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

ワイヤレス通信のための先進的な信号処理技術を用いた非線形補償法の研究

The inherit nonlinearity in analogue front-ends of transmitters and receivers have had primary impact on the overall performance of the wireless communication systems, as it gives arise of substantial distortion when transmitting and processing signals with such circuits. Therefore, the nonlinear compensation (linearization) techniques become essential to suppress the distortion to an acceptable extent in order to ensure sufficient low bit error rate. Furthermore, the increasing demands on higher data rate and ubiquitous interoperability between various multi-coverage protocols are two of the most important features of the contemporary communication system. The former demand pushes the communication system to use wider bandwidth and the latter one brings up severe coexistence problems. Having fully considered the problems raised above, the work in this Ph.D. thesis carries out extensive researches on the nonlinear compensations utilizing advanced digital signal processing techniques. The motivation behind this is to push more processing tasks to the digital domain, as it can potentially cut down the bill of materials (BOM) costs paid for the off-chip devices and reduce practical implementation difficulties. The work here is carried out using three approaches: numerical analysis & computer simulations; experimental tests using commercial instruments; actual implementation with FPGA. The primary contributions for this thesis are summarized as the following three points: 1) An adaptive digital predistortion (DPD) with fast convergence rate and low complexity for multi-carrier GSM system is presented. Albeit a legacy system, the GSM, however, has a very strict requirement on the out-of-band emission, thus it represents a much more difficult hurdle for DPD application. It is successfully implemented in an FPGA without using any other auxiliary processor. A simplified multiplier-free NLMS algorithm, especially suitable for FPGA implementation, for fast adapting the LUT is proposed. Many design methodologies and practical implementation issues are discussed in details. Experimental results have shown that the DPD performed robustly when it is involved in the multichannel transmitter. 2) The next generation system (5G) will unquestionably use wider bandwidth to support higher throughput, which poses stringent needs for using high-speed data converters. Herein the analog-to-digital converter (ADC) tends to be the most expensive single device in the whole transmitter/receiver systems. Therefore, conventional DPD utilizing high-speed ADC becomes unaffordable, especially for small base stations (micro, pico and femto). A digital predistortion technique utilizing spectral extrapolation is proposed in this thesis, wherein with band-limited feedback signal, the requirement on ADC speed can be significantly released. Experimental results have validated the feasibility of the proposed technique for coping with band-limited feedback signal. It has been shown that adequate linearization performance can be achieved even if the acquisition bandwidth is less than the original signal bandwidth. The experimental results obtained by using LTE-Advanced signal of 320 MHz bandwidth are quite satisfactory, and to the authors’ knowledge, this is the first high-performance wideband DPD ever been reported. 3) To address the predicament that mobile operators do not have enough contiguous usable bandwidth, carrier aggregation (CA) technique is developed and imported into 4G LTE-Advanced. This pushes the utilization of concurrent dual-band transmitter/receiver, which reduces the hardware expense by using a single front-end. Compensation techniques for the respective concurrent dual-band transmitter and receiver front-ends are proposed to combat the inter-band modulation distortion, and simultaneously reduce the distortion for the both lower-side band and upper-side band signals.電気通信大学201

Application of knowledge-based techniques to fault diagnosis of 16 QAM digital microwave radio equipment

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Técnica de redução de fator de crista saturada aplicada a amplificadores de potência linearizados por DPD

Orientador: Prof. Dr. Eduardo Gonçalves de LimaDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Elétrica. Defesa : Curitiba, 31/05/2019Inclui referências: p.63-65Área de concentração: TelecomunicaçõesResumo: Os sistemas modernos de comunicação oferecem uma alta capacidade de troca de informação, com taxas de transferências de dados cada vez maiores, entre um número quase ilimitado de usuários que têm fácil acesso a tecnologias da internet e de comunicação sem fio. Estes sistemas são compostos por um elemento transmissor e um elemento receptor, que interagem para garantir uma comunicação eficaz entre os usuários de uma rede. Os amplificadores de potência (PAs) são componentes essenciais no desempenho geral e no rendimento dos sistemas de comunicação, mas são inerentemente não lineares. A não linearidade produz um espalhamento espectral, o que leva a interferências entre canais adjacentes, radiações no canal principal, ao não cumprimento dos padrões de emissões fora da banda que exige a legislação e a degradação da taxa de transferência de dados no sistema de comunicação. Para evitar a não linearidade o PA deve operar com uma potência abaixo de sua capacidade para se manter na região linear de sua curva de operação. Além disso, os novos esquemas de transmissão como por exemplo Wideband Code Division Multiple Access (WCDMA) e Orthogonal Frequency Division Multiplexing (OFDM, WLAN/ 3GPP LTE) apresentam um alto valor da razão de potência de pico pela potência média (PAPR) traduzido em altos valores de picos em seu sinal de envoltória complexa. Isto traz uma baixa eficiência e, portanto, um maior consumo energético do elemento transmissor, pois o PA é obrigado a operar bem abaixo de sua potência de saturação, que é o ponto de fornecimento máximo de potência, para poder lidar com as severas flutuações dos picos provocadas pela elevada PAPR. Para reduzir essa elevada PAPR existe muito interesse, na comunidade científica, em métodos baseados na redução de fator de crista (CFR) visto que são técnicas de fácil implementação e alta eficácia. Outro método de grande interesse é a combinação de CFR com pré-distorção digital (DPD) que tem demonstrado bons resultados na literatura. Este trabalho visa propor um método que reduza a PAPR na saída de um sistema de comunicação com o menor custo computacional, baseado em CFR composto por um limitador do tipo hard-clipping seguido da implementação de um filtro de resposta ao impulso finita (FIR) no domínio do tempo e um DPD ideal saturado. Outra abordagem é realizada através de uma CFR em combinação com um filtro no domínio da frequência que conecta um DPD ideal sempre em saturação. Por fim são realizadas otimizações não lineares que permitem extrair os parâmetros nos quais o sistema de comunicação apresenta maior potência média de saída e menor PAPR. Como resultado, obteve-se uma maior redução da PAPR com o método CFR saturado que utiliza um filtro no domínio da frequência de até 4,58 dB. Além disso, este método conseguiu uma melhoria na eficiência energética obtendo uma potência média na saída de até 5,96 dBm. Por outro lado, as métricas de linearidade reguladas pela norma 3GPP foram respeitadas, obtendo-se valores de 17,5 % para a magnitude do vetor de erro (EVM) e -45 dB para a razão das potências dos canais adjacentes (ACPR). Palavras-chave: CFR, Hard-clipping, DPD, Saturação, Linearidade, PAPR, Eficiência.Abstract: Modern communication systems offer a high capacity for information exchange, with ever-increasing rates of data transfers, among an almost unlimited number of users who have easy access to internet technologies and wireless communication. These systems are conformed by a transmitting element and a receiving element, which interact to ensure effective communication between the users of a network. Power amplifiers (PAs) are essential components in the overall performance of communication systems, but are inherently nonlinear. Non-linearity produces spectral regrowth, which leads to interference from adjacent channels, radiations in the main channel, noncompliance with the out-of-band emission standards required by legislation, and degradation of the data transfer rate in the communication system. In order to avoid nonlinearity the PA must operate with a power below its capacity to remain in the linear region of its operating curve. In addition the new transmission schemes such as Wideband Code Division Multiple Access (WCDMA) and Orthogonal Frequency Division Multiplexing (OFDM, WLAN / 3GPP LTE) have a high peak-to-average power ratio (PAPR) translated into high peak values in their complex envelope signal. This brings a low efficiency and therefore a higher energy consumption of the transmitter element, because the PA is required to operate well below its saturation power than the bridge of maximum power supply, to be able to deal with the severe fluctuations of the peaks caused by high PAPR. In order to reduce this high PAPR there is a lot of interest, in the scientific community, in methods based on Crest Factor Reduction (CFR), since these techniques are easy to implement and high efficient. Another method of great interest is the combination of CFR and Digital Pre-Distortion (DPD) which has demonstrated good results in the literature. This work aims to propose a method that is able to reduce the PAPR in the output of a communication system with the lowest computational cost, based on hard-clipping type CFR followed by the implementation of a standard Finite Impulse Response (FIR) filter in the time domain and a saturated ideal DPD. Another approach is accomplished through a CFR in combination with a frequency domain filter that connects an ideal DPD always in saturation. Finally, nonlinear optimizations are performed that allow to extract the parameters in which the communication system has higher average output power and lowering PAPR. As a result, a larger reduction of the PAPR was achieved with the saturated CFR method using a frequency domain filter of up to 4.58 dB. In addition, this method achieved an improvement in energy efficiency obtaining an average output power of up to 5.96 dBm. On the other hand, the linearity metrics regulated by the 3GPP standard were respected, obtaining values of 17.5% for error vector magnitude (EVM) and -45 dB for the adjacent channel power ratio (ACPR). Keywords: CFR, Hard-clipping, DPD, Saturation, Linearity, PAPR, Efficiency

An enhanced modulated waveform measurement system

The microwave devices and circuits need to be characterized prior to being employed in the design of systems and components. Unfortunately the measurement systems required to characterize the microwave devices and circuits have not kept pace with the emerging telecommunication technologies demands. This has resulted into a situation where either the circuits being employed in the components are unoptimized or the yield and turn-around of optimized circuits are slow. One of the contributing factors of such situations is the limitations of the existing measurement systems to scale up in performance to fulfil the necessary requirements. This thesis presents an enhanced multi-tone, time domain waveform measurement and engineering system. The presented system allows for a more considered, and scientific process to be adopted in the characterisation and measurement of microwave power devices for modern day communications systems. The main contributions to the field of research come in two areas; firstly developments that allow for accurate time domain measurement of complex modulated signals using commercially available equipment; and secondly in the area of active impedance control, where significant developments were made allowing active control of impedance across a modulated bandwidth. The first research area addressed is the fundamental difficulty in sampling multi-tone waveforms, where the main achievements have been the realisation of a high quality trigger clock for the sampling oscilloscope and a “Time Domain Partitioning” approach to measure and average multi-tone waveforms on-board. This approach allows the efficient collection of high quality vectoral information for all significant distortion terms, for all bands of interest. The second area of research investigated suitable impedance control architectures to comprehensively investigate out-of-band impedance effects on the linearity performance of a device. The ultimate aim was to simultaneously present independent, baseband impedances to all the significant baseband (IF) frequency components and to 2nd harmonic that result from a multi-tone excitation. The main achievement in this area was the ability of the enhanced measurement system to present the broadband impedance. At baseband this has been achieved in the time domain using a single arbitrary waveform generator (AWG) to synthesise the necessary waveforms to allow a specific IF impedance environment to be maintained across a wide IF bandwidth. To engineer the RF out-of-band load terminations at RF frequencies and to emulate specific power amplifier modes, a Tektronix AWG7000 Arbitrary Waveform Generator was used to deliver the desired impedances, practically fulfilling the wideband application requirements for reliable device characterisation under complex modulated excitations.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An enhanced modulated waveform measurement system

The microwave devices and circuits need to be characterized prior to being employed in the design of systems and components. Unfortunately the measurement systems required to characterize the microwave devices and circuits have not kept pace with the emerging telecommunication technologies demands. This has resulted into a situation where either the circuits being employed in the components are unoptimized or the yield and turn-around of optimized circuits are slow. One of the contributing factors of such situations is the limitations of the existing measurement systems to scale up in performance to fulfil the necessary requirements. This thesis presents an enhanced multi-tone, time domain waveform measurement and engineering system. The presented system allows for a more considered, and scientific process to be adopted in the characterisation and measurement of microwave power devices for modern day communications systems. The main contributions to the field of research come in two areas; firstly developments that allow for accurate time domain measurement of complex modulated signals using commercially available equipment; and secondly in the area of active impedance control, where significant developments were made allowing active control of impedance across a modulated bandwidth. The first research area addressed is the fundamental difficulty in sampling multi-tone waveforms, where the main achievements have been the realisation of a high quality trigger clock for the sampling oscilloscope and a “Time Domain Partitioning” approach to measure and average multi-tone waveforms on-board. This approach allows the efficient collection of high quality vectoral information for all significant distortion terms, for all bands of interest. The second area of research investigated suitable impedance control architectures to comprehensively investigate out-of-band impedance effects on the linearity performance of a device. The ultimate aim was to simultaneously present independent, baseband impedances to all the significant baseband (IF) frequency components and to 2nd harmonic that result from a multi-tone excitation. The main achievement in this area was the ability of the enhanced measurement system to present the broadband impedance. At baseband this has been achieved in the time domain using a single arbitrary waveform generator (AWG) to synthesise the necessary waveforms to allow a specific IF impedance environment to be maintained across a wide IF bandwidth. To engineer the RF out-of-band load terminations at RF frequencies and to emulate specific power amplifier modes, a Tektronix AWG7000 Arbitrary Waveform Generator was used to deliver the desired impedances, practically fulfilling the wideband application requirements for reliable device characterisation under complex modulated excitations

Integrated realizations of reconfigurable low pass and band pass filters for wide band multi-mode receivers

With the explosive development of wireless communication systems the specifications of the supporting hardware platforms have become more and more demanding. According to the long term goals of the industry, future communications systems should integrate a wide variety of standards. This leads to the idea of software defined radio, implemented on fully reconfigurable hardware.Among other reconfigurable hardware blocks, suitable for the software radio concept, an outstanding importance belongs to the reconfigurable filters that are responsible for the selectivity of the system. The problematic of filtering is strictly connected to the architecture chosen for a multi-mode receiver realization. According to the chosen architecture, the filters can exhibit low pass or band pass frequency responses.The idea of reconfigurable frequency parameters has been introduced since the beginning of modern filtering applications due to the required precision of the frequency response. However, the reconfiguration of the parameters was usually done in a limited range around ideal values. The purpose of the presented research is to transform the classical filter structures with simple self-correction into fully reconfigurable filters over a wide range of frequencies. The ideal variation of the frequency parameters is continuous and consequently difficult to implement in real circuits. Therefore, it is usually sufficient to use a discrete programming template with reasonably small steps.There are several methods to implement variable frequency parameters. The most often used programming templates employ resistor and capacitor arrays, switched according to a given code. The low pass filter implementation proposed in this work uses a special switching template, optimized for a quasi-linear frequency variation over logarithmic axes. The template also includes the possibility to compensate errors caused by component tolerances and temperature. Another important topic concerns the implementation of programmable band pass filters, suitable for IF sampling receivers. The discussion is centered on the feasibility and the flexibility of different band pass filter architectures. Due to the high frequency requirements, the emphasis lays on filters that employ transconductance amplifiers and capacitors.Die rasch fortschreitende Entwicklung drahtloser Kommunikationssysteme führt zu immer anspruchsvolleren Spezifikationen der diese Systeme unterstützenden Hardwareplattformen. Zukünftige Kommunikationssysteme sollen übereinstimmend mit den längerfristigen Zielen der Industrie verschiedene Standards integrieren. Dies führt zu der Idee von vollständig rekonfigurierbarer Hardware, welche mittels Software gesteuert wird.Inmitten anderer rekonfigurierbarer Hardwareblöcke, die für das Software Radio Konzept geeignet sind, besitzen die steuerbaren Filter, welche wesentlichen Einfluss auf die Selektivität des Systems haben, eine enorme Bedeutung. Die Filterproblematik ist eng mit der gewählten Architektur der standardübergreifenden Empfängerrealisierung verknüpft. Die Filter können entsprechend der ausgesuchten Architektur Tiefpass- oder Bandpasscharakter annehmen.Die Idee rekonfigurierbarer Frequenzparameter wurde bereits mit Beginn moderner Filteranwendungen auf Grund geforderter Frequenzganggenauigkeit umgesetzt. Jedoch wurde die Parameterrekonfiguration üblicherweise nur in einem begrenzten Bereich um die Idealwerte herum vorgenommen. Das Ziel der vorgestellten Forschungsarbeit ist es, diese klassischen Filterstrukturen mit einfacher Selbstkorrektur in über große Frequenzbereiche voll rekonfigurierbare Filter zu transformieren. Idealerweise werden die Frequenzparameter kontinuierlich variiert weswegen sich die Implementierung in reellen Schaltkreisen als schwierig erweist. Deshalb ist es üblicherweise ausreichend, ein diskretes Steuerschema mit kleinen Schrittweiten zu verwenden.Es gibt verschiedene Methoden, variable Frequenzparameter zu implementieren. Die meisten Schemata verwenden Widerstands- und Kondensatorfelder, die entsprechend eines Kodes geschaltet werden. Die in dieser Arbeit vorgestellte Implementierung eines Tiefpassfilters nutzt ein spezielles Umschaltschema, welches für die quasi-lineare Frequenzvariation bei Darstellung über logarithmischen Axen optimiert wurde. Es beinhaltet weiterhin die Möglichkeit, Fehler zu kompensieren, die durch Bauelementtoleranzen und Temperaturschwankungen hervorgerufen werden.Ein weiteres interessantes Thema betrifft die Implementierung steuerbarer Bandpassfilter, die für Empfänger mit Zwischenfrequenzabtastung geeignet sind. Die Betrachtung beschränkt sich hierbei auf die Durchführbarkeit und Flexibilität verschiedener Bandpassfilterarchitekturen. Auf Grund hoher Frequenzanforderungen liegt der Schwerpunkt auf Filtern, die auf Transkonduktanzverstärkern und Kondensatoren basieren

Efficient solid state power amplifiers: power combining and highly accurate AM/AM and AM/PM behavioural models with application to linearisation

Radio Frequency (RF) Power Amplifiers (PAs) are a major contributor to modern communication systems, both in terms of being an enabling technology as well as having the most impact on overall system availability, linearity and power consumption. In order to achieve the most optimum system outcome there needs to be an appropriate method for selecting the most suitable RF PA design approach, as well as being able to select the most appropriate RF PA output device, based on a range of varying requirements, specifications and technologies. The ability to perform these tasks quickly, with improved accuracy, using existing available device data, with minimal or no further device testing and from a range of existing and emerging technologies would provide RF PA designers with significant benefits. The investigations and research provided in this thesis consider a range of existing and emerging RF PA technologies and power combining methods and compares them via a new selection and design methodology developed in this thesis. The new methodology builds on modern design and statistical approaches including manufacturing options that enable an appropriate technology to be selected for Solid State Power Amplifier (SSPA) design. In addition to hard design specifications, the current thesis also considers less tangible specifications, such as graceful degradation, time tomarket and ease of use, as well as alternative design approaches, such as fuzzy logic approaches. With a suitable technology approach determined, a selection of a suitable RF output device(s) is considered. As the demand for new communication services continues to increase, requiring tighter specifications and reduced product delivery time scales, then the ability to accurately and quickly compare available RF PA devices from a range of device technologies or devices from different manufacturers, at both the system and component level, makes such a selection paramount. In this thesis, simplememoryless (AmplitudeModulation/AmplitudeModulation (AM/AM) only) and Quasi-Memoryless (QM) Behavioural Models (BMs) (AM/AM combined with Amplitude Modulation/Phase Modulation (AM/PM)) are reviewed, extended and improved upon, with up to 20 dB Normalised Mean Squared Error (NMSE) modelling improvement achieved over a range of technologies, allowing effective RF PA device selection using these newly developed simple and fast models. This thesis uses recent existing accurate and powerful semi-physical memoryless BMs, suited to RF PA devices, and develops and extends their use for QM modelling. The trade-off from the improvement in the overall accuracy is some further simple processing steps. Furthermore, this thesis also provides a comparison of other models, presented in the literature. The improved simple RF PA device models and extension techniques presented in this thesis show, via simulation and measurement, that the new models are suitable for use over a wide range. Lineariser improvements, linked to the accuracy improvements of the proposed models of this thesis, are also investigated, showing further benefits from this research. Physically based simple QM BMs are also used to model thermal and bias network memory effects, which are becomingmore relevant tomodern communication services that use wider bandwidths, enabling the impacts of RF PA device memory effects to be determined and compared. The feasibility of the developed models and improvements are also utilised in the simulation of a low cost RF PA lineariser. With the trend to smaller localised low cost and power RF mobile wireless repeater cells being away from larger more expensive and complex hardware, used to perform linearisation, this thesis presents a trade-off between complexity and linearisation performance and demonstrates, through modelling and simulation, that 8-10 dB improvement in linearisation performance is achievable with the use of the newly developed models.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201

Novel power amplifier design using non-linear microwave characterisation and measurement techniques

This thesis, addresses some aspects of the well-known, problem, experienced by designer of radio frequency power amplifiers (RFPA): the efficiency/linearity trade-off. The thesis is focused on finding and documenting solution to linearity problem than can be used to advance the performance of radio frequency (RF) and microwave systems used by the wireless communication industry. The research work, this was undertaken by performing a detailed investigation of the behaviour of transistors, under complex modulation, when subjected to time varying baseband signals at their output terminal: This is what in this thesis will be referred to as “baseband injection”. To undertake this study a new approach to the characterisation of non-linear devices (NLD) in the radio frequency (RF) region, such as transistors, designated as device-under-test (DUT), subjected to time varying baseband signals at its output terminal, was implemented. The study was focused on transistors that are used in implementing RF power amplifiers (RFPA) for base station applications. The nonlinear device under test (NL-DUT) is a generalisation to include transistors and other nonlinear devices under test. Throughout this thesis, transistors will be referred to as ‘device’ or ‘radio frequency power amplifier (RFPA) device’. During baseband injection investigations the device is perturbed by multi-tone modulated RF signals of different complexities. The wireless communication industry is very familiar with these kinds of devices and signals. Also familiar to the industry are the effects that arise when these kind of signal perturb these devices, such as inter-modulation distortion and linearity, power consumption/dissipation and efficiency, spectral re-growth and spectral efficiency, memory effects and trapping effects. While the concept of using baseband injection to linearize RFPAs is not new the mathematical framework introduced and applied in this work is novel. This novel approach NOVEL POWER AMPLIFIER DESIGN USING NON-LINEAR MICROWAVE CHARACTERISATION AND MEASUREMENT TECHNIQUES CARDIFF UNIVERISTY - UK ABSTRACT vi has provided new insight to this very complex problem and highlighted solutions to how it could be a usable technique in practical amplifiers. In this thesis a very rigorous and complex investigative mathematical and measurement analysis on RFPA response to applied complex stimulus in a special domain called the envelope domain was conducted. A novel generic formulation that can ‘engineer’ signal waveforms by using special control keys with which to provide solution to some of the problems highlighted above is presented. The formulation is based on specific background principles, identified from the result of both mathematical theoretical analysis and detailed experimental device characterisation