Patent Publication Number: US-11398805-B2

Title: Power amplification module

Description:
This is a continuation of U.S. application Ser. No. 15/201,999, filed on Jul. 5, 2016, which claims priority of Japanese Patent Application No. 2015-246193 filed on Dec. 17, 2015 and Japanese Patent Application No. 2015-140390 filed Jul. 14, 2015. The contents of each of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates to a power amplification module. 
     A power amplification module is used in a mobile communication device such as a cellular phone in order to amplify the power of a radio frequency (RF) signal to be transmitted to a base station. For example, in the global system for mobile communications (GSM) (registered trademark), the gain of a power amplification module is controlled in order to realize slope control (ramp up and ramp down) for a transmission signal to be transmitted from a mobile communication device to a base station. 
     In Japanese Unexamined Patent Application Publication No. 2009-100197, a configuration is disclosed in which a voltage Vldo output from a low drop out (LDO) regulator is supplied to a collector terminal of each stage of a 3-stage amplifier in a power amplification module. In this configuration, the gain of the power amplification module is controlled by adjusting the level of the voltage Vldo on the basis of a level control voltage Vramp. 
     In addition, in U.S. Pat. No. 7,605,651, a configuration is disclosed in which a voltage Vreg output from an LDO regulator is supplied to first and second stages and a constant power supply voltage is supplied to a third stage in a power amplification module including a 3-stage amplifier. 
     In the configurations disclosed in Japanese Unexamined Patent Application Publication No. 2009-100197 and U.S. Pat. No. 7,605,651 described above, an LDO regulator is used in order to control the gain of a power amplification module. Generally, in order to supply a large current, the circuit scale of an LDO regulator is large. 
     BRIEF SUMMARY 
     The present disclosure was made in light of the above-described circumstances and the present disclosure suppresses an increase in the size of the circuit of a power amplification module that performs slope control on a transmission signal. 
     A power amplification module according to an embodiment of the present disclosure includes: an amplification transistor that has a constant power supply voltage supplied to a collector thereof, a bias current supplied to a base thereof and that amplifies an input signal input to the base thereof and outputs an amplified signal from the collector thereof; a first current source that outputs a first current that corresponds to a level control voltage that is for controlling a signal level of the amplified signal; and a bias transistor that has the first current supplied to a collector thereof, a bias control voltage connected to a base thereof and that outputs the bias current from an emitter thereof. 
     According to the embodiment of the present disclosure, an increase in circuit scale can be suppressed in a power amplification module that performs slope control on a transmission signal. 
     Other features, elements, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of embodiments of the present disclosure with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  illustrates an example configuration of a transmission unit that includes a power amplification module according to an embodiment of the present disclosure; 
         FIG. 2  illustrates an example of slope control of a transmission signal; 
         FIG. 3  illustrates an example of a voltage input to the power amplification module; 
         FIG. 4  illustrates the configuration of a power amplification module, which is an example of the power amplification module illustrated in  FIG. 1 ; 
         FIG. 5  illustrates an example of the configuration of an amplifier; 
         FIG. 6  illustrates an example of the configuration of a bias circuit; 
         FIG. 7  illustrates an example of the relationship between a base current and a collector current in a transistor; 
         FIG. 8  illustrates an example of a bias current that changes in a substantially square relationship with respect to a voltage; 
         FIG. 9  illustrates an example of the configuration of a current source; 
         FIG. 10  illustrates an example a proportional relationship between a voltage and a current; 
         FIG. 11  illustrates an example of the relationship between currents in a square circuit; 
         FIG. 12  illustrates an example of the relationship between a gate-source voltage and a drain current in a MOSFET; 
         FIG. 13  illustrates an example of the characteristics of a current output from the square circuit; 
         FIG. 14  illustrates the configuration of a power amplification module, which is an example of the power amplification module illustrated in  FIG. 1 ; 
         FIG. 15  illustrates an example of the configuration of a voltage source; 
         FIG. 16  illustrates the configuration of a power amplification module, which is an example of the power amplification module illustrated in  FIG. 1 ; 
         FIG. 17  illustrates the configuration of a power amplification module, which is an example of the power amplification module illustrated in  FIG. 1 ; 
         FIG. 18  illustrates the configuration of a power amplification module, which is an example of the power amplification module illustrated in  FIG. 1 ; 
         FIG. 19  illustrates an example of the configuration of a voltage source; 
         FIG. 20  illustrates the configuration of a power amplification module, which is an example of the power amplification module illustrated in  FIG. 1 ; 
         FIG. 21  illustrates the configuration of a level detection circuit, which is a modification of the level detection circuit illustrated in  FIG. 20 ; 
         FIG. 22  illustrates the configuration of a level detection circuit, which is a modification of the level detection circuit illustrated in  FIG. 20 ; 
         FIG. 23  illustrates the configuration of a level detection circuit, which is a modification of the level detection circuit illustrated in  FIG. 20 ; and 
         FIG. 24  illustrates the configuration of a level detection circuit, which is a modification of the level detection circuit illustrated in  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereafter, embodiments of the present disclosure will be described while referring to the drawings.  FIG. 1  illustrates an example configuration of a transmission unit that includes a power amplification module according to an embodiment of the present disclosure. A transmission unit  100  is for example used in a mobile communication device such as a cellular phone in order to transmit various signals such as speech and data to a base station. Although such a mobile communication device would also be equipped with a reception unit for receiving signals from the base station, the description of such a reception unit is omitted here. 
     As illustrated in  FIG. 1 , the transmission unit  100  includes a modulator  110 , a power amplification module  120 , a front end unit  130  and an antenna  140 . 
     The modulator  110  modulates an input signal on the basis of a modulation scheme such as GSM or enhanced data rates for GSM evolution (EDGE) and generates a radio frequency signal for performing wireless transmission. The RF signal has a frequency of around several hundred MHz to several GHz, for example. 
     The power amplification module  120  amplifies the power of the RF signal (RFin) up to the level that is required to transmit the RF signal to the base station, and outputs an amplified signal (RFout). In addition, the power amplification module  120  performs slope control on the amplified signal (transmission signal) by controlling the gain on the basis of a voltage Vramp (level control voltage), which is for controlling the signal level. 
       FIG. 2  illustrates an example of slope control of a transmission signal. As illustrated in  FIG. 2 , in slope control, it is necessary that the signal level of the transmission signal be controlled so as to lie within a range between a lower limit DL and an upper limit UL. In addition, it is necessary that the signal level be controlled so as to maintain a prescribed rate of change (slope) such that the signal level of the transmission signal does not exceed the upper limit UL and does not fall below the lower limit DL in a location indicated by A in  FIG. 2  (rising region). In addition, it is necessary that the signal level be controlled so as to maintain a prescribed rate of change such that the signal level of the transmission signal does not exceed the upper limit UL and does not fall below the lower limit DL in a location indicated by B in  FIG. 2  (falling region). 
       FIG. 3  illustrates an example of the voltage Vramp input to the power amplification module  120 . In the power amplification module  120 , the signal level of the transmission signal is controlled as illustrated in  FIG. 2  by controlling the gain on the basis of the voltage Vramp, which changes as illustrated in  FIG. 3 . 
     Returning to  FIG. 1 , the front end unit  130  filters the amplified signal and switches a reception signal received from the base station. The amplified signal output from the front end unit  130  is transmitted to the base station via the antenna  140 . 
       FIG. 4  illustrates the configuration of a power amplification module  120 A, which is an example of the power amplification module  120 . The power amplification module  120 A includes amplifiers  400 ,  401  and  402 , inductors  410 ,  411  and  412 , matching networks (MN&#39;s)  420 ,  421 ,  422  and  423 , bias circuits  430 ,  431  and  432 , a bias control circuit  440  and a current source  450 . 
     The amplifiers  400  to  402  form a three-stage amplifier. The amplifier  400  amplifies an RF signal input thereto and outputs an amplified signal. The amplifier  401  amplifies the amplified signal (RF signal) output from the amplifier  400  and outputs an amplified signal. The amplifier  402  amplifies the amplified signal (RF signal) output from the amplifier  401  and outputs an amplified signal. A constant power supply voltage Vcc is supplied to the amplifier  400 . In addition, a bias current Ibias 1  is supplied from the bias circuit  430  to the amplifier  400 . Similarly, the power supply voltage Vcc and a bias current Ibias 2  are supplied to the amplifier  401 . The power supply voltage Vcc and a bias current Ibias 3  are supplied to the amplifier  402 . The number of stages of the amplifier is not limited to three and may be two or less or four or more. 
       FIG. 5  illustrates an example of the configuration of the amplifier  400 . As illustrated in  FIG. 5 , the amplifier  400  includes a transistor  500  (amplification transistor). The transistor  500  is a heterojunction bipolar transistor (HBT), for example. The power supply voltage Vcc is supplied to the collector of the transistor  500  via the inductor  410 . The RF signal (RFin) is input to the base of the transistor  500 . In addition, the bias current Ibias 1  is supplied to the base of the transistor  500 . The transistor  500  has a common emitter. An amplified signal (RFout 1 ) is output from the collector of the transistor  500 . The amplifiers  401  and  402  have a similar configuration. 
     As illustrated in  FIG. 5 , the gain is controlled in the amplifier  400  by using the bias current Ibias 1 . Although a configuration can also be considered in which the gain is controlled by using a bias voltage instead of the bias current, there is better controllability with the bias current. This will be explained below. Ic represents the collector current, Vb the base voltage, Ib the base current, hFE the current amplification factor, Is the saturation current, k the Boltzmann coefficient, T the absolute temperature, q the elemental charge of an electron and Vt the thermal voltage=k×T/q. In the case of control using on the base voltage, ΔIc≈Is×exp (ΔVb/Vt). Therefore, controllability is poor since the collector current Ic rapidly rises when the base voltage Vb exceeds a threshold voltage. On the other hand, in the case of control using the base current, ΔIc=ΔIb×hFE. Therefore, controllability is good since the rate of change of the collector current Ic is constant with respect to the base current Ib. 
     Returning to  FIG. 4 , the matching networks  420  to  423  are provided in front of and behind the amplifiers  400  to  402 . The matching networks  420  to  423  are circuits for matching impedances between the circuits. The matching networks  420  to  423  are formed using capacitors and inductors, for example. 
     The bias circuits  430  to  432  supply the bias currents Ibias 1  to Ibias 3  to the amplifiers  400  to  402 . The bias currents Ibias 1  to Ibias 3  are adjusted on the basis of a bias control voltage V 1  output from the bias control circuit  440  and a current I 1  output from the current source  450 . 
       FIG. 6  illustrates an example of the configuration of the bias circuit  430 . The bias circuit  430  includes a transistor  600  and diodes  610  and  611 . The transistor  600  (bias transistor) is an HBT, for example. The diodes  610  and  611  are connected in series with each other, the anode of the diode  610  is connected to the base of the transistor  600  and the cathode of the diode  611  is grounded. The bias control voltage V 1  is supplied to the base of the transistor  600 . In addition, the current I 1  is supplied to the collector of the transistor  600 . The bias current Ibias 1  is output from the emitter of the transistor  600 . The bias circuits  431  and  432  have a similar configuration. Transistors, which each have the collector and the base thereof connected to each other (diode connected), may be used instead of the diodes  610  and  611 . 
     Returning to  FIG. 4 , the bias control circuit  440  outputs the bias control voltage V 1  on the basis of a control voltage Vcnt. The bias control voltage V 1  is constant while the transmission signal is subjected to slope control. 
     The current source  450  (first current source) outputs the current I 1  (first current) on the basis of the voltage Vramp. In the power amplification module  120 A, the current I 1  is controlled in accordance voltage Vramp and as a result the gains of the amplifiers  400  to  402  are controlled. The transmission signal is subjected to slope control as a result of the gains of the amplifiers  400  to  402  being controlled. 
     As illustrated in  FIG. 2 , in the slope control, it is necessary that the change in the signal level not be too gentle when the signal level is falling (that is, in region where signal level is high).  FIG. 7  illustrates an example of the relationship between the base current Ib and the collector current Ic in a transistor. As illustrated in  FIG. 7 , the change in the collector current Ic becomes gentle in a saturation region of the transistor. The characteristic illustrated in  FIG. 7  is the same as in the transistors forming the amplifiers  400  to  402 . Therefore, in the amplifiers  400  to  402 , it is necessary to increase the rate of change of the bias currents Ibias (make the slopes steeper) in a region where the voltage Vramp is large as exemplified in  FIG. 8  in order to ensure that the change in the signal level is not too gentle in the region where the signal level is high. The current source  450  controls the current I 1  in order that the bias currents Ibias change in this way. 
       FIG. 9  illustrates an example of the configuration of the current source  450 . The current source  450  includes operational amplifiers OP 1  and OP 2 , p-channel MOSFETs (MP 1 , MP 2 , MP 3 , MP 4 , MP 5 , MP 6 , MP 7 , MP 8 , MP 9  and MP 10 ), n-channel MOSFETs (MN 1  and MN 2 ), current sources Is 1  and Is 2  and resistors R 1 , R 2  and R 3 . 
     The operational amplifier OP 1 , the p-channel MOSFETs (MP 1  and MP 2 ) and the resistor R 1  form a voltage-current conversion circuit  900  that converts the voltage Vramp into a current Iin. 
     The operational amplifier OP 1  has the voltage Vramp supplied to a non-inverting input terminal thereof, an inverting input terminal thereof is connected to the drain of the p-channel MOSFET (MP 1 ) and an output terminal thereof is connected to the gate of the p-channel MOSFET (MP 1 ). The p-channel MOSFET (MP 1 ) has a power supply voltage Vdd supplied to the source thereof and the drain thereof is connected to a first terminal of the resistor R 1 . A second terminal of the resistor R 1  is grounded. The p-channel MOSFET (MP 2 ) has the power supply voltage Vdd supplied to the source thereof, the gate thereof is connected to the gate of the p-channel MOSFET (MP 1 ) and the drain thereof is connected to the drain of the n-channel MOSFET (MN 1 ). 
     The voltage at the first terminal of the resistor R 1  is the voltage Vramp due to an imaginary short between the non-inverting input terminal and the inverting input terminal of the operational amplifier OP 1 . If we denote the resistance value of the resistor R 1  as R 1 , a current Ia 1  that flows to the p-channel MOSFET (MP 1 ) is Vramp/R 1 . Then, since the p-channel MOSFETs (MP 1  and MP 2 ) are connected in a current mirroring manner, a current Iin output from the p-channel MOSFET (MP 2 ) has a value that corresponds to the voltage Vramp. 
     The n-channel MOSFETs (MN 1  and MN 2 ), the p-channel MOSFETs (MP 3  to MP 8 ) and the current source Is 1  form a square circuit  910  that outputs a current Iout that changes in a substantially square relationship with respect to the current Iin. 
     The n-channel MOSFET (MN 1 ) has the drain thereof connected to the drain of the p-channel MOSFET (MP 2 ), the gate thereof connected to the drain thereof and has a common source. The n-channel MOSFET (MN 2 ) has the drain thereof connected to the drain of the p-channel MOSFET (MP 3 ), the gate thereof connected to the gate of the n-channel MOSFET (MN 1 ) and has a common source. 
     The p-channel MOSFET (MP 5 ) has the power supply voltage Vdd supplied to the source thereof, has the gate thereof connected to the drain thereof and has the drain thereof connected to the source of the p-channel MOSFET (MP 3 ). The p-channel MOSFET (MP 3 ) has the gate thereof connected to the drain thereof and has the drain thereof connected to the drain of the n-channel MOSFET (MN 2 ). 
     The p-channel MOSFET (MP 6 ) has the power supply voltage Vdd supplied to the source thereof, has the gate thereof connected to the drain thereof and has the drain thereof connected to the current source Is 1 . The current source Is 1  outputs a constant current Iset. The p-channel MOSFET (MP 7 ) has the power supply voltage Vdd supplied to the source thereof, has the gate thereof connected to the gate of the p-channel MOSFET (MP 6 ) and has the drain thereof connected to the source of the p-channel MOSFET (MP 4 ). The p-channel MOSFET (MP 4 ) has the gate thereof connected to the gate of the p-channel MOSFET (MP 3 ) and has a common drain. 
     The p-channel MOSFET (MP 8 ) has the power supply voltage Vdd supplied to the source thereof, the gate thereof is connected to the source of the p-channel MOSFET (MP 4 ) and the drain thereof is connected to a first terminal of the resistor R 2 . 
     The square circuit  910  outputs the current Iout, which changes in a substantially square relationship with respect to the current Iin, from the drain of the p-channel MOSFET (MP 8 ). The details of operation of the square circuit  910  will be described later. 
     An output driver circuit  920  is formed of the operational amplifier OP 2 , the current source Is 2 , the p-channel MOSFETs (MP 9  and MP 10 ) and the resistors R 2  and R 3 . The output driver circuit  920  amplifies the current Iout up to the level that is required for the current I 1  to be supplied to the bias circuits  430  to  432 . In the case where the current Iout can be used as the current I 1  without being amplified, the output driver circuit  920  need not be provided. 
     The current source Is 2  outputs a constant current Ioff (offset current) to the first terminal of the resistor R 2 . The operational amplifier OP 2  has a non-inverting input terminal thereof connected to the first terminal of the resistor R 2 , an inverting input terminal thereof connected to a first terminal of the resistor R 3  and an output terminal thereof connected to the gate of the p-channel MOSFET (MP 9 ). The p-channel MOSFET (MP 9 ) has the power supply voltage Vdd supplied to the source thereof and has the drain thereof connected to the first terminal of the resistor R 3 . A second terminal of the resistor R 3  is grounded. The p-channel MOSFET (MP 10 ) has the power supply voltage Vdd supplied to the source thereof and has the gate thereof connected to the gate of the p-channel MOSFET (MP 9 ). 
     If we denote the resistance value of the resistor R 2  as R 2  and the current that is output from the current source IS 2  as Ioff, a voltage Va 1  that is supplied to the non-inverting input terminal of the operational amplifier OP 2  is (Iout+Ioff)×R 2 . The voltage at the first terminal of the resistor R 3  is the voltage Va 1  due to an imaginary short between the non-inverting input terminal and the inverting input terminal of the operational amplifier OP 2 . If we denote the resistance value of the resistor R 3  as R 3 , a current Ia 2  that flows to the p-channel MOSFET (MP 9 ) is Va 1 /R 3 . Then, since the p-channel MOSFETs (MP 9  and MP 10 ) are connected to each other in a current mirroring manner, the current I 1 , which is output from the p-channel MOSFET (MP 10 ), is a current obtained by amplifying the current Iout. 
     Next, the details of operation of the square circuit  910  will be described. The sizes of the p-channel MOSFETs (MP 3  and MP 4 ) are made to be the same and the sizes of the p-channel MOSFETs (MP 5  and MP 8 ) are made to be the same. Id 1  denotes a current that flows through the n-channel MOSFET (MN 2 ) and Id 2  denotes a current that flows through the p-channel MOSFET (MP 4 ). In addition, Iset denotes a current that is output from the current source Is 1 . Iset is constant, but it is assumed that Iset∝Iin for the purposes of this explanation. In addition, it is assumed that Id 1 =Id 2 . Under these conditions, Vramp∝Iin, Iin∝Id 1  and Iset∝Id 2 . 
     Va denotes the drain voltage of the p-channel MOSFET (MP 5 ), Vb denotes the drain voltage of the p-channel MOSFET (MP 7 ) and Vc denotes the gate voltage of the p-channel MOSFET (MP 4 ). In addition, Vgs 3 , Vgs 4 , Vgs 5  and Vgs 8  denote the gate-source voltages of the p-channel MOSFETs (MP 3 , MP 4 , MP 5  and MP 8 ), respectively. 
     Va=Vdd−Vgs 5 . In addition, Vc=Va−Vgs 3  and Vb=Vc+Vgs 4 . Therefore, Vb=Vdd−Vgs 5 −Vgs 3 +Vgs 4 . Furthermore, since Vb=Vdd−Vgs 8 , Vdd−Vgs 8 =Vdd−Vgs 5 −Vgs 3 +Vgs 4 . 
     In the case where Id 1 =Id 2 , since Vgs 3 =Vgs 4 , Vgs 5 =Vgs 8 . Therefore, the p-channel MOSFETs (MP 5  and MP 8 ) form a pseudo current mirror circuit. Consequently, as illustrated in  FIG. 10 , the proportional relationship Vramp∝Iout holds true. 
     However, in reality, as illustrated in  FIG. 11 , in the square circuit  910 , Id 1  is a current that is proportional to Vramp, but Id 2  is a current (constant current) that is proportional to Iset. Therefore, in the square circuit  910  Id 1  is not equal to Id 2 . In the square circuit  910 , the current Iout is made to change by utilizing the mismatch between the current Id 1  and the current Id 2 . This will be explained below. 
     First, a case where Id 1 &lt;Id 2  will be described. Vdd−Vgs 8 =Vdd−Vgs 5 −Vgs 3 +Vgs 4  from the relationship between Va and Vb described above. Therefore, Vgs 8 =Vgs 5 +Vgs 3 −Vgs 4 . In the case where Id 1 &lt;Id 2 , since Vgs 3 &lt;Vgs 4 , Vgs 8 &lt;Vgs 5 . Thus, Iout falls below the proportional relationship illustrated in  FIG. 10 . In the p-channel MOSFET (MP 8 ), since there is a region in which Vgs 6 &lt;a threshold voltage Vth, a curved characteristic appears between a dead zone and a non-linear region in Iout as illustrated in  FIG. 12 . 
     Next, a case in which Id 1 &gt;Id 2  will be described. As described above, Vgs 8 =Vgs 5 +Vgs 3 &lt;Vgs 4 . In the case where Id 1 &gt;Id 2 , since Vgs 3 &gt;Vgs 4 , Vgs 8 &gt;Vgs 5 . Thus, Iout exceeds the proportional relationship illustrated in  FIG. 10 . 
     Combining the case where Id 1 &lt;Id 2  and the case where Id 1 &lt;Id 2 , the characteristics of Iout are as illustrated in  FIG. 13 . Thus, the current Iout output from the square circuit  910  is a current that changes in a substantially square relationship with respect to the voltage Vramp. The current I 1  output from the current source  450  is a current obtained by amplifying the current Iout and therefore the current I 1  is also a current that changes in a substantially square relationship with respect to the voltage Vramp. In other words, the rate of change of the current I 1  in the case where the voltage Vramp is at a comparatively high level (second level) becomes larger than the rate of change of the current I 1  in the case where the voltage Vramp is at a comparatively low level (first level). Therefore, as illustrated in  FIG. 8 , the rates of change of the bias currents Ibias 1  to Ibias 3  that are supplied to the amplifiers  400  to  402  can be made large in a region where the voltage Vramp is large. Thus, it is easy to perform slope control on a transmission signal as illustrated in  FIG. 2 . 
       FIG. 14  illustrates the configuration of a power amplification module  120 B, which is an example of the power amplification module  120 . Constituent elements that are the same as those of the power amplification module  120 A illustrated in  FIG. 4  are denoted by the same symbols and description thereof is omitted. 
     The power amplification module  120 B includes a voltage source  1400  in addition to the elements included in the power amplification module  120 A. 
     The voltage source  1400  (first voltage source) outputs a constant voltage V 2  (first voltage) (for example, around 1.0 V). The voltage V 2  output from the voltage source  1400  is supplied to the collectors of the transistors that form the bias circuits  430  to  432 . The voltage V 2  is at a level at which the amplifiers  400  to  402  do not operate. 
       FIG. 15  illustrates an example of the configuration of the voltage source  1400 . As illustrated in  FIG. 15 , the voltage source  1400  includes an operational amplifier OP 3  and a p-channel MOSFET (MP 11 ). 
     The operational amplifier OP 3  has a constant voltage Vadd (for example, around 1.0 V) supplied to a non-inverting input terminal thereof, an inverting input terminal thereof is connected to the drain of the p-channel MOSFET (MP 11 ) and an output terminal thereof is connected to the gate of the p-channel MOSFET (MP 11 ). The voltage V 2  is output from the drain of the p-channel MOSFET (MP 11 ). In the voltage source  1400 , the voltage V 2  is controlled by the voltage Vadd through an imaginary short circuit between the non-inverting input terminal and the inverting input terminal of the operational amplifier OP 3 . 
     As described above, in the power amplification module  120 B, the voltage V 2  (for example, around 1.0 V) output from the voltage source  1400  is supplied to the bias circuits  430  to  432 . Parasitic capacitance and bypass capacitors can be charged by the voltage V 2 . Therefore, the response time for the voltage Vramp after starting slope control of the transmission signal can be shortened. The p-channel MOSFET (MP 11 ) may be replaced with an n-channel MOSFET. 
       FIG. 16  illustrates the configuration of a power amplification module  120 C, which is an example of the power amplification module  120 . Constituent elements that are the same as those of the power amplification module  120 B illustrated in  FIG. 14  are denoted by the same symbols and description thereof is omitted. 
     The power amplification module  120 C includes a switch circuit  1600  in addition to the elements included in the power amplification module  120 B. The switch circuit  1600  (first switch circuit) outputs the current I 1  from the current source  450  or the power supply voltage Vcc to the bias circuits  430  to  432  on the basis of a mode signal MODE. 
     The mode signal MODE indicates a GSM operation mode (first operation mode) in which the bias currents Ibias 1  to Ibias 3  are controlled in accordance with the voltage Vramp or an EDGE operation mode (second operation mode) in which the bias currents Ibias 1  to Ibias 3  are not controlled in accordance with the voltage Vramp. 
     In the case of the GSM operation mode, the switch circuit  1600  outputs the current I 1  from the current source  450 . In the case of the EDGE operation mode, the switch circuit  1600  outputs the power supply voltage Vcc. Thus, the power amplification module  120 C can support the EDGE mode. In addition, the power amplification module  120 C need not include the voltage source  1400 . 
       FIG. 17  illustrates the configuration of a power amplification module  120 D, which is an example of the power amplification module  120 . Constituent elements that are the same as those of the power amplification module  120 A illustrated in  FIG. 4  are denoted by the same symbols and description thereof is omitted. 
     The power amplification module  120 D includes a voltage source  1700 , a switch circuit  1710  and a switch control circuit  1720  in addition to the elements included in the power amplification module  120 A. 
     The voltage source  1700  (second voltage source) outputs a voltage V 3 . The voltage V 3  output from the voltage source  1700  changes in accordance with the mode signal MODE. In the case of the GSM mode, the voltage source  1700  outputs a constant voltage V 3  (second voltage) (for example, around 1.0 V). In the case of the EDGE mode, the voltage source  1700  outputs a constant voltage V 3  (third voltage) that is higher than that in the case of the GSM mode. 
     The switch circuit  1710  (second switch circuit) supplies the current I 1  output from the current source  450  or the voltage V 3  output from the voltage source  1700  to the bias circuits  430  to  432  on the basis of control performed by the switch control circuit  1720 . 
     The switch control circuit  1720  controls the switch circuit  1710  on the basis of the mode signal MODE and the voltage Vramp. 
     In the case of the EDGE mode, the switch control circuit  1720  controls the switch circuit  1710  such that the voltage V 3  (for example, power supply voltage Vcc) output from the voltage source  1700  is supplied to the bias circuits  430  to  432 . Thus, the power amplification module  120 D can support the EDGE mode. 
     In the case of the GSM mode, the switch control circuit  1720  controls the switch circuit  1710  in accordance with the voltage Vramp. Specifically, in the case where the voltage Vramp is smaller than a prescribed level (for example, 0.2 V), the switch control circuit  1720  controls the switch circuit  1710  such that the voltage V 3  (for example, around 1.0 V) output from the voltage source  1700  is supplied to the bias circuits  430  to  432 . In addition, in the case where the voltage Vramp is larger than a prescribed level, the switch control circuit  1720  controls the switch circuit  1710  such that the current I 1  output from the current source  450  is supplied to the bias circuits  430  to  432 . 
     As described above, in the case of the GSM mode, when the voltage Vramp is smaller than the prescribed threshold, the voltage V 3  (for example, around 1.0 V) output from the voltage source  1700  is supplied to the bias circuits  430  to  432 . Parasitic capacitances and bypass capacitors can be charged by the voltage V 3  before starting the slope control of the transmission signal. Therefore, the response time for the voltage Vramp after starting slope control of the transmission signal can be shortened. The voltage V 3  at this time is at level at which the amplifiers  400  to  402  do not operate. 
       FIG. 18  illustrates the configuration of a power amplification module  120 E, which is an example of the power amplification module  120 . Constituent elements that are the same as those of the power amplification module  120 A illustrated in  FIG. 4  are denoted by the same symbols and description thereof is omitted. 
     The power amplification module  120 E includes a voltage source  1800  instead of the current source  450  of the power amplification module  120 A. The voltage source  1800  (third voltage source) outputs a voltage V 4  (fourth voltage) on the basis of the voltage Vramp. The voltage V 4  is supplied to the collector of the transistor  600  that forms the bias circuit  430 . The voltage V 4  is similarly supplied to the bias circuits  431  and  432 . In the power amplification module  120 E, the gains of the amplifiers  400  to  402  are controlled by the voltage V 4  being controlled in accordance with the voltage Vramp. The transmission signal is subjected to slope control as a result of the gains of the amplifiers  400  to  402  being controlled. 
       FIG. 19  illustrates an example of the configuration of the voltage source  1800 . Elements that are the same as those of the current source  450  illustrated in  FIG. 9  are denoted by the same symbols and description thereof is omitted. 
     The voltage source  1800  includes an output driver circuit  1900  instead of the output driver circuit  920  of the current source  450 . The output driver circuit  1900  has the same configuration as the output driver circuit  920  except that the output driver circuit  1900  does not include the p-channel MOSFET (MP 10 ) and the resistor R 3  of the output driver circuit  920 . 
     As described in the description of the current source  450 , the voltage Va 1  supplied to the non-inverting input terminal of the operational amplifier OP 2  is (Iout+Ioff)×R 2 . In addition, the current Iout is a current that corresponds to the voltage Vramp. Therefore, the voltage V 4  (=Va 1 ) of the inverting output terminal of the operational amplifier OP 2  is a voltage that corresponds to the voltage Vramp. Then, since the current Iout changes in a substantially square relationship with respect to the voltage Vramp, the voltage V 4  also changes in a substantially square relationship with respect to the voltage Vramp. 
       FIG. 20  illustrates the configuration of a power amplification module  120 F, which is an example of the power amplification module  120 . Constituent elements that are the same as those of the power amplification module  120 A illustrated in  FIG. 4  are denoted by the same symbols and description thereof is omitted. 
     The power amplification module  120 F includes a level detection circuit  2000 A and a voltage control circuit  2010  in addition to the elements included in the power amplification module  120 A. 
     The level detection circuit  2000 A is a circuit that outputs a detected voltage Vdet that corresponds to the amplified signal RFout. In the configuration illustrated in  FIG. 20 , the level detection circuit  2000 A includes a coupler  2020  and a detector  2030 . 
     The coupler  2020  extracts and then outputs part of the amplified signal RFout output from the amplifier  402 . 
     The detector  2030  detects the signal extracted by the coupler  2020 , converts the extracted signal into a voltage and inputs the voltage to the voltage control circuit  2010 . The detected voltage Vdet output from the detector  2030  has a level that corresponds to the amplified signal RFout. 
     The voltage control circuit  2010  is a circuit that controls a voltage Vapc (level control voltage) on the basis of the voltage Vramp (reference voltage) and the detected voltage Vdet. In the configuration illustrated in  FIG. 20 , the voltage control circuit  2010  includes a differential amplifier  2040  and an error amplifier  2050 . 
     The differential amplifier  2040  amplifies the difference between the detected voltage Vdet input to the non-inverting input terminal thereof and an offset voltage Voff input to the inverting input terminal thereof and outputs a voltage Vfb. The level of the detected voltage Vdet input to the non-inverting input terminal corresponds to the level of the amplified signal RFout and therefore the level of the voltage Vfb also corresponds to the level of the amplified signal RFout. 
     The error amplifier  2050  outputs the voltage Vapc (level control voltage) obtained by amplifying the difference (error) between the voltage Vramp input to the non-inverting input terminal thereof and the voltage Vfb input to the inverting input terminal thereof. The current source  450  outputs the current I 1  corresponding to the voltage Vapc. 
     In the power amplification module  120 F, the level detection circuit  2000 A and the voltage control circuit  2010  form a feedback circuit that controls the voltage Vapc (level control voltage) such that the amplified signal RFout comes to have a level that corresponds to the voltage Vramp (reference voltage). Thus, variations in gain caused by changes in the power supply voltage, the temperature, the output load and so forth can be suppressed by using the feedback circuit. A feedback circuit may be similarly added to the power amplification modules  120 B to  120 E as well. 
     In addition, although the configuration for the case of a 3-stage amplifier is depicted in the power amplification module  120 F illustrated in  FIG. 20 , the same configuration as in  FIG. 20  can be also adopted for the output of the final-stage amplifier in configurations where there is a different number of stages. The same is true for the other level detection circuits  2000 B to  2000 E described below. 
       FIG. 21  illustrates the configuration of a level detection circuit  2000 B, which is a modification of the level detection circuit  2000 A. Constituent elements that are the same as those of the power amplification module  120 F illustrated in  FIG. 20  are denoted by the same symbols and description thereof is omitted. In addition, an RF signal input to the amplifier  402  is denoted as RFin′. 
     As illustrated in  FIG. 21 , the level detection circuit  2000 B includes capacitors C 1  and C 2  and a low pass filter (LPF)  2100 . 
     One end of the capacitor C 1  is connected to one end of the matching network  423  and the other end of the capacitor C 1  is connected to one end of the capacitor C 2 . The other end of the capacitor C 2  is grounded. The amplified signal RFout is supplied to the one end of the capacitor C 1 . Thus, the voltage at the connection point between the capacitors C 1  and C 2  is at a level that corresponds to the signal level of the amplified signal RFout. 
     One end of the low pass filter  2100  is connected to a connection point between the capacitors C 1  and C 2  and the low pass filter  2100  outputs the detected voltage Vdet from the other end thereof. The low pass filter  2100  smooths and then outputs the voltage generated at the connection point between the capacitors C 1  and C 2 . For example, the low pass filter  2100  can be formed by using a resistor and a capacitor, for example. 
     In the level detection circuit  2000 B, a detected voltage Vdet that corresponds to the signal level of the amplified signal RFout is output by detecting the voltage at the connection point between the capacitors C 1  and C 2 . Therefore, in this configuration as well, a feedback circuit can be formed that controls the voltage Vapc (level control voltage) such that the amplified signal RFout comes to have a level that corresponds to the voltage Vramp (reference voltage). 
       FIG. 22  illustrates the configuration of a level detection circuit  2000 C, which is another modification of the level detection circuit  2000 A. Constituent elements that are the same as those of the power amplification module  120 F illustrated in  FIG. 20  are denoted by the same symbols and description thereof is omitted. 
     As illustrated in  FIG. 22 , the level detection circuit  2000 C includes n diodes  2200 ,  2201 , . . . ,  220   n  and a low pass filter  2100 . 
     The diodes  2200 ,  2201 , . . .  220   n  are connected in series with one another. The amplified signal RFout is supplied to the anode of the diode  2200  and the cathode of the diode  220   n  is grounded. Transistors, which each have the collector and the base thereof connected to each other (diode connected), may be used instead of the diodes  2200 ,  2201 , . . .  220   n.    
     One end of the low pass filter  2100  is connected between any of the diodes  2200 ,  2201 , . . .  220   n  and the low pass filter  2100  outputs the detected voltage Vdet from the other end thereof. In the example illustrated in  FIG. 22 , the one end of the low pass filter  2100  is connected to the anode of the diode  220   n  that is closest to the ground, but the position at which the one end of the low pass filter  2100  is connected is not limited to this. 
     In the level detection circuit  2000 C, a detected voltage Vdet that corresponds to the signal level of the amplified signal RFout is output by detecting the voltage between any of the diodes. Therefore, in this configuration as well, a feedback circuit can be formed that controls the voltage Vapc (level control voltage) such that the amplified signal RFout comes to have a level that corresponds to the voltage Vramp (reference voltage). The number (n) of diodes can be appropriately chosen in accordance with the range of the signal level of the amplified signal RFout. 
       FIG. 23  illustrates the configuration of a level detection circuit  2000 D, which is another modification of the level detection circuit  2000 A. Constituent elements that are the same as those of the power amplification module  120 F illustrated in  FIG. 20  are denoted by the same symbols and description thereof is omitted. 
     As illustrated in  FIG. 23 , the level detection circuit  2000 D includes a transistor  503 , a resistor R 4  and a low pass filter  2100 . 
     The amplifier  402  includes a transistor  502  similarly to the amplifier  400  illustrated in  FIG. 5 . A RF signal RFin′ is input to the base of the transistor  502  via a capacitor C 3 . In addition, a bias current Ibias 3  is supplied to the base of the transistor  502  via a resistor R 5 . The transistor  503  is replica circuit that is provided in order to detect the signal level of the amplified signal RFout that flows to the collector of the transistor  502 . The collector of the transistor  503  is connected to the collector of the transistor  502  and the emitter of the transistor  503  is grounded (has a common emitter) via the resistor R 4 . The RF signal RFin′ is input to the base of the transistor  503  via a capacitor C 4 . In addition, the bias current Ibias 3  is supplied to the base of the transistor  503  via a resistor R 6 . The transistor  503  can be made to have a smaller size than the transistor  502 . For example, in the case where the transistors are formed using a plurality of unit transistors (fingers), the number of fingers of the transistor  502  can be made to be N (&gt;1) and the number of fingers of the transistor  503  can be made to be 1. 
     Here, the RF signal RFin′ is divided between the transistors  502  and  503  in accordance with the capacitance ratio between the capacitors C 3  and C 4 . In addition, the resistors R 5  and R 6  adjust the bias currents supplied to the bases of the transistors  502  and  503  on the basis of the bias current Ibias 3 . The resistance values of the resistors R 5  and R 6  can be chosen so that the transistors  502  and  503  come to have the same current densities. Thus, currents of sizes that correspond to the ratio between the sizes of the transistors  502  and  503  can be supplied to the transistors  502  and  503 . In other words, the current that flows through the transistor  503  has a size that corresponds to the signal level of the amplified signal RFout. 
     The resistor R 4  is a resistor (detection resistor) that is provided in order to detect the current that flows to the transistor  503  and is provided between the emitter of the transistor  503  and the ground. The resistance value of the resistor R 4  may be around several ohms, for example. 
     One end of the low pass filter  2100  is connected to the emitter of the transistor  503  and the low pass filter  2100  outputs the detected voltage Vdet from the other end thereof. 
     As described above, the level detection circuit  2000 D can supply to the transistor  503  a current that corresponds to the current that flows through the transistor  502 . A voltage that corresponds to the signal level of the amplified signal RFout can be detected by changing the current output from the emitter of the transistor  503  into a voltage using the resistor R 4 . Furthermore, by making the transistor  503  that forms the replica circuit smaller than the transistor  502 , power loss can be suppressed compared with a configuration where the current that flows to the transistor  502  is directly measured. In this configuration as well, a feedback circuit can be formed that controls the voltage Vapc (level control voltage) such that the amplified signal RFout comes to have a level that corresponds to the voltage Vramp (reference voltage). 
       FIG. 24  illustrates the configuration of a level detection circuit  2000 E, which is another modification of the level detection circuit  2000 A. Constituent elements that are the same as those of the power amplification module  120 F illustrated in  FIG. 20  are denoted by the same symbols and description thereof is omitted. 
     As illustrated in  FIG. 24 , the level detection circuit  2000 E includes the transistor  503 , p-channel MOSFETs (MP 12  and MP 13 ), a resistor R 7  and the low pass filter  2100 . 
     The transistor  503  forms a replica circuit that replicates the transistor  502  similarly to as in the above-described level detection circuit  2000 D. The collector of the transistor  503  is connected to the drain of the p-channel MOSFET (MP 12 ). The transistor  503  has a common emitter. The configuration of the base of the transistor  503  is the same as in the level detection circuit  2000 D and therefore detailed description thereof is omitted here. 
     The p-channel MOSFETs (MP 12  and MP 13 ) are connected to each other in a current mirroring manner. Specifically, the p-channel MOSFET (MP 12 ) has the power supply voltage Vcc supplied to the source thereof, the gate thereof is connected to the drain thereof and the drain thereof is connected to the collector of the transistor  503 . The p-channel MOSFET (MP 13 ) has the power supply voltage Vdd supplied to the source thereof, the gate thereof is connected to the gate of the p-channel MOSFET (MP 12 ) and the drain thereof is connected to the resistor R 7 . 
     The resistor R 7  is a resistor (detection resistor) that is provided in order to detect the current that flows to the p-channel MOSFET (MP 13 ) and is provided between the drain of the p-channel MOSFET (MP 13 ) and the ground. 
     One end of the low pass filter  2100  is connected to the drain of the p-channel MOSFET (MP 13 ) and the low pass filter  2100  outputs the detected voltage Vdet from the other end thereof. 
     In the level detection circuit  2000 E, a current that corresponds to the current that flows through the transistor  502  flows to the transistor  503 , similarly to as in the level detection circuit  2000 D. Furthermore, as a result of the p-channel MOSFETs (MP 12  and MP 13 ) being connected to each other in a current mirroring manner, the current that flows through the p-channel MOSFET (MP 13 ) has a size that corresponds to the current that flows through the p-channel MOSFET (MP 12 ). Therefore, the current that flows through the p-channel MOSFET (MP 13 ) has a size that corresponds to the current that flows through the transistor  502 . Thus, a detected voltage Vdet that corresponds to the signal level of the amplified signal RFout is output. Therefore, in this configuration as well, a feedback circuit can be formed that controls the voltage Vapc (level control voltage) such that the amplified signal RFout comes to have a level that corresponds to the voltage Vramp (reference voltage). 
     Exemplary embodiments of the present disclosure have been described above. In the power amplification modules  120 A and  120 B, the current I 1  output from the current source  450  is supplied to the collectors of the transistors that form the bias circuits  430  to  432 . A transmission signal is subjected to slope control by controlling the current I 1  in accordance with the voltage Vramp. Thus, with the power amplification modules  120 A and  120 B, a transmission signal can be subjected to slope control without the use of a LDO regulator. Therefore, an increase in circuit scale can be suppressed compared with the case where an LDO regulator is used. 
     Furthermore, in the power amplification modules  120 A to  120 D, the current I 1  changes in a substantially square relationship with respect to the voltage Vramp. Thus, the bias currents Ibias 1  to Ibias 3  can be made to change as illustrated in  FIG. 8 . Therefore, as illustrated in  FIG. 2 , it is easy to control the level of the transmission signal so that the change in the level is not too steep in a region where the transmission signal rises and to control the level of the transmission signal so that the change in the level is not too gentle in the region where the transmission signal falls. 
     In the power amplification modules  120 A to  120 B, the current I 1  changes in a substantially square relationship with respect to the voltage Vramp, but the current I 1  is not limited to changing in this type relationship so long as the current I 1  changes in response to the voltage Vramp. For example, the current I 1  may change in a substantially third power or higher relationship with respect to the voltage Vramp. In addition, the current I 1  may change in a substantially proportional relationship with respect to the voltage Vramp, for example. 
     In addition, in the power amplification module  120 B, a constant voltage V 2  (for example, around 1.0 V) is supplied to the bias circuits  430  to  432 . Parasitic capacitances and bypass capacitors can be charged by the voltage V 2 . Therefore, the response time for the voltage Vramp after starting slope control of the transmission signal can be shortened. 
     Furthermore, in the power amplification module  120 C, the switch circuit  1600  outputs the current I 1  from the current source  450  in the case of the GSM operation mode and outputs the power supply voltage Vcc in the case of the EDGE operation mode. Thus, the power amplification module  120 C can support the EDGE mode. 
     In addition, in the power amplification module  120 D, the voltage V 3  (for example, around 1.0 V) is supplied to the bias circuits  430  to  432  in the case where the voltage Vramp is smaller than a prescribed level (for example, 0.2 V) and the current I 1  that corresponds to the voltage Vramp is supplied to the bias circuits  430  to  432  in the case where the voltage Vramp is larger than a prescribed level (for example 0.2 V). Thus, parasitic capacitances and bypass capacitors can be charged before starting the slope control of the transmission signal. Therefore, the response time for the voltage Vramp after starting slope control of the transmission signal can be shortened. 
     Furthermore, in the power amplification module  120 D, the voltage V 3  (for example, power supply voltage Vcc) output from the voltage source  1700  is supplied to the bias circuits  430  to  432  in the case of the EDGE mode. Thus, the EDGE mode can be supported. 
     In addition, in the power amplification module  120 E, the voltage V 4  output from the voltage source  1800  is supplied to the collectors of the transistors that form the bias circuits  430  to  432 . A transmission signal is subjected to slope control by controlling the voltage V 4  in accordance with the voltage Vramp. Thus, with the power amplification module  120 E, a transmission signal can be subjected to slope control without the use of a LDO regulator. Therefore, an increase in circuit scale can be suppressed compared with the case where an LDO regulator is used. 
     In addition, in the power amplification module  120 E, the voltage V 4  changes in a substantially square relationship with respect to the voltage Vramp. Thus, the bias currents Ibias 1  to Ibias 3  can be made to change as illustrated in  FIG. 8 . Therefore, as illustrated in  FIG. 2 , it is easy to control the level of the transmission signal so that the change in the level is not too steep in a region where the transmission signal rises and to control the level of the transmission signal so that the change in the level is not too gentle in the region where the transmission signal falls. 
     In the power amplification module  120 E, the voltage V 4  changes in a substantially square relationship with respect to the voltage Vramp, but the voltage V 4  is not limited to changing in this type relationship so long as the voltage V 4  changes in response to the voltage Vramp. For example, the voltage V 4  may change in a substantially third power or higher relationship with respect to the voltage Vramp. In addition, the voltage V 4  may change in a substantially proportional relationship with respect to the voltage Vramp, for example. 
     Furthermore, in the power amplification module  120 F, the detected voltage Vdet that corresponds to the signal level of the amplified signal RFout is output from the level detection circuit  2000 A and the voltage Vapc that corresponds to the detected voltage Vdet is output from the voltage control circuit  2010 . Thus, feedback control is performed such that the voltage Vapc input to the current source  450  comes to have a level that corresponds to the amplified signal RFout. Thus, with the power amplification module  120 F, variations in gain caused by changes in the power supply voltage, the temperature, the output load and so forth can be suppressed. 
     The purpose of the embodiments described above is to enable easy understanding of the present disclosure and the embodiments are not to be interpreted as limiting the present disclosure. The present disclosure can be changed or improved without departing from the gist of the disclosure and equivalents to the present disclosure are also included in the present disclosure. In other words, appropriate design changes made to the embodiments by a person skilled in the art are included in the scope of the present disclosure so long as the changes have the characteristics of the present disclosure. For example, the elements included in the embodiments and the arrangements, materials, conditions, shapes, sizes and so forth of the elements are not limited to those exemplified in the embodiments and can be appropriately changed. In addition, the elements included in the embodiments can be combined as much as technically possible and such combined elements are also included in the scope of the present disclosure so long as the combined elements have the characteristics of the present disclosure. 
     While embodiments of the disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The scope of the disclosure, therefore, is to be determined solely by the following claims.