Patent Publication Number: US-11394407-B2

Title: Radio frequency module and communication device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority of Japanese Patent Application No. 2020-057647 filed on Mar. 27, 2020. The entire disclosure of the above-identified application, including the specification, drawings and claims is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a radio frequency module and a communication device. 
     BACKGROUND 
     A power amplifier that amplifies radio frequency transmission signals is provided in a mobile communication apparatus such as a mobile phone. Japanese Unexamined Patent Application Publication No. 2018-137522 discloses a front end circuit (a radio frequency (RF) module) that includes a power amplifier (PA) circuit (a transmission amplifier circuit) that transfers a transmission signal, and a low noise amplifier (LNA) circuit (a reception amplifier circuit) that transfers a reception signal. A PA controller that controls amplification characteristics of a power amplifier is disposed in the transmission amplifier circuit, and an LNA controller that controls amplification characteristics of a low noise amplifier is disposed in the reception amplifier circuit. 
     SUMMARY 
     Technical Problems 
     However, as recognized by the present inventor, amplification performance of a power amplifier is optimized in a specific frequency band (a communication band), and thus the RF module disclosed in Japanese Unexamined Patent Application Publication No. 2018-137522 needs to include power amplifiers that handle signals in frequency bands (communication bands). Consequently, development in multiband technology brings a problem that the size of an RF module increases due to an increase in the number of power amplifiers. 
     The present disclosure has been conceived in order to solve the above-identified and other problems, and provides a small radio frequency module and a small communication device that support multiband technology. 
     Solutions 
     In order to provide such a radio frequency module, a radio frequency module according to an aspect of the present disclosure includes: a module board that includes a first principal surface and a second principal surface on opposite sides of the module board; a first power amplifier disposed on the first principal surface and configured to amplify a transmission signal in a first frequency band; a second power amplifier disposed on the first principal surface and configured to amplify a transmission signal in a second frequency band different from the first frequency band; and a control circuit disposed on the second principal surface and configured to control the first power amplifier and the second power amplifier. 
     Advantageous Effects 
     According to the present disclosure, a small radio frequency module and a small communication device that support multiband technology are provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other advantages and features will become apparent from the following description thereof taken in conjunction with the accompanying Drawings, by way of non-limiting examples of embodiments disclosed herein. 
         FIG. 1  illustrates a circuit configuration of a radio frequency module and a communication device according to an embodiment. 
         FIG. 2  illustrates a circuit configuration of a transmission amplifier circuit. 
         FIG. 3A  is a schematic diagram illustrating a planar configuration of a radio frequency module (or RF front-end circuitry) according to Example 1. 
         FIG. 3B  is a schematic diagram illustrating a cross-sectional configuration of the radio frequency module according to Example 1. 
         FIG. 4A  is a schematic diagram illustrating a cross-sectional configuration of an output transformer according to Variation 1. 
         FIG. 4B  is a schematic diagram illustrating a cross-sectional configuration of an output transformer according to Variation 2. 
         FIG. 4C  is a schematic diagram illustrating a cross-sectional configuration of an output transformer according to Variation 3. 
         FIG. 5  is a schematic diagram illustrating a cross-sectional configuration of a radio frequency module according to Variation 4. 
         FIG. 6  is a schematic diagram illustrating a planar configuration of a radio frequency module according to Example 2. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes in detail embodiments of the present disclosure. Note that the embodiments described below each show a general or specific example. The numerical values, shapes, materials, elements, and the arrangement and connection of the elements, for instance, described in the following embodiments are examples, and thus are not intended to limit the present disclosure. Among the elements in the following examples and variations, elements not recited in any of the independent claims are described as arbitrary elements. In addition, the sizes of elements and the ratios of the sizes illustrated in the drawings are not necessarily accurate. Throughout the drawings, the same numeral is given to substantially the same element, and redundant description may be omitted or simplified. 
     In the following, a term that indicates a relation between elements such as “parallel” or “perpendicular”, a term that indicates the shape of an element such as “rectangular”, and a numerical range do not necessarily have only strict meanings, and also cover substantially equivalent ranges that include a difference of about several percent, for example. 
     In the following, regarding A, B, and C mounted on a board, “C is disposed between A and B in a plan view of a board (or a principal surface of a board)” means at least one of line segments that connect arbitrary points in A and B passes through a region of C in a plan view of a board. A plan view of a board means that a board and a circuit element mounted on the board are viewed, being orthogonally projected onto a plane parallel to a principal surface of the board. In addition, “on” in expressions such as mounted on, disposed on, provided on, and formed on, for example, does not necessarily indicate direct contact. 
     In the following, a “transmission path” means a transfer route that includes, for instance, a line through which a radio frequency transmission signal propagates, an electrode directly connected to the line, and a terminal directly connected to the line or the electrode. Further, a “reception path” means a transfer route that includes, for instance, a line through which a radio frequency reception signal propagates, an electrode directly connected to the line, and a terminal directly connected to the line or the electrode. In addition, a “transmission and reception path” means a transfer route that includes, for instance, a line through which a radio frequency transmission signal and a radio frequency reception signal propagate, an electrode directly connected to the line, and a terminal directly connected to the line or the electrode. 
     EMBODIMENT 
     [1. Circuit Configuration of Radio Frequency Module  1  and Communication Device  5 ] 
       FIG. 1  illustrates a circuit configuration of radio frequency module  1  and communication device  5  according to an embodiment. As illustrated in  FIG. 1 , communication device  5  includes radio frequency module  1 , antenna  2 , radio frequency (RF) signal processing circuit (RF integrated circuit (RFIC))  3 , and baseband signal processing circuit (BB integrated circuit (BBIC))  4 . 
     RFIC  3  is an RF signal processing circuit that processes radio frequency signals transmitted and received by antenna  2 . Specifically, RFIC  3  processes a reception signal input through a reception path of radio frequency module  1  by down-conversion, for instance, and outputs a reception signal generated by being processed to BBIC  4 . RFIC  3  processes a transmission signal input from BBIC  4  by up-conversion, for instance, and outputs a transmission signal generated by being processed to a transmission path of radio frequency module  1 . 
     BBIC  4  is a circuit that processes signals using an intermediate frequency band lower than the frequency range of a radio frequency signal transferred in radio frequency module  1 . A signal processed by BBIC  4  is used, for example, as an image signal for image display or as an audio signal for talk through a loudspeaker. 
     RFIC  3  also functions as a controller that controls connection made by switches  41   42 ,  43 , and  44  included in radio frequency module  1 , based on a communication band (a frequency band) to be used. Specifically, RFIC  3  changes connection made by switches  41  to  44  included in radio frequency module  1  according to control signals (not illustrated). Specifically, RFIC  3  outputs digital control signals for controlling switches  41  to  44  to power amplifier (PA) control circuit  80 . PA control circuit  80  of radio frequency module  1  controls connection and disconnection of switches  41  to  44  by outputting digital control signals to switches  41  to  44  according to the digital control signals input from RFIC  3 . 
     RFIC  3  also functions as a controller that controls gains of transmission amplifier circuits  10  and  20  included in radio frequency module  1 , and power supply voltage Vcc and bias voltage Vbias that are supplied to transmission amplifier circuits  10  and  20 . Specifically, RFIC  3  outputs digital control signals to control signal terminal  140  of radio frequency module  1 . PA control circuit  80  of radio frequency module  1  adjusts gains of transmission amplifier circuits  10  and  20  by outputting control signals, power supply voltage Vcc, or bias voltage Vbias to transmission amplifier circuits  10  and  20  according to digital control signals input through control signal terminal  140 . Note that a control signal terminal that receives, from RFIC  3 , digital control signals for controlling gains of transmission amplifier circuits  10  and  20  and a control signal terminal that receives, from RFIC  3 , digital control signals for controlling power supply voltage Vcc and bias voltage Vbias that are supplied to transmission amplifier circuits  10  and  20  may be different terminals. The controller may be disposed outside of RFIC  3 , and may be disposed in BBIC  4 , for example. 
     Antenna  2  is connected to antenna connection terminal  100  of radio frequency module  1 , radiates a radio frequency signal output from radio frequency module  1 , and receives and outputs a radio frequency signal from the outside to radio frequency module  1 . 
     Note that antenna  2  and BBIC  4  are not necessarily included in communication device  5  according to the present embodiment. 
     Next, a detailed configuration of radio frequency module  1  is to be described. 
     As illustrated in  FIG. 1 , radio frequency module  1  includes antenna connection terminal  100 , transmission amplifier circuits  10  and  20 , low noise amplifier  30 , transmission filters  61 T,  62 T, and  63 T, reception filters  61 R,  62 R, and  63 R, PA control circuit  80 , matching circuits  51 ,  52 ,  53 , and  54 , and switches  41 ,  42 ,  43 , and  44 . 
     Antenna connection terminal  100  is an antenna common terminal connected to antenna  2 . 
     Transmission amplifier circuit  10  is a difference amplifying type amplifier circuit that amplifies transmission signals in communication bands A and B input through transmission input terminals  111  and  112 . Note that radio frequency module  1  may include, instead of transmission amplifier circuit  10 , a first transmission amplifier circuit that amplifies a radio frequency signal in communication band A, and a second transmission amplifier circuit that amplifies a radio frequency signal in communication band B. 
     Transmission amplifier circuit  20  is a difference amplifying type amplifier circuit that amplifies transmission signals in communication band C input through transmission input terminals  121  and  122 . 
     PA control circuit  80  adjusts gains of amplifying elements included in transmission amplifier circuits  10  and  20  according to, for instance, digital control signals input through control signal terminal  140 . PA control circuit  80  may be formed as a semiconductor integrated circuit (IC). A semiconductor IC includes a complementary metal oxide semiconductor (CMOS), for example, and specifically, formed by a silicon on insulator (SOI) process. Accordingly, such a semiconductor IC can be manufactured at a low cost. Note that the semiconductor IC may include at least one of gallium arsenide (GaAs), silicon germanium (SiGe), or gallium nitride (GaN). Thus, a radio frequency signal having high amplification quality and high noise quality can be output. 
     Low noise amplifier  30  amplifies radio frequency signals in communication bands A, B, and C while noise is kept low, and outputs the amplified radio frequency signals to reception output terminal  130 . Note that radio frequency module  1  may include a plurality of low noise amplifiers. For example, radio frequency module  1  may include a first low noise amplifier that amplifies radio frequency signals in communication bands A and B, and a second low noise amplifier that amplifies a radio frequency signal in communication band C. 
     Note that in the present embodiment, communication bands A and B are lower than communication band C, communication bands A and B belong to, for example, a middle band group (ranging from 1.45 GHz to 2.2 GHz), and communication band C belongs to, for example, a high band group (ranging from 2.3 GHz to 2.7 GHz). Note that which of communication bands A, B, and C is the highest, the second highest, and the lowest is not limited to the above example, and communication bands A and B may be higher than communication band C. Note that the middle band group is an example of a first frequency band, and communication band C is an example of a second frequency band different from the first frequency band. 
     Transmission filter  61 T is disposed on transmission path AT that connects transmission input terminals  111  and  112  and antenna connection terminal  100 , and passes a transmission signal in the transmission band of communication band A, within a transmission signal amplified by transmission amplifier circuit  10 . Transmission filter  62 T is disposed on transmission path BT that connects transmission input terminals  111  and  112  and antenna connection terminal  100 , and passes a transmission signal in the transmission band of communication band B, within a transmission signal amplified by transmission amplifier circuit  10 . Transmission filter  63 T is disposed on transmission path CT that connects transmission input terminals  121  and  122  and antenna connection terminal  100 , and passes a transmission signal in the transmission band of communication band C, within a transmission signal amplified by transmission amplifier circuit  20 . 
     Reception filter  61 R is disposed on reception path AR that connects reception output terminal  130  and antenna connection terminal  100 , and passes a reception signal in the reception band of communication band A, within a reception signal input through antenna connection terminal  100 . Reception filter  62 R is disposed on reception path BR that connects reception output terminal  130  and antenna connection terminal  100 , and passes a reception signal in the reception band of communication band B, within a reception signal input through antenna connection terminal  100 . Reception filter  63 R is disposed on reception path CR that connects reception output terminal  130  and antenna connection terminal  100 , and passes a reception signal in the reception band of communication band C, within a reception signal input through antenna connection terminal  100 . 
     Transmission filter  61 T and reception filter  61 R constitute duplexer  61  having a passband that is communication band A. Duplexer  61  transfers a transmission signal and a reception signal in communication band A by frequency division duplex (FDD). Transmission filter  62 T and reception filter  62 R constitute duplexer  62  having a passband that is communication band B. Duplexer  62  transfers a transmission signal and a reception signal in communication band B by FDD. Transmission filter  63 T and reception filter  63 R constitute duplexer  63  having a passband that is communication band C. Duplexer  63  transfers a transmission signal and a reception signal in communication band C by FDD. 
     Note that duplexers  61  to  63  may each be a multiplexer that includes only a plurality of transmission filters, a multiplexer that includes only a plurality of reception filters, or a multiplexer that includes a plurality of duplexers. Transmission filter  61 T and reception filter  61 R may not constitute duplexer  61 , and may be a single filter for signals transferred by time division duplex (TDD). In this case, one or more switches that switch between transmission and reception are disposed upstream, disposed downstream, or disposed upstream and downstream from the single filter. Similarly, transmission filter  62 T and reception filter  62 R may not constitute duplexer  62 , and may be a single filter for signals transferred by TDD. Similarly, transmission filter  63 T and reception filter  63 R may not constitute duplexer  63 , and may be a single filter for signals transferred by TDD. 
     Matching circuit  51  is disposed on a path that connects switch  44  and duplexer  61 , and matches the impedance between (i) duplexer  61  and (ii) switch  44  and antenna  2 . Matching circuit  52  is disposed on a path that connects switch  44  and duplexer  62 , and matches the impedance between (i) duplexer  62  and (ii) switch  44  and antenna  2 . Matching circuit  53  is disposed on a path that connects switch  44  and duplexer  63 , and matches the impedance between (i) duplexer  63  and (ii) switch  44  and antenna  2 . 
     Matching circuit  54  is disposed on a reception path that connects low noise amplifier  30  and switch  43 , and matches the impedance between (i) low noise amplifier  30  and (ii) switch  43  and duplexers  61  to  63 . 
     Switch  41  includes common terminals  41   a  and  41   b  and selection terminals  41   c ,  41   d ,  41   e , and  41   f . Common terminal  41   a  is connected to input terminal  115  of transmission amplifier circuit  10 . Common terminal  41   b  is connected to input terminal  125  of transmission amplifier circuit  20 . Selection terminal  41   c  is connected to transmission input terminal  111 , selection terminal  41   d  is connected to transmission input terminal  112 , selection terminal  41   e  is connected to transmission input terminal  121 , and selection terminal  41   f  is connected to transmission input terminal  122 . Switch  41  is disposed on an input terminal side of transmission amplifier circuits  10  and  20 . This connection configuration allows switch  41  to switch connection of transmission amplifier circuit  10  between transmission input terminal  111  and transmission input terminal  112 , and to switch connection of transmission amplifier circuit  20  between transmission input terminal  121  and transmission input terminal  122 . Switch  41  includes a double pole four throw (DP4T) switch circuit, for example. 
     Note that switch  41  may include a single pole double throw (SPDT) switch that includes common terminal  41   a  and selection terminals  41   c  and  41   d , and an SPDT switch that includes common terminal  41   b  and selection terminals  41   e  and  41   f.    
     A transmission signal in communication band A, for example, is input through transmission input terminal  111 , and a transmission signal in communication band B, for example, is input through transmission input terminal  112 . Further, transmission signals in communication band C, for example, are input through transmission input terminals  121  and  122 . 
     A transmission signal in communication band A or B in the fourth generation mobile communication system (4G), for example, may be input through transmission input terminal  111 , and a transmission signal in communication band A or B in the fifth generation mobile communication system (5G), for example, may be input through transmission input terminal  112 . Further, a transmission signal in communication band C in 4G, for example, may be input through transmission input terminal  121 , and a transmission signal in communication band C in 5G, for example, may be input through transmission input terminal  122 . 
     Note that switch  41  may be an SPDT switch circuit in which the common terminal is connected to a transmission input terminal (referred to as a first transmission input terminal) out of transmission input terminals  111 ,  112 ,  121 , and  122 , one selection terminal is connected to input terminal  115  of transmission amplifier circuit  10 , and the other selection terminal is connected to input terminal  125  of transmission amplifier circuit  20 . 
     In this case, for example, a transmission signal in one of communication bands A, B, and C is selectively input through the first transmission input terminal, and switch  41  switches connection of the first transmission input terminal between transmission amplifier circuit  10  and transmission amplifier circuit  20  according to an input transmission signal. A 4G transmission signal and a 5G transmission signal, for example, may be input through the first transmission input terminal, and switch  41  may switch connection of the first transmission input terminal between transmission amplifier circuit  10  and transmission amplifier circuit  20  according to an input transmission signal. 
     Switch  41  may include a double pole double throw (DPDT) switch circuit that includes two common terminals and two selection terminals. In this case, the first transmission input terminal is connected to one of the common terminals, and the second transmission input terminal is connected to the other common terminal. One of the selection terminals is connected to transmission amplifier circuit  10 , and the other selection terminal is connected to transmission amplifier circuit  20 . This connection configuration allows switch  41  to switch connection of the one common terminal between the one selection terminal and the other selection terminal, and switches connection of the other common terminal between the one selection terminal and the other selection terminal. 
     In this case, for example, a transmission signal in communication band A or B is input through the first transmission input terminal, and a transmission signal in communication band C is input through the second transmission input terminal. For example, a 4G transmission signal may be input through the first transmission input terminal, and a 5G transmission signal may be input through the second transmission input terminal. 
     Switch  42  includes common terminals  42   a  and  42   b  and selection terminals  42   c ,  42   d , and  42   e . Common terminal  42   a  is connected to output terminal  116  of transmission amplifier circuit  10 , and common terminal  42   b  is connected to output terminal  126  of transmission amplifier circuit  20 . Selection terminal  42   c  is connected to transmission filter  61 T, selection terminal  42   d  is connected to transmission filter  62 T, and selection terminal  42   e  is connected to transmission filter  63 T. Switch  42  is disposed on an output terminal side of transmission amplifier circuits  10  and  20 . This connection configuration allows switch  42  to switch connection of transmission amplifier circuit  10  between transmission filter  61 T and transmission filter  62 T, and switches between connection and disconnection of transmission amplifier circuit  20  to/from transmission filter  63 T. Switch  42  includes a double pole three throw (DP3T) switch circuit, for example. 
     Note that switch  42  may include an SPDT switch that includes common terminal  42   a  and selection terminals  42   c  and  42   d , and a single pole single throw (SPST) switch that includes common terminal  42   b  and selection terminal  42   e.    
     Switch  43  includes common terminal  43   a  and selection terminals  43   b ,  43   c , and  43   d . Common terminal  43   a  is connected to an input terminal of low noise amplifier  30  via matching circuit  54 . Selection terminal  43   b  is connected to reception filter  61 R, selection terminal  43   c  is connected to reception filter  62 R, and selection terminal  43   d  is connected to reception filter  63 R. This connection configuration allows switch  43  to switch between connection and disconnection of low noise amplifier  30  to/from reception filter  61 R, switch between connection and disconnection of low noise amplifier  30  to/from reception filter  62 R, and switch between connection and disconnection of low noise amplifier  30  to/from reception filter  63 R. Switch  43  includes a single pole three throw (SP3T) switch circuit, for example. 
     Switch  44  is an example of an antenna switch, is connected to antenna connection terminal  100 , and switches among (1) connection of antenna connection terminal  100  to transmission path AT and reception path AR, (2) connection of antenna connection terminal  100  to transmission path BT and reception path BR, and (3) connection of antenna connection terminal  100  to transmission path CT and reception path CR. Note that switch  44  includes a multiple connection switch circuit that allows simultaneous connections of at least two of (1) to (3) above. 
     Note that transmission filters  61 T to  63 T and reception filters  61 R to  63 R described above may each be one of, for example, an acoustic wave filter that uses surface acoustic waves (SAWs), an acoustic wave filter that uses bulk acoustic waves (BAWs), an inductor-capacitor (LC) resonance filter, and a dielectric filter, and furthermore, are not limited to those filters. 
     Matching circuits  51  to  54  are not necessarily included in the radio frequency module according to the present disclosure. 
     Matching circuits may be disposed between transmission amplifier circuit  10  and switch  42  and between transmission amplifier circuit  20  and switch  42 . A diplexer and/or a coupler, for instance, may be disposed between antenna connection terminal  100  and switch  44 . 
     In the configuration of radio frequency module  1 , transmission amplifier circuit  10 , switch  42 , transmission filter  61 T, matching circuit  51 , and switch  44  are included in a first transmission circuit that transfers transmission signals in communication band A toward antenna connection terminal  100 . Further, switch  44 , matching circuit  51 , reception filter  61 R, switch  43 , matching circuit  54 , and low noise amplifier  30  are included in a first reception circuit that transfers reception signals in communication band A from antenna  2  through antenna connection terminal  100 . 
     Transmission amplifier circuit  10 , switch  42 , transmission filter  62 T, matching circuit  52 , and switch  44  are included in a second transmission circuit that transfers transmission signals in communication band B toward antenna connection terminal  100 . Further, switch  44 , matching circuit  52 , reception filter  62 R, switch  43 , matching circuit  54 , and low noise amplifier  30  are included in a second reception circuit that transfers reception signals in communication band B from antenna  2  through antenna connection terminal  100 . 
     Transmission amplifier circuit  20 , switch  42 , transmission filter  63 T, matching circuit  53 , and switch  44  are included in a third transmission circuit that transfers transmission signals in communication band C toward antenna connection terminal  100 . Further, switch  44 , matching circuit  53 , reception filter  63 R, switch  43 , matching circuit  54 , and low noise amplifier  30  are included in a third reception circuit that transfers reception signals in communication band C from antenna  2  through antenna connection terminal  100 . 
     According to the above circuit configuration, radio frequency module  1  can carry out at least one of transmission, reception, or transmission and reception of a radio frequency signal in communication band A, B, or C. Furthermore, radio frequency module  1  can carry out at least one of simultaneous transmission, simultaneous reception, or simultaneous transmission and reception of radio frequency signals in communication bands A, B, and C. 
     Note that in the radio frequency module according to the present disclosure, the three transmission circuits and the three reception circuits may not be connected to antenna connection terminal  100  via switch  44 , and may be connected to antenna  2  via different terminals. It is sufficient if the radio frequency module according to the present disclosure includes PA control circuit  80 , the first transmission circuit, and the third transmission circuit. 
     In the radio frequency module according to the present disclosure, it is sufficient if the first transmission circuit includes transmission amplifier circuit  10 . It is sufficient if the third transmission circuit includes transmission amplifier circuit  20 . 
     Low noise amplifier  30  and at least one switch out of switches  41  to  44  may be formed in a single semiconductor IC. The semiconductor IC includes a CMOS, for example, and is specifically formed by the SOI process. Accordingly, such a semiconductor IC can be manufactured at a low cost. Note that the semiconductor IC may include at least one of GaAs, SiGe, or GaN. Thus, a radio frequency signal having high amplification quality and high noise quality can be output. 
       FIG. 2  illustrates a circuit configuration of transmission amplifier circuit  10  according to the embodiment. As illustrated in  FIG. 2 , transmission amplifier circuit  10  includes input terminal  115 , output terminal  116 , amplifying element  12  (a first amplifying element), amplifying element  13  (a second amplifying element), amplifying element  11  (an upstream amplifying element), interstage transformer (transformer)  14 , capacitor  16 , and output transformer (unbalance-balance transforming element)  15 . Amplifying elements  11  to  13 , interstage transformer  14 , and capacitor  16  are included in power amplifier  10 A. Power amplifier  10 A is an example of a first power amplifier. 
     Interstage transformer  14  includes primary coil  14   a  and secondary coil  14   b.    
     An input terminal of amplifying element  11  is connected to input terminal  115 , and an output terminal of amplifying element  11  is connected to an unbalance terminal of interstage transformer  14 . One balance terminal of interstage transformer  14  is connected to an input terminal of amplifying element  12 , and another balance terminal of interstage transformer  14  is connected to an input terminal of amplifying element  13 . 
     A radio frequency signal input through input terminal  115  is amplified by amplifying element  11  in a state in which bias voltage Vcc 1  is applied to amplifying element  11 . Interstage transformer  14  applies an unbalance-balance transform (i.e., a transformation of an unbalanced line to a balanced line that carries non-inverted and inverted versions of the signal) to the amplified radio frequency signal. At this time, a non-inverted input signal is output through the one balance terminal of interstage transformer  14 , and an inverted input signal is output through the other balance terminal of interstage transformer  14 . 
     Output transformer  15  is an example of a first output transformer, and includes primary coil (first coil)  15   a  and secondary coil (second coil)  15   b . An end of primary coil  15   a  is connected to an output terminal of amplifying element  12 , and the other end of primary coil  15   a  is connected to an output terminal of amplifying element  13 . Bias voltage Vcc 2  is supplied to a middle point of primary coil  15   a . One end of secondary coil  15   b  is connected to output terminal  116 , and the other end of secondary coil  15   b  is connected to the ground. Stated differently, output transformer  15  is connected between (i) output terminal  116  and (ii) the output terminal of amplifying element  12  and the output terminal of amplifying element  13 . 
     Capacitor  16  is connected between the output terminal of amplifying element  12  and the output terminal of amplifying element  13 . 
     Respective impedances of lines that carry a non-inverted input signal amplified by amplifying element  12  and an inverted input signal amplified by amplifying element  13  are transformed by output transformer  15  and capacitor  16  while the signals are maintained in antiphase (or antipodal phase relationship) with each other. Specifically, output transformer  15  and capacitor  16  match the output impedance of power amplifier  10 A at output terminal  116  to input impedance of switch  42  and transmission filters  61 T and  62 T illustrated in  FIG. 1 . Note that a capacitive element connected between the ground and a path that connects output terminal  116  and secondary coil  15   b  contributes to the impedance matching. Further note that the capacitive element may be disposed in series on the path that connects output terminal  116  and secondary coil  15   b , or optionally need not be included. 
     Here, amplifying elements  11  to  13 , interstage transformer  14 , and capacitor  16  constitute power amplifier  10 A. In particular, amplifying elements  11  to  13  and interstage transformer  14  are integrally formed in various configurations such as being formed in a single chip or all mounted on a same substrate, for instance. In contrast, output transformer  15  needs to have a high Q factor to handle a high-power transmission signal, and thus is not formed integrally with amplifying elements  11  to  13  or interstage transformer  14 , for instance. Stated differently, among circuit components included in transmission amplifier circuit  10 , circuit components except output transformer  15  are included in power amplifier  10 A. 
     Note that amplifying element  11  and capacitor  16  are not necessarily included in power amplifier  10 A. 
     According to the circuit configuration of transmission amplifier circuit  10 , amplifying elements  12  and  13  operate in antiphase relationship with respect to each other. At this time, fundamental-wave currents flow through amplifying elements  12  and  13  in antiphase with each other, that is, in opposite directions, and thus a resultant fundamental-wave current does not flow into a ground line or a power supply line disposed at a substantially equal distance from amplifying elements  12  and  13 . Accordingly, inflow of unnecessary (or undesired) currents to the above lines can be avoided, and thus a decrease in power gain that is experienced in a conventional transmission amplifier circuit can be reduced. Further, a non-inverted signal and an inverted signal amplified by amplifying elements  12  and  13  are combined, and thus noise components superimposed similarly on the signals can be canceled out, and unnecessary waves such as harmonic components, for example, can be suppressed. 
     Note that amplifying element  11  is not necessarily included in transmission amplifier circuit  10 . An element that transforms an unbalanced input signal into a non-inverted input signal and an inverted input signal is not limited to interstage transformer  14 . Capacitor  16  is optional for impedance matching. 
     Although not illustrated, transmission amplifier circuit  20  has a similar circuit configuration to that of transmission amplifier circuit  10  illustrated in  FIG. 2 . Specifically, transmission amplifier circuit  20  includes input terminal  125 , output terminal  126 , amplifying element  22  (a third amplifying element), amplifying element  23  (a fourth amplifying element), amplifying element  21  (an upstream amplifying element), interstage transformer (transformer)  24 , capacitor  26 , and output transformer (unbalance-balance transforming element)  25 . Amplifying elements  21  to  23 , interstage transformer  24 , and capacitor  26  are included in power amplifier  20 A. Power amplifier  20 A is an example of a second power amplifier. 
     Interstage transformer  24  includes primary coil  24   a  and secondary coil  24   b.    
     An input terminal of amplifying element  21  is connected to input terminal  125 , and an output terminal of amplifying element  21  is connected to an unbalance terminal of interstage transformer  24 . One balance terminal of interstage transformer  24  is connected to an input terminal of amplifying element  22 , and another balance terminal of interstage transformer  24  is connected to an input terminal of amplifying element  23 . 
     Output transformer  25  is an example of a second output transformer, and includes primary coil (third coil)  25   a  and secondary coil (fourth coil)  25   b . One end of primary coil  25   a  is connected to an output terminal of amplifying element  22 , and the other end of primary coil  25   a  is connected to an output terminal of amplifying element  23 . Bias voltage Vcc 2  is supplied to a middle point of primary coil  25   a . One end of secondary coil  25   b  is connected to output terminal  126 , and the other end of secondary coil  25   b  is connected to the ground. Stated differently, output transformer  25  is connected between (i) output terminal  126  and (ii) the output terminal of amplifying element  22  and the output terminal of amplifying element  23 . 
     Capacitor  26  is connected between the output terminal of amplifying element  22  and the output terminal of amplifying element  23 . 
     Here, amplifying elements  21  to  23 , interstage transformer  24 , and capacitor  26  constitute power amplifier  20 A. In particular, amplifying elements  21  to  23  and interstage transformer  24  are integrally formed in various configurations such as formed in a single chip or all mounted on a same substrate, for instance. On the other hand, output transformer  25  is not integrally formed with amplifying elements  21  to  23  or interstage transformer  24 , for instance. 
     Note that amplifying element  21  and capacitor  26  are not necessarily included in power amplifier  20 A. 
     According to the circuit configuration of transmission amplifier circuit  20 , a decrease in power gain that is seen in a conventional transmission amplifier circuit can be reduced. Further, a non-inverted signal and an inverted signal amplified by amplifying elements  22  and  23  are combined, and thus noise components superimposed similarly on the signals can be canceled out, and unnecessary waves such as harmonic components, for example, can be decreased. 
     Note that amplifying element  21  is not necessarily included in transmission amplifier circuit  20 . An element that transforms an unbalanced input signal into a non-inverted input signal and an inverted input signal is not limited to interstage transformer  24 . Capacitor  26  is optional for impedance matching. 
     Amplifying elements  11  to  13  and  21  to  23  and low noise amplifier  30  each include a field effect transistor (FET) or a hetero-bipolar transistor (HBT) made of a silicon-based CMOS or GaAs, for example. 
     Note that transmission amplifier circuit  10  may not include difference amplifying type power amplifier  10 A, and may be an amplifier that includes a so-called single-ended amplifying element that receives an unbalanced signal, and outputs an unbalanced signal. Further, transmission amplifier circuit  20  may not include difference amplifying type power amplifier  20 A, and may be an amplifier that includes a so-called single-ended amplifying element that receives an unbalanced signal, and outputs an unbalanced signal. 
     Here, in radio frequency module  1 , transmission amplifier circuit  10  amplifies transmission signals in communication bands A and B, and transmission amplifier circuit  20  amplifies a transmission signal in communication band C. Accordingly, amplification performance of transmission amplifier circuits  10  and  20  is optimized in a specific frequency band (a communication band), and thus radio frequency module  1  needs to include a plurality of transmission amplifier circuits to handle signals in frequency bands (communication bands). Development in multiband technology that radio frequency module  1  supports brings a problem that the size of radio frequency module  1  increases due to an increase in the number of transmission amplifier circuits disposed. If the elements are mounted densely for size reduction, a high-power transmission signal output from a transmission amplifier circuit interferes with a circuit component included in radio frequency module  1 , which leads to a problem that the quality of a radio frequency signal output from radio frequency module  1  deteriorates. 
     To address this, the following describes a configuration of small radio frequency module  1  in which deterioration in quality of radio frequency signals output from radio frequency module  1  is reduced. 
     [2. Arrangement of Circuit Elements of Radio Frequency Module  1 A According to Example 1] 
       FIG. 3A  is a schematic diagram illustrating a planar configuration of radio frequency module  1 A according to Example 1.  FIG. 3B  is a schematic diagram illustrating a cross-sectional configuration of radio frequency module  1 A according to Example 1, and specifically, illustrates a cross section taken along line IIIB to IIIB in  FIG. 3A . Note that (a) of  FIG. 3A  illustrates a layout of circuit elements when principal surface  91   a  out of principal surfaces  91   a  and  91   b  on opposite sides of module board  91  is viewed from the positive z-axis. On the other hand, (b) of  FIG. 3A  is a perspective view of a layout of circuit elements when principal surface  91   b  is viewed from the positive z-axis. 
     Radio frequency module  1 A according to Example 1 shows a specific arrangement of circuit elements included in radio frequency module  1  according to the embodiment. 
     As illustrated in  FIGS. 3A and 3B , radio frequency module  1 A according to this example further includes module board  91 , resin members  92  and  93 , and external-connection terminals  150 , in addition to the circuit configuration illustrated in  FIG. 1 . 
     Module board  91  is a board which includes principal surface  91   a  (a first principal surface) and principal surface  91   b  (a second principal surface) on opposite sides of module board  91 , and on which the transmission circuits and the reception circuits described above are mounted. As module board  91 , one of a low temperature co-fired ceramics (LTCC) board, a high temperature co-fired ceramics (HTCC) board, a component-embedded board, a board that includes a redistribution layer (RDL), and a printed circuit board, each having a stacked structure of a plurality of dielectric layers, is used, for example. 
     Resin member  92  is provided on principal surface  91   a  of module board  91 , covers at least partially the transmission circuits, at least partially the reception circuits, and principal surface  91   a  of module board  91 , and has a function of ensuring reliability of mechanical strength and moisture resistance, for instance, of the circuit elements included in the transmission circuits and the reception circuits. Resin member  93  is provided on principal surface  91   b  of module board  91 , covers at least partially the transmission circuits, at least partially the reception circuits, and principal surface  91   b  of module board  91 , and has a function of ensuring reliability of mechanical strength and moisture resistance, for instance, of the circuit elements included in the transmission circuits and the reception circuits. Note that resin members  92  and  93  are not necessarily included in the radio frequency module according to the present disclosure. 
     As illustrated in  FIGS. 3A and 3B , in radio frequency module  1 A according to this example, power amplifiers  10 A and  20 A, output transformers  15  and  25 , duplexers  61 ,  62 , and  63 , and matching circuits  51 ,  52 ,  53 , and  54  are disposed on principal surface  91   a  (the first principal surface) of module board  91 . On the other hand, PA control circuit  80 , low noise amplifier  30 , and switches  41 ,  42 ,  43  and  44  are disposed on principal surface  91   b  (the second principal surface) of module board  91 . 
     Note that although not illustrated in  FIG. 3A , lines that extend as transmission paths AT, BT, and CT and reception paths AR, BR, and CR illustrated in  FIG. 1  are formed inside of module board  91  and on principal surfaces  91   a  and  91   b . The lines may each be a bonding wire having two ends each joined to any of principal surfaces  91   a  and  91   b  and circuit elements included in radio frequency module  1 A, or may each be a terminal, an electrode, or a line formed on a surface of a circuit element included in radio frequency module  1 A. 
     Thus, in this example, power amplifiers  10 A and  20 A are disposed on principal surface  91   a  (the first principal surface). On the other hand, PA control circuit  80  is mounted on principal surface  91   b  (the second principal surface). Power amplifier  10 A is an example of a first power amplifier that amplifies a transmission signal in the first frequency band that includes communication bands A and B, and power amplifier  20 A is an example of a second power amplifier that amplifies a transmission signal in the second frequency band that includes communication band C. In this example, the first frequency band (communication bands A and B) may be lower than the second frequency band (communication band C), and the first frequency band (communication bands A and B) may be higher than the second frequency band (communication band C). 
     According to the above configuration of radio frequency module  1 A according to this example, power amplifiers  10 A and  20 A and PA control circuit  80  that controls power amplifiers  10 A and  20 A are mounted on the two sides, and thus radio frequency module  1 A can be miniaturized. PA control circuit  80  that receives and outputs digital control signals and power amplifiers  10 A and  20 A are disposed with module board  91  being located therebetween, and thus power amplifiers  10 A and  20 A can be prevented from receiving digital noise. Accordingly, deterioration in the quality of radio frequency signals output from power amplifiers  10 A and  20 A can be reduced. 
     Furthermore, power amplifier  10 A includes at least amplifying elements  11  to  13  and interstage transformer  14 , and power amplifier  20 A includes at least amplifying elements  21  to  23  and interstage transformer  24 . Consequently, the number of circuit elements increases, resulting in a larger mounting area. The size of radio frequency module  1 A thus tends to be increased. When transmission amplifier circuits  10  and  20  are difference amplifying type amplifier circuits, a configuration in which power amplifiers  10 A and  20 A and PA control circuit  80  are separately disposed on the two sides of module board  91  greatly contributes to reduction in the size of radio frequency module  1 A. 
     In radio frequency module  1 A according to this example, in a plan view of module board  91 , desirably, a footprint of power amplifier  10 A at least partially overlaps a footprint of PA control circuit  80 , and a footprint of power amplifier  20 A at least partially overlaps a footprint PA control circuit  80 . 
     According to this configuration, a control line that connects power amplifier  10 A and PA control circuit  80  and a control line that connects power amplifier  20 A and PA control circuit  80  can be shortened, and thus noise generated from the control lines can be reduced. Further, transfer loss of control signals can be reduced, and thus amplification characteristics of power amplifiers  10 A and  20 A can be controlled highly precisely. 
     Note that output transformers  15  and  25 , duplexers  61  to  63 , and matching circuits  51  to  54  are mounted on principal surface  91   a  (the first principal surface), but may be mounted on principal surface  91   b  (the second principal surface). Low noise amplifier  30  and switches  41  to  44  are mounted on principal surface  91   b  (the second principal surface), but may be mounted on principal surface  91   a  (the first principal surface). 
     Note that desirably, module board  91  has a multilayer structure in which a plurality of dielectric layers are stacked, and a ground electrode pattern is formed on at least one of the dielectric layers. Accordingly, the electromagnetic field shielding function of module board  91  improves. 
     In radio frequency module  1 A according to this example, external-connection terminals  150  are disposed on principal surface  91   b  (the second principal surface) of module board  91 . Radio frequency module  1 A exchanges electrical signals with a motherboard disposed on the negative z-axis side of radio frequency module  1 A, via external-connection terminals  150 . As illustrated in (b) of  FIG. 3A , the external-connection terminals include antenna connection terminal  100 , transmission input terminals  111 ,  112 ,  121 , and  122 , reception output terminal  130 , and control signal terminal  140 . Potentials of some of external-connection terminals  150  are set to the ground potential of the motherboard. On principal surface  91   b  that faces the motherboard out of principal surfaces  91   a  and  91   b , power amplifiers  10 A and  20 A whose heights are not readily decreased are not disposed, and low noise amplifier  30 , PA control circuit  80 , and switches  41  to  44  whose heights are readily decreased are disposed, and thus the height of radio frequency module  1 A as a whole can be decreased. 
     In radio frequency module  1 A according to this example, power amplifiers  10 A and  20 A are disposed on principal surface  91   a , and low noise amplifier  30  is disposed on principal surface  91   b . According to this, power amplifiers  10 A and  20 A that amplify transmission signals and low noise amplifier  30  that amplifies a reception signal are separately disposed on the two sides, and thus isolation between transmission and reception can be improved. 
     Further, as illustrated in  FIGS. 3A and 3B , external-connection terminals  150  having the ground potential are disposed between low noise amplifier  30  and PA control circuit  80  disposed on principal surface  91   b  (the second principal surface), in a plan view of module board  91 . 
     According to this configuration, plural external-connection terminals  150  used as ground electrodes are disposed between low noise amplifier  30  that greatly affects reception sensitivity of the reception circuits and PA control circuit  80  that receives and outputs digital control signals, and thus deterioration in reception sensitivity due to digital noise can be reduced. 
     Power amplifiers  10 A and  20 A are components that generate a great amount of heat, out of circuit components included in radio frequency module  1 A. In order to improve heat dissipation of radio frequency module  1 A, it is important to dissipate heat generated by power amplifiers  10 A and  20 A to the motherboard through heat dissipation paths having low heat resistance. If power amplifiers  10 A and  20 A are mounted on principal surface  91   b , electrode lines connected to power amplifiers  10 A and  20 A are disposed on principal surface  91   b . Accordingly, the heat dissipation paths include a heat dissipation path along only a planar line pattern (in the xy plane direction) on principal surface  91   b . The planar line pattern is formed of a thin metal film, and thus has high heat resistance. Accordingly, if power amplifiers  10 A and  20 A are disposed on principal surface  91   b , heat dissipation deteriorates. 
     To address this, radio frequency module  1 A according to this example further includes heat-dissipating via-conductor  95 V that is connected, on principal surface  91   a , to a ground electrode of power amplifier  10 A, and extends from principal surface  91   a  to principal surface  91   b , as illustrated in  FIG. 3B . Heat-dissipating via-conductor  95 V is connected, on principal surface  91   b , to external-connection terminal  150  having the ground potential out of external-connection terminals  150 . 
     According to this configuration, when power amplifier  10 A is mounted on principal surface  91   a , power amplifier  10 A and external-connection terminal  150  can be connected through heat-dissipating via-conductor  95 V. Accordingly, as heat dissipation paths for power amplifier  10 A, a heat dissipation path extending along only a planar line pattern in the xy plane direction and having high heat resistance can be excluded from lines on and in module board  91 . Thus, miniaturized radio frequency module  1 A having improved heat dissipation from power amplifier  10 A to the motherboard can be provided. 
     Note that  FIG. 3B  illustrates, as an example, a configuration in which power amplifier  10 A, heat-dissipating via-conductor  95 V, and external-connection terminal  150  are connected, yet radio frequency module  1 A may have a configuration in which power amplifier  20 A, heat-dissipating via-conductor  95 V, and external-connection terminal  150  are connected. Accordingly, miniaturized radio frequency module  1 A having improved heat dissipation from power amplifier  20 A to the motherboard can be provided. 
     In radio frequency module  1 A according to this example, output transformers  15  and  25  are disposed on principal surface  91   a , but may be disposed on principal surface  91   b  or inside of module board  91 . When output transformers  15  and  25  are disposed inside of module board  91 , inductors included in output transformers  15  and  25  are planar coils formed by electric conduction patterns of module board  91 , for example. In such arrangement of output transformers  15  and  25 , desirably, footprints of power amplifiers  10 A and  20 A each do not overlap footprints of both output transformers  15  and  25 , in a plan view of module board  91 . 
     Output transformers  15  and  25  each need to have a high Q factor to handle a high-power transmission signal, and thus desirably, magnetic fields formed by output transformers  15  and  25  do not change due to power amplifiers  10 A and  20 A being adjacent thereto. Power amplifiers  10 A and  20 A are not disposed in regions where the transformers are disposed, and thus the Q factors of the inductors included in output transformers  15  and  25  can be maintained high. 
     In radio frequency module  1 A according to this example, as illustrated in  FIGS. 3A and 3B , desirably, output transformers  15  and  25  are disposed on principal surface  91   a , and in a plan view of module board  91 , no circuit component is disposed in a region included in principal surface  91   b  that overlaps a footprint of output transformer  15 , and no circuit component is disposed in a region included in principal surface  91   b  that overlaps a footprint of output transformer  25 . Output transformers  15  and  25  are surface mount chip elements each including a plurality of inductors, for example. Furthermore, output transformers  15  and  25  may be, for example, integrated passive devices (IPDs) in each of which one or more passive elements such as an inductor are mounted inside of or on the surface of a silicon substrate in an integrated manner. When output transformers  15  and  25  are IPDs, radio frequency module  1 A can be further miniaturized. 
     Output transformers  15  and  25  each need to have a high Q factor to handle a high-power transmission signal, and thus desirably, magnetic fields formed by output transformers  15  and  25  do not change due to other circuit components being adjacent thereto. No circuit component is formed in regions where the transformers are disposed, and thus the Q factors of the inductors included in output transformers  15  and  25  can be maintained high. 
     Furthermore, in a plan view of module board  91 , desirably, a ground electrode layer is not formed in a region included in module board  91  and overlapping formation regions in which output transformers  15  and  25  are formed. According to this configuration, it can be ensured that output transformers  15  and  25  are widely spaced apart from ground electrodes, and thus the Q factors of the inductors included in output transformers  15  and  25  can be maintained high. 
     The formation regions in which output transformers  15  and  25  are formed are defined as follows. Note that the following describes the formation region in which output transformer  15  is formed, yet the definition of the formation region in which output transformer  25  is formed is the same as that of the formation region in which output transformer  15  is formed, and thus defining the formation region in which output transformer  25  is formed is omitted. 
     The formation region in which output transformer  15  is formed is a minimum region that includes a formation region in which primary coil  15   a  is formed and a formation region in which secondary coil  15   b  is formed, in a plan view of module board  91 . 
     Here, secondary coil  15   b  is defined as a line conductor disposed along primary coil  15   a , in a section in which a first distance from primary coil  15   a  is substantially constant. At this time, portions of the line conductor located on both sides of the above section are spaced apart from primary coil  15   a  by a second distance longer than the first distance, and one end and the other end of secondary coil  15   b  are points at which a distance from the line conductor to primary coil  15   a  changes from the first distance to the second distance. Primary coil  15   a  is defined as a line conductor disposed along secondary coil  15   b , in a section in which the first distance from secondary coil  15   b  is substantially constant. At this time, portions of the line conductor located on both sides of the above section are spaced apart from secondary coil  15   b  by the second distance longer than the first distance, and one end and the other end of primary coil  15   a  are points at which a distance from the line conductor to secondary coil  15   b  changes from the first distance to the second distance. 
     Alternatively, secondary coil  15   b  is defined as a line conductor disposed along primary coil  15   a , in a first section in which the line width is a substantially constant first width. Primary coil  15   a  is defined as a line conductor disposed along secondary coil  15   b , in the first section in which the line width is the substantially constant first width. 
     Alternatively, secondary coil  15   b  is defined as a line conductor disposed along primary coil  15   a , in a first section in which the thickness is a substantially constant first thickness. Primary coil  15   a  is defined as a line conductor disposed along secondary coil  15   b , in the first section in which the thickness is the substantially constant first thickness. 
     Alternatively, secondary coil  15   b  is defined as a line conductor disposed along primary coil  15   a , in a first section in which a degree of coupling with primary coil  15   a  is a substantially constant first degree of coupling. Further, primary coil  15   a  is defined as a line conductor disposed along secondary coil  15   b , in the first section in which a degree of coupling with secondary coil  15   b  is the substantially constant first degree of coupling. 
       FIG. 4A  is a schematic diagram of a cross-sectional configuration illustrating the position of output transformer  15  in radio frequency module  1 D according to Variation 1.  FIG. 4A  illustrates the position of output transformer  15  in the cross-sectional configuration of radio frequency module  1 D according to Variation 1. Note that the arrangement of circuit components included in radio frequency module  1 D other than output transformers  15  and  25  is the same as that of radio frequency module  1 A according to Example 1. In radio frequency module  1 D, output transformers  15  and  25  are disposed on principal surface  91   b . In this case, desirably, no circuit component is disposed in regions included in principal surface  91   a  and overlapping the formation regions in which output transformers  15  and  25  are formed, in a plan view of module board  91 . 
     According to this configuration, no circuit component is disposed in the above regions in principal surface  91   a , and thus decreases in the Q factors of the inductors of output transformers  15  and  25  can be reduced. 
       FIG. 4B  is a schematic diagram of a cross-sectional configuration illustrating the position of output transformer  15  in radio frequency module  1 E according to Variation 2.  FIG. 4B  illustrates the position of output transformer  15  in the cross-sectional configuration of radio frequency module  1 E according to Variation 2. Note that the arrangement of circuit components included in radio frequency module  1 E other than output transformers  15  and  25  is the same as that of radio frequency module  1 A according to Example 1. In radio frequency module  1 E, output transformers  15  and  25  are formed inside of module board  91 , between principal surface  91   a  and principal surface  91   b , and are offset toward principal surface  91   a . In this case, in a plan view of module board  91 , no circuit component is disposed in regions included in principal surface  91   a  and overlapping the formation regions in which output transformers  15  and  25  are formed, and one or more circuit components may be disposed in regions included in principal surface  91   b  and overlapping the formation regions in which output transformers  15  and  25  are formed. 
     Also in this case, no circuit component is disposed in the above regions in principal surface  91   a  closer to output transformers  15  and  25 , and thus decreases in the Q factors of the inductors of output transformers  15  and  25  can be reduced. 
       FIG. 4C  is a schematic diagram of a cross-sectional configuration illustrating the position of output transformer  15  in radio frequency module  1 F according to Variation 3.  FIG. 4C  illustrates the position of output transformer  15  in the cross-sectional configuration of radio frequency module  1 F according to Variation 3. Note that the arrangement of circuit components included in radio frequency module  1 F other than output transformers  15  and  25  is the same as that of radio frequency module  1 A according to Example 1. In radio frequency module  1 F, output transformers  15  and  25  are formed inside of module board  91 , between principal surface  91   a  and principal surface  91   b , and are offset toward principal surface  91   b . In this case, in a plan view of module board  91 , no circuit component is disposed in regions included in principal surface  91   b  and overlapping the formation regions in which output transformers  15  and  25  are formed, and one or more circuit components (not illustrated) may be disposed in regions included in principal surface  91   a  and overlapping the formation regions in which output transformers  15  and  25  are formed. 
     Also in this case, no circuit component is disposed in the above regions in principal surface  91   b  closer to output transformers  15  and  25 , and thus decreases in the Q factors of the inductors of output transformers  15  and  25  can be reduced. 
     Note that in each of radio frequency module  1 E illustrated in  FIG. 4B  and radio frequency module  1 F illustrated in  FIG. 4C , in a plan view of module board  91 , more desirably, no circuit component is disposed in regions included in both principal surfaces  91   a  and  91   b  and overlapping output transformers  15  and  25 . 
     According to this configuration, decreases in the Q factors of the inductors of output transformers  15  and  25  can be further reduced. 
     In radio frequency module  1 A according to this example, power amplifiers  10 A and  20 A are disposed on principal surface  91   a , and PA control circuit  80  is disposed on principal surface  91   b , yet power amplifiers  10 A and  20 A may be disposed on principal surface  91   b , and PA control circuit  80  may be disposed on principal surface  91   a . This configuration also allows power amplifiers  10 A and  20 A and PA control circuit  80  to be mounted on the two sides, and thus radio frequency module  1 A can be miniaturized. PA control circuit  80  that receives and outputs digital control signals and power amplifiers  10 A and  20 A are disposed with module board  91  being located therebetween, and thus power amplifiers  10 A and  20 A can be prevented from receiving digital noise. Accordingly, deterioration in the quality of radio frequency signals output from power amplifiers  10 A and  20 A can be reduced. 
     In radio frequency module  1 A according to this example, PA control circuit  80  and switches  41  and  42  are included in single semiconductor IC  70 , and semiconductor IC  70  is disposed on principal surface  91   b . Accordingly, PA control circuit  80  connected to transmission amplifier circuits  10  and  20  is adjacent to switches  41  and  42 , and thus, radio frequency module  1 A can be miniaturized. A control line that connects switch  41  and PA control circuit  80  and a control line that connects switch  42  and PA control circuit  80  can be shortened, and thus noise generated from the control lines can be reduced. 
     Note that semiconductor IC  70  may not include at least one switch out of switches  41  and  42 . 
     In radio frequency module  1 A according to this example, low noise amplifier  30  and switches  43  and  44  are included in single semiconductor IC  75 , and semiconductor IC  75  is disposed on principal surface  91   b . Accordingly, low noise amplifier  30  and switches  43  and  44  disposed on the reception paths are adjacent to one another, and thus radio frequency module  1 A can be miniaturized. 
     Note that semiconductor IC  75  may not include at least one switch out of switches  43  and  44 . 
     Note that external-connection terminals  150  may be columnar electrodes passing through resin member  93  in the z-axis direction as illustrated in  FIGS. 3A and 3B , or may be bump electrodes  160  formed on principal surface  91   b  as in radio frequency module  1 B according to Variation 4 illustrated in  FIG. 5 . In this case, resin member  93  may not be provided on principal surface  91   b.    
     In each of radio frequency module  1 A according to Example 1 and radio frequency modules  1 D to  1 F according to Variations 1 to 3, external-connection terminals  150  may be disposed on principal surface  91   a . In radio frequency module  1 B according to Variation 4, bump electrodes  160  may be disposed on principal surface  91   a.    
     [3. Arrangement of Circuit Elements of radio Frequency Module  1 C According to Example 2] 
       FIG. 6  is a schematic diagram illustrating a planar configuration of radio frequency module  1 C according to Example 2. Note that (a) of  FIG. 6  illustrates a layout of circuit elements when principal surface  91   a  out of principal surfaces  91   a  and  91   b  on opposite sides of module board  91  is viewed from the positive z-axis. On the other hand, (b) of  FIG. 6  is a perspective view of a layout of circuit elements when principal surface  91   b  is viewed from the positive z-axis. 
     Radio frequency module  1 C according to Example 2 shows a specific arrangement of circuit elements included in radio frequency module  1  according to the embodiment. 
     Radio frequency module  1 C according to this example is different from radio frequency module  1 A according to Example 1, only in the location of semiconductor IC  70 . The following description of radio frequency module  1 C according to this example focuses on differences from radio frequency module  1 A according to Example 1 while a description of the same points is omitted. 
     As illustrated in  FIG. 6 , in radio frequency module  1 C according to this example, power amplifiers  10 A and  20 A, output transformers  15  and  25 , duplexers  61 ,  62 , and  63 , and matching circuits  51 ,  52 ,  53 , and  54  are disposed on principal surface  91   a  (the first principal surface) of module board  91 . On the other hand, PA control circuit  80 , low noise amplifier  30 , and switches  41 ,  42 ,  43 , and  44  are disposed on principal surface  91   b  (the second principal surface) of module board  91 . 
     Thus, in this example, power amplifiers  10 A and  20 A are mounted on principal surface  91   a  (the first principal surface). On the other hand, PA control circuit  80  is mounted on principal surface  91   b  (the second principal surface). 
     Power amplifier  10 A is an example of a first power amplifier that amplifies a transmission signal in the first frequency band that includes communication bands A and B, and power amplifier  20 A is an example of a second power amplifier that amplifies a transmission signal in the second frequency band that includes communication band C. In this example, the first frequency band (communication bands A and B) is lower than the second frequency band (communication band C). 
     In radio frequency module  1 C according to this example, in a plan view of module board  91 , a footprint of power amplifier  10 A at least partially overlaps a footprint of PA control circuit  80 , and a footprint of power amplifier  20 A does not overlap the footprint of PA control circuit  80 . 
     Out of power amplifiers  10 A and  20 A, power amplifier  20 A that amplifies a transmission signal having a higher frequency consumes more power. Thus, a heat dissipation member such as heat-dissipating via-conductor  95 V is desirably disposed in a region included in principal surface  91   b  and overlapping the footprint of power amplifier  20 A. On the other hand, from a viewpoint of reducing the occurrence of noise from control lines that connect power amplifiers  10 A and  20 A and PA control circuit  80 , the control lines are desirably short. 
     According to the above configuration, the control line can be shortened since the footprint of power amplifier  10 A at least partially overlaps the footprint of PA control circuit  80 , and the footprint of power amplifier  20 A does not overlap the footprint of PA control circuit  80  so that PA control circuit  80  can be prevented from being damaged by heat dissipated from power amplifier  20 A while heat dissipation of power amplifier  20 A improves. 
     In radio frequency module  1 C according to this example, as illustrated in  FIG. 6 , output transformer  15  is larger than output transformer  25 . Note that “output transformer  15  is larger than output transformer  25 ” means that the volume of output transformer  15  is greater than the volume of output transformer  25 . In the above relation in which the volume of output transformer  15  is greater than that of output transformer  25 , the footprint of power amplifier  10 A at least partially overlaps the footprint of PA control circuit  80 , and the footprint of power amplifier  20 A does not overlap the footprint of PA control circuit  80 . 
     Out of output transformers  15  and  25 , output transformer  25  that outputs a transmission signal having a higher frequency has a smaller volume. According to the above configuration, the control line can be shortened since the footprint of power amplifier  10 A at least partially overlaps the footprint of PA control circuit  80 , and the footprint of power amplifier  20 A does not overlap the footprint of PA control circuit  80 , so that PA control circuit  80  can be prevented from being damaged by heat dissipated from power amplifier  20 A while heat dissipation of power amplifier  20 A improves. 
     [4. Advantageous Effects and Others] 
     As described above, radio frequency module  1  according to the present embodiment includes: module board  91  that includes principal surfaces  91   a  and  91   b  on opposite sides of module board  91 ; power amplifier  10 A configured to amplify a transmission signal in a first frequency band; power amplifier  20 A configured to amplify a transmission signal in a second frequency band different from the first frequency band; and PA control circuit  80  configured to control power amplifiers  10 A and  20 A. Power amplifiers  10 A and  20 A are disposed on principal surface  91   a , and PA control circuit  80  is disposed on principal surface  91   b.    
     According to this configuration, power amplifiers  10 A and  20 A, and PA control circuit  80  that controls power amplifiers  10 A and  20 A are mounted on the two sides, and thus radio frequency module  1  can be miniaturized. PA control circuit  80  that receives and outputs digital control signals and power amplifiers  10 A and  20 A are disposed with module board  91  being located therebetween, and thus power amplifiers  10 A and  20 A can be prevented from receiving digital noise. Accordingly, deterioration in the quality of radio frequency signals output from power amplifiers  10 A and  20 A can be reduced. 
     Radio frequency module  1  may further include a plurality of external-connection terminals  150  disposed on principal surface  91   b.    
     Accordingly, on principal surface  91   b  that faces a motherboard out of principal surfaces  91   a  and  91   b , power amplifiers  10 A and  20 A whose heights are not readily decreased are not disposed, and PA control circuit  80  whose height is readily decreased is disposed, and thus the height of radio frequency module  1  as a whole can be decreased. 
     Radio frequency module  1  may further include heat-dissipating via-conductor  95 V connected to at least one of ground electrodes of power amplifiers  10 A and  20 A, heat-dissipating via-conductor  95 V extending from principal surface  91   a  to principal surface  91   b . Heat-dissipating via-conductor  95 V may be connected, on principal surface  91   b , to an external-connection terminal having a ground potential out of external-connection terminals  150 . 
     According to this configuration, when power amplifier  10 A is mounted on principal surface  91   a , power amplifier  10 A and external-connection terminal  150  can be connected through heat-dissipating via-conductor  95 V. Accordingly, as heat dissipation paths for power amplifier  10 A, a heat dissipation path extending along only a planar line pattern in the xy plane direction and having high heat resistance can be excluded from lines on and in module board  91 . Thus, miniaturized radio frequency module  1  having improved heat dissipation from power amplifier  10 A to the motherboard can be provided. 
     Radio frequency module  1  may further include low noise amplifier  30  disposed on principal surface  91   b  and configured to amplify a reception signal. In a plan view of module board  91 , an external-connection terminal having a ground potential may be disposed between PA control circuit  80  and low noise amplifier  30 , out of external-connection terminals  150 . 
     According to this configuration, plural external-connection terminals  150  used as ground electrodes are disposed between low noise amplifier  30  that greatly affects reception sensitivity of the reception circuits and PA control circuit  80  that receives and outputs digital control signals, and thus deterioration in reception sensitivity due to digital noise can be reduced. 
     In radio frequency module  1 A, in a plan view of module board  91 , the footprint of power amplifier  10 A may at least partially overlap the footprint of PA control circuit  80 , and the footprint of power amplifier  20 A may at least partially overlap the footprint of PA control circuit  80 . 
     According to this configuration, a control line that connects power amplifier  10 A and PA control circuit  80 , and a control line that connects power amplifier  20 A and PA control circuit  80  can be shortened, and thus noise generated from the control lines can be reduced. 
     In radio frequency module  1 C, the first frequency band is lower than the second frequency band, and in a plan view of module board  91 , the footprint of power amplifier  10 A may at least partially overlap the footprint of PA control circuit  80 , and the footprint of power amplifier  20 A may not overlap the footprint of PA control circuit  80 . 
     Out of power amplifiers  10 A and  20 A, power amplifier  20 A that amplifies a transmission signal having a higher frequency consumes more power. Thus, a heat dissipation member such as heat-dissipating via-conductor  95 V is desirably disposed in a region included in principal surface  91   b  and overlapping the footprint of power amplifier  20 A. According to the above configuration, the control line can be shortened since the footprint of power amplifier  10 A at least partially overlaps the footprint of PA control circuit  80 , and the footprint of power amplifier  20 A does not overlap the footprint of PA control circuit  80 , and thus PA control circuit  80  can be prevented from being damaged by heat dissipated from power amplifier  20 A while heat dissipation of power amplifier  20 A is improved. 
     Radio frequency module  1  may further include: output transformer  15  that includes primary coil  15   a  and secondary coil  15   b ; and output transformer  25  that includes primary coil  25   a  and secondary coil  25   b . Power amplifier  10 A may include amplifying elements  12  and  13 . Power amplifier  20 A may include amplifying elements  22  and  23 . An end of primary coil  15   a  may be connected to an output terminal of amplifying element  12 . Another end of primary coil  15   a  may be connected to an output terminal of amplifying element  13 . An end of secondary coil  15   b  may be connected to an output terminal of power amplifier  10 A. An end of primary coil  25   a  may be connected to an output terminal of amplifying element  22 . Another end of primary coil  25   a  may be connected to an output terminal of amplifying element  23 . An end of secondary coil  25   b  may be connected to an output terminal of power amplifier  20 A. Power amplifier  10 A and output transformer  15  may be included in transmission amplifier circuit  10 , and power amplifier  20 A and output transformer  25  may be included in transmission amplifier circuit  20 . 
     According to this, amplifying elements  12  and  13  operate in antiphase relationship with respect to each other, and thus a decrease in power gain of transmission amplifier circuit  10  can be reduced. Further, amplifying elements  22  and  23  operate in antiphase relationship with respect to each other, and thus a decrease in power gain of transmission amplifier circuit  20  can be reduced. Further, a non-inverted signal and an inverted signal amplified by amplifying elements  12  and  13  are combined, and a non-inverted signal and an inverted signal amplified by amplifying elements  22  and  23  are combined. Thus, unnecessary waves such as harmonic components, for instance, in radio frequency module  1 , can be decreased. 
     In radio frequency module  1 C, output transformer  15  may be larger than output transformer  25 , and in a plan view of module board  91 , the footprint of power amplifier  10 A may at least partially overlap the footprint of PA control circuit  80 , and the footprint of power amplifier  20 A may not overlap the footprint of PA control circuit  80 . 
     Out of output transformers  15  and  25 , output transformer  25  that outputs a transmission signal having a higher frequency has a smaller volume. According to the above configuration, the control line can be shortened since the footprint of power amplifier  10 A at least partially overlaps the footprint of PA control circuit  80 , and the footprint of power amplifier  20 A does not overlap the footprint of PA control circuit  80 , and thus PA control circuit  80  can be prevented from being damaged by heat dissipated from power amplifier  20 A while heat dissipation of power amplifier  20 A is improved. 
     In radio frequency module  1 , in a plan view of module board  91 , the footprints of power amplifiers  10 A and  20 A may not each overlap both of the footprints of output transformers  15  and  25 . 
     Output transformers  15  and  25  each need to have a high Q factor to handle a high-power transmission signal, and thus desirably, magnetic fields formed by output transformers  15  and  25  do not change due to power amplifiers  10 A and  20 A being adjacent thereto. According to the above configuration, power amplifiers  10 A and  20 A are not disposed in the regions in which the transformers are disposed, and thus the Q factors of the inductors included in output transformers  15  and  25  can be maintained high. 
     In radio frequency module  1 , output transformers  15  and  25  may be disposed on principal surface  91   a , and in the plan view of module board  91 , no circuit component may be disposed in a region included in principal surface  91   b  and overlapping the footprint of output transformer  15 , and no circuit component may be disposed in a region included in principal surface  91   b  and overlapping the footprint of output transformer  25 . 
     According to this configuration, no circuit component is disposed in the above regions in principal surface  91   b , and thus the Q factors of the inductors included in output transformers  15  and  25  can be maintained high. 
     In radio frequency module  1 , output transformers  15  and  25  may be disposed on principal surface  91   b , and in the plan view of module board  91 , no circuit component may be disposed in a region included in principal surface  91   a  and overlapping the footprint of output transformer  15 , and no circuit component may be disposed in a region included in principal surface  91   a  and overlapping the footprint of output transformer  25 . 
     According to this configuration, no circuit component is disposed in the above regions in principal surface  91   a , and thus the Q factors of the inductors included in output transformers  15  and  25  can be maintained high. 
     In radio frequency module  1 , output transformers  15  and  25  may be formed inside of module board  91 , between principal surface  91   a  and principal surface  91   b , and in the plan view of module board  91 , no circuit component may be disposed in a region included in principal surface  91   a  and overlapping the footprint of output transformer  15 , no circuit component may be disposed in a region included in principal surface  91   b  and overlapping the footprint of output transformer  15 , no circuit component may be disposed in a region included in principal surface  91   a  and overlapping the footprint of output transformer  25 , and no circuit component may be disposed in a region included in principal surface  91   b  and overlapping the footprint of output transformer  25 . 
     According to this configuration, no circuit component is disposed in the above regions in principal surfaces  91   a  and  91   b , and thus the Q factors of the inductors included in output transformers  15  and  25  can be maintained high. 
     In radio frequency module  1 , output transformers  15  and  25  may be disposed inside of module board  91 , between principal surface  91   a  and principal surface  91   b , output transformers  15  and  25  being offset toward one of principal surface  91   a  and principal surface  91   b , and in the plan view of module board  91 , no circuit component may be disposed in a region included in the one of principal surface  91   a  and principal surface  91   b  and overlapping the footprint of output transformer  15 , no circuit component may be disposed in a region included in the one of principal surface  91   a  and principal surface  91   b  and overlapping the footprint of output transformer  25 , a circuit component may be disposed in a region included in a remaining one of principal surface  91   a  and principal surface  91   b  and overlapping the footprint of output transformer  15 , and a circuit component may be disposed in a region included in the remaining one of principal surface  91   a  and principal surface  91   b  and overlapping the footprint of output transformer  25 . 
     Also in this case, no circuit component is disposed in the above regions in the one of principal surfaces  91   a  and  91   b  closer to output transformers  15  and  25 , and thus the Q factors of the inductors included in output transformers  15  and  25  can be maintained high. 
     Communication device  5  includes: antenna  2 ; RFIC  3  configured to process radio frequency signals transmitted and received by antenna  2 ; and radio frequency module  1  configured to transfer the radio frequency signals between antenna  2  and RFIC  3 . 
     According to this configuration, small communication device  5  that supports multiband technology can be provided. 
     Other Embodiments Etc. 
     The above has described the radio frequency module and the communication device according to the embodiment of the present disclosure, based on an embodiment, examples, and variations, yet the radio frequency module and the communication device according to the present disclosure are not limited to the above embodiment, examples, and variations. The present disclosure also encompasses another embodiment achieved by combining arbitrary elements in the embodiment, the examples, and the variations, variations as a result of applying various modifications that may be conceived by those skilled in the art to the embodiment, the examples, and the variations without departing from the scope of the present disclosure, and various apparatuses that include the radio frequency module and the communication device. 
     For example, in the radio frequency modules and the communication devices according to the embodiment, the examples, and the variations, another circuit element and another line, for instance, may be disposed between circuit elements and paths connecting signal paths that are illustrated in the drawings. 
     Although only some exemplary embodiments of the present disclosure have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure can be widely used in communication apparatuses such as mobile phones, as a radio frequency module disposed in a front-end portion, which supports multiband technology.