Abstract:
The present invention provides a radio frequency power amplifier which may not introduce radio frequency loss during switching power amplifier units between high and low output power levels. By connecting a first-stage matching network M12 and first-stage matching network M13 to respective output nodes of a power amplifier unit A11 and power amplifier unit A12 that either one operate by switching, connecting the output nodes of the first-stage matching network M12 and M13 in parallel, connecting a last-stage matching network M11 between the junction of M12 and M13 and the output terminal OUT, the first-stage matching networks M12, M13, and last-stage matching network M11 are formed, for both power amplifier units A11 and A12, so that impedance matching is established between the output terminal OUT and the power amplifier unit in operation when one unit is in operation the other is in stop of operation. The present invention allows switching from one power amplifier unit to the other without the need of a radio frequency switch.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to an improved efficiency of radio frequency power amplifiers for use in portable cellular phone terminals and base stations incorporated in a mobile communication system.  
         [0002]     Recently, in the field of the mobile communication, scaling down in the size and weight is requested not only for the portable cellular terminals but also for the base stations. Along with this trend is further requested the improvement of the efficiency of the power amplifiers, which affects mostly the electric consumption of the whole system. The portable cellular phone terminal, which usually use a battery for their main power source, may have a major problem that requires to improve the efficiency of the phone terminal, by saving the power consumption in the power amplifier unit which drains the most power in the circuitry, in order for the terminal to sustain its operating time. In addition, since the radio frequency power amplifier are installed near their antenna for the objective of decreasing some transmission line loss in the cable and the like, shrinking the size and improving the efficiency of radio frequency power amplifier is highly required.  
         [0003]     In general, the efficiency of an radio frequency power amplifier using semiconductor elements will be increasingly higher if the output power is higher, and will be highest at the yieldable maximum output, i.e., in vicinity of the saturated output power level. Also, the saturated output power level may be dependent on the size of semiconductor elements used.  
         [0004]     When making a power amplifier of low saturated output power level by using smaller semiconductor elements in order to improve the efficiency at lower output power, output power required may not be sufficient at higher output power state. On contrary, when making a power amplifier of higher efficiency at some high saturated output power level using larger semiconductor elements, the efficiency will be decreased at lower output level.  
         [0005]     It can be seen from the foregoing by those skilled in the art that it is quite difficult to operate one single power amplifier at high efficiency in both lower and higher output power mode. As a solution it has been proposed, as disclosed for example as a circuit embodiment in Japanese Patent Laid-open (Kokai) No. Hei 7-336168, a circuit arrangement which may be able to yield an improved efficiency at both higher and lower output power modes, by providing a plurality of output stage power amplifiers each having a different saturation output power level and by switching to one most convenable output stage power amplifier in accordance with the output power, by means of a switch.  
         [0006]     A typical example of conventional power amplifier capable of switching output power stage in accordance with the desired output level is shown in  FIG. 16 . In the figure, an incoming radio frequency signal that have been received by input terminal IN 1  will be amplified in high output power amplifier component A 161  designed to be used for high output power level. An amplified signal then will be passed through a matching network M 161  to a radio frequency switch SW 1  used for switching the signal path. Meanwhile a radio frequency signal incoming via input terminal IN 2  will be amplified by low output power amplifier component A 162  designed to be used for low output power level, and will be passed through another matching network M 162  to the radio frequency switch SW 1 . The radio frequency switch SW 1  will be turned to the high output power amplifier component A 161  for high output power mode (in which case the low output power amplifier component A 162  will be put into stop of operation state), or will be turned to the low output power amplifier component A 162  if lower output power is required. (in which case the high output power amplifier component A 161  will be put into stop of operation state). Thus through output terminal OUT will be delivered output a signal amplified either one of output power amplifier elements.  
       SUMMARY OF THE INVENTION  
       [0007]     In the Prior Art, as have been described in the foregoing description, improvement of the efficiency has been achieved in both high and low output power modes by switching by the radio frequency switch SW 1  the output signal from either the high output power amplifier component A 161  for use in the high output power mode or from the low output power amplifier component A 162  for use in the low output power mode. In this circuit design, the radio frequency switch SW 1  is placed after the high and low output power amplifier components A 161  and A 162 , so that inevitably the effective improvement of efficiency may not be sufficient because of decreased efficiency due to the loss at this section. In addition, some electric power will be needed in order to operate the radio frequency switch SW 1 , power consumption of the switch may also introduce inevitable loss of efficiency.  
         [0008]     Moreover, to supply a signal to the input terminal IN 1  and input terminal IN 2 , a radio frequency switch (not shown) is used. The insertion loss of the radio frequency switch may also cause some decrease of efficiency, as similar to the output side.  
         [0009]     Accordingly, an object of the present invention is to provide a radio frequency power amplifier which may not introduce radio frequency loss when switching power amplifiers (amplifying elements) for high output power and low output power.  
         [0010]     The object of the present invention may be efficiently achievable by connecting each of first-stage matching networks to the output node of respective one of at least two power amplifier units having a different saturated output power level from each other and being used in operation by switching, connecting the output nodes of the first-stage matching networks together in parallel to make a junction, connecting a last-stage matching network between the junction and an output terminal, and forming the first-stage matching networks and the last-stage matching network so that impedance matching is established between the output impedance of the power amplifier unit in operation and the output characteristic impedance at the output terminal, for each of the at least two power amplifier units, when any one of the at least two power amplifier units is in operation and the other in stop of operation. By adopting such a means, the power amplifier units may satisfy the condition of impedance matching while supplying an output signal to the output terminal, without the need of inserting a radio frequency switch.  
         [0011]     In addition, the object of the present invention may also be achieved by connecting each of other last-stage matching networks to an input node of respective one of at least two power amplifier units having a different saturated output power level from each other and being used in operation by switching, in addition to the connection to the above described output side thereof, connecting the input nodes of the last-stage matching networks together in parallel to make another junction, connecting another first-stage matching network between the another junction and an input terminal, and forming the other last-stage matching networks and the another first-stage matching network so that impedance matching is established between the input impedance of the power amplifier unit in operation and the input characteristic impedance at the input terminal, for each of the at least two power amplifier units, when any one of the at least two power amplifier units is in operation and the other in stop of operation. By adopting such a means, the power amplifier units may satisfy the condition of impedance matching while supplying an output signal to the output terminal, as well as may satisfy the condition of impedance matching while accepting an input signal from the input terminal.  
         [0012]     These and other objects and many of the attendant advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic block diagram illustrating a first preferred embodiment of the radio frequency power amplifier in accordance with the present invention;  
         [0014]      FIG. 2  is a schematic graph illustrating the relationship between the input power and output power of and between input power and efficiency of the small output power amplifier unit and the high output power amplifier unit shown in  FIG. 1 ;  
         [0015]      FIG. 3  is a chart depicting the output impedance in operation and in stop of operation of the high output power amplifier unit shown in  FIG. 1 ;  
         [0016]      FIG. 4  is a chart depicting the output impedance in operation and in stop of operation of the low output power amplifier unit shown in  FIG. 1 ;  
         [0017]      FIG. 5  is a schematic circuit diagram illustrating a typical example of matching network shown in  FIG. 1 ;  
         [0018]      FIG. 6  is a chart describing the matching condition of the impedance matching network when the high output power amplifier unit is in operation and the low output power amplifier unit is in stop of operation;  
         [0019]      FIG. 7  is another chart describing the matching condition of the impedance matching network when the low output power amplifier unit is in operation and the low output power amplifier unit is in stop of operation;  
         [0020]      FIG. 8  is a schematic circuit diagram illustrating another typical example of matching network shown in  FIG. 1 ;  
         [0021]      FIG. 9  is a schematic block diagram illustrating a second preferred embodiment of the radio frequency power amplifier in accordance with the present invention;  
         [0022]      FIG. 10  is a schematic circuit diagram illustrating a typical example of matching network for input node shown in  FIG. 9 ;  
         [0023]      FIG. 11  is a schematic block diagram illustrating a third preferred embodiment of radio frequency power amplifier in accordance with the present invention;  
         [0024]      FIG. 12  is a schematic block diagram illustrating a fourth preferred embodiment of radio frequency power amplifier in accordance with the present invention;  
         [0025]      FIG. 13  is a schematic block diagram illustrating a fifth preferred embodiment of radio frequency power amplifier in accordance with the present invention;  
         [0026]      FIG. 14  is a schematic block diagram illustrating a sixth preferred embodiment of a portable cellular phone base station using a radio frequency power amplifier in accordance with the present invention;  
         [0027]      FIG. 15  is a schematic block diagram illustrating a seventh preferred embodiment of a portable cellular phone base station using a radio frequency power amplifier in accordance with the present invention; and  
         [0028]      FIG. 16  is a schematic block diagram illustrating an exemplary radio frequency power amplifier in accordance with the Prior Art.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     A detailed description of some preferred embodiments shown in the accompanying drawings embodying the radio frequency power amplifier of the present invention will now be given, in greater details, by referring to the accompanying drawings.  
       First Embodiment  
       [0030]     Now referring to  FIG. 1 , reference numeral A 11  is designated to a high output power amplifier unit, A 12  is to a small output power amplifier unit, M 12  and M 13  are first-stage matching networks connected to the output nodes of power amplifier unit A 11  and power amplifier unit A 12 , respectively, M 11  is to a last-stage matching network connected between the junction node of the output nodes of matching networks M 12  and M 13  and the output terminal OUT. The power amplifier unit A 11  and power amplifier unit A 12  are both formed of one single amplifier chip. An input signal will be fed to the power amplifier unit A 11  via input terminal IN 1 , and to the power amplifier unit A 12  via input terminal IN 2 . The power amplifier unit A 11  incorporates base voltage terminal Vb 11  and collector voltage terminal Vc 11  and similarly the power amplifier unit A 12  incorporates base voltage terminal Vb 12  and collector voltage terminal Vc 12 .  
         [0031]     In operation at high output power mode, a radio frequency signal supplied from the input terminal IN 1  will be fed to the power amplifier unit A 11  with a larger saturated output power to be amplified therein and then will be passed through the matching network M 12  and matching network M 11  to output to the output terminal OUT. In this condition the power amplifier unit A 12  will be put into stop of operation mode by lowering the base potential to the base voltage terminal Vb 12  or the collector potential to the collector voltage terminal Vc 12 . Both of the base potential and collector potential to the base voltage terminal Vb 12  and collector voltage terminal Vc 12 , respectively, may be pulled down at the same time, instead of either one.  
         [0032]     In operation at low output power mode, a radio frequency signal fed from the input terminal IN 2  will be supplied to the power amplifier unit A 12  with a smaller saturated output power to be amplified therein and then will be passed through the matching network M 13  and matching network M 11  to output to the output terminal OUT. In this mode the power amplifier unit A 11  will be put into stop of operation mode by decreasing the base potential to the base voltage terminal Vb 11  or the collector potential to the collector voltage terminal Vc 11 . Both of the base potential and collector potential to the base voltage terminal Vb 11  and collector voltage terminal Vc 11 , respectively, may be pulled down at the same time.  
         [0033]     The power amplifier unit A 11  and power amplifier unit A 12  may have characteristics as shown in  FIG. 2 . The output from the power amplifier unit A 11  is indicated as high output power point of high output power amplifier unit POL 1 , and the efficiency at that point is indicated as high output power efficiency of high output power amplifier unit EL 1 . Similarly, the output from the power amplifier unit A 12  is indicated as small output power point of low output power amplifier unit POS 1 , and the efficiency at that point is indicated as small output power efficiency of small output power amplifier unit ES 1 . A large output power efficiency EL 1  and small output power efficiency ES 1  may be achieved at an approximately same high level by switching the operational unit between the power amplifier unit A 11  and power amplifier unit A 12  for large or small output power level.  
         [0034]     In an assumption that lower output power is supplied from the power amplifier unit A 11  by decreasing the input power level thereto, the output power level and efficiency of the power amplifier unit A 11  will be as indicated by respectively the low output power point of the high output power amplifier unit POL 2  and low output power efficiency of the high output power amplifier unit EL 2 , resulting in that significant decrease of efficiency.  
         [0035]     It is to be noted here that although the power amplifier unit A 11  and power amplifier unit A 12  in this preferred embodiment are both made as one single chip of amplifier element, as have been described above, these units may equivalently be arranged from a plurality of power amplifier elements.  
         [0036]     The impedance matching in order to achieve the switching operation in accordance with the present invention will be now described in greater details. Referring to  FIG. 3 , there is shown a Smith chart with output power impedance IMPL 1  at the time when the high output power amplifier unit is in operation and output power impedance IMPL 2  at the time when the high output power amplifier unit is in stop of operation. In a similar manner there is shown another Smith chart in  FIG. 4  with output power impedance IMPS 1  at the time when the low output power amplifier unit is in operation and output power impedance IMPS 2  at the time when the low output power amplifier unit is in stop of operation.  
         [0037]     In accordance with the configuration using the first-stage matching network M 12 , first-stage matching network M 13 , and last-stage matching network M 11 , impedance will be matched to satisfy matching conditions of both power amplifier unit A 11  and power amplifier unit A 12 , namely, when the power amplifier unit A 11  is in operation while the power amplifier unit A 12  is in stop of operation, impedance matching will be performed so as to satisfy such a matching condition that the output power impedance IMPL 1  with the high output power amplifier unit in operation may become the characteristic impedance at the output terminal OUT; when the power amplifier unit A 11  is in stop of operation while the power amplifier unit A 12  is in operation; when the high output power amplifier unit is in stop of operation and the power amplifier unit A 12  is in operation then impedance matching will be performed so as to satisfy such a matching that the output power impedance IMPS 1  with low output power amplifier unit in operation may become the characteristic impedance at the output terminal OUT.  
         [0038]     The circuit configuration of matching networks M 12 , M 13 , M 11  in accordance with the preferred embodiment is schematically shown in  FIG. 5 . The first-stage matching network M 12  may be formed of a microstrip line MSL 1 . The first-stage matching network M 13  may be formed of a microstrip line MSL 2  and another microstrip line MSL 3  in series thereto and a capacitance C 1  connected to the junction of two microstrip lines. The matching network M 11  may be formed of a microstrip line MSL 4  and a capacitor C 2  connected to the output terminal OUT thereof.  
         [0039]     When the output impedance of the high output power amplifier unit referred to as ZL 1  is designated to the output power impedance IMPL 1  of the high output power amplifier unit in operation mode and that the output impedance of the low output power amplifier unit referred to as ZL 2  is designated to the output power impedance IMPL 2  of the low output power amplifier unit in stop of operation mode, as shown in  FIG. 6 , point Al on the Smith chart of the output power impedance IMPL 1 , which indicates the output power impedance ZL 1  of the high output power amplifier unit, will be relocated to point B 1  if the microstrip line MSL 1  forming the first-stage matching network M 12  is connected thereto, and then will be relocated to point C 1  if the first-stage matching network M 13  connecting the output power impedance ZL 2  of the low output power amplifier unit is inserted in parallel thereto, and furthermore will be relocated to point D 1  if the microstrip line MSL 4  is connected thereto, and finally will be again relocated to point E 1  if the capacitor C 2  is connected in parallel thereto. The point E 1  is the characteristic impedance found at the output terminal OUT, to which characteristic impedance point the output power impedance ZL 1  of the high output power amplifier unit is to be matched.  
         [0040]     In addition if the output power impedance ZL 1  of the high output power amplifier unit is designated to as the output power impedance IMPL 2  of the high output power amplifier unit in stop of operation mode, and the output power impedance ZL 2  of the low output power amplifier unit is designated to as the output power impedance IMPS 1  of the low output power amplifier unit in operating mode, then as shown in  FIG. 7 , the point A 2  of the output power impedance ZL 2  of the low output power amplifier unit, which is output power impedance IMPS 1 , on the Smith chart, will be first relocated to point B 2  by connecting microstrip line MSL 2  thereto, then relocated to point C 2  by connecting the capacitor C 1  in parallel thereto, furthermore relocated to point D 2  by connecting microstrip line MSL 3  thereto, also relocated to point E 2  by connecting first-stage matching network M 12  connecting output power impedance ZL 1  of the high output power amplifier unit in parallel thereto, and further relocated to F 2  by connecting the microstrip line MSL 4  in parallel thereto, and finally relocated to point G 2  by connecting the capacitor C 2  in parallel thereto. The point G 2  is the characteristic impedance found at the output terminal OUT, to which characteristic impedance the output power impedance ZL 2  of the low output power amplifier unit is to be matched.  
         [0041]     As can be appreciated from the foregoing description, In both cases when the power amplifier unit A 11  is in operation and the power amplifier unit A 12  is in stop of operation, and when the power amplifier unit A 11  is in stop of operation and the power amplifier unit A 12  is in operation, the condition of impedance matching will be satisfied, so that no radio frequency switch is required for switching between high and low output power, to be able to achieve a radio frequency power amplifier of a higher efficiency.  
         [0042]     Next, referring to  FIG. 8  there are shown matching networks M 12 , M 13 , M 11 , which are designed with microstrip line MSL 1 , MSL 2 , MSL 3 , and MSL 4  being replaced with inductances L 1 , L 2 , L 3 , and L 4  respectively. The matching networks M 12 , M 13 , M 11  shown in  FIG. 8  are capable of operating in a manner exactly similar to those matching networks M 12 , M 13 , M 11  shown in  FIG. 5 .  
         [0043]     In the above description, a radio frequency power amplifier in accordance with the present invention have been described which may comprise two power amplifier units in correspondence to two output power levels, specifically high and low output power levels. However, it is quite possible that it may incorporate three power amplifier units, one power amplifier unit for each of high, medium, low output power levels. In such case each output of three power amplifier units may be connected to a first-stage matching network, output nodes of all three first-stage matching networks may be connected together, and a last-stage matching network may be inserted between the junction of three first-stage matching networks and the output terminal. Only one of three power amplifier units will be in operation in accordance with the output, and other two will be in stop of operation.  
         [0044]     Three first-stage matching networks and one last-stage matching network as have been described above will be formed so that, when either one of three power amplifier units in operation while two others are in stop of operation, the output power impedance of the power amplifier unit in operation may match to the characteristic impedance. Thus, any of three power amplifier units may be impedance matched during operation.  
       Second Embodiment  
       [0045]     A preferred embodiment of radio frequency power amplifier having impedance matching applied to the input in accordance with the present invention is shown in  FIG. 9 . When a high output power amplifier unit A 91  be in operation with a low output power amplifier unit A 92  being in stop of operation mode, the radio frequency signal fed from input terminal IN will be passed through a first-stage matching network M 91  and a last-stage matching network M 92 , then fed to the power amplifier unit A 91  to be amplified therein. Thus an amplified signal will be passed through a first-stage matching network M 95  and last-stage matching network M 94  to the output terminal OUT.  
         [0046]     In case when the high output power amplifier unit A 91  is in sto of operation while the low output power amplifier unit A 92  in operation, the radio frequency signal supplied from the input terminal IN will be passed through a first-stage matching network M 91  and a last-stage matching network M 93  to the low output power amplifier unit A 92  to be amplified therein. Thereafter the signal will be passed through a first-stage matching network M 96  and a last-stage matching network M 94  to output to the output terminal OUT.  
         [0047]     In this preferred embodiment, In both of two states that the high output power amplifier unit A 91  is in operation and the low output power amplifier unit A 92  is in stop of operation, and that on contrary the high output power amplifier unit A 91  is in stop of operation and the low output power amplifier unit A 92  is in operation, the matching networks M 91 , M 92 , M 93  will be fromed so as to satisfy the impedance matching condition of the input impedance of the high output power amplifier unit A 91  in operation and input impedance of the low output power amplifier unit A 92  in operation with the characteristic impedance at the input terminal IN, in a manner similar to the preceding first preferred embodiment of the present invention. For the matching networks M 94 , M 95 , M 96  the same circuit will be used as the networks M 11 , M 12 , M 13  of the preceding first preferred embodiment.  
         [0048]     Now referring to  FIG. 10  there is shown a typical example of networks M 91 , M 92 , M 93 . The matching network M 91  may be comprised of a capacitor C 5  connected to the input node and a microstrip line MSL 5 ; the matching network M 92  may be comprised of an inductor L 5 , and the matching network M 93  may be comprised of an inductor L 6 .  
         [0049]     As can be appreciated from the foregoing description, a radio frequency power amplifier of efficiency improved may be achieved without the need of a radio frequency switch for switching between high output power and low output power.  
         [0050]     Also in the present embodiment as similar to the preceding first preferred embodiment, it may be equivalently conceivable that the output levels may be divided into three levels of high, middle, and low by having a power amplifier unit for each of three levels. In such a case to each of input nodes of three power amplifier units will be connected a last-stage matching network, input nodes of three last-stage matching networks will be connected together, and a first-stage matching network will be connected to the junction of three input nodes of last-stage matching network and the input terminal. Furthermore, for each of output node of three power amplifier units a first-stage matching network will be connected, the output nodes of three first-stage matching networks will be connected together, and a last-stage matching network will be connected between the junction of three input nodes of first-stage matching networks and the output terminal.  
         [0051]     In addition, in accordance with the present embodiment of the present invention, it may also be devised in such a way that the matching networks are used solely in the input nodes, while on the other hand to the output nodes a radio frequency switch for output switching may be used. The switching of power amplifier units in accordance with their high or low output may be performed without using a radio frequency switch in the input nodes.  
       Third Embodiment  
       [0052]     Another preferred embodiment of the present invention is shown in  FIG. 11 , in which a low output power amplifier unit is used in front of the radio frequency power amplifier stage shown in  FIG. 9  to make a dual stage configuration. In FIG.  11 , reference numeral A 101  designates to an additional low output power amplifier unit, M 101  to an input stage matching network placed in front of input node of the low output power amplifier unit A 101 .  
         [0053]     When the high output power amplifier unit A 102  is in operation and the low output power amplifier unit A 103  is in stop of operation, the radio frequency signal applied from the input terminal IN will be fed through the input stage matching network M 101  to the low output power amplifier unit A 101  to be amplified therein. Thereafter the amplified signal will be passed through a first-stage matching network M 102  and a last-stage matching network M 103  and amplified then by the high output power amplifier unit A 102 . Thereafter the amplified signal will be passed through a first-stage matching network M 106  and a last-stage matching network M 105  to output to the output terminal OUT.  
         [0054]     When the high output power amplifier unit A 102  is suspended and the low output power amplifier unit A 103  is in operation, then the radio frequency signal supplied from the input terminal IN will be passed through the input stage matching network M 101  to the low output power amplifier unit A 101  so as to be amplified therein. Then the signal will pass the first-stage matching network M 102  and the last-stage matching network M 104  to the low output power amplifier unit A 103  so as to be amplified therein. Thereafter, the signal will be passed through the first-stage matching network M 107  and the last-stage matching network M 105  to output to the output terminal OUT.  
         [0055]     In the present embodiment, when the high output power amplifier unit A 102  is in operation and the low output power amplifier unit A 103  is in stop of operation, and when on contrary the high output power amplifier unit A 102  is in stop of operation and the low output power amplifier unit A 103  is in operation, the matching networks M 102 , M 103 , M 104  will be configured so as to satisfy the condition of impedance matching between the input impedance of the high output power amplifier unit A 102  and the input impedance of the low output power amplifier unit A 103  and the output impedance of the low output power amplifier unit A 101 , in a manner just similar to that described in the preceding second embodiment. With the above configuration, a radio frequency power amplifier with the efficiency improved may be achieved, without the need of a radio frequency switch for switching between the high output power and low output power. In addition, the present embodiment of the present invention has a higher amplitude because of a dual stage configuration of the power amplifier units.  
       Forth Embodiment  
       [0056]     Another preferred embodiment of the present invention is shown in  FIG. 12 , in which the first-stage matching network M 12 , first-stage matching network M 13 , and last-stage matching network M 11  shown in  FIG. 1  is formed by a unified microstrip line. The microstrip line MSL 1  in the first-.stage matching network M 12  may be replaced with a microstrip line MSL 111 , the microstrip line MSL 2  and microstrip line MSL 3  in the first-stage matching network M 13  with a microstrip line MSL 112 , and the microstrip line MSL 4  in the last-stage matching network M 11  with a microstrip line MSL 113 .  
         [0057]     A capacitor C 111  corresponding to the capacitor Cl in the first-stage matching network M 13  is connected to the middleway of the microstrip line MSL 112 , with a capacitor C 112  corresponding to the capacitor C 2  of the last-stage matching network M 11  being connected to the output node OUT of the microstrip line MSL 113 .  
         [0058]     In the present embodiment, the transmission line length of the microstrip line MSL 111  for use in the matching network for the high output power amplifier unit A 11  is formed to be shorter than the transmission line length of the microstrip line MSL 112  for use in the matching network for the low output power amplifier unit A 112 , so that the transmission line loss of the microstrip line MSL 111  may be suppressed to a lower level, allowing decreasing the operation loss of the high output power amplifier unit A 111  as well as improving the efficiency in the high output power amplifier unit A 111 .  
       Fifth Embodiment  
       [0059]     Still another preferred embodiment of radio frequency. power amplifier in accordance with the present invention is shown in  FIG. 13 , in which signals in frequency bands A and B mutually different each from other are further divided into high level and low level and either one of the signals is outputted. The radio frequency power amplifier may incorporate the power amplifier block  13 A for the frequency band A and a power amplifier block  13 B for the frequency band B.  
         [0060]     The power amplifier block  13 A may include a high output power amplifier unit A 131  and a low output power amplifier unit A 132 , which are each connected to a first-stage matching network M 137  and M 138  in the output node respectively, also connected to a last-stage matching network M 132  and M 133  in the input node, respectively.  
         [0061]     The power amplifier block  13 B may include a high output power amplifier unit A 133  and a low output power amplifier unit A 134 , which are each connected to a first-stage matching network M 139  and M 140  in the output node respectively, and to a last-stage matching network M 134  and M 135  in the input node, respectively.  
         [0062]     The outputs of the first-stage matching networks M 137  to M 140  are connected together to a junction. A last-stage matching network M 136  is connected between the junction and the output terminal OUT. The inputs of the last-stage matching networks M 132  to M 135  are also connected together to a junction. A first-stage matching network M 131  is connected between the junction and the input terminal IN.  
         [0063]     Controlling base voltage may allow operating any one among the power amplifier units A 131  to A 134  with other three in stop of operation. The matching networks M 136  to M 140  are formed so as to match the output impedance from the power amplifier unit in operation with the characteristic impedance at the output terminal OUT, for every power amplifier units. The matching networks M 131  to M 135  are also configured so as to match the input impedance to the power amplifier unit in operation with the characteristic impedance at the input terminal IN.  
         [0064]     As can be appreciated from the foregoing description, when outputting one of signals of different frequency bands, one power amplifier unit is allowed to use by switching in accordance with the high or low output level, without the need of using a radio frequency switch.  
         [0065]     Also it should be noted here that in the present embodiment, it is equivalently conceivable that the amplifier may be designed such that the signals may be switched by a radio frequency switch to feed to any power amplifier unit without using the input matching networks M 131  to M 135 . The power amplifier unit can be switched in response to the level of output without the need of radio frequency switches in the output node.  
       Sixth Embodiment  
       [0066]     A preferred embodiment of the radio frequency power amplifier in accordance with the present invention for use in a base station of mobile communication system is shown in  FIG. 14 . The base station is a component of a mobile communication system, together with portable cellular phone terminals (mobile terminals). A transmission signal St 1  inputs from the network via an inter-base-station interface INF will be first signal processed in a baseband circuit BB 1 , then modulated thereby to a radio frequency signal. The radio frequency signal will be then amplified in a radio frequency power amplifier HAMP 1  to emit from an antenna ANT 1  to the space. The radio frequency power amplifier unit HAMP 1  may use the present invention to have a significantly improved efficiency, allowing facilitating installation of the radio frequency power amplifier HAMP 1  in the vicinity of the antenna ANT 1 .  
         [0067]     The radio frequency signal received by the antenna ANT 1  will be fed to a low noise booster LNAMP 1  and amplified thereby to be demodulated and signal processed by the baseband circuit BB 1  to the receiving signal Sr 1 .  
       Seventh Embodiment  
       [0068]     Yet another preferred embodiment of the radio frequency power amplifier in accordance with the present invention for use in a portable cellular phone terminal (mobile terminal) of a mobile communication system is shown in  FIG. 15 . A transmission signal St 2  to be carried out will be signal processed and then modulated by a baseband circuit BB 2  to a radio frequency signal. The radio frequency signal will be amplified by a radio frequency power amplifier HAMP 2  to emit from an antenna ANT 2  to the space. The radio frequency power amplifier HAMP 2  uses the present invention to have a significantly improved efficiency, allowing achieving a cellular phone of much smaller in size with much lower power consumption.  
         [0069]     The radio frequency receiving signal from the antenna ANT 2  will be amplified by a low noise booster LNAMP 2  and then demodulated and signal processed by the baseband circuit BB 2  to a receiving signal Sr 2 .  
         [0070]     In accordance with the present invention, when providing at least two power amplifier units each having different saturated output level and operating only one of units with others in stop of operation mode, the power amplifier unit in operation may achieve matching networks to satisfy the matching condition, allowing switching among power amplifier units without the need of a radio frequency switch, as well as giving lower output loss at the time of power amplification. The present invention may therefore provide a radio frequency power amplifier effectively suited for the downsizing of cellular phone terminals as well as base station installations.  
         [0071]     It is further understood by those skilled in the art that the foregoing description is preferred embodiments of the disclosed device and that various changes and modifications may be made in the invention without departing from the spirit and scope thereof.