Class-E Power Amplifiers in Modern RF Transmitters

Power amplifiers have been playing a vital role in most wireless communication systems. In order to improve efficiency of wireless systems, advanced transmitter architectures, such as Doherty amplifiers, outphasing amplifiers, supply voltage modulation techniques are widely used. The goal of this work is to develop novel techniques for building load modulation transmitters based on class-E power amplifiers. The first contribution is an analytical model for derivation load network parameters. The proposed model derives the parameters for both the peak and back-off power levels providing high efficiency. The proposed model demonstrates, that class-E PA with shunt capacitance and shunt filter is capable of providing high drain efficiency for back-off output power levels. The second contribution is a design of a wideband class-E power amplifier (PA) with shunt capacitance and shunt filter. The broadband operation has been achieved by application of the double reactance compensation technique. Simulated and experimental results are presented. The performance of the fabricated PA is compared with existing wideband PAs. The third contribution is application of the proposed technique to outphasing PA design. The designed outphasing PA was optimized, fabricated and tested. A possibility to extend the operational bandwidth of the PA is considered. Also the application of the proposed technique to Doherty PA design is demonstrated. The fourth contribution is linearization of outphasing PA. Firstly, an analytical model describing the nonlinearity of nonisolated combiners under amplitude imbalance is presented. Secondly, a novel phase-only predistortion technique for class-E outphasing PAs is proposed. Thirdly, linearization of the fabricated outphasing PA based on memory polynomial model is demonstrated using a 64QAM OFDM modulated signal with 20 MHz bandwidth. Overall, this work provides novel techniques for load modulation transmitter design based on class-E power amplifiers with shunt capacitance and shunt filter

A review of technologies and design techniques of millimeter-wave power amplifiers

his article reviews the state-of-the-art millimeter-wave (mm-wave) power amplifiers (PAs), focusing on broadband design techniques. An overview of the main solid-state technologies is provided, including Si, gallium arsenide (GaAs), GaN, and other III-V materials, and both field-effect and bipolar transistors. The most popular broadband design techniques are introduced, before critically comparing through the most relevant design examples found in the scientific literature. Given the wide breadth of applications that are foreseen to exploit the mm-wave spectrum, this contribution will represent a valuable guide for designers who need a single reference before adventuring in the challenging task of the mm-wave PA design

Arquiteturas paralelas avançadas para transmissores 5G totalmente digitais

The fifth generation of mobile communications (5G) is being prepared and should be rolled out in the early coming years. Massive number of Radio-Frequency (RF) front-ends, peak data rates of 10 Gbps (everywhere and everytime), latencies lower than 10 msec and huge device densities are some of the expected disruptive capabilities. At the same time, previous generations can not be jeopardized, fostering the design of novel flexible and highly integrated radio transceivers able to support the simultaneous transmission of multi-band and multi-standard signals. The concept of all-digital transmission is being pointed out as a promising architecture to cope with such challenging requirements, due to its fully digital radio datapath. This thesis is focused on the proposal and validation of fully integrated and advanced digital transmitter architectures that excel the state-of-the-art in different figures of merit, such as transmission bandwidth, spectral purity, carrier agility, flexibility, and multi-band capability. The first part of this thesis introduces the concept of all-digital RF transmission. In particular, the foundations inherent to this thematic line are given, together with the recent advances reported in the state-of-the-art architectures.The core of this thesis, containing the main developments achieved during the Ph.D. work, is then presented and discussed. The first key contribution to the state-of-the-art is the use of cascaded Delta-Sigma (∆Σ) architectures to relax the analog filtering requirements of the conventional All-Digital Transmitters while maintaining the constant envelope waveform. Then, it is presented the first reported architecture where Antenna Arrays are directly driven by single-chip and single-bit All-Digital Transmitters, with promising results in terms of simplification of the RF front-ends and overall flexibility. Subsequently, the thesis proposes the first reported RF-stage All-Digital Transmitter that can be embedded within a single Field-Programmable Gate Array (FPGA) device. Thereupon, novel techniques to enable the design of wideband All-Digital Transmitters are reported. Finally, the design of concurrent multi-band transmitters is introduced. In particular, the design of agile and flexible dual and triple bands All-DigitalTransmitter (ADT) is demonstrated, which is a very important topic for scenarios that demand carrier aggregation. This Ph.D. contributes withseveral advances to the state-of-the-art of RF all-digital transmitters.A quinta geração de comunicações móveis (5G) está a ser preparada e deve ser comercializada nos próximos anos. Algumas das caracterı́sticas inovadoras esperadas passam pelo uso de um número massivo de font-ends de Rádio-Frequência (RF), taxas de pico de transmissão de dados de 10 Gbps (em todos os lugares e em todas as ocasiões), latências inferiores a 10 mseg e elevadas densidades de dispositivos. Ao mesmo tempo, as gerações anteriores não podem ser ignoradas, fomentando o design de novos transceptores de rádio flexı́veis e altamente integrados, capazes de suportar a transmissão simultânea de sinais multi-banda e multi-standard. O conceito de transmissão totalmente digital é considerado como um tipo de arquitetura promissora para lidar com esses requisitos desafiantes, devido ao seu datapath de rádio totalmente digital. Esta tese é focada na proposta e validação de arquiteturas de transmissores digitais totalmente integradas e avançadas que ultrapassam o estado da arte em diferentes figuras de mérito, como largura de banda de transmissão, pureza espectral, agilidade de portadora, flexibilidade e capacidade multibanda. A primeira parte desta tese introduz o conceito de transmissores de RF totalmente digitais. Em particular, os fundamentos inerentes a esta linha temática são apresentados, juntamente com os avanços mais recentes do estado-da-arte. O núcleo desta tese, contendo os principais desenvolvimentos alcançados durante o trabalho de doutoramento, é então apresentado e discutido. A primeira contribuição fundamental para o estado da arte é o uso de arquiteturas em cascata com moduladores ∆Σ para relaxar os requisitos de filtragem analógica dos transmissores RF totalmente digitais convencionais, mantendo a forma de onda envolvente constante. Em seguida, é apresentada a primeira arquitetura em que agregados de antenas são excitados diretamente por transmissores digitais de um único bit inseridos num único chip, com resultados promissores em termos de simplificação dos front-ends de RF e flexibilidade em geral. Posteriormente, é proposto o primeiro transmissor totalmente digital RF-stage relatado que pode ser incorporado dentro de um único Agregado de Células Lógicas Programáveis. Novas técnicas para permitir o desenho de transmissores RF totalmente digitais de banda larga são também apresentadas. Finalmente, o desenho de transmissores simultâneos de múltiplas bandas é exposto. Em particular, é demonstrado o desenho de transmissores de duas e três bandas ágeis e flexı́veis, que é um tópico essencial para cenários que exigem agregação de múltiplas bandas.Apoio financeiro da Fundação para a Ciência e Tecnologia (FCT) no âmbito de uma bolsa de doutoramento, ref. PD/BD/105857/2014.Programa Doutoral em Telecomunicaçõe

Baseband linearization schemes for high efficiency power amplifiers

High efficiency and high linearity microwave power amplifiers (PAs) are a critical element in modern wireless applications. Over recent years, modern communica-tions systems and the complex modulated signals they use have presented signif-icant challenges in terms of maintaining acceptable efficiency and achieving the high degrees of linearity required in microwave radio frequency power amplifier (RFPA) designs. The next ‘big’ challenge is the deployment of the fifth-generation (5G) mobile network, which is scheduled for commercial launch in 2020. Although the specification for 5G is not completely known at this point, the expectations in terms of what 5G will bring most certainly are; including 1000x more capacity, less than 1ms latency and 100x network energy efficiency. New 5G systems will need to provide higher spectral efficiency, wide and fragmented signal spectra and dy-namic spectrum access (DSA). As a result, the waveforms used in 5G systems will be characterised by high peak to average power ratio (PAPR) and high bandwidth, especially for high data rate applications, which brings additional challenges in terms of achieving system efficiency and linearity. Digital Predistortion (DPD) has been widely and very successfully applied in modern communication systems to linearize PAs and meet system require-ments. However, as the signal bandwidth widens and carrier aggregation be-comes commonplace in 5G system, higher complexity DPD algorithms and an Abstract II increased number of associated parameters will be required. This will inevitably result in a more complex DPD systems with higher power consumption and overall, lower system efficiency. This is especially problematic when systems advance into massive multiple-input, multiple-output (MIMO) scenarios, where the distrib-uted systems are smaller in size and massive in number. The research work in this thesis starts by analysing the different nonlinear distortion mechanisms present in the typical microwave power transistor devices that would be deployed in an RFPA within a 5G system. A tunable analytical device model is established to investigate the individual contributions of key nonlinear el-ements in the device. A number of important observations, such as “sweet-spots”, sideband asymmetry and drive dependent optimum baseband termination have been discovered and analysed in detail. Using the developed analytical model, a linearity optimization strategy in circuit design has been discussed and applied to a commercially available and widely used nonlinear device model CGH60015D from Cree (now Wolfspeed). For the first time, a systematic study of all main non-linear components has been done and the interaction between these components has been discussed. In the second part of the thesis, a pair of novel system-level envelope do-main linearization techniques are presented and analysed. They are applied at the input node and output node of the power amplifier, respectively. The envelop line-arization techniques have been demonstrated with both the analytical model, de-veloped in this thesis, and the nonlinear device model CGH60015D. The Abstract III advantages of envelope linearization has been discussed as well as the challenges such an approach presents. The Linearizability of a system, both in terms of circuit design and lineariza-tion techniques are discussed. In fact, linearity and linearizability of power amplifi-ers forms the central thread that runs through this thesis together with linearity, which provides guidance for a top-to-bottom level PA linearization strategy