Abstract:
A high frequency power amplifier includes first and second transistors connected in parallel and amplifying a high frequency signal; a first switch connected to outputs of the first and second transistors and which connects an input terminal selectively to first and second output terminals; a third transistor amplifying a signal output from the first output terminal of the first switch; and a second switch having a first input terminal connected to the third transistor, a second input terminal connected to the second output terminal of the first switch, and which selectively connects the first and the second input terminals to an output terminal of the second switch.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a high frequency power amplifier which makes it possible to improve the operating efficiency over a wide output power range. 
         [0003]    2. Background Art 
         [0004]    High frequency power amplifiers that amplify high frequency signals are used for cellular phones and portable terminals. Conventionally, a route in a high frequency power amplifier suitable for large power output operation is used to obtain large power output of 27.5 dBm and a route suitable for medium power output operation is used to obtain medium power output of 17 dBm, and operating efficiency at respective levels of output power is thereby improved (e.g., see Proceedings of the 36th European Microwave Conference, P 348-P 351). 
       SUMMARY OF THE INVENTION 
       [0005]    Output power required for a high frequency power amplifier used for a CDMA cellular phone terminal ranges from −50 dBm to 27.5 dBm. However, conventional high frequency power amplifiers are not good enough to improve operating efficiency when output power is as small as 17 dBm or below. 
         [0006]    In view of the above-described problems, an object of the present invention is to provide a high frequency power amplifier which makes it possible to improve the operating efficiency over a wide output power range. 
         [0007]    According to the present invention, a high frequency power amplifier comprises: first and second transistors which are connected parallel to each other and amplify a high frequency signal inputted from outside; a first switch which includes a first input terminal connected to outputs of the first and second transistors, a first output terminal, and a second output terminal and connects the first input terminal to any one of the first output terminal and the second output terminal; a third transistor which amplifies a signal outputted from the first output terminal; and a second switch which includes a second input terminal connected to an output of the third transistor, a third input terminal connected to the second output terminal, and a third output terminal and connects any one of the second input terminal and the third input terminal to the third output terminal, wherein an output power of the first transistor is greater than an output power of the second transistor and an operating efficiency of the first transistor is lower than an operating efficiency of the second transistor. 
         [0008]    The present invention makes it possible to improve the operating efficiency over a wide output power range. 
         [0009]    Other and further objects, features and advantages of the invention will appear more fully from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a circuit diagram illustrating a high frequency power amplifier according to a first embodiment. 
           [0011]      FIG. 2  is a circuit diagram illustrating a high frequency power amplifier according to a second embodiment. 
           [0012]      FIG. 3  is a circuit diagram illustrating a high frequency power amplifier according to a third embodiment. 
           [0013]      FIG. 4  is a circuit diagram illustrating a high frequency power amplifier according to a fourth embodiment. 
           [0014]      FIG. 5  is a circuit diagram illustrating the matching circuit  32  and the switch  34  according to the fourth embodiment. 
           [0015]      FIG. 6  is a circuit diagram illustrating a modification example of the matching circuit and the third switch according to the fourth embodiment. 
           [0016]      FIG. 7  is a circuit diagram illustrating a high frequency power amplifier according to a fifth embodiment. 
           [0017]      FIG. 8  is a circuit diagram illustrating a high frequency power amplifier according to a sixth embodiment. 
           [0018]      FIG. 9  is a circuit diagram illustrating a high frequency power amplifier according to a seventh embodiment. 
           [0019]      FIG. 10  is a circuit diagram illustrating a high frequency power amplifier according to an eighth embodiment. 
           [0020]      FIG. 11  is a circuit diagram illustrating a high frequency power amplifier according to a ninth embodiment. 
           [0021]      FIG. 12  is a circuit diagram illustrating a high frequency power amplifier according to a tenth embodiment. 
           [0022]      FIG. 13  is a circuit diagram illustrating a high frequency power amplifier according to an eleventh embodiment. 
           [0023]      FIG. 14  is a circuit diagram illustrating a high frequency power amplifier according to a twelfth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    A high frequency power amplifier according to the embodiments of the present invention will be described with reference to the drawings. The same components will be denoted by the same symbols, and the repeated description thereof may be omitted. 
       First Embodiment 
       [0025]      FIG. 1  is a circuit diagram illustrating a high frequency power amplifier according to a first embodiment. Transistors  10  and  12  are connected parallel to each other and their inputs are connected to a signal input terminal  16  via an input matching circuit  14 . The transistors  10  and  12  amplify a high frequency signal inputted from outside to the signal input terminal  16 . The input matching circuit  14  matches input impedances of the transistors  10  and  12  to their respective characteristic impedances. The emitter size of the transistor  10  is greater than the emitter size of the transistor  12 . 
         [0026]    A switch  18  has an input terminal  18   a  connected to an output of the transistor  10  and an output of the transistor  12 , an output terminal  18   b  and an output terminal  18   c . The switch  18  connects the input terminal  18   a  to any one of the output terminal  18   b  and the output terminal  18   c.    
         [0027]    An input of a transistor  20  is connected to the output terminal  18   b  via an inter-stage matching circuit  22 . The transistor  20  amplifies a signal outputted from the output terminal  18   b . The inter-stage matching circuit  22  matches an output impedance of the transistor  10  with an input impedance of the transistor  20 . 
         [0028]    A switch  24  has an input terminal  24   a  connected to an output of the transistor  20  via an output matching circuit  26 , an input terminal  24   b  connected to the output terminal  18   c  via an output matching circuit  28  and an output terminal  24   c . The switch  24  connects any one of the input terminal  24   a  and the input terminal  24   b  to the output terminal  24   c . The output terminal  24   c  is connected to a signal output terminal  30 . The output matching circuit  26  matches an output impedance of the transistor  20  with a characteristic impedance. The output matching circuit  28  matches an output impedance of the transistor  10  and an output impedance of the transistor  12  with a characteristic impedance. 
         [0029]    Next, operations of the above described high frequency power amplifier will be described. To obtain large power output of 17 dBm or more, the transistor  10  is turned ON, the transistor  12  is turned OFF and the transistor  20  is turned ON. The switch  18  connects the input terminal  18   a  to the output terminal  18   b  and the switch  24  connects the input terminal  24   a  to the output terminal  24   c . In this way, a signal inputted to the signal input terminal  16  is amplified by the transistor  10  and the transistor  20  by passing through a route  1  and outputted from the signal output terminal  30 . 
         [0030]    To obtain medium power output of 7 to 17 dBm, the transistor  10  is turned ON, the transistor  12  is turned OFF and the transistor  20  is turned OFF. The switch  18  connects the input terminal  18   a  to the output terminal  18   c  and the switch  24  connects the input terminal  24   b  to the output terminal  24   c . In this way, a signal inputted to the signal input terminal  16  is amplified by the transistor  10  by passing through a route  2  and outputted from the signal output terminal  30 . 
         [0031]    To obtain small power output of 7 dBm or less, the transistor  10  is turned OFF, the transistor  12  is turned ON and the transistor  20  is turned OFF. The switch  18  connects the input terminal  18   a  to the output terminal  18   c  and the switch  24  connects the input terminal  24   b  to the output terminal  24   c . In this way, a signal inputted to the signal input terminal  16  is amplified by the transistor  12  by passing through a route  3  and outputted from the signal output terminal  30 . 
         [0032]    As described above, the emitter size of the transistor  10  is greater than the emitter size of the transistor  12 . Therefore, the output power of the transistor  10  is greater than the output power of the transistor  12  and the operating efficiency of the transistor  10  is lower than the operating efficiency of the transistor  12 . Here, the operating efficiency is expressed by (output power−input power)/power consumption×100(%). Power consumption is an operating voltage×operating current. 
         [0033]    When obtaining small output power of 7 dBm or less, the present embodiment selects the transistor  12 , and can thereby improve operating efficiency. Therefore, although the conventional high frequency power amplifier cannot improve operating efficiency when small output power of 7 dBm or less is used, the present embodiment can improve the operating efficiency. Thus, it is possible to improve the operating efficiency over a wide output power range. 
       Second Embodiment 
       [0034]      FIG. 2  is a circuit diagram illustrating a high frequency power amplifier according to a second embodiment. In addition to the configuration of the first embodiment, a matching circuit  32  is connected between a connection point between the output of the transistor  10  and the input terminal  18   a , and the output of the transistor  12 . The matching circuit  32  matches an output impedance of the transistor  12  with an impedance of the route  3 . The matching circuit  32  improves operating efficiency of the transistor  12 . 
         [0035]    Table 1 shows operating efficiency of the conventional high frequency power amplifier, the high frequency power amplifier according to the first embodiment and the high frequency power amplifier according to the second embodiment in the case of 7 dBm output. As is understandable from Table 1, the second embodiment can improve operating efficiency compared to the first embodiment. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Operating efficiency in case 
               
               
                   
                   
                 of 7 dBm output 
               
               
                   
                   
               
             
             
               
                   
                 Conventional high frequency power 
                 6% 
               
               
                   
                 amplifier 
                   
               
               
                   
                 High frequency power amplifier 
                 8% 
               
               
                   
                 according to first embodiment 
                   
               
               
                   
                 High frequency power amplifier 
                 12%  
               
               
                   
                 according to second embodiment 
               
               
                   
                   
               
             
          
         
       
     
       Third Embodiment 
       [0036]      FIG. 3  is a circuit diagram illustrating a high frequency power amplifier according to a third embodiment. In addition to the configuration of the first embodiment, a switch  34  is connected between a connection point between the output of the transistor  10  and the input terminal  18   a , and the output of the transistor  12 . When the transistor  10  operates and the transistor  12  does not operate, the switch  34  turns OFF (is left open). The switch  34  can reduce the amount of output power of the transistor  10  leaking to the collector of the transistor  12 , and can thereby improve operating efficiency of the transistor  10 . 
         [0037]    Table 2 illustrates operating efficiency of the conventional high frequency power amplifier and the high frequency power amplifier according to the third embodiment in the case of 17 dBm output. As is understandable from Table 2, the third embodiment can improve operating efficiency by 3% compared to the conventional art. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Operating efficiency in case 
               
               
                   
                   
                 of 17 dBm output 
               
               
                   
                   
               
             
             
               
                   
                 Conventional high frequency power 
                 24% 
               
               
                   
                 amplifier 
                   
               
               
                   
                 High frequency power amplifier 
                 27% 
               
               
                   
                 according to third embodiment 
               
               
                   
                   
               
             
          
         
       
     
       Fourth Embodiment 
       [0038]      FIG. 4  is a circuit diagram illustrating a high frequency power amplifier according to a fourth embodiment. In addition to the configuration of the first embodiment, the fourth embodiment is provided with both the matching circuit  32  of the second embodiment and the switch  34  of the third embodiment. It is thereby possible to obtain the effects of both the second embodiment and the third embodiment. 
         [0039]      FIG. 5  is a circuit diagram illustrating the matching circuit  32  and the switch  34  according to the fourth embodiment. The matching circuit  32  is an inductor  36 . The switch  34  is a resistor  38  and a transistor  40  connected in parallel.  FIG. 6  is a circuit diagram illustrating a modification example of the matching circuit  32  and the switch  34  according to the fourth embodiment. The matching circuit  32  is an inductor  36  and a capacitor  42 . The connection positions of the matching circuit  32  and the switch  34  can be switched round. 
       Fifth Embodiment 
       [0040]      FIG. 7  is a circuit diagram illustrating a high frequency power amplifier according to a fifth embodiment. In addition to the configuration of the first embodiment, a line  44  is connected between a connection point between the output of the transistor  10  and the input terminal  18   a , and the output of the transistor  12 . The line  44  has an electric length of ¼ of the wavelength of a high frequency signal. The line  44  can reduce the amount of output power of the transistor  10  leaking to the collector of the transistor  12 , and can thereby improve operating efficiency of the transistor  10 . 
       Sixth Embodiment 
       [0041]      FIG. 8  is a circuit diagram illustrating a high frequency power amplifier according to a sixth embodiment. In addition to the configuration of the first embodiment, both the matching circuit  32  of the second embodiment and the line  44  of the fifth embodiment are provided. This makes it possible to obtain the effects of both the second embodiment and the fifth embodiment. 
       Seventh Embodiment 
       [0042]      FIG. 9  is a circuit diagram illustrating a high frequency power amplifier according to a seventh embodiment. Unlike the first embodiment, the output of the transistor  12  is connected to the output terminal  18   c  and is also connected to the input terminal  24   b  via the output matching circuit  28 . This prevents the route  3  from being affected by loss at the switch  18 . It is thereby possible to improve operating efficiency in the case of small power output of 7 dBm or less compared to the first embodiment. 
       Eighth Embodiment 
       [0043]      FIG. 10  is a circuit diagram illustrating a high frequency power amplifier according to an eighth embodiment. In addition to the configuration of the seventh embodiment, the matching circuit  32  is connected between a connection point between the output terminal  18   c  and the output matching circuit  28  (input terminal  24   b ) and the output of the transistor  12 . The matching circuit  32  matches an output impedance of the transistor  12  with an impedance of the route  3 . The matching circuit  32  improves operating efficiency of the transistor  12 . 
       Ninth Embodiment 
       [0044]      FIG. 11  is a circuit diagram illustrating a high frequency power amplifier according to a ninth embodiment. In addition to the configuration of the seventh embodiment, the switch  34  is connected between a connection point between the output terminal  18   c  and the output matching circuit  28  (input terminal  24   b ) and the output of the transistor  12 . When the transistor  10  operates and the transistor  12  does not operate, the switch  34  turns OFF (is left open). The switch  34  can reduce the amount of output power of the transistor  10  leaking to the collector of the transistor  12 , and can thereby improve operating efficiency of the transistor  10 . 
       Tenth Embodiment 
       [0045]      FIG. 12  is a circuit diagram illustrating a high frequency power amplifier according to a tenth embodiment. In addition to the configuration of the seventh embodiment, both the matching circuit  32  of the eighth embodiment and the switch  34  of the ninth embodiment are provided. This makes it possible to obtain the effects of both the eighth embodiment and the ninth embodiment. 
       Eleventh Embodiment 
       [0046]      FIG. 13  is a circuit diagram illustrating a high frequency power amplifier according to an eleventh embodiment. In addition to the configuration of the seventh embodiment, the line  44  is connected between a connection point between the output terminal  18   c  and the output matching circuit  28  (input terminal  24   b ), and the output of the transistor  12 . The line  44  has an electric length of ¼ of the wavelength of a high frequency signal. The line  44  can reduce the amount of output power of the transistor  10  leaking to the collector of the transistor  12 , and can thereby improve operating efficiency of the transistor  10 . 
       Twelfth Embodiment 
       [0047]      FIG. 14  is a circuit diagram illustrating a high frequency power amplifier according to a twelfth embodiment. In addition to the configuration of the seventh embodiment, both the matching circuit  32  of the eighth embodiment and the line  44  of the eleventh embodiment are provided. This makes it possible to obtain the effects of both the eighth embodiment and the eleventh embodiment. 
         [0048]    Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 
         [0049]    The entire disclosure of a Japanese Patent Application No. 2010-101027, filed on Apr. 26, 2010 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.