Load line switching for push-pull power amplifiers

Abstract

An amplifier system comprising: a push-pull power amplifier having an input for receiving a radio frequency (RF) input signal and an output, the push-pull power amplifier configured to amplify the RF input signal and provide an RF output signal at the output, the RF output signal being an amplified version of the RF input signal; a switchable bypass capacitance switchably connected between a load line of the output of the push-pull power amplifier and a reference potential; and a switch configured to selectively connect and disconnect the switchable bypass capacitance to and from the reference potential to vary an impedance of the load line.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 736,540, filed September 26, 2018, entitled “LOAD-LINE SWITCHING FOR PUSH-PULL POWER AMPLIFIERS,” pursuant to Section 119 of Title 35 of the United States Code, the entire contents of which are incorporated herein by reference. Background Technology

[0003] In mobile applications such as cellular, extending battery life to allow mobile devices to operate for relatively long periods without recharging is crucial. Power amplification is one of the functions that consumes a significant amount of battery power in mobile applications. Several system and circuit implementations have been designed to reduce current consumption to extend battery life and improve the thermal reliability of mobile devices. Some common methods for improving the efficiency of power amplifiers in cellular or other mobile applications include average power tracking (APT), envelope tracking (ET), and dynamic load line tuning. However, these methods can involve complex processing and calibration, and are therefore not always desirable in some applications. Summary of the Invention

[0004] The aspects and embodiments described herein relate to a method and circuit implementation for providing programmable load line impedance tuning in a push-pull power amplifier.

[0005] According to one embodiment, a push-pull power amplifier system with variable load line impedance includes: a power amplifier having an input terminal for receiving a radio frequency (RF) input signal and an output terminal, the power amplifier being configured to amplify the RF input signal and provide an RF output signal at the output terminal, the RF output signal being an amplified version of the RF input signal; an output transformer coupled to the output terminal of the power amplifier and configured to provide the RF output signal on a load line coupled to the output terminal of the power amplifier; a switchable bypass capacitor switchably connected between the load line and a reference potential; and a switch configured to selectively connect the switchable bypass capacitor to the reference potential and disconnect the switchable bypass capacitor from the reference potential to change the impedance of the load line.

[0006] In one example, the power amplifier includes a pair of complementary transistors.

[0007] In one example, the impedance of the load line is changed to tune the power level of the RF output signal.

[0008] In one example, the switchable bypass capacitor includes a single fixed-value capacitor. In another example, the switchable bypass capacitor includes a variable capacitor. In yet another example, the switchable bypass capacitor includes multiple capacitors configured to be selectively connected in series and / or in parallel to provide a selected capacitance value.

[0009] In one example, the push-pull power amplifier system further includes an input transformer coupled to the input terminal of the power amplifier. The input transformer is configured to receive the RF input signal, decompose the RF input signal into a pair of balanced RF input signals, and provide a pair of balanced RF input signals to the power amplifier; and the output transformer is configured to receive a pair of balanced RF output signals from the power amplifier and recombine the pair of balanced RF output signals to provide the RF output signal on the load line. In another example, the push-pull power amplifier system further includes an input amplifier coupled to the input terminal of the input transformer, such that the input transformer is connected between the input amplifier and the power amplifier.

[0010] According to another embodiment, a power amplifier system includes: a push-pull power amplifier having an input terminal for receiving a radio frequency (RF) input signal and an output terminal, the power amplifier being configured to amplify the RF input signal and provide an RF output signal at the output terminal, the RF output signal being an amplified version of the RF input signal; a switchable bypass capacitor switchably connected between a load line coupled to the output terminal of the push-pull power amplifier and a reference potential; a switch configured to selectively connect the switchable bypass capacitor to the reference potential and disconnect the switchable bypass capacitor from the reference potential to change the impedance of the load line; and a controller coupled to the switch and configured to control the switch to selectively connect the switchable bypass capacitor to the reference potential and disconnect the switchable bypass capacitor from the reference potential.

[0011] In one example, the impedance of the load line is changed to tune the power level of the RF output signal.

[0012] In one example, the controller is further coupled to the push-pull power amplifier and configured to control one or more parameters of the push-pull power amplifier. In another example, the controller is configured to use the Mobile Industry Processor Interface (MIPI) control protocol to control one or more parameters of the push-pull power amplifier and the switch.

[0013] In one example, the switchable bypass capacitor includes a single fixed-value capacitor. In another example, the switchable bypass capacitor includes a variable capacitor. In one example, the controller is coupled to the variable capacitor and configured to tune the capacitance value of the variable capacitor. In another example, the switchable bypass capacitor includes multiple capacitors and multiple switches configured to selectively connect selected capacitors from the multiple capacitors in series and / or parallel to provide the selected capacitance value of the switchable bypass capacitor. In one example, the controller is coupled to the multiple switches and configured to control the multiple switches to connect the selected capacitors from the multiple capacitors together to provide the selected capacitance value.

[0014] According to another embodiment, a method of operating a power amplifier system having at least two operating modes includes: receiving a radio frequency (RF) input signal at an input of the power amplifier system; amplifying the RF input signal via a push-pull power amplifier to provide the amplified RF signal to a load line; adjusting the impedance of the load line based on the operating mode of the power amplifier system; and providing the amplified RF signal to an output of the power amplifier system via the load line.

[0015] In one example, adjusting the impedance of the load line includes connecting a bypass capacitor between the load line and a reference potential during at least one operating mode. In another example, adjusting the impedance of the load line includes tuning the capacitance value of a variable bypass capacitor coupled between the load line and the reference potential. In one example, adjusting the impedance of the load line includes controlling a plurality of switches to connect a selected bypass capacitor among a plurality of bypass capacitors coupled between the load line and the reference potential together.

[0016] In one example, the impedance of the load line is adjusted based on the operating mode to tune the power level of the amplified RF signal to a target output power level.

[0017] Another embodiment relates to a radio frequency (RF) front-end module, comprising: a transceiver configured to provide an RF transmit signal and receive and process an RF receive signal; a duplexer; an antenna switch coupled to the duplexer, the antenna switch and the duplexer together configured to switch the operation of the RF front-end module between a transmit mode and a receive mode; and a push-pull power amplifier coupled between the transceiver and the duplexer and configured to receive and amplify the RF transmit signal, the push-pull power amplifier including a bypass capacitor switchably connected between the output load line of the push-pull power amplifier and a reference potential, and a switch configured to selectively connect the switchable bypass capacitor to the reference potential and disconnect the switchable bypass capacitor from the reference potential to change the impedance of the output load line.

[0018] In one example, the switchable bypass capacitor includes a single fixed-value capacitor. In another example, the switchable bypass capacitor includes a variable capacitor. In yet another example, the switchable bypass capacitor includes multiple capacitors configured to be selectively connected in series and / or in parallel to provide a selected capacitance value.

[0019] In one example, the transceiver includes transmitter circuitry configured to provide the RF transmitted signal and receiver circuitry configured to receive and process the RF received signal. The RF front-end module may also include a low-noise amplifier coupled between the duplexer and the receiver circuitry and configured to amplify the RF received signal.

[0020] According to another embodiment, a wireless device includes: an antenna; a transceiver configured to provide an RF transmitted signal and receive and process an RF received signal; an antenna switch module coupled between the transceiver and the antenna and configured to switch the operation of the wireless device between a transmit mode and a receive mode; and a power amplifier module coupled between the transceiver and the antenna switch module and configured to receive and amplify the RF transmitted signal, the power amplifier module including at least one push-pull power amplifier having a variable load line impedance, the at least one push-pull power amplifier including a bypass capacitor switchably connected between a load line of the at least one push-pull power amplifier and a reference potential, and a switch configured to selectively connect the switchable bypass capacitor to the reference potential and disconnect the switchable bypass capacitor from the reference potential to change the load line impedance.

[0021] In one example, the switchable bypass capacitor includes a single fixed-value capacitor. In another example, the switchable bypass capacitor includes a variable capacitor. In yet another example, the switchable bypass capacitor includes multiple capacitors configured to be selectively connected in series and / or in parallel to provide a selected capacitance value.

[0022] The wireless device may further include a power management system coupled to the power amplifier module and configured to control the switches of the at least one push-pull power amplifier to selectively change the load line impedance. In one example, the power management system is further coupled to the transceiver and configured to control at least one operating parameter of the transceiver.

[0023] The wireless device may further include a directional coupler connected between the power amplifier module and the antenna switch module, the directional coupler being configured to extract a portion of each of the RF transmitted signals via electromagnetic coupling to provide an RF coupled signal. In one example, the wireless device also includes a sensor coupled to the directional coupler and the transceiver, the sensor being configured to receive the RF coupled signal and provide feedback information to the transceiver to adjust the output power level of the power amplifier module based on the RF coupled signal.

[0024] The wireless device may further include a low-noise amplifier coupled between the antenna switch module and the transceiver and configured to amplify the RF received signal during the receive mode.

[0025] According to another embodiment, an amplifier system includes: a push-pull power amplifier having an input terminal for receiving a radio frequency (RF) input signal and an output terminal, the push-pull power amplifier being configured to amplify the RF input signal and provide an RF output signal at the output terminal, the RF output signal being an amplified version of the RF input signal; a switchable bypass capacitor being switchably connected between a load line connected to the output terminal of the push-pull power amplifier and a reference potential; and a switch configured to selectively connect the switchable bypass capacitor to the reference potential and disconnect the switchable bypass capacitor from the reference potential to change the impedance of the load line.

[0026] In one example, the switchable bypass capacitor includes a single fixed-value capacitor. In another example, the switchable bypass capacitor includes a variable capacitor. In yet another example, the switchable bypass capacitor includes multiple capacitors configured to be selectively connected in series and / or in parallel to provide a selected capacitance value.

[0027] Other aspects, embodiments, and advantages of these exemplary aspects and embodiments are discussed in detail below. The embodiments disclosed herein may be combined with other embodiments in any manner consistent with at least one of the principles disclosed herein, and references to “an embodiment,” “some embodiments,” “an alternative embodiment,” “various embodiments,” “one embodiment,” etc., are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one embodiment. The use of these terms herein does not necessarily refer to the same embodiment. Attached Figure Description

[0028] At least one embodiment will now be discussed with reference to the accompanying drawings, which are not intended to be drawn to scale. The drawings are included to provide illustration and further understanding of the aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended to be a definition of limitation of the invention. In the drawings, each identical or substantially identical component shown in the various figures is represented by the same numerals. For clarity, not every component may be labeled in each figure. In the drawings:

[0029] Figure 1 This is a simplified circuit diagram of an example of a push-pull amplifier with load line switching according to various aspects of the present invention;

[0030] Figure 2 This is a block diagram of an example amplifier system according to various aspects of the present invention;

[0031] Figure 3A This illustrates aspects of the invention. Figure 1 The Smith chart shows the simulation results of the push-pull amplifier example shown.

[0032] Figure 3B This illustrates aspects of the invention. Figure 1 Smith chart of further simulation results for the push-pull amplifier example shown;

[0033] Figure 4A This illustrates an aspect of the invention in which the switchable capacitor is variable. Figure 2 A block diagram of another example of an amplifier system;

[0034] Figure 4B It is applicable to the implementation of various aspects of the present invention. Figure 1 and Figure 2 A block diagram of an example of a capacitor bank arrangement with switchable capacitors.

[0035] Figure 5 This is a block diagram of an example of an RF front-end module incorporated into a push-pull power amplifier according to various aspects of the present invention; and

[0036] Figure 6 This is a block diagram of an example of a wireless device incorporating one or more push-pull power amplifiers according to various aspects of the present invention. Detailed Implementation

[0037] The aspects and embodiments described herein are for improving the efficiency of a power amplifier by introducing a programmable load line that can be switched to present a selected load line impedance to the power amplifier for a given target transmit power, and thus extending battery life and improving device reliability.

[0038] Load line switching can be implemented statically or dynamically. Generally, when driven by a composite modulated signal, dynamic load line switching can potentially improve power amplifier efficiency more than static load line switching. However, implementing dynamic load line switching can be too complex for many applications and may require complex calibration routines. Static load line switching refers to adjusting the load line impedance against the average power without needing to track the modulation envelope. Therefore, because the adjustment only needs to be above the average power, static load line switching can be implemented with less complexity than dynamic load line switching. Furthermore, depending on certain aspects, static load line switching can be implemented in a way that improves power amplifier efficiency without requiring additional device-level calibration routines.

[0039] It should be understood that embodiments of the methods and apparatus discussed herein are not limited in application to the details of the construction and arrangement of components set forth in the following description or shown in the accompanying drawings. The methods and apparatus can be implemented in other embodiments and can be practiced or carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. Furthermore, the wording and terminology used herein are for descriptive purposes and should not be considered limiting. The use of “comprising,” “including,” “having,” “containing,” “involving,” and variations thereof herein is intended to cover the items listed thereafter and their equivalents, as well as additional items. The reference to “or” can be interpreted inclusively, such that any term described using “or” can refer to any one, more than one, or all of the described terms.

[0040] According to certain embodiments described herein, static load line switching is implemented as part of a push-pull power amplifier architecture. Figure 1An example is shown. In this example, the push-pull amplifier 100 includes an input amplifier 102 that amplifies an input radio frequency (RF) signal (RFIN) 104. A first transformer 106 decomposes the single / unbalanced RF input signal 104 into a pair of balanced signals and couples the balanced input signals to a pair of complementary amplifiers 108, 110. A second transformer 112 recombines the amplified balanced signals output from amplifiers 108, 110 and couples the unbalanced output RF signal (RFOUT) 114 to a load line 116. Amplifiers 108, 110 can be implemented as complementary transistors, one transistor dissipating or "sinking" current from the load line 116 to ground or a negative power supply, and the other transistor supplying or draining current from a positive power supply to the load line 116. The transistors can be bipolar junction transistors (BJTs), field-effect transistors (FETs), or other types of transistors. In some examples, amplifiers 108, 110 can be included in a power amplifier.

[0041] exist Figure 1 In the example of the push-pull amplifier 100 shown, a bypass capacitor 118 is connected at a single-ended terminal of the second transformer 112 to adjust the impedance of the load line 116. The bypass capacitor 118 is switchably connected between the load line 116 and a reference potential, which may be ground. By connecting or disconnecting the bypass capacitor 118 from the reference potential using the switch 120 shown, the impedance of the load line 116 can be transformed to the optimal load line at the output of the power amplifiers comprising amplifiers 108 and 110. When connected to the reference potential, the bypass capacitor 118 adjusts both the real and imaginary parts of the load line impedance and provides important tuning parameters for the power amplifier load line 116 in addition to the tuning provided by the transformer 112 itself. Some embodiments described herein may include one or more additional switchable bypass capacitors 118 to increase or decrease the impedance value of the power amplifier load line 116 by selectively connecting or disconnecting (programming) the switchable capacitor(s) 118 from the reference potential. Figure 1 The example shown includes a single switchable capacitor 118 controlled by switch 120; however, other examples and embodiments may include multiple switchable capacitors 118 that can be programmed to adjust the impedance of load line 116 across different target power levels. Additionally, in some examples, one or more switchable capacitors 118 may be variable capacitors.

[0042] The switch 120 that controls (multiple) switchable bypass capacitors 118 can be controlled by a controller, which can be part of or coupled to the push-pull amplifier 100. Figure 2A block diagram of an example amplifier system including a push-pull amplifier 100 and a controller 200 is shown. In this example, the components of the push-pull amplifier 100, except for the switchable bypass capacitor(s) 118 and the associated switch 120, are generally represented at block 202, which connects the input 204 (where the signal RFIN 104 is received) and the output 206 (where the amplified signal RFOUT 114 is provided). The controller 200 can provide control signals to the components 202 of the push-pull amplifier 100 and can also control the switch 120, as indicated by arrow 208. In some examples, the controller 200 controls the components 202 of the push-pull amplifier 100 via a digital control protocol or interface known as the Mobile Industry Processor Interface (MIPI). Thus, in some examples, the switch 120 can also be controlled via MIPI, allowing the impedance adjustment of the load line 116 to be seamlessly integrated into existing amplifier systems or modules without requiring additional calibration, software, or application annotation changes. It should be understood that different serial communication interfaces other than MIPI can be used, such as I... 2 C, SPI, etc. In some examples, parallel communication interfaces can be used.

[0043] Examples of load line programmability have been demonstrated through simulation. Figure 3A and Figure 3B The simulation results shown confirm the programmability of the load line 116 when the switchable capacitor 118 is connected to the reference potential by the switch 120 (“on”) and disconnected from the reference potential (“off”). The simulation was performed in the frequency range of 2.0 GHz to 3.0 GHz and confirmed the impedance of the load line 116 within this range. Figure 3A Simulation results are shown for a lower desired power output from the push-pull amplifier 100 achieved by switching on the switchable capacitor 11, and consequently, a higher load line impedance. Figure 3B Simulation results show the higher desired power output from the push-pull amplifier 100 achieved by turning off the switchable capacitor 118, and consequently, the lower load line impedance. See reference... Figure 3A and 3B As can be seen, switching the bypass capacitor 118 from the reference potential changes the load line impedance while maintaining good matching over the analog frequency range.

[0044] Refer again Figure 1According to some examples, the impedance of the load line 116 can be adjusted to a desired target value by selecting the value of (or a plurality of) switchable capacitors 118 relative to the value of a fixed capacitor 122 typically present at the output of the push-pull amplifier 100. As mentioned above, in some examples, the switchable capacitors 118 may include a variable capacitor and / or a set of switchable capacitors. This allows the load line impedance to be tuned with a specific tolerance or resolution, and / or extends the tuning range of the impedance values. For example, Figure 4A An example is shown in which the switchable capacitor 118 is a variable capacitor whose capacitance value can be dynamically adjusted, for example, under the control of the controller 200. Using a variable switchable capacitor 118 allows for greater tuning of the load line impedance compared to tuning achievable using only a single fixed-value switchable capacitor. In an example where a set of switchable capacitors can be used to implement the switchable capacitor 118, the set can contain any number of capacitors that can be connected together in series, parallel, or in a combination thereof. Figure 4B An example of a switchable capacitor 118 implemented as a capacitor bank is shown. Internal switches 402 can be used to connect any number of capacitors 404 together using combinations of series and parallel connections. In some examples, each of the internal switches 402 can be independently controlled to provide different configurations of series and parallel connections. While in Figure 4B Not specifically shown, but any of the capacitors 404 can be a variable capacitor. In some examples, switch 402 can be controlled by controller 200.

[0045] Embodiments of the push-pull power amplifier 100 can be advantageously used in a variety of electronic devices. For example, embodiments of the push-pull power amplifier 100 can be used as a power amplifier or as part of a power amplifier module included in a variety of communication modules and devices, including, for example, RF front-end modules and wireless devices.

[0046] Figure 5 This is a block diagram illustrating an example of a typical arrangement of an RF "front-end" subsystem or module (FEM) 500, for example, to transmit and receive RF signals, which can be used in a communication device (such as a mobile phone). The FEM 500 is connected to an antenna 610 and includes a duplexer 510 and an antenna switch 520, allowing the FEM 500 to be configured to switch between different frequency bands and different operating modes (e.g., transmit and receive modes). Figure 5In the example shown, antenna switch 520 is positioned between duplexer 510 and antenna 610; however, in other examples, duplexer 510 may be positioned between antenna switch 520 and antenna 610, or antenna switch 520 and duplexer 510 may be integrated into a single module. FEM 500 includes transceiver 530 configured to generate RF signals for transmission and process received RF signals. Transceiver 530 may include transmitter circuitry 532 and receiver circuitry 534. In some embodiments, the transmission and reception functions may be implemented in separate components (e.g., a transmission module and a receiver module) or in the same module, such as... Figure 5 As shown. The signal generated by transmitter circuit 532 is received by push-pull power amplifier 100, which amplifies the signal generated from transceiver 530. As those skilled in the art will understand, push-pull power amplifier 100 refers to one or more push-pull power amplifiers 100 that may be included in FEM 500. As described above, push-pull power amplifier 100 may include one or more switchable, optionally variable, capacitors to adjust the output load line (in Figure 5 The impedance connected to duplexer 510 in the example shown is optimally adapted to accommodate different desired power levels or amplifications provided by push-pull power amplifier 100. Front-end module 500 also includes low-noise amplifier module 540, which amplifies the received signal from antenna 610 and provides the amplified signal to receiver circuitry 534 of transceiver 520. Transceiver 530 can communicate with wireless devices or other circuitry in other components using FEM 500, as indicated by arrow 536. The ability to tune the load line impedance of push-pull power amplifier 100 using switchable bypass capacitors 118 as described above allows FEM 500 to operate effectively in various situations and applications, such as where the power level of the input RF signal from transmitter circuitry 532 can vary and / or where the desired power level of the output transmitted signal transmitted by antenna 610 can be dynamically adjusted (e.g., in response to environmental conditions) or changed to comply with different communication protocols.

[0047] Figure 6This is a block diagram of an example of a wireless device 600 that may include an embodiment of FEM 500 or similar components. Wireless device 600 may be a cellular phone, smartphone, tablet, modem, communication network, or any other portable or non-portable device configured for voice and / or data communication. Wireless device 600 may receive and transmit signals from antenna 610. Wireless device 600 includes antenna switch module 620, which may be used, for example, to switch between transmit and receive modes of wireless device 600, or to switch between different transmit or receive frequency bands. In some examples, antenna switch module 620 includes the antenna switch 520 and duplexer 510 of the FEM 500 described above. Wireless device 600 also includes transceiver 530, which is configured to generate signals for transmitting and / or processing received signals. Figure 6 As shown, in some embodiments, antenna 610 receives signals provided to transceiver 530 via antenna switch module 620 and also transmits signals from wireless device 600. However, in other examples, multiple antennas may be used.

[0048] The signal generated for transmission is received by power amplifier (PA) module 100a, which amplifies the signal generated from transceiver 530. Power amplifier module 100a may include one or more push-pull power amplifiers 100 as described above. Power amplifier module 100a can be used to amplify a wide variety of RF or other frequency band transmission signals. For example, power amplifier module 100a may receive an enable signal that can be used to pulse the output of the power amplifier to assist in transmitting wireless local area network (WLAN) signals or any other suitable pulsed signal. Power amplifier module 100a can be configured to amplify signals of various signal types, including, for example, Global System for Mobile Communications (GSM) signals, Code Division Multiple Access (CDMA) signals, W-CDMA signals, Long Term Evolution (LTE) signals, or EDGE signals. As described above, the ability to tune the load line impedance of any one or more push-pull power amplifiers 100a in power amplifier module 100a allows power amplifier module 100a to operate efficiently with any of these or other different signal types and communication protocols. In some examples, the receiving path may include a low-noise amplifier (LNA) 540 configured to amplify the received signal.

[0049] The directional coupler 630 can be used to extract a portion of the power from the RF signal traveling between the power amplifier module 100a and the antenna 610, and to provide the coupled signal(s) to the sensor module 640. The sensor module 640 can send information to the transceiver 530 and / or directly to the power amplifier module 100a as feedback for adjustments to regulate the output power level of the power amplifier module 100a. In some embodiments where the wireless device 600 is a mobile phone with a Time Division Multiple Access (TDMA) architecture, the directional coupler 530 can advantageously manage the amplification of the RF transmit power signal from the power amplifier module 100a. In mobile phones with a Time Division Multiple Access (TDMA) architecture, such as those found in Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), and Wideband Code Division Multiple Access (W-CDMA) systems, the power amplifier module 100a can be used to move the power envelope up and down within a specified power-to-time constraint. For example, a particular mobile phone can be assigned a transmission time slot for a particular channel. In this configuration, power amplifier module 100a can be used to assist in adjusting the power level of one or more RF power signals over time, thereby preventing signal interference from the transmitted signal during the allocated receive time slot and reducing power consumption. In such a system, directional coupler 630 can be used to measure the power of the power amplifier output signal to help control power amplifier module 100a. As described above, since the power level of power amplifier module 100a is adjusted, the switchable capacitors 118 associated with the push-pull amplifier(s) constituting power amplifier module 100a can be switched on or off to adjust the load line impedance, thereby improving the efficiency of power amplifier module 100a and helping to conserve battery life in wireless device 600.

[0050] Still referencing Figure 6The wireless device 600 also includes a power management system 650 connected to the transceiver 530 and managing power during operation of the wireless device 600. The power management system 650 can also control the operation of the baseband subsystem 660 and other components of the wireless device 600. The power management system 650 may include or be connected to a battery (not shown) that supplies power to the various components of the wireless device 600. The power management system 650 may further include one or more processors or controllers, such as the controller 200 described above, which can provide control signals to configure the operation of various components of the wireless device 600, including, for example, the power amplifier module 100a and the directional coupler 630. In one embodiment, the baseband subsystem 660 is connected to a user interface 670 to facilitate various inputs and outputs of voice and / or data provided to and received from the user. The baseband subsystem 660 may also be connected to a memory 680 configured to store data and / or instructions to facilitate the operation of the wireless device and / or to provide information to the user.

[0051] Several aspects of at least one embodiment have been described above, and it should be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. Such changes, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Therefore, the foregoing description and drawings are merely illustrative, and the scope of the invention should be determined by the appropriate construction of the appended claims and their equivalents.

Claims

1. A push-pull power amplifier system having an input, an output, and a variable load line impedance, comprising: an input amplifier coupled to the input of the push-pull power amplifier system to receive an unbalanced radio frequency (RF) input signal and provide an unbalanced amplified RF signal at an output of the input amplifier; an input transformer having a primary winding coupled to the output of the input amplifier and a secondary winding to provide a pair of balanced RF signals based on the unbalanced amplified RF signal; a pair of complementary amplifiers to receive respective ones of the pair of balanced RF signals and provide a pair of amplified balanced RF signals; an output transformer having a primary winding to receive respective ones of the pair of amplified balanced RF signals and a secondary winding to provide an unbalanced amplified RF output signal on a load line coupled to the output of the push-pull power amplifier system; a switchable bypass capacitance switchably connected between the load line and a reference potential; and a switch configured to selectively connect and disconnect the switchable bypass capacitance to and from the reference potential to vary an impedance of the load line. the impedance of the load line is varied to tune a power level of the unbalanced amplified RF output signal.

2. The push-pull power amplifier system of claim 1, wherein, the switchable bypass capacitance comprises a single fixed value capacitor.

3. The push-pull power amplifier system of claim 1, wherein, the switchable bypass capacitance comprises a variable capacitor.

4. The push-pull power amplifier system of claim 1, wherein, the switchable bypass capacitance comprises a plurality of capacitors configured to be selectively connected together in series and / or parallel to provide a selected capacitance value.

5. The push-pull power amplifier system of claim 1, wherein, 6. The push-pull power amplifier system of claim 1, further comprising: a controller coupled to the switch and configured to control the switch to selectively connect and disconnect the switchable bypass capacitance to and from the reference potential. the controller is further coupled to the pair of complementary amplifiers and configured to control one or more parameters of the pair of complementary amplifiers.

7. The push-pull power amplifier system of claim 6, wherein, the controller is configured to control the one or more parameters of the pair of complementary amplifiers and the switch using a Mobile Industry Processor Interface (MIPI) control protocol.

8. The push-pull power amplifier system of claim 7, wherein, the switchable bypass capacitance comprises a variable capacitor, and wherein the controller is coupled to the variable capacitor and configured to tune a capacitance value of the variable capacitor.

9. The push-pull power amplifier system of claim 6, wherein, the switchable bypass capacitance comprises a plurality of capacitors and a plurality of switches configured to selectively connect selected ones of the plurality of capacitors together in series and / or parallel to provide a capacitance value of the selected ones of the plurality of capacitors.

10. The push-pull power amplifier system of claim 6, wherein, the controller is coupled to the plurality of switches and configured to control the plurality of switches to connect the selected ones of the plurality of capacitors together to provide the selected capacitance value.

11. The push-pull power amplifier system of claim 10, wherein, 12. A method of operating the push-pull power amplifier system of claim 1 having an input, an output, and a variable load line impedance, the push-pull power amplifier system having at least two modes of operation, the method comprising: ​ receiving a radio frequency (RF) input signal at an input of the power amplifier system; amplifying the RF input signal via an amplifier in the power amplifier system to provide an amplified RF signal to a load line; adjusting an impedance of the load line based on the operating mode of the power amplifier system; and providing the amplified RF signal to an output of the power amplifier system via the load line.

13. The method of claim 12, wherein, Adjusting the impedance of the load line also includes connecting a bypass capacitor between the load line and a reference potential during at least one operating mode.

14. The method of claim 12, wherein, Adjusting the impedance of the load line also includes tuning a capacitance value of a variable bypass capacitor coupled between the load line and a reference potential.

15. The method of claim 12, wherein, Adjusting the impedance of the load line also includes controlling a plurality of switches to connect together selected ones of a plurality of bypass capacitors coupled between the load line and a reference potential.

16. The method of any one of claims 12-15, wherein, Adjusting the impedance of the load line based on the operating mode to tune a power level of the amplified RF signal to a target output power level.

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