JP2016158233A - Multifrequency transmitter-receiver circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multifrequency transmitter-receiver circuit capable of achieving tuning by efficiently adjusting resonance capacitance and further reducing spurious oscillation.SOLUTION: A multifrequency transmitter-receiver circuit comprises: a coil 2; one main capacitor 51 having main capacities connected to the coil 2 respectively in series and connected to each other in parallel; a resonator composed to a plurality of capacitors 5 consisting of one or a plurality of correction capacitors 52 having a correction capacity less than the main capacity; a plurality of switch elements 7 turned ON and OFF on receiving a capacity control signal and having a diode connected in series with each capacitor 5 to allow a current in a reverse direction; and an inverter 20 connected to the coil 2. A switch element 7 for controlling conduction of the main capacitor 51 has a series circuit of a resistance 511 and a capacitor 512 for spurious suppressing in parallel, and a resonance frequency of a resonator 1 is adjusted by selecting the main capacitor 51 for activating the switch element 7 and an added correction capacitor 52.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a multi-frequency transmission / reception circuit including a high-frequency tuning capacitance switch circuit, and relates to a technique for selecting and transmitting / receiving signals of a plurality of frequencies and reducing spurious.

  A conventional multi-frequency transmission / reception circuit includes a resonator capable of selecting a resonance frequency, outputs a resonance signal corresponding to the selected resonance frequency, receives an excitation signal corresponding to the selected resonance frequency, and outputs a detection signal. The resonator has one coil and a plurality of capacitors, and selects a resonance frequency by a high frequency tuning capacitance switch circuit.

  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, a configuration can be realized in which an excitation signal is detected by the multi-frequency transmission / reception circuit and a drive signal is generated by the same coil of the resonator to issue a warning such as a buzzer .

  The configuration of a conventional multi-frequency transmission / reception circuit will be described below with reference to the circuit diagram of FIG. As shown in FIG. 9, in a conventional multi-frequency transmitting / receiving circuit, a resonator 20 for receiving a weak excitation signal is configured by connecting a capacitor 22 and a tapped coil 21 in parallel. A capacitor 23 is further connected to the resonator 20 in parallel with the capacitor 22, and the capacitor 23 generates a low-frequency drive signal such as a buzzer.

  The resonator 20 includes a diode 24 and a diode 25 connected in opposite directions to each other, and a capacitor is used for receiving a weak excitation signal by using a forward voltage drop of the diode 24 and the diode 25. The coil 21 and the capacitor 22 form a resonance circuit by blocking the current flowing through the capacitor 23, and the capacitor 23 operates with a resonance capacitor added to the large amplitude drive signal.

In addition, if a piezoelectric buzzer which shows the characteristic of a capacity | capacitance is used as the capacitor | condenser 23, it will become possible to sound a buzzer in this circuit.
The resonator 20 is supplied with power from a DC power supply 26. The resonator 20 is connected to the collector terminal of the transistor 27 from the left end of the tapped coil 21. The transistor 27 inputs a drive signal to the base terminal via the resistor 28 and is activated by the input value of the drive signal. Let Furthermore, the resonator 20 is connected to the amplifier 30 via the capacitor 29, and when 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 transmission state or the reception state is switched by the drive signal input to the transistor 27. That is, when the transistor 27 is active, the transmission state is established, and when the transistor 27 is inactive, the reception state is established. The resonance frequency of the received signal is adjusted by adding a capacitor 23 to the transmission signal by the capacitor 22 constituting the resonator 20.

JP 2008-9007 A

  However, the circuit shown in FIG. 9 only handles two resonance frequencies, and the efficiency is degraded due to the voltage drop of the diode. In order to efficiently handle high-frequency power in the transmission / reception circuit, it is necessary to adjust the resonance capacitance to achieve tuning. The resonance capacity can be adjusted with a trimmer capacitor if the frequency to be handled is high at a medium wave or higher, but a gate signal or non-contact power supply of a store crime prevention system using a long wave band requires a capacity of tens of nF. In this case, for example, it is necessary to prepare a plurality of capacitors having capacitance values different from each other by a power of 2, and to connect the capacitors by switching wiring with jumper pins or the like. In addition, it is difficult to efficiently generate a high-frequency intermittent output high-frequency signal when the signal rises and stops, and it is also difficult to generate a high-frequency signal while changing the frequency in a short time.

  It is an object of the present invention to provide a multi-frequency transmission / reception circuit that can adjust the resonance capacity efficiently to achieve tuning, and can reduce spurious oscillation.

In order to solve the above problems, a multi-frequency transmission / reception circuit according to the present invention includes a coil, a resonator including a plurality of capacitors connected in series to each other and connected in parallel to each other, and A plurality of switching elements that respectively control conduction; and a driving transistor connected to the coil, wherein the plurality of capacitors include one main capacitor having a main capacity and one or more having a correction capacity smaller than the main capacity. Comprising a compensation capacitor
Each switch element has a diode connected in series with the capacitor and flowing in the reverse current direction. The switch element receives and opens a capacitance control signal, selects a main capacitor activated by conduction and a correction capacitor to be added. The resonance frequency of the resonator is adjusted according to the capacitance of the capacitor and the selected correction capacitor.

  The multi-frequency transmission / reception circuit of the present invention is characterized in that the switch element is composed of a bipolar transistor and the diode that causes a collector reverse current to flow between a collector and an emitter of the bipolar transistor.

  The multi-frequency transmission / reception circuit according to the present invention is characterized in that the switch element includes a MOS transistor and the diode that allows a drain reverse current to flow between a drain and a source of the MOS transistor.

The multi-frequency transmitting / receiving circuit of the present invention is characterized in that the correction capacity of each correction capacitor is a power of 2 with respect to the capacity of the correction capacitor having the minimum correction capacity.
The multi-frequency transmission / reception circuit of the present invention further includes a control device and a measurement device, wherein the measurement device measures a current value or phase of a resonance signal flowing through the resonator, and the current value or the phase becomes a predetermined value. Thus, the control device automatically controls the capacity control signal.

  The multi-frequency transmission / reception circuit of the present invention stores the energy of the resonator in the main capacitor and the correction capacitor by shutting off the switch element at a timing when a reverse current flows through the diode in the output stop operation, and when the output is resumed. The switch element for controlling the main capacitor and the correction capacitor is selectively turned on so as to be in a tuned state, and then the drive signal of the drive transistor is input 90 seconds behind the timing to perform an output operation. The output is resumed by releasing the energy stored at the time of stopping.

  The multi-frequency transmission / reception circuit of the present invention is characterized in that a series circuit of a capacitor and a resistor for suppressing spurious is provided in parallel with the diode in a switch element for controlling conduction of a main capacitor having a main capacity.

  As described above, according to the multi-frequency transmission / reception circuit including the high-frequency tuning capacitance switch circuit of the present invention, tuning can be performed by efficiently adjusting the resonance capacitance. Further, it is possible to efficiently suppress spurious generated when the transmission operation of the multi-frequency transmission / reception circuit is stopped.

The circuit diagram explaining the structure of the multi-frequency transmission / reception circuit in embodiment of this invention The circuit diagram which illustrates the composition of the switch element used for the high frequency tuning capacity switch circuit of the present invention The circuit diagram which illustrates the composition of the switch element used for the high frequency tuning capacity switch circuit of the present invention The figure explaining the operation | movement at the time of the output stop in the multifrequency transmission / reception circuit of this invention The figure explaining the operation | movement at the time of the output restart in the multifrequency transmission / reception circuit of this invention The circuit diagram explaining the structure of the multi-frequency transmission / reception circuit in other embodiment of this invention The graph figure explaining the operation | movement at the time of the output stop in the multifrequency transmission / reception circuit of this invention A graph illustrating the state of spurious generation in a multi-frequency transceiver circuit Circuit diagram for explaining the configuration of a conventional multi-frequency transmission / reception circuit

A multi-frequency transmission / reception circuit including a high-frequency tuning capacitance switch circuit according to an embodiment of the present invention will be described.
(Embodiment 1)
FIG. 1 is a diagram illustrating a configuration of a multi-frequency transmission / reception circuit, and FIGS. 2 and 3 are diagrams illustrating a configuration of a switch element used in a high-frequency tuning capacitance switch circuit.

  As shown in FIG. 1, the multi-frequency transmission / reception circuit of the present embodiment includes a resonator 1 and an inverter 20 that forms a drive transistor that drives the resonator 1. The resonator 1 includes a coil 2 and a plurality of capacitors 5 having different capacities connected to the coil 2. Each capacitor 5 is connected in series to the coil 2 and is connected in parallel to each other.

  The plurality of capacitors 5 are composed of a main capacitor 51 having one main capacity and a correction capacitor 52 having a correction capacity smaller than the main capacity in order to tune the resonator 1 to a specific frequency. A plurality of them are provided and used for fine adjustment of tuning as a correction capacity. If a synchronized main capacity can be selected, the correction capacity is unnecessary.

  The drive transistor may be activated by receiving a drive signal in addition to the inverter 20, and may be a transistor having one end grounded and the other end connected to the coil 2. However, as shown in FIG. It is efficient that the inverter 20 forms a circuit.

  The inverter 20 has a push-pull circuit configuration including complementary transistors that connect the drains of the Pch transistor 8 and the Nch transistor 9 and input a drive signal to the gate terminals of the Pch transistor 8 and the Nch transistor 9. Is input via the gate driver 11. The coil 2 of the resonator 1 is connected to the output terminal of the inverter 20. The inverter 20 may be a drive circuit in which a push-pull circuit is configured using the same type of transistor. Here, the diode 13 is included for circuit protection, but may be omitted in principle.

  Normally, in a push-pull circuit using a Pch transistor 8 and an Nch transistor 9 having equivalent current-voltage characteristics, when the circuit changes to a low output, the response time of the Pch transistor 8 is temporarily reduced. Both transistors become conductive, causing losses, adversely affecting the transistors, and generating noise.

  However, the time constant circuit constituted by the resistor 31 disposed between the gate driver 11 and the gate of the Nch transistor 9 and the capacitor 32 having one connected to the gate of the Nch transistor 9 and grounded to the other is the Nch transistor 9. Thus, the above-described operation in which both transistors are turned on can be avoided. The response delay of the Nch transistor 9 can also be realized by incorporating a dedicated gate driver in the Nch transistor 9 and incorporating a delay circuit therein.

  The high-frequency tuning capacitance switch circuit 12 includes the resonator 1 and a plurality of switch elements 7 respectively provided between the capacitors 5 (51, 52) and the ground. 5 (51, 52) is controlled. The resonator 1 can be tuned corresponding to various frequencies by setting the resonance capacitance by the combination of the capacitors 5 (51, 52) to be conducted and adjusting the resonance capacitance.

  The main capacity of the main capacitor 51 is set to be slightly smaller than the capacity required for tuning, and the correction capacity of the correction capacitor 52 is relatively small with respect to the main capacity. By selectively controlling each switch element 7 to make the correction capacitor 52 having a necessary correction capacity conductive, the correction capacity of one correction capacitor 52 is added to the main capacity of the main capacitor 51 or a plurality of correction capacitors. By combining 52 correction capacitors, a capacitor that is closest to the correction capacitor necessary for tuning is added to the main capacitor to perform frequency tuning.

  As the correction capacity, a minimum correction capacity and a power correction capacity of 2 that is twice or four times that of the correction capacity are adopted, and each correction is made so that the total sum of the selected correction capacity is about twice the capacity that is insufficient. By combining the capacitors, tuning can be performed by adding a correction capacitor proportional to a binary number representing the conduction state of the capacitor control signal to the main capacitor, and the frequency to be tuned can be adjusted efficiently.

  The high-frequency tuning capacitor switch circuit 12 can also replace one of the correction capacitors 52 with a piezoelectric buzzer, and the piezoelectric buzzer can be handled as a capacitor when viewed as a circuit component, so that it can be a buzzer control circuit.

  Further, the high-frequency tuning capacitor switch circuit 12 uses, as a characteristic configuration, a MOS element 4 including a diode 3 that flows a reverse drain current between a drain and a source as shown in FIG. As shown in FIG. 3, a bipolar transistor 6 having a diode 3 for flowing a collector reverse current between the collector and the emitter is used.

  In this embodiment, the MOS transistor 4 is used, and the diode 3 flows a current in the reverse current direction with respect to the current direction when the MOS transistor 4 is turned on. Each of the switch elements 7 is controlled by a capacitance control signal. Here, the capacitance control signal is input via the gate driver 10.

  In the present embodiment, the high-frequency tuning capacitance switch circuit 12 is connected to the source side of the switch element 7 in order to measure the current flowing through the resonator 1, and is grounded through the current measurement resistor 14. This configuration is not limiting.

  The magnitude of the current flowing through the current measuring resistor 14 or the phase of the resonance signal flowing through the resonator 1 can be measured using a measuring instrument, an AD converter of the microcomputer 15 or a timer.

  That is, when resonance occurs, the current flowing through the resonance circuit of the multi-frequency transmission / reception circuit is maximized. Therefore, the value of the current flowing through the current measurement resistor 14 is measured, and a plurality of capacitors 5 having different tuning capacities are connected. The resonance signal can be automatically tuned by controlling the connection so as to be closest to the maximum output of the multi-frequency transmission / reception circuit.

  Alternatively, when resonance occurs, the drive signal of the drive transistor and the current waveform of the sine wave output current of the resonator 1 flowing through the current measurement resistor 14 have the same phase, and the phase of the sine wave output voltage of the resonator 1 is the drive transistor. Therefore, the switch element 7 is opened and closed sequentially while measuring the phase of the current waveform or voltage waveform flowing through the current measuring resistor 14 with the microcomputer 15 or the like so as to be closest to the predetermined phase. By adjusting to, the phase of the current waveform or voltage waveform of the resonance signal can be automatically tuned.

  The current measuring resistor 14 uses a low-resistance resistor, reduces the voltage generated at both ends of the resistor, and reduces the influence on the operation of the switch element 7. Further, the measurement of the magnitude of the current of the resonance signal flowing through the resonator 1 or the measurement of the phase may be performed by another measuring device without providing the current measuring resistor 14 and the measuring device. In the case of a simple high-frequency tuning capacitance switch circuit 12 that is not automatically tuned, the current measuring resistor 14 and the measuring device are unnecessary.

  The drive signal and the capacity control signal for the tuning capacity need to be adjusted in timing for efficient operation, and are therefore generated by a control device such as the microcomputer 15 and controlled by a timer provided in the microcomputer 15. The

  The output voltage of the resonator 1 can be adjusted by the pulse width of the drive signal of the inverter 20, and becomes the maximum when the duty cycle is 50%, and the output becomes small even if it becomes larger or smaller than 50%.

  The above-described high frequency tuning capacitance switch circuit 12 can be controlled at high speed within one cycle of high frequency. Therefore, in the intermittent high frequency output operation, when the output is stopped, the high frequency tuning capacitance switch circuit 12 has a half cycle in which a current flows through the diode 3 connected in parallel to the transistor 4 or the diode 3 connected in parallel to the transistor 8. When the transistor 4 or the transistor 8 is turned off during the period, the current continues to flow through the diode 3 until the direction of the current changes, and the transistor 4 of the switch element 7 is cut off at the timing when the direction of the current changes, and the switch element 7 is cut off. .

  At that moment, all the energy of the resonator 1 exists as the electric charge of the capacitor 5 (51, 52), and is stored and stored in the capacitor 5 (51, 52) clamped at the positive maximum voltage of the high frequency output. Each capacitor 5 (51, 52) immediately stops the output operation in that state. When the output is resumed, by controlling the timing of the drive signal of the switch element 7 and the resonator 1, it becomes possible to start up the output with an amplitude close to a steady state using this stored charge. Furthermore, it is possible to generate a high frequency signal while changing the frequency in a short time. It should be noted that the correction capacitor 52 unnecessary for tuning is always cut off and no current flows.

  A high-efficiency control method using the above operation will be described with reference to FIGS. FIG. 4 is a diagram for explaining the operation when output is stopped in the multi-frequency transmission / reception circuit of this embodiment, and FIG. 5 is a diagram for explaining the operation when output is resumed in the multi-frequency transmission / reception circuit of this embodiment.

  The capacitance control signal is a control signal for the capacitance control switch element 7 that individually controls all the capacitors 5 (51, 52) used as the resonance capacitance. When the capacitance control signal is at a high level, the switch element 7 that controls the capacitor 5 (51, 52) used as the tuning capacitance is selectively turned on to achieve tuning. When the output is stopped, as shown in FIG. 4, the output of the inverter 20 as the drive transistor may be cut off while a negative current is flowing through the capacitance control switch element 7, and the control signal for controlling the drive transistor It shows that there is a half-cycle time margin in the input timing. When the output stops, energy is accumulated in the capacitor 5 of the resonator 1.

  Further, when the output is resumed, the energy accumulated in the capacitor 5 (51, 52) is used, and as shown in FIG. 5, the signal output starts to oscillate with a substantially steady state amplitude from the beginning, and generates a high-frequency signal with a good rise. It can also be generated. That is, after the switch element 7 that controls the capacitor 5 (51, 52) is selectively turned on so as to be in a tuned state, the multi-frequency transmission / reception circuit is operated with a drive signal delayed by 90 degrees from the timing. A multi-frequency transmission / reception circuit that performs such control to generate a high-frequency intermittent output not only becomes a power-efficient device but also can stop the output instantaneously.

  In store security systems equipped with a resonator with the same frequency as the high frequency excitation signal, the security tag uses the characteristic of continuing to emit a damped vibration wave for a while after the high frequency excitation signal is lost. The presence of a security tag is detected. For this reason, by using the above-described configuration, it is possible to improve the reliability of detecting the damped vibration wave of the security tag in the store security system.

As described above, in the high-frequency tuning capacitance switch circuit 12 of the present embodiment, the multi-frequency transmission / reception circuit is configured by controlling and combining the connection and non-connection of the plurality of capacitors 5 (51, 52) having different tuning capacitances. Can be tuned by obtaining the maximum output, and can be tuned even using the current waveform and voltage waveform. By controlling the switch element 7, it is possible to control the connection and release of the capacitors 5 (51, 52) within one cycle of the high frequency, so that it is possible to generate a high-frequency signal with an intermittent output that is efficient and well cut. Become.
(Embodiment 2)
Next, another embodiment of the present invention will be described. When the multi-frequency transmission / reception circuit described above is operated to transmit, when the output is stopped, the multi-frequency transmission / reception circuit may cause a damped vibration at a frequency higher than the set frequency to generate spurious. This embodiment suppresses this spurious.

  As shown in FIG. 4, in the multi-frequency transmission / reception circuit, the voltage and current waveforms change in a substantially sinusoidal shape during the output operation, and their phases are shifted by 90 degrees. When stopping the output, the output operation can be stopped at the next positive current period by cutting the capacity control signal during the negative current output period, and most of the energy during the output operation is tuned. Can be stored in a capacitor.

  This operation is enabled by the diode 3 added to the transistors 4 and 6 used as the switch element 7. That is, a negative current flows through the diode 3 during a period in which the current output is negative, and a negative current can flow even if there is no control signal for conducting the resonant capacitance to the switch element 7. .

  However, it is an ideal diode that can be cut off immediately when the negative current becomes zero, and a normal diode accumulates charge at the junction of the diode when positive forward current is flowing, and the charge is It gradually disappears by recombination in the crystal with time. However, if a reverse voltage is applied to the diode, it will flow for a while until the charge disappears as a current for extracting the accumulated charge, which causes spurious generation.

  FIG. 8 shows an operation waveform in which an actual spurious is generated. The waveform shown in the lower part of FIG. 8 is the waveform of the voltage measurement point of the circuit of FIG. 1, and the waveform shown in the upper part is the voltage waveform at the drain of the main control MOS transistor, causing a damped oscillation at a high frequency. This damped oscillation not only causes unwanted radiation as spurious, but the initial rebound voltage is extremely high, and the breakdown voltage of the transistor must be able to withstand this voltage.

  However, the built-in diode that flows a current equivalent to the maximum operating current of the transistor stores a considerable amount of accumulated charge due to the diode forward current flowing so far, and reverse cutoff recovery takes time. Become. When the waveform during the operation stop operation in FIG.

  Originally, the stop operation is completed when the voltage waveform reaches the minimum value as shown in FIG. However, in the actual voltage waveform shown in the lower part of FIG. 8, the voltage suddenly jumps in the positive direction for a while from the minimum value. At this time, the charge accumulated in the reverse direction diode 3 has disappeared, and it is time for the transistor 4 and the diode 3 that control the capacitance to be completely cut off.

  However, in the configuration shown in FIG. 1, the diode 3 is turned on and a positive current flows through the coil 2 until it is cut off. Then, the coil 2 excites a drain-source (collector-emitter) capacitance of the transistor 4 to be controlled and a resonant circuit made up of the stray capacitance of the wiring and the coil in order to maintain the current that has been flowing so far. Then, it operates at a high frequency with a high voltage.

  When this oscillating operation starts, the diode 3 incorporated in the transistor 4 is continuously applied with a forward voltage and a reverse voltage, so that charges are stored in the forward direction, and the conduction state is established using the charges accumulated in the reverse direction. Continue to vibrate while maintaining. At this time, only the charge stored in the forward direction cannot maintain the same reverse conduction state, and the vibration is attenuated by the loss of the resonance circuit.

For this reason, the following measures are desired.
(1) Reduce the accumulated charge of the reverse diode.
(2) The energy of the damped vibration due to the accumulated charge of the reverse diode is quickly absorbed.

  As the method (1), there is a method of improving by utilizing a diode having a small forward voltage drop and a small accumulated charge, for example, a Schottky barrier diode. In the control circuit using the bipolar transistor 6 shown in FIG. 3, a Schottky barrier diode may be used as the diode 3. However, in the case of the MOS transistor 4 shown in FIG. 2, the diode 3 is incorporated from the beginning. In this case, since the forward voltage drop of the Schottky barrier diode is lower than that of the junction type diode, by connecting the Schottky barrier diode in parallel between the drain and the source of the MOS transistor 4, almost no forward current is generated. Accumulated charge can be reduced by flowing through the Schottky barrier diode.

  However, the current Schottky barrier diode has a small forward voltage drop but a low reverse withstand voltage and a large reverse leakage current. For this reason, it is difficult to increase the output and the loss during operation increases, and the development of a diode with good characteristics is desired.

  The present embodiment relates to the method (2), and energy that is damped and oscillated at a high frequency for a while due to the electric charge accumulated in the diode in the stop operation is consumed by the series circuit of the capacitor C and the resistor R to be quickly attenuated. The vibration is terminated.

  FIG. 6 shows a configuration for suppressing spurious in the multi-frequency transmission / reception circuit according to the present embodiment. A series circuit of an appropriate capacitance C and an appropriate resistor R for suppressing spurious, that is, a capacitor 511 and a resistor 512 is shown. Is provided in parallel with the diode 3 and added to the switch element 7. Note that the multi-frequency transmission / reception circuit controls a plurality of small correction capacitor correction capacitors 52 for fine adjustment in addition to the main capacitor 51 by the switch element 7 in order to achieve tuning. Even in such a circuit, the series circuit of the capacitor C and the resistor R may be attached only to the switch element 7 forming a circuit for controlling the main capacitor 51 of the main capacitor in order to suppress spurious.

  This is because the main capacitor 51 and the correction capacitor 52 are connected when they are tuned, and are coupled with sufficiently low impedance due to their capacitances for high spurious frequencies.

  In the multi-frequency transmission / reception circuit in which the switch element 7 that controls the conduction of the main capacitor 51 having the main capacity is provided with a series circuit of the capacitor 511 and the resistor 512, the operation is suppressed with spurious as shown in FIG.

  That is, the transistor 4 is cut off when the charge stored in the diode 3 is lost, and the voltage jumps rapidly. The current flowing at this time is passed through a series circuit of the capacitor 511 and the resistor 512, and the energy is absorbed by the resistor R of the resistor 512, whereby subsequent vibrations can be suppressed.

  In FIG. 7, there is a spike-like voltage at the beginning of the stop operation, but it can be seen that the energy that causes vibration is absorbed and stabilized immediately during this operation. As described above, the energy that causes the damped oscillation due to the accumulated charge of the diode 3 when the output is stopped causes the loss of the circuit even if spurious is generated or suppressed by the series circuit of the resistor 512 and the capacitor 511. Become. This is a factor of the operation in which the amplitude starts slightly smaller and gradually approaches the steady amplitude in several cycles in the early stage of output restart.

DESCRIPTION OF SYMBOLS 1 Resonator 2 Coil 3 Diode 4 Bipolar transistor 5 Capacitor 6 MOS transistor 7 Switch element 8 Pch transistor 9 Nch transistor 10 Gate driver 11 Gate driver 12 High frequency tuning capacity switch circuit 13 Diode 14 Current measurement resistance 15 Microcomputer 20 Resonator 21 Coil 22 capacitor 23 capacitor 24 diode 25 diode 26 DC power supply 27 transistor 28 resistor 29 capacitor 30 amplifier 31 resistor 32 capacitor 51 main capacitor 52 correction capacitor 511 capacitor 512 resistor

Claims (7)

A resonator composed of a coil and a plurality of capacitors connected in series with each other and connected in parallel to each other, a plurality of switching elements that respectively control conduction of the capacitors, and connected to the coils A drive transistor,
The plurality of capacitors include one main capacitor having a main capacity and one or more correction capacitors having a correction capacity smaller than the main capacity,
Each switch element has a diode connected in series with the capacitor and flowing in the reverse current direction. The switch element receives and opens a capacitance control signal, selects a main capacitor activated by conduction and a correction capacitor to be added. A multi-frequency transmission / reception circuit, wherein a resonance frequency of the resonator is adjusted by a capacitance of a capacitor and a selected correction capacitor.   2. The multi-frequency transmission / reception circuit according to claim 1, wherein the switch element includes a bipolar transistor and the diode that causes a collector reverse current to flow between a collector and an emitter of the bipolar transistor.   2. The multi-frequency transmission / reception circuit according to claim 1, wherein the switch element includes a MOS transistor and the diode that allows a drain reverse current to flow between a drain and a source of the MOS transistor.   The multi-frequency transmission / reception circuit according to any one of claims 1 to 3, wherein the correction capacity of each correction capacitor is a power of 2 with respect to the capacity of the correction capacitor having the minimum correction capacity. .   A control device and a measurement device, wherein the measurement device measures a current value or phase of a resonance signal flowing through the resonator, and the control device controls the capacity so that the current value or the phase becomes a predetermined value. 5. The multi-frequency transmission / reception circuit according to claim 1, wherein the signal is automatically controlled.   In the output stop operation, the switching element is cut off at a timing when a reverse current flows through the diode, whereby the energy of the resonator is stored in the main capacitor and the correction capacitor, and the main capacitor and the correction capacitor are controlled when the output is resumed. After the switch element is selectively turned on so as to be in a tuned state, the drive transistor drive signal is input 90 degrees later than the timing to perform the output operation, thereby releasing the energy stored when the output is stopped. The multi-frequency transmission / reception circuit according to claim 1, wherein the output is restarted.   The switch element for controlling the conduction of the main capacitor forming the main capacitor is provided with a series circuit of a capacitor and a resistor for suppressing a bias in parallel with the diode. Multi-frequency transceiver circuit.

Images