JP6640452B2 - Multi-frequency transceiver circuit - Google Patents

Description

  The present invention relates to a multi-frequency transmitting / receiving circuit for selecting and transmitting signals of a plurality of frequencies.

  The multi-frequency transmission / reception circuit includes a resonator capable of selecting a resonance frequency, outputs a resonance signal corresponding to the resonance frequency of the selected resonator, and receives an excitation signal corresponding to the resonance frequency of the selected resonator. , And outputs a detection signal. In the case of a receiving circuit, a predetermined operation can be performed when an excitation signal is received. For example, when a multi-frequency transmission / reception circuit is incorporated in a security tag, the multi-frequency transmission / reception circuit may generate a warning such as a buzzer by detecting an excitation signal.

Hereinafter, the configuration of the conventional multi-frequency transmission / reception circuit will be described with reference to FIG.
FIG. 5 is a circuit diagram illustrating a configuration of a conventional multi-frequency transmission / reception circuit.
As shown in FIG. 5, a resonator 20 in which a capacitor 22 for receiving a weak excitation signal and a coil 21 with a tap are connected in parallel is formed in the conventional multi-frequency transmitting / receiving circuit. The resonator 20 further includes a capacitor 23 connected in parallel with the capacitor 22 to generate a low-frequency drive signal such as a buzzer. Here, the diode 24 and the diode 25 connected in opposite directions use the forward voltage drop to prevent the current flowing through the capacitor 23 from receiving the weak excitation signal, and the coil 21 and the diode 21 are connected to each other. The capacitor 22 forms the resonator 20, and the capacitor 23 operates as a resonance capacitor for a large-amplitude drive signal. Power is supplied to the resonator 20 from a DC power supply 26, and the resonator 20 is connected to the collector terminal of the transistor 27. A drive signal is input to the base terminal of the transistor 27 via the resistor 28, and the transistor 27 is activated by the input value of the drive signal, so that the resonator 20 can be excited. Note that if a piezoelectric buzzer exhibiting a capacitive characteristic is used as the capacitor 23, the buzzer can be sounded by this circuit. In FIG. 5, the left ends of the capacitors 22 and 23 are connected to the upper end of the DC power supply. However, the left ends of the capacitors 22 and 23 may be directly grounded as long as they are grounded as an AC signal. . Further, the resonator 20 is connected to the amplifier 30 via the capacitor 29, and upon receiving the excitation signal, the amplifier 30 receives the resonance signal and outputs a detection signal.

  In such a conventional multi-frequency transmission / reception circuit, the state is switched to a transmission state or a reception state by a drive signal input to the transistor 27. That is, when the transistor 27 is in the active state, it is in the transmission state, and when the transistor 27 is in the inactive state, it is in the reception state. The resonance frequency of the received signal can be adjusted by adding a capacitor 23 to the transmission signal by the capacitor 22 constituting the resonator 20.

JP 2008-9007 A

  However, in the conventional multi-frequency transmission / reception circuit, it is difficult to increase the output of the resonance signal, and the output of the resonance signal is determined according to the excitation signal. The drive voltage of the buzzer is reduced by the forward voltage drop voltage of the diode 24 and the diode 25, and the loss cannot be avoided.

  An object of the present invention is to improve the output of a resonance signal.

To achieve the above object, a multi-frequency transmitting / receiving circuit according to the present invention includes a first coil, a second coil electromagnetically coupled to the first coil and having a larger number of turns than the first coil, A first capacitor connected in parallel with a second coil to form a resonator with the second coil; and one or more second capacitors connected in parallel to the first capacitor and one end of which is grounded A capacitor, one or more operation circuits connected in parallel to the first capacitor and one end of which is grounded, and a switch provided between each end of the second capacitor and the operation circuit until the one end is grounded And a first transistor that drives the resonator during transmission to output a resonance signal of a predetermined frequency from the resonator and that is in an inactive state during reception.

  As described above, according to the multifrequency transmitting / receiving circuit of the present invention, the output of the resonance signal can be improved.

FIG. 3 illustrates a configuration of a multi-frequency transmission / reception circuit in Embodiment 1. FIG. 3 illustrates a configuration of a multi-frequency transmission / reception circuit in Embodiment 2. FIG. 10 illustrates a configuration of a multi-frequency transmission / reception circuit in Embodiment 3. FIG. 10 illustrates a configuration of a multi-frequency transmission / reception circuit in Embodiment 3. Circuit diagram illustrating the configuration of a conventional multi-frequency transmission / reception circuit

  The multi-frequency transmission / reception circuit of the present invention connects an excitation coil electromagnetically coupled to a coil constituting a resonator, drives the excitation coil with an element such as a transistor, sends energy to the resonance coil, and generates a resonance signal constituting the resonator. By forming a transformer with a dexterous coil and an output amplifying coil, a high-output resonance signal can be generated and a received resonance signal can be taken out to a sense amplifier. Further, when the multi-frequency transmission / reception circuit of the present invention is incorporated in a security tag, when an excitation signal of a predetermined frequency is received by a resonator, an operation circuit that acts as a capacitor such as an electromagnetic buzzer having a property as a capacitor is provided as a resonator coil. When the switch is connected to a buzzer or the like, the switch connected to the buzzer or the like can be turned on, so that the buzzer or the like can be sounded with a loud sound, for example. Further, by connecting a switch in series to a frequency selection capacitor connected in parallel to a resonator capacitor constituting the resonator, the resonance frequency of the multi-frequency transmission / reception circuit can be easily selected.

  When the multi-frequency transmission / reception circuit of the present invention is used as a multi-frequency transmission circuit, the energy excited from the transistor to the excitation coil is transmitted to the coil constituting the resonator that is electromagnetically coupled, and is selectively set by the switch. A high frequency signal of a frequency can be output. Here, it is possible to transmit a large amount of energy to the resonator by changing the winding ratio of the electromagnetically coupled coil and the exciting coil.

Hereinafter, a specific configuration will be described as an embodiment with reference to the drawings.
(Embodiment 1)
First, the configuration of the multi-frequency transmission / reception circuit according to the first embodiment will be described with reference to FIG.

FIG. 1 is a diagram illustrating a configuration of a multi-frequency transmission / reception circuit according to the first embodiment.
As shown in FIG. 1, the multi-frequency transmission / reception circuit according to the first embodiment includes a resonator 1, a coil 2, and a transmission / reception control transistor 3 connected to the resonator 1 via the coil 2. In the resonator 1, a coil 4 and a capacitor 5 are connected in parallel, and one or a plurality of capacitors 6 are independently connected in parallel with the capacitor 5, and each of the capacitors 6 is grounded via one switch 7. Configuration. The resonator 1 is powered by a DC power supply 8. An output circuit such as a sense amplifier 10 may be connected to the resonator 1 via a capacitor 9. When an excitation signal is received, the resonance signal is detected by the sense amplifier 10 and a predetermined signal such as an alarm is issued. Actions can be taken. Further, a drive signal is input to the transmission / reception control transistor 3, and the transmission / reception control transistor 3 can be activated by the drive signal.

  In the multi-frequency transmitting / receiving circuit having such a configuration, the transformer 11 is configured with the primary coil for excitation as the coil 2 and the secondary coil as the coil 4. When functioning as a transmission circuit, the transmission / reception control transistor 3 connected to the coil 2 serving as the primary coil is driven by a drive signal to output a resonance signal generated by the resonator 1. When functioning as a receiving circuit, the transmission / reception control transistor 3 is deactivated, the excitation signal is received by the resonator 1, and the resonance signal is transmitted to the sense amplifier 10 connected to the upper end of the secondary coil 4. Output. In order to increase the receiving sensitivity, the coil 4 itself may be a coil with a tap. Further, the closing and opening of the switches 7 can be controlled by a control signal input to each switch 7 independently from the outside.

  In this circuit, the capacitor 5 is for the highest frequency capacitor. In order to correspond to a lower frequency, a capacitor 6 controlled by a switch 7 is used. The selection of the resonance frequency is performed by opening and closing the switch 7. That is, by setting one or a plurality of switches 7 to the connected state, the corresponding capacitor 6 is made conductive, and the capacitor 6 and the capacitor 5 that are made conductive set the resonance frequency of the resonator 1. The resonance frequency is determined by setting the capacitance of the resonator 1 by the combination of the capacitors 6 to be conducted. As the capacity of each of the capacitors 6, a capacitor having a capacity corresponding to a resonance frequency to be selected can be used.

As described above, the transformer 11 is formed by using the coil 4 of the resonator 1 as a secondary coil and the coil 2 tightly coupled to the coil 4 as a primary coil. Also, by increasing the voltage of the resonance signal, the voltage of the resonance signal can be increased, and the output of the resonance signal can be improved. Also, by providing one or a plurality of capacitors 6 connected in parallel to the capacitor 5 so that conduction can be controlled by the switch 7, the switch 7 is selectively made conductive so that the capacitor 6 is connected to the coil 4. The resonator 1 is connected in parallel, and the resonator 1 corresponding to an arbitrary frequency lower than the resonance frequency determined by the coil 4 and the capacitor 5 can be configured, and a transmission / reception circuit compatible with multiple frequencies can be easily realized.
(Embodiment 2)
Next, the configuration of the multi-frequency transmitting / receiving circuit according to the second embodiment will be described with reference to FIG.

  FIG. 2 is a diagram illustrating a configuration of a multi-frequency transmission / reception circuit according to the second embodiment. In FIG. 2, the capacitor 6 (FIG. 1) is omitted, but one or a plurality of capacitors 6 connected in parallel to the capacitor 5 can be provided according to FIG.

  As shown in FIG. 2, the multi-frequency transmission / reception circuit of the second embodiment is characterized in that one capacitor 6 (FIG. 1) in the multi-frequency transmission / reception circuit of the first embodiment is replaced with a buzzer 16.

  As the buzzer 16, a piezoelectric buzzer utilizing the piezo effect is often used, and the piezoelectric buzzer becomes a capacitive load in an electronic circuit. Therefore, if the capacity of the buzzer 16 is used as the capacitor 6 (FIG. 1) which is a low-frequency resonance capacitance, one resonance frequency can be selected from two resonance frequencies with only one capacitor 5 as shown in FIG. Thus, a buzzer drive circuit having transmission / reception of a gate signal and a boosting function can be realized. Further, by providing a plurality of buzzers 16 having different capacities and the switches 7 provided for each of the plurality of buzzers 16, a multi-frequency transmission / reception circuit that can select one resonance frequency from the plurality of resonance frequencies can be configured.

  Further, the security tag receives a high-frequency excitation signal emitted from a gate installed at an entrance of a store or the like, and upon detecting the reception of the excitation signal, generates an attenuation signal of the same frequency to notify the presence of the tag. May be required. This signal can also be generated by tuning the received signal and exciting it with the transistor 3.

  When the multi-frequency transmission / reception circuit of the present embodiment is used for a security tag, a resonance signal of a predetermined frequency generated by a combination of a capacitor 6 (FIG. 1) is transmitted, and an excitation signal of a predetermined frequency supplied from a gate is transmitted. A buzzer sound of several kHz can be generated when a signal is received or an abnormality occurs in the tag. The transformer 11 is formed by using the coil 4 of the resonator 1 as a secondary coil and the coil 2 tightly coupled to the coil 4 as a primary coil, so that the number of turns of the coil 4 is larger than the number of turns of the coil 2. Thus, the voltage of the resonance signal can be increased, the output of the resonance signal can be improved, and the sound of the buzzer 16 can be increased.

  Further, when the capacitance value of the buzzer is small as the resonance capacitance, the capacitor 17 may be provided in parallel with the buzzer 16. Providing the capacitor 17 makes it easier for the resonator 1 to resonate, and makes it possible to increase the sound emitted from the buzzer 16.

As described above, in the multi-frequency transmission / reception circuit of the first embodiment, by replacing one capacitor 6 (FIG. 1) with the buzzer 16, it is possible to easily realize the multi-frequency transmission / reception circuit and to output the resonance signal. The output of the buzzer can be easily improved while improving the output.
(Embodiment 3)
Next, the configuration of the multi-frequency transmitting / receiving circuit according to the third embodiment will be described with reference to FIGS.

  3 and 4 are diagrams illustrating the configuration of the multi-frequency transmission / reception circuit according to the third embodiment. FIG. 3 is a diagram illustrating the configuration of the multi-frequency transmission / reception circuit controlled by the bipolar transistor according to the second embodiment. FIG. 9 is a diagram illustrating a configuration of a multi-frequency transmission / reception circuit controlled by a MOSFET according to a second embodiment.

  Since the switch 7 (see FIGS. 1 and 2) for controlling the capacitor 6 and the buzzer 16 controls the AC signal, the switch 7 must be configured to conduct bidirectionally. Therefore, as shown in FIG. May be connected in parallel. In such a switch, if the transistor 12 is turned off while the current flows through the diode 13, the switch 7 is turned off when the current starts to flow through the transistor 12, thereby realizing the function of the capacitor 6 as a capacitor and the switch of the buzzer 16. .

  As a switch for controlling the capacitor 6 and the buzzer 16, a MOSFET 14 may be provided as shown in FIG. 4 instead of the switch 7 (see FIGS. 1 and 2). In the case where the MOSFET 14 is used, in general, the MOSFET includes a diode necessary for the proposed circuit, and thus the diode 13 does not need to be provided. Further, since the switching of the MOSFET can be controlled by the voltage, the resistor 15 which is necessary for the bipolar transistor and which is interposed in the control signal becomes unnecessary. In this way, by using MOSFETs as switches, simplification of a multi-frequency transmission / reception circuit can be realized.

DESCRIPTION OF SYMBOLS 1 Resonator 2 Coil 3 Transmission / reception control transistor 4 Coil 5 Capacitor 6 Capacitor 7 Switch 8 DC power supply 9 Capacitor 10 Sense amplifier 11 Transformer 12 Transistor 13 Diode 14 MOSFET
15 Resistance 16 Buzzer 17 Capacitor 20 Resonator 21 Coil 22 Capacitor 23 Capacitor 24 Diode 25 Diode 26 DC Power Supply 27 Transistor 28 Resistance 29 Capacitor 30 Amplifier

Claims (5)

A first coil;
A second coil electromagnetically coupled to the first coil and having a larger number of turns than the first coil;
A first capacitor connected in parallel with the second coil to form a resonator with the second coil;
One or more second capacitors connected in parallel to the first capacitor and having one end grounded;
One or more operation circuits connected in parallel to the first capacitor and one end of which is grounded, and a switch provided until one end of each of the second capacitor and the operation circuit is grounded;
A multi-frequency transmission / reception circuit, comprising: a first transistor that drives the resonator during transmission to output a resonance signal of a predetermined frequency from the resonator and that is in an inactive state during reception.   2. The multi-frequency transmission / reception circuit according to claim 1, wherein said operation circuit is a buzzer. The switch is
A second transistor provided between each of the second capacitors and a ground point at which one end of each of the second capacitors is grounded ;
A diode disposed in parallel with the second transistor and conducting only in a direction from the ground point to the second capacitor, wherein the second capacitor is connected to a base terminal of the second transistor by an input signal. 3. The multi-frequency transmission / reception circuit according to claim 1, wherein conduction between the power supply and the ground point is controlled. The switch is configured by a MOSFET, and controls conduction between the second capacitor and a ground point at which one end of each of the second capacitors is grounded by an input voltage to a gate terminal of the MOSFET. The multi-frequency transmission / reception circuit according to claim 1 or 2, wherein:   The multi-frequency transmitting / receiving circuit according to claim 2, further comprising a third capacitor connected in parallel to the buzzer.

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