JP4880263B2 - Antenna circuit - Google Patents

Description

  The present invention relates to an antenna circuit suitable for use in a wearable information communication device such as a non-contact IC card.

  In recent years, contactless IC cards have been put into practical use as wearable information communication devices having functions such as electronic money and electronic tickets. FIG. 7 is a block diagram showing a configuration of a non-contact IC card system using an electromagnetic coupling method. In this figure, a reader / writer device 10 (reading device) uses a 13.56 MHz carrier (carrier wave) obtained by amplitude modulation (ASK modulation) of data and commands generated by the carrier generation unit E, a load resistor R1 and an impedance. Wireless transmission is performed via an antenna coil L1 to which a matching capacitor C1 is connected in parallel. That is, the reader / writer device 10 outputs a 13.56 MHz carrier wave that simultaneously performs power transmission and data transmission.

  A non-contact IC card 20 that exchanges data with the reader / writer device 10 by an electromagnetic coupling method includes an antenna circuit 100 and an IC chip 200. The antenna circuit 100 includes a resonance unit 101, a rectification unit 102, and a load modulation unit 103. The resonating unit 101 includes an antenna coil L2 and a tuning capacitor C2, and generates an induced voltage in synchronization with a carrier radio wave (magnetic field) from the reader / writer device 10. The rectifying unit 102 includes a rectifying element D and a smoothing capacitor C3, and rectifies the induced voltage generated by the resonance unit 101 and outputs a rectified voltage. The load modulation unit 103 includes a load modulation resistor R2 and a switching element Tr that are connected in parallel to the resonance unit 101. The load modulation unit 103 drives the switching element Tr on and off by an output of a modulation circuit, which will be described later, thereby reducing the load of the resonance unit 101. Then, the received carrier is remodulated (load modulation) and transmitted from the antenna coil L2 of the resonance unit 101.

  The IC chip 200 includes a power supply circuit 201, a demodulation circuit 202, a clock recovery circuit 203, a modulation circuit 204, a CPU 205, and a memory 206. In the power supply circuit 201, the rectified voltage generated by the rectifying unit 102 is converted into a constant drive voltage and supplied to each circuit in the chip. The demodulation circuit 202 performs demodulation detection and waveform shaping on the received carrier, and detects data and commands included in the carrier. The clock recovery circuit 203 extracts a transmission clock from the received carrier.

  The CPU 205 writes data to or reads data from a memory (for example, a nonvolatile memory such as an EEPROM) according to the demodulated data and commands. The modulation circuit 204 modulates the data read by the CPU 205 with a predetermined encoding method and outputs the data. The switching element Tr is driven on and off by the output of the modulation circuit 204, the carrier is load-modulated and transmitted to the reader / writer device side. Such a non-contact IC card system is disclosed in, for example, Patent Document 1 or Patent Document 2.

Japanese Patent Laid-Open No. 10-145987 JP-A-11-355186

  In the non-contact IC card system configured as described above, the mutual inductance between the antenna coil L1 on the reader / writer device 10 side and the antenna coil L2 on the non-contact IC card 20 side is determined by the degree of coupling between the antenna coils L1 and L2. It is known that the degree of coupling between the antenna coils L1 and L2 varies depending on the distance between the two coils, the coil size, and the like, and generally varies in the range of “0.05” to “0.5”. On the non-contact IC card 20 side, even if the degree of coupling between the antenna coils L1 and L2 changes, a large impedance change (load modulation degree) is required in order to make a stable response to the reader / writer device 10. However, in the conventional antenna circuit 100 described above, since only the impedance change due to the load modulation resistor R2 is obtained, a sufficient load modulation degree cannot be obtained, and the non-contact IC card 20 cannot respond to the reader / writer device 10. Can also happen.

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide an antenna circuit capable of obtaining a sufficient degree of load modulation.

In order to achieve the above object, according to the first aspect of the present invention, a second antenna that resonates with an external carrier signal provided with a first antenna coil and outputs a load modulation signal in response to the carrier signal. In an antenna circuit including a resonance part including a coil and a tuning capacitor, the antenna circuit includes a coil connected in parallel to the resonance part, a resistor and a switching element connected in series to the coil, and performs load modulation in response to the carrier signal. An impedance transition unit is provided that increases a resonance frequency of the resonance unit to increase an impedance change at a carrier signal frequency during load modulation when outputting a signal.

According to the second aspect of the present invention, the resonance is made up of the tuning antenna and the second antenna coil that resonates with an external carrier signal including the first antenna coil and outputs a load modulation signal in response to the carrier signal. An antenna circuit including a capacitor, a capacitor connected in parallel to the resonance unit, a resistor and a switching element connected in series to the capacitor, and an inverter that reverses the polarity of a drive signal for driving the switching element on and off, An impedance transition unit is provided that increases a resonance frequency of the resonance unit to increase an impedance change at the carrier signal frequency during load modulation when outputting a load modulation signal in response to the carrier signal .

According to the first aspect of the present invention, even if the coupling state between the first antenna coil and the second antenna coil becomes dense and the resonance frequency of the antenna circuit decreases, the combined inductance of the resonance unit during load modulation The resonance frequency rises due to the decrease in the components, and a sufficient load modulation degree can be obtained by increasing the impedance change at the carrier signal frequency (carrier frequency) .

According to the second aspect of the present invention, when the switching element is set to the on state, the resonance frequency of the antenna circuit is lowered due to an increase in the combined capacitance component of the resonance unit, but the inverter reverses the modulation polarity. The resonance frequency of the antenna circuit at the time of load modulation (switching element Tr is off) is relatively increased. Therefore, even if the coupling state between the first antenna coil and the second antenna coil becomes dense and the resonance frequency of the antenna circuit decreases, the resonance frequency increases during load modulation (the switching element Tr is in an off state) A sufficient load modulation degree can be obtained by increasing the impedance change in the carrier signal frequency (carrier frequency) .

In the following, the principle of the present invention will be described first, and then embodiments of the present invention will be described with reference to the drawings.
(1) Principle of the Invention As described above, in the antenna circuit 100 of the non-contact IC card 20, even if the degree of coupling between the antenna coil L1 and the antenna coil L2 on the reader / writer device 10 changes, the reader / writer device. The impedance change (load modulation degree) is required to be as large as possible in order to provide a stable response. However, when the degree of coupling between the antenna coils L1 and L2 changes, the resonance characteristics change accordingly, so that a sufficient load modulation degree cannot be obtained only by the impedance change by the load modulation resistor R2. Specifically, when the degree of coupling between the antenna coils L1 and L2 is high (the coupling state is dense), the resonance frequency of the antenna circuit 100 is lowered, thereby reducing the impedance change at the carrier frequency. Therefore, in the present invention, control is performed so as to obtain a sufficient degree of load modulation by changing the resonance frequency of the antenna circuit 100 during load modulation to generate a large impedance transition.

(2) First Embodiment Next, a first embodiment will be described with reference to FIGS. FIG. 1 is a block diagram showing a configuration of an antenna circuit 100 according to the first embodiment. In this figure, circuit elements common to the conventional example shown in FIG. 7 are denoted by the same reference numerals, and description thereof is omitted. The antenna circuit 100 shown in FIG. 1 is different from the conventional example shown in FIG. 7 in that the load modulation unit 104 has a tap Tp at a position close to the ground side of the antenna coil L2 of the resonance unit 101, and the tap Tp. The load modulation resistor R2 and the switching element Tr are connected in series. According to such a configuration, since the inductance component of the antenna coil L2 decreases during load modulation, the resonance frequency of the antenna circuit 100 during load modulation is controlled to be set high.

  An experimental result using such an antenna circuit 100 is shown in FIG. 2 shows the potential V1 generated on the reader / writer device 10 side when the antenna circuit 100 having the configuration shown in FIG. 1 is subjected to load modulation, and the degree of coupling between antennas (k = 0.1, 0.2, 0.5). It represents the result of measurement separately. In this experiment, instead of causing the carrier generator E on the reader / writer device 10 side to output a carrier of 13.56 MHz with an amplitude of ± 15 V, the switching element Tr of the antenna circuit 100 is actually driven on and off, The potential V1 on the reader / writer device 10 side when the load modulation resistor R2 is set to 10Ω corresponding to the ON state of the switching element Tr and the load modulation resistor R2 is set to 1 MΩ corresponding to the OFF state of the switching element Tr is set. Measuring. The degree of load modulation corresponding to the ON setting of the switching element Tr is also shown in parentheses.

  As is clear from the experimental results shown in FIG. 2, the degree of load modulation increases as the degree of coupling between antennas increases. That is, even if the degree of coupling between the antenna coils L1 and L2 is high (the coupling state is dense) and the resonance frequency of the antenna circuit 100 is lowered, the resonance frequency is forcibly increased so as to compensate for the load modulation. Increase impedance change at frequency (13.56 MHz). As a result, it is possible to avoid the disadvantage that the contactless IC card cannot respond to the reader / writer device without obtaining a sufficient degree of load modulation. Further, since the load modulation resistor R2 and the switching element Tr are connected in series to the tap Tp provided at a position close to the ground side of the antenna coil L2, there is also an advantage that it can be realized extremely easily without increasing circuit elements. . In this embodiment, the load modulation resistor R2 is provided. However, this is not essential, and the switching element Tr may be directly connected to the tap Tp provided at a position close to the ground side of the antenna coil L2. I do not care.

(2) Second Embodiment Next, a second embodiment will be described with reference to FIGS. FIG. 3 is a circuit diagram showing a configuration of the antenna circuit 100 according to the second embodiment. The antenna circuit 100 shown in this figure is different from the conventional example shown in FIG. 7 in that a load modulation unit 105 includes a coil L3 connected in parallel to a resonance unit 101 including an antenna coil L2 and a tuning capacitor C2, and this coil. The load modulation resistor R2 and the switching element Tr are connected in series to L3. According to this configuration, since the combined inductance component of the resonance unit 101 decreases during load modulation, the resonance frequency of the antenna circuit 100 during load modulation is controlled to be set high.

  Also in the second embodiment, as is clear from the experimental results shown in FIG. 4, even when the coupling degree between the antenna coils L1 and L2 is high (the coupling state is dense) and the resonance frequency of the antenna circuit 100 is lowered. In order to compensate for the load modulation, the resonance frequency is forcibly increased, and the impedance change at the carrier frequency (13.56 MHz) is increased, so that a sufficient degree of load modulation cannot be obtained and the non-contact IC card is read / writer It is possible to avoid the adverse effect of being unable to respond to the device. In the present embodiment, the load modulation resistor R2 is provided, but this is not essential, and the switching element Tr may be directly connected to one end on the ground side of the antenna coil L3.

(3) Third Embodiment Next, a third embodiment will be described with reference to FIGS. FIG. 5 is a circuit diagram showing a configuration of the antenna circuit 100 according to the third embodiment. The point where the antenna circuit 100 shown in this figure differs from the conventional example shown in FIG. 7, the load modulation section 106, a capacitor C 4 connected in parallel to the resonance part 101 consisting of the antenna coil L2 and the tuning capacitor C2, this A load modulation resistor R2 and a switching element Tr are connected in series to the capacitor C4 , and an inverter for inverting the polarity of a drive signal for driving the switching element on and off is provided.

  In the above configuration, when the switching element Tr is set to the on state, the resonance frequency of the antenna circuit 100 is lowered due to an increase in the combined capacitance component of the resonance unit 101. However, since the modulation polarity is inverted by the inverter INV, In addition, the resonance frequency of the antenna circuit 100 during load modulation (the switching element Tr is in an off state) is controlled to be set high. Therefore, as is apparent from the experimental results shown in FIG. 6, even when the coupling degree between the antenna coils L1 and L2 is high (the coupling state is dense) and the resonance frequency of the antenna circuit 100 is lowered, the load modulation (switching) The resonance frequency rises when the element Tr is in the off state), and the impedance change at the carrier frequency (13.56 MHz) can be greatly increased. As a result, it is possible to avoid the disadvantage that the contactless IC card cannot respond to the reader / writer device without obtaining a sufficient degree of load modulation.

As described above, in the present invention, even if the degree of coupling between the antenna coils L1 and L2 increases and the impedance change at the carrier frequency decreases, the resonance frequency of the antenna circuit 100 is increased during load modulation. The modulation degree can be obtained. Therefore, the conventional adverse effect that the contactless IC card cannot respond to the reader / writer device without obtaining a sufficient load modulation degree can be prevented.
In each of the above-described embodiments, the antenna circuit 100 of the non-contact IC card has been described. However, the gist of the present invention is not limited to this, and the reader / writer device 10 may be an electromagnetic coupling method such as an RFID (wireless tag). Needless to say, this is applicable to all data carriers that exchange data.

It is a circuit diagram which shows the structure of 1st Embodiment. It is a figure which shows the experimental result of 1st Embodiment. It is a circuit diagram which shows the structure of 2nd Embodiment. It is a figure which shows the experimental result of 2nd Embodiment. It is a circuit diagram which shows the structure of 3rd Embodiment. It is a figure which shows the experimental result of 3rd Embodiment. It is a block diagram which shows the structure of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Reader / writer apparatus 20 Non-contact IC card 100 Antenna circuit 101 Resonance part 104,105,106 Load modulation part (control part)
200 IC chip L1 antenna coil (first antenna coil)
L2 antenna coil (second antenna coil)
C2 capacitor (tuning capacity)
Tp Tap Tr Switching element L3 Coil C4 Capacitor INV Inverter

Claims (2)

In an antenna circuit comprising a second antenna coil that resonates with an external carrier signal provided with a first antenna coil, and outputs a load modulation signal in response to the carrier signal, and a resonance part composed of a tuning capacitor,
A coil connected in parallel to the resonance unit, and a resistor and a switching element connected in series to the coil, and at the time of load modulation when outputting a load modulation signal in response to the carrier signal, the resonance unit An antenna circuit comprising an impedance transition unit that increases a resonance frequency to increase an impedance change at a carrier signal frequency . In an antenna circuit comprising a second antenna coil that resonates with an external carrier signal provided with a first antenna coil, and outputs a load modulation signal in response to the carrier signal, and a resonance part composed of a tuning capacitor,
A capacitor connected in parallel to the resonance unit, a resistor and a switching element connected in series to the capacitor, and an inverter that reverses the polarity of a drive signal that drives the switching element on and off, and responds to the carrier signal. An antenna circuit, comprising: an impedance changing unit that increases a resonance frequency of the resonance unit to increase an impedance change at a carrier signal frequency during load modulation when outputting a load modulation signal.

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