Power amplifier module and power amplification method

An amplifier transistor operates in two operation modes having different characteristics. A first bias circuit including a first bias supply transistor supplies an output current of the first bias supply transistor to the amplifier transistor as a bias current. A second bias circuit including a second bias supply transistor supplies a portion of an output current of the second bias supply transistor to the amplifier transistor as a bias current. At least one of the first bias circuit and the second bias circuit is selected and operates in accordance with an operation mode of the amplifier transistor by using a bias control signal input to a bias control terminal. The second bias circuit includes a current path along which a portion of the output current of the second bias supply transistor is returned to the second bias circuit.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2019-195308 filed on Oct. 28, 2019. The content of this application is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to a power amplifier module and a power amplification method. A mobile communication device, such as a mobile terminal includes a power amplifier module to amplify the power of a signal to be transmitted to a base station. A mobile terminal and the like are required to reduce power consumption to increase the length of time during which communication is possible. To reduce power consumption, an envelope tracking (ET) scheme may be used for a power amplifier module in a mobile terminal and the like. Also, an average power tracking (APT) scheme may be used to enhance the linearity of the relationship (AM-AM) between the input amplitude and the output amplitude during a low-power operation. Accordingly, a single amplifier circuit may have a mode of operation in accordance with the ET scheme and a mode of operation in accordance with the APT scheme.

Japanese Unexamined Patent Application Publication No. 2016-192590 discloses a power amplifier module having a mode of operation in accordance with the ET scheme and a mode of operation in accordance with the APT scheme. In the power amplifier module, a bias circuit supplies a bias current to the base of an amplifier transistor from a bias power supply via a base ballast resistor. The bias circuit has a function of making the resistance value of the base ballast resistor different depending on the operation mode of the power amplifier module.

A power amplifier module configured to operate in accordance with the APT scheme may have two operation modes, namely, a low output mode and a high output mode. For example, the operation mode of the power amplifier module is switched between the low output mode and the high output mode in accordance with the output signal level. In the low output mode and the high output mode, the base ballast resistor of the bias circuit has different resistance values.

As described above, in the existing power amplifier module having a function of switching between two operation modes and operating in one of the two operation modes, the resistance value of the base ballast resistor of the bias circuit is switched in accordance with the operation mode of the power amplifier module.

BRIEF SUMMARY

If the requirements for the characteristics of the power amplifier module are stringent in each of the two operation modes, it is difficult to meet the requirements merely by switching the resistance value of the base ballast resistor of the bias circuit. Accordingly, the present disclosure provides a power amplifier module having a function of operating in at least two operation modes, in which the characteristics of the power amplifier module for each of the two operation modes can be exploited. The present disclosure further provides a power amplification method using the power amplifier module.

According to embodiments of the present disclosure, a power amplifier module includes an amplifier transistor that amplifies an input signal and outputs the amplified signal and that operates in at least two operation modes having different characteristics, a first bias circuit that includes a first bias supply transistor and that supplies an output current of the first bias supply transistor to the amplifier transistor as a bias current, a second bias circuit that includes a second bias supply transistor and that supplies a portion of an output current of the second bias supply transistor to the amplifier transistor as a bias current, and a bias control terminal that receives a bias control signal for selecting and operating at least one of the first bias circuit and the second bias circuit in accordance with an operation mode of the amplifier transistor. The second bias circuit includes a current path along which a portion of the output current of the second bias supply transistor is returned to the second bias circuit.

According to embodiments of the present disclosure, a power amplification method is a method for operating a power amplifier module to perform power amplification. The power amplifier module includes an amplifier transistor that amplifies an input signal and outputs the amplified signal, a first bias circuit that includes a first bias supply transistor and that supplies an output current of the first bias supply transistor to the amplifier transistor as a bias current, and a second bias circuit that includes a second bias supply transistor and that supplies a portion of an output current of the second bias supply transistor to the amplifier transistor as a bias current, the second bias circuit including a current path along which a portion of the output current of the second bias supply transistor is returned to the second bias circuit. The power amplification method includes supplying a bias current from the first bias circuit to the amplifier transistor when the amplifier transistor is caused to operate in accordance with an envelope tracking scheme; and supplying a bias current from the second bias circuit to the amplifier transistor when the amplifier transistor is caused to operate in accordance with an average power tracking scheme.

According to embodiments of the present disclosure, a power amplification method is a method for operating a power amplifier module to perform power amplification. The power amplifier module includes an amplifier transistor that amplifies an input signal and outputs the amplified signal, a first bias circuit that includes a first bias supply transistor and that supplies an output current of the first bias supply transistor to the amplifier transistor as a bias current, and a second bias circuit that includes a second bias supply transistor and that supplies a portion of an output current of the second bias supply transistor to the amplifier transistor as a bias current, the second bias circuit including a current path along which a portion of the output current of the second bias supply transistor is returned to the second bias circuit. The power amplification method includes switching between a state of supplying a bias current from the first bias circuit to the amplifier transistor and a state of supplying a bias current from both the first bias circuit and the second bias circuit to the amplifier transistor in accordance with a signal level output from the amplifier transistor.

Since a portion of the output current of the second bias supply transistor is returned to the second bias circuit along the current path, the second bias circuit can perform feedback control by using the returned current. At least one of the first bias circuit and the second bias circuit capable of performing feedback control is selected and operates in accordance with the operation mode of the amplifier transistor, and thus the characteristics of each operation mode can be utilized as desired.

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.

DETAILED DESCRIPTION

First Exemplary Embodiment

A power amplifier module according to a first exemplary embodiment will be described with reference toFIGS. 1 to 3 and 4A and 4B.

FIG. 1is an equivalent circuit diagram of an amplifier circuit element45in the power amplifier module according to the first exemplary embodiment. The amplifier circuit element45includes a power-stage amplifier circuit10, a driver-stage amplifier circuit11, a first bias circuit20and a second bias circuit30for the power stage, and a driver-stage bias circuit40for the driver stage. The amplifier circuit element45further includes an input-side impedance matching circuit12, an inter-stage impedance matching circuit13, a plurality of external terminals81,82,83,84,85,86, and87, and a plurality of external terminals for ground. The plurality of external terminals81,82,83,84,85,86, and87, and the plurality of external terminals for ground are each implemented as a Cu pillar bump, for example. The plurality of components described above are formed on a single semiconductor chip, for example. InFIG. 1, the external terminals for ground are not given reference numerals.

A radio-frequency (RF) input signal RFin is input from the external terminal85. The RF input signal RFin is input to the driver-stage amplifier circuit11via the input-side impedance matching circuit12. A signal amplified by the driver-stage amplifier circuit11is input to the power-stage amplifier circuit10via the inter-stage impedance matching circuit13. A signal Pout amplified by the power-stage amplifier circuit10is output from the external terminal87.

The power-stage amplifier circuit10includes an amplifier transistor Q1, a direct current (DC) cut capacitor C1, and a base ballast resistor R1. The amplifier transistor Q1is constituted by a plurality of transistor cells connected in parallel with each other. The DC cut capacitor C1and the base ballast resistor R1are disposed for each of the transistor cells. The emitter of the amplifier transistor Q1is grounded. The collector of the amplifier transistor Q1is connected to the external terminal87. Each of the plurality of transistor cells is configured as a heterojunction bipolar transistor (HBT), for example.

The DC cut capacitor C1is connected to the base of the amplifier transistor Q1, and an RF signal amplified by the driver-stage amplifier circuit11is input to the base of the amplifier transistor Q1via the DC cut capacitor C1. A base bias current is supplied to the base of the amplifier transistor Q1from the first bias circuit20and the second bias circuit30via the base ballast resistor R1. A power supply voltage is supplied to the collector of the amplifier transistor Q1from the external terminal87.

The driver-stage amplifier circuit11includes an amplifier transistor Q2, a DC cut capacitor C2, and a base ballast resistor R2. The driver-stage amplifier circuit11has a configuration similar to that of the power-stage amplifier circuit10. A power supply voltage Vcc2is supplied to the collector of the amplifier transistor Q2from the external terminal86.

The first bias circuit20and the second bias circuit30supply a bias current to the base of the amplifier transistor Q1via the base ballast resistor R1. The driver-stage bias circuit40supplies a bias current to the base of the amplifier transistor Q2via the base ballast resistor R2.

Next, the circuit configuration of the first bias circuit20will be described. The first bias circuit20includes a first bias supply transistor Q11and transistors Q12and Q13. The first bias supply transistor Q11and the transistors Q12and Q13are each a heterojunction bipolar transistor, by way of example.

The collector of the first bias supply transistor Q11is connected to the external terminal84. A bias power supply voltage Vbat is applied to the external terminal84, and thus the bias power supply voltage Vbat is applied to the collector of the first bias supply transistor Q11. The emitter of the first bias supply transistor Q11is connected to the base ballast resistor R1via an output resistor R12. The output resistor R12may be removed. The first bias supply transistor Q11constitutes an emitter-follower circuit, and all of the emitter current is supplied to the amplifier transistor Q1as a bias current. A circuit that supplies all of the emitter current to the amplifier transistor Q1as a bias current, such as the first bias circuit20, is referred to herein as “emitter-follower-type bias circuit”.

The base and collector of each of the transistors Q12and Q13are short-circuited. A connection of a transistor whose base and collector are short-circuited is referred to as diode connection, and each of the transistors Q12and Q13operates as a diode.

A resistor R11and the transistors Q12and Q13are connected in series in this order between the external terminal81and ground. A forward voltage is applied to the diodes constituted by the transistors Q12and Q13. The external terminal81is connected to a variable current source. The variable current source generates, for example, a bias control signal IB1for the amount of current corresponding to the output power of the power-stage amplifier circuit10and outputs the bias control signal IB1. Since the transistors Q12and Q13operate as diodes, a voltage of a predetermined level (for example, about 2.6 V) is generated between the collector and base of the transistor Q12.

The base of the first bias supply transistor Q11and the base of the transistor Q12are connected to each other. The base of the first bias supply transistor Q11and the base of the transistor Q12are grounded via a bypass capacitor C11.

Next, the operation of the first bias circuit20will be described.

When the bias control signal IB1is supplied from the variable current source connected to the external terminal81, a voltage corresponding to the amount of voltage drop generated across a series circuit of the transistors Q12and Q13is applied to the base of the first bias supply transistor Q11. An emitter current (output current) flows through the first bias supply transistor Q11in accordance with the voltage applied to the base of the first bias supply transistor Q11. The emitter current is supplied to the base of the amplifier transistor Q1via the output resistor R12and the base ballast resistor R1as a bias current.

When the bias control signal IB1is not supplied to the external terminal81, the first bias supply transistor Q11is turned off. Accordingly, no bias current is supplied to the base of the amplifier transistor Q1from the first bias circuit20.

Next, the circuit configuration of the second bias circuit30will be described. The second bias circuit30includes a second bias supply transistor Q21and transistors Q22and Q23. The second bias supply transistor Q21and the transistors Q22and Q23are each a heterojunction bipolar transistor, by way of example.

The collector of the second bias supply transistor Q21is connected to the external terminal84, and the bias power supply voltage Vbat is applied to the collector of the second bias supply transistor Q21. The emitter of the second bias supply transistor Q21is connected to the base ballast resistor R1and is also connected to the base of the transistor Q23via a resistor R22. The resistor R22functions as a current path along which a portion of the emitter current of the second bias supply transistor Q21is returned to the second bias circuit30. A circuit including a current path along which a portion of the emitter current of the second bias supply transistor Q21is returned to the second bias circuit30, such as the second bias circuit30, is referred to herein as “feedback-type bias circuit”.

The transistor Q22is diode-connected and operates as a diode. The base and collector of the transistor Q23are connected to each other via a capacitor C22. A resistor R21and the transistors Q22and Q23are connected in series in this order between the external terminal82and ground. Each of the transistors Q22and Q23is connected in such a manner that the emitter thereof is close to ground.

The external terminal82is connected to a variable current source, and a bias control signal IB2, which is a constant current, is supplied from the external terminal82to the resistor R21. The base of the second bias supply transistor Q21and the base of the transistor Q22are connected to each other. The base of the second bias supply transistor Q21and the base of the transistor Q22are grounded via a bypass capacitor C21.

Next, the operation of the second bias circuit30will be described.

When the bias control signal IB2is supplied from the variable current source connected to the external terminal82, a voltage corresponding to the amount of voltage drop generated across the series circuit of the transistors Q22and Q23is applied to the base of the second bias supply transistor Q21. An emitter current (output current) flows through the second bias supply transistor Q21in accordance with the voltage applied to the base of the second bias supply transistor Q21. A portion of the emitter current is supplied to the base of the amplifier transistor Q1via the base ballast resistor R1as a bias current.

When the output power of the amplifier transistor Q1increases, the bias current supplied from the emitter of the second bias supply transistor Q21to the base of the amplifier transistor Q1increases, resulting in an increase in the emitter voltage of the second bias supply transistor Q21. At this time, the base voltage of the transistor Q23also increases through the resistor R22. Accordingly, the amount of current flowing through the transistor Q23increases, and the collector voltage of the transistor Q22decreases. In response to the decrease in the collector voltage of the transistor Q22, the base voltage of the second bias supply transistor Q21decreases, and the amount of current flowing through the second bias supply transistor Q21decreases.

Accordingly, in the second bias circuit30, when the output power of the amplifier transistor Q1increases and the emitter current of the second bias supply transistor Q21increases, negative feedback control to decrease the emitter current of the second bias supply transistor Q21is performed through the resistor R22. As a result, the emitter current of the second bias supply transistor Q21is stabilized.

When the bias control signal IB2is not supplied to the external terminal82, the second bias supply transistor Q21is turned off. Thus, no bias current is supplied to the base of the amplifier transistor Q1from the second bias circuit30.

The capacitor C22connects an RF signal flowing from the power-stage amplifier circuit10to ground for alternating current (AC) via the transistor Q23. Thus, the base current of the transistor Q23is less affected by the RF signal.

Next, the circuit configuration of the driver-stage bias circuit40will be described. The driver-stage bias circuit40includes a bias supply transistor Q31, a resistor R31, transistors Q32and Q33, and a bypass capacitor C31. The basic circuit configuration of the driver-stage bias circuit40is substantially the same as the circuit configuration of the first bias circuit20.

A bias control signal IB3is supplied to the resistor R31from a variable current source connected to the external terminal83. The emitter current of the bias supply transistor Q31is supplied to the base of the amplifier transistor Q2of the driver-stage amplifier circuit11as a bias current.

FIG. 2is a block diagram of a power amplifier module50according to the first exemplary embodiment. The power amplifier module50according to the first exemplary embodiment includes the amplifier circuit element45(FIG. 1), an output-side impedance matching circuit60, and inductors L1and L2. InFIG. 2, some of the components of the amplifier circuit element45are not illustrated. The amplifier circuit element45, the output-side impedance matching circuit60, the inductors L1and L2, and so on are mounted on a common module substrate. The power amplifier module50includes bias control terminals51,52, and53, a driver-stage power supply terminal54, a power-stage power supply terminal55, a signal input terminal56, and a signal output terminal57. The bias control terminals51,52, and53, the driver-stage power supply terminal54, the power-stage power supply terminal55, the signal input terminal56, and the signal output terminal57are mounted on the module substrate.

The external terminal85of the amplifier circuit element45is connected to the signal input terminal56. The RF input signal RFin is input to the amplifier circuit element45from the signal input terminal56. The bias control terminal53is connected to the external terminal83of the amplifier circuit element45. The bias control signal IB3is supplied from the bias control terminal53to the driver-stage bias circuit40of the amplifier circuit element45. The external terminal86of the amplifier circuit element45is connected to the driver-stage power supply terminal54via the inductor L2. The power supply voltage Vcc2is supplied to the collector of the amplifier transistor Q2of the driver-stage amplifier circuit11via the inductor L2.

The external terminals81,82, and83of the amplifier circuit element45are connected to the bias control terminals51,52, and53, respectively. The bias control terminals51,52, and53are connected to an external bias control circuit70. The bias control circuit70includes an operation mode notification terminal71. The bias control circuit70selects at least one of the bias control terminals51and52in accordance with an operation mode notification signal MODE provided to the operation mode notification terminal71. The bias control circuit70supplies the bias control signal IB1to the first bias circuit20in response to the selection of the bias control terminal51, and supplies the bias control signal IB2to the second bias circuit30in response to the selection of the bias control terminal52. Further, the bias control circuit70supplies the bias control signal IB3to the driver-stage bias circuit40via the bias control terminal53and the external terminal83.

The external terminal87of the amplifier circuit element45is connected to the power-stage power supply terminal55via the inductor L1. A power supply voltage Vreg is supplied to the collector of the amplifier transistor Q1of the power-stage amplifier circuit10via the inductor L1. The external terminal87is further connected to the signal output terminal57via the output-side impedance matching circuit60. An RF signal amplified by the power-stage amplifier circuit10is output from the signal output terminal57as an RF output signal RFout.

FIG. 3is a block diagram of a transmission module including the power amplifier module50according to the first exemplary embodiment. The transmission module includes a baseband section90, an RF section91, the power amplifier module50, a front-end section92, an antenna93, the bias control circuit70, and a power supply circuit94.

The baseband section90modulates an input signal, such as an audio signal or a data signal, in accordance with a predetermined modulation scheme and outputs the modulated signal. For example, the baseband section90performs orthogonal modulation of an input signal and outputs an IQ signal (in-phase (I) signal and quadrature (Q) signal) as a modulated signal. Further, the baseband section90outputs the operation mode notification signal MODE specifying the operation mode of the power amplifier module50to the bias control circuit70and the power supply circuit94.

For example, the operation mode notification signal MODE indicates either a first operation mode or a second operation mode. The first operation mode is a mode for operating the power-stage amplifier circuit10(FIGS. 1 and 2) of the power amplifier module50in accordance with an envelope tracking (ET) scheme, and the second operation mode is a mode for operating the power-stage amplifier circuit10(FIGS. 1 and 2) of the power amplifier module50in accordance with an average power tracking (APT) scheme. For example, when the output level of the power-stage amplifier circuit10(FIGS. 1 and 2) of the power amplifier module50is greater than or equal to a predetermined level, the baseband section90notifies the bias control circuit70and the power supply circuit94of the first operation mode corresponding to the ET scheme. When the output level of the power amplifier module50is less than the predetermined level, the baseband section90notifies the bias control circuit70and the power supply circuit94of the second operation mode corresponding to the APT scheme.

The RF section91generates, from the IQ signal input from the baseband section90, the RF input signal RFin for performing wireless transmission and outputs the RF input signal RFin to the power amplifier module50. The power amplifier module50amplifies the RF input signal RFin in accordance with the operation mode and outputs the RF output signal RFout to the front-end section92. In the operation in the first operation mode corresponding to the ET scheme, the power-stage amplifier circuit10(FIGS. 1 and 2) is supplied with a bias current from the emitter-follower-type first bias circuit20. In the operation in the second operation mode corresponding to the APT scheme, the power-stage amplifier circuit10(FIGS. 1 and 2) is supplied with a bias current from the feedback-type second bias circuit30.

The power supply circuit94supplies one of a first power supply voltage for the ET scheme and a second power supply voltage for the APT scheme to the power amplifier module50as the power supply voltage Vreg in accordance with the operation mode notification signal MODE. The power supply circuit94is supplied with a power supply voltage Vcc1.

Voltage control signals CTRL and CTR2for controlling the power supply voltage Vreg are supplied from the baseband section90to the power supply circuit94. When the power amplifier module50is caused to operate in the first operation mode corresponding to the ET scheme, the baseband section90detects the amplitude level of the modulated signal and outputs the voltage control signal CTR1corresponding to the change in the amplitude level of the modulated signal to the power supply circuit94. When the power amplifier module50is caused to operate in the second operation mode corresponding to the APT scheme, the baseband section90detects the average power of the modulated signal and outputs the voltage control signal CTR2corresponding to the average power of the modulated signal to the power supply circuit94.

In response to being notified of the first operation mode corresponding to the ET scheme by using the operation mode notification signal MODE, the power supply circuit94changes the power supply voltage Vreg with a change in the amplitude level of the modulated signal in accordance with the voltage control signal CTR1. In response to being notified of the second operation mode corresponding to the APT scheme by using the operation mode notification signal MODE, the power supply circuit94changes the power supply voltage Vreg with a change in the average power of the modulated signal in accordance with the voltage control signal CTR2.

In response to being notified of the first operation mode corresponding to the ET scheme by using the operation mode notification signal MODE, the bias control circuit70supplies the bias control signal IB1to the first bias circuit20(FIGS. 1 and 2) and does not supply the bias control signal IB2to the second bias circuit30(FIGS. 1 and 2). In response to being notified of the second operation mode corresponding to the APT scheme by using the operation mode notification signal MODE, the bias control circuit70supplies the bias control signal IB2to the second bias circuit30(FIGS. 1 and 2) and does not supply the bias control signal IB1to the first bias circuit20(FIGS. 1 and 2).

The front-end section92performs a filtering process on the input RF output signal RFout. An RF signal output from the front-end section92is transmitted from the antenna93. Further, the front-end section92switches between an RF reception signal received by the antenna93and an RF signal to be transmitted to perform transmission or reception.

Next, advantages of the first exemplary embodiment will be described with reference toFIGS. 4A and 4B.

FIG. 4Ais a graph illustrating an example of the relationship between the gain and output power of the power-stage amplifier circuit10(FIGS. 1 and 2). The horizontal axis represents output power in “dBm”, and the vertical axis represents gain in “dB”.FIG. 4Bis a graph illustrating an example of the relationship between the modulation accuracy (error vector magnitude (EVM)) and output power of the power-stage amplifier circuit10(FIGS. 1 and 2). The horizontal axis represents output power in “dBm”, and the vertical axis represents EVM in “%”. In the graphs illustrated inFIGS. 4A and 4B, the solid line indicates characteristics in the first operation mode corresponding to the ET scheme, and the broken line indicates characteristics in the second operation mode corresponding to the APT scheme.

The bias current from the first bias circuit20(FIGS. 1 and 2) is set so that gain expansion is achieved in a high output power region when the power-stage amplifier circuit10(FIGS. 1 and 2) operates in the first operation mode corresponding to the ET scheme. In the region where gain expansion is achieved, the gain shows a peak value at a peak point PP. It is desirable that the basic design of an amplifier circuit be performed using, as a compression point CP, a point at which the gain is decreased by a predetermined value, for example, about 2 dB, relative to the gain at the peak point PP. In this way, gain expansion is achieved by using the emitter-follower-type first bias circuit20(FIGS. 1 and 2), thereby making it easy to determine the gain at the peak point PP. As a result, advantageously, the compression point CP is stabilized.

The gain expansion causes a decrease in the linearity of the relationship (AM-AM) between the amplitude of the input signal and the amplitude of the output signal. Consequently, as illustrated inFIG. 4B, the EVM deteriorates in a high output power region. When the power-stage amplifier circuit10is caused to operate in the first operation mode corresponding to the ET scheme, it is desirable to perform digital predistortion (DPD) to compensate for the decrease in the linearity of AM-AM. DPD can suppress a decrease in the linearity of AM-AM in the overall amplifier circuit from the baseband section90(FIG. 3) to the signal output terminal57of the power amplifier module50(FIG. 2).

When the power-stage amplifier circuit10is caused to operate in the second operation mode corresponding to the APT scheme, gain expansion using an emitter-follower-type bias circuit causes a decrease in the linearity of AM-AM, resulting in deterioration of the EVM. In general, DPD is not performed in the operation of an amplifier circuit in accordance with the APT scheme. Thus, the deterioration of the EVM caused by the gain expansion is noticeable.

In the first exemplary embodiment, when the power-stage amplifier circuit10is caused to operate in the second operation mode corresponding to the APT scheme, the feedback-type second bias circuit30(FIGS. 1 and 2) is used. The increase in the emitter current of the second bias supply transistor Q21, which is caused by the self-bias when the output power is increased, is suppressed by the negative feedback control of the second bias circuit30. Accordingly, as illustrated inFIG. 4A, gain expansion is less likely to occur. Consequently, as illustrated inFIG. 4B, the deterioration of the EVM can be suppressed. Since the deterioration of the EVM is suppressed, it is possible to achieve a power amplifier module that meets stringent EVM requirements for the fifth-generation mobile communication system.

Next, a modification of the first exemplary embodiment will be described with reference toFIG. 5. The first bias circuit20in the power amplifier module50according to the first exemplary embodiment, which is used for ET, is not limited to the circuit configuration illustrated inFIG. 1. In the following modification, the circuit configuration of the first bias circuit20is different from the circuit configuration of the first bias circuit20of the power amplifier module50according to the first exemplary embodiment. The first bias circuit20may be a bias circuit designed such that all of the emitter current output from the first bias supply transistor Q11is supplied to the power-stage amplifier circuit10as a bias current to achieve gain expansion.

FIG. 5is an equivalent circuit diagram of the emitter-follower-type first bias circuit20in the power amplifier module50according to the modification of the first exemplary embodiment. In this modification, the emitter-follower-type first bias circuit20includes diodes D12and D13in place of the transistors Q12and Q13in the first bias circuit20(FIG. 1) of the power amplifier module50according to the first exemplary embodiment. In this modification, a voltage corresponding to the amount of voltage drop generated across the two diodes D12and D13, which are connected in series, is applied to the base of the first bias supply transistor Q11.

Also, in this modification, a base voltage of a predetermined level can be supplied to the base of the first bias supply transistor Q11in accordance with the bias control signal IB1.

Next, other modifications of the first exemplary embodiment will be described with reference toFIGS. 6A to 7C. The second bias circuit30in the power amplifier module50according to the first exemplary embodiment, which is used for APT, is not limited to the circuit configuration illustrated inFIG. 1. In the following modifications, the circuit configuration of the second bias circuit30is different from the circuit configuration of the second bias circuit30of the power amplifier module50according to the first exemplary embodiment. The second bias circuit30may be a bias circuit including a current path along which a portion of the emitter current output from the second bias supply transistor Q21is returned to the second bias circuit30such that negative feedback control is performed on the emitter current of the second bias supply transistor Q21. The second bias circuit30can be a bias circuit designed such that no gain expansion can be achieved.

FIGS. 6A to 7Bare equivalent circuit diagrams of the feedback-type second bias circuit30in the power amplifier module50according to modifications of the first exemplary embodiment. The following describes the differences from the second bias circuit30of the power amplifier module50according to the first exemplary embodiment.

In the modification illustrated inFIG. 6A, the capacitor C22is connected between the base of the transistor Q23and ground. In this configuration, an RF signal flowing from the power-stage amplifier circuit10is connected to ground for AC without necessarily the intervention of the transistor Q23.

In the modification illustrated inFIG. 6B, the transistor Q22(FIG. 1) is removed, and the collector of the transistor Q23is connected directly to the resistor R21. The collector of the transistor Q23is connected to the base of the second bias supply transistor Q21. In this configuration, a voltage corresponding to the amount of voltage drop across the transistor Q23is applied to the base of the second bias supply transistor Q21.

In the modification illustrated inFIG. 6C, as in the modification illustrated inFIG. 6A, the capacitor C22is connected between the base of the transistor Q23and ground. Also, as in the modification illustrated inFIG. 6B, the transistor Q22(FIG. 1) is removed.

In the modification illustrated inFIG. 7A, the emitter of the second bias supply transistor Q21is grounded via the resistor R22and a transistor Q24. The transistor Q23is diode-connected, and the base of the transistor Q24is connected to the base of the transistor Q23. The transistor Q23and the transistor Q24constitute a current mirror.

Also, in this modification, like the second bias circuit30(FIG. 1) in the power amplifier module50according to the first exemplary embodiment, the increase in the bias current caused by the self-bias when the output power increases is suppressed by the negative feedback control of the second bias circuit30. Consequently, advantageously, gain expansion is less likely to occur.

In the modification illustrated inFIG. 7B, the resistor R22of the second bias circuit30is connected at a different location from that in the modification illustrated inFIG. 7A. In this modification, the resistor R22is connected between the base of the transistor Q24and the base of the transistor Q23. Also, in this modification, as in the modification illustrated inFIG. 7A, advantageously, gain expansion is less likely to occur when the output power increases.

In the modification illustrated inFIG. 7C, the emitter of the second bias supply transistor Q21is grounded via a diode-connected transistor Q24. The base of the transistor Q24and the base of the transistor Q23are connected, and the transistor Q24and the transistor Q23form a current mirror.

Also, in this modification, as in the modification illustrated inFIG. 7A, advantageously, gain expansion is less likely to occur when the output power increases.

Next, still another modification of the first exemplary embodiment will be described.

In the first exemplary embodiment, the first bias circuit20(FIG. 1) and the second bias circuit30(FIG. 1) are each implemented as a heterojunction bipolar transistor. Alternatively, each of the first bias circuit20(FIG. 1) and the second bias circuit30(FIG. 1) may be implemented as a homojunction bipolar transistor, a junction field-effect transistor, a metal-insulator-semiconductor (MIS) field-effect transistor, a metal-semiconductor (MES) field-effect transistor, or the like.

In the first exemplary embodiment, furthermore, the external terminal81of the first bias circuit20(FIG. 1) and the external terminal82of the second bias circuit30(FIG. 1) are each connected to a variable current source. Alternatively, the external terminal81of the first bias circuit20(FIG. 1) and the external terminal82of the second bias circuit30(FIG. 1) may be each connected to a variable voltage source.

In the first exemplary embodiment, furthermore, the power-stage amplifier circuit10of the power amplifier module50is capable of operating in two operation modes. Alternatively, the power-stage amplifier circuit10may be capable of operating in three or more operation modes. The two operation modes include the first operation mode corresponding to the ET scheme and the second operation mode corresponding to the APT scheme. Alternatively, at least two operation modes with different relationships between the gain and output level of the power-stage amplifier circuit10may be used. For example, an operation mode based on a fixed voltage scheme or an operation mode based on a variable voltage scheme may be used.

Second Exemplary Embodiment

Next, a power amplifier module50according to a second exemplary embodiment will be described with reference toFIG. 8. In the following, the configuration common to the power amplifier module50according to the first exemplary embodiment (FIGS. 1 and 2) will not be described.

FIG. 8is a block diagram of the power amplifier module50according to the second exemplary embodiment. In the first exemplary embodiment (FIG. 2), the bias control circuit70is connected to the bias control terminals51,52, and53of the power amplifier module50. In the second exemplary embodiment, the bias control circuit70is mounted on the same module substrate as that on which the amplifier circuit element45is mounted, and is included in the power amplifier module50. In this case, the external terminals81,82, and83of the amplifier circuit element45may be regarded as bias control terminals. The operation mode notification terminal71is included in the external terminals of the power amplifier module50.

Next, advantages of the second exemplary embodiment will be described.

The second exemplary embodiment also achieves advantages similar to those in the first exemplary embodiment. Specifically, when the power-stage amplifier circuit10(FIG. 1) is caused to operate in the first operation mode corresponding to the ET scheme, the gain at the peak point PP (FIG. 4A) is easily determined. As a result, advantageously, the compression point CP (FIG. 4A) is stabilized. When the power-stage amplifier circuit10(FIG. 1) is caused to operate in the second operation mode corresponding to the APT scheme, the deterioration of the EVM can be suppressed.

Third Exemplary Embodiment

Next, a power amplifier module according to a third exemplary embodiment will be described with reference toFIGS. 9, 10A, and 10B. In the following, the configuration common to the power amplifier module according to the first exemplary embodiment (FIGS. 1, 2, and 3) will not be described.

In the first exemplary embodiment, the two operation modes of the power-stage amplifier circuit10(FIGS. 1 and 2) include the first operation mode corresponding to the ET scheme and the second operation mode corresponding to the APT scheme. In the third exemplary embodiment, the first operation mode of the power-stage amplifier circuit10(FIGS. 1 and 2) is an operation mode in which an RF output signal has low power (hereinafter referred to as “low-power operation mode”), and the second operation mode of the power-stage amplifier circuit10(FIGS. 1 and 2) is an operation mode in which an RF output signal has relatively high (hereinafter referred to as “high-power operation mode”). The low-power operation mode and the high-power operation mode have different relationships between the gain and output level of the power-stage amplifier circuit10. The relationship between the gain and output level of the power-stage amplifier circuit10in the high-power operation mode is different from the relationship between the gain and output level of the power-stage amplifier circuit10in the low-power operation mode such that in the high-power operation mode, a high gain is maintained at a higher output level than in the low-power operation mode.

FIG. 9is block diagram of a transmission module including the power amplifier module50according to the third exemplary embodiment. In the first exemplary embodiment, the power supply voltage Vreg is supplied from the power supply circuit94(FIG. 3) to the power-stage amplifier circuit10of the power amplifier module50(FIG. 1). The power supply voltage Vreg is switched between the first power supply voltage for the ET scheme and the second power supply voltage for the APT scheme in accordance with the operation mode of the power-stage amplifier circuit10(FIG. 1). In the third exemplary embodiment, the power supply voltage Vcc1for the APT scheme is supplied to the power-stage amplifier circuit10of the power amplifier module50(FIG. 1). That is, the power-stage amplifier circuit10of the power amplifier module50operates in accordance with the APT scheme.

The baseband section90outputs the operation mode notification signal MODE to the bias control circuit70in accordance with the signal level (the magnitude of the power) of the RF output signal RFout. For example, when the RF output signal RFout has a level greater than or equal to a predetermined level, the baseband section90notifies the bias control circuit70of the high-power operation mode as the operation mode. When the RF output signal RFout has a level less than the predetermined level, the baseband section90notifies the bias control circuit70of the low-power operation mode as the operation mode.

The bias control circuit70supplies at least one of the bias control signals IB1and IB2to the power amplifier module50in accordance with the operation mode indicated by the operation mode notification signal MODE. In this exemplary embodiment, in response to being notified of the low-power operation mode as the operation mode, the bias control circuit70supplies the bias control signal IB1and does not supply the bias control signal IB2. Accordingly, the first bias circuit20(FIG. 1) operates, whereas the second bias circuit30(FIG. 1) does not operate. In response to being notified of the high-power operation mode as the operation mode, the bias control circuit70supplies both the bias control signals IB1and IB2. Accordingly, both the first bias circuit20(FIG. 1) and the second bias circuit30(FIG. 1) operate.

Next, advantages of the third exemplary embodiment will be described with reference toFIGS. 10A and 10B.

FIG. 10Ais a timing chart illustrating the operating state of the first bias circuit20(FIG. 1) and the second bias circuit30(FIG. 1) in the power amplifier module50according to the third exemplary embodiment.FIG. 10Aillustrates an example in which a low-power operation mode LPM is switched to a high-power operation mode HPM and then the high-power operation mode HPM is switched to the low-power operation mode LPM.

The first bias circuit20constantly operates, regardless of the operation mode. The second bias circuit30operates only during a period corresponding to the high-power operation mode HPM. A delay time Td occurs between the start of supply of the bias control signal IB2and the start of the operation of the second bias circuit30. During the delay time Td, a bias current is supplied to the power-stage amplifier circuit10only from the first bias circuit20.

FIG. 10Bis a timing chart illustrating the operating state of the first bias circuit20and the second bias circuit30in a power amplifier module in a comparative example. In the comparative example, the bias control circuit70(FIG. 9) supplies the bias control signal IB1only to the first bias circuit20during a period corresponding to the low-power operation mode LPM, and supplies the bias control signal IB2only to the second bias circuit30during a period corresponding to the high-power operation mode HPM.

When the operation mode is switched from the low-power operation mode LPM to the high-power operation mode HPM, the operation of the first bias circuit20is stopped substantially instantaneously. A delay time Td occurs until the operation of the second bias circuit30is started. Accordingly, there is a time period during which the first bias circuit20and the second bias circuit30are not in operation. Also, when the operation mode is switched from the high-power operation mode HPM to the low-power operation mode LPM, there is a time period during which the first bias circuit20and the second bias circuit30are not in operation.

In the period during which the first bias circuit20and the second bias circuit30are not in operation, the power amplifier module50does not perform amplification, and thus the RF output signal RFout is not output. That is, instantaneous interruption of a transmission signal occurs.

In the third exemplary embodiment, in contrast, the first bias circuit20constantly operates. Thus, instantaneous interruption of a transmission signal can be prevented.

In particular, when the feedback-type second bias circuit30is in use during operation at low temperatures, at the time when the power-stage amplifier circuit10(FIG. 1) starts an amplification operation in response to the rise edge of the waveform of the RF input signal RFin, feedback control becomes unstable, and the EVM is likely to deteriorate. In the third exemplary embodiment, the emitter-follower-type first bias circuit20is caused to operate in the low-power operation mode. This can suppress the deterioration of the EVM at the rise time of the waveform of the RF input signal RFin. In the low-power operation mode, furthermore, there is substantially no influence of the self-bias. Thus, no gain expansion occurs, resulting in high linearity of AM-AM being maintained.

When the operation mode is the high-power operation mode, the feedback-type second bias circuit30also operates in addition to the first bias circuit20. Thus, gain expansion caused by an increase in the power of the RF output signal RFout is suppressed, resulting in high linearity of AM-AM being maintained.

In the first exemplary embodiment, the output resistor R12of the first bias circuit20(FIG. 1) may be removed. In contrast, as in the third exemplary embodiment, when there is a period during which both the first bias circuit20and the second bias circuit30are caused to operate simultaneously, the output resistor R12can be connected between the first bias supply transistor Q11and the base ballast resistor R1.

Next, a modification of the third exemplary embodiment will be described.

In the third exemplary embodiment, the emitter-follower-type first bias circuit20is caused to operate constantly, regardless of the operation mode. Alternatively, the operation of the first bias circuit20may be stopped in the high-power operation mode on the condition that no instantaneous interruption occurs at the time of switching between operation modes. For example, the operation of the first bias circuit20may be stopped at a point in time when a longer time than the delay time Td (FIGS. 10A and 10B) elapses from the point in time when the low-power operation mode is switched to the high-power operation mode.

It is to be understood that the exemplary embodiments described above are illustrative and that configurations provided in different embodiments may be partially replaced or combined. Similar operational effects achieved with similar configurations in a plurality of embodiments are not described in the individual embodiments. In addition, the present disclosure is not limited to the exemplary embodiments described above. It will be apparent to a person skilled in the art that, for example, various changes, improvements, combinations, and so on may be made.