Radio wave emitting device

Abstract

This radio wave radiation device comprises a cavity, a signal generation unit, a signal amplification unit, a radio wave radiation unit, a control unit, an open / close detection unit, and a gate voltage control circuit. The cavity has a door and houses an object. The signal generation unit generates a high frequency signal. The signal amplification unit has at least one amplifier including a transistor, and amplifies the high frequency signal. The radio wave radiation unit radiates radio waves corresponding to the high frequency signal amplified by the signal amplification unit toward the object. The control unit controls the signal generation unit and the signal amplification unit. The open / close detection unit detects and notifies an open state and a closed state of the door. The gate voltage control circuit, when notified of the open state of the door from the open / close detection unit, controls a gate voltage of the transistor included in the at least one amplifier of the signal amplification unit, to thereby stop the radiation of radio waves.

Description

[Technical Field]

[0001] The present disclosure relates to radio wave emitting devices. [Background technology]

[0002] Patent Document 1 discloses a microwave cooking device, which is a type of radio wave emitting device. As disclosed in Patent Document 1, the microwave cooking device includes a door that covers the front opening of a cavity, and a high-frequency power supply for providing high-frequency radio waves. The high-frequency power supply includes a high-frequency oscillation circuit, at least one semiconductor amplifier, a door switch (open / close detection unit), and a control unit.

[0003] The high-frequency oscillator circuit generates a high-frequency signal at a specified frequency within a predetermined frequency band. At least one semiconductor amplifier amplifies the high-frequency signal from the high-frequency oscillator circuit. The door switch detects whether the door is open or closed. The control unit stops the high-frequency oscillator circuit when the door is opened while radio waves are being emitted, thereby stopping the emission of high-frequency radio waves. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 78898 Summary of the Invention

[0005] In this type of radio wave emitting device, it is desired to further shorten the time it takes for the radiation of radio waves to stop after the door is opened. An object of the present disclosure is to provide a radio wave emitting device that can quickly stop the radiation of radio waves when the door of the cavity is opened during radiation of radio waves.

[0006] A radio wave emitting device according to one aspect of the present disclosure includes a cavity, a signal generating unit, a signal amplifying unit, a radio wave emitting unit, a control unit, an open / close detection unit, and a gate voltage control circuit. The signal generating unit generates a high-frequency signal. The signal amplifying unit has at least one amplifier with a transistor and amplifies the high-frequency signal. The radio wave emitting unit radiates radio waves to an object in accordance with the high-frequency signal amplified by the signal amplifying unit.

[0007] The control unit controls the signal generating unit and the signal amplifying unit. The open / close detection unit detects and notifies whether the door is open or closed. When the open / close detection unit notifies the door that it is open, the gate voltage control circuit controls the gate voltage of a transistor included in at least one amplifier of the signal amplifying unit to stop the emission of radio waves.

[0008] This aspect provides a radio wave emitting device that can quickly stop radio wave radiation when the cavity door is opened during radio wave radiation. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a circuit diagram illustrating an example of a radio wave emission device according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a circuit diagram showing an example of an amplifier of the signal amplifying unit in the radio wave emitting device according to the first embodiment. [Figure 3] FIG. 3 is a waveform diagram showing an example of the operation of stopping radio wave radiation in the radio wave radiation device according to the first embodiment. [Figure 4] FIG. 4 is a circuit diagram showing an example of a radio wave emitting device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings, where appropriate. However, detailed descriptions of known matters and redundant descriptions of substantially identical configurations may be omitted.

[0011] (Embodiment 1) 1 is a circuit diagram illustrating an example of a radio wave emission device 1 according to a first embodiment of the present disclosure. As shown in Fig. 1, the radio wave emission device 1 is, for example, a microwave oven that emits radio waves into a cavity 20 to dielectrically heat an object 21, such as food, contained in the cavity.

[0012] The cavity 20 is a heating chamber having a rectangular parallelepiped shape and includes a main body 20a and a door 20b. The main body 20a includes walls (left wall, right wall, bottom wall, top wall, and back wall) made of a material that blocks radio waves, for example. The door 20b is attached to cover the front opening of the main body 20a.

[0013] In this disclosure, shielding means attenuating the energy of radio waves by absorption or the like, or confining the radio waves within the cavity 20 by reflection, multiple reflection, etc. To shield radio waves, materials that reflect radio waves, such as metal materials, and materials that absorb radio waves, such as ferrite rubber, are used.

[0014] As shown in FIG. 1, the radio wave emission device 1 includes a signal generating unit 2, a signal amplifying unit 3, a radio wave emitting unit 4, a control unit 5, an open / close detecting unit 6, a gate voltage control circuit 7, a bias voltage control circuit 8, a DC power supply 9, a variable amplifier 10, and an isolator 11.

[0015] The signal generating unit 2 generates a high-frequency signal having an arbitrary frequency within a predetermined frequency band in accordance with instructions from the control unit 5. The frequency band of the high-frequency signal is, for example, 1 MHz to 10 GHz. The radio wave emitting device 1 heats the object 21 by emitting radio waves corresponding to the high-frequency signal in this frequency band.

[0016] The signal generating unit 2 includes a voltage controlled oscillator and generates a high frequency signal. When generating a plurality of high frequency signals over a wider band, the signal generating unit 2 may include a PLL (phase lock loop) frequency synthesizer.

[0017] 1, signal generating section 2 is connected to signal amplifying section 3 via variable amplifier 10. Variable amplifier 10 adjusts the power of the high frequency signal from signal generating section 2, and is, for example, a digital attenuator.

[0018] The signal amplifying unit 3 amplifies the high-frequency signal from the signal generating unit 2 and provides the amplified high-frequency signal. The signal amplifying unit 3 has at least one amplifier. In this embodiment, the signal amplifying unit 3 has multiple amplifiers (amplifiers 30a, 30b). Hereinafter, the amplifiers 30a, 30b may be collectively referred to as amplifier 30.

[0019] Fig. 2 is a circuit diagram showing an example of the amplifier 30 of the signal amplification unit 3 in the radio wave emission device 1. As shown in Fig. 2, the amplifier 30 includes a transistor 31, an input matching circuit 32, an output matching circuit 33, choke circuits 34 and 35, capacitors C1 and C2, and a resistor R1.

[0020] The amplifier 30 has an input terminal RFin, an output terminal RFout, a gate bias terminal Vin, and a power supply terminal Vdd. The input terminal RFin is connected to the signal generating unit 2 via a variable amplifier 10. The output terminal RFout is connected to the radio wave emitting unit 4 via an isolator 11.

[0021] The transistor 31 is, for example, a field-effect transistor. The transistor 31 is, for example, a normally-on type transistor. The source terminal of the transistor 31 is grounded. Therefore, the amplifier 30 is a source-grounded circuit. The transistor 31 amplifies a high-frequency signal input to its gate terminal and outputs the amplified high-frequency signal from its drain terminal.

[0022] The amplifier 30 includes an input matching circuit 32 and an output matching circuit 33, which are respectively arranged in the input path and output path of the high-frequency signal. More specifically, the input matching circuit 32 is connected between the gate terminal of the transistor 31 and the input terminal RFin. The output matching circuit 33 is connected between the drain terminal of the transistor 31 and the output terminal RFout.

[0023] The input matching circuit 32 matches the impedance of the transistor 31 with the impedance on the variable amplifier 10 side, allowing high-frequency signals to pass efficiently. The output matching circuit 33 matches the impedance of the transistor 31 with the impedance on the isolator 11 side, allowing high-frequency signals to pass efficiently.

[0024] The amplifier 30 includes a circuit arranged in the gate bias path, the circuit being composed of a capacitor C1, a choke circuit 34, and a resistor R1. More specifically, a series circuit of the choke circuit 34 and the resistor R1 is connected between the gate bias terminal Vin and the gate terminal of the transistor 31. The capacitor C1 is connected between the gate bias terminal Vin, the choke circuit 34, and ground.

[0025] The capacitor C1 functions as a bypass capacitor to reduce power supply noise. The choke circuit 34 prevents high frequency signals from leaking into the bias circuit. The resistor R1 suppresses abnormal oscillations caused by gate bias noise.

[0026] The amplifier 30 includes a circuit arranged in the power supply path, the circuit being composed of a capacitor C2 and a choke circuit 35. More specifically, the choke circuit 35 is connected between the power supply terminal Vdd and the drain terminal of the transistor 31. The capacitor C2 is connected between the power supply terminal Vdd, the choke circuit 35, and ground.

[0027] Capacitor C2 functions as a bypass capacitor to reduce power supply noise. Choke circuit 35 prevents high frequency signals from leaking into the bias circuit.

[0028] 1, the signal amplification unit 3 is a multi-stage amplifier configured by connecting an amplifier 30a and an amplifier 30b in series. The amplifier 30a is a driver stage (input stage) amplifier, and the amplifier 30b is a final stage (output stage) amplifier.

[0029] The amplifier 30 receives a small high-frequency signal generated by the signal generating unit 2 and outputs a high-frequency signal of the desired magnitude by amplifying the high-frequency signal multiple times using a multi-stage amplifier. For example, amplifier 30a amplifies a 0.1 mW high-frequency signal to generate a 10 W high-frequency signal. Amplifier 30b amplifies the 10 W high-frequency signal to generate a 250 W high-frequency signal. This configuration gives the signal amplifying unit 3 excellent wideband characteristics. Since the amplification rate per amplifier in the signal amplifying unit 3 is small, heat generation can also be suppressed.

[0030] 1, the signal amplifier 3 is connected to the radio wave emitting section 4 via an isolator 11. This makes it possible to protect the signal amplifier 3 from high frequency signals from the outside.

[0031] The radio wave emitting unit 4 is, for example, an antenna that radiates radio waves corresponding to the high-frequency signal amplified by the signal amplifier 3 into the cavity 20. As shown in FIG. 1 , the radio wave emitting unit 4 is, for example, disposed in the cavity 20 and radiates radio waves into the cavity 20.

[0032] The open / close detection unit 6 detects the open state and the closed state of the door 20b and notifies the control unit 5 of the result. The open / close detection unit 6 includes, for example, a detection switch that is turned on when the door 20b is closed and turned off when the door 20b is open.

[0033] For example, the detection switch is disposed on the main body 20a of the cavity 20. When the door 20b is closed, the detection switch is operated by a protrusion on the surface of the door 20b. The open / close detection unit 6 can detect the open or closed state of the door 20b based on the on or off state of the detection switch.

[0034] The open / close detection unit 6 outputs a low (L) level detection signal S1 when the door 20b is open, and outputs a high (H) level detection signal S1 when the door 20b is closed (see FIG. 3 described later).

[0035] The detection signal S1 at L level is a signal for notifying that the door 20b is in an open state. The detection signal S1 at H level is a signal for notifying that the door 20b is in a closed state. The open / close detection unit 6 can be realized by a well-known configuration. For example, it is possible to detect the open and closed states of the door 20b by using a proximity switch.

[0036] The gate voltage control circuit 7 controls the gate voltage of the transistor 31 included in at least one amplifier 30 of the signal amplification unit 3. In this embodiment, the gate voltage control circuit 7 controls the gate voltage of each of the transistors 31 of the amplifiers 30a and 30b of the signal amplification unit 3.

[0037] In particular, when the gate voltage control circuit 7 receives an L-level detection signal S1 from the open / close detection unit 6 and recognizes that the door 20b is open, it controls the gate voltage of the transistor 31 included in at least one of the amplifiers 30a and 30b of the signal amplification unit 3 to stop the emission of radio waves.

[0038] As shown in FIG. 1, the gate voltage control circuit 7 includes D / A (digital / analog) converters 70a and 70b, voltage shift circuits 71a and 71b, buffer amplifiers 72a and 72b, switch elements 73a and 73b, a reference power supply 74, and a latch circuit 75.

[0039] The D / A converter 70a is a gate bias circuit connected to the gate terminal of the transistor 31 of the amplifier 30a to provide a gate voltage. The D / A converter 70b is a gate bias circuit connected to the gate terminal of the transistor 31 of the amplifier 30b to provide a gate voltage. More specifically, the gate terminal of the transistor 31 of the amplifiers 30a and 30b is the gate bias terminal Vin shown in FIG. 2.

[0040] The gate bias circuit provides a gate voltage to the transistor 31 to operate the transistor 31 in the driving region. The D / A converters 70a and 70b convert the digital signal from the control unit 5 into a DC voltage and output the DC voltage, thereby providing the gate voltage to the transistor 31.

[0041] The output voltage of D / A converter 70a is input to the gate terminal of transistor 31 of amplifier 30a via voltage shift circuit 71a and buffer amplifier 72a. The output voltage of D / A converter 70b is input to the gate terminal of transistor 31 of amplifier 30b via voltage shift circuit 71b and buffer amplifier 72b.

[0042] Since the output voltage of the D / A converter 70a is a positive voltage, the voltage shift circuit 71a shifts the output voltage to a negative voltage and supplies it to the gate terminal of the transistor 31 of the amplifier 30a.

[0043] 1 is based on the premise that amplifier 30a includes a normally-on type transistor that controls the amount of current by applying a negative voltage, such as a gallium nitride HEMT (high electron mobility transistor) structure. The operating state of the gate terminal is compared using a potential difference and output to control unit 5.

[0044] Since the output voltage of D / A converter 70b is a positive voltage, voltage shift circuit 71b shifts the output power to a negative voltage and supplies it to the gate terminal of transistor 31 of amplifier 30b. The configuration shown in FIG. 1 assumes that amplifier 30b includes a normally-on type transistor. The operating state of the gate terminal is compared using a potential difference and output to control unit 5.

[0045] The switch element 73a is connected between the gate terminal of the transistor 31 of the amplifier 30a and the reference power supply 74. More specifically, one end of the switch element 73a is connected between the voltage shift circuit 71a and the buffer amplifier 72a and is connected to the gate terminal of the transistor 31 of the amplifier 30a.

[0046] The switch element 73b is connected between the gate terminal of the transistor 31 of the amplifier 30b and the reference power supply 74. More specifically, one end of the switch element 73b is connected between the voltage shift circuit 71b and the buffer amplifier 72b, and is connected to the gate terminal of the transistor 31 of the amplifier 30b. The switch elements 73a and 73b are, for example, transistors.

[0047] The reference power supply 74 provides a reference voltage for turning off the transistor 31 of each of the amplifiers 30a and 30b. The transistor 31 is, for example, a normally-on type, and the reference voltage is a negative voltage (for example, −5 V). The reference power supply 74 generates the reference voltage based on the output voltage from the DC power supply 9. If the transistor 31 is a normally-off type, the reference voltage may be a ground voltage.

[0048] The latch circuit 75 controls the switch elements 73a and 73b. When the latch circuit 75 receives an L-level detection signal S1 from the open / close detection unit 6 and is notified that the door 20b is open, the latch circuit 75 maintains the switch elements 73a and 73b in the ON state. When the latch circuit 75 receives a reset signal S2 from the control unit 5, the latch circuit 75 turns off the switch elements 73a and 73b.

[0049] In the gate voltage control circuit 7, the switch elements 73a and 73b are in the off state until the latch circuit 75 receives the low-level detection signal S1. The output voltages of the D / A converters 70a and 70b are input to the gate terminals of the transistors 31 of the amplifiers 30a and 30b, and provide the gate voltages of the transistors 31 of the amplifiers 30a and 30b.

[0050] When the latch circuit 75 receives the low-level detection signal S1, it turns on the switch elements 73a and 73b. A reference voltage is input from the reference power supply 74 to the gate terminals of the transistors 31 of the amplifiers 30a and 30b, turning off the transistors 31 of the amplifiers 30a and 30b.

[0051] This stops the operation of amplifiers 30a and 30b, and stops the radiation of radio waves from radio wave emitting unit 4. At this time, control unit 5 shifts the output voltages of D / A converters 70a and 70b to a standby state (reference voltage).

[0052] The latch circuit 75 performs analog control on the switch elements 73a and 73b. As will be described later, the control unit 5 can turn on the switch elements 73a and 73b faster than when the control unit 5 performs digital control on the switch elements 73a and 73b. Digital control of the switch elements will be described later.

[0053] When the latch circuit 75 receives the reset signal S2 from the control unit 5, it turns off the switch elements 73a and 73b. Therefore, the control unit 5 controls the output voltages of the D / A converters 70a and 70b, thereby enabling the radio wave emitting unit 4 to resume emitting radio waves.

[0054] The bias voltage control circuit 8 controls the bias voltage supplied from the DC power supply 9 to the drain terminal of the transistor 31 included in at least one amplifier of the signal amplification unit 3. In this embodiment, the bias voltage control circuit 8 controls the bias voltage supplied from the DC power supply 9 to the drain terminal of the transistor 31 included in each of the amplifiers 30 a and 30 b of the signal amplification unit 3.

[0055] The bias voltage supplied to amplifier 30a may be different from that supplied to amplifier 30b depending on the output power levels of amplifier 30a and amplifier 30b and the type of transistor 31. For example, the bias voltage supplied to amplifier 30a, which has a relatively low power level, may be 30V, and the bias voltage supplied to amplifier 30b, which has a relatively high power level, may be 48V.

[0056] As shown in FIG. 1, the bias voltage control circuit 8 includes switch elements 80a and 80b and a latch circuit 81.

[0057] The switch element 80a is connected between the DC power supply 9 and the drain terminal of the transistor 31 of the amplifier 30a. The switch element 80b is connected between the DC power supply 9 and the drain terminal of the transistor 31 of the amplifier 30b. The switch elements 80a and 80b are, for example, transistors. More specifically, the drain terminals of the transistors 31 of the amplifiers 30a and 30b are connected to the power supply terminal Vdd shown in FIG. 2.

[0058] The latch circuit 81 controls the switch elements 80a and 80b. When the latch circuit 81 receives an L-level detection signal S1, it maintains the switch elements 80a and 80b in the OFF state. That is, when the latch circuit 81 is notified by the open / close detection unit 6 that the door 20b is open, it maintains the switch elements 80a and 80b in the OFF state. When the latch circuit 81 receives a reset signal S2 from the control unit 5, it turns on the switch elements 80a and 80b.

[0059] In the bias voltage control circuit 8, the switch elements 80a and 80b are in the ON state until the latch circuit 81 receives the L-level detection signal S1. The DC power supply 9 provides a drain voltage to the drain terminal of each of the transistors 31 in the amplifiers 30a and 30b.

[0060] When the latch circuit 81 receives the low-level detection signal S1, it turns off the switch elements 80a and 80b. As a result, the DC power supply 9 is disconnected from the drain terminal of each of the transistors 31 in the amplifiers 30a and 30b. This stops the operation of each of the amplifiers 30a and 30b, and stops the radiation of radio waves from the radio wave emitter 4.

[0061] The latch circuit 81 performs analog control on the switch elements 80a and 80b. Meanwhile, as will be described later, the control unit 5 includes a processor. When the control unit 5 performs digital control on the switch elements 80a and 80b, the response of the control depends on the cycle of software control in the processor. Therefore, the analog control by the latch circuit 81 can turn off the switch elements 80a and 80b faster than the digital control by the control unit 5.

[0062] When the latch circuit 81 receives the reset signal S2 from the control unit 5, it turns on the switch elements 80a and 80b, thereby enabling the radio wave emitting unit 4 to resume emitting radio waves.

[0063] The DC power supply 9 generates one or more predetermined DC voltages. These DC voltages are used, for example, as bias voltages for the amplifiers 30a and 30b of the signal amplifier 3, and as drive power sources for the signal generator 2, the control unit 5, the gate voltage control circuit 7, and the bias voltage control circuit 8. For this purpose, the DC power supply 9 is connected to a commercial AC power supply and includes a well-known rectifier circuit.

[0064] 1, when the signal amplifying unit 3 includes amplifiers 30a and 30b, the signal amplifying unit 3 amplifies the low-power-level high-frequency signal from the signal generating unit 2 in two stages to a final output power level. Each of the amplifiers 30a and 30b may use a type of transistor 31 according to the power level of the high-frequency signal to be output.

[0065] The input and output impedances depend on the type of transistor 31. Therefore, the circuit configurations of the input matching circuit 32 and the output matching circuit 33 may be adjusted according to the type of transistor 31. The gate bias path (the circuit configuration of the choke circuit 34, resistor R1, and capacitor C1) and the power supply path (the choke circuit 35 and capacitor C2) may also be adjusted according to the type of transistor 31.

[0066] The control unit 5 controls the signal generating unit 2 and the signal amplifying unit 3 to emit radio waves from the radio wave emitting unit 4 to the object 21 in the cavity 20. The control unit 5 includes, for example, one or more processors and one or more semiconductor memories. The control unit 5 may include, for example, an FPGA (field-programmable gate array) or an ASIC (application specific integrated circuit).

[0067] To control the signal amplifier 3, the control unit 5 causes the gate voltage control circuit 7 to set the gate voltages of the amplifiers 30a and 30b.

[0068] More specifically, the control unit 5 outputs a digital signal corresponding to the target voltage of the gate terminal to the D / A converters 70a and 70b of the gate voltage control circuit 7. The D / A converters 70a and 70b convert the digital signal into a DC voltage and output it. This allows the control unit 5 to set the gate voltage of each transistor 31 in the amplifiers 30a and 30b to the target voltage.

[0069] When the gate voltage of transistor 31 of amplifier 30 (30a or 30b) is the reference voltage and the control unit 5 receives an H-level detection signal S1 notifying of a closed state from open / close detection unit 6, the control unit 5 outputs a reset signal S2 to latch circuit 75. Similarly, when the gate voltage of transistor 31 of amplifier 30 (30a or 30b) is the reference voltage and the control unit 5 receives an H-level detection signal S1, the control unit 5 outputs a reset signal S2 to latch circuit 81.

[0070] More specifically, the control unit 5 determines whether the gate voltage of the transistor 31 of the amplifier 30 is at the reference voltage. Based on this determination, the control unit 5 determines whether the radio wave radiation has stopped because the door 20b is open. If the gate voltage of the transistor 31 of the amplifier 30 is at the reference voltage, the control unit 5 determines that the radio wave radiation has stopped; if not, the control unit 5 determines that the radio wave radiation has not stopped.

[0071] When the door 20b is open and radio wave radiation is stopped, upon receiving the detection signal S1 at H level, the control unit 5 outputs a reset signal S2 to the latch circuits 75 and 81. This puts the radio wave radiation device 1 into a standby state, enabling it to resume radio wave radiation.

[0072] When the control unit 5 receives the detection signal S1 at an L level, it stores the control states of the signal generating unit 2 and the signal amplifying unit 3. The control states of the signal generating unit 2 and the signal amplifying unit 3 may include, for example, parameters for defining the frequency and output of the radio waves from the radio wave emitting unit 4, as well as the elapsed time since the radio waves were emitted from the radio wave emitting unit 4. The control states of the signal generating unit 2 and the signal amplifying unit 3 may be stored, for example, in a semiconductor memory of the control unit 5.

[0073] When the control unit 5 receives the H-level detection signal S1, it resumes control of the signal generating unit 2 and the signal amplifying unit 3 based on the stored control state. This allows the control unit 5 to continue control of the signal generating unit 2 and the signal amplifying unit 3 after the door 20b is opened or closed.

[0074] As described above, in the radio wave emission device 1, when the gate voltage control circuit 7 receives the detection signal S1 at an L level, it controls the bias voltage to stop the emission of radio waves. When the bias voltage control circuit 8 receives the detection signal S1 at an L level, it controls the bias voltage to stop the emission of radio waves.

[0075] Therefore, it is possible to stop the radiation of radio waves even if a malfunction occurs in the gate voltage control circuit 7 or the bias voltage control circuit 8. This improves the robustness of stopping the radiation of radio waves when the door 20b is opened.

[0076] When the gate voltage control circuit 7 and the bias voltage control circuit 8 are used together, the gate voltage control circuit 7 may be used to stop the radio wave radiation from the radio wave radiation unit 4, and then the bias voltage control circuit 8 may be used to perform control.

[0077] In particular, the gate voltage control circuit 7 stops the emission of radio waves earlier than the bias voltage control circuit 8 stops the emission of radio waves. This point will be described with reference to FIG.

[0078] Fig. 3 is a waveform diagram showing an example of the operation of stopping radio wave radiation in the radio wave radiation device 1 of Fig. 1. In Fig. 3, Vo is the output voltage of the DC power supply 9, which corresponds to the bias voltage supplied to the amplifier 30. W is the output power of the high-frequency signal, which corresponds to the strength of the radio wave from the radio wave radiation unit 4. Vg represents the voltage (gate voltage) at the gate terminal of the amplifier 30.

[0079] S1 is a detection signal from the open / close detection unit 6. In the detection signal S1, the H level and the L level correspond to the closed state of the door 20b and the open state of the door 20b, respectively.

[0080] 3, the door 20b is in a closed state until time t1, and radio waves are emitted from the radio wave emitting unit 4. The detection signal S1 is at an H level until time t1.

[0081] In the gate voltage control circuit 7, the switch elements 73a and 73b are in the OFF state, and the gate voltage Vg is provided, turning on the transistor 31. In the bias voltage control circuit 8, the switch elements 80a and 80b are in the ON state, and the DC power supply 9 provides the bias voltage Vo. This causes the radio wave emitting unit 4 to emit radio waves in response to the amplified high-frequency signal from the signal amplifier 3.

[0082] 3, when the door 20b opens at time t1, the detection signal S1 changes from H level to L level. That is, the open / close detection unit 6 provides the L-level detection signal S1 to the latch circuit 75 of the gate voltage control circuit 7 and the latch circuit 81 of the bias voltage control circuit 8.

[0083] In the gate voltage control circuit 7, when the latch circuit 75 receives the L-level detection signal S1, it turns on the switch elements 73a and 73b, thereby providing the reference voltage Vr from the reference power supply 74 to the gate terminal of the transistor 31 of the amplifier 30 (time t2).

[0084] In this case, it takes a time period from time t1 to time t2 for the voltage value to change due to the influence of factors such as discharge from capacitor C1 in the gate bias path. When transistor 31 of amplifier 30 turns off and amplifier 30 stops operating, the output power W of the high-frequency signal becomes zero (time t3). This causes radio wave radiation from radio wave radiator 4 to stop.

[0085] The time P1 from time t1 to time t2 is, for example, several nanoseconds to several microseconds, and the time P2 from time t2 to time t3 is, for example, several nanoseconds to several microseconds.

[0086] In the bias voltage control circuit 8, when the latch circuit 81 receives the L-level detection signal S1, it turns off the switch elements 80a and 80b. This disconnects the drain terminal of the transistor 31 of the amplifier 30 from the DC power supply 9.

[0087] However, due to factors such as the discharge from capacitor C2 in the power supply path of transistor 31, bias voltage Vo gradually decreases and eventually becomes zero (time t4). Bias voltage Vo has a higher voltage than gate voltage Vg and also has a large power supply capacity. For this reason, bias voltage Vo takes longer to change than gate voltage Vg.

[0088] At time t2, the transistor 31 is turned off, and therefore the signal amplifier 3 does not amplify the high-frequency signal from the signal generator 2. As a result, even if the bias voltage Vo is not zero, the radio wave emitter 4 stops emitting radio waves.

[0089] On the other hand, if the transistor 31 is not turned off at time t2, when the bias voltage Vo becomes zero, the radio wave radiation from the radio wave radiation portion 4 stops at time t4. The time P3 from time t2 to time t4 is, for example, several ms to several tens of ms.

[0090] In this way, when the bias voltage control circuit 8 stops the radio wave emission, the bias voltage Vo gradually decreases, so it takes some time for the radio wave emission to stop. On the other hand, when the gate voltage control circuit 7 stops the radio wave emission, the radio wave emission stops immediately when the transistor 31 is turned off.

[0091] Therefore, the gate voltage control circuit 7 stops the radio wave radiation earlier than the bias voltage control circuit 8 stops the radio wave radiation. That is, the radio wave radiation stops before the bias voltage Vo of the transistor 31 becomes zero.

[0092] Since the switch elements 80a and 80b are turned off when no current flows through the transistor 31, the possibility of problems such as contact welding occurring is reduced even if the switch elements 80a and 80b are mechanical contacts.

[0093] (Embodiment 2) 4 is a circuit diagram illustrating an example of a radio wave emission device 1A according to embodiment 2 of the present disclosure. As shown in FIG. 4, the radio wave emission device 1A includes a signal generating unit 2, a signal amplifying unit 3, a radio wave emitting unit 4, a control unit 5, an open / close detecting unit 6, a gate voltage control circuit 7A, a bias voltage control circuit 8, a DC power supply 9, a variable amplifier 10, and an isolator 11.

[0094] The gate voltage control circuit 7A includes integrating circuits 76a and 76b, voltage shift circuits 71a and 71b, buffer amplifiers 72a and 72b, switch elements 73a and 73b, a reference power supply 74, and a latch circuit 75.

[0095] The integrator circuit 76a is a gate bias circuit connected to the gate terminal of the transistor 31 of the amplifier 30a to provide a gate voltage. The integrator circuit 76b is a gate bias circuit connected to the gate terminal of the transistor 31 of the amplifier 30b to provide a gate voltage. More specifically, the gate terminal of the transistor 31 of the amplifiers 30a and 30b is the gate bias terminal Vin shown in FIG. 2.

[0096] The gate bias circuit provides a gate voltage to the transistor 31 to operate the transistor 31 in the driving region. The integrating circuits 76a and 76b receive a PWM (pulse width modulation) signal and output a DC voltage according to the received PWM signal.

[0097] In this embodiment, the control unit 5 provides a PWM signal to the integrating circuits 76a and 76b. The integrating circuits 76a and 76b provide a DC voltage corresponding to the PWM signal from the control unit 5 as the gate voltage of the transistor 31.

[0098] More specifically, the output voltage of integrator circuit 76a is provided to the gate terminal of transistor 31 of amplifier 30a via voltage shift circuit 71a and buffer amplifier 72a. The output voltage of integrator circuit 76b is provided to the gate terminal of transistor 31 of amplifier 30b via voltage shift circuit 71b and buffer amplifier 72b.

[0099] In controlling the signal amplifier 3, the control unit 5 causes the gate voltage control circuit 7A to set the gate voltage of the transistor 31 of each of the amplifiers 30 (30a, 30b). More specifically, the control unit 5 provides a PWM signal with a duty ratio corresponding to the gate target voltage to each of the integrator circuits 76a, 76b of the gate voltage control circuit 7. As a result, the control unit 5 sets the gate voltage of each of the transistors 31 of the amplifiers 30a, 30b to the target voltage.

[0100] (Variation) The present disclosure is not limited to the above-described embodiment. Modifications of the above-described embodiment will be described below. Each of the following modifications can be appropriately combined with the above-described embodiment and other modifications.

[0101] In one modification, the transistor 31 of the amplifier 30 may be a normally-off type. In this case, the reference voltage of the reference power supply 74 does not necessarily have to be a negative voltage. In this case, the voltage shift circuits 71a and 71b are not necessary.

[0102] In one modification, the number of amplifiers included in signal amplification unit 3 is not limited to two as in the above embodiment, but may be one, or three or more. The number of gate bias circuits included in each of gate voltage control circuits 7 and 7A may be set according to the number of amplifiers included in signal amplification unit 3. Similarly, the number of switch elements included in each of gate voltage control circuits 7 and 7A and the number of switch elements included in bias voltage control circuit 8 may be set according to the number of amplifiers included in signal amplification unit 3.

[0103] However, the number of gate bias circuits included in the gate voltage control circuits 7 and 7A does not necessarily have to match the number of amplifiers 30. Similarly, the number of switch elements in the gate voltage control circuits 7 and 7A and the number of switch elements included in the bias voltage control circuit 8 do not necessarily have to match the number of amplifiers 30.

[0104] For example, the gate bias circuit may be shared by multiple amplifiers. For example, the switch element 73a or the switch element 73b may be shared by multiple amplifiers. For example, the switch element 80a or the switch element 80b may be shared by multiple amplifiers.

[0105] In one variant, when the signal amplification unit 3 has multiple amplifiers 30, the gate voltage control circuits 7 and 7A may control the gate voltage of the transistor 31 of at least the output stage amplifier among the multiple amplifiers to stop the emission of radio waves.

[0106] In one modification, the gate voltage control circuits 7 and 7A may set the gate voltage of the transistor 31 of the amplifier 30 to a sufficiently low voltage, rather than to a voltage that turns off the transistor 31, to essentially stop the emission of radio waves.

[0107] In one modification, in the gate voltage control circuits 7 and 7A, the switch elements 73a and 73b are not limited to transistors, but may be semiconductor switches other than transistors, or mechanical contacts such as relays.

[0108] In one modification, instead of disconnecting the DC power supply 9 from the amplifier 30, the bias voltage control circuit 8 may lower the bias voltage sufficiently to substantially stop the radiation of radio waves.

[0109] In one modification, the switch elements 80a and 80b included in the bias voltage control circuit 8 are not limited to transistors, but may be semiconductor switches other than transistors, or mechanical contacts such as relays.

[0110] In one variation, the control unit 5 may output the reset signal S2 not only when it receives the detection signal S1 at an H level but also when an additional condition is satisfied. The additional condition is that it is confirmed that there is no problem with emitting radio waves. For example, if it is confirmed that turning on the transistor 31 does not cause any problem in the circuit of the radio wave emission device 1, the control unit 5 recognizes that there is no problem with emitting radio waves.

[0111] In one variation, the bias voltage control circuit 8, the variable amplifier 10 and the isolator 11 are optional components.

[0112] In one modification, the detection signal S1 may be set to H level and L level when the door 20b is in the open state and the closed state, respectively.

[0113] (Mode and effect) The radio wave emitting device 1 (1A) of the first aspect of the present disclosure comprises a cavity 20, a signal generating unit 2, a signal amplifying unit 3, a radio wave emitting unit 4, a control unit 5, an open / close detection unit 6, and a gate voltage control circuit 7 (7A).

[0114] The signal generating unit 2 generates a high-frequency signal. The signal amplifying unit 3 has at least one amplifier 30 (30a, 30b) including a transistor 31, and amplifies the high-frequency signal. The radio wave emitting unit 4 emits radio waves corresponding to the high-frequency signal amplified by the signal amplifying unit 3 to the object 21.

[0115] The control unit 5 controls the signal generating unit 2 and the signal amplifying unit 3. The open / close detecting unit 6 detects and notifies the open or closed state of the door 20b. When the open / close detecting unit 6 notifies the gate voltage control circuits 7 and 7A that the door 20b is open, the gate voltage control circuits 7 and 7A control the gate voltage of the transistor 31 included in at least one amplifier 30 (30a, 30b) of the signal amplifying unit 3 to stop the emission of radio waves.

[0116] According to this embodiment, if the door 20b of the cavity 20 is opened during the radiation of radio waves, the radiation of radio waves can be stopped quickly.

[0117] A second aspect of the present disclosure is a radio wave emission device 1 or 1A based on the first aspect. In the second aspect, the signal amplification unit 3 includes a plurality of amplifiers. 30 The plurality of amplifiers 30 (30a, 30b) includes an output stage amplifier 30b.

[0118] The gate voltage control circuits 7 and 7A control the gate voltage of the transistor 31 included in at least the amplifier 30b at the output stage among the plurality of amplifiers 30 (30a, 30b) to stop the emission of radio waves.

[0119] According to this embodiment, when the door 20b of the cavity 20 is opened during radio wave radiation, the radiation of radio waves can be stopped quickly with a simple structure.

[0120] A third aspect of the present disclosure is a radio wave emission device 1 and 1A based on the first aspect. In the third aspect, the signal amplification unit 3 has a plurality of amplifiers 30 (30a, 30b). The plurality of amplifiers 30 (30a, 30b) includes output stage amplifiers 30 (30a, 30b). The gate voltage control circuits 7 and 7A control the gate voltages of all transistors 31 included in the plurality of amplifiers 30 (30a, 30b) to stop the emission of radio waves.

[0121] According to this embodiment, when the door 20b of the cavity 20 is opened during radio wave radiation, the radiation of radio waves can be stopped quickly with a simple structure.

[0122] A fourth aspect of the present disclosure is a radio wave emission device 1 based on the third aspect. In the fourth aspect, the gate voltage control circuits 7 and 7A include at least one gate bias circuit (D / A converters 70a and 70b, integrating circuits 76a and 76b), at least one switch element (73a, 73b), and a latch circuit 75.

[0123] At least one gate bias circuit provides a gate voltage for a transistor 31 included in at least one amplifier 30 (30a, 30b).

[0124] At least one switch element (73a, 73b) is connected between the gate terminal of the transistor 31 included in at least one amplifier 30 (30a, 30b) and a reference power supply 74 that provides a reference voltage for turning off the transistor 31.

[0125] The latch circuit 75 is an open / close detection unit 6 From the door 20b When the open state of the switch element (73a, 73b) is notified, at least one of the switch elements (73a, 73b) is maintained in the ON state.

[0126] Control Unit 5 The gate voltage of the transistor 31 included in at least one amplifier 30 (30a, 30b) is a reference voltage, and when the open / close detection unit 6 notifies the door 20b that it is closed, the latch circuit 75 outputs a reset signal. 5 When a reset signal is received from the power supply 73, at least one of the switch elements (73a, 73b) is turned off.

[0127] According to this aspect, it is possible to prevent radio waves from being emitted when the door 20b is open.

[0128] A fifth aspect of the present disclosure is the radio wave emission devices 1 and 1A based on the fourth aspect. In the fifth aspect, at least one gate bias circuit includes D / A converters 70a and 70b or integrating circuits 76a and 76b. According to this aspect, with a simple structure, if the door 20b of the cavity 20 is opened during radio wave emission, the emission of radio waves can be quickly stopped.

[0129] A sixth aspect of the present disclosure is radio wave emission devices 1 and 1A based on any one of aspects 1 to 5. In the sixth aspect, the radio wave emission devices 1 and 1A further include a bias voltage control circuit 8 that controls a bias voltage supplied from a DC power supply 9 to a drain terminal of a transistor 31 included in at least one amplifier 30 (30a, 30b) of the signal amplification unit 3.

[0130] When the open / close detection unit 6 notifies the bias voltage control circuit 8 that the door 20b is open, the bias voltage control circuit 8 controls the bias voltage to stop the emission of radio waves.

[0131] The gate voltage control circuits 7 and 7A stop the radiation of radio waves earlier than the bias voltage control circuit 8 stops the radiation of radio waves.

[0132] According to this aspect, it is possible to stop the radiation of radio waves even if a malfunction occurs in either the gate voltage control circuit 7 or the bias voltage control circuit 8. As a result, robustness in stopping the radiation of radio waves is improved when the door 20b of the cavity 20 is opened during radiation of radio waves.

[0133] A seventh aspect of the present disclosure is the radio wave emission devices 1 and 1A based on the sixth aspect. In the seventh aspect, the bias voltage control circuit 8 has one or more switch elements (80a, 80b) connected between the DC power supply 9 and the drain terminal of the transistor 31 included in at least one amplifier 30 (30a, 30b) of the signal amplification unit 3.

[0134] When the bias voltage control circuit 8 is notified by the open / close detection unit 6 that the door 20b is open, it turns off at least one of the switch elements (80a, 80b).

[0135] According to this embodiment, with a simple structure, when the door 20b of the cavity 20 is opened during radiation of radio waves, the radiation of radio waves can be stopped quickly.

[0136] An eighth aspect of the present disclosure is the radio wave emission devices 1 and 1A based on the seventh aspect. In the eighth aspect, the one or more switch elements (80a, 80b) are semiconductor switches or relays. This aspect has a simple structure and can quickly stop radio wave emission when the door 20b of the cavity 20 is opened during radio wave emission.

[0137] The ninth aspect is the radio wave emission device 1 or 1A based on any one of the first to eighth aspects. In the ninth aspect, when the open / close detection unit 6 notifies the control unit 5 that the door 20b is open, the control unit 5 resumes control of the signal generation unit 2 and the signal amplification unit 3 based on the control states of the signal generation unit 2 and the signal amplification unit 3 at the time the open / close detection unit 6 notifies the control unit 5 that the door 20b is closed.

[0138] According to this embodiment, the control of the signal generating unit 2 and the signal amplifying unit 3 can be continued after the door 20b is opened or closed. [Industrial Applicability]

[0139] The present disclosure is applicable to radio wave emitting devices such as microwave ovens. [Explanation of symbols]

[0140] 1. 1A Radio wave emitting device 2. Signal Generator 3. Signal amplifier 30, 30a, 30b amplifiers 31 Transistor 4 Radio wave emitting part 5. Control section 6 Open / close detection unit 7, 7A gate voltage control circuit 70a, 70b D / A converter 73a, 73b Switch elements 74 Reference power supply 75, 81 Latch circuit 76a, 76b Integrator circuit 8 Bias voltage control circuit 80a, 80b Switch elements 9 DC power supply 10 Variable Amplifier 11 Isolator 20 cavities 20a Main body 20b Door 21 Object 32 Input matching circuit 33 Output matching circuit 34, 35 Choke circuit

Claims

1. a cavity having a door and configured to receive an object; a signal generating unit configured to generate a high frequency signal having an arbitrary frequency within a predetermined frequency band; a signal amplifier section having at least one amplifier including a transistor and configured to amplify the high frequency signal; a radio wave emitting unit configured to emit radio waves corresponding to the high frequency signal amplified by the signal amplifying unit to the object; a control unit configured to control the signal generating unit and the signal amplifying unit; an open / close detection unit configured to detect and notify an open state and a closed state of the door; a gate voltage control circuit configured to control a gate voltage of a transistor included in at least one amplifier of the signal amplification unit to stop radiation of the radio wave when the open / close detection unit notifies the open state of the door; Equipped with Radio wave emitting device.

2. the signal amplification unit includes a plurality of amplifiers; the plurality of amplifiers include an output stage amplifier; the gate voltage control circuit is configured to control a gate voltage of a transistor included in at least the output stage amplifier among the plurality of amplifiers.

2. The radio wave emitting device according to claim 1.

3. the signal amplification unit includes a plurality of amplifiers; the plurality of amplifiers include an output stage amplifier; the gate voltage control circuit is configured to control gate voltages of all transistors included in the plurality of amplifiers to stop the emission of the radio waves.

2. The radio wave emitting device according to claim 1.

4. the gate voltage control circuit includes at least one gate bias circuit, at least one switch element, and a latch circuit; the at least one gate bias circuit is configured to provide the gate voltage of the transistor included in the at least one amplifier; the at least one switch element is connected between a gate terminal of the transistor included in the at least one amplifier and a reference power supply that provides a reference voltage for turning off the transistor; the latch circuit is configured to maintain the at least one switch element in an on state when the open / close detection unit notifies the open state of the door, the control unit is configured to output a reset signal to the latch circuit when the gate voltage of the transistor included in the at least one amplifier is the reference voltage and the open / close detection unit notifies the door of a closed state, the latch circuit is configured to turn off the at least one switch element upon receiving the reset signal from the control unit.

2. The radio wave emitting device according to claim 1.

5. the at least one gate bias circuit includes a D / A converter or an integrating circuit; 5. The radio wave emitting device according to claim 4.

6. a bias voltage control circuit configured to control a bias voltage supplied from a DC power supply to a drain terminal of the transistor included in the at least one amplifier of the signal amplification unit; the bias voltage control circuit is configured to control the bias voltage so as to stop the emission of the radio wave when the open / close detection unit notifies the open state of the door, the gate voltage control circuit stops the radiation of the radio wave earlier than the bias voltage control circuit stops the radiation of the radio wave; 2. The radio wave emitting device according to claim 1.

7. the bias voltage control circuit has at least one switch element connected between the DC power supply and a drain terminal of a transistor of the at least one amplifier of the signal amplification unit, the bias voltage control circuit is configured to turn off the at least one switch element when the open / close detection unit notifies the open state of the door.

7. The radio wave emitting device according to claim 6.

8. The at least one switch element is a semiconductor switch or a relay.

8. The radio wave emitting device according to claim 7.

9. the control unit is configured to resume control of the signal generating unit and the signal amplifying unit based on control states of the signal generating unit and the signal amplifying unit when the control unit is notified of the closed state of the door by the open / close detection unit.

2. The radio wave emitting device according to claim 1.

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