JP4934659B2 - Shared antenna and matching circuit - Google Patents

Description

  The present invention relates to a shared antenna technology that can be used for both inductive coupling communication and electrostatic coupling communication.

Inductive coupling communication performs communication using a magnetic field, and electrostatic coupling communication performs communication using an electric field. For example, as a communication using inductive coupling, an RF tag, a non-contact type IC card, or the like is known. As communication using electrostatic coupling, a technique described in Non-Patent Document 1 is known.
Japanese Patent Application Laid-Open No. 07-221529 “RedTacton”, [online], Nippon Telegraph and Telephone Corporation, [searched on August 15, 2008], Internet <URL: http://www.redtacton.com/>

  When realizing a communication device that can use both inductively coupled communication and electrostatically coupled communication, two types of antennas are required: a coiled antenna for inductively coupled communication and an electrode antenna for electrostatically coupled communication. There is a problem that it is undesirable in terms of space.

  In addition, when different carrier frequencies are used for inductive coupling communication and electrostatic coupling communication, the impedance of the antenna unit is different. A method of preparing two types of matching sections and switching them with a switch is conceivable, but there is a problem that they are not suitable for downsizing and cost reduction.

  Patent Document 1 proposes an antenna that can be used for a plurality of frequencies with one antenna. However, the technique described in Patent Document 1 includes an antenna that can be used for a plurality of frequencies, but different input terminals for each frequency. There is a problem that a plurality of transmission devices are necessary.

  The present invention has been made in view of the above, and an object of the present invention is to provide a shared antenna that can be shared by both communication methods in a communication device capable of inductive coupling communication and electrostatic coupling communication with different frequencies. It is to be realized.

A shared antenna according to a first aspect of the present invention is a shared antenna connected to a communication device capable of communication by both inductive coupling communication and electrostatic coupling communication, and a coil that generates a magnetic field used in inductive coupling communication; are arranged on opposite sides of the substrate to the coil, the electrode connected to the ground terminal of the receiving circuit of the communication device, connect one end of the coil at the time of inductive coupling communications to a ground terminal, one end of the coil at the time of electrostatic coupling communication And a switch for disconnecting from the ground terminal .

A shared antenna according to a second aspect of the present invention is a shared antenna connected to a communication device capable of communicating by both inductive coupling communication and electrostatic coupling communication, and generates a pair of electric fields used in electrostatic coupling communication. It has an electrode and a coil which is disposed between a pair of electrodes and generates a magnetic field used in inductively coupled communication .

  In the shared antenna, the electrode has a horseshoe shape.

A shared antenna according to a third aspect of the present invention is a shared antenna connected to a communication device capable of communicating by both inductive coupling communication and electrostatic coupling communication, and includes a coil wound around each layer of the substrate. An electric field used for electrostatic coupling communication is generated using a stray capacitance between layers .

A matching circuit according to a fourth aspect of the present invention is a matching circuit connected to the shared antenna, a parallel capacitor connected in parallel with the shared antenna, a series capacitor connected in series with the shared antenna, and a parallel capacitor; A first correction circuit including a first parallel resonance circuit and a first correction capacitor, which are connected in parallel and resonate at a carrier frequency of either inductive coupling communication or electrostatic coupling communication, and a series capacitor in parallel. And a second correction circuit including a second parallel resonance circuit that resonates at a carrier frequency of either inductive coupling communication or electrostatic coupling communication, and a second correction capacitor. And

  In the present invention, the coil for inductively coupled communication and the electrode for electrostatically coupled communication are arranged to face each other, and the coil is used as an electrode for electrostatically coupled communication. A space-saving shared antenna that can be used for both communications can be provided. The coil is used as an electrode for electrostatic coupling communication by providing a switch for connecting the coil to the ground terminal of the transmission / reception circuit during inductive coupling communication and disconnecting the coil from the ground terminal during electrostatic coupling communication. Further, by sandwiching the coil between the two electrodes, the location where the electrode is disposed can be shared with the coil, so that a shared antenna that can be used for either inductive coupling communication or electrostatic coupling communication can be configured in a small space.

  In the present invention, the magnetic field radiated by the coil is not weakened by making the electrodes have a horseshoe shape.

  In the present invention, since the stray capacitance increases by winding the coil on each layer of the substrate, it can function as an electrode for electrostatic coupling communication.

  In the present invention, by having a correction circuit having a parallel resonance circuit that resonates at a predetermined carrier frequency, when a carrier wave having a predetermined frequency is input, the parallel resonance circuit resonates and the correction circuit is matched. Since it is separated from the circuit, it is possible to provide a matching circuit that can achieve matching at two different frequencies.

  Thus, according to the present invention, it is possible to realize a shared antenna that can be shared by both communication methods in a communication device capable of inductively coupled communication and electrostatically coupled communication having different frequencies.

[First Embodiment]
FIG. 1 is a schematic diagram illustrating a schematic configuration of a shared antenna according to the first embodiment. The shared antenna shown in FIG. 1 includes a coil 11 for inductively coupled communication and an electrode 12 for electrostatically coupled communication. The coil 11 is disposed on one surface of a double-sided substrate (not shown), and the electrode 12 is disposed so as to be opposed to the coil 11 and the other surface on the coaxial line. The electrode 12 has a horseshoe shape having an opening in a part of the ring. By making the electrode 12 into a horseshoe shape, the magnetic field radiated by the coil 11 is not weakened.

  The coil 11 is connected to an RF (Radio Frequency) signal input / output terminal and a ground terminal of a transmission / reception unit (not shown) via the matching unit 30. A switch 20 is disposed on the ground terminal side of the coil 11. The electrode 12 is connected to the ground terminal of the transmission / reception unit via the matching unit 30.

  By disconnecting the ground terminal side of the coil 11 with the switch 20, the coil 11 is used as an electrode for electrostatic coupling communication connected only to the RF signal input / output terminal. Thus, when the switch 20 is on, the coil 11 functions as an inductively coupled communication antenna that generates a magnetic field, and when the switch 20 is off, the coil 11 is an electrostatically coupled communication antenna that generates an electric field. Function as.

  Therefore, according to the present embodiment, the coil 11 and the electrode 12 are disposed so as to face each other, and the switch 20 is disposed between the coil 11 and the matching unit 30, so that when the switch 20 is on, the coil 11 is used as an antenna for inductive coupling communication, and when the switch 20 is off, the coil 11 can be used as an antenna for electrostatic coupling communication, and can be used for both inductive coupling communication and electrostatic coupling communication. A shared antenna can be realized, and the cost and size of the shared reader / writer can be reduced.

[Second Embodiment]
FIG. 2 is a schematic diagram illustrating a schematic configuration of the shared antenna according to the second embodiment. The shared antenna shown in FIG. 2 includes a coil 11 for inductively coupled communication and two electrodes 12 for electrostatically coupled communication. The two horseshoe-shaped electrodes 12 are disposed to face the front and back surfaces of a multilayer substrate (not shown), respectively. The coil 11 is disposed so as to be sandwiched between two electrodes 12 in an intermediate layer of a multilayer substrate. The coil 11 is connected to the RF signal input / output terminal and the ground terminal of the transmission / reception unit via the matching unit 30. Each of the two electrodes 12 is connected to the RF signal input / output terminal and the ground terminal of the transmission / reception unit via the matching unit 30.

  Therefore, according to the present embodiment, it is not necessary to secure a new place for placing the antenna for electrostatic coupling communication by placing the coil 11 between the electrodes 12, so that inductive coupling is possible. A shared antenna that can be used for both communication and electrostatic coupling communication can be configured in a space-saving manner.

[Third Embodiment]
FIG. 3 is a schematic diagram illustrating a schematic configuration of the shared antenna according to the third embodiment. The common antenna shown in the figure includes a coil 13 wound around each layer of a multilayer substrate (not shown) with a pattern having a large width.

  Generally, an inductively coupled communication antenna coil has a minute stray capacitance between windings. When the space between the coils 13 is narrowed or divided and wound on a multilayer substrate, the stray capacitance of the coil 13 itself increases. When a carrier wave is applied in this state, an electric field is generated in the stray capacitance in addition to the magnetic field generated by the coil, so that it can function as an antenna for electrostatic coupling communication.

  Therefore, according to the present embodiment, by providing the coil 13 in each layer of the substrate, the stray capacitance of the coil 13 itself can be increased and function as an antenna for electrostatic coupling communication.

  Here, FIG. 4 shows an equivalent circuit of the shared antenna. As shown in the figure, the shared antenna is represented by the inductance L of the inductively coupled communication antenna coil, the resistance RL due to the skin effect of the inductively coupled communication antenna coil, and the capacitance C due to the stray capacitance of the electrostatically coupled communication antenna. Is done. In inductively coupled communication, an air core coil having a large diameter is used to generate a magnetic field, and a capacitor is used to match impedance with a transmitting / receiving unit. On the other hand, in electrostatic coupling communication, a pair of electrodes is used to generate an electric field, and a coil is used to match impedance with a transmitting / receiving unit. Thus, when the antenna is viewed as an AC circuit, the inductively coupled communication antenna and the electrostatic coupled communication antenna have the same configuration. Since inductively coupled communication does not require an electric field, the electric field is not emitted to the outside by a capacitor or an electrostatic shield sandwiching a dielectric. On the other hand, since a magnetic field is unnecessary in the electrostatic coupling communication, a magnetic field is prevented from being emitted to the outside by a coil having a high permeability core.

  In the antenna coil for inductively coupled communication, the present invention actively uses an electric field component that has been removed by providing a shield in the past for electrostatically coupled communication. Thereby, it is not necessary to separately arrange two types of antennas, that is, an inductively coupled communication antenna and an electrostatic coupled communication antenna, and a shared antenna that is advantageous in terms of space can be provided.

[Fourth Embodiment]
When the shared antennas of the first to third embodiments are used at different frequencies for inductive coupling communication and electrostatic coupling communication, the impedances of the shared antennas are different. In order to radiate a magnetic field and an electric field efficiently, it is necessary to switch the constant of the capacitor of the matching unit for matching with the output impedance of the transmission / reception unit. As a method of switching the constant of the capacitor, it is conceivable to switch using a switch or use a variable capacitance diode, but the mechanism for controlling these becomes complicated. Therefore, in the present embodiment, by utilizing the property that the impedance of the parallel resonant circuit becomes infinite when the parallel resonant circuit is resonating, by resonating the parallel resonant circuit at a specific carrier frequency, The capacitor was disconnected from the matching section, and the capacitance of the capacitor in the matching section was switched.

  FIG. 5 is a circuit diagram showing a configuration of the matching unit in the fourth embodiment. The matching unit 30 shown in the figure includes a capacitor C1a connected in parallel with the antenna unit 10, a resistor R, and a capacitor C2a connected in series with the antenna unit 10. Furthermore, a parallel resonance circuit composed of a capacitor C3 and an inductor L3 and a circuit connected in series with the capacitor C1b are connected in parallel with the capacitor C1a, and a parallel resonance circuit composed of the capacitor C4 and the inductor L4 and a capacitor C2b are connected in series. The connected circuit is connected in parallel with the capacitor C2a.

  Capacitor C1a and capacitor C2a are set so that matching is obtained at the higher frequency of the input carrier waves. The two parallel resonant circuits set capacitors C3 and C4 and inductors L3 and L4 so as to resonate at a higher frequency. Accordingly, when a carrier wave having a higher frequency is input, the capacitors C1b and C2b are disconnected from the matching unit 30.

  On the other hand, when a carrier wave having a lower frequency is input, the parallel resonant circuit becomes inductive. Therefore, the capacitors C1b and C2b are set so as to cancel this and to obtain matching at the lower frequency. .

  Therefore, according to the present embodiment, a parallel resonant circuit that resonates at the other carrier frequency is incorporated in series into capacitors C1b and C2b set so as to obtain matching at one of the carrier frequencies. Since the capacitors C1b and C2b are separated from the matching unit 30 when resonating, matching with the antenna unit 10 can be obtained even when two different carrier frequencies are used.

[Example]
Next, examples of the present invention and simulation results thereof will be described. FIG. 6 shows a matching unit connected to a transmission / reception unit that performs both inductive coupling communication using a carrier having a first frequency and electrostatic coupling communication using a carrier having a second frequency lower than the first frequency. 30 shows an embodiment of the antenna unit 10.

  The antenna unit 10 uses a shared antenna in which thick pattern air-core coils are installed on both sides of the substrate. The two air-core coils installed on both sides are assumed to be a Japanese-style connection. By adjusting how the two air-core coils overlap each other and the line width of the coils, the antenna unit 10 has an inductance of 1 μH, a stray capacitance of 80 pF, and a resistance of 1Ω including the skin effect.

  As shown in FIG. 6, the matching unit 30 has C1a = 10 pF, C1b = 420 pF, C2a = 50 pF, C2b = 105 pF, C3, C4 = 138 pF, L3, L4 = 1 μH (resistance component is 1Ω). In this state, the output impedance of the transmission / reception unit can be matched to 50Ω at the first and second frequencies.

  7 and 8 are simulation results when an AC signal is applied to the matching unit of the above embodiment. FIG. 7 shows the time change of the voltage between the input and the ground of the antenna unit when an AC signal of the first frequency is applied, and FIG. 8 shows the antenna when an AC signal of the second frequency is added. The time change of the voltage between the input of a part and ground is shown. It was confirmed that a large voltage amplitude was obtained at the antenna at two frequencies.

  FIG. 9 shows a voltage change between the input and the ground of the antenna unit when the applied frequency is changed. It was confirmed that the frequency characteristics were such that peaks were obtained at the first and second frequencies.

It is a schematic diagram which shows schematic structure of the shared antenna in 1st Embodiment. It is a schematic diagram which shows schematic structure of the shared antenna in 2nd Embodiment. It is a schematic diagram which shows schematic structure of the shared antenna in 3rd Embodiment. It is a circuit diagram which shows the equivalent circuit of the said shared antenna. It is a circuit diagram which shows the structure of the matching part in 4th Embodiment. It is a circuit diagram which shows the Example of this invention. It is a simulation result when an alternating current signal is added to the matching part of the said Example. It is a simulation result when another alternating current signal is added to the matching part of the said Example. It is a graph which shows the frequency characteristic of the said Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Antenna part 11, 13 ... Coil 12 ... Electrode 20 ... Switch 30 ... Matching part

Claims (5)

A shared antenna connected to a communication device capable of communicating by both inductively coupled communication and electrostatically coupled communication,
A coil that generates a magnetic field for use in inductively coupled communication;
An electrode connected to the coil across a substrate, and connected to a ground terminal of a transmission / reception circuit of the communication device ;
A switch that connects one end of the coil to the ground terminal during inductive coupling communication, and disconnects one end of the coil from the ground terminal during electrostatic coupling communication;
A shared antenna characterized by comprising: A shared antenna connected to a communication device capable of communicating by both inductively coupled communication and electrostatically coupled communication,
A pair of electrodes for generating an electric field for use in electrostatic coupling communication;
A coil that is disposed between the pair of electrodes and generates a magnetic field for use in inductively coupled communication;
A shared antenna characterized by comprising: Shared antenna according to claim 1 or 2, wherein the electrode is horseshoe-shaped. A shared antenna connected to a communication device capable of communicating by both inductively coupled communication and electrostatically coupled communication,
Having coils wound on each layer of the substrate,
An electric field used for electrostatic coupling communication is generated using a stray capacitance between layers of the coil. A matching circuit connected to the shared antenna according to claim 1 ,
A parallel capacitor connected in parallel with the shared antenna;
A series capacitor connected in series with the shared antenna;
A first correction circuit including a first parallel resonance circuit that is connected in parallel with the parallel capacitor and resonates at a carrier frequency of either inductive coupling communication or electrostatic coupling communication; and a first correction capacitor;
A second correction circuit including a second parallel resonance circuit that is connected in parallel with the series capacitor and resonates at a carrier frequency of either inductive coupling communication or electrostatic coupling communication; and a second correction capacitor;
A matching circuit comprising:

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