 90% or more, in the RFID reader / writer system. This is a monitor value output from the corresponding carrier leak monitor circuit 33.

  In step S2, the impedance adjusting unit 35 sets a control value in the termination circuit 30 by the control signal, and proceeds to step S3. Here, the termination circuit 30 may be termination circuits 30-1 to 30-3 having any configuration shown in FIGS. 10 to 12, but representatively, the termination circuit 30-1 shown in FIG. It will be explained as being. In the first capacitor 53A and the second capacitor 54A in FIG. 10, for example, the capacitance value can be varied in increments of 0.15 pF in the range of 0 pF to 5 pF according to the control values 0 to 31. To do.

  In step S3, the impedance adjusting unit 35 acquires the monitor value of the carrier leak amount from the carrier leak monitor circuit 33, and proceeds to step S4.

  In step S4, the impedance adjusting means 35 compares the monitor value acquired in step S3 with the monitor minimum value set in step S1, and if the monitor value is less than the monitor minimum value (YES), the process proceeds to step S5, where the monitor is monitored. If it is equal to or greater than the minimum value (NO), the process proceeds to step S6.

  In step S5, the MPU 20 updates the best control value to the current control value and the minimum monitor value to the latest monitor value determined as YES in step S4, and proceeds to step S6.

  In step S6, the MPU 20 adds 1 to the control value to the impedance adjusting unit 35, and proceeds to step S7.

  In step S7, the MPU 20 compares the control value with 31. If the control value is 31 or less (NO), the MPU 20 returns to step S2 and repeats the processing of steps S2 to S7 until the control value becomes larger than 31, If the control value is greater than 31 (YES), the process proceeds to step S8. By repeating the processes of steps S2 to S7, the monitor value of the carrier leak amount is controlled to the minimum control value that minimizes.

  In step S8, the impedance adjustment means 35 controls the capacitance values of the first capacitor 53A and the second capacitor 54A of the termination circuit 31-1 to the optimum values by the control signal, and performs the impedance adjustment processing of the termination circuit. finish.

  FIG. 14 is a diagram showing the relationship between the control value and the carrier leak amount in FIG. 13, FIG. 14 (a) shows the relationship between the control value and the capacitance, and FIG. 14 (b) shows the control value and The relationship of carrier leak amount is shown.

  In FIG. 14A, when the control value is set to 0 to 31, the capacitances of the variable capacitors 53A and 54A in the termination circuit 31-1 in FIG. 10 change. For example, if the control value is set to 10, the capacitance is 1.7 (pF), and if the control value is set to 20, the capacitance is 3.0 (pF). FIG. 14A corresponds to step S2 in the flowchart shown in FIG.

  Next, in FIG. 14B, when the control value is changed, the capacitance changes according to FIG. 14A, and the carrier leak amount changes with the change in the characteristics of the coupler 30 in FIG. The situation is shown.

  In FIG. 14B, when the minimum value of the carrier leak amount in the range of the control values 0 to 31 is the control value 17, the carrier leak amount is the minimum value −27 (dB). FIG. 14B corresponds to the processing in steps S2 to S8 in the flowchart shown in FIG. 13, and the best control value 17 is set in the termination circuit 31-1 in step S8 in the flowchart in FIG. Then, the variable capacitors 53A and 54A in the termination circuit 31-1 are set to 2.6 (pF).

  Here, looking at the termination circuit 31-1 shown in FIG. 10, the variable capacitors 53 </ b> A and 54 </ b> A are configured such that the capacitance is controlled by one control signal. The 54A may be configured to control the capacitance by an individual control signal. That is, the variable capacitor 53A is processed by the impedance adjusting means shown in FIGS. 13 and 14 to adjust the capacitance of the variable capacitor 53A to the minimum amount of carrier leakage, and thereafter, the variable capacitor 54A has the same impedance. If the capacitance of the variable capacitor 54A is adjusted to the minimum carrier leak amount by performing the process of the adjusting means, the carrier leak amount can be increased more than the capacitance of the two variable capacitors 53A, 54A determined by one control signal. Expect to keep it low.

  In the above description, for convenience of explanation, the termination circuit 31 has been described as the termination circuit 31-1 shown in FIG. 10, but the termination circuit 31-2 shown in FIG. 11 and the termination circuit shown in FIG. The same applies to 31-3.

(Embodiment 2)
FIG. 15 is a circuit diagram illustrating an example of the impedance adjusting unit according to the second embodiment of the present invention. Elements common to FIGS. 2, 3, and 10 illustrating the first embodiment of the present invention are denoted by common reference numerals. It is attached.

  The circuit diagram shown in FIG. 15 is an example of a circuit that realizes the processing of the impedance adjusting means described with reference to FIGS. 13 and 14.

  First, the configuration of the second embodiment of the present invention shown in FIG. 15 will be described in comparison with the configuration of the first embodiment of the present invention.

  The carrier leak monitor 33A is configured by removing the ADC 33c in the carrier leak monitor 33 shown in FIG. 3, and outputs a monitor value Vmon of a direct current (DC) carrier leak amount.

  The impedance adjusting unit 35A includes a differential amplifier 35A-1 and two bias resistors 35A-2 and 35A-3 that apply a reference voltage Vmonmax to the inverting input terminal of the differential amplifier 35A-1.

  The termination circuit 31B is a modification of FIG. The first capacitor 53A has a varicap 53A-1 whose capacitance changes in accordance with the DC control voltage when a reverse bias DC control voltage is applied between the cathode and the anode, and the cathode and inductor 52 of the varicap 53A-1. And a capacitor 53A-2 for DC cut and a resistor 53A-3 for noise removal. Similarly, the second capacitor 54A includes a varicap 54A-1, a capacitor 54A-2, and a resistor 54A-3.

Next, the operation of the second embodiment of the present invention shown in FIG. 15 will be described.
In FIG. 15, the two bias resistors 35A are set so that the value of the reference voltage Vmonmax applied to the inverting input terminal of the differential amplifier 35-1 becomes the monitor allowable maximum value in step S1 in the flowchart shown in FIG. -2, 35A-3 resistance values are set.

  When the impedance adjusting unit 35A is configured as described above, the differential amplifier 35A-1 is non-inverted (+) according to the virtual grounding principle of the operational amplifier (hereinafter referred to as “OP amplifier”) constituting the differential amplifier 35A-1. ) The monitor value Vmon given to the input terminal operates so as to be equal to Vmonmax given to the inverting (−) input terminal.

  As a result, a control voltage that minimizes the monitor value Vmon output from the carrier leak monitor circuit 33A is output from the differential amplifier 35A-1 to the termination circuit 31B.

(RFID Reader / Writer System of Embodiment)
Finally, the overall operation of the RFID reader / writer system will be described with reference to FIG. 3 and the transition of the transmission / reception waveform shown in FIG.

  FIG. 16 is a diagram for explaining the operation of the RFID reader / writer system of the present invention. FIG. 16 (a) shows a temporal change in the transmission output waveform, and FIG. 16 (b) shows that carrier leakage can be ignored. FIG. 16C shows the temporal change in the received waveform when the carrier leak is large and the impedance of the termination circuit is not adjusted (conventional RFID reader / writer system). FIG. 16D shows a temporal change in the reception waveform of the RFID reader / writer system of the present invention that adjusts the impedance of the termination circuit when the carrier leak is large.

  In FIG. 16A, when the amplifier 21d in FIG. 3 is turned on at time t0, an unmodulated carrier wave is output from time t0 to time t1, and the modulated waveform of the RFID read command is from time t1 to t2. After that, the unmodulated carrier wave is output between times t2 and t5.

  FIG. 16B shows a received waveform when the electromagnetic environment in the vicinity of the antenna 12 is good, the impedance of the antenna 12 is approximately 50Ω, and the carrier leak can be ignored. As shown in FIG. 16B, no received signal is output between time t0 to t1, time t2 to t3, and time t4 to t5. This is because the receiving / demodulating unit 34 in FIG. 2 is adjusted so that the demodulated output becomes 0 when an unmodulated carrier wave is received from the RFID 41 except during the period when the response waveform of the RFID 41 is returned. Because it is.

  Therefore, a saturated reception waveform is output during the period from time t1 to t2 when the modulation waveform of the RFID read command is output, and the response waveform of the RFID tag is output as the reception waveform during time t3 to t4. . In the received waveform shown in FIG. 16B, since the response waveform of the RFID tag is at a position that is substantially symmetrical with respect to the reference level, the identification code of the RFID tag can be read correctly.

  On the other hand, FIG. 16C shows a temporal change in the reception waveform of the conventional RFID reader / writer system in which the carrier leak is large and the impedance of the termination circuit 31A is not adjusted. Referring to FIG. 16C, the received waveform of the response waveform of the RFID tag is offset upward with respect to the reference level, and does not cross the reference level. Thus, in the conventional RFID reader / writer system in which the carrier leak is large and the impedance of the termination circuit 31A cannot be adjusted, the identification code cannot be read correctly from the RFID 41.

  FIG. 16D shows a temporal change in the received waveform of the RFID reader / writer system of the present invention that solves the problems of the conventional RFID reader / writer system. FIG. 16D shows that the amount of carrier leak is decreasing between times t0 and t1. This is because the impedance of the termination circuit 31 is adjusted by the impedance adjusting means 35 so that the amount of carrier leakage is minimized. Thereby, since the received waveform of the response waveform of the RFID tag is at a position that is substantially symmetrical up and down with respect to the reference level, the identification code of the RFID tag can be read correctly.

(Modification)
As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment described above, In the range which does not deviate from the summary of this invention, various structures or embodiment can be taken. it can.

  The present invention is not limited to the first and second embodiments, and various utilization forms and modifications are possible. As such usage forms and modifications, for example, there are the following (a) to (c).

  (A) In the process of the impedance adjusting unit of the first embodiment described with reference to FIGS. 13 and 14, the termination circuit 31 is set to the control value 0 to 31, and the control value that minimizes the carrier leak amount is searched. The termination circuit 31 is set with the best control value that minimizes the amount of carrier leakage. However, even if the carrier leak amount is not minimized, it is sufficient that the RFID reading rate is not affected. Therefore, when the control value is set in the termination circuit 31 and the carrier leak amount becomes less than the predetermined value. Thus, the control value set in the termination circuit 31 may be fixed. In this way, the time required for adjusting the impedance of the termination circuit 31 can be shortened.

  (B) The first capacitor 53A of the termination circuit 31B according to the second embodiment described with reference to FIG. 15 has a configuration in which the varicap 53A-1 and the capacitor 53A-2 are connected in series. A capacitor (not shown) may be connected in parallel to 53A-1. By connecting a capacitor in parallel to the varicap 53A-1 and adjusting the capacitance of the capacitor as appropriate, the ratio of change in capacitance with respect to the control voltage can be adjusted.

  (C) In the transmission / reception waveform diagram shown in FIG. 16, the RFID read command is output after adjusting the impedance of the termination circuit 31 so that the amount of carrier leakage is minimized. When the tag response waveform is received, the impedance adjustment means 35 may adjust the impedance of the termination circuit 31.

10, 10A RFID reader / writer device 11 Search button 12, 41a Antenna 13 Display unit 20 MPU
21 Transmitter / Modulator 21a Modulator 21b, 34b Filter 21c, 34a Mixer 21d, 32 Amplifier 23 Local Transmitter 30, 33a Coupler 31, 31A, 31B, 31-1, 31-2, 31-3 Termination Circuit 33, 33A Carrier leak monitor circuit 33b Power detector 33c ADC
34 reception / demodulation unit 34c demodulation unit 35, 35A impedance adjustment means 35A-1 differential amplifier 40 article 41 RFID tag 35A-2, 35A-3, 51, 53A-3, 54A-3 resistor 51A variable resistor 52 inductor 52A variable Inductors 53, 54, 53A-2, 54A-2 Capacitors 53A, 54A Variable capacitors 53A-1, 54A-1 Varicaps

Claims (9)

A transmission / modulation unit that outputs transmission power of an unmodulated carrier wave and performs modulation including an RFID read command on the carrier wave;
A coupler that guides transmission power output from the transmission / modulation unit to an antenna and guides reflected power from an RFID input from the antenna to a reception / demodulation unit;
A termination circuit for terminating one terminal of the coupler for impedance matching;
In the coupler, a carrier leak monitor circuit that measures a carrier leak amount that is a transmission power amount leaking from the transmission / modulation unit to the reception / demodulation unit;
Impedance adjusting means for outputting a control signal for adjusting impedance so as to minimize the amount of carrier leakage to the termination circuit while outputting transmission power of an unmodulated carrier wave to the RFID, and
The transmission / modulation unit includes:
The RFID reader / writer device characterized in that the impedance adjustment means adjusts the impedance of the termination circuit so that the amount of carrier leakage is minimized, and then modulates the RFID read command to the carrier wave. The carrier leak monitor circuit is
A second coupler that extracts a portion of the carrier leak power;
A power detector for detecting the power as a DC voltage;
An analog / digital converter (A / D converter) that converts the detected DC voltage into a digital value;
The impedance adjusting means includes
2. The RFID reader / writer device according to claim 1, wherein a control signal corresponding to the digital value is output and an impedance of the termination circuit is adjusted so that the amount of carrier leakage is minimized. The termination circuit is:
A termination resistor with one terminal grounded;
An inductor having one terminal connected to one terminal of the coupler and the other terminal connected to the other terminal of the termination resistor;
The first terminal of the inductor, one terminal is connected, the other terminal is grounded, and a first capacitor whose capacitance is changed by the control signal;
The other terminal of the inductor, one terminal is connected, the other terminal is grounded, and a second capacitor whose capacitance is changed by the control signal;
The RFID reader / writer device according to claim 1, wherein the RFID reader / writer device is provided. The termination circuit is:
One terminal is grounded, and a termination resistor whose resistance value is changed by the control signal;
An inductor having one terminal connected to one terminal of the coupler and the other terminal connected to the other terminal of the termination resistor;
The one terminal of the inductor, a first capacitor connected to one terminal and the other terminal grounded;
A second capacitor having one terminal connected to the other terminal of the inductor and the other terminal grounded;
The RFID reader / writer device according to claim 1, wherein the RFID reader / writer device is provided. The termination circuit is:
A termination resistor with one terminal grounded;
One terminal is connected to one terminal of the coupler, the other terminal is connected to the other terminal of the termination resistor, and an inductor whose inductance value changes according to the control signal;
The one terminal of the inductor, a first capacitor connected to one terminal and the other terminal grounded;
A second capacitor having one terminal connected to the other terminal of the inductor and the other terminal grounded;
The RFID reader / writer device according to claim 1, wherein the RFID reader / writer device is provided. The carrier leak monitor circuit is
A second coupler that extracts a portion of the carrier leak power;
A power detector for detecting the power as a DC voltage,
The impedance adjusting means includes
2. The RFID reader / writer device according to claim 1, wherein the impedance of the termination circuit is adjusted by outputting a control voltage that minimizes the DC voltage as the control signal. The termination circuit is:
A termination resistor with one terminal grounded;
An inductor having one terminal connected to one terminal of the coupler and the other terminal connected to the other terminal of the termination resistor;
A first capacitor whose capacitance is changed by the control voltage, wherein the one terminal of the inductor is connected to one terminal and the other terminal is grounded;
A second capacitor whose capacitance is changed by the control voltage, wherein the other terminal of the inductor is connected to one terminal, the other terminal is grounded,
The RFID reader / writer device according to claim 6, further comprising: An RFID reader / writer device according to any one of claims 1 to 7,
RFID that is powered by transmission power transmitted from the RFID reader / writer device and receives the RFID read command, and returns an identification code to the RFID reader / writer device by reflected power; and
An RFID reader / writer system comprising: An RFID reading method using an RFID reader / writer device having a coupler that guides transmission power output from a transmission unit of an RFID reader / writer device to an antenna and guides reflected power from the RFID input from the antenna to a reception unit,
A first process of measuring a carrier leak amount that is a transmission power amount leaking from the transmission unit to the reception unit;
While outputting transmission power of an unmodulated carrier wave from the transmitter to the RFID, the impedance of a termination circuit connected to one terminal of the coupler is adjusted so that the amount of carrier leakage is minimized. A second process;
A third process of modulating the RFID read command to the carrier wave after adjusting the impedance of the termination circuit so that the carrier leak amount is minimized;
An RFID reading method comprising: