JPH10290187A - Resonant transmission/reception antenna circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To share an antenna and to unnecessitate a changeover means such as a switch by constituting a resonant antenna while using a loop coil and a capacitor, operating the antenna as a parallel resonant antenna upon reception and operating it as a serial resonant antenna in transmission. SOLUTION: A loop coil 1 and a capacitor 2 are serially connected and consist of the resonant antenna, and the other terminal of the loop coil 1 is connected to the output of the driver circuit 3 as a low output impedance. The input of amplifier circuit 4 as a high input impedance is connected to the connecting part of the loop 1 and the capacitor 2, and a transmission terminal 5 and a reception terminal 6 are provided. At the time of transmission, the antenna circuit watched from the output of transmission driver is operated as serial resonance due to the capacitance of antenna and the inductance of loop coil and at the time of reception, the antenna circuit watched from the input of reception antenna is operated as parallel resonance due to the capacitance and the inductance of loop coil since the output of transmission driver is a low impedance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication for transmitting and receiving data using electromagnetic induction.

[0002]

2. Description of the Related Art A conventional technique will be described with reference to FIGS. When an antenna that constitutes a resonance circuit using a loop coil and a capacitor is used for wireless communication using electromagnetic induction, even if the induction current flowing through the loop coil is small due to a change in the magnetic field during reception at the resonance frequency compared to the series resonance type, When using a parallel resonance type that can obtain a large reception voltage signal, and using a series resonance type that can send a large current to the loop coil and change a large magnetic field even with a small transmission voltage signal compared to the parallel resonance type during transmission, Can obtain a large voltage signal and can transmit with a small voltage signal at the time of transmission. This is because, for example, when a battery is used as the power supply of the circuit, the power supply voltage is limited or only a low power supply voltage can be obtained. A large transmission output is obtained.

However, in order to use a parallel resonance type at the time of reception and a series resonance type at the time of transmission as antennas constituting a resonance circuit using a loop coil and a capacitor, reception and transmission antennas are separately provided, or It is necessary to use a switch to switch the current path so as to be a parallel resonance type at the time of reception and a series resonance type at the time of transmission.

FIG. 5 shows a case where transmission and reception antennas are separately provided. The reception loop coil 31 and the reception resonance capacitor 32 are connected in parallel to form a reception antenna, and the transmission loop coil 33 and the transmission resonance capacitor 34 are connected in series to form a transmission antenna. 35
Is a reception terminal, and 36 is a transmission terminal.

FIG. 6 shows a configuration in which transmission and reception are switched using a switch. During reception, the switch 40 is off,
When the switch 41 is turned on, the loop coil 3
7 and the reception resonance capacitor 38 are connected in parallel, and during transmission, the switch 40 is turned on and the switch 41 is turned off, whereby the loop coil 37 and the transmission resonance capacitor 39 are connected in series. 42 is a receiving terminal, and 43 is a transmitting terminal.

[0006]

As described above, in order to use a parallel resonance type at the time of reception and a series resonance type at the time of transmission as an antenna constituting a resonance circuit using a loop coil and a capacitor, separate antennas for transmission and reception are required. Antennas and switches need to be prepared. In the case of switching using switches, an operation of switching those switches in accordance with transmission and reception is further required. In addition, by providing the switch in the signal path, the resistance and capacitance of the switch itself may reduce the efficiency of signal transmission or affect the resonance frequency.

Accordingly, the present invention uses a parallel resonance type for reception and a series resonance type for transmission as antennas constituting a resonance circuit using the above-described loop coil and capacitor. It is an object of the present invention to configure a resonant transmission / reception antenna circuit that functions as a series resonance antenna during transmission and functions as a parallel resonance antenna during reception without using transmission / reception switching means such as a switch.

[0008]

According to the present invention, a resonance antenna is formed by using a set of a loop coil and a capacitor. The resonance antenna functions as a parallel resonance antenna during reception, and functions as a series resonance antenna during transmission. It consists of a resonant antenna in which a loop coil and a capacitor are connected in series, a transmission driver with low output impedance, and a reception amplifier with high input impedance. The output of the transmission driver having a low output impedance is connected in series to a resonance type antenna in which a loop coil and a capacitor are connected in series, and the input of the reception amplifier having a high input impedance is connected to a connection between the loop coil and the capacitor.

Thus, the antenna circuit viewed from the output of the transmission driver at the time of transmission functions as a series resonance due to the capacitance of the antenna and the inductance of the loop coil, and the antenna circuit viewed from the input of the reception amplifier at the time of reception operates as the transmission driver. Since the output is low impedance, it acts as parallel resonance due to the capacitance of the antenna capacitor and the inductance of the loop coil. With such a configuration, the present invention provides a resonance type transmission / reception antenna circuit characterized in that it operates as a series resonance antenna during transmission and acts as a parallel resonance antenna during reception without using transmission / reception switching means. is there.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 shows an embodiment of a resonant transmission / reception antenna circuit to which the present invention is applied. The loop coil 1 and the capacitor 2 are connected in series to form a resonant antenna, the other end of the loop coil 1 is connected to the ground, and the other end of the capacitor 2 is connected to the output of the driver circuit 3 having a low output impedance. . Further, the input of the amplifier circuit 4 having a high input impedance is connected to the connection between the loop coil 1 and the capacitor 2. As the driver circuit 3 having a low output impedance and the amplifier circuit 4 having a high input impedance, those having an output impedance of 10Ω or less and an input impedance of 10kΩ or more are suitable. For example, a voltage follower in which the inverting input of an operational amplifier is subjected to full feedback. A circuit or the like can be used. 5 is a transmission terminal and 6 is a reception terminal. Although the connection between the loop coil 1 and the capacitor 2 has been described in the case where the loop coil side is connected to the ground, the same effect can be obtained even if the connection between the loop coil 1 and the capacitor 2 is switched and the capacitor side is connected to the ground. Can be

(Embodiment 2) FIG. 2 shows another embodiment of a resonant transmission / reception antenna circuit to which the present invention is applied. The loop coil 7 and the capacitor 8 are connected in series to form a resonant antenna, the other end of the loop coil 7 is connected to one output of a differential driver circuit 9 having a low output impedance, and the other end of the capacitor is a differential antenna. Connected to another output of amplifier circuit 9. Further, a differential amplifier circuit 10 having a high input impedance is provided at both ends of the loop coil 7.
Are connected. As the differential driver circuit 9 having a low output impedance and the differential amplifier circuit 10 having a high input impedance, those having an output impedance of 10Ω or less and an input impedance of 10kΩ or more are suitable. For example, an operational amplifier can be used. 11 and 12 are transmission terminals, and 13 and 14 are reception terminals. In addition,
Although the case where the respective inputs of the differential amplifier circuit 10 having high input impedance are connected to both ends of the loop coil 7 has been described, the same effect can be obtained by connecting these inputs to both ends of the capacitor 8.

(Embodiment 3) FIG. 3 shows an embodiment of a resonant transmission / reception antenna circuit to which the present invention is applied. The loop coil 15 and the capacitor 16 are connected in series to form a resonance type antenna. The other end of the loop coil 15 is connected to the ground, and the other end of the capacitor 16 is connected to the resistor 17. The other end of the resistor 17 is connected to the output of the driver circuit 18 having a low output impedance. Further, an input of an amplifier circuit 19 having a high input impedance is connected to a connection between the loop coil 15 and the capacitor 16. The Q of resonance can be changed by the value of the resistor 17. As a driver circuit 18 having a low output impedance and an amplifier circuit 19 having a high input impedance,
An output impedance of 10Ω or less and an input impedance of 10kΩ or more are suitable. For example, a voltage follower circuit in which the inverting input of an operational amplifier is subjected to full feedback can be used. Reference numeral 20 denotes a transmission terminal, and reference numeral 21 denotes a reception terminal. Although the connection between the loop coil 15 and the capacitor 16 has been described in the case where the loop coil side is connected to the ground, the same effect can be obtained even if the connection between the loop coil 15 and the capacitor 16 is exchanged and the capacitor side is connected to the ground. Can be

(Embodiment 4) FIG. 4 shows another embodiment of a resonant transmission / reception antenna circuit to which the present invention is applied. The loop coil 22 and the capacitor 23 are connected in series to form a resonant antenna. The other end of the loop coil 22 is connected to one output of a differential driver circuit 25 having a low output impedance, and the other end of the capacitor 23 is connected to a resistor. 2
4 is connected. The other end of the resistor 24 is connected to another output of the differential driver circuit 25. Further, both ends of the loop coil 22 are connected to respective inputs of a differential amplifier circuit 26 having a high input impedance. This resistance 2
The Q of resonance can be changed by the value of 4. The differential driver circuit 25 having a low output impedance and the differential amplifier circuit 26 having a high input impedance have an output impedance of 10Ω or less and an input impedance of 10Ω or less.
Those having kΩ or more are suitable, and for example, an operational amplifier can be used. 27 and 28 are transmission terminals, and 29 and 30 are reception terminals. Although the case where the respective inputs of the differential amplifier circuit 26 having a high input impedance are connected to both ends of the loop coil 22 has been described, the same effect can be obtained by connecting these inputs to both ends of the capacitor 23 and the resistor 24. Can be

[0015]

As described above, according to the present invention, a parallel resonance type is used as an antenna constituting a resonance circuit using a loop coil and a capacitor, which can obtain a larger received voltage signal than a series resonance type during reception. In order to use a series resonance type that can obtain a large transmission output compared to the parallel resonance type at the time of transmission, it is necessary to provide separate antennas for transmission and reception, or to use a series resonance antenna at the time of transmission without using transmission and reception switching means such as a switch. It has an advantageous effect that it can operate as a parallel resonant antenna during reception.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a resonant transmission / reception antenna circuit according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the resonant transmission / reception antenna circuit according to the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the resonant transmission / reception antenna circuit according to the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the resonant transmission / reception antenna circuit according to the present invention.

FIG. 5 is a circuit diagram showing a conventional resonance type transmitting / receiving antenna circuit.

FIG. 6 is a circuit diagram showing a conventional resonant transmission / reception antenna circuit.

[Explanation of symbols]

1,7,15,22,31,37 Loop coil 2,8,16,23,32,33,38,39 Capacitor 3,18 Driver circuit with low output impedance 4,19 Amplifier circuit with high input impedance 5 , 11,12,20,27,28,36,43 Transmission terminal 6,13,14,21,29,30,35,42 Reception terminal 9,25 Differential driver circuit with low output impedance 10,26 High input Differential amplifier circuit that is impedance

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Izuo Takamiya 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A resonance type antenna having a loop coil and a capacitor connected in series, a transmission driver having a low output impedance, and a reception amplifier having a high input impedance, wherein an output of the transmission driver is serially connected to the resonance type antenna. By connecting the input of the receiving amplifier to the connection part of the loop coil and the capacitor, it operates as a series resonance antenna at the time of transmission and operates as a parallel resonance antenna at the time of reception without using transmission / reception switching means. A resonant transmission / reception antenna circuit. And a differential transmission driver having a low output impedance and a differential reception amplifier having a high input impedance. The output of the differential transmission driver is A resonance type transmission / reception antenna circuit connected to both ends of a resonance type antenna, connected to the input of the differential reception amplifier to both ends of a loop coil or both ends of a capacitor of the resonance type antenna, and transmitting and receiving a balanced signal. . 3. The resonant transmission / reception antenna circuit according to claim 1, wherein a resistor is connected in series between the output of the transmission driver and the resonance antenna, and the Q of the resonance is varied by changing the resistance value. 4. A resistor is connected in series to one or both of an output of a differential transmission driver and a resonance type antenna in which a loop coil and a capacitor are connected in series, and the resonance value is changed by changing the resistance value. Claim 2 wherein Q is variable
13. The resonant transmission / reception antenna circuit according to claim 1.