Patent Publication Number: US-2023155558-A1

Title: Power amplifier circuit

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2021-186221 filed on Nov. 16, 2021. The content of this application is incorporated herein by reference in its entirety. 
     BACKGROUND ART 
     The present disclosure relates to power amplifier circuits. 
     There is a power amplifier circuit in which amplifying operations of four transistors are controlled by three control currents that are respectively supplied to three control terminals (for example, see Japanese Unexamined Patent Application Publication No. 2021-13055 (Patent Document 1)). 
     BRIEF SUMMARY 
     In a power amplifier circuit described in Patent Document 1 (see  FIG.  9   ), a control current IB 2  is supplied to a base of a transistor T 7   b  of a bias circuit  111 A through a resistive element R 5   b.  When the control current IB 2  is at a high level, the transistor T 7   b  is turned ON, and a bias current Ibias 2  is supplied to a base of a transistor T 2  from an emitter of the transistor T 7   b  through a resistive element R 2 . This turns the transistor T 2  ON. 
     A transistor T 8  of a bias circuit  112 A supplies a bias current Ibias 4  to a transistor T 4  of an amplifier Q 4 . A switch circuit  131 A is provided between a ground and a path B 1  through which the bias current Ibias 4  is supplied from the bias circuit  112 A to the amplifier Q 4 . 
     The switch circuit  131 A operates based on a base potential of the transistor T 7   b.  Specifically, when the control current IB 2  is at the high level, the base potential of the transistor T 7   b  rises, and the switch circuit  131 A is turned ON. In this case, as described above, the transistor T 2  is also turned ON. 
     When the switch circuit  131 A is ON, the switch circuit  131 A causes part of the bias current Ibias 4 , which is to be supplied to the amplifier Q 4  from the bias circuit  112 A, to flow into the ground. Because of this, even when the transistor T 8  is ON, if the transistor T 7   b  is ON, that is to say, if the transistor T 2  is ON, the state of the transistor T 4  of the amplifier Q 4  becomes close to OFF. 
     Incidentally, there are cases where the gain of the transistor T 2  changes depending on the input power to the transistor T 2 . In such cases, in the power amplifier circuit described in Patent Document 1, the overall gain of the circuit changes depending on the input power. 
     The switch circuit  131 A operates based on the base potential of the transistor T 7   b,  which is based on nonlinearity of the transistor T 2  and nonlinearity of the transistor T 7   b.  Therefore, even if the switch circuit  131 A draws out the bias current Ibias 4  and as a result the gain of the transistor T 4  changes, the gain change of the transistor T 2  cannot be fully compensated. That is to say, it is difficult to suppress the change in the overall gain of the power amplifier circuit described in Patent Document 1. 
     The present disclosure provides a power amplifier circuit capable of suppressing the change in gain. 
     A power amplifier circuit according to one aspect of the present disclosure includes: a plurality of amplifying transistors including at least a first amplifying transistor and a second amplifying transistor, the plurality of amplifying transistors being electrically cascade-connected, each of the plurality of amplifying transistors amplifying a signal supplied to a base or gate thereof and outputting an amplified signal; a first resistive element having a first end part and a second end part connected to the base or gate of the first amplifying transistor; a second resistive element having a first end part and a second end part connected to the base or gate of the second amplifying transistor; a first bias supplying transistor having an emitter or source connected to the first end part of the first resistive element; a second bias supplying transistor having an emitter or source connected to the first end part of the second resistive element; and a bias current compensation transistor having a base or gate connected to the first end part of the first resistive element, a collector or drain connected to the first end part of the second resistive element, and an emitter or source connected to ground. 
     According to the present disclosure, it becomes possible to provide a power amplifier circuit capable of suppressing the change in the gain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a circuit diagram of a power amplifier circuit  101 ; 
         FIGS.  2 A- 2 E  are diagrams to illustrate an amplifying operation of the power amplifier circuit  101 ; 
         FIG.  3    is a diagram illustrating a first modified example of a low pass filter circuit  61 ; 
         FIG.  4    is a diagram illustrating a second modified example of the low pass filter circuit  61 ; 
         FIG.  5    is a circuit diagram of a power amplifier circuit  103 ; 
         FIG.  6    is a circuit diagram of a power amplifier circuit  102 ; 
         FIG.  7    is a circuit diagram of a power amplifier circuit  104 ; 
         FIG.  8    is a circuit diagram of a power amplifier circuit  105 ; and 
         FIG.  9    is a diagram illustrating a typical configuration of a power amplifier circuit. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Same reference characters are given to same constituent elements, and overlapping descriptions are omitted as much as possible. 
     First Embodiment 
     A power amplifier circuit according to the first embodiment is described.  FIG.  1    is a circuit diagram of a power amplifier circuit  101 . As illustrated in  FIG.  1   , the power amplifier circuit  101  according to the first embodiment includes a multistage amplifier  11  and a bias part  12 . The multistage amplifier  11  includes a final stage amplifier  201 , a first stage amplifier  202 , an output matching circuit  501 , an interstage matching circuit  502 , and an input matching circuit  503 . The bias part  12  includes a bias current control circuit  41 , a final stage bias circuit  311 , and a first stage bias circuit  312 . 
     Multistage Amplifier  11   
     The multistage amplifier  11  is a circuit that amplifies an input signal (radio frequency signal) RFin supplied to an input terminal  31  and outputs an output signal (amplified signal) RFout from an output terminal  32 . 
     The input matching circuit  503  of the multistage amplifier  11  is a circuit that provides impedance matching between the first stage amplifier  202  and a circuit in a stage preceding the multistage amplifier  11 , and allows the input signal RFin to pass. The first stage amplifier  202  amplifies the input signal RFin, which is supplied from the input terminal  31  through the input matching circuit  503 , and outputs an amplified signal RF 1  to the interstage matching circuit  502 . 
     The interstage matching circuit  502  is a circuit that provides impedance matching between the first stage amplifier  202  and the final stage amplifier  201  and allows the amplified signal RF 1  to pass. The final stage amplifier  201  amplifies the amplified signal RF 1 , which is supplied from the first stage amplifier  202  through the interstage matching circuit  502 , and outputs the output signal RFout to the output matching circuit  501 . 
     The output matching circuit  501  is a circuit that provides impedance matching between the final stage amplifier  201  and a circuit in a stage subsequent to the multistage amplifier  11  and allows the output signal RFout to pass. 
     In the following section, the first stage amplifier  202  is described in detail. The first stage amplifier  202  includes an amplifying transistor  202   a  (second amplifying transistor), a resistive element  202   b  (second resistive element), capacitors  202   c  and  202   e,  and an inductor  202   d.    
     The present embodiment is described assuming that the transistors such as the amplifying transistor  202   a  and the like are each formed of, for example, a bipolar transistor such as a heterojunction bipolar transistor (HBT) or the like. Alternatively, the transistors such as the amplifying transistor  202   a  and the like may each be formed of another transistor such as a field-effect transistor (MOSFET: Metal-oxide-semiconductor Field-Effect Transistor) or the like. In that case, the base, the collector, and the emitter may be replaced with the gate, the drain, and the source, respectively. 
     A power voltage Vcc 2  of the amplifying transistor  202   a  is supplied to a terminal  202   f.  The capacitor  202   c  has a first end part connected to the input terminal  31  through the input matching circuit  503  and a second end part. 
     The amplifying transistor  202   a  has a base connected to the second end part of the capacitor  202   c,  a collector connected to the terminal  202   f  through the inductor  202   d , and an emitter connected to the ground. 
     The capacitor  202   e  has a first end part connected to the terminal  202   f  and a second end part connected to the ground. The resistive element  202   b  has a first end part connected to the first stage bias circuit  312  and a second end part connected to the base of the amplifying transistor  202   a.    
     In the following section, the final stage amplifier  201  is described in detail. The final stage amplifier  201  includes an amplifying transistor  201   a  (first amplifying transistor and final stage amplifying transistor), a resistive element  201   b  (first resistive element), capacitors  201   c  and  201   e,  and an inductor  201   d.    
     A power voltage Vcc 1  of the amplifying transistor  201   a  is supplied to a terminal  201   f.  The capacitor  201   c  has a first end part connected to the collector of the amplifying transistor  202   a  through the interstage matching circuit  502  and a second end part. 
     The amplifying transistor  201   a  has a base connected to the second end part of the capacitor  201   c,  a collector connected to the terminal  201   f  through the inductor  201   d  and further connected to the output terminal  32  through the output matching circuit  501 , and an emitter connected to the ground. 
     The capacitor  201   e  has a first end part connected to the terminal  201   f  and a second end part connected to the ground. The resistive element  201   b  has a first end part connected to the final stage bias circuit  311  and a second end part connected to the base of the amplifying transistor  201   a.    
     Bias Part  12   
     The bias part  12  supplies a bias to each of the final stage amplifier  201  and the first stage amplifier  202  of the multistage amplifier  11  in such a manner as to suppress the change in the gain of the power amplifier circuit  101 . 
     The final stage bias circuit  311  of the bias part  12  includes a bias supplying transistor  301   a  (first bias supplying transistor) and a voltage applying circuit  411 . The voltage applying circuit  411  includes transistors  401   a  (first transistor) and  401   b  (second transistor) and a capacitor  401   c.    
     The final stage bias circuit  311  supplies a bias current Ibb 1  to the base of the amplifying transistor  201   a  using the bias supplying transistor  301   a  that is connected to the base of the amplifying transistor  201   a  in an emitter-follower configuration. 
     Specifically, the bias supplying transistor  301   a  has a collector connected to a terminal Tb that supplies a battery voltage Vbat, a base, and an emitter connected to the first end part of the resistive element  201   b.    
     The voltage applying circuit  411  supplies a bias at a predetermined level of voltage (first voltage) to the base of the bias supplying transistor  301   a.  Specifically, for example, a constant current is supplied to a control signal terminal  601  (first current source). The control signal terminal  601  is connected to the base of the bias supplying transistor  301   a.    
     The transistor  401   b  has a collector connected to the control signal terminal  601  and the base of the bias supplying transistor  301   a,  a base connected to this collector, and an emitter. Hereinafter, the connection between the collector of a transistor and the base of the same transistor is sometimes referred to as “diode connection”. 
     The transistor  401   a  is diode-connected. The transistor  401   a  has a collector connected to the emitter of the transistor  401   b  and an emitter connected to the ground. The capacitor  401   c  has a first end part connected to the collector of the transistor  401   b  and a second end part connected to the ground. The capacitor  401   c  stabilizes the voltage of the collector of the transistor  401   b.    
     Each of the transistors  401   a  and  401   b  functions as a diode. A voltage drop corresponding to two diodes occurs at the path between the collector and the emitter of the transistor  401   b  and the path between the collector and the emitter of the transistor  401   a.  That is to say, when the ground is used as the reference, the voltage of the collector of the transistor  401   b  is at a level of voltage corresponding to the voltage drop of two diodes. This voltage is applied to the base of the bias supplying transistor  301   a.    
     The first stage bias circuit  312  includes a bias supplying transistor  302   a  (second bias supplying transistor) and a voltage applying circuit  412 . The voltage applying circuit  412  includes transistors  402   a  (third transistor) and  402   b  (fourth transistor) and a capacitor  402   c.    
     The first stage bias circuit  312  supplies the bias current Ibias 2  to the base of the amplifying transistor  202   a  using the bias supplying transistor  302   a  that is connected to the base of the amplifying transistor  202   a  in an emitter-follower configuration. 
     Specifically, the bias supplying transistor  302   a  has a collector connected to the terminal Tb, a base, and an emitter connected to the first end part of the resistive element  202   b.    
     The voltage applying circuit  412  supplies a bias at a predetermined level of voltage (second voltage) to the base of the bias supplying transistor  302   a.  Specifically, for example, a constant current is supplied to a control signal terminal  602  (second current source). The control signal terminal  602  is connected to the base of the bias supplying transistor  302   a.    
     The transistor  402   b  is diode-connected. The transistor  402   b  has a collector connected to the base of the bias supplying transistor  302   a  and an emitter. 
     The transistor  402   a  is diode-connected and has a collector connected to the emitter of the transistor  402   b  and an emitter connected to the ground. The capacitor  402   c  has a first end part connected to the collector of the transistor  402   b  and a second end part connected to the ground. The capacitor  402   c  stabilizes the voltage of the collector of the transistor  402   b.    
     When the ground is used as the reference, the voltage of the collector of the transistor  402   b  is at a level of voltage corresponding to the voltage drop of the transistors  402   a  and  402   b,  each of which serves as a diode. This voltage is applied to the base of the bias supplying transistor  302   a.    
     A bias current control circuit  41  includes a bias current compensation transistor  51 , and a low pass filter circuit  61 . The low pass filter circuit  61  includes a capacitor  61   a.    
     In response to a rise of the emitter voltage of the bias supplying transistor  301   a,  the bias current control circuit  41  allows part of an emitter current Ieef 2  of the bias supplying circuit  302   a  to flow into the ground. 
     The capacitor  61   a  of the low pass filter circuit  61  has a first end part connected to the emitter of the bias supplying transistor  301   a  and a second end part connected to the ground. 
     The bias current compensation transistor  51  has a collector connected to the emitter of the bias supplying circuit  302   a,  a base connected to the emitter of the bias supplying transistor  301   a,  and an emitter connected to the ground. 
     Actions and Effects 
       FIGS.  2 A- 2 E  are diagrams to illustrate the amplifying operation of the power amplifier circuit  101 . The horizontal axis of each of the graphs in  FIGS.  2 A to  2 E  represent the output power Pout of the power amplifier circuit  101 . The vertical axis of the graph in  FIG.  2 A  represents the gain G 1  of the final stage amplifier  201 . The vertical axis of the graph in  FIG.  2 B  represents the bias current Ibb 1 , the bias voltage Vbb 1 , the current Ibsk, or the current Icsk. The vertical axis of the graph in  FIG.  2 C  represents the bias current Ibb 2  or bias voltage Vbb 2 . The vertical axis of the graph in  FIG.  2 D  represents the gain G 2  of the first stage amplifier  202 . The vertical axis of the graph in  FIG.  2 E  represents the overall gain Gt of the power amplifier circuit  101 . 
     The bias current Ibb 1  is a current to be supplied from the final stage bias circuit  311  to the final stage amplifier  201 . The bias voltage Vbb 1  is the voltage of the emitter of the bias supplying transistor  301   a.  The bias current Ibb 2  is a current to be supplied from the first stage bias circuit  312  to the first stage amplifier  202 . The bias voltage Vbb 2  is the voltage of the emitter of the bias supplying transistor  302   a.  The current Ibsk is a current obtained by subtracting the bias current Ibb 1  from an emitter current Ieef 1  of the bias supplying transistor  301   a.  The current Icsk is a current obtained by subtracting the bias current Ibb 2  from the emitter current Ieef 2  of the bias supplying transistor  302   a.    
     For example, in the case where the bias current Ibb 1  for the final stage amplifier  201  is reduced, as indicated by a curve Ca 1 , the gain G 1  (graph in  FIG.  2 A ) increases with an increase in the output power Pout when the output power Pout is less than P 1  and decreases with an increase in the output power Pout when the output power Pout is greater than or equal to P 1 . 
     As described above, by reducing the bias current Ibb 1 , it becomes possible to reduce the power consumption of the final stage amplifier  201  when the output power Pout is small. 
     As illustrated in the graph in  FIG.  2 B , when the gain G 1  changes like the curve Ca 1 , the bias current Ibb 1  changes as indicated by a curve Ca 2  that has a shape similar to that of the curve Ca 1 . The voltage drop of the resistive element  201   b  increases or decreases in response to an increase or decrease in the bias current Ibb 1 , and thus the bias voltage Vbb 1  changes like the curve Ca 2  as is the case with the bias current Ibb 1 . 
     The current Ibsk is the base current of the bias current compensation transistor  51  and thus increases or decreases in response to an increase or decrease in the bias voltage Vbb 1 . The current Icsk is the collector current of the bias current compensation transistor  51  and thus increases or decreases in response to an increase or decrease in the current Ibsk. That is to say, as is the case with the bias current Ibb 1 , the currents Ibsk and Icsk change like a curve Ca 2 . 
     When the current Icsk increases, the bias current Ibb 2  decreases according to Kirchhoff&#39;s current law (see  FIG.  1   ). Further, when the bias current Ibb 2  decreases, the voltage drop of the resistive element  202   b  becomes smaller, and thus, the bias voltage Vbb 2  also decreases. Accordingly, as indicated by the curve Ca 3 , the bias current Ibb 2  and the bias voltage Vbb 2  decrease with an increase in the output power Pout (graph in  FIG.  2 C ). 
     Further, because of the decrease in the bias current Ibb 2  and the bias voltage Vbb 2 , the bias supplied to the base of the amplifying transistor  202   a  decreases. Thus, as indicated by a curve Ca 4 , the gain G 2  decreases with an increase in the output power Pout (graph in  FIG.  2 D ). 
     On the other hand, as illustrated in the graph in  FIG.  2 A , for example, the gain G 1  decreases with an increase in the output power Pout in some cases as indicated by a curve Cb 1 . 
     In this case, the bias current Ibb 1 , the bias voltage Vbb 1 , the current Ibsk, and the current Icsk change like a curve Cb 2  that has a shape similar to that of the curve Cb 1  (graph in  FIG.  2 B ). 
     Further, the bias current Ibb 2  and the bias voltage Vbb 2  change like a curve Cb 3  that has a shape similar to that of the curve Ca 1  (graph in  FIG.  2 C ). The gain G 2  changes like a curve Cb 4  that has a shape similar to that of the curve Ca 1  (graph in  FIG.  2 D ). 
     That is to say, the bias current compensation transistor  51  enables to perform the control in such a way that the change in the gain G 2  relative to the output power Pout and the change in the gain G 1  relative to the output power Pout are opposite to each other. This enables to suppress the change in the gain Gt relative to the output power Pout. 
     Further, when the amplifying transistor  201   a  amplifies a radio frequency signal, the bias voltage Vbb 1  vibrates at a high frequency although the resistive element  201   b  can isolate in some degree. 
     When the high frequency vibration of the bias voltage Vbb 1  is transmitted to the first stage amplifier  202  through the bias current control circuit  41 , the power amplifier circuit  101  may oscillate, or the noise level of the output signal RFout may increase. 
     On the other hand, with the configuration in which the low pass filter circuit  61  is provided between the base of the bias current compensation transistor  51  and the resistive element  201   b,  it becomes possible to suppress the transmission of the high frequency vibration of the bias voltage Vbb 1  to the first stage amplifier  202 , and thus it becomes possible to facilitate the suppression of oscillation of the power amplifier circuit  101  and the reduction of noise level of the output signal RFout. 
     Note that the configuration is not limited to the one in which the base and collector of the bias current compensation transistor  51  are connected to the emitter of the bias supplying transistor  301   a  and the emitter of the bias supplying transistor  302   a,  respectively, and the configuration may alternatively be such that the base and collector of the bias current compensation transistor  51  are connected to the emitter of the bias supplying transistor  302   a  and the emitter of the bias supplying transistor  301   a , respectively. 
     First Modified Example of Low Pass Filter Circuit  61   
       FIG.  3    is a diagram illustrating a low pass filter circuit  62 , which is a first modified example of the low pass filter circuit  61 , and a peripheral circuit of the low pass filter circuit  62 . As illustrated in  FIG.  3   , the low pass fit circuit  62  is different from the low pass filter circuit  61  illustrated in  FIG.  1    in that a resistive element  61   b  is further provided. 
     The resistive element  61   b  of the low pass filter circuit  62  has a first end part connected to the emitter of the bias supplying transistor  301   a  and a second end part connected to the base of the bias current compensation transistor  51 . The capacitor  61   a  has a first end part connected to the base of the bias current compensation transistor  51  and a second end part connected to the ground. 
     Second Modified Example of Low Pass Filter Circuit  61   
       FIG.  4    is a diagram illustrating a low pass filter circuit  63 , which is a second modified example of the low pass filter circuit  61 , and a peripheral circuit of the low pass filter circuit  63 . As illustrated in  FIG.  4   , the low pass fit circuit  63  is different from the low pass filter circuit  61  illustrated in  FIG.  1    in that an inductor  61   c  is further provided. 
     The inductor  61   c  of the low pass filter circuit  63  has a first end part connected to the emitter of the bias supplying transistor  301   a  and a second end part connected to the base of the bias current compensation transistor  51 . The capacitor  61   a  has a first end part connected to the base of the bias current compensation transistor  51  and a second end part connected to the ground. 
     Second Embodiment 
     A power amplifier circuit according to the second embodiment is described. In the description of the second embodiment and subsequent embodiments, descriptions regarding matters common to the first embodiment will be omitted, and only points different from the first embodiment will be described. Particularly, similar actions and effects of similar constituent elements will not be repeated in each embodiment. 
       FIG.  5    is a circuit diagram of a power amplifier circuit  103 . As illustrated in  FIG.  5   , the power amplifier circuit  103  according to the second embodiment is different from the power amplifier circuit  101  according to the first embodiment in that the final stage bias circuit  311  and the first stage bias circuit  312  are each formed as a negative feedback bias circuit. 
     Compared with the bias part  12  illustrated in  FIG.  1   , the bias part  12  of the power amplifier circuit  103  includes a voltage applying circuits  431  (first voltage applying circuit) and  432  (second voltage applying circuit) instead of the voltage applying circuits  411  and  412 , respectively. 
     Compared with the voltage applying circuit  411  illustrated in  FIG.  1   , instead of the transistor  401   b,  the voltage applying circuit  431  includes a resistive element  401   e  (first negative feedback resistive element) and a capacitor  401   f  (first capacitor). The resistive element  401   e  has a first end part connected to the emitter of the bias supplying transistor  301   a  and a second end part. 
     The transistor  401   a  has a collector connected to the control signal terminal  601  and the base of the bias supplying transistor  301   a,  a base connected to the second end part of the resistive element  401   e,  and an emitter connected to the ground. The capacitor  401   f  has a first end part connected to the collector of the transistor  401   a  and a second end part connected to the base of the transistor  401   a.    
     Compared with the voltage applying circuit  412  illustrated in  FIG.  1   , instead of the transistor  402   b,  the voltage applying circuit  432  includes a resistive element  402   e  (second negative feedback resistive element) and a capacitor  402   f  (second capacitor). The resistive element  402   e  has a first end part connected to the emitter of the bias supplying transistor  302   a  and a second end part. 
     The transistor  402   a  has a collector connected to the control signal terminal  602  and the base of the bias supplying transistor  302   a,  a base connected to the second end part of the resistive element  402   e,  and an emitter connected to the ground. The capacitor  402   f  has a first end part connected to the collector of the transistor  402   a  and a second end part connected to the base of the transistor  402   a.    
     The voltage applying circuit  431  has the configuration similar to that of the voltage applying circuit  432 . Thus, in the following section, the operation of the voltage applying circuit  431  is described as a representative case, and the description of the operation of the voltage applying circuit  432  is omitted. 
     In the final stage bias circuit  311 , the bias supplying transistor  301   a,  the resistive element  401   e,  and the transistor  401   a  form a negative feedback path. With this negative feedback path, the rise and fall of the emitter potential of the bias supplying transistor  301   a , that is to say, the rise and fall of the bias voltage Vbb 1  are both reduced. 
     Further, in the final stage bias circuit  311 , when a constant current Ictr 1  is supplied from the control signal terminal  601 , the base potential of the bias supplying transistor  301   a  rises, and the bias supplying transistor  301   a  is turned to ON state. When the bias supplying transistor  301   a  is turned to ON state, the transistor  401   a  is turned to ON state. 
     In the power amplifier circuit  103 , when the ground is used as the reference, the potential of the collector of the transistor  401   a  is substantially equal to the potential obtained by adding the base-emitter voltage (Vbe) of the transistor  401   a  and Vbe of the bias supplying transistor  301   a.    
     On the other hand, in the power amplifier circuit  102  (see  FIG.  6   ) which will be described below, when the ground is used as the reference, the potential of the collector of the transistor  401   a  is substantially equal to Vbe of the transistor  401   a.    
     That is to say, in the power amplifier circuit  103 , it becomes possible to increase the collector potential of the transistor  401   a  from Vbe to 2xVbe. This enables to increase the gain of the transistor  401   a,  and thus, it becomes possible to further reduce the rise and fall of the bias voltage Vbb 1  caused by the negative feedback. 
     Further, in the power amplifier circuit  103 , the transistors  401   b  and  402   b  of the power amplifier circuit  101  (see  FIG.  1   ) are not provided, and thus it becomes possible to reduce the circuit size. This enables to reduce the size of the power amplifier circuit  103 , and further, this enables to reduce the cost of the power amplifier circuit  103 . 
     Third Embodiment 
     A power amplifier circuit  102  according to the third embodiment is described.  FIG.  6    is a circuit diagram of a power amplifier circuit  102 . As illustrated in  FIG.  6   , the power amplifier circuit  102  according to the third embodiment is different from the power amplifier circuit  101  according to the first embodiment in that the final stage bias circuit  311  and the first stage bias circuit  312  are each a negative feedback bias circuit. 
     Compared with the bias part  12  illustrated in  FIG.  1   , the bias part  12  of the power amplifier circuit  102  includes a voltage applying circuits  421  (first voltage applying circuit) and  422  (second voltage applying circuit) instead of the voltage applying circuits  411  and  412 , respectively. 
     Compared with the voltage applying circuit  411  illustrated in  FIG.  1   , the voltage applying circuit  421  further includes the resistive element  401   e  (first negative feedback resistive element) and the capacitor  401   f  (first capacitor). The resistive element  401   e  has a first end part connected to the emitter of the bias supplying transistor  301   a  and a second end part. 
     The transistor  401   a  has a collector connected to the emitter of the transistor  401   b,  a base connected to the second end part of the resistive element  401   e,  and an emitter connected to the ground. The capacitor  401   f  has a first end part connected to the collector of the transistor  401   a  and a second end part connected to the base of the transistor  401   a.    
     Compared with the voltage applying circuit  412  illustrated in  FIG.  1   , the voltage applying circuit  422  further includes the resistive element  402   e  (second negative feedback resistive element) and the capacitor  402   f  (second capacitor). The resistive element  402   e  has a first end part connected to the emitter of the bias supplying transistor  302   a  and a second end part. 
     The transistor  402   a  has a collector connected to the emitter of the transistor  402   b,  a base connected to the second end part of the resistive element  402   e,  and an emitter connected to the ground. The capacitor  402   f  has a first end part connected to the collector of the transistor  402   a  and a second end part connected to the base of the transistor  402   a.    
     The voltage applying circuit  421  has the configuration similar to that of the voltage applying circuit  422 . Thus, in the following section, the operation of the voltage applying circuit  421  is described as a representative case, and the description of the operation of the voltage applying circuit  422  is omitted. 
     In the final stage bias circuit  311 , the bias supplying transistor  301   a,  the resistive element  401   e,  and the transistors  401   a  and  401   b  form a negative feedback path. With this negative feedback path, the rise and fall of the emitter potential of the bias supplying transistor  301   a , that is to say, the rise and fall of the bias voltage Vbb 1  are both reduced. 
     Specifically, when the bias voltage Vbb 1  rises, the base potential of the transistor  401   a  rises, and the base current of the transistor  401   a  increases. This increases the collector current of the transistor  401   a  and a collector current Ic 1  of the transistor  401   b.    
     Further, a base current Ibef 1  of the bias supplying transistor  301   a  is a current obtained by subtracting the collector current Ic 1  of the transistor  401   b  and a base current Ib 1  of the transistor  401   b  from the constant current Ictr 1  supplied from the control signal terminal  601 . That is to say, Ibef 1 =Ictr 1 −Ic 1 −Ib 1 . Here, Ib 1 =Ic 1 /β, and thus, Ibef 1 =Ictr 1 −Ic 1 ×(1+1/β) where β is the grounded emitter current amplification factor. 
     The constant current Ictr 1  is constant. Thus, when the collector current Ic 1  increases, the base current Ibef 1  decreases, and furthermore, the emitter current Ieef 1  of the bias supplying transistor  301   a  decreases. This reduces the voltage drop of the resistive element  201   b  and causes the bias voltage Vbb 1  to fall. 
     On the other hand, when the bias voltage Vbb 1  falls, the collector current Ic 1  decreases, and furthermore, the base current Ibef 1  increases. This increases the emitter current Ieef 1 . Thus, the voltage drop of the resistive element  201   b  becomes greater, and the bias voltage Vbb 1  rises. 
     As described above, with the configuration that adjusts the base current Ibef 1  in such a manner as to suppress the rise and fall of the bias voltage Vbb 1 , the voltage applying circuit  421  enables to reduce the amount of compensation achieved by the bias current control circuit  41 . This enables to further suppress the change in the overall gain of the power amplifier circuit  101 . 
     Further, with the configuration that connects the capacitor  401   f  between the collector of the transistor  401   a  and the base of the transistor  401   a,  it becomes possible to ground the base of the transistor  401   a  AC-wise through the collector of the transistor  401   a.    
     When the power of the input signal RFin is high, in some cases, a radio frequency signal flows into the final bias circuit  311  from the final stage amplifier  201 . In such a case, it becomes possible to cause the radio frequency signal to flow into the ground through the capacitor  401   f  and the transistor  401   a,  and this enables to suppress an impact of the radio frequency signal on the base current of the transistor  401   a.  That is to say, it becomes possible to hinder the transistor  401   a  from amplifying the radio frequency signal. This enable to suppress oscillation of the radio frequency signal in the negative feedback path or generation of noise. Note that a configuration without necessarily the capacitor  401   f  may alternatively be used. 
     Fourth Embodiment 
     A power amplifier circuit  104  according to the fourth embodiment is described.  FIG.  7    is a circuit diagram of the power amplifier circuit  104 . As illustrated in  FIG.  7   , the power amplifier circuit  104  according to the fourth embodiment is different from the power amplifier circuit  101  according to the first embodiment in including three or more sets of the amplifier, the bias circuit, and the matching circuit. 
     Compared with the power amplifier circuit  101  illustrated in  FIG.  1   , the power amplifier circuit  104  further includes N number of intermediate stage amplifiers  2001  to  200 N, N number of intermediate stage bias circuits  3101  to  310 N, and N number of intermediate stage matching circuits  5001  to  500 N. Here, N is an integer greater than or equal to 1. 
     Each of the intermediate stage amplifiers  2001  to  200 N has a configuration substantially similar to that of the final stage amplifier  201  or the first stage amplifier  202 . Each of the intermediate stage bias circuits  3101  to  310 N has a configuration substantially similar to that of the final stage bias circuit  311  or the first stage bias circuit  312 . Each of the intermediate stage matching circuits  5001  to  500 N has a configuration substantially similar to that of the output matching circuit  501  or the interstage matching circuit  502 . 
     The intermediate stage amplifiers  2001  to  200 N are cascade-connected in this order between the first stage amplifier  202  and the final stage amplifier  201 . Here, the term “cascade-connected” means that a plurality of amplifiers are connected in series and further, of two adjacent amplifiers, an output terminal of one of the amplifiers is connected to an input terminal of the other amplifier. 
     In the following section, the intermediate stage amplifier  200 N, the intermediate bias circuit  310 N, and the intermediate stage matching circuit  500 N may sometimes be referred to as the (N+1)th stage amplifier, the (N+1)th bias circuit, and the (N+1)th stage matching circuit, respectively. Note that the first stage and the (N+2)th stage are the first stage and the final stage, respectively. 
     The intermediate stage bias circuit  310  (N−1) supplies a bias to the intermediate stage amplifier  200  (N−1). The intermediate stage amplifier  200  (N−1) has an input terminal connected to an output terminal of the (N−1)th stage amplifier through the (N−1)th stage matching circuit and an output terminal connected to an input terminal of the (N+1)th stage amplifier through the Nth stage matching circuit, that is to say, the intermediate stage matching circuit  500  (N−1). 
     The bias current compensation transistor  51  has a collector connected to the emitter of the bias supplying transistor of the intermediate stage bias circuit  310 N, a base connected to the emitter of the bias supplying transistor  301   a  of the final stage bias circuit  311  through the low pass filter circuit  61 , and an emitter connected to the ground. 
     Fifth Embodiment 
     A power amplifier circuit  105  according to the fifth embodiment is described.  FIG.  8    is a circuit diagram of the power amplifier circuit  105 . As illustrated in  FIG.  8   , the power amplifier circuit  105  according to the fifth embodiment is different from the power amplifier circuit  104  according to the fourth embodiment in that the bias current control circuit  41  is provided between the output terminal of the final stage bias circuit  311  and the output terminal of the bias circuit that is located closer to the input side than the intermediate stage bias circuit  310 N. 
     In the present embodiment, the bias current compensation transistor  51  has a collector connected to the emitter of the bias supplying transistor of the intermediate stage bias circuit  310  (N−1), a base connected to the emitter of the bias supplying transistor  301   a  of the final stage bias circuit  311  through the low pass filter circuit  61 , and an emitter connected to the ground. 
     Note that the configuration may alternatively be such that the collector of the bias current compensation transistor  51  is connected to the emitter of the bias supplying transistor of the bias circuit that is located closer to the input side than the intermediate stage bias circuit  310  (N−1) such as the (N−1)th stage bias circuit, the (N−2)th stage bias circuit, or the like. 
     Further, in the power circuits  104  and  105 , the configuration is described, in which the base of the bias current compensation transistor  51  is connected to the emitter of the bias supplying transistor  301   a  of the final stage bias circuit  311 . However, the configuration is not limited thereto. The configuration may alternatively be such that the base of the bias current compensation transistor  51  is connected to the emitter of the bias supplying transistor of any one of the N number of bias circuits from the second stage bias circuit, that is to say, the intermediate stage bias circuit  3101 , to the intermediate bias circuit  310 N. 
     Further, in the power amplifier circuits  101  to  105 , the configuration in which the low pass filter circuit  61  is provided is described. However, the configuration is not limited thereto. In the power amplifier circuits  101  to  105 , a configuration without necessarily the low pass filter circuit  61  may alternatively be used. 
     Exemplary embodiments of the present disclosure have been described. The power amplifier circuits  101  to  105  each includes a plurality of amplifying transistors that are electrically cascade-connected and include at least the amplifying transistors  201   a  and  202   a.  Each of this plurality of amplifying transistors amplifies a signal supplied to the base thereof and outputs an amplified signal, and in the power amplifier circuits  101  to  103 , the resistive element  201   b  has the first end part and the second end part connected to the base of the amplifying transistor  201   a.  The resistive element  202   b  has the first end part and the second end part connected to the base of the amplifying transistor  202   a.  The bias supplying transistor  301   a  has the emitter connected to the first end part of the resistive element  201   b.  The bias supplying transistor  302   a  has the emitter connected to the first end part of the resistive element  202   b.  The bias current compensation transistor  51  has the base connected to the first end part of the resistive element  201   b,  the collector connected to the first end part of the resistive element  202   b,  and the emitter connected to the ground. 
     As described above, with the configuration in which the base of the bias current compensation transistor  51  is connected to the first end part of the resistive element  201   b,  that is to say, the emitter of the bias supplying transistor  301   a,  it becomes possible to cause the bias current compensation transistor  51  to operate based on the emitter potential of the bias supplying transistor  301   a , that is to say, the bias voltage Vbb 1 . The bias current compensation transistor  51  enables to increase or decrease the current Icsk that flows from the emitter of the bias supplying transistor  302   a  into the ground in response to an increase or decrease in the gain of the amplifying transistor  201   a  without necessarily being affected by nonlinearity of the bias supplying transistor  301   a.  Because of this, it becomes possible to realize the negative feedback that reduces the gain of the amplifying transistor  202   a  when the gain of the amplifying transistor  201   a  increases and increases the gain of the amplifying transistor  202   a  when the gain of the amplifying transistor  201   a  decreases, and thus, it becomes possible to fully compensate the gain change of the amplifying transistor  201   a.  Therefore, it becomes possible to suppress the change in the overall gain of the power amplifier circuit. 
     Further, it becomes possible to drive the amplifying transistor  201   a  and the bias supplying transistor  301   a  by applying a voltage that is approximately equal to the sum of Vbe of the amplifying transistor  201   a  and Vbe of the bias supplying transistor  301   a  to the collector of the bias supplying transistor  301   a.  The same applies to the amplifying transistor  202   a  and the bias supplying transistor  302   a.  Accordingly, it becomes possible to operate the power amplifier circuits  101  to  103  at low voltage. 
     Further, in the power amplifier circuit  103 , the voltage applying circuit  431  is electrically connected to the base of the bias supplying transistor  301   a  and applies the first voltage to the base of the bias supplying transistor  301   a.  In the voltage applying circuit  431 , the resistive element  401   e  has the first end part connected to the emitter of the bias supplying transistor  301   a  and the second end part. The transistor  401   a  has the base connected to the second end part of the resistive element  401   e,  the collector connected to the base of the bias supplying transistor  301   a  and the control signal terminal  601 , and the emitter connected to the ground. 
     According to such configuration, it becomes possible to form the negative feedback path from the bias supplying transistor  301   a,  the resistive element  401   e,  and the transistor  401   a.  Such a negative feedback path enables the adjustment of the base current Ibef 1  of the bias supplying transistor  301   a  in such a manner as to suppress the rise and fall of the emitter potential of the bias supplying transistor  301   a,  that is to say, the bias voltage Vbb 1 . This enables to reduce the amount of compensation achieved by the bias current compensation transistor  51 , and thus, it becomes possible to further suppress the change in the overall gain of the power amplifier circuit  103 . Further, it becomes possible to set the collector potential of the transistor  401   a  to a high voltage that is the sum of Vbe of the transistor  401   a  and Vbe of the bias supplying transistor  301   a,  and thus, the gain of the transistor  401   a  can be increased. This enables to further reduce the rise and fall of the bias voltage Vbb 1  caused by the negative feedback. Further, it becomes possible to eliminate one of the transistors compared with the voltage applying circuits  411  and  421 , and thus it becomes possible to reduce the circuit size. This enables to reduce the size of the power amplifier circuit  103 , and further, this enables to reduce the cost of the power amplifier circuit  103 . 
     Further, in the power amplifier circuit  102 , the voltage applying circuit  421  is electrically connected to the base of the bias supplying transistor  301   a  and applies the first voltage to the base of the bias supplying transistor  301   a.  In the voltage applying circuit  421 , the resistive element  401   e  has the first end part connected to the emitter of the bias supplying transistor  301   a  and the second end part. The transistor  401   a  has the base connected to the second end part of the resistive element  401   e,  the collector, and the emitter connected to the ground. The transistor  401   b  has the collector and the base that are connected to the base of the bias supplying transistor  301   a  and the control signal terminal  601  and the emitter connected to the collector of the transistor  401   a.    
     According to such configuration, it becomes possible to form the negative feedback path from the bias supplying transistor  301   a,  the resistive element  401   e,  and the transistors  401   a  and  401   b.  Such a negative feedback path enables the adjustment of the base current Ibef 1  of the bias supplying transistor  301   a  in such a manner as to suppress the rise and fall of the emitter potential of the bias supplying transistor  301   a,  that is to say, the bias voltage Vbb 1 . This enables to reduce the amount of compensation achieved by the bias current compensation transistor  51 , and thus, it becomes possible to further suppress the change in the overall gain of the power amplifier circuit  102 . 
     Further, in the voltage applying circuits  421  and  431 , the capacitor  401   f  is connected between the base of the transistor  401   a  and the collector of the transistor  401   a.    
     Such configuration enables the base of the transistor  401   a  to be grounded AC-wise through the collector of the transistor  401   a.  Because of this, for example, even in the case where a radio frequency signal flows from the final stage amplifier  201  into the final stage bias circuit  311 , it becomes possible to cause that radio frequency signal to flow into the ground through the capacitor  401   f  and the transistor  401   a,  and thus, it becomes possible to suppress an impact of the radio frequency signal on the base current of the transistor  401   a.  That is to say, it becomes possible to hinder the transistor  401   a  from amplifying the radio frequency signal. This enable to suppress oscillation of the radio frequency signal in the negative feedback path or generation of noise. 
     Further, in the power amplifier circuit  103 , the voltage applying circuit  432  is electrically connected to the base of the bias supplying transistor  302   a  and applies the second voltage to the base of the bias supplying transistor  302   a.  In the voltage applying circuit  432 , the resistive element  402   e  has the first end part connected to the emitter of the bias supplying transistor  302   a  and the second end part. The transistor  402   a  has the base connected to the second end part of the resistive element  402   e,  the collector connected to the base of the bias supplying transistor  302   a  and the control signal terminal  602 , and the emitter connected to the ground. 
     According to such configuration, it becomes possible to form the negative feedback path from the bias supplying transistor  302   a,  the resistive element  402   e,  and the transistor  402   a.  Such a negative feedback path enables the adjustment of the base current Ibef 2  of the bias supplying transistor  302   a  in such a manner as to suppress the rise and fall of the emitter potential of the bias supplying transistor  302   a,  that is to say, the bias voltage Vbb 2 . This enables to reduce the amount of compensation achieved by the bias current compensation transistor  51 , and thus, it becomes possible to further suppress the change in the overall gain of the power amplifier circuit  103 . Further, it becomes possible to set the collector potential of the transistor  402   a  to a high voltage that is the sum of Vbe of the transistor  402   a  and Vbe of the bias supplying transistor  302   a,  and thus, the gain of the transistor  402   a  can be increased. This enables to further reduce the rise and fall of the bias voltage Vbb 2  caused by the negative feedback. Further, it becomes possible to reduce one of the transistors compared with the voltage applying circuits  412  and  422 , and thus it becomes possible to reduce the circuit size. This enables to reduce the size of the power amplifier circuit  103 , and further, this enables to reduce the cost of the power amplifier circuit  103 . 
     Further, in the power amplifier circuit  102 , the voltage applying circuit  422  is electrically connected to the base of the bias supplying transistor  302   a  and applies the second voltage to the base of the bias supplying transistor  302   a.  In the voltage applying circuit  422 , the resistive element  402   e  has the first end part connected to the emitter of the bias supplying transistor  302   a  and the second end part. The transistor  402   a  has the base connected to the second end part of the resistive element  402   e,  the collector, and the emitter connected to the ground. The transistor  402   b  has the collector and the base that are connected to the base of the bias supplying transistor  302   a  and the control signal terminal  602  and the emitter connected to the collector of the transistor  402   a.    
     According to such configuration, it becomes possible to form the negative feedback path from the bias supplying transistor  302   a,  the resistive element  402   e,  and the transistors  402   a  and  402   b.  Such a negative feedback path enables the adjustment of the base current Ibef 2  of the bias supplying transistor  302   a  in such a manner as to suppress the rise and fall of the emitter potential of the bias supplying transistor  302   a,  that is to say, the bias voltage Vbb 2 . This enables to reduce the amount of compensation achieved by the bias current compensation transistor  51 , and thus, it becomes possible to further suppress the change in the overall gain of the power amplifier circuit  102 . 
     Further, in the voltage applying circuits  422  and  432 , the capacitor  402   f  is connected between the base of the transistor  402   a  and the collector of the transistor  402   a.    
     Such configuration enables the base of the transistor  402   a  to be grounded AC-wise through the collector of the transistor  402   a.  For example, even in the case where a radio frequency signal flows from the first stage amplifier  202  into the first stage bias circuit  312 , this enables to cause that radio frequency signal to flow into the ground through the capacitor  402   f  and the transistor  402   a,  and thus, it becomes possible to suppress an impact of the radio frequency signal on the base current of the transistor  402   a.  That is to say, it becomes possible to hinder the transistor  402   a  from amplifying the radio frequency signal. This enable to suppress oscillation of the radio frequency signal in the negative feedback path or generation of noise. 
     Further, in the power amplifier circuits  101  to  105 , the amplifying transistor  201   a  is the final stage amplifying transistor. 
     Such configuration enables the bias current compensation transistor  51  to operate based on the bias voltage Vbb 1  for the final stage amplifying transistor  201   a  whose gain is easy to increase. This enables to suppress the change in the overall gain of the power amplifier circuit effectively. 
     Further, the power amplifier circuit  105  includes (N+2) number of the amplifiers. The amplifier in the Nth stage, the (N−1)th stage, the (N−2)th stage, or the like is connected to the final stage amplifier  201  through one or more amplifiers. 
     As described above, with the configuration in which the bias current compensation transistor  51  is connected between the emitter of the bias supplying transistor connected to the final stage amplifier  201  and the emitter of the bias supplying transistor connected to the amplifier in the stage where the bias current is smaller, such as the Nth stage, the (N−1)th stage, the(N−2)th stage, or the like, it becomes possible to reduce the amount of compensation achieved by the bias current compensation transistor  51  while keeping the effect of suppressing the change in the overall gain of the power amplifier circuit  105 . 
     Further, in the power amplifier circuits  101  to  105 , the low pass filter circuit  61  is connected between the first end part of the resistive element  202   b  and the base of the bias current compensation transistor  51 . 
     Even in the case where the bias voltage Vbb 1  vibrates at a high frequency, such configuration enables to suppress the transmission of the high frequency vibration of the bias voltage Vbb 1  to the first stage amplifier  202 , and thus, it becomes possible to suppress oscillations of the power amplifier circuits  101  to  105  and reduce the noise level in the output signal RFout. 
     Note that each of the embodiments described above is provided to facilitate understanding of the present disclosure and is not to be construed as limiting the present disclosure. The present disclosure can be modified or improved without necessarily departing from its spirit, and the present disclosure also includes equivalents thereof. That is to say, ones obtained by suitably modifying designs of the respective embodiments by those skilled in the art are also included within the scope of the present disclosure as long as they include features of the present disclosure. For example, each constituent element included in each embodiment as well as its arrangement, material, condition, shape, size, and the like are not limited to those exemplified, and may be suitably changed. Needless to say, each embodiment is for illustrative purposes only, and constituent elements illustrated in different embodiments may be combined or partially exchanged. Resulting embodiments are also included in the scope of the present disclosure so long as the characteristic features of the present disclosure are included. Further, the meaning of “connect” includes “direct or indirect connection” and “electrical connection”.