Power amplifier circuit

A power amplifier circuit includes a first amplifier that, in a region where an input signal level is a first level or higher, amplifies a signal split from an input signal and outputs an amplified signal; a first converter connected to an output side of the first amplifier and converts an impedance on the output side of the first amplifier; and at least one or more second amplifiers that, in a region where the input signal level is a second level or higher, amplify a signal split from the input signal and output an amplified signal. Output sides of the second amplifiers are connected in series with an output side of the first converter. The first converter makes an absolute value of the impedance on the output side of the first amplifier larger than absolute values of impedances on the output sides of the second amplifiers.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2020-098348 filed on Jun. 5, 2020. The content of this application is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to a power amplifier circuit.

A Doherty amplifier is a high-efficiency power amplifier. In a typical Doherty amplifier, a carrier amplifier that operates regardless of the power level of an input signal is connected in parallel with a peaking amplifier that is turned off when the power level of the input signal is low and that is turned on when the power level is high. When the power level of an input signal is high, the carrier amplifier operates at a saturation output power level while being kept in saturation. In other words, in a back-off state in which only the carrier amplifier is performing an amplification operation, only the carrier amplifier operates, and the peaking amplifier does not consume unnecessary current, thereby increasing efficiency. Furthermore, there is a load modulation effect in which, in an input power range from the minimum power at which the peaking amplifier operates to the power at which the peaking amplifier reaches saturation, the impedance of the carrier amplifier is reduced typically by half. Note that load modulation in the present disclosure refers to a reduction in load impedance of the carrier amplifier associated with an increase in output power of the peaking amplifier. When the peaking amplifier and the carrier amplifier are of the same size, a reduction in load impedance of the carrier amplifier by half is regarded as ideal. The saturation output power of the carrier amplifier has the property of being inversely proportional to the load impedance thereof, and thus the load modulation effect causes the saturation power of the carrier amplifier to increase as the output power of the peaking amplifier increases. In other words, in a power range in which the peaking amplifier is operating, the carrier amplifier is operating near saturation power all the time, and it can be said that the carrier amplifier is operating with high efficiency. That is to say, the load modulation effect is important for achieving high-efficiency operation of the Doherty amplifier.

In the Doherty amplifier, a combiner is necessary that combines an output of the carrier amplifier and an output of the peaking amplifier. In the combiner, although a quarter-wave line is used, the quarter-wave line is unsuitable for achieving miniaturization and wideband characteristics. Thus, a Doherty amplifier that does not use a quarter-wave line is disclosed (for example, see Ercan Kaymaksüt, Patrick Reynaert, “A 2.4 GHz fully integrated Doherty power amplifier using series combining transformer”, Proceedings of ESSCIRC, pp. 302-305, 2010).

A Doherty amplifier disclosed in Ercan Kaymaksüt, Patrick Reynaert, “A 2.4 GHz fully integrated Doherty power amplifier using series combining transformer”, Proceedings of ESSCIRC, pp. 302-305, 2010 is constructed without necessarily using a quarter-wave line and with two transformers. Thus, the miniaturization and wideband characteristics of the Doherty amplifier can be achieved. However, in a configuration of the Doherty amplifier disclosed in Ercan Kaymaksüt, Patrick Reynaert, “A 2.4 GHz fully integrated Doherty power amplifier using series combining transformer”, Proceedings of ESSCIRC, pp. 302-305, 2010, there is a possibility that the load modulation effect may not be able to be achieved in which the load of a carrier amplifier is reduced by half at the time of a transition from a back-off state to a saturation state. Consequently, there is a possibility that efficiency may not be able to be increased by the Doherty amplifier disclosed in Ercan Kaymaksüt, Patrick Reynaert, “A 2.4 GHz fully integrated Doherty power amplifier using series combining transformer”, Proceedings of ESSCIRC, pp. 302-305, 2010.

BRIEF SUMMARY

Thus, the present disclosure provides a power amplifier circuit in which a Doherty amplifier produces an appropriate load modulation effect without necessarily using a quarter-wave line.

A power amplifier circuit according to one aspect of the present disclosure includes a first amplifier configured to, in a region where a power level of an input signal is not less than a first level, amplify a first signal split from the input signal and output a second signal; a first converter connected to an output side of the first amplifier and configured to convert an impedance on the output side of the first amplifier; and at least one or more second amplifiers configured to, in a region where the power level of the input signal is not less than a second level higher than the first level, amplify a third signal split from the input signal and output a fourth signal. Output sides of the respective second amplifiers are connected in series with an output side of the first converter. The first converter is configured to make an absolute value of the impedance on the output side of the first amplifier larger than absolute values of impedances on the output sides of the respective second amplifiers.

A power amplifier circuit according to one aspect of the present disclosure includes a third amplifier configured to, in a region where a power level of an input signal is not less than a third level, amplify a fifth signal split from the input signal and output a sixth signal; a third converter connected to an output side of the third amplifier and configured to convert an impedance on the output side of the third amplifier; and at least one or more fourth amplifiers configured to, in a region where the power level of the input signal is not less than a fourth level higher than the third level, amplify a seventh signal split from the input signal and output an eighth signal. Output sides of the respective fourth amplifiers are connected in parallel with an output side of the third converter. The third converter is configured to make an absolute value of the impedance on the output side of the third amplifier smaller than absolute values of impedances on the output sides of the respective fourth amplifiers.

A power amplifier circuit according to one aspect of the present disclosure includes a fifth amplifier configured to, in a region where a power level of an input signal is not less than a fifth level, amplify a ninth signal split from the input signal and output a tenth signal; at least one or more sixth amplifiers configured to, in a region where the power level of the input signal is not less than a sixth level higher than the fifth level, amplify an eleventh signal split from the input signal and output a twelfth signal; and fifth converters connected to output sides of the respective sixth amplifiers and configured to convert impedances on the output sides of the respective sixth amplifiers. Output sides of the respective fifth converters are connected in series with an output side of the fifth amplifier. The respective fifth converters are configured to make an absolute value of an impedance on the output side of the fifth amplifier smaller than absolute values of the impedances on the output sides of the respective sixth amplifiers.

The present disclosure can provide the power amplifier circuit in which a Doherty amplifier produces an appropriate load modulation effect without necessarily using a quarter-wave line.

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

Embodiments of the present disclosure will be described below with reference to the drawings. Here, circuit elements denoted by the same reference numerals refer to the same circuit element, and repeated descriptions of the circuit elements are omitted.

Configuration of Power Amplifier Circuit100According to First Embodiment

A configuration of a power amplifier circuit100according to a first embodiment will be described with reference toFIGS.1to5.FIG.1is a configuration diagram illustrating a schematic configuration of the power amplifier circuit100according to the first embodiment.FIG.2is a configuration diagram illustrating a modification of the power amplifier circuit100according to the first embodiment.FIG.3is a configuration diagram illustrating an example of a converter140that can be regarded as a current source.FIG.4is a configuration diagram illustrating an example of a converter150that can be regarded as a voltage source.FIG.5is a configuration diagram illustrating an example of a configuration of the power amplifier circuit100according to the first embodiment.

The power amplifier circuit100is incorporated, for example, in a cellular phone and is used to amplify power of a signal to be transmitted to a base station. The power amplifier circuit100can amplify power of signals of communication standards, such as the second generation mobile communication system (2G), the third generation mobile communication system (3G), the fourth generation mobile communication system (4G), the fifth generation mobile communication system (5G), long term evolution (LTE)-frequency division duplex (FDD), LTE-time division duplex (TDD), LTE-Advanced, and LTE-Advanced Pro. The communication standard of a signal to be amplified by the power amplifier circuit100is not limited to these.

The power amplifier circuit100amplifies an input signal RFin and outputs an output signal RFout. An input signal is a radio-frequency (RF) signal, and the frequency of the input signal is, for example, about several GHz.

As illustrated inFIG.1, the power amplifier circuit100includes, for example, a splitter110, a carrier amplifier120, a peaking amplifier130, the converter140, and the converter150. Each component will be described below.

The splitter110splits an incoming input signal RFin, for example, into a signal RFin_a (first signal, fifth signal, ninth signal) and a signal RFin_b (third signal, seventh signal, eleventh signal) that leads the signal RFin_a by substantially 90 degrees. In this embodiment, the carrier amplifier120and the peaking amplifier130are differential amplifiers as described later, and thus each of the signals RFin_a and RFin_b is further split into two input signals that differ in phase by about 180 degrees.

The carrier amplifier120(first amplifier) amplifies an incoming signal RFin_a and outputs an amplified signal RFamp_a (second signal, sixth signal, tenth signal), for example. Furthermore, the peaking amplifier130(second amplifier) amplifies an incoming signal RFin_b and outputs an amplified signal RFamp_b (fourth signal, eighth signal, twelfth signal). In this embodiment, for example, the carrier amplifier120is biased so as to operate in class AB, and the peaking amplifier130is biased so as to operate in class C.

In other words, the carrier amplifier120operates in a region where the power level of the input signal RFin is not less than zero (first level) regardless of the power level. On the other hand, the peaking amplifier130operates in a region where a voltage level of the input signal RFin is not less than a level Vback (second level) that is lower than a maximum level Vmax by a certain level. Hereinafter, this is also referred to as back-off. In other words, the peaking amplifier130operates in a region where the power level of the input signal RFin is not less than the level (second level) that is lower than the maximum level by the certain level (for example, about 6 dB) and higher than zero (first level). Thus, by combining operations performed by two amplifiers in accordance with the power level of an input signal, a region where the carrier amplifier120operates at a saturation output is expanded. Hence, in comparison with a power amplifier circuit including only one amplifier, power efficiency is increased.

The carrier amplifier120and the peaking amplifier130are differential amplifiers. A differential amplifier includes two amplifier elements forming a pair and amplifies and outputs mainly a potential difference between signals input to the respective two amplifier elements and being equal in amplitude and opposite in phase. Hence, if signals (for example, noise or the like) equal in amplitude and phase are simultaneously input to the respective two amplifier elements, the signals equal in amplitude and phase are cancelled out. In other words, the use of differential amplifiers as the carrier amplifier120and the peaking amplifier130can keep noise or a harmonic of an input signal from occurring.

Incidentally, an amplifier element included in each differential amplifier is not limited to a particular element. The amplifier element may be, for example, a bipolar transistor, such as a heterojunction bipolar transistor (HBT), or a field-effect transistor, such as a metal-oxide-semiconductor field-effect transistor (MOSFET).

The converter140and the converter150are respectively connected to output sides of the carrier amplifier120and the peaking amplifier130. For example, the converters140and150convert characteristics (impedance, phase, and so forth) regarding the respective amplifiers120and130and also transmit amplified power to a load1000. The following description will be given assuming that the converter150connected to one peaking amplifier130is connected in series with the load1000as illustrated inFIG.1. Incidentally, as illustrated inFIG.2, converters150connected to a plurality of peaking amplifiers130may be individually connected in series with the load1000.

The converters140and150substantially convert characteristics (impedance, phase, and so forth) regarding amplifier elements constituting the respective amplifiers120and130, and thus an adjustment is made as to whether each of the amplifiers120and130can be regarded as a current source or can be regarded as a voltage source when the amplifiers120and130are seen from a load1000side. Incidentally, a determination is made, in accordance with a relative comparison between absolute values of output impedances of the amplifiers120and130, as to whether each of the amplifiers120and130can be regarded as a current source or can be regarded as a voltage source. Here, an output impedance may be calculated by using a reflection coefficient obtained from a traveling wave and a reflected wave that are measured from the load1000side when a transistor of each of the amplifiers120and130is biased without necessarily an idle current being caused to flow therethrough.

In the power amplifier circuit100according to the first embodiment, the converter140and the converter150are configured so that a carrier amplifier120side can be regarded as a current source by the converter140and so that a peaking amplifier130side can be regarded as a voltage source by the converter150. In other words, the converter140and the converter150are configured to make an absolute value of an impedance on the output side of the carrier amplifier120(output side of the converter140) larger than an absolute value of an impedance on the output side of the peaking amplifier130(output side of the converter150).

Examples of configurations of the converter140and the converter150will be described below with reference toFIGS.3and4.

As illustrated inFIG.3, the converter140that can be regarded as a current source includes, for example, a first transformer141, a first capacitor142, and a second capacitor143.

The first transformer141is, for example, a winding transformer including an input-side winding141aand an output-side winding141b. The first transformer141propagates a signal input to the input-side winding141ato the output-side winding141b. Specifically, in the first transformer141, the amplified signal RFamp_a (current Ia) output from the carrier amplifier120is input to the input-side winding141a(first input-side winding) and is output from the output-side winding141b(first output-side winding).

A power supply voltage Vcc is supplied to a midpoint g1of the input-side winding141aof the first transformer141. Here, two input signals opposite in phase are supplied from the carrier amplifier120to the midpoint g1, and thus the midpoint g1is a virtual ground point. Hence, the power supply voltage Vcc is supplied to the midpoint g1, thereby enabling a reduction in noise caused by a power supply circuit. In other words, the power amplifier circuit100does not have to include a power supply choke coil or bypass capacitor. This enables a reduction in circuit size.

Incidentally, when a turns ratio between the input-side winding141aand the output-side winding141bis adjusted, the first transformer141can also have an impedance matching function. Thus, impedance matching can be performed by the first transformer141formed on a chip without necessarily an output matching network being formed outside the chip. Hence, the power amplifier circuit100can be reduced in circuit size.

The first capacitor142is connected in parallel with the input-side winding141a, for example. The second capacitor143is connected directly to the output-side winding141b, for example. The first capacitor142and the second capacitor143are provided, for example, for impedance matching performed by the first transformer141in the case where the influence of parasitic inductance of the first transformer141is taken into account. Incidentally, the first capacitor142can be replaced with capacitance parasitic in the carrier amplifier120and therefore may be omitted.

As illustrated inFIG.4, the converter150that can be regarded as a voltage source includes, for example, a second transformer151, a third capacitor152, and a fourth capacitor153. Characteristics of the components of the converter150are the same as those of the components of the converter140. In place of the second capacitor143of the converter140, the fourth capacitor153is connected in parallel with an output-side winding. Here, for convenience of explanation, a description of the same components as those of the converter140is omitted.

As seen fromFIGS.3and4described above, the power amplifier circuit100is configured so that an output impedance of the converter140as seen from the load1000side is larger than an output impedance of the converter150as seen from the load1000side. Hence, in the power amplifier circuit100, the converter140is relatively regarded as a current source, and the converter150is relatively regarded as a voltage source.

In other words, in the power amplifier circuit100, when the carrier amplifier120side can be regarded as a current source and the peaking amplifier130side can be regarded as a voltage source, a current that flows into the load1000is determined only by the current source. For this reason, in the power amplifier circuit100, with the transition from a small-signal state to a saturation state in the carrier amplifier120, output impedances as seen from the amplifier elements of the carrier amplifier120can be appropriately reduced by half without necessarily using a quarter-wave line. Hence, a compact and wideband Doherty amplifier can be implemented, and the high efficiency of the Doherty amplifier can also be achieved.

Furthermore, when a differential amplifier is used in the power amplifier circuit100, a circuit can be implemented that is resistant to power-supply noise. Additionally, a simple bias circuit and a circuit exhibiting excellent linearity can be implemented.

FIG.1schematically illustrates the amplifiers120and130of the power amplifier circuit100, whereas, in the power amplifier circuit100, for example, one amplifier may constitute a first stage (driver stage), and the configuration of the above-described Doherty amplifier may be used for an output stage (power stage). Furthermore, in the power amplifier circuit100, an amplifier serving as the first stage (driver stage) may be connected to each of the carrier amplifier120and the peaking amplifier130in the output stage (power stage).

An example of how to determine parameters of elements constituting the converter140and the converter150will be described below with reference toFIGS.3to5.FIG.5illustrates an example of a configuration of the power amplifier circuit100in which the carrier amplifier120and the peaking amplifier130are differential pairs and that provides a single-ended output.

As illustrated inFIG.5, the power amplifier circuit100includes, for example, the carrier amplifier120composed of a differential pair, the converter140connected to the carrier amplifier120, the peaking amplifier130composed of a differential pair, and the converter150connected to the peaking amplifier130.

First, parameters of elements constituting the converter140will be described with reference toFIG.3. In the power amplifier circuit100, when appropriate parameters of the elements constituting the converter140are selected, the converter140as seen from the load1000side can be regarded as a current source. Specifically, in the converter140illustrated inFIG.3, when parameters are selected to meet conditions of the following Equations (1) and (2), the converter140can be regarded as a current source.
ω02×La×Ca=1  (1)
ω02×Lb×Cb=1/(1−kab2)  (2)

In Equations (1) and (2), ω0represents angular frequency (2πf), Larepresents the inductance of the input-side winding141a, Lbrepresents the inductance of the output-side winding141b, Carepresents the capacitance of the first capacitor142, Cbrepresents the capacitance of the second capacitor143, and kabrepresents the coupling coefficient of the first transformer141.

The above-described conditions are conditions under which a cascade matrix of a circuit represented by the converter140illustrated inFIG.3is obtained and off-diagonal elements of the cascade matrix are 0. When capacitors and inductors that meet Equations (1) and (2) are selected, the converter140illustrated inFIG.3performs an operation represented by a cascade matrix represented by Equation (3).

In Equation (3), Vais an input voltage of the converter140, Vbis an output voltage of the converter140, Iais an input current of the converter140corresponding to the amplified signal RFamp_a, and Ibis an output current output from the converter140to the load1000.

The converter140having characteristics of the cascade matrix represented by Equation (3) is the circuit that multiplies each of a voltage and a current by a constant to provide an output. In other words, when a current source, such as the carrier amplifier120, is connected to an input side of the converter140, the converter140can be regarded as a current source when seen from the output side of the converter140(load1000side).

Next, parameters of elements constituting the converter150will be described with reference toFIG.4. In the power amplifier circuit100, when appropriate parameters of the elements constituting the converter150are selected, the converter150as seen from the load1000side can be regarded as a voltage source. Specifically, in the converter150illustrated inFIG.4, when parameters are selected to meet conditions of the following Equations (4) and (5), the converter150can be regarded as a voltage source.
ω02×La×Ca=1/(1−kab2)  (4)
ω02×Lb×Cb=1/(1−kab2)  (5)

The above-described conditions are conditions under which a cascade matrix of a circuit represented by the converter150illustrated inFIG.4is obtained and diagonal elements of the cascade matrix are 0. When capacitors and inductors that meet Equations (4) and (5) are selected, the converter150illustrated inFIG.4performs an operation represented by a cascade matrix represented by Equation (6).

The converter150having characteristics of the cascade matrix represented by Equation (6) is the circuit that interchanges a voltage and a current and multiplies each of the voltage and the current by a constant to provide an output. In other words, when a voltage source, such as the peaking amplifier130, is connected to an input side of the converter150, the converter150can be regarded as a voltage source when seen from the output side of the converter150.

Incidentally, the amplifier elements constituting the carrier amplifier120and the peaking amplifier130and being connected in parallel with capacitors are occasionally illustrated. In this case, the capacitances of the respective capacitors are considered as parts of primary capacitances of the converter140and the converter150, and parameters may be selected.

In conditions for parameters represented by Equations (3) and (6), as illustrated inFIG.5, the converter140is connected to the carrier amplifier120, and the converter150is connected to the peaking amplifier130. Under such circumstances, an output impedance ZCas seen from the carrier amplifier120is represented by Equation (7), and an output impedance ZPas seen from the peaking amplifier130is represented by Equation (8).

In Equations (7) and (8), RLrepresents the impedance of the load1000, kCLis the coupling coefficient of the first transformer141, kPLis the coupling coefficient of the second transformer151, LCis the inductance of the input-side winding141aof the converter140, LLCis the inductance of the output-side winding141b(load1000side) of the converter140, LPis the inductance of an input-side winding151aof the converter150, LLPis the inductance of an output-side winding151b(load1000side) of the converter150, ICis a complex AC current output from the carrier amplifier120, and IPis a complex AC current output from the peaking amplifier130.

Incidentally, assuming that the amplifier elements constituting the carrier amplifier120and the peaking amplifier130are of the same size, maximum values of current amplitudes are equal, and thus an absolute value of (IP/IC) is 1. Furthermore, optimum impedances ROPTof the load1000for the amplifier elements of the respective amplifiers120and130can also be regarded as substantially equal. Hence, when the power amplifier circuit100illustrated inFIG.5is in saturation, to match the output impedances ZCand ZPto an impedance ROPTon the load1000side, each element is selected so as to meet conditions of Equation (9) for the first transformer141and meet conditions of Equation (10) for the second transformer151.
(1/kCL2)×(LC/LLC)=ROPT/RL(9)
(ω02×LP×LPL)×(1−kPL2)2/kPL(10)

More specifically, in a radio-frequency system, the impedance RLof the load1000is about 50Ω. Furthermore, in a mobile communication terminal, such as a cellular phone, power of a maximum of the order of watts (W) has to be output at a power supply voltage of about a few V. Hence, the optimum impedance ROPTof the load1000is about a few Q. Consequently, ROPT/RLis smaller than 1.

Furthermore, an absolute value of a coupling coefficient of a transformer is smaller than 1, and thus the inductance LCon an input side of the first transformer141of the converter140is smaller than the inductance LLCon an output side. In other words, the line length of the input-side winding141ais designed to be shorter than the line length of the output-side winding141b. Alternatively, the line width of the input-side winding141ais designed to be thicker than the line width of the output-side winding141b.

On the other hand, in designing a transformer in a high-frequency region, it is difficult to design inductance while reducing the influence of a parasitic component. Hence, the design of a coupling coefficient is also restricted.

In consideration of these, the coupling coefficient kPLhas to be designed from a range of about 0.28 to about 0.99. Furthermore, it is not easy to obtain a coupling coefficient of about 0.99 in the high-frequency region, and thus it is seen that the transformer only has to be designed in consideration of a lower limit of about 0.28 of the coupling coefficient kPLwithout necessarily considering an upper limit.

Power Amplifier Circuit200According to Second Embodiment

A power amplifier circuit200according to a second embodiment will be described with reference toFIGS.6to8.FIG.6is a configuration diagram illustrating a schematic configuration of the power amplifier circuit200according to the second embodiment.FIG.7is a configuration diagram illustrating a modification of the power amplifier circuit200according to the second embodiment.FIG.8is a configuration diagram illustrating an example of a configuration of the power amplifier circuit200according to the second embodiment. In the power amplifier circuit200according to the second embodiment, a description of things in common with the above-described embodiment is omitted, and only respects in which the second embodiment differs from the above-described embodiment will be described. In particular, similar function effects achieved by similar configurations are not described one by one.

As illustrated inFIG.6, in comparison with the power amplifier circuit100according to the first embodiment, in the power amplifier circuit200, a converter250(fourth converter) connected to one peaking amplifier230(fourth amplifier) is connected in parallel with the load1000. Furthermore, as illustrated inFIG.7, converters250connected to a plurality of peaking amplifiers230may be individually connected in parallel with the load1000. Moreover, as illustrated inFIG.8, a configuration may be employed in which a converter on a peaking amplifier230side is removed.

In comparison with the power amplifier circuit100according to the first embodiment, in the power amplifier circuit200, a converter240(third converter) and the converter250are configured so that a carrier amplifier220(third amplifier) side can be regarded as a voltage source by the converter240and so that the peaking amplifier230side can be regarded as a current source by the converter250. In other words, the converter240and the converter250are configured to make an absolute value of an impedance on an output side of a carrier amplifier220(output side of the converter240) smaller than an absolute value of an impedance on an output side of the peaking amplifier230(each of peaking amplifiers230, if more than one peaking amplifier230is provided) (output side of the converter250). In the power amplifier circuit200, a voltage source and a current source are connected in parallel, and thus a current that flows into a resistor is determined by the voltage source and the current source. Then, a current coming from the voltage source is a current obtained by subtracting a current coming from the current source from the current that flows into the resistor.

Incidentally, the converter240is the same as the converter150according to the first embodiment, the converter250is the same as the converter140according to the first embodiment, and thus a description of these converters is omitted.

The power amplifier circuit200in which the converter250on the peaking amplifier230side is removed will be described below with reference toFIG.8. As illustrated inFIG.8, the power amplifier circuit200performs matching between the impedance RLof the load1000and an output impedance as seen from the peaking amplifier230by using a balun260. The balun260includes, for example, a matching-purpose transformer261, an input-purpose capacitor262, and an output-purpose capacitor263.

The matching-purpose transformer261is, for example, a winding transformer including an input-side winding261aand an output-side winding261bconnected to a ground. The matching-purpose transformer261propagates a signal input to the input-side winding261ato the output-side winding261b. Specifically, in the matching-purpose transformer261, an amplified signal obtained by combining an amplified signal output from the carrier amplifier220and an amplified signal output from the peaking amplifier230is input to the input-side winding261aand is output from the output-side winding261bafter subjection to impedance conversion. The power supply voltage Vcc is supplied to a midpoint g0of the input-side winding261aof the matching-purpose transformer261.

The input-purpose capacitor262is connected in parallel with the input-side winding261a, for example. The output-purpose capacitor263is electrically connected directly to the output-side winding261b, for example. The input-purpose capacitor262and the output-purpose capacitor263are provided, for example, for impedance matching performed by the matching-purpose transformer261in the case where the influence of parasitic inductance of an input-side transformer is taken into account.

Incidentally, the power amplifier circuit200may include an element that can perform impedance matching in addition to the balun260.

In the power amplifier circuit200, since the converter250for the peaking amplifier230is removed, the lower limit of about 0.28 of the coupling coefficient kPLdescribed above does not have to be taken into account. Hence, even in design conditions under which it is difficult to implement a transformer having a high coupling coefficient, an appropriate Doherty amplifier can be implemented. Furthermore, in the power amplifier circuit200, since the converter250is removed, the secondary leakage inductance of a transformer241of the converter240or the primary leakage inductance of the matching-purpose transformer261of the balun260is caused to absorb capacitance so as to increase output impedances of amplifier elements constituting the peaking amplifier230. Furthermore, inductances may be connected in parallel at an appropriate portion to absorb capacitance.

Power Amplifier Circuit300According to Third Embodiment

A power amplifier circuit300according to a third embodiment will be described with reference toFIG.9.FIG.9is a configuration diagram illustrating an example of a configuration of the power amplifier circuit300according to the third embodiment. In the power amplifier circuit300according to the third embodiment, a description of things in common with the above-described embodiments is omitted, and only respects in which the third embodiment differs from the above-described embodiments will be described. In particular, similar function effects achieved by similar configurations are not described one by one.

As illustrated inFIG.9, in comparison with the power amplifier circuit100according to the first embodiment, in the power amplifier circuit300, a carrier amplifier320(fifth amplifier) is configured as a single-ended amplifier, and a converter on a carrier amplifier320side (converter corresponding to the converter140of the power amplifier circuit100) is removed.

The power amplifier circuit300includes an impedance matching network360to perform matching between the impedance RLof the load1000and an impedance on an output side of a peaking amplifier330(sixth amplifier). AlthoughFIG.9illustrates, as an example of the impedance matching network360, a single-stage low pass filter composed of an inductor361and a capacitor362, the impedance matching network360may be, for example, a multi-stage low pass filter, a high pass filter, a band pass filter obtained by combining a low pass filter and a high pass filter, or a matching network using a transformer and is not limited to a particular filter or network.

Furthermore, the power amplifier circuit300includes, at a stage subsequent to the carrier amplifier320configured as a single-ended amplifier, a bias circuit370that supplies a bias to the carrier amplifier320. A configuration of the bias circuit370is not limited to a particular configuration. In fact, it is desirable that an inductor371included in the bias circuit370is selected so as to provide susceptance that is the same as the imaginary part of the output admittance of an amplifier element constituting the carrier amplifier320. This can increase an absolute value of an output impedance of the carrier amplifier320and can thus cause the bias circuit370to operate like the converter140.

In comparison with the power amplifier circuit100according to the first embodiment, the power amplifier circuit300can omit a converter for the carrier amplifier320and can thus be reduced in circuit size. Furthermore, the carrier amplifier320is configured as a single-ended amplifier, thus facilitating measuring characteristics thereof.

SUMMARY

The power amplifier circuit100according to an exemplary embodiment of the present disclosure includes the carrier amplifier120(first amplifier) that, in a region where a power level of an input signal RFin (input signal) is not less than a first level, amplifies a signal RFin_a (first signal) split from the input signal and outputs an amplified signal RFamp_a (second signal); the converter140(first converter) that is connected to an output side of the carrier amplifier120(first amplifier) and converts an impedance on the output side of the carrier amplifier120(first amplifier); and at least one or more peaking amplifiers130(second amplifiers) that, in a region where the power level of the input signal RFin (input signal) is not less than a second level higher than the first level, amplify a signal RFin_b (third signal) split from the input signal RFin (input signal) and output an amplified signal RFamp_b (fourth signal). Output sides of the respective peaking amplifiers130(second amplifiers) are connected in series with an output side of the converter140(first converter). The converter140(first converter) is configured to make an absolute value of the impedance on the output side of the carrier amplifier120(first amplifier) larger than absolute values of impedances on the output sides of the respective peaking amplifiers130(second amplifiers). Thus, an appropriate load modulation effect can be produced without necessarily using a quarter-wave line.

Furthermore, the converter140(first converter) of the power amplifier circuit100according to the exemplary embodiment of the present disclosure includes the first transformer141including the input-side winding141a(first input-side winding) to which the amplified signal RFamp_a (second signal) is input and the output-side winding141b(first output-side winding) coupled to the input-side winding141a(first input-side winding) via an electromagnetic field, the first capacitor142connected in parallel with the input-side winding141a(first input-side winding), and the second capacitor143connected in series with the output-side winding141b(first output-side winding). Thus, the converter140can be implemented in a simple configuration.

Furthermore, the power amplifier circuit100according to the exemplary embodiment of the present disclosure further includes the converters150(second converters) that are connected to the output sides of the respective peaking amplifiers130(second amplifiers) and convert characteristics regarding the peaking amplifiers130(second amplifiers). The output sides of the respective peaking amplifiers130(second amplifiers) are connected in series with the output side of the converter140(first converter) through the converters150(second converters). The converter140(first converter) and the converters150(second converters) are configured to make an absolute value of the impedance on the output side of the carrier amplifier120(first amplifier) larger than absolute values of the impedances on the output sides of the respective peaking amplifiers130(second amplifiers). This enables more appropriate impedance matching.

Furthermore, the converters150(second converters) of the power amplifier circuit100according to the exemplary embodiment of the present disclosure include the second transformer151including the input-side winding151a(second input-side winding) to which the fourth signal is input and the output-side winding151b(second output-side winding) coupled to the input-side winding151a(second input-side winding) via an electromagnetic field, the third capacitor152connected in parallel with the input-side winding151a(second input-side winding), and the fourth capacitor153connected in parallel with the output-side winding151b(second output-side winding). Thus, the converters150can be implemented in a simple configuration.

Furthermore, the carrier amplifier120(first amplifier) of the power amplifier circuit100according to the exemplary embodiment of the present disclosure is a differential amplifier. Thus, a circuit can be implemented that is resistant to power supply noise. Furthermore, a simple bias circuit and a circuit exhibiting excellent linearity can be implemented.

Furthermore, each of the peaking amplifiers130(second amplifiers) of the power amplifier circuit100according to the exemplary embodiment of the present disclosure is a differential amplifier. Thus, a circuit can be implemented that is resistant to power supply noise. Furthermore, a simple bias circuit and a circuit exhibiting excellent linearity can be implemented.

The power amplifier circuit200according to an exemplary embodiment of the present disclosure includes the carrier amplifier220(third amplifier) that, in a region where a power level of an input signal is not less than a third level, amplifies a signal RFin_a (fifth signal) split from the input signal RFin (input signal) and outputs an amplified signal RFamp_a (sixth signal); the converter240(third converter) that is connected to an output side of the carrier amplifier220(third amplifier) and converts an impedance on the output side of the carrier amplifier220(third amplifier); and at least one or more peaking amplifiers230(fourth amplifiers) that, in a region where the power level of the input signal RFin (input signal) is not less than a fourth level higher than the third level, amplify a signal RFin_b (seventh signal) split from the input signal RFin (input signal) and output an amplified signal RFamp_b (eighth signal). Output sides of the respective peaking amplifiers230(fourth amplifiers) are connected in parallel with an output side of the converter240(third converter). The converter240(third converter) is configured to make an absolute value of the impedance on the output side of the carrier amplifier220(third amplifier) smaller than absolute values of impedances on the output sides of the respective peaking amplifiers230(fourth amplifiers). Thus, an appropriate load modulation effect can be produced without necessarily using a quarter-wave line.

The converter240(third converter) of the power amplifier circuit200according to the exemplary embodiment of the present disclosure includes the transformer241(third transformer) including an input-side winding241a(third input-side winding) to which the amplified signal RFamp_a (sixth signal) is input and an output-side winding241b(third output-side winding) coupled to the input-side winding241a(third input-side winding) via an electromagnetic field, a capacitor242(fifth capacitor) connected in parallel with the input-side winding241a(third input-side winding), and a capacitor243(sixth capacitor) connected in parallel with the output-side winding241b(third output-side winding). Thus, the converter240can be implemented in a simple configuration.

The power amplifier circuit200according to the exemplary embodiment of the present disclosure further includes the converters250(fourth converters) that are connected to the output sides of the respective peaking amplifiers230(fourth amplifiers) and convert characteristics regarding the peaking amplifiers230(fourth amplifiers). The respective peaking amplifiers230(fourth amplifiers) are connected in parallel with the output side of the converter240(third converter) through the converters250(fourth converters). The converter240(third converter) and the converters250(fourth converters) are configured to make an absolute value of the impedance on the output side of the carrier amplifier220(third amplifier) smaller than absolute values of the impedances on the output sides of the respective peaking amplifiers230(fourth amplifiers). This enables more appropriate impedance matching.

The converters250(fourth converters) of the power amplifier circuit200according to the exemplary embodiment of the present disclosure include a transformer251(fourth transformer) including an input-side winding251a(fourth input-side winding) to which the eighth signal is input and an output-side winding251b(fourth output-side winding) coupled to the input-side winding251a(fourth input-side winding) via an electromagnetic field, a capacitor252(seventh capacitor) connected in parallel with the input-side winding251a(fourth input-side winding), and a capacitor253(eighth capacitor) connected in series with the output-side winding251b(fourth output-side winding). Thus, the converters250can be implemented in a simple configuration.

The carrier amplifier220(third amplifier) of the power amplifier circuit200according to the exemplary embodiment of the present disclosure is a differential amplifier. Thus, a circuit can be implemented that is resistant to power supply noise. Furthermore, a simple bias circuit and a circuit exhibiting excellent linearity can be implemented.

Each of the peaking amplifiers230(fourth amplifiers) of the power amplifier circuit200according to the exemplary embodiment of the present disclosure is a differential amplifier. Thus, a circuit can be implemented that is resistant to power supply noise. Furthermore, a simple bias circuit and a circuit exhibiting excellent linearity can be implemented.

The power amplifier circuit300according to an exemplary embodiment of the present disclosure includes the carrier amplifier320(fifth amplifier) that, in a region where a power level of an input signal is not less than a fifth level, amplifies a signal RFin_a (ninth signal) split from the input signal RFin (input signal) and outputs an amplified signal RFamp_a (tenth signal); at least one or more peaking amplifiers330(sixth amplifiers) that, in a region where the power level of the input signal RFin (input signal) is not less than a sixth level higher than the fifth level, amplify a signal RFin_b (eleventh signal) split from the input signal RFin (input signal) and output an amplified signal RFamp_b (twelfth signal); and converters350(fifth converters) that are connected to output sides of the respective peaking amplifiers330(sixth amplifiers) and convert impedances on the output sides of the respective peaking amplifiers330(sixth amplifiers). Output sides of the respective converters350(fifth converters) are connected in series with an output side of the carrier amplifier320(fifth amplifier). The respective converters350(fifth converters) are configured to make an absolute value of an impedance on the output side of the carrier amplifier320(fifth amplifier) smaller than absolute values of the impedances on the output sides of the respective peaking amplifiers330(sixth amplifiers). Thus, an appropriate load modulation effect can be produced without necessarily using a quarter-wave line.

The converters350(fifth converters) of the power amplifier circuit300according to the exemplary embodiment of the present disclosure include a transformer351(fifth transformer) including an input-side winding351a(fifth input-side winding) to which the amplified signal RFamp_b (twelfth signal) is input and an output-side winding351b(fifth output-side winding) coupled to the input-side winding351a(fifth input-side winding) via an electromagnetic field, a capacitor352(ninth capacitor) connected in parallel with the input-side winding351a(fifth input-side winding), and a capacitor353(tenth capacitor) connected in parallel with the output-side winding351b(fifth output-side winding). Thus, the converters350can be implemented in a simple configuration.

Each of the peaking amplifiers330(sixth amplifiers) of the power amplifier circuit300according to the exemplary embodiment of the present disclosure is a differential amplifier. Thus, a circuit can be implemented that is resistant to power supply noise. Furthermore, a simple bias circuit and a circuit exhibiting excellent linearity can be implemented.

The above-described embodiments are intended to facilitate understanding of the present disclosure but are not intended for a limited interpretation of the present disclosure. The present disclosure can be changed or improved without necessarily departing from the gist thereof and also encompasses equivalents thereof. In other words, appropriate design changes made to the embodiments by those skilled in the art are also encompassed in the scope of the present disclosure as long as the changes have features of the present disclosure. The elements included in the embodiments, and the arrangement and so forth of the elements are not limited to those exemplified herein and can be appropriately changed.