Download or read book Broadband Doherty Power Amplifiers with Enhanced Linearity for Emerging Radio Transmitters written by Hamed Golestaneh and published by . This book was released on 2016 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: The ever-increasing demand for utilizing wireless spectra has led to development of spectrally efficient radio systems. While these systems offer much higher data throughput, they employ more sophisticated modulation schemes, which result in wideband signals with high peak-to-average power ratios. These signal characteristics significantly complicate the design of RF transmitters, particularly power amplifiers, in terms of power efficiency and linearity requirements. Furthermore, upcoming wireless standards, such as long term evolution advanced (LTE-A) require adoption of carrier aggregation which incorporates multiple component carriers to yield aggregated channels of larger bandwidth (up to 100 MHz). On the other hand, the emerging systems are expected to support legacy standards with minimum area, cost, and power overhead, and thus call for highly-efficient linear broadband power amplifiers capable of efficiently amplifying concurrent modulated signals located over a broad carrier frequency range. This thesis focuses on Doherty power amplifiers (DPAs) with extended high-efficiency range, enhanced bandwidth and improved linearity as a solution for high-efficiency multi-band multi-standard transmitters. It addresses three major concerns associated with DPAs, namely, back-off efficiency, bandwidth, and linearity.

Download or read book Bandwidth and Efficiency Enhancement in Radio Frequency Power Amplifiers for Wireless Transmitters written by Karun Rawat and published by Springer Nature. This book was released on 2020-03-05 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on broadband power amplifier design for wireless communication. Nonlinear model embedding is described as a powerful tool for designing broadband continuous Class-J and continuous class F power amplifiers. The authors also discuss various techniques for extending bandwidth of load modulation based power amplifiers, such as Doherty power amplifier and Chireix outphasing amplifiers. The book also covers recent trends on digital as well as analog techniques to enhance bandwidth and linearity in wireless transmitters. Presents latest trends in designing broadband power amplifiers; Covers latest techniques for using nonlinear model embedding in designing power amplifiers based on waveform engineering; Describes the latest techniques for extending bandwidth of load modulation based power amplifiers such as Doherty power amplifier and Chireix outphasing amplifiers; Includes coverage of hybrid analog/digital predistortion as wideband solution for wireless transmitters; Discusses recent trends on on-chip power amplifier design with GaN /GaAs MMICs for high frequency applications.

Download or read book High Efficiency Load Modulation Power Amplifiers for Wireless Communications written by Zhancang Wang and published by Artech House. This book was released on 2017-06-30 with total page 389 pages. Available in PDF, EPUB and Kindle. Book excerpt: This cutting-edge resource presents a complete and systematic overview of the practical design considerations of radio frequency (RF) high efficiency load modulation power amplifiers (PA) for modern wireless communications for 4G and beyond. It provides comprehensive insight into all aspects of load modulation PA design and optimization not only covering design approaches specifically for passive and active load modulation operation but also hybrid with dynamic supply modulation and digital signal processing algorithms required for performance enhancement. Passive load impedance tuner design, dynamic load modulation PA, active load modulation PA and Doherty PA design for efficiently enhancement are explained. Readers find practical guidance into load modulation PA design for bandwidth extension, including video bandwidth enhancement techniques, broadband dynamic load amplifiers, topology selection, design procedures, and network output. This book presents the evolution and integration of classical load modulation PA topologies in order to meet new challenges in the field.

Download or read book RADIO FREQUENCY AND MICROWAVE POWER AMPLIFIERS written by and published by . This book was released on 2019 with total page 499 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Doherty Power Amplifiers written by Bumman Kim and published by Academic Press. This book was released on 2018-03-28 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: Doherty Power Amplifiers: From Fundamentals to Advanced Design Methods is a great resource for both RF and microwave engineers and graduate students who want to understand and implement the technology into future base station and mobile handset systems. The book introduces the very basic operational principles of the Doherty Amplifier and its non-ideal behaviors. The different transconductance requirements for carrier and peaking amplifiers, reactive element effect, and knee voltage effect are described. In addition, several methods to correct imperfections are introduced, such as uneven input drive, gate bias adaptation, dual input drive and the offset line technique. Advanced design methods of Doherty Amplifiers are also explained, including multistage/multiway Doherty power amplifiers which can enhance the efficiency of the amplification of a highly-modulated signal. Other covered topics include signal tracking operation which increases the dynamic range, highly efficient saturated amplifiers, and broadband amplifiers, amongst other comprehensive, related topics. Specifically written on the Doherty Power Amplifier by the world’s leading expert, providing an in-depth presentation of principles and design techniques Includes detailed analysis on correcting non-ideal behaviors of Doherty Power Amplifiers Presents advanced Doherty Power Amplifier architectures

Download or read book Linear CMOS RF Power Amplifiers for Wireless Applications written by Paulo Augusto Dal Fabbro and published by Springer Science & Business Media. This book was released on 2010-06-22 with total page 171 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in electronics have pushed mankind to create devices, ranging from - credible gadgets to medical equipment to spacecraft instruments. More than that, modern society is getting used to—if not dependent on—the comfort, solutions, and astonishing amount of information brought by these devices. One ?eld that has continuously bene?tted from those advances is the radio frequency integrated c- cuit (RFIC) design, which in its turn has promoted countless bene?ts to the mankind as a payback. Wireless communications is one prominent example of what the - vances in electronics have enabled and their consequences to our daily life. How could anyone back in the eighties think of the possibilities opened by the wireless local area networks (WLANs) that can be found today in a host of places, such as public libraries, coffee shops, trains, to name just a few? How can a youngster, who lives this true WLAN experience nowadays, imagine a world without it? This book dealswith the design oflinearCMOS RF PowerAmpli?ers(PAs). The RF PA is a very important part of the RF transceiver, the device that enables wireless communications. Two important aspects that are key to keep the advances in RF PA design at an accelerate pace are treated: ef?ciency enhancement and frequen- tunable capability. For this purpose, the design of two different integrated circuits realizedina0. 11μmtechnologyispresented,eachoneaddressingadifferentaspect. With respect to ef?ciency enhancement, the design of a dynamic supply RF power ampli?er is treated, making up the material of Chaps. 2 to 4.

Download or read book High Efficiency CMOS Power Amplifiers for Drain Modulation Based RF Transmitters written by Mohammad Reza Ghajar and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Broadband RF and Microwave Amplifiers written by Andrei Grebennikov and published by CRC Press. This book was released on 2017-07-12 with total page 750 pages. Available in PDF, EPUB and Kindle. Book excerpt: Broadband RF and Microwave Amplifiers provides extensive coverage of broadband radio frequency (RF) and microwave power amplifier design, including well-known historical and recent novel schematic configurations, theoretical approaches, circuit simulation results, and practical implementation strategies. The text begins by introducing two-port networks to illustrate the behavior of linear and nonlinear circuits, explaining the basic principles of power amplifier design, and discussing impedance matching and broadband power amplifier design using lumped and distributed parameters. The book then: Shows how dissipative or lossy gain-compensation-matching circuits can offer an important trade-off between power gain, reflection coefficient, and operating frequency bandwidth Describes the design of broadband RF and microwave amplifiers using real frequency techniques (RFTs), supplying numerous examples based on the MATLAB® programming process Examines Class-E power amplifiers, Doherty amplifiers, low-noise amplifiers, microwave gallium arsenide field-effect transistor (GaAs FET)-distributed amplifiers, and complementary metal-oxide semiconductor (CMOS) amplifiers for ultra-wideband (UWB) applications Broadband RF and Microwave Amplifiers combines theoretical analysis with practical design to create a solid foundation for innovative ideas and circuit design techniques.

Download or read book High efficiency Linear RF Power Amplifiers Development written by Nuttapong Srirattana and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Next generation mobile communication systems require the use of linear RF power amplifier for higher data transmission rates. However, linear RF power amplifiers are inherently inefficient and usually require additional circuits or further system adjustments for better efficiency. This dissertation focuses on the development of new efficiency enhancement schemes for linear RF power amplifiers. The multistage Doherty amplifier technique is proposed to improve the performance of linear RF power amplifiers operated in a low power level. This technique advances the original Doherty amplifier scheme by improving the efficiency at much lower power level. The proposed technique is supported by a new approach in device periphery calculation to reduce AM/AM distortion and a further improvement of linearity by the bias adaptation concept. The device periphery adjustment technique for efficiency enhancement of power amplifier integrated circuits is also proposed in this work. The concept is clearly explained together with its implementation on CMOS and SiGe RF power amplifier designs. Furthermore, linearity improvement technique using the cancellation of nonlinear terms is proposed for the CMOS power amplifier in combination with the efficiency enhancement technique. In addition to the efficiency enhancement of power amplifiers, a scalable large-signal MOSFET model using the modified BSIM3v3 approach is proposed. A new scalable substrate network model is developed to enhance the accuracy of the BSIM3v3 model in RF and microwave applications. The proposed model simplifies the modeling of substrate coupling effects in MOS transistor and provides great accuracy in both small-signal and large-signal performances.

Download or read book Design of Linear RF Outphasing Power Amplifiers written by Xuejun Zhang and published by Artech House. This book was released on 2003 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the first book devoted exclusively to the outphasing power amplifier, covering the most recent research results on important aspects in practical design and applications. A compilation of all the proposed outphasing approaches, this is an important resource for engineers designing base station and mobile handset amplifiers, engineering managers and program managers supervising power amplifier designs, and R&D personnel in industry. The work enables you to: design microwave power amplifiers with higher efficiency and improved linearity at a lower cost; understand linearity and performance tradeoffs in microwave power amplifiers; and understand the effect of new modulation techniques on microwave power amplifiers.

Download or read book High Efficiency and High Linearity Doherty Amplifiers for Portable Wireless Communications written by Yu Zhao and published by . This book was released on 2006 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt: The design of power amplifiers for wireless systems has become a challenging task due to increasingly stringent requirements on transmitters. The Doherty amplifier is an important candidate for this type of application due to its feature of high efficiency over an extended power range. However, Doherty amplifiers in practice have often failed to exhibit the superb efficiency predicted by theory and their linearity is not always adequate to meet strict specifications of systems with high Peak-to-Average Ratio (PAR) signals such as CDMA systems. The objective of this dissertation is to provide a path for Doherty amplifiers that leads to a simultaneous high efficiency and high linearity performance. First, based on detailed understanding of Doherty amplifier theory and careful investigation of behavior of Doherty amplifiers, a series of guidelines for designing a Doherty amplifier was created. A Doherty amplifier based on GaAs FET devices was accordingly designed in simulation and then fabricated. Simulation and measurement results were compared to provide a description of performance issues of the Doherty amplifier. Following the studies on characteristics of the Doherty amplifier, a new digital signal processing (DSP) control strategy was developed, which involves control of the gate bias voltage of the auxiliary amplifier. DSP was utilized to mitigate gain variations through this bias control and to eliminate phase distortion through baseband phase predistortion. The strategy was shown to significantly improve linearity of the Doherty amplifier, enabling it to meet ACPR specifications with IS-95 signals. The Doherty amplifier also maintained its high efficiency performance. Advantages of analog component based predistortion were also studied and demonstrated by experiments. Finally, in an effort to find a circuit solution for high linearity Doherty amplifiers, nonlinear behavior in Doherty amplifiers was investigated. A simple analytical model was developed based on full transistor models. The model enables nonlinearity analysis associated with each nonlinear component in the transistor. This results in accurate distortion prediction for a Doherty amplifier implemented with HBTs. The model provides diagnosis of nonlinearity in the Doherty amplifier. Accordingly, simple circuit modifications were made to significantly enhance linearity. Experimental results demonstrate the efficacy of this model.

Download or read book Highly Linear Integrated Wideband Amplifiers written by Henrik Sjoland and published by Springer Science & Business Media. This book was released on 1999-01-31 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: Highly Linear Integrated Wideband Amplifiers: Design and Analysis Techniques for Frequencies from Audio to RF deals with the complicated issues involved in the design of high-linearity integrated wideband amplifiers for different operating frequencies. The book demonstrates these principles using a number of high-performance designs. New topologies for high linearity are presented, as well as a novel method for estimating the intermodulation distortion of a wideband signal. One of the most exciting results presented is an enhanced feedback configuration called feedback boosting that is capable of very low distortion. Also important is a statistical method for relating the intermodulation distortion of a wideband signal to the total harmonic distortion (THD) of a single tone. The THD, as opposed to the intermodulation distortion of the wideband signal, is easy to measure and use as a design parameter. Three different applications where high linearity is needed are identified, namely audio power amplifiers, wideband IF amplifiers and RF power amplifiers. For these applications high-performance integrated amplifier designs using novel topologies are presented together with measurement results. The audio amplifiers are built in CMOS and are capable of driving 8Omega loudspeaker loads directly without using any external components. One of the designs can operate on a supply voltage down to 1.5V. Both bipolar and CMOS wideband IF amplifiers are built; they are fully differential and have linearity from DC to 20 MHz. Finally, an RF power amplifier is built in CMOS, without using inductors, in order to investigate what performance can be achieved without them. Highly Linear Integrated Wideband Amplifiers: Design and Analysis Techniques for Frequencies from Audio to RF is an excellent reference for researchers and designers of integrated amplifiers, and may be used as a text for advanced courses on the topic.

Download or read book Development of High Efficiency and High Linearity Power Amplifiers written by Mohamed Magdi Ahmed Darwish and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Power amplifiers typically dominate transmitter and system characteristics. They have the highest DC power consumption, power dissipation, and heat dissipation. Power MMICs have the largest chip area which means higher cost. Modern communication digital modulation techniques require that PAs should have high linear characteristics. On the other hand, PAs are required to be efficient to decrease power consumption and to extend the operation life of battery operated devices. Gallium Nitride PAs became the focus of industry in the last decade. They provide the highest power density among other technologies, as well as providing high efficiency and are suitable for wide bandwidth applications. On the other hand, they suffer from soft compression, AM/AM and AM/PM distortions at higher levels compared to GaAs and Si based devices. Also, since GaN is considered a new technology power gain decreases for mm-wave frequencies. In this Ph.D. research, we address 3 problems: linearity, efficiency and gain of mm-wave power amplifiers. We present 4 contributions; First, we demonstrate the design of a linear and high efficient power amplifier (PA) by using different gate bias voltages for parallelly combined Gallium Nitride (GaN) high electron mobility transistors (HEMTs). The experimental results show that the linearized PA achieves the gain flatness of 0.3 dB over a 35 dB power range and has a measured sharp output power at 1 dB compression point (P1dB) of 38.5 dBm, less than 2 dB below the saturated power (P[subscript SAT]). The measured adjacent channel power ratio (ACPR) of the proposed linearized PA shows up to 8 dB improvements over the PA biased ~ class A (47% Idss) Second, we propose a new modulating load range for a Doherty power amplifier (DPA) that will maintain maximum drain voltage swing and consequently peak efficiency in over 6-dB power back-off (PBO). At 6-dB PBO, the real part of the new modulating load seen by the main amplifier is less than 2*R[subscript opt]. The new load range allows for the design of a compact, low loss output matching and combiner circuit and a simple single drain bias line for the main and auxiliary amplifiers. The proposed 2-stage DPA using the new modulating loads is designed at 15 GHZ in a 0.15 [mu]m enhancement mode (E-mode) Gallium Arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) process. The proposed DPA achieves a measured P[subscript sat] of 27 dBm, a peak power added efficiency (PAE) of 41% and a PAE of 34% at 6 dB PBO with a gain of 17 dB. Third, we propose an extended range Doherty power amplifier (DPA) to achieve high efficiency at 9-dB power back-off (PBO) using a novel loading impedance range. The proposed loading impedance range enables the auxiliary transistor to deliver more current so that symmetric devices can be used in the DPA and results in a compact and low loss output combining circuit. A 20-Watt DPA using Gallium nitride high electron mobility transistors (GaN HEMTs) at 3.5 GHz has been developed to demonstrate the concept. Measurements show power added efficiency (PAE) of 69% at 42.9 dBm saturation output power, PAE of 55% at 9-dB PBO, and gain of 12 dB. We believe our proposed DPA has the highest 9-dB PBO PAE of 55% among reported GaN DPA’s. Finally, we introduce an inductive feedback technique to enhance the gain of mm-wave power amplifiers. A 3-stage 60 GHz PA was designed with 22 dB gain and output power of almost 1-watt.

Download or read book RF and mm Wave Power Generation in Silicon written by Hua Wang and published by Academic Press. This book was released on 2015-12-10 with total page 578 pages. Available in PDF, EPUB and Kindle. Book excerpt: RF and mm-Wave Power Generation in Silicon presents the challenges and solutions of designing power amplifiers at RF and mm-Wave frequencies in a silicon-based process technology. It covers practical power amplifier design methodologies, energy- and spectrum-efficient power amplifier design examples in the RF frequency for cellular and wireless connectivity applications, and power amplifier and power generation designs for enabling new communication and sensing applications in the mm-Wave and THz frequencies. With this book you will learn: Power amplifier design fundamentals and methodologies Latest advances in silicon-based RF power amplifier architectures and designs and their integration in wireless communication systems State-of-the-art mm-Wave/THz power amplifier and power generation circuits and systems in silicon Extensive coverage from fundamentals to advanced design topics, focusing on various layers of abstraction: from device modeling and circuit design strategy to advanced digital and mixed-signal architectures for highly efficient and linear power amplifiers New architectures for power amplifiers in the cellar and wireless connectivity covering detailed design methodologies and state-of-the-art performances Detailed design techniques, trade-off analysis and design examples for efficiency enhancement at power back-off and linear amplification for spectrally-efficient non-constant envelope modulations Extensive coverage of mm-Wave power-generation techniques from the early days of the 60 GHz research to current state-of the-art reconfigurable, digital mm-Wave PA architectures Detailed analysis of power generation challenges in the higher mm-Wave and THz frequencies and novel technical solutions for a wide range for potential applications, including ultrafast wireless communication to sensing, imaging and spectroscopy Contributions from the world-class experts from both academia and industry

Download or read book Extended Bandwidth Doherty Power Amplifier for Carrier Aggregated Signals written by Mehdi Naseri Ali Abadi and published by . This book was released on 2014 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the conventional classes of power amplifiers the efficiency drops at power back-off, whereas in order to maximize the spectral efficiency and data rate, wireless communication standards employ signals with high peak to average power ratio. This results in low average efficiency for power amplifiers, which in turn results in heavy cooling requirements and damage to the environment. To improve the low back-off efficiency Doherty technique has been widely investigated. But, the conventional Doherty power amplifiers are fairly narrowband, while modern transmitters are needed to support multiple standards and operate at multiple frequency bands. This thesis proposes two novel output combiners for Doherty power amplifiers with extended bandwidth. It will be shown analytically how the problem of wideband Doherty can be converted into an impedance synthesization problem. Then two networks to synthesize the desired impedance are proposed. To achieve the proper load modulation over a wide bandwidth, the first proposed combiner employs a quarter-wave short-circuited stub at the output of the peaking transistor and the second proposed combiner uses a parallel LC tank at the same node. In addition to inherent wideband characteristics, the proposed Doherty output combiners have three other important benefits. First, they present small low-frequency impedance for both the main and peaking transistors, which results in improved linearity and linearizability when the amplifier is concurrently driven with multi-band modulated signals. Second, the new combiners result in smaller group delay variation across the band compared to the conventional Doherty amplifier, which results in improved linearizability when the amplifier is driven with extra wideband modulated signals. Finally, the output capacitance of the peaking transistor can be easily absorbed into the combiners without compromising the performance of the amplifier. The thesis starts with an overview of the Doherty power amplifier principles and provides a bandwidth analysis for the conventional Doherty power amplifier. Then it continues with the new approach to extend the bandwidth of Doherty amplifiers with respect to requirements of multi-band transmission. Based on the proposed combiners, two Gallium Nitride 20 W Doherty power amplifiers have been designed and fabricated. The measurement results have been provided to validate the developed theory. The first amplifier covers 1.72 to 2.27 GHz and the second one covers 700 to 950 MHz and both maintain higher than 48 % of drain efficiency at 6 dB back-off across the band. The two amplifiers are successfully linearized when driven with carrier aggregated modulated signals.

Download or read book Concurrent Multi band Envelope Tracking Power Amplifiers for Emerging Wireless Communications written by Hassan Sarbishaei and published by . This book was released on 2014 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: Emerging wireless communication is shifting toward data-centric broadband services, resulting in employment of sophisticated and spectrum efficient modulation and access techniques. This yields communication signals with large peak-to-average power ratios (PAPR) and stringent linearity requirements. For example, future wireless communication standard, such as long term evolution advanced (LTE-A) require adoption of carrier aggregation techniques to improve their effective modulation bandwidth. The carrier aggregation technique for LTE-A incorporates multiple carriers over a wide frequency range to create a wider bandwidth of up to 100MHz. This will require future power amplifiers (PAs) and transmitters to efficiently amplify concurrent multi-band signals with large PAPR, while maintaining good linearity. Different back-off efficiency enhancement techniques are available, such as envelope tracking (ET) and Doherty. ET has gained a lot of attention recently as it can be applied to both base station and mobile transmitters. Unfortunately, few publications have investigated concurrent multi-band amplification using ET PAs, mainly due to the limited bandwidth of the envelope amplifier. In this thesis, a novel approach to enable concurrent amplification of multi-band signals using a single ET PA will be presented. This thesis begins by studying the sources of nonlinearities in single-band and dual-band PAs. Based on the analysis, a design methodology is proposed to reduce the sources of memory effects in single-band and dual-band PAs from the circuit design stage and improve their linearizability. Using the proposed design methodology, a 45W GaN PA was designed. The PA was linearized using easy to implement, memoryless digital pre-distortion (DPD) with 8 and 28 coefficients when driven with single-band and dual-band signals, respectively. This analysis and design methodology will enable the design of PAs with reduced memory effects, which can be linearized using simple, power efficient linearization techniques, such as lookup table or memoryless polynomial DPD. Note that the power dissipation of the linearization engine becomes crucial as we move toward smaller base station cells, such as femto- and pico-cells, where complicated DPD models cannot be implemented due to their significant power overhead. This analysis is also very important when implementing a multi-band ET PA system, where the sources of memory effects in the PA itself are minimized through the proposed design methodology. Next, the principle of concurrent dual-band ET operation using the low frequency component (LFC) of the envelope of the dual-band signal is presented. The proposed dual-band ET PA modulates the drain voltage of the PA using the LFC of the envelope of the dual-band signal. This will enable concurrent dual-band operation of the ET PA without posing extra bandwidth requirements on the envelope amplifier. A detailed efficiency and linearity analysis of the dual-band ET PA is also presented. Furthermore, a new dual-band DPD model with supply dependency is proposed in this thesis, capable of capturing and compensating for the sources of distortion in the dual-band ET PA. To the best of our knowledge, concurrent dual-band operation of ET PAs using the LFC of the envelope of the dual-band signal is presented for the first time in the literature. The proposed dual-band ET operation is validated using the measurement results of two GaN ET PA prototypes. Lastly, the principle of concurrent dual-band ET operation is extended to multi-band signals using the LFC of the envelope of the multi-band signal. The proposed multi-band ET operation is validated using the measurement results of a tri-band ET PA. To the best of our knowledge, this is the first reported tri-band ET PA in literature. The tri-band ET PA is linearized using a new tri-band DPD model with supply dependency.

Download or read book Feedforward Amplifiers for Wideband Communication Systems written by Jon Legarda and published by Springer. This book was released on 2010-10-29 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book has been possible thanks to the research carried out in the field of the linearization techniques applied to digital communication systems, particularly to those with high spectral efficient modulation techniques. It merges in the need of developing frequency efficient modulations with widespread codification techniques. The book puts into practice the Feedforward linearization technique, aimed at improving either the linearity or efficiency parameters of power amplifiers.