JP2008199536A - Communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication apparatus or the like which solves the problem that a null point that is generated at a certain position, so as to solve the problem that the null point is generated at the other position different from the above position. <P>SOLUTION: A control unit 12 inputs a receiving signal by detecting an antenna voltage Va and detecting and amplifying the received data by a detection and amplification unit 15, and varies a DC voltage Vd as needed, based on a signal voltage δV, the antenna voltage Va and a preset threshold value. The DC voltage Vd is input to a variable capacitor C1 and by varying the DC voltage Vd, impedance is varied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a communication device or the like in a data carrier system that transmits and receives signals to and from a non-contact information recording medium.

  Currently, the introduction of data carrier systems including communication devices capable of non-contact communication with an information recording medium with a built-in IC (non-contact) is becoming popular. As such a non-contact information recording medium, for example, an “IC card” (non-contact type IC card) with a built-in IC in a card, a “IC tag” with a built-in IC, and a wristwatch type “IC with built-in IC”. "Wristband" etc. are known. As a system using these non-contact information recording media, for example, a traffic gate entrance / exit system using an “IC card”, an entrance / exit management system, a logistics management system for managing articles by attaching “IC tags” to articles, An entry / exit management system using an “IC wristband” is known.

The operation when the communication device reads arbitrary information from the non-contact information recording medium will be described with reference to FIG.
FIG. 10 is an overall configuration diagram of the contactless data carrier system.

  In FIG. 10, the communication device includes a signal processing circuit 110, an antenna 130 (loop antenna), and a digital signal processing unit 140. The digital signal processing unit 140 is connected to a host device (computer 150).

The signal processing circuit 110 includes a carrier signal generator 111, an amplifier 112, an impedance adjustment circuit 113, and a demodulation circuit 120.
The demodulation circuit 120 includes a detection circuit 121, an amplification circuit 122, and a binarization unit 123.

  In the signal processing circuit 110, the carrier signal generator 111 generates a carrier signal having a predetermined frequency (for example, a frequency of 13.56 MHz), the amplifier 112 amplifies the carrier signal to a predetermined voltage level, and then the impedance adjustment circuit 113. To be emitted as a magnetic field from the antenna 130 via. The non-contact information recording medium 160 includes a loop antenna 161 that detects this magnetic field and a data processing IC 162. The frequency determined by the loop antenna 161 and the illustrated capacitor in the data processing IC 162 is the predetermined frequency. It is set in advance. Arbitrary data (such as electronic money) is stored in a memory (not shown) in the data processing IC 162.

  Here, when the non-contact information recording medium 160 is sufficiently within a range that causes electromagnetic induction, electric power is supplied to the non-contact information recording medium 160. At this time, when the data processing IC 162 reads the stored data and controls ON / OFF of the illustrated switch 162a according to this data, the carrier level changes (amplitude modulation). The amplitude-modulated signal is detected by the detection circuit 121 of the signal processing circuit 110, and the detection signal is amplified by the amplification circuit 122 having a predetermined amplification degree, and then converted into digital data by the binarization unit 123. Data on the non-contact information recording medium 160 is read and passed to the digital signal processing unit 140.

  Further, the antenna 130 in the communication apparatus is configured by a primary loop and a secondary loop as shown in FIG. 11 in order to extend the communicable distance. In the example shown in FIG. 11, the primary coil is connected to the signal processing circuit 110, and a capacitor is connected to the secondary coil.

  By the way, in the conventional communication apparatus, in the signal processing circuit 110 that has received the amplitude-modulated signal, the demodulation circuit 120 may not be demodulated normally. For example, the data read from the non-contact information recording medium 160 is the data shown in FIG. 12A, and when the switch 162a is controlled to be turned on / off according to this data, if normal, the data shown in FIG. An amplitude-modulated carrier wave as shown will appear at the loop antenna 130 of the communication device.

  In the example shown in FIG. 12B, there is a potential difference between the received signal voltage Vdn when the data is “1” and the received signal voltage Vup when the data is “0” (Vup−Vdn = 0). Therefore, it can be demodulated normally as shown in FIG. Of course, in order to enable normal demodulation in this way, the resonance frequency of the non-contact information recording medium 160 is set near the carrier frequency (here, 13.56 MHz, for example). However, the resonance frequency also varies due to product variations. Further, as described in Patent Document 1, for example, the resonance frequency may be set to a value different from the carrier frequency, such as 15 to 17 MHz, in order to enable identification of a plurality of sheets.

  Here, the antenna 161 of the non-contact information recording medium 160 and the antenna 130 of the communication apparatus are arranged so that the loop surfaces face each other as shown in FIG. 13, and the resonance frequency fc of the non-contact information recording medium 160 is used as a parameter. FIG. 14 shows the results of experiments on the relationship between the distance L and δV (= Vup−Vdn) while changing the distance L.

  14A shows a case where a communication device is set for the non-contact information recording medium 160 having a resonance frequency fc = 17 MHz, and FIG. 14B shows a communication for the non-contact information recording medium 160 having a resonance frequency fc = 13.5 MHz. The experimental result when the apparatus is set is shown.

  As shown in FIG. 14A, for a recording medium with fc = 17 MHz, δV> 0 is always established, and communication is possible at any distance. However, for a recording medium of fc = 13.5 MHz, δV = 0 (null point) at the distance L1 shown in the figure, and communication is impossible at this distance L1.

  Similarly, in FIG. 14B, δV <0 is always established and communication is possible with respect to a recording medium with fc = 13.5 MHz. However, for the recording medium of fc = 17 MHz, the “null point” occurs at the distance L2 shown in the figure.

  As described above, in the communication apparatus set corresponding to the recording medium 160 having a certain resonance frequency, a “null point” is generated for the recording medium 160 having a resonance frequency different from the resonance frequency. Problems arise.

  Therefore, in a system that can handle a plurality of types of recording media 160 (such as a plurality of types of IC cards), communication is possible without generating a “null point” corresponding to a plurality of types of recording media 160 having different resonance frequencies. Communication device is desired.

Here, the reason why the “null point” is generated is described in, for example, Patent Document 2 as follows.
First, the modulation signal f (t) from the IC card by amplitude modulation is approximated by the following equation (1).

  In the right side of the above equation (1), the first term is the carrier wave, the second term is the upper sideband of the modulated signal, and the third term is the lower sideband of the modulated signal. Also, Ac is the amplitude of the carrier wave, Ab is Ac × k (k: a predetermined coefficient relating to amplitude modulation), ωc is the angular frequency of the carrier wave, ωb is the angular frequency of the modulation data, and φ1 and φ2 are the modulation data The initial phases of the upper sideband and the lower sideband are shown.

  Here, when the initial phases φ1 and φ2 of the upper sideband and lower sideband of the modulated data satisfy certain conditions, a situation occurs where δV≈0 (null point generation). The certain conditions are φ1 = π and φ2 = 0, φ1 = 0 and φ2 = π, and the like.

In order to solve the null point generation problem, the invention of Patent Document 2 proposes a method of correcting the frequency characteristics of a signal. The state of this correction is shown in FIGS.
First, FIG. 15A shows the frequency characteristics of the received signal at the null point. As shown in the figure, there are an upper sideband wave and a lower sideband wave, which are data components, in the frequency regions above / below the carrier frequency, and the amplitudes of both are substantially equal. In the invention of Patent Document 2, for example, as shown in FIG. 15B, the null point problem is solved by increasing the amplitude of the upper sideband and decreasing the amplitude of the lower sideband.

  However, a problem arises because the same correction is performed at a distance other than the distance at which the null point occurs (L1 or L2). For example, when correction similar to the above (the amplitude of the upper sideband is increased and the amplitude of the lower sideband is reduced) is performed on the reception signal having the frequency characteristics shown in FIG. As shown in (d), there is a possibility that the frequency characteristic is substantially the same as that before the correction at the null point. That is, in the method of Patent Document 2, if the above correction is performed to eliminate a null point generated at a certain position, a null point may be generated at another position different from this position.

  Similarly, when performing communication with a recording medium having a different resonance frequency as described above, even if the null point of the storage medium having a certain resonance frequency is eliminated, a null point is generated in the recording medium having another resonance frequency. There is a problem that there is a possibility.

  As another conventional technique corresponding to the above-mentioned null point generation problem, for example, the technique of Patent Document 3 is known. The invention of Patent Document 3 relates to an IC card reader of a type in which a user inserts a non-contact type IC card into a slot of a case and communicates with the IC card, and after the IC card is inserted, a command is transmitted and a response is received. If not, the impedance is switched. Although the present invention is effective for the type in which an IC card is inserted, the current method of using a non-contact type IC card is mainly to put the IC card on a reader / writer. In such a case, since the presence of the IC card itself cannot be detected, the invention of Patent Document 3 cannot cope with it.

Also, as a method for performing communication normally, a method for controlling carrier power according to the magnitude of a received signal, which is described in Patent Document 4, is known, but this does not solve the null point problem. Absent.
JP 2002-222400 A JP 2001-103101 A JP 2003-36418 A Japanese Patent Laid-Open No. 2002-170082

An object of the present invention is to solve the problem of null point generation in a communication device in a system that can use a plurality of types of non-contact information recording media having different resonance frequencies. It is to provide a communication device or the like that can solve the problem that a null point is generated at another position different from this position by eliminating it.

  A first communication device according to the present invention is a communication device that performs non-contact communication with a plurality of types of information recording media having different resonance frequencies, wherein an antenna and a transmission signal corresponding to any one of the resonance frequencies are transmitted to the antenna. Transmission means for outputting from the output, variable impedance means for adjusting the impedance of the transmission means, detection means for detecting a modulation signal by the information recording medium for the transmission signal, and an absolute value of the output signal voltage of the detection means Control means for controlling the variable impedance means to change the impedance when the value becomes equal to or less than a predetermined first threshold value.

  For example, when the absolute value of the output signal voltage of the detection unit is equal to or less than the predetermined first threshold value, the control unit sets the impedance adjustment unit so that the absolute value becomes larger than the first threshold value. Control.

  In the first communication apparatus, the impedance is adjusted so that the absolute value of the detection output signal voltage of the modulation signal by the information recording medium does not become less than a predetermined first threshold, that is, does not approach ‘0’.

For example, the variable impedance means is a variable capacitor whose capacitance changes according to the voltage value of the input control voltage, and the control means outputs the control voltage.
For example, when the absolute value of the output signal voltage of the detection unit is equal to or less than the predetermined first threshold value, the control unit determines the voltage value of the control voltage if the output signal voltage is a positive value. If the output signal voltage is a negative value, the voltage value of the control voltage is reduced.

  A second communication device according to the present invention is a communication device that performs non-contact communication with a plurality of types of information recording media having different resonance frequencies, wherein the transmission signal is transmitted with respect to a modulation signal by the information recording medium with respect to a transmission signal. Are obtained by multiplying two signals having different phases from each other and synthesizing the results of the multiplication, and combining and demodulating the modulated signal, and output of the combining and demodulating means It has detection / amplification means for inputting and detecting / amplifying.

  The synthesizing / demodulating means, for example, inputs the transmission signal and changes its phase or outputs it as it is, and inputs the output of the first phaser and changes the 90 ° phase. The first and second phase shifters output the two signals having different phases from each other.

  According to the communication device or the like of the present invention, in a system that can use a plurality of types of non-contact information recording media having different resonance frequencies, the null point problem in the communication device can be solved. By eliminating the null point, it is possible to solve the problem that the null point is generated at another position different from this position.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a configuration diagram of a communication apparatus according to the present embodiment. This configuration is the configuration of the first embodiment.

The illustrated communication apparatus 10 includes a signal processing unit 11, a control unit 12, a (carrier wave) amplification unit 13, a variable capacitor C 1, a binarization unit 14, a reception signal detection / amplification unit 15, and an antenna unit 20.
Have Note that, in the configuration of the communication device 10, the entire configuration other than the signal processing unit 11 and the antenna unit 20 is a signal processing circuit.

  The antenna unit 20 includes a primary loop antenna 21 and a secondary loop antenna 22, and a variable capacitor C <b> 2 is connected to the secondary loop antenna 22. The primary loop antenna 21 and the secondary loop antenna 22 are magnetically coupled. Although not shown in particular, the variable capacitor C1 is connected to the primary loop antenna 21. The detection / amplification unit 15 is connected to the output side of the amplification unit 13 and the like, similar to the demodulation circuit 120.

  The signal processing unit 11 is a processor that performs output processing of a carrier wave having a predetermined frequency and data processing of reception data output from the binarization unit 14. The carrier signal is amplified to a predetermined voltage level by the amplifying unit 13 and then wirelessly output from the antenna unit 20 via the variable capacitor C1. The variable capacitor C1 is an impedance adjustment capacitor provided between the amplifying unit 13 and the primary loop antenna 21, and the capacitance thereof is changed by changing the DC voltage Vd output from the illustrated control unit 12. Change (impedance changes).

  When the detection / amplification unit 15 receives a reply signal (modulation signal) to the carrier wave from the non-contact information recording medium 160 (IC card or the like) (not shown here) described heretofore, the antenna unit 20 receives this response signal. The received signal is detected and amplified, and output to the binarization unit 14 and the control unit 12. The binarization unit 14 binarizes this output signal and outputs it to the signal processing unit 11. The detection / amplification unit 15 + binarization unit 14 has a configuration corresponding to the conventional demodulation circuit 120, and the output of the detection / amplification unit 15 is, for example, FIG. It will be shown in

  The control unit 12 detects the voltage of the antenna unit 20 (antenna voltage Va). Further, the signal voltage δV (potential difference Vup−Vdn explained in the prior art) of the output signal from the detection / amplification unit 15 is detected. Based on the antenna voltage Va and the signal voltage δV, the DC voltage Vd is adjusted. An example of this adjustment process is shown in FIG. 3, and FIG. 2 shows how δV and the like change due to this adjustment process. Refer to FIG. 2 and FIG. A method will be described.

  First, FIGS. 2A to 2D show the relationship between the distance L between the antenna unit 20 and the recording medium 160 and δV, Va, Vd. The parameter is the resonance frequency of the recording medium 160, and here, there are two types, 13.5 MHz and 17 MHz. FIG. 2A shows the relationship between the distance L and the signal voltage δV when this control is not performed, and FIG. 2D shows the case where this control is performed. FIG. 2B shows the relationship between the distance L and the antenna voltage Va when this control is performed, and FIG. 2C shows the relationship between the distance L and the DC voltage Vd when this control is performed.

  First, as shown in FIG. 2A, generally, when the sharing frequency of the recording medium 160 is different (here, 13.5 MHz and 17 MHz), the value of the signal voltage δV corresponding to the distance L from the antenna unit 20 is Of course, it is different, and the polarity (positive / negative) may be different. Further, when a null point is generated as in the illustrated 13.5 MHz recording medium 160, the polarity (positive / negative) is different at the null point. In the example shown in FIG. 2A, for the 13.5 MHz recording medium 160, the distance L1 is a null point, a positive value in an area closer to the antenna unit 20 than the distance L1, and a distance farther than the distance L1. It is a negative value.

The “positive value” and the “negative value” mean the states shown in FIGS. 8C and 8E of Patent Document 2, for example. That is, FIG. 8C is a “positive value” and FIG. 8E is a “negative value”. That is, when the switch signal shown in FIG. 8A of Patent Document 2 is ON, both FIG. 8C and FIG. 8E are “0”, and when the switch signal is OFF, FIG. "Positive value"
FIG. 8E shows a “negative value”.

  Further, the position of the null point can be moved to a position closer to / away from L1 by adjusting the DC voltage Vd to change the capacitance of the variable capacitor C1 (change the impedance). As will be described later with reference to FIG. 4B, this utilizes the property that the entire signal voltage δV characteristic shown in FIG. 2A shifts in the horizontal direction in the figure in accordance with the impedance. Details will be described later.

  The antenna voltage Va is greatest when the recording medium 160 is not present, and monotonously decreases as the recording medium 160 approaches the antenna unit 20 as shown in FIG. Therefore, it is possible to set the antenna current Va corresponding to an arbitrary distance L.

  First, as an initial setting (for example, a setting at the time of factory shipment), a person in charge of setting or the like sets a carrier frequency so as to correspond to any one of the resonance frequencies of the plurality of types of recording media 160 in advance. . Here, it is assumed that two types of recording media 160 of 13.5 MHz and 17 MHz can be used, and a setting corresponding to 17 MHz is performed. In the recording medium 160 of fc = 17 MHz, as shown in FIG. 2A, the signal voltage δV is set to a positive value (δV> 0) at any distance (null). In this case, for example, the carrier frequency is set to around 17 MHz and the value of the DC voltage Vd is set to Vd1 shown in FIG. .

  In addition, after the setting corresponding to the 17 MHz is completed, the person in charge of setting confirms the change in the polarity of δV when the null point is generated using the recording medium 160 of fc = 13.5 MHz. In the example shown in FIG. 2A, when the recording medium 160 with fc = 13.5 MHz is gradually separated from the state in which the recording medium 160 is in close contact with the antenna unit 20, from the distance L1 (null point), δV> 0. It changes to δV <0.

  Thus, in this example, the person in charge of setting makes settings so that the control shown in FIG. 3 described later is performed. That is, it is possible to select and set whether the determination in step S4 in FIG. 3 is “δV> 0” or “δV <0” as shown in the figure. In the example shown in FIG. By selecting and setting “δV> 0”, the processing of FIG. 3 is performed.

  On the other hand, if the recording medium is a recording medium whose polarity change is opposite to that of the recording medium 160 of fc = 13.5 MHz (if the recording medium 160 is gradually separated from the state in which the recording medium 160 is in close contact with the antenna unit 20). In this case, “δV <0” is selected and set. In this case, the determination in step S4 of FIG. 3 is performed. Becomes “δV <0?”. In any case, when the absolute value of the signal voltage δV becomes equal to or lower than a threshold value described later, if the signal voltage δV is a positive value, the signal voltage δV increases in the positive direction, and if the signal voltage δV is a negative value. Control is performed so as to increase in the negative direction (that is, not to become zero). In other words, it can be said that the absolute value of the signal voltage δV is controlled to be larger than the threshold value when the absolute value of the signal voltage δV becomes equal to or less than the threshold value described later. Of course, this control is performed by adjusting the value of the DC voltage Vd.

The reason for performing the above setting will be described with reference to FIGS.
FIG. 4A is a diagram showing the relationship between the DC voltage Vd and the capacitance of the variable capacitor C1.
As shown in the figure, the variable capacitor C1 has a capacitor capacity that decreases (inversely proportional) as the applied voltage value increases.

FIG. 4B shows the relationship between the capacitor capacity and the signal voltage δV. This shows the distance-signal voltage δV characteristic using the capacitor capacity (large, medium, small) as a parameter.

  As shown in the figure, the entire distance-signal voltage δV characteristic shifts in the left-right direction in the figure according to the capacitor capacity. That is, the larger the capacitor capacity (the smaller the DC voltage Vd), the more the shift to the left in the figure. In other words, as the capacitor capacitance increases (the DC voltage Vd decreases), the null point approaches the distance 0.

  As a result, for example, when the recording medium 160 of fc = 13.5 MHz is gradually approached to the antenna unit 20 from a distance, and when the recording medium 160 approaches the null point (distance L1 in the initial state), direct current is applied as in step S7 described later. By reducing the voltage Vd, the null point moves (escapes) toward the distance 0. Similarly, when the recording medium 160 is gradually separated from the state in which the recording medium 160 is in close contact with the antenna unit 20, the null point is moved away from the antenna unit 20 by increasing the DC voltage Vd as in step S5 described later. It will follow. Thereby, the null point problem can be solved.

  In addition, as a method of using an IC card, for example, a method of touching the IC card from a distance by bringing it close to the communication device is common, as in the case of a ticket gate at a station, for example. There is also a usage method that instructs the communication device to start communication after placing it on the communication device, and there are cases where the IC card is separated from the communication device after the instruction, so this method can handle both usage methods as described above It becomes.

  Also, the person in charge of setting determines the distance L3 shown in the figure. This distance L3 only needs to satisfy the condition of L1 <L3, and may be arbitrarily determined. Then, the person in charge of setting refers to the distance-antenna voltage characteristic shown in FIG. 2B, confirms the antenna voltage Va3 corresponding to the distance L3, and registers this Va3. This is because, as will be described later, it is not necessary to perform control of the present method at a distance that is more than the distance L3. In this example, even when the recording medium 160 of fc = 13.5 MHz is used, a null point does not occur at a position away from the antenna unit 20 by a distance L3 or more (as shown in FIG. 2A). .

  Then, the person in charge of setting, for example, sets the minimum value of the signal voltage δV of the recording medium 160 of fc = 17 MHz within the range of the distance 0 to the distance L3 that is the control target range of this method (here, FIG. 2D). And an arbitrary positive value δV1 smaller than the voltage δV2 (small absolute value) is set as a threshold value.

The value of Vd1 is also set (in order to return to the initial state after changing the value of Vd).
Then, at the time of operation, the processing of FIG. 3 is performed using Va3, δV1, Vd1, etc. set in advance as described above.

  Naturally, an application program for causing the control unit 12 (CPU or the like) to execute the processing of the flowchart shown in FIG. 3 is stored in advance in, for example, the control unit 12 built-in memory or a memory (not shown).

  During operation, the control unit 12 inputs the output signal voltage δV from the detection / amplification unit 15 and detects the antenna voltage Va as described above, and performs the processing shown in FIG. By executing this, the value of the DC voltage Vd is adjusted and controlled.

Hereinafter, the process of FIG. 3 will be described.
In the process of FIG. 3, first, the DC voltage Vd is set to an initial state (Vd = Vd1) (step S1). If the antenna voltage Va ≧ Va3 (step S2, NO), that is, if the distance is more than the distance L3 as described above, the problem of the null point is fc = 13.5 MHz or 17 MHz. Since it does not occur, the DC voltage Vd remains in the initial state. Also, when | δV | ≧ δV1 (step S3, NO), the problem of the null point does not occur, so the DC voltage Vd remains in the initial state.

  Here, as described above, since | δV2 |> δV1, when the recording medium 160 with fc = 17 MHz is used, the determination in step S3 is always NO. Therefore, when the recording medium 160 of fc = 17 MHz is used, the DC voltage Vd always remains in the initial state, so that this adjustment does not adversely affect (a new null point is generated. Does not arise.

  Accordingly, the determination in step S3 is YES only when the recording medium 160 of fc = 13.5 MHz is used. Hereinafter, the recording medium 160 of fc = 13.5 MHz is used as shown in FIG. Processing contents will be described.

  If the determinations in steps S2 and S3 are YES, that is, the distance between the recording medium 160 of fc = 13.5 MHz and the antenna unit 20 is less than L3, and the absolute value of the signal voltage δV is a predetermined threshold value (δV1). If it is less than this, depending on whether this δV is positive or negative (determination in step S4), one of steps SS5 and S6 or steps S7 and S8 is executed (however, However, there is no change in the control so that the absolute value of δV is equal to or larger than δV1 (so as not to approach “0”).

  If δV is a positive value (δV> 0) (step S4, YES), this δV is controlled to be greater than δV1 (in other words, the absolute value of δV is greater than δV1). To control). That is, the value of Vd is increased little by little (by a value α set in advance in advance) until δV> + δV1 (step S6, YES) (the process of step S5 (Vd = Vd + α) is repeated). In this case, the characteristic shown in FIG. 4B is shifted to the right side in the figure. This means that the null point moves to the right side in the figure as described above. In this case, when the recording medium 160 reaches the distance L3, the process of step S1 is performed, so that the position of the null point returns to L1.

  When δV is a negative value (δV <0) (step S4, NO), the δV is controlled so as to be smaller than −δV1 (in other words, the absolute value of δV is the δV1). Control to be larger). That is, the value of Vd is decreased little by little (by a value α set in advance in advance) until δV <−δV1 (step S8, YES) (the process of step S7 (Vd = Vd−α)). Repeat). In this case, the characteristic shown in FIG. 4B (the null point is as described above) shifts to the left in the figure.

  When the recording medium 160 of fc = 13.5 MHz is brought closer to the antenna unit 20, the processes of steps S7 and S8 are performed. On the other hand, when the recording medium 160 of fc = 13.5 MHz is moved away from the state in which the recording medium 160 is in close contact with the antenna unit 20, the processes of steps S5 and S6 are performed.

Then, the process returns to step S2.
By performing the above-described control, it is possible to prevent a null point problem in the communication apparatus from occurring in a system that can handle a plurality of types of recording media having different resonance frequencies. In particular, by eliminating a null point that occurs at a certain position, it is possible to solve the problem that a null point occurs at a position other than this position (the “position” in the description is “recording medium”) The same applies to the case).

  Although the variable capacitor C1 is controlled in the process shown in FIG. 3, the control using the DC voltage Vd is performed on the variable capacitor C2 connected to the secondary loop antenna 22 as shown in FIG. Similarly, the null point generation problem can be solved.

  The configuration of the communication device may be the configuration shown in FIG. In the configuration of the communication device 30 in FIG. 5, the control unit 31 detects not the antenna voltage Va but the antenna current Ia, and uses the antenna current Ia to perform the same processing (distance determination) as in step S2. 1 is different from the case of FIG.

Next, a second embodiment will be described below.
FIG. 6 is a configuration diagram of a communication apparatus according to the second embodiment.
A communication device 40 shown in FIG. 6 includes a digital signal processing unit 41, an amplifier 42, a control unit 43, a detection circuit 44, a filter unit 45, an amplifier 46, a binarization unit 47, a synthesis demodulation unit 50, and an antenna unit 60. .

  The digital signal processing unit 41, the amplifier 42, and the binarization unit 47 may be the same as the signal processing unit 11, the amplification unit 13, and the binarization unit 14. The “detection circuit 44 + filter unit 45 + amplifier 46” has a configuration corresponding to the detection / amplification unit 15 (although not shown or described, the detection / amplification unit 15 also includes a filter unit). Or, in other words, “detection circuit 44 + filter unit 45” corresponds to the conventional detection circuit 121). In the conventional filter unit, a predetermined constant is set, thereby cutting the carrier frequency component and extracting only the modulation frequency component. However, as will be described later, the filter unit 45 of this example has a carrier frequency component. Since the frequency component is cut about twice, and the constant is different from the conventional one, only the filter unit 45 is shown here.

The feature of the second embodiment is mainly in the synthesis demodulator 50.
The synthesis demodulator 50 includes a phase shifter 51, a 90 ° phase shifter 52, a multiplier 53, a multiplier 54, and an adder 55.

  The phase shifter 51 receives the carrier wave (Accos (ωct)), changes the phase, and outputs it (outputs cos (ωct + δ)). For example, the control unit 43 sets the phase change amount δ. As will be described later, the output may be performed without changing the phase of the carrier wave (with phase change amount δ = 0).

The 90 ° phase shifter 52 receives the output of the phase shifter 51, changes the 90 ° phase, and outputs it (outputs sin (ωct + δ)).
The output of the phase shifter 51 is input to the multiplier 54, and the output of the 90 ° phase shifter 52 is input to the multiplier 53. Each of the multipliers 53 and 54 further receives a modulated signal f (t) from the recording medium 160 for the carrier wave. The approximate expression of f (t) is the expression (1) described in the prior art. The outputs of the multipliers 53 and 54 are added (synthesized) by the adder 55.

From the above, the multiplier 54 multiplies cos (ωct + δ) and f (t), and the multiplier 53 multiplies sin (ωct + δ) and f (t), which are combined by the adder 55. As a result, the output of the adder 55 (that is, the output of the synthesis demodulator 50) is
f (t) × [cos (ωct + δ) + sin (ωct + δ)]
This is output to the detection circuit 44. As a result, the above-mentioned conventional problems can be solved. That is, if control for eliminating a null point occurring at a certain position is performed, the problem that a null point occurs at another position different from this position can be solved. The reason will be described below.

  First, in the equation (1) described above, the initial phase φ1 = π and the initial phase φ2 = 0 (which is one of the conditions for generating a null point as described above), and the phase When the change amount δ = 0, the above equation (1) is expressed by the following equation (2).

  In this case, the output of the adder 55 is expressed by the following equation (3).

In addition, although the said (2) Formula and (3) Formula have an underline part, this is for using for the description mentioned later, and an underline is not related to Formula itself.
In the above equation (3), the first term is a signal component having a frequency twice the carrier frequency fc including the DC component Ac / 2, and the second term includes the DC component Ab / 2. , A signal component of the modulated data frequency fb amplitude-modulated at a frequency twice the carrier frequency fc.

  Here, as can be seen by comparing the second term of the above equation (2) and the second term of the equation (3) (especially, refer to the underlined portion), the amplitude variation of the modulation data frequency fb is greater in the equation (3). Is big. Therefore, even under the condition where the null point is generated, demodulation can be performed without the generation of the null point.

Further, it has been confirmed by experiments (simulations) that the above problem can be solved by the configuration of FIG.
7 to 9 show the results of the experiment (simulation).

This experiment (simulation) was performed under the following conditions.
Carrier frequency (= ωc / 2π): 13.56 MHz
・ Modulation data frequency (= ωb / 2π): 212 kHz
Carrier wave amplitude Ac: 1.0
-Upper and lower sideband amplitude Ab: 0.1
・ Initial phase of modulation data φ1, φ2: π, 0
-Phase change amount δ: 0
7A and 7B show the received waveform and the demodulated waveform at the position where the null point occurs, and FIGS. 9A and 9B show the position other than the position where the null point occurs. The received waveform and demodulated waveform are shown.

  First, as shown in FIG. 7A, the received wave of the modulated signal f (t) is δV≈0 and a null point is generated. The output (demodulation) of the composite demodulator 50 that receives this received wave is generated. As shown in FIG. 7B, the waveform is a waveform modulated at the modulation data frequency, and no null point is generated. By detecting and filtering this waveform, the data is demodulated without any problem. it can.

FIGS. 8A and 8B show enlarged waveforms of the waveforms shown in FIGS. 7A and 7B, respectively.
As shown in the figure, the demodulated waveform shown in FIG. 8B has a higher frequency than the received waveform shown in FIG. That is, according to the configuration of FIG. 6, the modulation data is superimposed on a frequency (about twice, etc.) higher than the carrier frequency. Thus, the frequency component to be cut by the filter unit 45 needs to be higher than the carrier frequency (about twice, etc.), and a constant according to this is set. Is a little different.

  Here, in general, if the filter has a steep attenuation characteristic, the circuit becomes complicated. With a simple configuration, the S / N is lowered, and the signal component itself is also attenuated. According to the configuration of FIG. 6, since the frequency to be filtered is far away from twice the carrier wave, there is also an advantage that the filter can be simplified without reducing the S / N.

  FIGS. 9A and 9B show received waveforms and demodulated waveforms under conditions in which a null point does not occur (for example, initial phase φ1 = π / 2, φ2 = −π / 2 of modulated data). However, even in this case as shown in the figure, the demodulated waveform is observed at a frequency modulated with the frequency of the modulated data, as in FIG. 7B, and can be demodulated without any problem.

  6 may be configured to be inserted between the antenna unit 20 and the detection / amplification unit 15 shown in FIG. 1 or FIG. Demodulation is possible.

  As described above, both of the first embodiment and the second embodiment can solve the null point problem without generating a new null point. Furthermore, in the second embodiment, it is not necessary to perform the control process as shown in FIG. 3 (the control unit 43 simply sets the phase change amount δ, for example).

It is a block diagram of the communication apparatus of this Embodiment. (A)-(d) is a figure for demonstrating an operation principle. It is a process flowchart figure by a control part. (A) Relationship between control voltage and capacitance, (b) is a diagram showing the relationship between capacitance and signal voltage. It is a block diagram of the communication apparatus of a modification. It is a block diagram of the communication apparatus of 2nd Example. (A) is a received waveform, (b) is a demodulated waveform. FIG. 8 is an enlarged view of FIG. 7. (A) is a received waveform, (b) is a demodulated waveform. It is a whole block diagram of a non-contact data carrier system. It is a structural example of an antenna. (A) to (c) are received waveforms and the like. It is a figure which shows the positional relationship of an antenna. (A), (b) is a figure which shows the relationship between a signal voltage and distance. (A)-(d) are the frequency characteristics of the received signal when the upper sideband is corrected.

Explanation of symbols

10 communication device 11 signal processing unit 12 control unit 13 (carrier wave) amplification unit 13
C1 variable capacitor 14 binarization unit 15 (received signal) detection / amplification unit 20 antenna unit 21 primary loop antenna 22 secondary loop antenna C2 variable capacitor 30 communication device 31 control unit 40 communication device 41 digital signal processing unit 42 amplifier 43 Control Unit 44 Detection Circuit 45 Filter 46 Amplifier 50 Synthesis Demodulation Unit 51 Phaser 52 90 ° Phaser 53 Multiplier 54 Multiplier 55 Adder 60 Antenna Unit

Claims (8)

A communication device that performs non-contact communication with a plurality of types of information recording media having different resonance frequencies,
An antenna,
Transmitting means for outputting a transmission signal corresponding to any one of the resonance frequencies from the antenna;
Variable impedance means for adjusting the impedance of the transmission means;
Detection means for detecting a modulation signal by the information recording medium for the transmission signal;
Control means for controlling the variable impedance means to change the impedance when the absolute value of the output signal voltage of the detection means is equal to or less than a predetermined first threshold;
A communication apparatus comprising:   The control means controls the impedance adjustment means so that the absolute value becomes larger than the first threshold when the absolute value of the output signal voltage of the detection means becomes equal to or less than the predetermined first threshold. The communication apparatus according to claim 1. The variable impedance means is a variable capacitor whose capacitance changes according to the voltage value of the input control voltage.
The communication apparatus according to claim 1, wherein the control unit outputs the control voltage.   The control means increases the voltage value of the control voltage if the output signal voltage is a positive value when the absolute value of the output signal voltage of the detection means is less than or equal to the predetermined first threshold, 4. The communication apparatus according to claim 3, wherein if the output signal voltage is a negative value, the voltage value of the control voltage is reduced. The antenna is composed of a primary loop and a secondary loop that are electromagnetically coupled,
The communication apparatus according to claim 1, wherein the variable impedance unit is connected between the primary loop and the transmission unit or to the secondary loop.   The control means further detects a voltage or current of the antenna, and does not perform the control when the voltage value or current value is equal to or greater than a predetermined second threshold value. Any one of the communication apparatuses. A communication device that performs non-contact communication with a plurality of types of information recording media having different resonance frequencies,
By multiplying a modulated signal by the information recording medium for the transmission signal with two signals obtained based on the transmission signal and having different phases from each other, and synthesizing the results of the multiplication, Synthetic demodulation means for demodulating the modulation signal;
Detection / amplification means for receiving and amplifying the output of the combining demodulation means;
A communication apparatus comprising:   The synthesizing / demodulating means inputs the transmission signal and changes its phase or outputs it as it is, and inputs the output of the first phaser and changes the phase by 90 ° and outputs it. 8. The communication apparatus according to claim 7, further comprising: a second phase shifter that outputs two signals having different phases from each other.