HK1240414B - Doherty power amplifier with tunable input network - Google Patents

Description

Doherty power amplifier with tunable input network

Cross-reference to related applications

This application claims priority to U.S. Provisional Application No. 62/068,629, filed on October 25, 2014, entitled “PROGRAMMABLE INPUT NETWORK WITH AMPLITUDE AND PHASE CONTROL FOR LINEARIZED BROAD-BAND DOHERTY POWER AMPLIFIER,” the disclosure of which is hereby expressly incorporated herein by reference in its entirety.

Technical Field

The present disclosure generally relates to radio frequency (RF) power amplifiers (PAs).

Background Art

Multimode/multiband (MMMB) power amplifier modules (PAMs) may face competition from envelope tracking (ET) PAMs in, for example, the 4G LTE market. To succeed in such a market, it is desirable for MMMB PAMs to offer significant performance improvements over existing MMMB PAMs while also being competitive with ET-based PAMs (based on cost, performance, and size).

In the 4G LTE standard, new modulation protocols such as OFDMA (Orthogonal Frequency Division Multiple Access) and SC-FDMA (Single Carrier FDMA) can be used to support high data rates in scalable channel bandwidths of, for example, 5 MHz to 20 MHz and even 40 MHz. High data rate transmission using many independently modulated subcarriers over the variable channel bandwidth in the 4G LTE communication protocol typically comes at the expense of a high peak-to-average power ratio (PAPR) for the transmitter. From a power amplifier perspective, high PAPR modulation schemes typically translate into low average efficiency, as power amplifiers typically need to operate in deep-back-off mode, away from their peak efficiency point, most of the time to prevent clipping of the transmitted signal. Therefore, for the 4G standard, new configurations of power amplifiers that can operate with high linearity and high PAE even under significant back-off conditions are desired.

Regarding efficiency improvements under back-off, Doherty PAM can meet high efficiency with high linearity under back-off, with significantly reduced system complexity and reduced calibration and digital pre-distortion (DPD) specifications compared to envelope tracking PAM. However, due to the narrowband nature of existing Doherty power combiners, some Doherty power amplifier configurations are bandwidth-limited. Furthermore, due to dynamically changing load lines, some Doherty PAMs may have significant AM-AM (amplitude modulation to amplitude modulation) and AM-PM (amplitude modulation to phase modulation) distortion under back-off, which may affect the FOM (figure of merit) achievable at the rated power level of the 4G LTE communication standard. For wideband Doherty PAM, it may be desirable to be able to control such distortion under back-off conditions, especially when the wideband Doherty PAM is implemented over a wideband.

Summary of the Invention

According to certain embodiments, the present disclosure relates to an input network for a Doherty power amplifier. The input network includes a splitter circuit configured to receive a radio frequency (RF) signal and branch the RF signal into a first portion along a first path to a carrier amplifier of the Doherty power amplifier and a second portion along a second path to a peaking amplifier of the Doherty power amplifier. The input network also includes a tunable input circuit implemented along either or both of the first and second paths. The tunable input circuit is configured to provide amplitude and phase control of either or both of the first and second portions.

In some embodiments, the tunable input circuit may include an RC circuit. In some embodiments, the RC circuit may include a first capacitor along a first path, a first resistor in a bypass configuration between the first capacitor and the carrier amplifier, a second resistor along a second path, and a second capacitor in a bypass configuration between the second resistor and the peaking amplifier. In some embodiments, the first capacitor, the first resistor, the second capacitor, and the second resistor may each be tunable. In some embodiments, the first capacitor and the second capacitor may each include a switchable capacitor bank, and the first resistor and the second resistor may each include a switchable resistor bank.

In some embodiments, the tunable input circuit may include an RLC circuit. In some embodiments, the RLC circuit may include a capacitor along a first path, a first resistor along the first path, an inductor along a second path, and a second resistor along the second path. In some embodiments, the capacitor and inductor may be configured to provide phase control of either or both of the first portion and the second portion, and the first and second resistors may be configured to provide amplitude control of either or both of the first portion and the second portion.

In certain embodiments, the tunable input circuit may include a balun-based circuit. In certain embodiments, the balun-based circuit may include a balun having a first node configured to receive an input signal, a second node coupled to a carrier amplifier via a first resistor, a third node coupled to a peak amplifier via a second resistor, and a fourth node coupled to ground potential via a terminating impedance. The balun-based circuit may also include a first capacitor coupled between the first node and a third node, and a second capacitor coupled between the second node and a fourth node. In certain embodiments, the balun may include a first inductor coupled between the first node and the second node, and a second inductor coupled between the third node and the fourth node.

In certain embodiments, the input network may further include a controller configured to tune the tunable input network. In certain embodiments, the controller may be configured to tune the tunable input network based on the frequency of the RF signal. In certain embodiments, the controller may be configured to tune the tunable input network so that the amplitude of the first portion and the amplitude of the second portion are not equal. In certain embodiments, the controller may be configured to tune the tunable input network so that the phase of the first portion and the phase of the second portion are non-orthogonal. In certain embodiments, the controller may be configured to tune the tunable input network so that the harmonics generated by the carrier amplifier and the harmonics generated by the peaking amplifier are canceled by the combiner. In certain embodiments, the controller may be configured to perform broadband linearization of the Doherty power amplifier.

In certain embodiments, the present disclosure relates to a Doherty power amplifier module comprising a packaging substrate configured to accommodate multiple components. The Doherty power amplifier module includes a Doherty PA system implemented on the packaging substrate. The Doherty PA system includes a splitter circuit configured to receive a radio frequency (RF) signal and branch the RF signal into a first portion along a first path and a second portion along a second path. The Doherty PA system includes a tunable input circuit implemented along either or both of the first path and the second path. The tunable input circuit is configured to provide control of the amplitude and phase of either or both of the first portion and the second portion. The Doherty PA system includes a carrier amplifier configured to amplify the first portion and a peak amplifier configured to amplify the second portion. The Doherty PA includes an output circuit configured to combine the outputs of the carrier amplifier and the peak amplifier to produce an amplified RF signal.

In some embodiments, the output circuit includes a tunable impedance circuit.

In certain embodiments, the present disclosure relates to a wireless device including a transceiver configured to generate a radio frequency (RF) signal. The wireless device includes a power amplifier (PA) module in communication with the transceiver. The PA module includes a package substrate configured to accommodate multiple components and a PA system implemented on the package substrate. The PA system includes a splitter circuit configured to receive a radio frequency (RF) signal and branch the RF signal into a first portion along a first path and a second portion along a second path. The PA system includes a tunable input circuit implemented along either or both of the first path and the second path. The tunable input circuit is configured to provide amplitude and phase control for either or both of the first portion and the second portion. The PA system includes a carrier amplifier configured to amplify the first portion and a peaking amplifier configured to amplify the second portion. The PA system includes an output circuit configured to combine the outputs of the carrier amplifier and the peaking amplifier to produce an amplified RF signal. The wireless device also includes an antenna in communication with the PA module. The antenna is configured to facilitate transmission of the amplified RF signal.

For purposes of summarizing this disclosure, certain aspects, advantages, and novel features of the present invention have been described herein. It will be understood that not all of these advantages may be achieved according to any particular embodiment of the present invention. Thus, the present invention may be implemented or realized in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 shows an example configuration of a Doherty power amplifier.

FIG. 2 illustrates that, in some embodiments, the tunable input network may include an RC circuit.

FIG3 illustrates that, in some embodiments, the tunable input network may include an RLC circuit.

FIG. 4 illustrates that, in some embodiments, the tunable input network may include a balun-based circuit.

FIG5 depicts a module having one or more features as described herein.

FIG6 depicts a wireless device having one or more features as described herein.

DETAILED DESCRIPTION

The headings provided herein, if any, are for convenience only and do not necessarily affect the scope or meaning of the claimed invention.

FIG1 illustrates an example configuration of a Doherty power amplifier 100. The example power amplifier 100 is shown as including an input port (RF_IN) for receiving an RF signal to be amplified. Such an input RF signal may be partially amplified by a pre-driver amplifier 102 before being branched (e.g., by a splitter 104) into a carrier amplification path 110 and a peaking amplification path 130.

In FIG1 , a carrier amplification path 110 is shown as including a phase shifter 112, an attenuator 113, and an amplifier stage collectively designated 114. Amplifier stage 114 is shown as including a driver stage 116 and an output stage 120. Driver stage 116 is shown as being biased by a driver bias circuit 118, and output stage 120 is shown as being biased by an output bias circuit 122. In some embodiments, there may be more or fewer amplifier stages. In various examples described herein, amplifier stage 114 is sometimes described as an amplifier; however, it will be understood that such an amplifier may include one or more stages.

In FIG1 , peak amplification path 130 is shown as including a phase shifter 132, an attenuator 133, and an amplifier stage collectively designated 134. Amplification stage 134 is shown as including a driver stage 136 and an output stage 140. Driver stage 136 is shown as being biased by driver bias circuit 138, and output stage 140 is shown as being biased by output bias circuit 142. In some embodiments, there may be more or fewer amplifier stages. In various examples described herein, amplifier stage 134 is sometimes described as an amplifier; however, it will be understood that such an amplifier may include one or more stages.

FIG1 further illustrates that the carrier amplifier path 110 and the peak amplifier path 130 can be combined by a combiner 144 to produce an amplified RF signal at an output port (RF-OUT). In certain embodiments, the combiner 144 includes a tunable impedance circuit. Examples of the combiner 144 are described in more detail in U.S. patent application Ser. No. 14/824,856, filed on August 12, 2015, entitled “DOHERTYPOWER AMPLIFIER COMBINER WITH TUNABLE IMPEDANCE TERMINATION CIRCUIT,” which is hereby incorporated by reference herein in its entirety.

In some Doherty PA implementations, the inputs to the carrier amplifier 114 and the peaking amplifier 134 are equal in amplitude and orthogonal in phase to ensure that the load line is modulated according to the output power, resulting in high efficiency under back-off. However, such implementations may suffer from high AM-AM and AM-PM distortion, which is typically caused by the abrupt turn-off of the peaking amplifier 134, which causes the carrier amplifier 114 load line to change dynamically.

The abrupt change in the carrier amplifier 114 load line and the resulting change in the current through the carrier amplifier 114 may cause drastic changes in inherent parasitics, such as the collector-base and base-emitter capacitances of transistors within the carrier amplifier 114. The nonlinear nature of such changes may result in AM-AM and AM-PM distortion.

In broadband Doherty PAM, the frequency responses of combiner 144 and splitter 104 may be such that such AM-AM and AM-PM distortions are frequency dependent. Thus, in certain embodiments, improved linearity may be achieved by using tunable input network 160 (also referred to as a programmable input network).

The tunable input network 160 includes a controller 162 that tunes the phase shifters 112, 132 and attenuators 113, 133 of each path so that the inputs to the carrier amplifier 114 and the peaking amplifier 134 are unequal in amplitude and non-orthogonal in phase.

The controller 162 can control the attenuators 113 and 133 of each path to change the amplitude of the signals input to the carrier amplifier 114 and the peaking amplifier 134. Specifically, the controller 162 can control the attenuators 113 and 133 of each path so that the output current of the carrier amplifier 114 and the output current of the peaking amplifier 134 are in appropriate proportion over a wide range of frequencies. The controller 162 can ensure that the carrier amplifier 114 and the peaking amplifier 134 have the same dynamic load line over a wide range of frequencies, which eliminates the frequency dependence of AM-AM and AM-PM distortion. To this end, the controller 162 can control the attenuators 113 and 133 of each path based on the frequency of the signal received at the input port (e.g., based on a control signal indicating the frequency of the input signal).

When the collector-base and base-emitter capacitances of the transistors of carrier amplifier 114 and peaking amplifier 134 change due to dynamic load lines, the phase response of carrier amplifier 114 and peaking amplifier 134 changes. Controller 162 can control the phase shifters 112 and 132 of each path to change the relative phases of the signals input to carrier amplifier 114 and peaking amplifier 134. Specifically, controller 162 can control the phase shifters 112 and 132 of each path so that the overall carrier amplifier 114 and peaking amplifier 134 transfer function (from the input of the phase shifters to the output of the amplifiers) remains substantially constant over frequency. Controller 162 can control the phase shifters 112 and 132 of each path in an appropriate manner to cancel AM-AM and AM-PM distortion. To this end, controller 162 can control the phase shifters 112 and 132 of each path based on the frequency of the signal received at the input port (e.g., based on a control signal indicating the frequency of the input signal).

Thus, the controller 162 can linearize the Doherty power amplifier 100 by approximately controlling the amplitude and phase differences of the inputs to the carrier amplifier 114 and the peaking amplifier 134 to ensure that the carrier amplifier 114 harmonics and the peaking amplifier 134 harmonics are at the appropriate amplitude and phase, thereby being canceled in the final combined Doherty PAM output. By controlling the amplitude and phase of the harmonics from the input, the Doherty power amplifier can use low-Q, low-breakdown components, resulting in cost benefits. By maintaining the appropriate amplitude and phase differences over a wide range of frequencies via the controller of the tunable input network, the controller 162 can compensate for any effects of distortion mechanisms caused by the frequency response of the splitter 104 and/or combiner 144.

2 shows that, in some embodiments, the tunable input network 260 may include an RC circuit. The tunable input network 260 includes an input node 201 configured to receive an input signal; a carrier output node 202 configured to output a first portion of the input signal (e.g., a carrier signal) to a carrier amplifier; and a peak output node 203 configured to output a second portion of the input signal (e.g., a peak signal) to a peak amplifier.

The tunable input network 260 includes a first path from the input node 201 to the carrier output node 202 and a second path from the input node 201 to the peak output node 203. The tunable input network 260 includes a first capacitor 211 along the first path, a first resistor 212 in a shunt configuration between the first capacitor 211 and the carrier output node 202, a second resistor 221 along the second path, and a second capacitor 222 in a shunt configuration between the second resistor 221 and the peak output node 203.

The first capacitor 211, the first resistor 212, the second capacitor 222, and the second resistor 221 are each tunable. In some embodiments, the first capacitor 211 and the second capacitor 222 each comprise a switchable capacitor bank, and the first resistor 212 and the second resistor 221 each comprise a switchable resistor bank.

The capacitance of the first capacitor 211 and the second capacitor 222, and the resistance of the first resistor 212 and the second resistor 221 can be controlled (e.g., by a controller) to change the amplitude and phase of the carrier signal and the peak signal. Specifically, the carrier signal and the peak signal can be unequal in amplitude and non-orthogonal in phase.

3 shows that, in some embodiments, tunable input network 360 may include an RLC circuit. Tunable input network 360 includes an input node 301 configured to receive an input signal; a carrier output node 302 configured to output a first portion of the input signal (e.g., a carrier signal) to a carrier amplifier; and a peak output node 303 configured to output a second portion of the input signal (e.g., a peak signal) to a peak amplifier.

Tunable input network 360 includes a first path from input node 301 to carrier output node 302 and a second path from input node 301 to peak output node 303. Tunable input network 360 includes capacitor 311 along the first path, first resistor 312 along the first path, inductor 321 along the second path, and second resistor 322 along the second path.

Capacitor 311, first resistor 312, and second resistor 322 are each tunable. In some embodiments, inductor 321 is tunable. In some embodiments, capacitor 311 comprises a switchable capacitor bank, and first resistor 312 and second resistor 322 each comprise a switchable resistor bank.

The capacitance of capacitor 311 can be controlled (e.g., by a controller) to change the relative phase of the carrier signal and the peak signal. Specifically, the carrier signal and the peak signal can be non-orthogonal in phase. The resistance of first resistor 312 and second resistor 322 can be controlled (e.g., by a controller) to change the amplitude of the carrier signal and the peak signal. Specifically, the carrier signal and the peak signal can be unequal in amplitude.

4 shows that, in some embodiments, the tunable input network 460 may include a balun-based circuit. The tunable input network 460 includes an input node 460 configured to receive an input signal; a carrier output node 402 configured to output a first portion of the input signal (e.g., a carrier signal) to a carrier amplifier; and a peak output node 403 configured to output a second portion of the input signal (e.g., a peak signal) to a peak amplifier.

Tunable input network 460 includes a first path from input node 401 to carrier output node 402 and a second path from input node 401 to peak output node 403. Tunable input network 460 includes balun 420 having a first node coupled to input node 401 and configured to receive an input signal, a second node coupled to carrier output node 402 via a first resistor 421, a third node coupled to peak output node 403 via a second resistor 422, and a fourth node coupled to ground potential via a terminating impedance 423. Tunable input network 460 also includes a first capacitor 411 coupled between the first node and the third node of balun 420, and a second capacitor 412 coupled between the second node and the fourth node of balun 420. The balun 420 includes a first inductor coupled between a first node and a second node and a second inductor coupled between a third node and a fourth node.

Each of the first capacitor 411, the second capacitor 412, the first resistor 421, and the second resistor 422 is tunable. In some embodiments, the terminal impedance 423 is tunable. In some embodiments, the first capacitor 411 and the second capacitor 412 each comprise a switchable capacitor bank, and the first resistor 421 and the second resistor 422 each comprise a switchable resistor bank.

The capacitance of the first capacitor 411 and the second capacitor 412, and the resistance of the first resistor 421 and the second resistor 422 can be controlled (e.g., by a controller) to change the amplitude and phase of the carrier signal and the peak signal. Specifically, the carrier signal and the peak signal can be unequal in amplitude and non-orthogonal in phase.

FIG5 illustrates that, in certain embodiments, some or all of the configurations (e.g., the configurations shown in FIG1-4 ) may be implemented in whole or in part in a module. Such a module may be, for example, a front-end module (FEM). In the example of FIG5 , module 500 may include a package substrate 502 , and a number of components may be mounted on such package substrate 502 . For example, FE-PMIC assembly 504 , power amplifier assembly 506 (which may include a tunable input network 507 ), matching assembly 508 , and multiplexer assembly 510 may be mounted and/or implemented on and/or within package substrate 502 . Other components, such as a number of SMT devices 514 and an antenna switch module (ASM) 512 , may also be mounted on package substrate 502 . Although all of the various components are depicted as being arranged on package substrate 502 , it will be understood that certain components may be implemented on top of other components.

In some embodiments, devices and/or circuits having one or more features described herein may be included in RF electronic devices such as wireless devices. Such devices and/or circuits may be implemented directly in the wireless device, in a modular form as described herein, or in some combination thereof. In some embodiments, such wireless devices may include, for example, cellular phones, smartphones, handheld wireless devices with or without telephone functionality, wireless tablets, and the like.

6 depicts an example wireless device 600 having one or more advantageous features described herein. In the context of a module having one or more features as described herein, such a module may be generally depicted by a dashed box 500 and may be implemented, for example, as a front-end module (FEM).

6 , power amplifiers (PAs) 60a-60d can receive their respective RF signals from a transceiver 610, which can be configured and operated in a known manner to generate RF signals to be amplified and transmitted, and to process received signals. The transceiver 610 is shown interacting with a baseband subsystem 608, which is configured to provide conversion between data and/or voice signals intended for a user and RF signals intended for the transceiver 610. The transceiver 610 can also communicate with a power management component 606, which is configured to manage power for operation of the wireless device 600. Such power management can also control the operation of the baseband subsystem 608 and the module 500.

The baseband subsystem 608 is shown connected to the user interface 602 to facilitate various inputs and outputs of voice and/or data to and from the user. The baseband subsystem 608 may also be connected to a memory 604 configured to store data and/or instructions to facilitate operation of the wireless device and/or provide storage of information for the user.

In the example wireless device 600, the outputs of PAs 60a-60d are shown matched (via respective matching circuits 620a-620d) and routed to their respective duplexers 612a-612d. Such amplified and filtered signals can be routed to antenna 616 (or multiple antennas) via antenna switch 614 for transmission. In certain embodiments, duplexers 612a-612d can allow simultaneous transmission and reception operations using a common antenna (e.g., 616). In FIG6, received signals are shown routed to an "Rx" path (not shown), which may include, for example, a low noise amplifier (LNA).

Many other wireless device configurations can utilize one or more of the features described herein. For example, a wireless device need not be a multi-band device. In another example, a wireless device can include additional antennas such as a diversity antenna and additional connectivity features such as Wi-Fi, Bluetooth, and GPS.

Unless the context clearly requires otherwise, throughout this specification and claims, the words "comprises," "comprising," and the like are to be interpreted in an inclusive sense, and not in an exclusive or exhaustive sense; that is, in the sense of "including, but not limited to." The word "coupled," as used generally in this document, refers to two or more elements that may be connected directly or through one or more intermediate elements. Additionally, the words "herein," "above," "below," and words of similar meaning, when used in this application, shall refer to this application as a whole and not to any particular part of this application. Where the context permits, words used in the singular or plural in the above specific embodiments may also include the plural or singular, respectively. When referring to a list of two or more items, the word "or" covers all of the following interpretations of the word: any item in the list, all items in the list, and any combination of items in the list.

The above specific description of the embodiment of the present invention is not intended to be exhaustive, and the present invention is not limited to the precise form disclosed above. Although specific embodiments of the present invention and examples are described above for illustrative purposes, it will be appreciated by those skilled in the art that various equivalent modifications within the scope of the present invention are possible. For example, although processes or square blocks are presented in a given order, alternative embodiments can perform routines with steps or use systems with square blocks in different orders, and can delete, move, add, segment, combine and/or modify some processes or square blocks. Each of these processes or square blocks can be realized in many different ways. Similarly, although processes or square blocks are sometimes shown as serial executions, these processes or square blocks can alternatively be performed in parallel, or can be performed at different times.

The teachings of the invention provided herein can be applied to other systems, not necessarily to the system described above.The elements and acts of the various embodiments described above can be combined to provide further embodiments.

Although certain embodiments of the present invention have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the present disclosure. Indeed, the novel methods and systems described herein may be embodied in many other forms; further, various omissions, substitutions, and changes in the form of the methods and systems described herein may be made without departing from the spirit of the present disclosure. The appended claims and their equivalents are intended to cover such forms or modifications as fall within the scope and spirit of the present disclosure.

Claims (13)

1. A circuit network for a Doherty power amplifier, the circuit network comprising: A splitter circuit is configured to receive a radio frequency (RF) signal and branch the RF signal into a first portion along a first path to the input of a carrier amplifier of the Doherty power amplifier and a second portion along a second path to the input of a peak amplifier of the Doherty power amplifier; and A tunable circuit includes at least one of a portion of a first path and a portion of a second path, the tunable circuit being configured to provide amplitude and phase control of at least one of the first portion and the second portion, the tunable circuit including a balun-to-unbalun based circuit having a first node configured to receive an input signal, a second node coupled to a carrier amplifier via a first resistor, a third node coupled to a peak amplifier via a second resistor, and a fourth node coupled to ground potential via a terminating impedance, the balun-to-unbalun based circuit further including a first capacitor coupled between the first node and the third node and a second capacitor coupled between the second node and the fourth node. 2. The circuit network of claim 1, wherein the balun includes a first inductor coupled between a first node and a second node and a second inductor coupled between a third node and a fourth node. 3. The circuit network of claim 1, further comprising a controller configured to tune the circuit network. 4. The circuit network of claim 3, wherein the controller is configured to tune the circuit network based on the frequency of the radio frequency signal. 5. The circuit network of claim 3, wherein the controller is configured to tune the circuit network such that the amplitudes of the first portion and the second portion are not equal. 6. The circuit network of claim 3, wherein the controller is configured to tune the circuit network such that the phase of the first portion and the phase of the second portion are non-orthogonal. 7. The circuit network of claim 3, wherein the controller is configured to tune the circuit network such that harmonics generated by the carrier amplifier and harmonics generated by the peak amplifier are canceled out by the combiner. 8. The circuit network of claim 3, wherein the controller is configured to perform broadband linearization of the Doherty power amplifier. 9. A Doherty power amplifier module, comprising: The encapsulation substrate is configured to accommodate multiple components; and A Doherty power amplifier system, implemented on the package substrate, includes: a splitter circuit configured to receive a radio frequency (RF) signal and branch the RF signal into a first portion along a first path to an input of a carrier amplifier and a second portion along a second path to an input of a peak amplifier; and a tunable circuit including at least one portion of the first path and a portion of the second path, the tunable circuit being configured to provide amplitude and phase control of at least one of the first and second portions, the tunable circuit including a balun-to-unbalance converter-based circuit comprising a balun-to-unbalance converter... The balanced-to-unbalanced converter has a first node configured to receive an input signal, a second node coupled to a carrier amplifier via a first resistor, a third node coupled to a peak amplifier via a second resistor, and a fourth node coupled to ground potential via a terminating impedance. The circuit based on the balanced-to-unbalanced converter further includes a first capacitor coupled between the first and third nodes and a second capacitor coupled between the second and fourth nodes; a carrier amplifier configured to amplify the first portion; a peak amplifier configured to amplify the second portion; and an output circuit configured to combine the outputs of the carrier amplifier and the peak amplifier to generate an amplified radio frequency signal. 10. The Doherty power amplifier module of claim 9, wherein the output circuitry includes a tunable impedance circuit. 11. The Doherty power amplifier module of claim 9, wherein the balun includes a first inductor coupled between a first node and a second node and a second inductor coupled between a third node and a fourth node. 12. The Doherty power amplifier module of claim 9, wherein the Doherty power amplifier system includes a controller configured to tune the Doherty power amplifier system such that harmonics generated by the carrier amplifier and harmonics generated by the peak amplifier are canceled out by a combiner. 13. A wireless device, comprising: The transceiver is configured to generate radio frequency signals; A power amplifier module, communicating with the transceiver, the power amplifier module comprising a package substrate configured to accommodate multiple components and a power amplifier system implemented on the package substrate, the power amplifier system comprising: a splitter circuit configured to receive a radio frequency signal and branch the radio frequency signal into a first portion along a first path to an input of a carrier amplifier and a second portion along a second path to an input of a peak amplifier; a tunable circuit including at least one of a portion of the first path and a portion of the second path, the tunable circuit being configured to provide amplitude and phase control of at least one of the first portion and the second portion, the tunable circuit including circuitry based on a balanced-to-unbalanced converter. The converter circuitry includes a balanced-to-unbalanced converter having a first node configured to receive an input signal, a second node coupled to a carrier amplifier via a first resistor, a third node coupled to a peak amplifier via a second resistor, and a fourth node coupled to ground potential via a terminating impedance. The circuitry further includes a first capacitor coupled between the first and third nodes and a second capacitor coupled between the second and fourth nodes; a carrier amplifier configured to amplify the first portion; a peak amplifier configured to amplify the second portion; and an output circuit configured to combine the outputs of the carrier amplifier and the peak amplifier to generate an amplified radio frequency signal. An antenna that communicates with the power amplifier module is configured to facilitate the transmission of amplified radio frequency signals.