Patent Publication Number: US-11031910-B2

Title: Power amplifier module

Description:
This is a continuation of U.S. patent application Ser. No. 16/371,349 filed on Apr. 1, 2019, which is a continuation of U.S. patent application Ser. No. 15/896,701 filed on Feb. 14, 2018, which claims priority from Japanese Patent Application No. 2017-028227 filed on Feb. 17, 2017. The contents of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates to a power amplifier module. In a mobile communication terminal, such as a cellular phone, a power amplifier for amplifying a radio frequency (RF) signal to be transmitted to a base station is used. As this type of power amplifier, a power amplifier including a common-emitter heterojunction bipolar transistor (HBT) which amplifies an RF signal and an emitter-follower HBT which supplies a bias signal to the base terminal of this common-emitter HBT is known, as disclosed in Japanese Unexamined Patent Application Publication No. 2007-288736. 
     BRIEF SUMMARY 
     To drive the common-emitter HBT which amplifies an RF signal, the base-emitter voltage of about 1.3 V or higher is required. Likewise, to drive the emitter-follower HBT which supplies a bias signal, the base-emitter voltage of about 1.3 V or higher is required. Hence, to operate the power amplifier, the operating voltage of about 2.6 V is required. In a mobile communication terminal, the operating voltage is supplied from a battery. In order to operate the power amplifier correctly even if the battery voltage somewhat drops, it is desirable to decrease the operating voltage. 
     Accordingly, the present disclosure decreases the operating voltage of a power amplifier module. 
     According to embodiments of the present disclosure, there is provided a power amplifier module including a power amplifier circuit and a control integrated circuit (IC). The power amplifier circuit includes a bipolar transistor that amplifies power of a radio frequency (RF) signal and outputs an amplified signal, and a diode-connected bipolar transistor that is thermally coupled with the bipolar transistor. The control IC includes a field-effect transistor and a diode-connected field-effect transistor. A drain terminal of the field-effect transistor is connected to a battery voltage, and a bias signal is input into a gate terminal of the field-effect transistor and is supplied from a source terminal of the field-effect transistor to the bipolar transistor via a first wire. A cathode of the diode-connected bipolar transistor is grounded. An anode of the diode-connected bipolar transistor is connected to a cathode of the diode-connected field-effect transistor via a second wire. An anode of the diode-connected field-effect transistor is connected to the gate terminal of the field-effect transistor. 
     According to embodiments of the present disclosure, it is possible to decrease the operating voltage of a power amplifier module. 
     Other features, elements, and characteristics 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 of the configuration of a transmit unit according to a first embodiment of the disclosure; 
         FIG. 2  illustrates an example of the configuration of a power amplifier module according to the first embodiment; 
         FIG. 3  illustrates an example of the configuration of a power amplifier module according to a second embodiment; 
         FIG. 4  illustrates an example of the configuration of a power amplifier module according to a third embodiment; and 
         FIG. 5  illustrates an example of the configuration of a power amplifier module according to a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described below with reference to the accompanying drawings. The same circuit element is designated by like reference numeral, and the same explanation thereof will not be repeated. 
       FIG. 1  illustrates an example of the configuration of a transmit unit  100  according to a first embodiment. The transmit unit  100  is used in a mobile communication device, such as a cellular phone, and for transmitting various signals, such as audio signals and data signals, to a base station. The mobile communication device also includes a receive unit for receiving signals from the base station, though an explanation thereof will be omitted. 
     The transmit unit  100  includes a modulator  110 , a power amplifier module  120 , a front-end portion  130 , and an antenna  140 . The modulator  110  modulates an input signal by using a modulation method, such as High-Speed Uplink Packet Access (HSUPA) or Long Term Evolution (LTE), so as to generate an RF signal. The frequency of the RF signal is about several hundreds of megahertz to several gigahertz. The power amplifier module  120  amplifiers power of the RF signal (RF IN ) output from the modulator  110  to a level high enough to be transmitted to a base station, and outputs the amplified signal (RF OUT ). The front-end portion  130 , which is constituted by a band pass filter and an antenna switch, for example, performs filtering on the amplified signal (RF OUT ) and switches between signal paths. The amplified signal output from the front-end portion  130  is transmitted to the base station via the antenna  140 . 
       FIG. 2  illustrates an example of the configuration of the power amplifier module  120  according to the first embodiment. The power amplifier module  120  includes a power amplifier circuit  200  manufactured by a bipolar process, a control integrated circuit (IC)  300  manufactured by a metal-oxide-semiconductor (MOS) process, and wires  410 ,  420 ,  430 , and  440  for connecting the power amplifier circuit  200  and the control IC  300 . The power amplifier circuit  200  includes amplifiers  210  and  220 , matching circuits  230 ,  240 , and  250 , bipolar transistors Tr 3  and Tr 4 , and base ballast resistors R 11  and R 21 . The amplifier  220  serves as an output-stage amplifier, while the amplifier  210  serves as a driver-stage amplifier connected to the input of the amplifier  220 . Two stages of amplifiers  210  and  220  are used in the power amplifier circuit  200 . However, the number of stages of amplifiers may be determined according to the output of the amplified signal (RF OUT ). 
     The amplifier  210  includes one or plural bipolar transistors Tr 1  which amplify the RF signal (RF IN ) and output the amplified signal. The amplifier  210  may be formed in a multi-finger structure by using the bipolar transistor Tr 1  as a finger (unit transistor) in which plural fingers are connected in parallel with each other. The amplifier  220  includes one or plural bipolar transistors Tr 2  which amplify the RF signal amplified by the amplifier  210  and output the amplified signal (RF OUT ). The amplifier  220  may be formed in a multi-finger structure by using the bipolar transistor Tr 2  as a finger (unit transistor) in which plural fingers are connected in parallel with each other. The bipolar transistors Tr 1  and Tr 2  are common-emitter transistors, for example. The bipolar transistors Tr 1  and Tr 2  may be heterojunction bipolar transistors (HBTs), for example. The matching circuit  230  is connected to the input of the amplifier  210 . The matching circuit  240  is connected between the amplifiers  210  and  220 . The matching circuit  250  is connected to the output of the amplifier  220 . The matching circuits  230 ,  240 , and  250 , each performs impedance matching between the preceding-stage circuit and the following-stage circuit. 
     The control IC  300  includes field-effect transistors (FETs) Tr 5 , Tr 6 , Tr 7 , and Tr 8  and base ballast resistors R 12  and R 22 . 
     The FET Tr 5  serves as a bias circuit which supplies a bias signal Bias 1  to the amplifier  210  via the wire  410 . The drain terminal of the FET Tr 5  is connected to the battery voltage Vbat, and the bias signal Bias 1  is input into the gate terminal of the FET Tr 5  and is supplied from the source terminal to the amplifier  210  via the wire  410 . The base ballast resistor R 11  is connected between the input of the amplifier  210  and the wire  410 . Similarly, the base ballast resistor R 12  is connected between the source terminal of the FET Tr 5  and the wire  410 . When the bipolar transistor Tr 1  is a common-emitter transistor, the bias signal Bias 1  is supplied to the base terminal of the bipolar transistor Tr 1 . The bias signal Bias 1  is a bias current or a bias voltage for controlling a bias point of the bipolar transistor Tr 1 . 
     The FET Tr 6  serves as a bias circuit which supplies a bias signal Bias 2  to the amplifier  220  via the wire  430 . The drain terminal of the FET Tr 6  is connected to the battery voltage Vbat, and the bias signal Bias 2  is input into the gate terminal of the FET Tr 6  and is supplied from the source terminal to the amplifier  220  via the wire  430 . The base ballast resistor R 21  is connected between the input of the amplifier  220  and the wire  430 . Similarly, the base ballast resistor R 22  is connected between the source terminal of the FET Tr 6  and the wire  430 . When the bipolar transistor Tr 2  is a common-emitter transistor, the bias signal Bias 2  is supplied to the base terminal of the bipolar transistor Tr 2 . The bias signal Bias 2  is a bias current or a bias voltage for controlling a bias point of the bipolar transistor Tr 2 . 
     The bipolar transistor Tr 3  is a transistor in which the base terminal and the collector terminal are connected. Such a connection state is called a diode-connected state. The bipolar transistor Tr 3  behaves like a bipolar element which is equivalent to a diode. For the sake of convenience, in this specification, between the two terminals of a diode-connected bipolar transistor, the terminal having a higher potential when the diode-connected bipolar transistor is forward-biased is called an anode, while the other terminal having a lower potential when the diode-connected bipolar transistor is forward-biased is called a cathode. The anode A 3  of the diode-connected bipolar transistor Tr 3  is connected to the wire  420 , while the cathode C 3  is grounded within the power amplifier circuit  200 . Likewise, the anode A 4  of the diode-connected bipolar transistor Tr 4  is connected to the wire  440 , while the cathode C 4  is grounded within the power amplifier circuit  200 . 
     The FET Tr 7  is a transistor in which the gate terminal and the drain terminal are connected. Such a connection state is called a diode-connected state. The FET Tr 7  behaves like a bipolar element which is equivalent to a diode. For the sake of convenience, in this specification, between the two terminals of a diode-connected FET, the terminal having a higher potential when the diode-connected FET is forward-biased is called an anode, while the other terminal having a lower potential when the diode-connected FET is forward-biased is called a cathode. The anode A 7  of the diode-connected FET Tr 7  is connected to the gate terminal of the FET Tr 5 , while the cathode C 7  is connected to the wire  420 . Likewise, the anode A 8  of the diode-connected FET Tr 8  is connected to the gate terminal of the FET Tr 6 , while the cathode C 8  is connected to the wire  440 . 
     The diode-connected bipolar transistor Tr 3  is thermally coupled with one or plural bipolar transistors Tr 1 . The distance between the diode-connected bipolar transistor Tr 3  and the bipolar transistor Tr 1  is about 300 μm or smaller, for example. If the amplifier  210  is formed in a multi-finger structure, the distance between the diode-connected bipolar transistor Tr 3  and the finger of the amplifier  210  positioned closest to the diode-connected bipolar transistor Tr 3  is about 300 μm or smaller, for example. 
     Likewise, the diode-connected bipolar transistor Tr 4  is thermally coupled with one or plural bipolar transistors Tr 2 . The distance between the diode-connected bipolar transistor Tr 4  and the bipolar transistor Tr 2  is about 300 μm or smaller, for example. If the amplifier  220  is formed in a multi-finger structure, the distance between the diode-connected bipolar transistor Tr 4  and the finger of the amplifier  220  positioned closest to the diode-connected bipolar transistor Tr 4  is about 300 μm or smaller, for example. 
     The diode-connected FET Tr 7  may be thermally coupled with the FET Tr 5 . Likewise, the diode-connected FET Tr 8  may be thermally coupled with the FET Tr 6 . 
     If it is necessary to distinguish the wires  410  and  420  from each other, the wire  410  may be called a first wire, and the wire  420  may be called a second wire. Likewise, if it is necessary to distinguish the wires  430  and  440  from each other, the wire  430  may be called a first wire, and the wire  440  may be called a second wire. 
     The power amplifier module  120  according to the first embodiment achieves the following features. 
     The FETs Tr 5  and Tr 6 , which serve as bias circuits, are operable at a threshold voltage lower than that of bipolar transistors, thereby making it possible to decrease the operating voltage of the power amplifier module  120 . As a result, the power amplifier module  120  can be operated correctly for a longer time even if the battery voltage Vbat somewhat drops. 
     When the bipolar transistor Tr 1  is driven with a constant base-emitter voltage, a collector current increases due to a temperature rise. An increased collector current increases power consumption, which raises the temperature of the bipolar transistor Tr 1  and further increases the collector current. This is called positive feedback (thermal runaway). On the other hand, however, the diode-connected bipolar transistor Tr 3  and the diode-connected FET Tr 7  both exhibit temperature characteristics in which the forward voltage decreases in accordance with a temperature rise. Accordingly, the potential of the gate terminal of the FET Tr 5 , which serves as a bias circuit, decreases in accordance with a temperature rise, thereby suppressing the occurrence of thermal runaway of the bipolar transistor Tr 1 . To suppress the occurrence of thermal runaway, it is desirable, not only that the diode-connected bipolar transistor Tr 3  and the bipolar transistor Tr 1  are thermally coupled with each other, but also that the diode-connected FET Tr 7  and the FET Tr 5  are thermally coupled with each other. Likewise, the diode-connected bipolar transistor Tr 4  and the diode-connected FET Tr 8  both exhibit temperature characteristics in which the forward voltage decreases in accordance with a temperature rise. Accordingly, the potential of the gate terminal of the FET Tr 6 , which serves as a bias circuit, decreases in accordance with a temperature rise, thereby suppressing the occurrence of thermal runaway of the bipolar transistor Tr 2 . To suppress the occurrence of thermal runaway, it is desirable, not only that the diode-connected bipolar transistor Tr 4  and the bipolar transistor Tr 2  are thermally coupled with each other, but also that the diode-connected FET Tr 8  and the FET Tr 6  are thermally coupled with each other. 
     Inductor components of the wire  410  can prevent high-frequency components of the RF signal from entering the FET Tr 5 . Similarly, inductor components of the wire  430  can prevent high-frequency components of the RF signal from entering the FET Tr 6 . 
     When the diode-connected bipolar transistor Tr 3  and the bipolar transistor Tr 1  are thermally coupled and also when the diode-connected FET Tr 7  and the FET Tr 5  are thermally coupled, it is possible to reduce overshooting of a current change which may occur in the case of an excessive response of the bipolar transistor Tr 1 . Likewise, when the diode-connected bipolar transistor Tr 4  and the bipolar transistor Tr 2  are thermally coupled and also when the diode-connected FET Tr 8  and the FET Tr 6  are thermally coupled, it is possible to reduce overshooting of a current change which may occur in the case of a transient response of the bipolar transistor Tr 2 . 
       FIG. 3  illustrates an example of the configuration of a power amplifier module  150  according to a second embodiment. The power amplifier module  150  differs from the power amplifier module  120  of the first embodiment in the connection state among the diode-connected bipolar transistor Tr 3  (Tr 4 ) within the power amplifier circuit  200 , the diode-connected FET Tr 7  (Tr 8 ) within the control IC  300 , and the FET Tr 5  (Tr 6 ) within the control IC  300 . The other points of the power amplifier module  150  are the same as those of the power amplifier module  120 . The power amplifier module  150  will be described below mainly by referring to the points different from the power amplifier module  120 , and a detailed explanation of the same points will be omitted. 
     The cathode C 7  of the diode-connected FET Tr 7  is grounded within the control IC  300 . The anode A 7  of the diode-connected FET Tr 7  is connected to the cathode C 3  of the diode-connected bipolar transistor Tr 3  via a wire  450 . The anode A 3  of the diode-connected bipolar transistor Tr 3  is connected to the gate terminal of the FET Tr 5  via a wire  460 . 
     The cathode C 8  of the diode-connected FET Tr 8  is grounded within the control IC  300 . The anode A 8  of the diode-connected FET Tr 8  is connected to the cathode C 4  of the diode-connected bipolar transistor Tr 4  via a wire  470 . The anode A 4  of the diode-connected bipolar transistor Tr 4  is connected to the gate terminal of the FET Tr 6  via a wire  480 . 
     If it is necessary to distinguish the wires  410 ,  450 , and  460  from each other, the wire  410  may be called a first wire, the wire  450  may be called a second wire, and the wire  460  may be called a third wire. Likewise, if it is necessary to distinguish the wires  430 ,  470 , and  480  from each other, the wire  430  may be called a first wire, the wire  470  may be called a second wire, and the wire  480  may be called a third wire. 
     Features achieved by the power amplifier module  150  of the second embodiment are similar to those achieved by the power amplifier module  120  of the first embodiment. 
       FIG. 4  illustrates an example of the configuration of a power amplifier module  160  according to a third embodiment. The power amplifier module  160  differs from the power amplifier module  120  in that the diode-connected bipolar transistors Tr 3  and Tr 4  within the power amplifier circuit  200  of the power amplifier module  120  are replaced by diodes D 13  and D 14 , respectively, and the diode-connected FETs Tr 7  and Tr 8  within the control IC  300  of the power amplifier module  120  are replaced by diodes D 17  and D 18 , respectively. The power amplifier module  160  will be described below mainly by referring to the points different from the power amplifier module  120 , and a detailed explanation of the same points will be omitted. 
     The anode A 13  of the diode D 13  is connected to the wire  420 , while the cathode C 13  is grounded within the power amplifier circuit  200 . The anode A 17  of the diode D 17  is connected to the gate terminal of the FET Tr 5 , while the cathode C 17  is connected to the wire  420 . 
     The anode A 14  of the diode D 14  is connected to the wire  440 , while the cathode C 14  is grounded within the power amplifier circuit  200 . The anode A 18  of the diode D 18  is connected to the gate terminal of the FET Tr 6 , while the cathode C 18  is connected to the wire  440 . 
     If it is necessary to distinguish the diodes D 13  and D 17  from each other, the diode D 13  may be called a first diode, and the diode D 17  may be called a second diode. Likewise, if it is necessary to distinguish the diodes D 14  and D 18  from each other, the diode D 14  may be called a first diode, and the diode D 18  may be called a second diode. 
     Features achieved by the power amplifier module  160  of the third embodiment are similar to those achieved by the power amplifier module  120  of the first embodiment. 
       FIG. 5  illustrates an example of the configuration of a power amplifier module  170  according to a fourth embodiment. The power amplifier module  170  differs from the power amplifier module  150  of the second embodiment in that the diode-connected bipolar transistors Tr 3  and Tr 4  within the power amplifier circuit  200  of the power amplifier module  150  are replaced by diodes D 13  and D 14 , respectively, and the diode-connected FETs Tr 7  and Tr 8  within the control IC  300  of the power amplifier module  150  are replaced by diodes D 17  and D 18 , respectively. The power amplifier module  170  will be described below mainly by referring to the points different from the power amplifier module  150 , and a detailed explanation of the same points will be omitted. 
     The cathode C 17  of the diode D 17  is grounded within the control IC  300 . The anode A 17  of the diode D 17  is connected to the cathode C 13  of the diode D 13  via the wire  450 . The anode A 13  of the diode D 13  is connected to the gate terminal of the FET Tr 5  via the wire  460 . 
     The cathode C 18  of the diode D 18  is grounded within the control IC  300 . The anode A 18  of the diode D 18  is connected to the cathode C 14  of the diode D 14  via the wire  470 . The anode A 14  of the diode D 14  is connected to the gate terminal of the FET Tr 6  via the wire  480 . 
     Features achieved by the power amplifier module  170  of the fourth embodiment are similar to those achieved by the power amplifier module  150  of the second embodiment. 
     The above-described embodiments are provided for facilitating the understanding of the invention, but are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Modifications and/or improvements may be made without departing from the scope and spirit of the invention, and equivalents of the invention are also encompassed in the invention. That is, suitable design changes made to the embodiments by those skilled in the art are also encompassed in the invention within the scope and spirit of the invention. For example, the elements and the positions thereof of the embodiments are not restricted to those described in the embodiments and may be changed in an appropriate manner. 
     While preferred embodiments of the invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The scope of the invention, therefore, is to be determined solely by the following claims.