Patent Publication Number: US-2023163796-A1

Title: High-frequency circuit and communication device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of International Application No. PCT/JP2021/032658 filed on Sep. 6, 2021 which claims priority from Japanese Patent Application No. 2020-161139 filed on Sep. 25, 2020. The contents of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND ART 
     Technical Field 
     The present disclosure relates to a high-frequency circuit and a communication device. 
     With the progress of multiband technology, mobile communication equipment such as mobile phones have been required to have a front end circuit that is capable of simultaneously transmitting high-frequency signals having mutually-different frequencies. For example, Patent Document 1 discloses a circuit configuration of an electronic system (high-frequency front end module) including a first transmission circuit and a second transmission circuit. 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-17691 
     BRIEF SUMMARY 
     In the above-mentioned related art, however, when a plurality of high-frequency signals are simultaneously transmitted and simultaneously transmitted and received, intermodulation distortion (IMD) among the plurality of high-frequency signals overlaps with a reception band and receiving sensitivity sometimes degrades disadvantageously. 
     Therefore, the present disclosure provides a high-frequency circuit and a communication device that are capable of suppressing degradation of receiving sensitivity caused by intermodulation distortion in simultaneous transmission and simultaneous transmission and reception of a plurality of high-frequency signals. 
     A high-frequency circuit of an aspect of the present disclosure includes: a first filter that has a pass band including a transmission band of a first communication band; a second filter that has a pass band including a transmission band of a second communication band which is different from the first communication band; a third filter that has a pass band including a reception band of a third communication band; a first power amplifier that is connected with the first filter; and a second power amplifier that is connected with the second filter. Transmission in the first communication band, transmission in the second communication band, and reception in the third communication band can be simultaneously used. At least part of a frequency range of intermodulation distortion, which is generated between a second harmonic wave of a transmission signal of the first communication band and a fundamental wave of a transmission signal of the second communication band, overlaps with at least part of the reception band of the third communication band. The first power amplifier includes a first amplifying element, a second amplifying element, and an output converter that is a first transformer including a first coil and a second coil. One end of the first coil is connected with an output of the first amplifying element, the other end of the first coil is connected with an output of the second amplifying element, and one end of the second coil is connected with an output terminal of the first power amplifier. 
     According to the high-frequency circuit of the aspect of the present disclosure, degradation of receiving sensitivity caused by intermodulation distortion can be suppressed when a plurality of high-frequency signals are simultaneously transmitted and simultaneously transmitted and received. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a circuit configuration diagram of a high-frequency circuit and a communication device according to an embodiment. 
         FIG.  2    is a circuit configuration diagram of a power amplifier included in the high-frequency circuit according to the embodiment. 
         FIG.  3    is a diagram illustrating signal flow in the communication device according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments according to the present disclosure will be described in detail below with reference to the accompanying drawings. All of the embodiments described below are generic or specific examples. Numerical values, shapes, materials, components, arrangement and connection forms of the components, and the like shown in the following embodiments are examples, and are not intended to limit the present disclosure. 
     Each drawing is a schematic diagram with emphasis, omission, or proportion adjustment performed as appropriate to illustrate the present disclosure. Thus, each drawing is not necessarily a strict illustration and may differ from the actual shapes, positioning, and proportions. In each drawing, the same reference characters are applied to substantially identical configurations and redundant description may be omitted or simplified. 
     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 being connected with both of A and B between A and B. 
     EMBODIMENT 
     1.1 Circuit Configurations of High-frequency Circuit  1  and Communication Device  5   
     Circuit configurations of a high-frequency circuit  1  and a communication device  5  according to the present 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  5  according to the embodiment. 
     1.1.1 Circuit Configuration of Communication Device  5   
     The circuit configuration of the communication device  5  will be first described. As illustrated in  FIG.  1   , the communication device  5  according to the present embodiment includes the high-frequency circuit  1 , an antenna  2 , an RFIC  3 , and a BBIC  4 . 
     The high-frequency circuit  1  transmits a high-frequency signal between the antenna  2  and the RFIC  3 . The circuit configuration of the high-frequency circuit  1  will be described later. 
     The antenna  2  is connected with an antenna connection terminal  100  of the high-frequency circuit  1 . The antenna  2  receives a high-frequency signal from the outside and outputs the high-frequency signal to the high-frequency circuit  1 . 
     The RFIC  3  is an example of a signal processing circuit that processes a high-frequency signal. Specifically, the RFIC  3  processes a high-frequency reception signal, inputted via a reception path of the high-frequency circuit  1 , by down-conversion or the like and outputs the reception signal generated by this signal processing to the BBIC  4 . Further, the RFIC  3  includes a control unit that controls switches, amplifiers, and the like included in the high-frequency circuit  1 . Here, part or all of the function as the control unit of the RFIC  3  may be mounted on the outside of the RFIC  3 , and may be mounted, for example, on the BBIC  4  or the high-frequency circuit  1 . 
     The BBIC  4  is a baseband signal processing circuit that processes a signal by using an intermediate frequency band which is lower in frequency than the high-frequency signal transmitted by the high-frequency circuit  1 . Examples of a signal processed in the BBIC  4  include an image signal for displaying an image and/or an audio signal for calls through speakers. 
     In the communication device  5  according to the present embodiment, the antenna  2  and the BBIC  4  are optional components. 
     1.1.2 Circuit Configuration of High-frequency Circuit  1   
     The circuit configuration of the high-frequency circuit  1  will now be described. As illustrated in  FIG.  1   , the high-frequency circuit  1  includes power amplifiers  11  and  12 , a low noise amplifier  21 , a switch  51 , filters  61  to  63 , the antenna connection terminal  100 , high-frequency input terminals  111  and  112 , and a high-frequency output terminal  121 . 
     The antenna connection terminal  100  is connected to the antenna  2 . 
     Each of the high-frequency input terminals  111  and  112  is a terminal for receiving a high-frequency transmission signal from the outside of the high-frequency circuit  1 . The high-frequency input terminal  111  can receive a transmission signal of a communication band A from the RFIC  3 . The high-frequency input terminal  112  can receive a transmission signal of a communication band B from the RFIC  3 . In the present embodiment, both of transmission signals received at the high-frequency input terminals  111  and  112  are unbalanced signals. 
     The high-frequency output terminal  121  is a terminal for providing a high-frequency reception signal to the outside of the high-frequency circuit  1 . Specifically, the high-frequency output terminal  121  is a terminal for providing a reception signal of a communication band C to the RFIC  3 . 
     The communication band means a frequency band predefined by a standards body (for example, 3rd Generation Partnership Project (3GPP) and Institute of Electrical and Electronics Engineers (IEEE)) or the like for communication systems. 
     Here, the communication systems mean communication systems built by using the radio access technology (RAT). Examples of the communication systems include 5th generation new radio (5GNR) systems, long term evolution (LTE) systems, and wireless local area network (WLAN) systems, but the communication systems are not limited to these. 
     The communication band A is an example of a first communication band. The communication band B is an example of a second communication band and is a different frequency band from the communication band A. The communication band C is an example of a third communication band. The communication band C may be the same as either one of the communication bands A and B or may be different from the communication bands A and B. The communication bands A, B, and C may be either a frequency division duplex (FDD) communication band or a time division duplex (TDD) communication band. 
     Here, transmission in the communication band A, transmission in the communication band B, and reception in the communication band C can be simultaneously used. “Transmission in the communication band A, transmission in the communication band B, and reception in the communication band C can be simultaneously used” means that a transmission signal of the communication band A, a transmission signal of the communication band B, and a reception signal of the communication band C are allowed to be simultaneously transmitted and received. However, it is not excluded that transmission and reception of a plurality of communication bands are each used independently. A combination of communication bands that can be simultaneously used is predefined by, for example, a standards body. 
     The power amplifier  11  is an example of a first power amplifier. An input terminal  115  of the power amplifier  11  is connected with the high-frequency input terminal  111  and an output terminal  116  of the power amplifier  11  is connected with the filter  61 . The power amplifier  11  is capable of amplifying a transmission signal of the communication band A received at the high-frequency input terminal  111 . At this time, the power amplifier  11  is capable of converting an unbalanced signal received at the high-frequency input terminal  111  into a balanced signal and amplifying the balanced signal. This kind of power amplifier  11  is sometimes called a differential amplifier. The detailed configuration of the power amplifier  11  will be described later with reference to  FIG.  2   . 
     A balanced signal means a pair of signals that have mutually-opposite phases. A balanced signal is sometimes called a differential signal. On the other hand, an unbalanced signal means a signal expressed by a potential difference from ground. An unbalanced signal is sometimes called a single end signal. 
     The power amplifier  12  is an example of a second power amplifier. An input terminal  125  of the power amplifier  12  is connected with the high-frequency input terminal  112  and an output terminal  126  of the power amplifier  12  is connected with the filter  62 . The power amplifier  12  is a multi-stage amplifier and includes two amplifying elements  12 A and  12 B which are connected in series. The amplifying element  12 A is equivalent to an input stage of a multi-stage amplifier. The amplifying element  12 B is equivalent to an output stage of a multi-stage amplifier. 
     The power amplifier  12  is capable of amplifying a transmission signal of the communication band B received at the high-frequency input terminal  112 . At this time, the power amplifier  12  is capable of amplifying the transmission signal of the communication band B as an unbalanced signal without necessarily conversion. That is, the power amplifier  12  is capable of amplifying an unbalanced signal of the communication band B received at the high-frequency input terminal  111  without necessarily converting the unbalanced signal into a balanced signal. This kind of power amplifier  12  is sometimes called a non-differential amplifier. 
     The configuration of the power amplifier  12  is not limited to the configuration of  FIG.  1   . For example, the power amplifier  12  may be a single-stage amplifier. Alternatively, the power amplifier  12  may be a differential amplifier or a Doherty amplifier. 
     The power amplifiers  11  and  12  correspond to a high-power class and a non-high-power class respectively. A power class is a classification of terminal output power which is defined as maximum output power or the like, and a smaller power class value indicates that it corresponds to higher power output. The maximum output power of a high-power class is larger than the maximum output power of a non-high-power class. The maximum output power is defined by output power at an antenna end of a terminal. The maximum output power is measured by a method defined by, for example, 3GPP. For example, the maximum output power is measured by measuring radiation power of the antenna  2 , in  FIG.  1   . Instead of measuring radiation power, output power of the antenna  2  can be measured by providing a terminal near the antenna  2  and connecting a measuring instrument (such as a spectrum analyzer) to the terminal. 
     The high-power class is an example of a first power class and is expressed by a numerical value which is lower than a predetermined value. The non-high-power class is an example of a second power class and is expressed by a numerical value which is a predetermined value or greater. The predetermined value can be, for example, 3. In this case, the high-power class includes power classes 1, 1.5, and 2, and the non-high-power class includes power classes 3 and 4. 
     An input of the low noise amplifier  21  is connected with the filter  63  and an output of the low noise amplifier  21  is connected with the high-frequency output terminal  121 . The low noise amplifier  21  is capable of amplifying a reception signal of the communication band C received at the antenna connection terminal  100 . The reception signal of the communication band C amplified by the low noise amplifier  21  is outputted to the high-frequency output terminal  121 . 
     Amplifying elements included in the power amplifiers  11  and  12  and low noise amplifier  21  can be composed of, for example, a field effect transistor (FET) or a hetero bipolar transistor (HBT) that is made of Si-based complementary metal oxide semiconductor (CMOS) or GaAs. 
     The switch  51  is connected between the antenna connection terminal  100  and the filters  61  to  63 . The switch  51  includes terminals  511  to  514 . The terminal  511  is connected with the antenna connection terminal  100 . The terminals  512  to  514  are connected with the filters  61  to  63  respectively. 
     In this connection configuration, the switch  51  is capable of connecting at least one of the terminals  512  to  514  to the terminal  511  in response to, for example, a control signal from the RFIC  3 . That is, the switch  51  is capable of switching connection and disconnection between the antenna connection terminal  100  and each of the filters  61  to  63 . The switch  51  is composed of, for example, a multi-connection switching circuit and is called an antenna switch. 
     The filter  61  (A-Tx) is an example of a first filter and has a pass band including the transmission band of the communication band A. One end of the filter  61  is connected with the antenna connection terminal  100  via the switch  51 . The other end of the filter  61  is connected with the output terminal  116  of the power amplifier  11 . 
     The filter  62  (B-Tx) is an example of a second filter and has a pass band including the transmission band of the communication band B. One end of the filter  62  is connected with the antenna connection terminal  100  via the switch  51 . The other end of the filter  62  is connected with the output terminal  126  of the power amplifier  12 . 
     The filter  63  (C-Rx) is an example of a third filter and has a pass band including the reception band of the communication band C. One end of the filter  63  is connected with the antenna connection terminal  100  via the switch  51 . The other end of the filter  63  is connected with the input of the low noise amplifier  21 . 
     A transmission band is a frequency band for transmission in a communication band. As to a communication band for FDD, its transmission band is equivalent to an uplink operating band which is a portion in the communication band designated for uplink. As to a communication band for TDD, its transmission band is equivalent to the entire communication band. 
     A reception band is a frequency band for reception in a communication band. As to a communication band for FDD, its reception band is equivalent to a downlink operating band which is a portion in the communication band designated for downlink. As to a communication band for TDD, its reception band is equivalent to the entire communication band. 
     These filters  61  to  63  may be any of an acoustic wave filter using a surface acoustic wave (SAW), an acoustic wave filter using a bulk acoustic wave (BAW), an LC resonance filter, and a dielectric filter, for example, and further, the filters  61  to  63  are not limited to these. 
     Some of the circuit elements illustrated in  FIG.  1    do not have to be included in the high-frequency circuit  1 . For example, the high-frequency circuit  1  just has to include at least the power amplifiers  11  and  12  and the filters  61  to  63 , and does not have to include other circuit elements (such as the switch  51  and the low noise amplifier  21 ). 
     1.1.3 Circuit Configuration of Power Amplifier  11   
     An example of the circuit configuration of the power amplifier  11  will now be described with reference to  FIG.  2   .  FIG.  2    is a circuit configuration diagram of the power amplifier  11  included in the high-frequency circuit  1  according to the embodiment. Hereinafter, a transformer is abbreviated as a trans. 
     As illustrated in  FIG.  2   , the power amplifier  11  includes the input terminal  115 , the output terminal  116 , amplifying elements  11 A to  11 C, an output trans  31 , a capacitor  32 , and an input trans  33 . 
     The input terminal  115  is connected with the high-frequency input terminal  111  of the high-frequency circuit  1 . An unbalanced signal received at the high-frequency input terminal  111  from the outside is transmitted to the input terminal  115 . 
     The amplifying element  11 C is equivalent to an input stage of a multi-stage amplifier. An input of the amplifying element  11 C is connected with the input terminal  115  of the power amplifier  11 , and an output of the amplifying element  11 C is connected with the input trans  33 . In this connection configuration, the amplifying element  11 C is capable of amplifying an unbalanced signal received at the input terminal  115  in a state that a power supply voltage Vcc 1  is applied. 
     The input trans  33  is an example of an input converter. The input trans  33  includes a coil  33   a  on the primary side and a coil  33   b  on the secondary side. The coil  33   a  is an example of a third coil. One end of the coil  33   a  is connected with an output terminal of the amplifying element  11 C, and the power supply voltage Vcc 1  is applied to the other end. The coil  33   b  is an example of a fourth coil. One end of the coil  33   b  is connected with an input of the amplifying element  11 A, and the other end is connected with an input of the amplifying element  11 B. 
     The input trans  33  is capable of converting an unbalanced signal amplified in the amplifying element  11 C into a balanced signal. That is, the input trans  33  is an unbalance-balance converter. Specifically, the input trans  33  is capable of converting a transmission signal of the communication band A amplified in the amplifying element  11 C into an inverted signal whose phase is inverted and a non-inverted signal whose phase is not inverted. 
     The amplifying elements  11 A and  11 B are examples of a first amplifying element and a second amplifying element respectively and are capable of individually amplifying balanced signals outputted from the input trans  33 . The input of the amplifying element  11 A is connected with one end of the coil  33   b  of the input trans  33 , and an output of the amplifying element  11 A is connected with one end of a coil  31   a  of the output trans  31  and one end of the capacitor  32 . The input of the amplifying element  11 B is connected with the other end of the coil  33   b  of the input trans  33 , and an output of the amplifying element  11 B is connected with the other end of the coil  31   a  of the output trans  31  and the other end of the capacitor  32 . 
     The output trans  31  is an example of an output converter. The output trans  31  includes the coil  31   a  on the primary side and a coil  31   b  on the secondary side. The coil  31   a  is an example of a first coil. One end of the coil  31   a  is connected with the output of the amplifying element  11 A, and the other end is connected with the output of the amplifying element  11 B. Further, a power supply voltage Vcc 2  is applied to a midpoint of the coil  31   a.  The coil  31   b  is an example of a second coil. One end of the coil  31   b  is connected with the output terminal  116 , and the other end is connected to the ground. That is, the output trans  31  is connected between the output of the amplifying element  11 A and the output terminal  116  and between the output of the amplifying element  11 B and the output terminal  116 . 
     The output trans  31  is capable of converting a balanced signal into an unbalanced signal by combining balanced signals amplified in the amplifying elements  11 A and  11 B. That is, the output trans  31  is a balance-unbalance converter. Specifically, the output trans  31  is capable of combining an inverted signal and a non-inverted signal of a transmission signal of the communication band A. 
     The capacitor  32  is connected between the output of the amplifying element  11 A and the output of the amplifying element  11 B. Specifically, one end of the capacitor  32  is connected with the output of the amplifying element  11 A and one end of the coil  31   a.  Further, the other end of the capacitor  32  is connected with the output of the amplifying element  11 B and the other end of the coil  31   a.    
     According to the circuit configuration of the power amplifier  11 , the amplifying elements  11 A and  11 B operate in inverted phases. At this time, current in a fundamental wave of the amplifying element  11 A and current in a fundamental wave of the amplifying element  11 B flow in inverted phases, that is, flow in opposite directions. Therefore, it becomes hard for current in the fundamental wave to flow toward ground wiring and power supply wiring which are arranged at substantially the same distance from the amplifying elements  11 A and  11 B. This can suppress unwanted current flow into the ground wiring and the power supply wiring, being able to suppress reduction of power gain which have been found in conventional power amplifiers. Also, a non-inverted signal and an inverted signal that are amplified in the amplifying elements  11 A and  11 B respectively are combined. Therefore, noise components that are similarly superimposed on both of the signals can be canceled and even-order harmonic wave components can be reduced. 
     The circuit configuration of the power amplifier  11  in  FIG.  2    is an example and is not limited to this. For example, the power amplifier  11  does not have to include the amplifying element  11 C and the capacitor  32 . Further, when a balanced signal is inputted into the power amplifier  11 , the power amplifier  11  does not have to include the input trans  33 . 
     In addition, a trans is used for unbalance-balance conversion and balance-unbalance conversion in the present embodiment, but the present disclosure is not limited to this. Namely, an input converter and an output converter are not limited to the input trans  33  and the output trans  31 . For example, delay lines can be used as an input converter and an output converter. 
     1.2 Signal Flow in High-frequency Circuit  1   
     Simultaneous use of transmission in the communication band A, transmission in the communication band B, and reception in the communication band C in the communication device  5  will now be described.  FIG.  3    is a diagram illustrating signal flow in the communication device  5  according to the embodiment. Dashed arrows in  FIG.  3    indicate signal flow. 
     In  FIG.  3   , transmission in the communication band A, transmission in the communication band B, and reception in the communication band C are simultaneously used. That is,  FIG.  3    illustrates a state of carrying out simultaneous transmission of a transmission signal of the communication band A, a transmission signal of the communication band B, and a reception signal of the communication band C. 
     In this example, all of the terminals  512  to  514  of the switch  51  are connected with the terminal  511 . Accordingly, a transmission signal of the communication band A is transmitted from the RFIC  3  through the high-frequency input terminal  111 , power amplifier  11 , filter  61 , switch  51 , and antenna connection terminal  100  in this order to the antenna  2 . Further, a transmission signal of the communication band B is transmitted from the RFIC  3  through the high-frequency input terminal  112 , power amplifier  12 , filter  62 , switch  51 , and antenna connection terminal  100  in this order to the antenna  2 . Further, a reception signal of the communication band C is transmitted from the antenna  2  through the antenna connection terminal  100 , switch  51 , filter  63 , low noise amplifier  21 , and high-frequency output terminal  121  in this order to the RFIC  3 . 
     At this time, in the switch  51  and/or the filters  61  to  63 , for example, IMD is generated between a second harmonic wave of the transmission signal of the communication band A and a fundamental wave of the transmission signal of the communication band B. A frequency fIMD of IMD is expressed as the following by using a frequency fA of a fundamental wave of the transmission signal of the communication band A and a frequency fB of the fundamental wave of the transmission signal of the communication band B. 
         f IMD=2 fA−fB    
     As the frequency fA, an arbitrary frequency within the transmission band of the communication band A can be used. In a similar manner, as the frequency fB, an arbitrary frequency within the transmission band of the communication band B can be used. Thus, the frequency fIMD of IMD also varies within a frequency range defined depending on the transmission bands of the communication bands A and B. 
     If the frequency fIMD of IMD is included in the reception band of the communication band C, an unwanted wave of the IMD interferes a reception signal of the communication band C and reception sensitivity is accordingly degraded. In such circumstances, the high-frequency circuit  1  according to the present embodiment includes a differential amplifier as the power amplifier  11  for amplifying a transmission signal of the communication band A. This can suppress generation of a second harmonic wave of a transmission signal of the communication band A and reduce an unwanted wave of the IMD. 
     1.3 Specific Examples of Communication Bands A, B, and C 
     Specific examples of the communication bands A, B, and C will now be described. In the present embodiment, the communication bands A, B, and C satisfy the following conditions (1) and (2). (1) Transmission in the communication band A, transmission in the communication band B, and reception in the communication band C can be simultaneously used. (2) At least part of a frequency range of IMD, which is generated between a second harmonic wave of a transmission signal of the communication band A and a fundamental wave of a transmission signal of the communication band B, overlaps with at least part of the reception band of the communication band C. 
     Combinations shown in Table 1 are the conceivable specific examples of the communication bands A to C satisfying the conditions (1) and (2). 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Communication  
                 Communication  
                 Communication  
               
               
                   
                 band A 
                 band B 
                 band C 
               
               
                   
                 (transmission band) 
                 (transmission band) 
                 (reception band) 
               
               
                   
                   
               
             
            
               
                   
                 Band 1 
                 Band 3 
                 Band 1 
               
               
                   
                 Band 3 
                 Band 1 
                 Band 32 
               
               
                   
                 Band 40 
                 Band 1 
                 Band 41 
               
               
                   
                 Band 40 
                 Band 1 
                 Band 7 
               
               
                   
                 Band 1 
                 Band 7 
                 Band 32 
               
               
                   
                 Band 1 
                 Band 40 
                 Band 7 
               
               
                   
                 Band 1 
                 Band 40 
                 Band 41 
               
               
                   
                   
               
            
           
         
       
     
     The combinations of communication bands shown in Table 1 be examples and the communication bands A to C be not limited to the above. 
     1.4 Effects Etc. 
     As described above, the high-frequency circuit  1  according to the present embodiment includes: the filter  61  that has a pass band including the transmission band of the communication band A; the filter  62  that has a pass band including the transmission band of the communication band B which is different from the communication band A; the filter  63  that has a pass band including the reception band of the communication band C; the power amplifier  11  that is connected with the filter  61 ; and the power amplifier  12  that is connected with the filter  62 . Transmission in the communication band A, transmission in the communication band B, and reception in the communication band C can be simultaneously used. At least part of a frequency range of intermodulation distortion, which is generated between a second harmonic wave of a transmission signal of the communication band A and a fundamental wave of a transmission signal of the communication band B, overlaps with at least part of the reception band of the communication band C. The power amplifier  11  includes the amplifying elements  11 A and  11 B and the output trans including the coils  31   a  and  31   b.  One end of the coil  31   a  is connected with the output of the amplifying element  11 A, the other end of the coil  31   a  is connected with the output of the amplifying element  11 B, and one end of the coil  31   b  is connected with the output terminal  116  of the power amplifier  11 . 
     According to this configuration, the power amplifier  11  is capable of individually amplifying balanced signals by the amplifying elements  11 A and  11 B and combining the amplified balanced signals at the output trans  31  so as to generate an unbalanced signal. Accordingly, second harmonic wave components contained in an unbalanced signal can be reduced and therefore, intermodulation distortion, which is generated between a second harmonic wave of a transmission signal of the communication band A and a fundamental wave of a transmission signal of the communication band B, can also be reduced. As a result, interference by an unwanted wave of the intermodulation distortion to a reception signal of the communication band C can be suppressed and degradation of reception sensitivity caused by the intermodulation distortion can be suppressed. Further, the output trans  31  is capable of performing impedance conversion in addition to balance-unbalance conversion and accordingly, impedance matching can be achieved between an output impedance of the power amplifier  11  and an input impedance of the filter  61 . 
     Further, for example, in the high-frequency circuit  1  according to the present embodiment, the power amplifier  11  may correspond to a high-power class, the power amplifier  12  may correspond to a non-high-power class, and the maximum output power of the high-power class may be larger than the maximum output power of the non-high-power class. 
     According to this configuration, generation of a second harmonic wave can be suppressed in the power amplifier  11  which is required to have greater output power. Thus, a second harmonic wave of a transmission signal of the communication band A can be effectively reduced and intermodulation distortion, which is generated between a second harmonic wave of a transmission signal of the communication band A and a fundamental wave of a transmission signal of the communication band B, can also be more effectively reduced. 
     Further, for example, in the high-frequency circuit  1  according to the present embodiment, the amplifying elements  11 A and  11 B may be capable of individually amplifying a balanced signal that is a transmission signal of the communication band A, and by combining the balanced signal amplified in the amplifying element  11 A and the balanced signal amplified in the amplifying element  11 B with each other, the output trans  31  may be capable of converting the balanced signals into an unbalanced signal. 
     According to this configuration, balanced signals can be individually amplified and the amplified balanced signals can be combined to generate an unbalanced signal. 
     Further, for example, in the high-frequency circuit  1  according to the present embodiment, the power amplifier  12  may be capable of amplifying a transmission signal of the communication band B as an unbalanced signal without necessarily conversion. 
     According to this configuration, a so-called non-differential amplifier can be used as the power amplifier  12 . In a non-differential amplifier, the number of amplifying elements can be reduced and elements for balance-unbalance conversion and the like can be omitted. Accordingly, the power amplifier  12  can be downsized compared to a differential amplifier, being able to contribute to downsizing of the high-frequency circuit  1 . Further, in the present embodiment, a second harmonic wave generated in the power amplifier  12  has little effect on intermodulation distortion included in the reception band of the communication band C described above. Accordingly, even when a differential amplifier is not used as the power amplifier  12 , degradation of reception sensitivity caused by intermodulation distortion can be suppressed with the use of a differential amplifier as the power amplifier  11 . 
     Further, for example, in the high-frequency circuit  1  according to the present embodiment, the power amplifier  11  may further include an input converter that is connected with the amplifying element  11 A and the amplifying element  11 B and is capable of converting a transmission signal of the first communication band from an unbalanced signal into the balanced signal. 
     According to this configuration, the power amplifier  11  is capable of converting an unbalanced signal into a balanced signal and therefore, the power amplifier  11  can receive a transmission signal of the communication band A from the RFIC  3  as the transmission signal is an unbalanced signal. Thus, a conventional high-frequency circuit can be replaced with the high-frequency circuit  1  according to the present embodiment. 
     Further, for example, in the high-frequency circuit  1  according to the present embodiment, the input converter may be the input trans  33  that includes the coil  33   a  and the coil  33   b.  One end of the coil  31   a  may be connected with the input terminal  115  of the power amplifier  11 , one end of the coil  33   b  may be connected with the input of the amplifying element  11 A, and the other end of the coil  33   b  may be connected with the input of the amplifying element  11 B. 
     According to this configuration, a transformer can be used as an input converter. Thus, the input converter is capable of performing impedance conversion in addition to unbalance-balance conversion. 
     Further, for example, in the high-frequency circuit  1  according to the present embodiment, both of the communication band A and the communication band C may be a band 1 for LTE or 5GNR and the communication band B may be a band 3 for LTE or 5GNR. Further, for example, in the high-frequency circuit  1  according to the present embodiment, the communication band A may be the band 3 for LTE or 5GNR, the communication band B may be the band 1 for LTE or 5GNR, and the communication band C may be a band 32 for LTE or 5GNR. Further, for example, in the high-frequency circuit  1  according to the present embodiment, the communication band A may be a band 40 for LTE or 5GNR, the communication band B may be the band 1 for LTE or 5GNR, and the communication band C may be a band 41 for LTE or 5GNR. Further, for example, in the high-frequency circuit  1  according to the present embodiment, the communication band A may be the band 40 for LTE or 5GNR, the communication band B may be the band 1 for LTE or 5GNR, and the communication band C may be a band 7 for LTE or 5GNR. Further, for example, in the high-frequency circuit  1  according to the present embodiment, the communication band A may be the band 1 for LTE or 5GNR, the communication band B may be the band 7 for LTE or 5GNR, and the communication band C may be the band 32 for LTE or 5GNR. 
     The use of these communication bands as the communication bands A to C can effectively suppress degradation of reception sensitivity caused by intermodulation distortion. 
     Further, the communication device  5  according to the present embodiment includes the RFIC  3  that processes a high-frequency signal and the high-frequency circuit  1  that transmits the high-frequency signal between the RFIC  3  and the antenna  2 . 
     Accordingly, the same effects as those of the high-frequency circuit  1  can be realized in the communication device  5 . 
     Other Embodiments 
     The high-frequency circuit and communication device according to the present disclosure have been described above based on the embodiment. However, the high-frequency circuit and communication device according to the present disclosure are not limited to the above-described embodiment. The disclosure also includes modifications that can be obtained by making various changes, which a person skilled in the art can think of, to the above-described embodiment without necessarily departing from the scope of the present disclosure, and various devices incorporating the above-described high-frequency circuit and communication device. 
     For example, in the circuit configurations of the high-frequency circuit and communication device according to the above-described embodiment, another circuit element and wiring, for example, may be inserted between the paths connecting the circuit elements and signal paths disclosed in the drawings. For example, an impedance matching circuit may be inserted between the switch  51  and each of the filters  61  to  63 . This impedance matching circuit can be composed, for example, of an inductor and/or a capacitor. 
     Further, for example, each of the power amplifiers  11  and  12  and low noise amplifier  21  may be shared by a plurality of communication bands, in the circuit configurations of the high-frequency circuit and communication device according to the above-described embodiment. For example, the power amplifier  11  may be connected with a plurality of filters via a switch. 
     Furthermore, for example, when the communication bands A and C are identical communication bands, the filters  61  and  63  may be configured as a duplexer, in the circuit configuration of the high-frequency circuit according to the above-described embodiment. 
     Also, for example, the communication device according to the above-described embodiment may include a plurality of antennas. In this configuration, the filters  61  to  63  may be individually connected with different filters. Alternatively, two of the filters  61  to  63  may be connected with one antenna and the remaining one of the filters  61  to  63  may be connected with another antenna. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is widely applicable to communication devices, such as mobile phones, as a high-frequency circuit arranged in a front end portion. 
     REFERENCE SIGNS LIST 
     
         
           1  high-frequency circuit 
           2  antenna 
           3  RFIC 
           4  BBIC 
           5  communication device 
           11 ,  12  power amplifier 
           11 A,  11 B,  11 C,  12 A,  12 B amplifying element 
           21  low noise amplifier 
           31  output trans 
           31   a,    31   b,    33   a,    33   b  coil 
           32  capacitor 
           33  input trans 
           51  switch 
           61 ,  62 ,  63  filter 
           100  antenna connection terminal 
           111 ,  112  high-frequency input terminal 
           115 ,  125  input terminal 
           116 ,  126  output terminal 
           121  high-frequency output terminal 
           511 ,  512 ,  513 ,  514  terminal