Abstract:
A power amplification circuit amplifies and then outputs transmission signals of a first frequency and a second frequency, which are different from each other. When the transmission signal of the first frequency is input, a first switch is turned ON, a first LC parallel resonant circuit enters a resonant state and the transmission signal is transmitted using a line containing a first capacitor as a main line. When the transmission signal of the second frequency is input, a second switch is turned ON, a second LC parallel resonant circuit enters a resonant state and the transmission signal is transmitted using a line containing a second capacitor as a main line. Therefore, a transmission signal does not pass through, using as a main line, a line into which a switch has been incorporated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to power amplification circuits preferably for use in power amplification modules that amplify signals of a plurality of frequency bands. 
     2. Description of the Related Art 
     In general, known wireless communication devices, such as cellular phones, are equipped with a transmission device for transmitting a plurality of transmission signals. A transmission device  102  described in Japanese Unexamined Patent Application Publication No. 2008-154201 and illustrated in  FIG. 5  is used as such a transmission device of a multiband wireless communication device. A power amplification module  104  is used in the transmission device  102  and a power amplification circuit  110  of the power amplification module  104  has the following configuration. 
     The power amplification circuit  110  employs a power amplifier  109 , a power detector  119 , an isolator  121  and so forth for both first and second transmission signals and the two types of signal are separated by a switch  122  on the output side. 
     In such a power amplification circuit  110 , the switch  122  is incorporated into a main line through which a transmission signal passes and as a result the following problems and issues arise. That is, power loss occurs in the switch  122 , distortion occurs due to the large amount of power entering the switch  122  and the switch is required to have a high electrical power handling capability. 
     SUMMARY OF THE INVENTION 
     In light of such circumstances, preferred embodiments of the present invention provide a power amplification circuit in which power loss of a transmission signal and signal distortion due to an output-side switch and the electrical power handling capability of the switch are not issues. 
     A power amplification circuit according to a preferred embodiment of the present invention amplifies and outputs transmission signals of a first frequency and a second frequency, the first and the second frequency being different from each other. The power amplification circuit includes a power amplifier that amplifies the transmission signals of the first and second frequencies. A first LC parallel resonant circuit whose resonant frequency is set to the first frequency and that includes a switch, and a second LC parallel resonant circuit whose resonant frequency is set to the second frequency and that includes a switch, are connected in parallel with each other to an output side of the power amplifier. When the power amplifier operates with the transmission signal of the first frequency, the switch on the first LC parallel resonant circuit side enters an on state and the switch on the second LC parallel resonant circuit side enters an off state. When the power amplifier operates with the transmission signal of the second frequency, the switch on the first LC parallel resonant circuit side enters an off state and the switch on the second LC parallel resonant circuit side enters an on state. 
     With this power amplification circuit, a transmission signal does not pass through using, as a main line, a line along which a switch is arranged and therefore problems of power loss of a transmission signal caused by a switch and signal distortion caused by a large amount of power being input to a switch do not arise. In addition, there is no need for a switch to have a high electrical power handling capability. 
     Preferably, the first LC parallel resonant circuit and the second LC parallel resonant circuit share the same inductor. With this power amplification circuit, the number of wiring lines and inductors in the amplification circuit can be reduced. 
     In each of the LC parallel resonant circuits including a switch, the switch preferably is connected to the inductor. With this power amplification circuit, a signal does not pass through a switch or an inductor and therefore power loss can be prevented or significantly reduced. 
     With various preferred embodiments of the present invention, power loss of a transmission signal and signal distortion in a switch in a power amplification circuit is significantly reduced. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram of a power amplification circuit according to Preferred Embodiment 1 of the present invention. 
         FIGS. 2A and 2B  are structural diagrams of a circuit module that includes the power amplification circuit according to Preferred Embodiment 1 of the present invention. 
         FIG. 3  is a circuit diagram of a power amplification circuit according to Preferred Embodiment 2 of the present invention. 
         FIG. 4  is a circuit diagram of a power amplification circuit according to a modification of Preferred Embodiment 2 of the present invention. 
         FIG. 5  is a circuit diagram of a power amplification circuit of the related art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, power amplification circuits according to preferred embodiments of the present invention will be described in detail while referring to the drawings. 
     Preferred Embodiment 1 
       FIG. 1  is a circuit diagram of a power amplification circuit  10  of the present preferred embodiment. 
     The power amplification circuit  10  of the present preferred embodiment, as illustrated in  FIG. 1 , includes a power amplifier  15 , capacitors C 11  and C 12 , inductors L 11  and L 12  and switches SW 11  and SW 12 . The switches SW 11  and SW 12  each include an input terminal IN and an output terminal OUT for a transmission signal and an input terminal Vdd for a driving voltage signal and respectively include input terminals Vc 1  and Vc 2 , which are used for input of a control signal. 
     The capacitor C 11  and the inductor L 11 , along with the switch SW 11 , define an LC parallel resonant circuit  13   a , the switch SW 11  being connected in series with the inductor L 11 . Similarly, an LC parallel resonant circuit  13   b  is defined by the capacitor C 12 , the inductor L 12  and the switch SW 12 . 
     The power amplifier  15  and the LC parallel resonant circuits  13   a  and  13   b  are connected to each other via a branching point  16 . 
     Regarding predetermined frequencies of signals that are used by the power amplification circuit  10 , for example, there are a transmission signal of a first frequency of 824 MHz to 849 MHz (transmission signal of US cellular scheme) and a transmission signal of a second frequency of 898 MHz to 925 MHz (transmission signal of J-CDMA scheme). The resonant frequency of the LC parallel resonant circuit  13   a  is set to the first frequency, which is the frequency of a transmission signal blocked by the LC parallel resonant circuit  13   a , and the resonant frequency of the LC parallel resonant circuit  13   b  is set to the second frequency, which is the frequency of a transmission signal blocked by the LC parallel resonant circuit  13   b.    
     Next, operation of the power amplification circuit  10  will be described. 
     When a transmission signal of the first frequency is input from the input terminal  11 , for example, a positive voltage control signal is input to the control signal input terminal Vc 1  of the switch SW 11  and the switch SW 11  enters a conductive state (ON). Then, the LC parallel resonant circuit  13   a  enters a resonant state and the first frequency transmission signal passes through using the line containing the capacitor C 12  as a main line and is output to the output terminal  12   b , without being able to pass through the LC parallel resonant circuit  13   a . Similarly, when a transmission signal of the second frequency is input from the input terminal  11 , for example, a positive voltage control signal is input to the control signal input terminal Vc 2  of the switch SW 12  and the switch SW 12  enters a conductive state (ON). Then, the LC parallel resonant circuit  13   b  enters a resonant state and the second frequency transmission signal passes through using the line containing the capacitor C 11  as a main line and is output to the output terminal  12   a , without being able to pass through the LC parallel resonant circuit  13   b . That is, the first frequency transmission signal is separated to the output terminal  12   b  and the second frequency transmission signal is separated to the output terminal  12   a  by the power amplification circuit  10 . 
     With the above-described circuit configuration, the first and second frequency transmission signals are not able to pass through using lines along which the switches SW 11  and SW 12  are arranged as main lines and therefore power loss of a transmission signal due to a switch is significantly reduced and occurrence of signal distortion due input of a large amount of power to a switch is prevented. In addition, there is no need for the switches to have high power handling capabilities and therefore cost reduction is possible. 
     Next, an example structure of a circuit module including the power amplification circuit of the present preferred embodiment will be described. 
       FIG. 2A  is an external perspective view of a circuit board  41  preferably composed of, for example, a ceramic or a glass epoxy resin and a circuit module formed preferably by mounting elements such as capacitors, inductors, switches and a power amplifier with solder on one main surface  41   a  of the circuit board  41 .  FIG. 2B  is an external perspective view of a circuit module  40  in a state in which the above-mentioned elements have been sealed by an insulating resin  42 . 
     The correspondence between the mounted elements of  FIG. 2A  and the elements of the power amplification circuit  10  of  FIG. 1  is as follows. The capacitors C 11  and C 12  correspond to Fc 1  and Fc 2 , the inductors L 11  and L 12  correspond to F 11  and F 12 , the switches SW 11  and SW 12  correspond to Fsw 1  and Fsw 2  and the power amplifier  15  corresponds to F 15 . In addition, although not illustrated, the elements are connected to each other through wiring electrodes located on the circuit board  41  and a large number of connection terminals that are enable connection to another board are located on the circuit board  41 . 
     The above-described example structure is not limiting and a structure in which the circuit board is defined by a multilayer board, in which passive elements and so forth are built into the multilayer board and that achieves size reduction, profile reduction and cost reduction is also possible. 
     Preferred Embodiment 2 
       FIG. 3  is a circuit diagram of a power amplification circuit  20  of the present preferred embodiment. In the present preferred embodiment, constituent elements that are the same as those in the above-described Preferred Embodiment 1 will be denoted by the same symbols and description thereof will be omitted. 
     The power amplification circuit  20 , as illustrated in  FIG. 3 , includes a power amplifier  15 , capacitors C 21  and C 22 , an inductor L 21  and a switch SW 21 . The switch SW 21  is called a single pole double throw (SPDT) type switch and includes two switching terminals (OUT 1  and OUT 2 ) for one common terminal (IN). 
     The capacitor C 21  and the inductor L 21 , along with the switch SW 21 , define an LC parallel resonant circuit  23   a , the switch SW 21  being connected in series with the inductor L 21 . An LC parallel resonant circuit  23   b  is similarly defined by the capacitor C 22 , the inductor L 21  and the switch SW 21 . The power amplifier  15  and the LC parallel resonant circuits  23   a  and  23   b  are connected to each other via a branching point  26 . 
     The resonant frequency of the LC parallel resonant circuit  23   a  is set to the first frequency, which is the frequency of a transmission signal blocked by the LC parallel resonant frequency circuit  23   a  and the resonant frequency of the LC parallel resonant circuit  23   b  is set to the second frequency, which is the frequency of a transmission signal blocked by the LC parallel resonant frequency circuit  23   b.    
     When a transmission signal of the first frequency is input from the input terminal  11 , for example, a positive voltage control signal is input to a control signal input terminal Vc 1  of the switch SW 21  and the switch SW 21  switches the LC parallel resonant circuit  23   a  side ON and switches the LC parallel resonant circuit  23   b  side OFF. Then, the LC parallel resonant circuit  23   a  enters a resonant state and the first frequency transmission signal passes through using the line containing the capacitor C 22  as a main line and is output to the output terminal  22   b , without being able to pass through the LC parallel resonant circuit  23   a  side. Similarly, when a transmission signal of the second frequency is input from the input terminal  11 , for example, a negative voltage control signal is input to the control signal input terminal Vc 1  of the switch SW 21  and the switch SW 21  switches the LC parallel resonant circuit  23   a  side OFF and switches the LC parallel resonant circuit  23   b  side ON. Then, the LC parallel resonant circuit  23   b  enters a resonant state and the second frequency transmission signal passes through using the line containing the capacitor C 21  as a main line and is output to the output terminal  22   a , without being able to pass through the LC parallel resonant circuit  23   b  side. That is, the first frequency transmission signal is separated to the output terminal  22   b  and the second frequency transmission signal is separated to the output terminal  22   a  by the power amplification circuit  20 . 
     With the above-described circuit configuration, in addition to the effect obtained in Preferred Embodiment 1, the number of inductors and switches can be reduced and the size and cost of the circuit module can be reduced. 
       FIG. 4  is a circuit diagram of a power amplification circuit  30  according to a modification of Preferred Embodiment 2. 
     The power amplification circuit  30 , as illustrated in  FIG. 4 , includes a power amplifier  15 , capacitors C 31  and C 32 , inductors L 31  and L 32  and a switch SW 31 . The switch SW 31  is called a double pole double throw (DPDT) type switch and includes two common terminals (IN 1  and IN 2 ) and two switching terminals (OUT 1  and OUT 2 ). 
     The capacitor C 31  and the inductor L 31 , along with the switch SW 31 , define an LC parallel resonant circuit  33   a , the switch SW 31  being connected in series with the inductor L 31 . An LC parallel resonant circuit  33   b  is similarly defined by the capacitor C 32 , the inductor L 32  and the switch SW 31 . The power amplifier  15  and the LC parallel resonant circuits  33   a  and  33   b  are connected to each other via a branching point  36 . 
     The resonant frequency of the LC parallel resonant circuit  33   a  is set to the first frequency, which is the frequency of a transmission signal blocked by the LC parallel resonant frequency circuit  33   a , and the resonant frequency of the LC parallel resonant circuit  33   b  is set to the second frequency, which is the frequency of a transmission signal blocked by the LC parallel resonant frequency circuit  33   b.    
     When a transmission signal of the first frequency is input from the input terminal  11 , for example, a positive voltage control signal is input to the control signal input terminal Vc 1  of the switch SW 31  and a zero voltage control signal is input to the control signal input terminal Vc 2  of the switch SW 31 , the switch SW 31  switches the LC parallel resonant circuit  33   a  side ON and switches the LC parallel resonant circuit  33   b  OFF side. Then, the LC parallel resonant circuit  33   a  enters a resonant state and the first frequency transmission signal passes through using the line containing the capacitor C 32  as a main line and is output to the output terminal  32   b , without being able to pass through the LC parallel resonant circuit  33   a  side. Similarly, when a transmission signal of the second frequency is input from the input terminal  11 , for example, a zero voltage control signal is input to the control signal input terminal Vc 1  of the switch SW 31  and a positive voltage is input to the control signal input terminal Vc 2  of the switch SW 31  and the switch SW 31  switches the LC parallel resonant circuit  33   a  side OFF and switches the LC parallel resonant circuit  33   b  side ON. Then, the LC parallel resonant circuit  33   b  enters a resonant state and the second frequency transmission signal passes through using the line containing the capacitor C 31  as a main line and is output to the output terminal  32   a , without being able to pass through the LC parallel resonant circuit  33   b  side. That is, the first frequency transmission signal is separated to the output terminal  32   b  and the second frequency transmission signal is separated to the output terminal  32   a  by the power amplification circuit  30 . 
     With the above-described circuit configuration, in addition to the advantageous effects obtained in Preferred Embodiment 1, the number of switches can be reduced and the size and cost of the circuit module can be reduced. 
     The present invention is not limited to the circuits described in the above preferred embodiments. The above-described circuits are basic configurations and can be changed to a circuit configuration including, for example, elements such as a power detector and an isolator as in the power amplification circuit  110  described in the background art. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.