High frequency circuit and communication apparatus

Abstract

A high frequency circuit (1) comprises a 90° hybrid circuit (10) including an input terminal (10a) and output terminals (10b and 10c), a synthesis circuit (30) including input terminals (30b and 30c) and an output terminal (30a), power amplifiers (21 and 22), a switch (43) including a common terminal (43a) and selection terminals (43b and 43c), and a clamp circuit (65). An input end of the power amplifier (21) is connected to the output terminal (10b), an output end of the power amplifier (21) is connected to the input terminal (30b) and the selection terminal (43c), an input end of the power amplifier (22) is connected to the output terminal (10c), an output end of the power amplifier (22) is connected to the input terminal (30c) and the selection terminal (43b), and the clamp circuit (65) is connected between the common terminal (43a) and the ground.

Description

High-frequency circuits and communication devices

[0001] The present invention relates to a high-frequency circuit and a communication device.

[0002] Patent Document 1 discloses a radio frequency power amplifier that includes a first amplifier connected to a first input bias circuit, a second amplifier connected to a second input bias circuit, and a coupler connected to a combined output section of these, and that controls the input bias level in response to a detection signal from the coupler.

[0003] Japanese Patent Application Laid-Open No. 2008-35487

[0004] 2. Description of the Related Art With the demand for higher output power in mobile communications, high-frequency circuits having power amplifiers are increasingly required to have higher power durability and lower loss.

[0005] The present invention has been made to solve the above-mentioned problems, and has an object to provide a high-frequency circuit and a communication device that can achieve both improved power durability and reduced loss.

[0006] In order to achieve the above object, a high-frequency circuit according to one aspect of the present invention includes: a 90° hybrid circuit having a first input terminal, a first output terminal, and a second output terminal; a combiner circuit having a second input terminal, a third input terminal, and a third output terminal; first and second power amplifiers; a first switch having a first common terminal, a first selection terminal, and a second selection terminal; and a first clamp circuit, wherein an input terminal of the first power amplifier is connected to the first output terminal, an output terminal of the first power amplifier is connected to the second input terminal and the first selection terminal, an input terminal of the second power amplifier is connected to the second output terminal, and an output terminal of the second power amplifier is connected to the third input terminal and the second selection terminal, and the first clamp circuit is connected between the first common terminal and ground.

[0007] According to the present invention, it is possible to provide a high-frequency circuit and a communication device that can achieve both improved power durability and reduced loss.

[0008] FIG. 1 is a circuit configuration diagram of a high-frequency circuit and a communication device according to an embodiment. FIG. 2A is a diagram showing a first circuit configuration example of a combining circuit according to an embodiment. FIG. 2B is a diagram showing a second circuit configuration example of a combining circuit according to an embodiment. FIG. 3A is a diagram showing a circuit configuration example of a clamp circuit according to an embodiment. FIG. 3B is a graph showing an example of characteristics of a clamp circuit according to an embodiment. FIG. 4 is a circuit configuration diagram of a high-frequency circuit according to a first modification of an embodiment. FIG. 5 is a circuit configuration diagram of a high-frequency circuit according to a second modification of an embodiment. FIG. 6 is a circuit configuration diagram of a high-frequency circuit according to a third modification of an embodiment. FIG. 7 is a circuit configuration diagram of a high-frequency circuit according to a fourth modification of an embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangements and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the present invention.

[0010] It should be noted that the drawings are schematic diagrams in which emphasis, omission, or adjustment of proportions has been appropriately made to illustrate the present invention, and are not necessarily strictly illustrated, and may differ from the actual shapes, positional relationships, and proportions. In the drawings, the same reference numerals are used to denote substantially the same components, and redundant explanations may be omitted or simplified.

[0011] In the circuit configuration of the present disclosure, "connected" includes not only direct connection by connection terminals and / or wiring conductors, but also electrical connection via other circuit elements. "Connected between A and B" means connected to both A and B between A and B.

[0012] In addition, in this disclosure, a planar view of a board means that the board and the circuit elements mounted on the board are viewed by orthogonal projection onto a plane parallel to the main surface of the board.

[0013] Furthermore, in the component placement of the present disclosure, "a component is placed on a substrate" includes a component being placed on the main surface of the substrate and a component being placed within the substrate. "A component is placed on the main surface of the substrate" includes a component being placed in contact with the main surface of the substrate, as well as a component being placed above the main surface without contacting the main surface (for example, a component being stacked on another component placed in contact with the main surface). "A component is placed on the main surface of the substrate" may also include a component being placed in a recess formed in the main surface. "A component is placed within the substrate" includes a component being encapsulated within a module substrate, as well as a component being entirely placed between both main surfaces of the substrate but partially not covered by the substrate, and a component being only partially placed within the substrate.

[0014] In addition, in this disclosure, a "path" means a transmission line composed of a wiring through which a high-frequency signal propagates, an electrode directly connected to the wiring, and a terminal directly connected to the wiring or the electrode.

[0015] In addition, in this disclosure, "component A is arranged in series on path B" means that both the signal input terminal and the signal output terminal of component A are connected to wiring, electrodes, or terminals that make up path B.

[0016] In the present invention, the terms "terminal," "input end," and "output end" refer to the points at which conductors within elements terminate. However, if the impedance of the conductor between elements is sufficiently low, a terminal is interpreted as any point on the conductor between elements or the entire conductor, not just a single point.

[0017] Furthermore, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of elements, such as "rectangle," and numerical ranges do not only represent strict meanings, but also include substantially equivalent ranges, for example, including an error of a few percent.

[0018] The "passband of a filter" is defined as the portion of the frequency spectrum transmitted by the filter over which the output power is not attenuated by more than 3 dB below the maximum output power. The upper and lower ends of the passband of a bandpass filter are therefore identified as the higher and lower frequencies of the two points at which the output power is attenuated by 3 dB below the maximum output power.

[0019] The term "transmission band" refers to a frequency band used for transmission in a communication device. The term "reception band" refers to a frequency band used for reception in a communication device. For example, in frequency division duplex (FDD), different frequency bands are used as the transmission band and the reception band, while in time division duplex (TDD), the same frequency band is used as the transmission band and the reception band. In particular, in FDD, when a communication device is implemented in a user equipment (UE) of a cellular network, an uplink operation band is used as the transmission band, and a downlink operation band is used as the reception band. Conversely, when a communication device is implemented as a base station (BS) of a cellular network, the downlink band is used as the transmission band, and the uplink band is used as the reception band.

[0020] The "passing phase" of a high frequency signal between two terminals can be obtained by applying a measurement RF probe to the two terminals and measuring the passing characteristic (S21 or S12) with a network analyzer.

[0021] In the present invention, the values ​​of the phase and passing phase of the high frequency signal do not only indicate the strict meaning, but also include a substantially equivalent range, and include a difference of, for example, about 30%.

[0022] (Embodiment) [1. Circuit Configuration of High-Frequency Circuit 1 and Communication Device 4] The circuit configuration of a high-frequency circuit 1 and a communication device 4 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a circuit configuration diagram of the high-frequency circuit 1 and the communication device 4 according to an embodiment.

[0023] [1.1 Circuit Configuration of Communication Device 4] First, a description will be given of the circuit configuration of the communication device 4. As shown in Fig. 1 , the communication device 4 according to the embodiment includes a high-frequency circuit 1, an antenna 2, and an RF signal processing circuit (RFIC: Radio Frequency Integrated Circuit) 3.

[0024] The high-frequency circuit 1 transmits high-frequency signals between the antenna 2 and the RFIC 3. The detailed circuit configuration of the high-frequency circuit 1 will be described later.

[0025] The antenna 2 is connected to the antenna connection terminal 100 of the high frequency circuit 1 and transmits the high frequency signal output from the high frequency circuit 1. The antenna 2 may also receive a high frequency signal from the outside and output it to the high frequency circuit 1.

[0026] The RFIC 3 is an example of a signal processing circuit that processes high-frequency signals. Specifically, the RFIC 3 performs signal processing on a transmission signal input from a baseband signal processing circuit (BBIC, not shown) by up-conversion or the like, and outputs the transmission signal generated by the signal processing to the transmission path of the high-frequency circuit 1. The RFIC 3 may also perform signal processing on a reception signal input via the reception path of the high-frequency circuit 1 by down-conversion or the like, and output the reception signal generated by the signal processing to the BBIC. The RFIC 3 also has a control unit that controls the high-frequency circuit 1. Note that part or all of the functions of the RFIC 3 as the control unit may be implemented outside the RFIC 3, for example, may be implemented in the BBIC or the high-frequency circuit 1. The control circuit 70 of the high-frequency circuit 1 may also be implemented in the RFIC 3.

[0027] The RFIC 3 may function as a control unit that controls the power supply voltage Vcc and bias voltage Vb supplied to the power amplifiers 21 and 22 included in the high-frequency circuit 1. Specifically, the RFIC 3 may output control signals to a power supply circuit (not shown) and a bias circuit (not shown). The power supply circuit and the bias circuit may be disposed in the high-frequency circuit 1. The power amplifiers 21 and 22 may be supplied with the power supply voltage Vcc controlled by the control signal from the power supply circuit, and may be supplied with the bias voltage Vb controlled by the control signal from the bias circuit.

[0028] The RFIC 3 may also function as a control unit that controls the connection of the switches 41 and 42 included in the high-frequency circuit 1 based on the communication band (frequency band) used.

[0029] In the communication device 4 according to this embodiment, the antenna 2 is not an essential component.

[0030] 1.2 Circuit Configuration of High-Frequency Circuit 1 Next, a description will be given of the circuit configuration of the high-frequency circuit 1. As shown in Fig. 1 , the high-frequency circuit 1 includes a 90° hybrid circuit 10, power amplifiers 21 and 22, a combining circuit 30, switches 41, 42, and 43, a coupler 60, a clamp circuit 65, filters 51 and 52, matching circuits 56, 57, and 58, a control circuit 70, an antenna connection terminal 100, and a signal input terminal 110.

[0031] The antenna connection terminal 100 is connected to the antenna 2 and the switch 42 of the high-frequency circuit 1 via the coupler 60. The signal input terminal 110 is connected to the RFIC 3 and the 90° hybrid circuit 10 of the high-frequency circuit 1. Note that the antenna connection terminal 100 and the signal input terminal 110 do not necessarily have to be included in the high-frequency circuit 1.

[0032] The 90° hybrid circuit 10 has an input terminal 10a (first input terminal), an output terminal 10b (first output terminal), and an output terminal 10c (second output terminal), and is configured so that the phase difference between the first output signal output from the output terminal 10b and the second output signal output from the output terminal 10c is 90°. In this embodiment, the second output signal output from the output terminal 10c leads the first output signal output from the output terminal 10b by 90°.

[0033] The power amplifier 21 is an example of a first power amplifier, and is capable of amplifying signals of band A and band B. The input terminal of the power amplifier 21 is connected to the output terminal 10b, and the output terminal of the power amplifier 21 is connected to the input terminal 30b.

[0034] The power amplifier 22 is an example of a second power amplifier, and is capable of amplifying signals of band A and band B. The input end of the power amplifier 22 is connected to the output terminal 10c, and the output end of the power amplifier 22 is connected to the input terminal 30c.

[0035] Each of the power amplifiers 21 and 22 includes an amplifying transistor. The amplifying transistor may be, for example, a bipolar transistor such as a heterojunction bipolar transistor (HBT) or a field-effect transistor such as a metal-oxide-semiconductor field-effect transistor (MOSFET). If the amplifying transistor is a bipolar transistor, the input terminals of the power amplifiers 21 and 22 are, for example, the base terminals of the bipolar transistors, and the output terminals of the power amplifiers 21 and 22 are, for example, the collector terminals of the bipolar transistors. If the amplifying transistors are field-effect transistors, the input terminals of the power amplifiers 21 and 22 are, for example, the gate terminals of the field-effect transistors, and the output terminals of the power amplifiers 21 and 22 are, for example, the drain terminals of the field-effect transistors.

[0036] The synthesis circuit 30 has an input terminal 30b (second input terminal), an input terminal 30c (third input terminal), and an output terminal 30a (third output terminal), and is configured to synthesize a first input signal input to the input terminal 30b and a second input signal input to the input terminal 30c, and output the synthesized output signal from the output terminal 30a.

[0037] FIG. 2A illustrates a first exemplary circuit configuration of a combining circuit 30 according to an embodiment. In the first exemplary circuit configuration, the combining circuit 30 includes a high-pass filter 31 and a low-pass filter 32. The high-pass filter 31 is connected between an input terminal 30b and an output terminal 30a. The low-pass filter 32 is connected between an input terminal 30c and an output terminal 30a. The high-pass filter 31 attenuates signals lower in frequency than a predetermined frequency and transmits signals higher in frequency than the predetermined frequency with low loss. The high-pass filter 31 is configured to have a pass phase of +45° (the phase at the output terminal is 45° ahead of the phase at the input terminal). The low-pass filter 32 attenuates signals higher in frequency than the predetermined frequency and transmits signals lower in frequency than the predetermined frequency with low loss. The low-pass filter 32 is configured to have a pass phase of −45° (the phase at the output terminal is 45° behind the phase at the input terminal).

[0038] 2A , the low-pass filter 32 (LPF) has a configuration in which, for example, an inductor 321 is arranged in series in a series arm path connecting the input terminal 30 c and the output terminal 30 a, and a capacitor 322 is connected between the series arm path and ground. Note that the low-pass filter 32 may have only one of a configuration in which the inductor 321 is arranged in series in the series arm path or a configuration in which the capacitor 322 is connected between the series arm path and ground. Also, the high-pass filter 31 (HPF) has a configuration in which, for example, a capacitor 311 is arranged in series in a series arm path connecting the input terminal 30 b and the output terminal 30 a, and an inductor 312 is connected between the series arm path and ground. Note that the high-pass filter 31 may have only one of a configuration in which the capacitor 311 is arranged in series in the series arm path or a configuration in which the inductor 312 is connected between the series arm path and ground.

[0039] With the above configuration, for example, a first input signal with a phase of 0° is input through input terminal 30b, and a second input signal with a phase of 90° is input through input terminal 30c. The first input signal passes through high-pass filter 31 to become a first input signal with a phase of +45°. Meanwhile, the second input signal passes through low-pass filter 32 to become a second input signal with a phase of +45°. Then, the first input signal with a phase of +45° and the second input signal with a phase of +45° are in-phase combined at output terminal 30a, and the combined output signal is output from output terminal 30a.

[0040] According to this, in the high-frequency circuit 1, the phase difference between the signal at the output end of power amplifier 21 and the signal at the output end of power amplifier 22 is 90°, and the phase difference between the first input signal and the second input signal at output terminal 30 a is 0°, so it is possible for the circuit to operate as a current-combining type balanced amplifier that is resistant to load fluctuations.

[0041] 2B is a diagram illustrating a second circuit configuration example of a combining circuit 30A according to an embodiment. In the second circuit configuration example, the combining circuit 30A includes a transformer 33, a high-pass filter 31, and a low-pass filter 32. The transformer 33 has an input coil and an output coil that are magnetically coupled to each other. The low-pass filter 32 is connected between the input terminal 30b and one end of the input coil. The high-pass filter 31 is connected between the input terminal 30c and the other end of the input coil. One end of the output coil is connected to the output terminal 30a, and the other end of the output coil is connected to ground.

[0042] With the above configuration, for example, a first input signal with a phase of 0° is input through input terminal 30b, and a second input signal with a phase of 90° is input through input terminal 30c. The first input signal passes through low-pass filter 32 to become a first input signal with a phase of −45°. Meanwhile, the second input signal passes through high-pass filter 31 to become a second input signal with a phase of +135°. Then, the first input signal with a phase of −45° and the second input signal with a phase of +135° are differentially (opposite phase) combined by transformer 33, and the combined output signal is output from output terminal 30a.

[0043] According to this, the high-frequency circuit 1 has a phase difference of 90° between the signal at the output end of the power amplifier 21 and the signal at the output end of the power amplifier 22, and a phase difference of approximately 180° between the first input signal and the second input signal at the input side coil, so it can operate as a voltage-synthesizing balanced amplifier that is resistant to load fluctuations.

[0044] Switch 43 is an example of a first switch, and has a common terminal 43a (first common terminal), a selection terminal 43b (second selection terminal), and a selection terminal 43c (first selection terminal). Common terminal 43a is connected to clamp circuit 65, selection terminal 43b is connected to the output terminal of power amplifier 22, and selection terminal 43c is connected to the output terminal of power amplifier 21. In this connection configuration, switch 43 switches between connecting and disconnecting power amplifier 21 and clamp circuit 65, and between connecting and disconnecting power amplifier 22 and clamp circuit 65.

[0045] The clamp circuit 65 is an example of a first clamp circuit and is connected between the common terminal 43a and ground. Specifically, the terminal 65a is connected to the common terminal 43a, and the terminal 65b is connected to ground. The clamp circuit 65 is configured to limit the voltage at the terminal 65a to a value equal to or lower than a predetermined voltage when a voltage higher than a predetermined voltage is applied to the terminal 65a. This prevents the characteristics of the circuit components connected to the terminal 65a from deteriorating or being destroyed by an overvoltage.

[0046] 3A is a diagram showing an example of the circuit configuration of a clamp circuit 65 according to an embodiment. As shown in the figure, the clamp circuit 65 has a configuration in which a series-connected circuit of diodes 651 to 655 is arranged between terminals 65a and 65b. The anode side of the series-connected circuit is connected to terminal 65a, and the cathode side is connected to terminal 65b. With this connection configuration, the clamp circuit 65 exhibits the characteristics shown in FIG. 3B. When the diodes 651 to 655 are silicon diodes, the forward voltage V of each diode is Ｆis approximately 0.6 V, the forward voltage of the series-connected circuit of diodes 651 to 655 is approximately 3.0 V. As a result, when the voltage applied to terminal 65 a is greater than 3.0 V, a forward current flows from terminal 65 a to terminal 65 b, and the voltage at terminal 65 a is limited to 3.0 V. Note that while FIG. 3B shows the voltage waveform at terminal 65 a when clamp circuit 65 does not have a capacitive component (peak clipper), when a capacitive component is added to clamp circuit 65, the voltage waveform at terminal 65 a becomes a waveform that is a sine waveform with a peak value of 3.0 V shifted to the negative voltage side.

[0047] 2A is an exemplary circuit configuration and should not be construed as limiting. The clamp circuit 65 included in the high-frequency circuit 1 of the present invention can be realized using a wide variety of circuit technologies.

[0048] Because there is a phase difference of 90° between the first output signal of power amplifier 21 and the second output signal of power amplifier 22, there is a phase difference of approximately 180° between the impedance seen from the output terminal of power amplifier 21 toward combiner circuit 30 and the impedance seen from the output terminal of power amplifier 22 toward combiner circuit 30. Therefore, when one of power amplifiers 21 and 22 has a high impedance, the other has a low impedance. With the above-described configuration of high-frequency circuit 1, by switching switch 43 and connecting clamp circuit 65 to the output terminal of one of the power amplifiers that has a high impedance, it is possible to prevent the one power amplifier from deteriorating in characteristics or being destroyed by an overvoltage.

[0049] While it is possible to further strengthen the resistance to breakdown of antenna 2 against load fluctuations by constantly connecting a clamp circuit that operates at a low voltage, the voltage is limited even under normal load conditions, degrading basic characteristics such as the power efficiency of the power amplifier. In contrast, in radio-frequency circuit 1 according to this embodiment, clamp circuit 65 is connected to power amplifiers 21 and 22 via switch 43, so that clamp circuit 65 can be disconnected from power amplifiers 21 and 22 when the impedance is not high, thereby reducing signal transmission loss due to the connection of clamp circuit 65. Therefore, it is possible to provide radio-frequency circuit 1 that can simultaneously prevent breakdown of power amplifiers 21 and 22 and reduce signal transmission loss.

[0050] Furthermore, even when clamp circuit 65 is connected to power amplifier 21 or 22, power amplifiers 21 and 22 are not turned off. Rather, the control circuit 70 continues to acquire the detection signal from coupler 60 while clamp circuit 65 is connected. Therefore, if the output impedance of power amplifiers 21 and 22 falls below a predetermined threshold, clamp circuit 65 can be disconnected.

[0051] Furthermore, since a clamp circuit is not provided for each of the power amplifiers 21 and 22 but is shared, the high frequency circuit 1 can be made smaller.

[0052] The coupler 60 is a directional coupler and is arranged on a common signal path connecting the antenna connection terminal 100 and the output terminal 30a. This allows a single coupler 60 to detect a signal obtained by combining the first output signal of the power amplifier 21 and the second output signal of the power amplifier 22, thereby enabling the high-frequency circuit 1 to be miniaturized. The coupler 60 can detect a forward-direction high-frequency signal traveling along the common signal path from the output terminal 30a to the antenna connection terminal 100, and a reflected signal traveling in the reverse direction from the antenna connection terminal 100 to the output terminal 30a. The circuit configuration of the coupler 60 is not particularly limited, and examples thereof include a branch-line coupler, a rat-race coupler, and a coupled-line coupler.

[0053] The control circuit 70 is connected between the coupler 60 and the switch 43. The control circuit 70 is connected to the coupler 60 via a high-frequency transmission line and to the switch 43 via a control wiring. This allows the control circuit 70 to output a control signal to the switch 43 based on a detection signal detected by the coupler 60. The control circuit 70 is included in, for example, a semiconductor IC. The semiconductor IC may include, for example, a control circuit that controls the power supply voltage Vcc and bias voltage Vb supplied to the power amplifiers 21 and 22. The semiconductor IC may be configured using, for example, a complementary metal oxide semiconductor (CMOS) and, more specifically, may be manufactured using an SOI (silicon-on-insulator) process. The semiconductor IC may also be configured of at least one of GaAs, SiGe, and GaN. Note that the semiconductor material of the semiconductor IC is not limited to the above-mentioned materials. The control circuit 70 does not necessarily have to be included in the high-frequency circuit 1, but may instead be included in the RFIC 3.

[0054] Control circuit 70 receives signals corresponding to the forward-direction (forward mode) high-frequency signal and the reverse-direction (reverse mode) reflected signal detected by coupler 60, and calculates the output impedance of power amplifiers 21 and 22 based on the VSWR (voltage standing wave ratio) and phase difference. This makes it possible to match the output impedance of power amplifiers 21 and 22 with the switching of switch 43.

[0055] The switch 43 is configured to be switchable between (1) a first connection mode in which the common terminal 43a and the selection terminal 43c are connected and the common terminal 43a and the selection terminal 43b are disconnected, (2) a second connection mode in which the common terminal 43a and the selection terminal 43c are disconnected and the common terminal 43a and the selection terminal 43b are connected, and (3) a third connection mode in which the common terminal 43a and the selection terminal 43c are disconnected and the common terminal 43a and the selection terminal 43b are disconnected.

[0056] The control circuit 70 operates the switch 43 in the first connection mode when the calculated output impedance of the power amplifier 21 is greater than a predetermined threshold. Furthermore, the control circuit 70 operates the switch 43 in the second connection mode when the calculated output impedance of the power amplifier 22 is greater than the predetermined threshold. Furthermore, the control circuit 70 operates the switch 43 in the third connection mode when the calculated output impedances of the power amplifiers 21 and 22 are both equal to or less than the predetermined thresholds.

[0057] This makes it possible to highly accurately prevent a power amplifier with high output impedance from being destroyed by overvoltage, and also reduces signal transmission loss by disconnecting the clamp circuit 65 when the output impedance is not high.

[0058] The filter 51 has a passband that includes the transmission band (A-Tx) of band A (first band) and is connected between the switches 41 and 42. The filter 52 has a passband that includes the transmission band (B-Tx) of band B (second band) and is connected between the switches 41 and 42.

[0059] In the present disclosure, each of band A and band B refers to a frequency band predefined by a standardization organization (e.g., 3GPP (registered trademark: 3rd Generation Partnership Project), IEEE (Institute of Electrical and Electronics Engineers), etc.) for a communication system built using radio access technology (RAT). In this embodiment, the communication system may be, for example, a 4G-LTE (Long Term Evolution) system, a 5G-NR (New Radio) system, and a WLAN (Wireless Local Area Network) system, but is not limited to these.

[0060] The switch 41 is connected between the combining circuit 30 and the filters 51 and 52. The switch 42 is connected between the filters 51 and 52 and the antenna connection terminal 100.

[0061] Matching circuit 56 is connected between combiner circuit 30 and switch 41, and achieves impedance matching between combiner circuit 30 and switch 41. Matching circuit 57 is connected between filter 51 and switch 42, and achieves impedance matching between filter 51 and switch 42. Matching circuit 58 is connected between filter 52 and switch 42, and achieves impedance matching between filter 52 and switch 42.

[0062] At least one of the coupler 60 , the control circuit 70 , the switches 41 and 42 , the filters 51 and 52 , and the matching circuits 56 to 58 does not necessarily have to be included in the high-frequency circuit 1 .

[0063] Although the high-frequency circuit 1 according to this embodiment operates as a balanced amplifier, it can also operate as a Doherty amplifier. In this case, for example, the second output signal output from the output terminal 10c of the 90° hybrid circuit 10 is delayed in phase by 90° from the first output signal output from the output terminal 10b. The power amplifier 21 is, for example, a carrier amplifier, and the power amplifier 22 is, for example, a peaking amplifier. The combining circuit 30 includes, for example, a phase-shift line connected between the output end of the power amplifier 21 and the output terminal 30a. The phase-shift line is configured to delay the output signal of the power amplifier 21 by 90°. As a result, the first output signal of the power amplifier 21 and the second output signal of the power amplifier 22 are in-phase combined at the output terminal 30a. Alternatively, the combining circuit 30 includes, for example, a transformer having an input coil and an output coil, and a phase-shift line. One end of the input coil is connected to the output end of the power amplifier 21. The phase-shift line is connected between the output end of the power amplifier 22 and the other end of the input coil. One end of the output coil is connected to the output terminal 30a, and the other end of the output coil is connected to ground. The phase-shift line is configured to delay the output signal of the power amplifier 22 by 90°. As a result, the first output signal of the power amplifier 21 and the second output signal of the power amplifier 22 are differentially (out-of-phase) combined at the output terminal 30a. This makes it possible to prevent breakdown and reduce signal transmission loss in the Doherty high-frequency circuit 1 when the power amplifiers 21 and 22 are operating simultaneously.

[0064] [2 Configuration of High-Frequency Circuit 1A According to Modification 1] Next, the configuration of the high-frequency circuit 1A according to Modification 1 will be described. FIG. 4 is a circuit configuration diagram of the high-frequency circuit 1A according to Modification 1. As shown in the figure, the high-frequency circuit 1A includes a 90° hybrid circuit 10, power amplifiers 21 and 22, a combining circuit 30, switches 41, 42, and 43, couplers 61 and 62, a clamp circuit 65, filters 51 and 52, matching circuits 56, 57, and 58, a control circuit 70, an antenna connection terminal 100, and a signal input terminal 110. The high-frequency circuit 1A according to Modification 1 differs from the high-frequency circuit 1 according to the embodiment in the arrangement of the couplers 61 and 62. Therefore, the following description of the high-frequency circuit 1A according to this modification will omit a description of the same configuration as the high-frequency circuit 1 according to the embodiment, and will focus on the different configuration.

[0065] The coupler 61 is a directional coupler and is disposed on a first signal path connecting the output end of the power amplifier 21 and the input terminal 30b. The coupler 61 can detect a high-frequency signal traveling in the forward direction along the first signal path from the power amplifier 21 to the combining circuit 30.

[0066] The coupler 62 is a directional coupler and is arranged on a second signal path connecting the output end of the power amplifier 22 and the input terminal 30c. The coupler 62 can detect a high-frequency signal traveling in the forward direction along the second signal path from the power amplifier 22 to the combining circuit 30.

[0067] The control circuit 70 is connected between the couplers 61 and 62 and the switch 43. The control circuit 70 is connected to the couplers 61 and 62 via high-frequency transmission lines, and to the switch 43 via control wiring. This allows the control circuit 70 to output a control signal to the switch 43 based on the detection signals detected by the couplers 61 and 62.

[0068] Control circuit 70 receives a signal corresponding to the forward direction (forward mode) high frequency signal detected by coupler 61, and also receives a signal corresponding to the forward direction (forward mode) high frequency signal detected by coupler 62, and calculates the output impedance of power amplifiers 21 and 22.

[0069] With this, the first output signal of power amplifier 21 and the second output signal of power amplifier 22 are detected individually by couplers 61 and 62, respectively, allowing control circuit 70 to calculate the output impedances of power amplifiers 21 and 22 with high accuracy. Furthermore, only forward mode detection by couplers 61 and 62 is required, simplifying the detection process by couplers 61 and 62. Therefore, it is possible to provide high-frequency circuit 1A that can prevent damage to power amplifiers 21 and 22 and reduce signal transmission loss at the same time.

[0070] [3 Configuration of High-Frequency Circuit 1B According to Modification 2] Next, the configuration of the high-frequency circuit 1B according to Modification 2 will be described. FIG. 5 is a circuit configuration diagram of the high-frequency circuit 1B according to Modification 2. As shown in the figure, the high-frequency circuit 1B includes a 90° hybrid circuit 10, power amplifiers 21 and 22, a combining circuit 30, switches 41, 42, and 43, a coupler 62, a clamp circuit 65, filters 51 and 52, matching circuits 56, 57, and 58, a control circuit 70, an antenna connection terminal 100, and a signal input terminal 110. The high-frequency circuit 1B according to Modification 2 differs from the high-frequency circuit 1A according to Modification 1 in that the coupler 61 is not provided. Therefore, the following description of the high-frequency circuit 1B according to this modification will omit description of the same configuration as the high-frequency circuit 1A according to Modification 1, and will focus on the different configuration.

[0071] The coupler 62 is a directional coupler and is disposed on a second signal path connecting the output end of the power amplifier 22 and the input terminal 30c. The coupler 62 can detect a high-frequency signal traveling in the forward direction along the second signal path from the power amplifier 22 to the combining circuit 30, and a reflected signal traveling in the reverse direction from the combining circuit 30 to the power amplifier 22.

[0072] The control circuit 70 is connected between the coupler 62 and the switch 43. The control circuit 70 is connected to the coupler 62 via a high-frequency transmission line, and to the switch 43 via a control wiring. This allows the control circuit 70 to output a control signal to the switch 43 based on the detection signal detected by the coupler 62.

[0073] The control circuit 70 receives a signal corresponding to the forward direction (forward mode) high frequency signal detected by the coupler 62 and calculates the output impedance of the power amplifiers 21 and 22 .

[0074] Because there is a phase difference of 180° between the output impedance of power amplifier 21 and the output impedance of power amplifier 22, calculating the output impedance of one of power amplifiers 21 and 22 makes it possible to estimate the output impedance of the other. Therefore, by detecting the second output signal of power amplifier 22 with coupler 62, it becomes possible to calculate not only the output impedance of power amplifier 22 but also the output impedance of power amplifier 21. This makes it possible to calculate the output impedances of both power amplifiers 21 and 22, making it possible to provide a small-sized high-frequency circuit 1B that can prevent damage to power amplifiers 21 and 22 and reduce signal transmission loss.

[0075] Note that, instead of arranging the coupler 62 in the second signal path, the coupler 61 may be arranged in the first signal path.

[0076] [4 Configuration of High-Frequency Circuit 1C According to Modification 3] Next, the configuration of the high-frequency circuit 1C according to Modification 3 will be described. FIG. 6 is a circuit configuration diagram of the high-frequency circuit 1C according to Modification 3. As shown in the figure, the high-frequency circuit 1C includes a 90° hybrid circuit 10, power amplifiers 21 and 22, a combining circuit 30, switches 41, 42, and 44, a coupler 60, a clamp circuit 65, a capacitor 66, filters 51 and 52, matching circuits 56, 57, and 58, a control circuit 70, an antenna connection terminal 100, and a signal input terminal 110. The high-frequency circuit 1C according to Modification 3 differs from the high-frequency circuit 1 according to the embodiment in the configuration of the switch 44 and the presence of the capacitor 66. Therefore, the following description of the high-frequency circuit 1C according to this modification will omit a description of the same configuration as the high-frequency circuit 1 according to the embodiment, and will focus on the different configuration.

[0077] The switch 44 is an example of a first switch, and has a common terminal 44a (first common terminal), a common terminal 44b (second common terminal), a selection terminal 44c (first selection terminal), and a selection terminal 44d (second selection terminal). The common terminal 44a is connected to the clamp circuit 65, the common terminal 44b is connected to the capacitor 66, the selection terminal 44c is connected to the output terminal of the power amplifier 21, and the selection terminal 44d is connected to the output terminal of the power amplifier 22. In this connection configuration, the switch 44 is configured to be switchable between (1) a fourth connection mode in which the common terminal 44a is connected to the selection terminal 44c and the common terminal 44b is connected to the selection terminal 44d, (2) a fifth connection mode in which the common terminal 44a is connected to the selection terminal 44d and the common terminal 44b is connected to the selection terminal 44c, and (3) a sixth connection mode in which the common terminal 44a is not connected to the selection terminals 44c and 44d and the common terminal 44b is not connected to the selection terminals 44c and 44d.

[0078] The clamp circuit 65 is an example of a first clamp circuit, and is connected between the common terminal 44a and ground.

[0079] The capacitor 66 is an example of an impedance element and is connected between the common terminal 44b and ground. Note that instead of the capacitor 66, an inductor or an impedance matching circuit including an inductor and a capacitor may be connected between the common terminal 44b and ground.

[0080] The control circuit 70 is connected between the coupler 60 and the switch 44. The control circuit 70 is connected to the coupler 60 via a high-frequency transmission line and to the switch 44 via a control wiring. This allows the control circuit 70 to output a control signal to the switch 44 based on the detection signal detected by the coupler 60. The control circuit 70 receives signals corresponding to the forward-direction (forward mode) high-frequency signal and the reverse-direction (reverse mode) reflected signal detected by the coupler 60, and calculates the output impedance of the power amplifiers 21 and 22 based on the VSWR (voltage standing wave ratio) and the phase difference. This makes it possible to match the output impedance of the power amplifiers 21 and 22 with the switching of the switch 44.

[0081] The control circuit 70 operates the switch 44 in the fourth connection mode when the calculated output impedance of the power amplifier 21 is greater than a predetermined threshold. Furthermore, the control circuit 70 operates the switch 44 in the fifth connection mode when the calculated output impedance of the power amplifier 22 is greater than the predetermined threshold. Furthermore, the control circuit 70 operates the switch 44 in the sixth connection mode when the calculated output impedances of the power amplifiers 21 and 22 are both equal to or less than the predetermined thresholds.

[0082] Connecting clamp circuit 65 to one of power amplifiers 21 and 22 adds capacitive impedance to the output terminal of that power amplifier, causing the output impedance to fluctuate. In this case, the phase difference between the first output signal of power amplifier 21 and the second output signal of power amplifier 22 fluctuates at output terminal 30a, resulting in a deterioration in power combining efficiency. In contrast, connecting capacitor 66 to the output terminal of the other power amplifier to which clamp circuit 65 is not connected can suppress the fluctuation in the phase difference at output terminal 30a and prevent the deterioration in power combining efficiency caused by connecting clamp circuit 65. Therefore, it is possible to accurately prevent a power amplifier with high output impedance from being destroyed by an overvoltage, and by disconnecting clamp circuit 65 when the output impedance is not high, it is possible to reduce signal transmission loss.

[0083] [5. Configuration of High-Frequency Circuit 1D According to Modification 4] Next, the configuration of the high-frequency circuit 1D according to Modification 4 will be described. FIG. 7 is a circuit configuration diagram of the high-frequency circuit 1D according to Modification 4. As shown in the figure, the high-frequency circuit 1D includes a 90° hybrid circuit 10, power amplifiers 21 and 22, a combining circuit 30, switches 41, 42, and 44, a coupler 60, clamp circuits 65 and 67, filters 51 and 52, matching circuits 56, 57, and 58, a control circuit 70, an antenna connection terminal 100, and a signal input terminal 110. The high-frequency circuit 1D according to Modification 4 differs from the high-frequency circuit 1 according to the embodiment in the configuration of the switch 44 and the inclusion of a clamp circuit 67. Therefore, the following description of the high-frequency circuit 1D according to this modification will omit a description of the same configuration as the high-frequency circuit 1 according to the embodiment, and will focus on the different configuration.

[0084] The switch 44 is an example of a first switch, and has a common terminal 44 a (first common terminal), a common terminal 44 b, a selection terminal 44 c (first selection terminal), and a selection terminal 44 d (second selection terminal). The common terminal 44 a is connected to the clamp circuit 65, the common terminal 44 b is connected to the clamp circuit 67, the selection terminal 44 c is connected to the output terminal of the power amplifier 21, and the selection terminal 44 d is connected to the output terminal of the power amplifier 22.

[0085] The switch 41 is an example of a second switch and has a common terminal 41 a (third common terminal), a selection terminal 41 b (third selection terminal), and a selection terminal 41 c (fourth selection terminal). The common terminal 41 a is connected to the output terminal 30 a via a matching circuit 56, the selection terminal 41 b is connected to the filter 51, and the selection terminal 41 c is connected to the filter 52.

[0086] The switch 42 has a common terminal 42 a and selection terminals 42 b and 42 c. The common terminal 42 a is connected to the antenna connection terminal 100 via the coupler 60, the selection terminal 42 b is connected to the filter 51, and the selection terminal 42 c is connected to the filter 52.

[0087] In the above connection configuration, switches 41, 42, and 44 are configured to be switchable between (1) a seventh connection mode in which common terminal 44a is connected to selection terminal 44c or 44d, common terminal 41a is connected to selection terminal 41b, and common terminal 42a is connected to selection terminal 42b; (2) an eighth connection mode in which common terminal 44b is connected to selection terminal 44c or 44d, common terminal 41a is connected to selection terminal 41c, and common terminal 42a is connected to selection terminal 42c; and (3) a ninth connection mode in which common terminal 44a is not connected to selection terminals 44c and 44d, and common terminal 44b is not connected to selection terminals 44c and 44d.

[0088] Clamp circuit 65 is an example of a first clamp circuit and is connected between common terminal 44a and ground. Clamp circuit 67 is an example of a second clamp circuit and is connected between common terminal 44b and ground. While clamp circuit 65 is configured to limit the voltage at terminal 65a to a first predetermined voltage or less, clamp circuit 67 is configured to limit the voltage at terminal 67a to a second predetermined voltage or less that is different from the first predetermined voltage. This prevents the characteristics of circuit components connected to terminal 67a from deteriorating or being destroyed by overvoltage.

[0089] The control circuit 70 is connected between the coupler 60 and the switch 44. The control circuit 70 is connected to the coupler 60 via a high-frequency transmission line and to the switch 44 via a control wiring. This allows the control circuit 70 to output a control signal to the switch 44 based on the detection signal detected by the coupler 60. The control circuit 70 receives signals corresponding to the forward-direction (forward mode) high-frequency signal and the reverse-direction (reverse mode) reflected signal detected by the coupler 60, and calculates the output impedance of the power amplifiers 21 and 22 based on the VSWR (voltage standing wave ratio) and the phase difference. This makes it possible to match the output impedance of the power amplifiers 21 and 22 with the switching of the switch 44.

[0090] The control circuit 70 operates the switch 44 in the seventh connection mode connecting the common terminal 44a and the selection terminal 44c when the high-frequency circuit 1D transmits a transmission signal of band A and the calculated output impedance of the power amplifier 21 is greater than a predetermined threshold. Furthermore, the control circuit 70 operates the switch 44 in the eighth connection mode connecting the common terminal 44b and the selection terminal 44c when the high-frequency circuit 1D transmits a transmission signal of band B and the calculated output impedance of the power amplifier 21 is greater than a predetermined threshold. Furthermore, the control circuit 70 operates the switch 44 in the seventh connection mode connecting the common terminal 44a and the selection terminal 44d when the high-frequency circuit 1D transmits a transmission signal of band A and the calculated output impedance of the power amplifier 22 is greater than the predetermined threshold. Furthermore, the control circuit 70 operates the switch 44 in the eighth connection mode connecting the common terminal 44b and the selection terminal 44d when the high-frequency circuit 1D transmits a transmission signal of band B and the calculated output impedance of the power amplifier 22 is greater than the predetermined threshold. Furthermore, when the calculated output impedances of the power amplifiers 21 and 22 are both equal to or less than the predetermined thresholds, the control circuit 70 operates the switch 44 in the ninth connection mode.

[0091] This allows the selection of the most suitable clamp circuit from clamp circuits 65 and 67 depending on the selected band, facilitating optimization of transmission characteristics and breakdown characteristics. Therefore, it is possible to highly accurately prevent a power amplifier with high output impedance from being destroyed by overvoltage, and by disconnecting clamp circuits 65 and 67 when the output impedance is not high, it is possible to reduce signal transmission loss.

[0092] [6. Effects, etc.] As described above, the high-frequency circuit 1 according to the embodiment includes: 90° hybrid circuit 10 having input terminal 10a and output terminals 10b and 10c; combiner circuit 30 having input terminals 30b and 30c and output terminal 30a; power amplifiers 21 and 22; switch 43 having common terminal 43a and selection terminals 43b and 43c; and clamp circuit 65; the input terminal of power amplifier 21 is connected to output terminal 10b, the output terminal of power amplifier 21 is connected to input terminal 30b and selection terminal 43c, the input terminal of power amplifier 22 is connected to output terminal 10c, and the output terminal of power amplifier 22 is connected to input terminal 30c and selection terminal 43b; and clamp circuit 65 is connected between common terminal 43a and ground.

[0093] According to this, by switching switch 43 to connect clamp circuit 65 to the output terminal of one of the power amplifiers that becomes high impedance, it is possible to prevent the one power amplifier from deteriorating in characteristics and being destroyed due to an overvoltage. Furthermore, because clamp circuit 65 is connected to power amplifiers 21 and 22 via switch 43, clamp circuit 65 can be disconnected from power amplifiers 21 and 22 when the impedance is not high, thereby reducing signal transmission loss due to the connection of clamp circuit 65. Therefore, it is possible to provide a high-frequency circuit 1 that can prevent destruction of power amplifiers 21 and 22 and reduce signal transmission loss at the same time.

[0094] For example, the high-frequency circuit 1 further includes an antenna connection terminal 100 connected to the output terminal 30a, a coupler 60 arranged in at least one of a first signal path connecting the output terminal of the power amplifier 21 and the antenna connection terminal 100 and a second signal path connecting the output terminal of the power amplifier 22 and the antenna connection terminal 100, and a control circuit 70 connected between the coupler 60 and the switch 43.

[0095] This allows the control circuit 70 to output a control signal to the switch 43 based on the detection signal detected by the coupler 60 .

[0096] Furthermore, for example, in the high-frequency circuit 1, the coupler 60 is disposed on a common signal path connecting the output terminal 30a and the antenna connection terminal 100.

[0097] According to this, the signal obtained by combining the first output signal of the power amplifier 21 and the second output signal of the power amplifier 22 is detected by one coupler 60, so that the high frequency circuit 1 can be made smaller.

[0098] Furthermore, for example, in the high-frequency circuit 1B according to the second modification, the coupler 62 is disposed in the second signal path connecting the output end of the power amplifier 22 and the input terminal 30c.

[0099] Because the output impedance of power amplifier 21 and the output impedance of power amplifier 22 have a phase difference of 180°, calculating the output impedance of one of power amplifiers 21 and 22 allows the output impedance of the other to be estimated. Therefore, by detecting the output signal of power amplifier 22 using coupler 62, it is possible to calculate not only the output impedance of power amplifier 22 but also the output impedance of power amplifier 21. Furthermore, only forward mode detection by coupler 62 is required, simplifying the detection process by coupler 62. Since the output impedances of both power amplifiers 21 and 22 can be calculated, a small-sized high-frequency circuit 1B can be provided that can prevent damage to power amplifiers 21 and 22 and reduce signal transmission loss.

[0100] Also, for example, in the high-frequency circuit 1, the coupler 60 detects a forward signal traveling from the output terminal 30a to the antenna connection terminal 100 and a reverse reflected signal traveling from the antenna connection terminal 100 to the output terminal 30a, and the control circuit 70 calculates the output impedance of the power amplifiers 21 and 22 from the forward signal and the reverse reflected signal detected by the coupler 60.

[0101] This allows the output impedance of the power amplifiers 21 and 22 to correspond to the switching of the switch 43 .

[0102] For example, in the high-frequency circuit 1, the switch 43 is configured to be switchable between a first connection mode in which the common terminal 43a and the selection terminal 43c are connected and the common terminal 43a and the selection terminal 43b are disconnected, a second connection mode in which the common terminal 43a and the selection terminal 43c are disconnected and the common terminal 43a and the selection terminal 43b are connected, and a third connection mode in which the common terminal 43a and the selection terminal 43c are disconnected and the common terminal 43a and the selection terminal 43b are disconnected.

[0103] Furthermore, for example, in the high-frequency circuit 1, the control circuit 70 operates the switch 43 in the first connection mode when the calculated output impedance of the power amplifier 21 is greater than a predetermined threshold, operates the switch 43 in the second connection mode when the calculated output impedance of the power amplifier 22 is greater than the predetermined threshold, and operates the switch 43 in the third connection mode when the calculated output impedance of the power amplifier 21 and the output impedance of the power amplifier 22 are both equal to or less than the predetermined threshold.

[0104] This makes it possible to highly accurately prevent a power amplifier with high output impedance from being destroyed by overvoltage, and also reduces signal transmission loss by disconnecting the clamp circuit 65 when the output impedance is not high.

[0105] For example, in a high-frequency circuit 1C according to variant example 3, the switch 44 has common terminals 44a and 44b and selection terminals 44c and 44d, and the high-frequency circuit 1C further includes a capacitor 66 connected between the common terminal 44b and ground.

[0106] According to this, by connecting capacitor 66 to the output end of the power amplifier to which clamp circuit 65 is not connected, it is possible to suppress fluctuations in the phase difference between the first output signal and the second output signal at output terminal 30a and suppress deterioration of power combining efficiency caused by connecting clamp circuit 65. Therefore, it is possible to highly accurately prevent a power amplifier with high output impedance from being destroyed by overvoltage, and by disconnecting clamp circuit 65 when the output impedance is not high, it is possible to reduce signal transmission loss.

[0107] For example, in the high-frequency circuit 1C, the switch 44 is configured to be switchable between a fourth connection mode in which the common terminal 44a is connected to the selection terminal 44c and the common terminal 44b is connected to the selection terminal 44d, a fifth connection mode in which the common terminal 44a is connected to the selection terminal 44d and the common terminal 44b is connected to the selection terminal 44c, and a sixth connection mode in which the common terminal 44a is not connected to the selection terminals 44c and 44d and the common terminal 44b is not connected to the selection terminals 44c and 44d.

[0108] Also, for example, in a high-frequency circuit 1D according to Modification 4, the switch 44 has common terminals 44a and 44b and selection terminals 44c and 44d, and the high-frequency circuit 1D includes a clamp circuit 65 connected between the common terminal 44a and ground, a clamp circuit 67 connected between the common terminal 44b and ground, a switch 41 having a common terminal 41a and selection terminals 41b and 41c, a filter 51 having a pass band that includes the transmission band of band A, and a filter 52 having a pass band that includes the transmission band of band B, and the common terminal 41a is connected to the output terminal 30a, the selection terminal 41b is connected to filter 51, and the selection terminal 41c is connected to filter 52.

[0109] This allows the selection of the most suitable clamp circuit from clamp circuits 65 and 67 depending on the selected band, facilitating optimization of transmission characteristics and breakdown characteristics. Therefore, it is possible to highly accurately prevent a power amplifier with high output impedance from being destroyed by overvoltage, and by disconnecting clamp circuits 65 and 67 when the output impedance is not high, it is possible to reduce signal transmission loss.

[0110] For example, in the high-frequency circuit 1D, the switches 44 and 41 are configured to be switchable between a seventh connection mode in which the common terminal 44a is connected to the selection terminal 44c or 44d and the common terminal 41a is connected to the selection terminal 41b, an eighth connection mode in which the common terminal 44b is connected to the selection terminal 44c or 44d and the common terminal 41a is connected to the selection terminal 41c, and a ninth connection mode in which the common terminal 44a is not connected to the selection terminals 44c and 44d and the common terminal 44b is not connected to the selection terminals 44c and 44d.

[0111] For example, in the high-frequency circuit 1, the second output signal output from the output terminal 10c is 90° ahead in phase with the output signal output from the output terminal 10b, and the synthesis circuit 30 includes a high-pass filter 31 connected between the input terminal 30b and the output terminal 30a, and a low-pass filter 32 connected between the input terminal 30c and the output terminal 30a.

[0112] According to this, in the high-frequency circuit 1, the phase difference between the signal at the output end of power amplifier 21 and the signal at the output end of power amplifier 22 is 90°, and the phase difference between the first input signal and the second input signal at output terminal 30 a is 0°, so it is possible for the circuit to operate as a current-combining type balanced amplifier that is resistant to load fluctuations.

[0113] For example, in the high-frequency circuit 1, the second output signal output from the output terminal 10c is 90° ahead in phase with the first output signal output from the output terminal 10b, and the combining circuit 30A includes a transformer 33 having an input coil and an output coil, a low-pass filter 32 connected between the input terminal 30b and one end of the input coil, and a high-pass filter 31 connected between the input terminal 30c and the other end of the input coil, and one end of the output coil is connected to the output terminal 30a and the other end of the output coil is connected to ground.

[0114] According to this, the high-frequency circuit 1 has a phase difference of 90° between the signal at the output end of power amplifier 21 and the signal at the output end of power amplifier 22, and a phase difference of approximately 180° between the first input signal and the second input signal at output terminal 30 a, so it can operate as a voltage-combining type balanced amplifier that is resistant to load fluctuations.

[0115] The communication device 4 according to this embodiment also includes an RFIC 3 that processes high-frequency signals, and a high-frequency circuit 1 that transmits high-frequency signals between the RFIC 3 and the antenna 2 .

[0116] This allows the effects of the high frequency circuit 1 to be realized in the communication device 4.

[0117] (Other Embodiments, etc.) While the high-frequency circuits and communication devices according to the embodiments of the present invention have been described above with reference to the embodiments and modifications thereof, the high-frequency circuits and communication devices according to the present invention are not limited to the above-described embodiments and modifications. The present invention also includes other embodiments realized by combining any of the components in the above-described embodiments and modifications, modifications obtained by applying various modifications to the above-described embodiments and modifications that would occur to those skilled in the art without departing from the spirit of the present invention, and various devices incorporating the above-described high-frequency circuits.

[0118] For example, in the high-frequency circuits and communication devices according to the above-described embodiments and modifications, other circuit elements, wiring, etc. may be inserted between the paths connecting the circuit elements and signal paths disclosed in the drawings.

[0119] The following describes the features of the high-frequency circuit and communication device described based on the above embodiment and modifications.

[0120] <1> A radio frequency circuit comprising: a 90° hybrid circuit having a first input terminal, a first output terminal, and a second output terminal; a combiner circuit having a second input terminal, a third input terminal, and a third output terminal; a first power amplifier and a second power amplifier; a first switch having a first common terminal, a first selection terminal, and a second selection terminal; and a first clamp circuit, wherein an input terminal of the first power amplifier is connected to the first output terminal, and an output terminal of the first power amplifier is connected to the second input terminal and the first selection terminal, an input terminal of the second power amplifier is connected to the second output terminal, and an output terminal of the second power amplifier is connected to the third input terminal and the second selection terminal, and the first clamp circuit is connected between the first common terminal and ground.

[0121] <2> The high-frequency circuit according to <1>, further comprising: an antenna connection terminal connected to the third output terminal; a coupler arranged in at least one of a first signal path connecting an output end of the first power amplifier and the antenna connection terminal and a second signal path connecting an output end of the second power amplifier and the antenna connection terminal; and a control circuit connected between the coupler and the first switch.

[0122] <3> The high-frequency circuit according to <2>, wherein the coupler is disposed on a common signal path connecting the third output terminal and the antenna connection terminal.

[0123] <4> The high-frequency circuit according to <2>, wherein the coupler is arranged in either a first signal path connecting an output end of the first power amplifier and the second input terminal or a second signal path connecting an output end of the second power amplifier and the third input terminal.

[0124] <5> The radio-frequency circuit according to any one of <2> to <4>, wherein the coupler detects a forward signal traveling from the third output terminal to the antenna connection terminal and a reflected signal traveling in a reverse direction from the antenna connection terminal to the third output terminal, and the control circuit calculates output impedances of the first power amplifier and the second power amplifier from the forward signal and the reflected signal traveling in the reverse direction detected by the coupler.

[0125] <6> The high-frequency circuit according to <5>, wherein the first switch is configured to be switchable between: a first connection mode in which the first common terminal and the first selection terminal are connected and the first common terminal and the second selection terminal are disconnected; a second connection mode in which the first common terminal and the first selection terminal are disconnected and the first common terminal and the second selection terminal are connected; and a third connection mode in which the first common terminal and the first selection terminal are disconnected and the first common terminal and the second selection terminal are disconnected.

[0126] <7> The radio-frequency circuit according to <6>, wherein the control circuit operates the first switch in the first connection mode when the calculated output impedance of the first power amplifier is greater than a predetermined threshold, operates the first switch in the second connection mode when the calculated output impedance of the second power amplifier is greater than the predetermined threshold, and operates the first switch in the third connection mode when the calculated output impedance of the first power amplifier and the output impedance of the second power amplifier are both equal to or less than the predetermined threshold.

[0127] <8> The high-frequency circuit according to any one of <1> to <5>, wherein the first switch further has a second common terminal, and the high-frequency circuit further includes an impedance element connected between the second common terminal and ground.

[0128] <9> The high-frequency circuit according to <8>, wherein the first switch is configured to be switchable between: a fourth connection mode in which the first common terminal and the first selection terminal are connected and the second common terminal and the second selection terminal are connected; a fifth connection mode in which the first common terminal and the second selection terminal are connected and the second common terminal and the first selection terminal are connected; and a sixth connection mode in which the first common terminal is not connected to the first selection terminal and the second selection terminal and the second selection terminal is not connected to the second common terminal.

[0129] <10> The high-frequency circuit according to any one of <1> to <5>, wherein the first switch further has a second common terminal, and the high-frequency circuit further comprises: a second clamp circuit connected between the second common terminal and ground; a second switch having a third common terminal, a third selection terminal, and a fourth selection terminal; a first filter having a pass band including a transmission band of a first band; and a second filter having a pass band including a transmission band of a second band, wherein the third common terminal is connected to the third output terminal, the third selection terminal is connected to the first filter, and the fourth selection terminal is connected to the second filter.

[0130] <11> The high-frequency circuit according to <10>, wherein the first switch and the second switch are configured to be switchable between: a seventh connection mode in which the first common terminal is connected to the first selection terminal or the second selection terminal, and the third common terminal is connected to the third selection terminal; an eighth connection mode in which the second common terminal is connected to the first selection terminal or the second selection terminal, and the third common terminal is connected to the fourth selection terminal; and a ninth connection mode in which the first common terminal is not connected to the first selection terminal and the second selection terminal, and the second common terminal is not connected to the first selection terminal and the second selection terminal.

[0131] <12> The high-frequency circuit according to any one of <1> to <11>, wherein the second output signal output from the second output terminal is 90° ahead in phase with the first output signal output from the first output terminal, and the combining circuit includes: a high-pass filter connected between the second input terminal and the third output terminal; and a low-pass filter connected between the third input terminal and the third output terminal.

[0132] <13> The high-frequency circuit according to any one of <1> to <11>, wherein the second output signal output from the second output terminal is 90° ahead in phase with the first output signal output from the first output terminal, the combining circuit includes: a transformer having an input coil and an output coil; a low-pass filter connected between the second input terminal and one end of the input coil; and a high-pass filter connected between the third input terminal and the other end of the input coil, one end of the output coil being connected to the third output terminal, and the other end of the output coil being connected to ground.

[0133] <14> A communication device comprising: a signal processing circuit that processes a high-frequency signal; and the high-frequency circuit according to any one of <1> to <13> that transmits the high-frequency signal between the signal processing circuit and an antenna.

[0134] The present invention can be widely used as an amplifier circuit disposed in a front end portion of communication devices such as mobile phones.

[0135] REFERENCE SIGNS LIST 1, 1A, 1B, 1C, 1D High frequency circuit 2 Antenna 3 RFIC 4 Communication device 10 90° hybrid circuit 10a, 30b, 30c Input terminal 10b, 10c, 30a Output terminal 21, 22 Power amplifier 30, 30A Combiner circuit 31 High pass filter 32 Low pass filter 33 Transformer 41, 42, 43, 44 Switch 41a, 42a, 43a, 44a, 44b Common terminal 41b, 41c, 42b, 42c, 43b, 43c, 44c, 44d Selection terminal 51, 52 Filter 56, 57, 58 Matching circuit 60, 61, 62 Coupler 65, 67 Clamp circuit 65a, 65b, 67a, 67b Terminal 66, 311, 322 Capacitor 70 Control circuit 100 Antenna connection terminal 110 Signal input terminal 312, 321 Inductors 651, 652, 653, 654, 655 Diodes

Claims

1. A high frequency circuit comprising: a 90° hybrid circuit having a first input terminal, a first output terminal, and a second output terminal; a combiner circuit having a second input terminal, a third input terminal, and a third output terminal; first and second power amplifiers; a first switch having a first common terminal, a first selection terminal, and a second selection terminal; and a first clamp circuit, wherein the input terminal of the first power amplifier is connected to the first output terminal, and the output terminal of the first power amplifier is connected to the second input terminal and the first selection terminal, the input terminal of the second power amplifier is connected to the second output terminal, and the output terminal of the second power amplifier is connected to the third input terminal and the second selection terminal, and the first clamp circuit is connected between the first common terminal and ground.

2. The high-frequency circuit according to claim 1, further comprising: an antenna connection terminal connected to said third output terminal; a coupler arranged in at least one of a first signal path connecting the output end of said first power amplifier and said antenna connection terminal and a second signal path connecting the output end of said second power amplifier and said antenna connection terminal; and a control circuit connected between said coupler and said first switch.

3. The high-frequency circuit according to claim 2, wherein the coupler is disposed on a common signal path connecting the third output terminal and the antenna connection terminal.

4. The high-frequency circuit according to claim 2, wherein the coupler is disposed in either a first signal path connecting the output end of the first power amplifier and the second input terminal, or a second signal path connecting the output end of the second power amplifier and the third input terminal.

5. The radio frequency circuit according to any one of claims 2 to 4, wherein the coupler detects a forward signal traveling from the third output terminal to the antenna connection terminal and a reflected signal traveling in a reverse direction from the antenna connection terminal to the third output terminal, and the control circuit calculates the output impedances of the first power amplifier and the second power amplifier from the forward signal and the reflected signal traveling in a reverse direction detected by the coupler.

6. The high-frequency circuit according to claim 5, wherein the first switch is configured to be switchable between a first connection mode in which the first common terminal and the first selection terminal are connected and the first common terminal and the second selection terminal are not connected, a second connection mode in which the first common terminal and the first selection terminal are not connected and the first common terminal and the second selection terminal are connected, and a third connection mode in which the first common terminal and the first selection terminal are not connected and the first common terminal and the second selection terminal are not connected.

7. The radio frequency circuit according to claim 6, wherein the control circuit operates the first switch in the first connection mode when the calculated output impedance of the first power amplifier is greater than a predetermined threshold, operates the first switch in the second connection mode when the calculated output impedance of the second power amplifier is greater than the predetermined threshold, and operates the first switch in the third connection mode when the calculated output impedance of the first power amplifier and the output impedance of the second power amplifier are both equal to or less than the predetermined threshold.

8. The high-frequency circuit according to any one of claims 1 to 5, wherein the first switch further has a second common terminal, and the high-frequency circuit further comprises an impedance element connected between the second common terminal and ground.

9. The high-frequency circuit according to claim 8, wherein the first switch is configured to be switchable between a fourth connection mode in which the first common terminal and the first selection terminal are connected and the second common terminal and the second selection terminal are connected, a fifth connection mode in which the first common terminal and the second selection terminal are connected and the second common terminal and the first selection terminal are connected, and a sixth connection mode in which the first common terminal is not connected to the first selection terminal and the second selection terminal and is not connected to the second common terminal and the first selection terminal and the second selection terminal.

10. The high-frequency circuit according to any one of claims 1 to 5, wherein the first switch further has a second common terminal, and the high-frequency circuit further comprises: a second clamp circuit connected between the second common terminal and ground; a second switch having a third common terminal, a third selection terminal, and a fourth selection terminal; a first filter having a pass band including the transmission band of a first band; and a second filter having a pass band including the transmission band of a second band, wherein the third common terminal is connected to the third output terminal, the third selection terminal is connected to the first filter, and the fourth selection terminal is connected to the second filter.

11. The high-frequency circuit according to claim 10, wherein the first switch and the second switch are configured to be switchable between: a seventh connection mode in which the first common terminal is connected to the first selection terminal or the second selection terminal, and the third common terminal is connected to the third selection terminal; an eighth connection mode in which the second common terminal is connected to the first selection terminal or the second selection terminal, and the third common terminal is connected to the fourth selection terminal; and a ninth connection mode in which the first common terminal is not connected to the first selection terminal or the second selection terminal, and the second common terminal is not connected to the first selection terminal or the second selection terminal.

12. The high-frequency circuit according to any one of claims 1 to 11, wherein the second output signal output from the second output terminal is 90° ahead in phase with the first output signal output from the first output terminal, and the combining circuit includes a high-pass filter connected between the second input terminal and the third output terminal, and a low-pass filter connected between the third input terminal and the third output terminal.

13. The high-frequency circuit according to any one of claims 1 to 11, wherein the second output signal output from the second output terminal is 90° ahead in phase with the first output signal output from the first output terminal, and the combining circuit includes: a transformer having an input coil and an output coil; a low-pass filter connected between the second input terminal and one end of the input coil; and a high-pass filter connected between the third input terminal and the other end of the input coil, one end of the output coil being connected to the third output terminal, and the other end of the output coil being connected to ground.

14. A communication device comprising: a signal processing circuit that processes a high-frequency signal; and a high-frequency circuit according to any one of claims 1 to 13 that transmits a high-frequency signal between the signal processing circuit and an antenna.

Images