JP6631480B2 - Reader writer - Google Patents

Description

  The present invention relates to a reader / writer for performing data communication with a tag, and particularly to a technique for demodulating a received signal.

  As a reader / writer, a reader / writer that transmits a carrier signal modulated according to data toward a tag from an antenna and demodulates a received signal received from the tag to generate data has been proposed. (See Patent Document 1). Further, in Patent Document 2, an external noise is captured by a receiving antenna that receives a signal from the wireless tag, and the level of the external noise is detected. A technique is described in which a period in which wireless communication is possible is specified, and wireless communication is performed in the specified period.

JP 2007-193780 A JP 2011-149890 A

  By the way, in the reader / writer, since the level of the signal received from the tag is minute, the influence of noise generated inside the reader / writer on the received signal becomes a problem. That is, as a reader / writer, a small-level reception signal is input to a digital signal output unit including a converter and the like, and a reference voltage to be compared with the reception signal in order to accurately convert the reception signal into a digital signal. It is conceivable to reduce the value, but in this case the converter is susceptible to noise. On the other hand, if the value of the reference voltage is set to a relatively high value, the influence of noise is reduced, but it becomes difficult to cope with a received signal of a minute level, so that the communicable distance between the reader / writer and the tag is shortened. .

  Further, the noise varies variously according to the noise source around the reader / writer. For this reason, there is a problem that a digital signal output unit that always balances the effect of noise with the length of a communicable distance is required. However, none of the techniques described in Patent Literature 1 and Patent Literature 2 solve the problem.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a digital signal output unit capable of always reducing the influence of noise and the length of a communicable distance in a well-balanced manner.

A reader / writer according to one aspect of the present invention includes a carrier generation unit that generates a carrier signal, an amplifier that amplifies and outputs a carrier signal from the carrier generation unit, and an amplifier that controls amplification on / off of the amplifier and the amplifier. A carrier control unit that modulates a carrier signal output from the amplifier, a carrier output circuit that outputs the carrier signal, and is connected to an output side of the amplifier, and transmits the carrier signal output from the amplifier to a tag. An antenna for receiving a sub-carrier signal from the tag, a first capacitor to which a carrier signal output from the amplifier and a sub-carrier signal received by the antenna are input, and an amplifier side of the first capacitor. Is connected in series with the first capacitor on the opposite side, and is received by the antenna and the carrier signal output from the amplifier. A subcarrier signal is input as a reception signal via the first capacitor, and a detection unit that outputs an analog signal corresponding to an envelope of the reception signal; and a first detection unit connected to an output side of the detection unit. A second capacitor different from the capacitor, a reference voltage, and an analog signal input from the detection unit via the second capacitor are compared, and a digital signal is output when the analog signal is equal to or higher than the reference voltage. A digital signal output unit, and a voltage level setting unit that changes and sets the level of the reference voltage and outputs the set reference voltage to the digital signal output unit. The analog signal output from the detection unit is input to the one input terminal of the pair of input terminals through the second capacitor. The reference voltage output from the voltage level setting unit is input to the other input terminal of the slaves, and a converter that outputs a voltage signal when the analog signal is equal to or higher than the reference voltage; and A switching element that receives the voltage signal and outputs a digital signal when the voltage signal is equal to or greater than a threshold, wherein the carrier control unit amplifies the amplifier at the start of data communication between the tags. Switching from amplification on, to output a non-modulated carrier signal from the amplifier, the carrier control unit, during the period of receiving data from the tag, by outputting a non-modulated carrier signal from the amplifier, An unmodulated carrier signal output from the amplifier and a subcarrier signal received by the antenna are input to the detection unit via the first capacitor. It is what is done.

  According to the present invention, the digital signal output unit always reduces the influence of noise and the length of the communicable distance in a well-balanced manner, accurately converts the subcarrier signal received by the antenna into a digital signal, and outputs the digital signal. be able to.

It is a block diagram showing one embodiment of a reader / writer of the present invention. 5 is a graph conceptually showing a relationship between a reference voltage output from a voltage level setting unit, noise resistance, and a communicable distance.

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

  FIG. 1 is a block diagram showing an embodiment of the reader / writer of the present invention. The reader / writer 1 of the present embodiment performs data communication with a passive or active tag TG, modulates a carrier signal in accordance with data, and transmits the modulated carrier signal to the tag TG. The sub-carrier signal transmitted and received from the tag TG is demodulated to generate data. Similarly, the tag TG also modulates the sub-carrier signal according to the data, transmits the modulated sub-carrier signal to the reader / writer 1, or demodulates the carrier signal received from the reader / writer 1 to demodulate the data. Or generate it. Here, the frequency of the subcarrier signal is assumed to be different from the frequency of the carrier signal. However, even if the frequency of the subcarrier signal is the same as the frequency of the carrier signal, that is, the reader / writer 1 and the tag TG have the same frequency. Signals may be transmitted and received.

  As shown in FIG. 1, the reader / writer 1 includes a carrier output circuit 2, an antenna 6, an envelope detector 7, a converter 8, an A / D converter 9, a voltage level setting unit 10, and capacitors C1 and C2. It is provided with. Note that the converter 8 and the A / D conversion circuit 9 are an example of a digital signal output unit in the claims.

  The carrier output circuit 2 includes a carrier generator 3, an amplifier 4, and a carrier controller 5. The carrier generation unit 3 generates and outputs a carrier signal of a specified frequency. Note that an operational amplifier or a comparator can be applied to the converter 8. Further, as the amplifier 4, a transistor, an inverter, an operational amplifier, or the like can be applied.

  The amplifier 4 amplifies and outputs the carrier signal from the carrier generator 3. The carrier control unit 5 controls the amplification on / off of the amplifier 4. In addition, the carrier control unit 5 controls the amplification factor of the amplifier 4 according to data input from the outside, and modulates the carrier signal output from the amplifier 4.

  The antenna 6 is used for both transmission and reception, and transmits the carrier signal output from the amplifier 4 and receives the sub-carrier signal transmitted from the tag TG.

  The envelope detector 7 receives the carrier signal amplified by the amplifier 4 and the sub-carrier signal received by the antenna 6 as reception signals, and outputs an analog signal corresponding to the envelope of the reception signal.

  The carrier signal output from the amplifier 4 and the subcarrier signal received by the antenna 6 are input to the envelope detector 7 via the capacitor C1. The envelope detector 7 is constituted by, for example, a voltage doubler circuit, receives a carrier signal and a subcarrier signal as a reception signal, extracts an envelope of the reception signal, and outputs an analog signal corresponding to the envelope. .

  The high-frequency components (signals corresponding to the rising and falling edges of the envelope) of the analog signal corresponding to the envelope output from the envelope detector 7 are input to the converter 8 through the capacitor C2. A signal si corresponding to the rise and fall of the envelope and the reference voltage Vref generated by the voltage level setting unit 10 are input to a pair of input terminals of the converter 8. That is, the voltage level setting unit 10 changes and sets the level of the reference voltage Vref, and outputs the set reference voltage Vref to the converter 8. From the output terminal of the converter 8, when the analog signal is equal to or higher than the reference voltage Vref, a voltage signal so corresponding to the rise and fall of the envelope is output. The voltage signal so is set to be higher than the threshold voltage Vth of the transistor (an example of a switching element in the claims) 11 when the reader / writer 1 operates normally.

  The A / D conversion circuit 9 is, for example, a common emitter circuit including a transistor 11 and a resistor 12. The voltage signal so from the converter 8 is input to the base of the transistor 11. The transistor 11 is turned off when the level of the voltage signal so is lower than the threshold voltage Vth, and turned on when the level of the voltage signal so is higher than the threshold voltage Vth. Thus, the A / D conversion circuit 9 outputs a digital signal Dg corresponding to the envelope.

  Here, in the reader / writer 1, at the start of data communication between the reader / writer 1 and the tag TG, the carrier control unit 5 switches the amplifier 4 from amplification-off to amplification-on, and transmits an unmodulated carrier signal from the amplifier 4. Output. This unmodulated carrier signal is transmitted from the antenna 6. The carrier signal (radio wave) is received by the antenna of the tag TG, the tag TG is precharged by the power of the carrier signal, and the tag TG becomes operable.

  After that, in the reader / writer 1, the carrier control unit 5 controls the amplification on / off of the amplifier 4 according to the data input from the outside, and modulates the carrier signal output from the amplifier 4. This modulated carrier signal is transmitted from the antenna 6. In the tag TG, the carrier signal (radio wave) is received by an antenna and demodulated, and a digital signal indicating data is generated.

  In the reader / writer 1, during the period of receiving data from the tag TG, the carrier control unit 5 causes the amplifier 4 to output an unmodulated carrier signal, and the unmodulated carrier signal is transmitted from the antenna 6. In the tag TG, a sub-carrier signal modulated according to data to be transmitted to the reader / writer 1 is generated by reflection of a carrier signal (radio wave) by an antenna on the tag TG side, load control of the antenna, and the like. This subcarrier signal is transmitted to the reader / writer 1.

  In the reader / writer 1, the unmodulated carrier signal output from the amplifier 4 and the subcarrier signal modulated by the tag TG and received by the antenna 6 are input to the envelope detector 7 via the capacitor C1. The envelope detector 7 receives the carrier signal and the subcarrier signal as a received signal, extracts an envelope of the received signal, and outputs an analog signal corresponding to the envelope. At this time, since the carrier signal output from the amplifier 4 is unmodulated and the subcarrier signal received by the antenna 6 is modulated, the envelope changes due to the level change of the subcarrier signal received by the antenna 6. It will correspond. Then, the high-frequency component of the analog signal corresponding to this envelope, that is, the signal si corresponding to the rise and fall of the envelope of the subcarrier signal is applied to the converter 8 through the capacitor C2. Further, a voltage signal so corresponding to the rise and fall of the envelope is applied from the converter 8 to the A / D conversion circuit 9, and the data from the tag TG is output from the A / D conversion circuit 9. The digital signal Dg shown is output.

  In the reader / writer 1, for example, when noise occurs in the carrier output circuit 2, this noise is output together with the carrier signal. Then, this noise is superimposed on the received signal composed of the carrier signal and the sub-carrier signal and is added to the envelope detector 7, so that the output of the envelope detector 7 contains noise. At this time, the level of the subcarrier signal received by the antenna 6 is very small, and the level of the analog signal corresponding to the envelope output from the envelope detector 7 is also very small. Receive.

  Further, the level of noise generated in the carrier wave output circuit 2 greatly varies depending on whether or not a noise source such as a power supply circuit or a motor that generates electromagnetic noise exists around the reader / writer 1.

  When an error occurs in the digital signal Dg output from the A / D conversion circuit 9 due to the influence of the noise, a data error occurs, and the retry processing of data transmission / reception is repeated.

  Therefore, in the reader / writer 1 of the present embodiment, the reference voltage Vref applied to one input terminal of the converter 8 can be appropriately changed and set by the voltage level setting unit 10. By appropriately changing and setting the reference voltage Vref by the voltage level setting unit 10, it becomes possible to select and use the value of the reference voltage Vref which can appropriately suppress the influence of various noises. Once the reference voltage Vref is set, the voltage level setting unit 10 outputs the same reference voltage Vref to the converter 8 until another reference voltage Vref is set.

  In the above embodiment, when the level of the voltage signal so outputted from the converter 8 is lower than the threshold voltage Vth, the transistor 11 is turned off by the A / D conversion circuit 9, and the level of the voltage signal so becomes lower than the threshold voltage Vth. At this time, the transistor 11 is turned on, so that the reference signal Vref input to the converter 8 is appropriately changed, so that the voltage signal so output from the converter 8 becomes unstable. However, the A / D conversion circuit 9 outputs an accurate digital signal Dg corresponding to the envelope.

  Generally, as a reader / writer, a value of a reference voltage Vref to be compared with a received signal is low in order to input a received signal from a tag of a minute level to an operational amplifier and accurately convert the received signal into a digital signal. Value. However, in this case, the operational amplifier is susceptible to noise. On the other hand, when the value of the reference voltage Vref is set to a relatively high value, the influence of noise is reduced, but it becomes difficult to cope with the received signal at a minute level, so that the communicable distance between the reader / writer and the tag increases. Be shorter.

  On the other hand, according to the above embodiment, the converter 8 and the A / D conversion circuit 9 always balance the reduction of the influence of noise and the length of the communicable distance with the tag TG in a well-balanced manner. Can accurately convert the received subcarrier signal into a digital signal and output it.

  FIG. 2 is a graph conceptually showing the relationship between the reference voltage Vref, the noise resistance, and the communicable distance. As is clear from the graph of FIG. 2, as the reference voltage Vref increases, the communicable distance decreases, and the noise resistance improves. Conversely, as the reference voltage Vref decreases, the communicable distance increases, and the noise resistance decreases.

In the present embodiment, for example, the voltage level setting unit 10 raises and lowers the reference voltage Vref according to an external input such as a CPU, and adjusts the communicable distance and the noise resistance in a well-balanced manner. In this case, since the reference voltage Vref can be increased or decreased at any time, when the noise source is activated and the noise level increases, the voltage level setting unit 10 sets the reference voltage in accordance with an external input such as a CPU. The voltage Vref is increased to increase the noise resistance. Further, when the noise source stops and the noise bell becomes low, the voltage level setting unit 10 lowers the reference voltage Vref in accordance with an input from the outside such as a CPU, so as to extend the communicable distance.

  Further, as the voltage level setting unit 10, a unit in which the reference voltage Vref is adjusted by operating an unillustrated operation unit can be applied. In this case, when the reader / writer 1 is arranged near the noise source, the reference voltage Vref of the voltage level setting unit 10 is adjusted to be high to increase the noise resistance, and the reader / writer 1 is separated from the noise source. When they are arranged in a position, the reference voltage Vref of the voltage level setting unit 10 can be adjusted to be low to extend the communicable distance.

  On the other hand, conventionally, since the reference voltage Vref applied to one input terminal of the converter 8 is fixed, even if the communicable distance is sufficient, the noise resistance is insufficient or the noise resistance is low. In some cases, the communication distance may be insufficient even if the communication performance is sufficient.

  According to the reader / writer 1 according to the present embodiment, the reference voltage Vref that can lead to a cross point in which the reduction of the influence of noise and the length of the communicable distance are well-balanced is set according to the noise environment. Is possible.

  Note that the configuration and processing described with reference to FIGS. 1 and 2 are merely embodiments of the present invention, and are not intended to limit the present invention to the configuration and processing.

REFERENCE SIGNS LIST 1 reader / writer 2 carrier output circuit 3 carrier generation unit 4 amplifier 5 carrier control unit 6 antenna 7 envelope detection unit 8 converter 9 A / D conversion circuit 10 voltage level setting unit 11 transistor 12 resistor TG tag

Claims (3)

A carrier generation unit that generates a carrier signal; an amplifier that amplifies and outputs the carrier signal from the carrier generation unit; and a carrier control that controls amplification on / off of the amplifier and modulates a carrier signal output from the amplifier. And a carrier output circuit that outputs the carrier signal,
An antenna connected to the output side of the amplifier, for transmitting a carrier signal output from the amplifier to a tag, and receiving a subcarrier signal from the tag,
A first capacitor to which a carrier signal output from the amplifier and a subcarrier signal received by the antenna are input ;
The first capacitor is connected in series with the first capacitor on the side opposite to the amplifier, and the carrier signal output from the amplifier and the subcarrier signal received by the antenna are transmitted through the first capacitor. A detection unit that is input as a reception signal and outputs an analog signal corresponding to an envelope of the reception signal;
A second capacitor connected to the output side of the detection unit and different from the first capacitor;
A digital signal output unit that compares a reference voltage and an analog signal input from the detection unit via a second capacitor, and outputs a digital signal when the analog signal is equal to or higher than the reference voltage;
A voltage level setting unit that changes and sets the level of the reference voltage, and outputs the set reference voltage to the digital signal output unit.
The digital signal output unit includes:
The analog signal output from the detection unit is input to the one input terminal of the pair of input terminals through the second capacitor, and the voltage level setting is performed to the other input terminal of the pair of input terminals. A converter that receives the reference voltage output from the unit and outputs a voltage signal when the analog signal is equal to or higher than the reference voltage;
A switching element that receives the voltage signal from the converter and outputs a digital signal when the voltage signal is equal to or greater than a threshold,
The carrier control unit, at the start of data communication between the tags, switches the amplifier from amplification off to amplification on, to output a non-modulated carrier signal from the amplifier,
The carrier control unit outputs a non-modulated carrier signal from the amplifier during a period of receiving data from the tag, so that a non-modulated carrier signal output from the amplifier and a sub-carrier received by the antenna are output. A reader / writer, wherein a carrier signal is input to the detection unit via the first capacitor.   The reader / writer according to claim 1, wherein the voltage level setting unit changes and sets the level of the reference voltage according to an external instruction.   The reader / writer according to claim 1, wherein the voltage level setting unit changes and sets the level of the reference voltage according to a manual operation.