Design and Implementation of Novel FPGA Based Time-Interleaved Variable Centre-Frequency Digital Sigma-Delta Modulators

Novel, multi-path, time-interleaved digital sigma-delta modulators that can operate at any arbitrary frequency from DC to Nyquist are designed, analysed and synthesized in this study. Dual- and quadruple-path fourth-order Butterworth, Chebyshev, Inverse Chebyshev and Elliptical based digital sigma-delta modulators, which offer designers the flexibility of specifying the centre-frequency, pass-band/stop-band attenuation as well as the signal bandwidth are presented. These topologies are compared in terms of their signal-to-noise ratios, hardware complexity, stability, tonality and sensitivity to non-idealities. Detailed simulations performed at the behavioural-level in MATLAB are compared with the experimental results of the FPGA implementation of the designed modulators. The signal-to-noise ratios between the simulated and empirical results are shown to be different by not more than 3-5 dBs. Furthermore, this paper presents the mathematical modelling and evaluation of the tones caused by the finite wordlengths of these digital multi-path sigma-delta modulators when excited by sinusoidal input signals

Analysis and design of ΣΔ Modulators for Radio Frequency Switchmode Power Amplifiers

Power amplifiers are an integral part of every basestation, macrocell, microcell and mobile phone, enabling data to be sent over the distances needed to reach the receiver’s antenna. While linear operation is needed for transmitting WCDMA and OFDM signals, linear operation of a power amplifier is characterized by low power efficiency, and contributes to unwanted power dissipation in a transmitter. Recently, a switchmode power amplifier operation was considered for reducing power losses in a RF transmitter. A linear and efficient operation of a PA can be achieved when the transmitted RF signal is ΣΔ modu- lated, and subsequently amplified by a nonlinear device. Although in theory this approach offers linearity and efficiency reaching 100%, the use of ΣΔ modulation for transmitting wideband signals causes problems in practical implementation: it requires high sampling rate by the digital hardware, which is needed for shaping large contents of a quantization noise induced by the modulator but also, the binary output from the modulator needs an RF power amplifier operating over very wide frequency band. This thesis addresses the problem of noise shaping in a ΣΔ modulator and nonlinear distortion caused by broadband operation in switchmode power amplifier driven by a ΣΔ modulated waveform. The problem of sampling rate increase in a ΣΔ modulator is solved by optimizing structure of the modulator, and subsequent processing of an input signal’s samples in parallel. Independent from the above, a novel technique for reducing quan- tization noise in a bandpass ΣΔ modulator using single bit quantizer is presented. The technique combines error pulse shaping and 3-level quantization for improving signal to noise ratio in a 2-level output. The improvement is achieved without the increase of a digital hardware’s sampling rate, which is advantageous also from the perspective of power consumption. The new method is explored in the course of analysis, and verified by simulated and experimental results. The process of RF signal conversion from the Cartesian to polar form is analyzed, and a signal modulator for a polar transmitter with a ΣΔ-digitized envelope signal is designed and implemented. The new modulator takes an advantage of bandpass digital to analog conversion for simplifying the analog part of the modulator. A deformation of the pulsed RF signal in the experimental modulator is demonstrated to have an effect primarily on amplitude of the RF signal, which is correctable with simple predistortion

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

Integrated design of high performance pulsed power converters : application to klystron modulators for the compact linear colider (CLIC)

Ce travail de recherche présente l’étude, conception et validation d’une topologie de convertisseur de puissance pulsé qui compense la chute de tension pour des modulateurs de type klystron de haute performance. Cette topologie est capable de compenser la chute de tension du banc de condensateur principal et, en même temps, de faire fonctionner le modulateur avec une consommation de puissance constante par rapport au réseau électrique. Ces spécifications sont requises par le projet Compact Linear Collider (CLIC) pour les modulateurs klystron de son Drive Beam. Le dimensionnement du système est effectué à partir d’un outil d’optimisation globale développé à partir des modèles analytiques qui décrivent les performances de chaque composant du système. Tous les modèles sont intégrés dans un processus optimal intermédiaire de conception qui utilise des techniques d’optimisation afin de réaliser un dimensionnement optimal du système. Les performances de cette solution optimale intermédiaire sont alors évaluées à l’aide d’un modèle plus fin basé sur des simulations numériques. Une technique d’optimisation utilisant l’approche «space mapping» est alors mise en oeuvre. Si l’écart entre les performances prédites et les performances simulées est important, des facteurs de correction sont appliqués aux modèles analytiques et le processus d’optimisation est relancé. Cette méthode permet d’obtenir une solution optimale validée par le modèle fin en réduisant le nombre de simulations. La topologie finale sélectionnée pour le cahier des charges du modulateur CLIC est validée expérimentalement sur des prototypes à échelle réduite. Les résultats valident la méthodologie de dimensionnement et respectent les spécifications.This research work presents the study, design and validation of a pulsed power converter topology that performs accurate voltage droop compensation for high performance klystron modulators. This topology is capable of compensating the voltage droop of the intermediate capacitor bank and, at the same time, it makes possible a constant power consumption operation of the modulator from the utility grid. These two main specifications are required for the Compact Linear Collider (CLIC) Drive Beam klystron modulators. The dimensioning of the system is performed by developing a global optimization design tool. This tool is first based on developed analytical models describing the performances of each system subcomponent. All these models are integrated into an intermediate design environment that uses nonlinear optimization techniques to calculate an optimal dimensioning of the system. The intermediate optimal solution performances are then evaluated using a more accurate model based on numerical simulation. Therefore, an optimization technique using «space mapping» is implemented. If differences between predicted performances and simulated results are non-negligible, correction factors are applied to the analytical models and the optimization process is launched again. This method makes possible to achieve an optimal solution validated by numerical simulation while reducing the number of numerical simulation steps. The selected final topology for the CLIC klystron modulator is experimentally validated using reduced scale prototypes. Results validate the selected methodology and fulfill the specifications

Design and implementation of generalized topologies of time-interleaved variable bandpass Σ−Δ modulators

In this thesis, novel analog-to-digital and digital-to-analog generalized time-interleaved variable bandpass sigma-delta modulators are designed, analysed, evaluated and implemented that are suitable for high performance data conversion for a broad-spectrum of applications. These generalized time-interleaved variable bandpass sigma-delta modulators can perform noise-shaping for any centre frequency from DC to Nyquist. The proposed topologies are well-suited for Butterworth, Chebyshev, inverse-Chebyshev and elliptical filters, where designers have the flexibility of specifying the centre frequency, bandwidth as well as the passband and stopband attenuation parameters. The application of the time-interleaving approach, in combination with these bandpass loop-filters, not only overcomes the limitations that are associated with conventional and mid-band resonator-based bandpass sigma-delta modulators, but also offers an elegant means to increase the conversion bandwidth, thereby relaxing the need to use faster or higher-order sigma-delta modulators. A step-by-step design technique has been developed for the design of time-interleaved variable bandpass sigma-delta modulators. Using this technique, an assortment of lower- and higher-order single- and multi-path generalized A/D variable bandpass sigma-delta modulators were designed, evaluated and compared in terms of their signal-to-noise ratios, hardware complexity, stability, tonality and sensitivity for ideal and non-ideal topologies. Extensive behavioural-level simulations verified that one of the proposed topologies not only used fewer coefficients but also exhibited greater robustness to non-idealties. Furthermore, second-, fourth- and sixth-order single- and multi-path digital variable bandpass digital sigma-delta modulators are designed using this technique. The mathematical modelling and evaluation of tones caused by the finite wordlengths of these digital multi-path sigmadelta modulators, when excited by sinusoidal input signals, are also derived from first principles and verified using simulation and experimental results. The fourth-order digital variable-band sigma-delta modulator topologies are implemented in VHDL and synthesized on Xilinx® SpartanTM-3 Development Kit using fixed-point arithmetic. Circuit outputs were taken via RS232 connection provided on the FPGA board and evaluated using MATLAB routines developed by the author. These routines included the decimation process as well. The experiments undertaken by the author further validated the design methodology presented in the work. In addition, a novel tunable and reconfigurable second-order variable bandpass sigma-delta modulator has been designed and evaluated at the behavioural-level. This topology offers a flexible set of choices for designers and can operate either in single- or dual-mode enabling multi-band implementations on a single digital variable bandpass sigma-delta modulator. This work is also supported by a novel user-friendly design and evaluation tool that has been developed in MATLAB/Simulink that can speed-up the design, evaluation and comparison of analog and digital single-stage and time-interleaved variable bandpass sigma-delta modulators. This tool enables the user to specify the conversion type, topology, loop-filter type, path number and oversampling ratio

Novas arquiteturas para transmissores digitais flexíveis e de banda larga

Next generation of wireless communication (5G) devices must achieve higher data rates, lower power consumption and better coverage by making a more efficient use of the RF spectrum and adopting highly exible radio architectures. To meet these requirements, the development of new radio devices will be far more complex and challenging than their predecessors. The future of radio communications have a twofold evolution, being one the low power consumption and the other the adaptability and intelligent use of the available resources. Conventional approaches for the radio physical layer are not capable to cope with the new demand for multi-band, multi-standard radio signals and present an inefficient and expensive solution for simultaneous transmission of multiple and heterogeneous radio signals. Digital radio transmitters have been presented as a solution for a newer and more exible architecture for future radios. All-digital transmitters use a completely digital implementation of the entire radio datapath from the baseband processing to the digital RF up-conversion. This concept bene ts from the use of highly integrated hardware together with a strong radio digitalization, motivated by the exibility and high performance from cognitive and software defi ned radio. However, such devices are still far from a massive deployment in most of communication scenarios due to some limiting factors that hinder their use. This PhD thesis aims to the development of novel radio architectures and ideas based on all-digital transmitters capable of improving the adaptability and use intelligently the available resources for software de ned and cognitive radio systems. The focus of this thesis is on the improvement of some of the common limitations for all-digital transmitters such as power efficiency, bandwidth, noise-shaping and exibility while using efficient and adaptable digital architectures. In the initial part of the thesis a review of the state-of-the-art is presented showing the most common digital transmitter architectures as well as their major bene ts and key limitations. A comparative analysis of such architectures is made considering their power and spectral efficiency, exibility, performance and cost. Following this initial analysis, the work developed on the course of this PhD is presented and discussed. The initial focus is on the improvement of all-digital transmitters bandwidth trough the study and use of parallel processing techniques capable of greatly improve common bandwidth values presented in the state-of-the-art. The presented work has resulted in several publications where FPGA-based architectures use parallel digital processing techniques to improve the system's bandwidth by a factor higher than 10. Other fundamental contribution of this thesis is focused on the pulsedtransmitters coding efficiency. In this section of the thesis, a method is presented showing the reduction of the quantization noise created by low amplitude resolution digital transmitters using multiple combined pulsedtransmitters to cancel the noise in speci c frequencies. This work has resulted in two main publications that showed how to increase the coding efficiency of the pulse-transmitters as well as the overall efficiency of the transmission system. Lastly, new-noise shaping methods are presented in order to develop new and more exible architectures for all-digital transmitters. The methods presented use new quantization processes that allow for the shaping of the quantization noise produced in pulsed-transmitters while using very simple and adaptable architectures. With these new techniques, it is possible to adjust the noise frequency distribution and deliberately change the noise shape in order to change some of the transmitter's characteristics such as central frequency or bandwidth. The work presented on this thesis has shown promising improvements to the all-digital transmitters' state-of-the-art, either in simulations and laboratory prototype measurements. It has contributed to advance the state-of-the-art in agile and power efficient all-digital RF transmitters with multi-mode and multi-channel capabilities and the improvement of the transceiver's bandwidth enabling the development of true software de ned and cognitive radio systemsA próxima geração de comunicações sem os (5G) exigirá taxas de transmissão mais elevadas, maior efi ciência energética e uma melhor cobertura fazendo um uso mais efi ciente do espectro de radiofrequência e adotando o uso de arquiteturas rádio mais flexíveis. Para cumprir tais requisitos, o desenvolvimento de novos dispositivos rádio será substancialmente mais complexo do que nas gerações anteriores. O futuro das comunicações rádio depende maioritariamente de dois fatores; o baixo consumo de potência e o uso inteligente dos recursos e tecnologias disponíveis. As abordagens convencionais para a camada física dos sistemas rádio não são as mais adequadas para lidar com a necessidade de dispositivos multi-banda e que usem múltiplos standards, por serem soluções inefi cientes e demasiado caras para esse efeito. Os transmissores rádio completamente digitais têm vindo a ser apresentados na literatura como uma solução inovadora e mais flexível para a implementação dos futuros sistemas de rádio. Os transmissores completamente digitais apresentam uma implementação da cadeia de processamento rádio, desde a banda-base até à conversão para RF, completamente constituída por lógica digital. Este conceito tira partido da vasta integração alcançada nas arquiteturas digitais, juntamente com a flexibilidade proveniente da digitalização das arquiteturas rádio que já se encontra em curso com a evolução dos rádios cognitivos e definidos por software. No entanto, devido a algumas limitações inerentes à tecnologia, este tipo de transmissores ainda não é amplamente utilizado na maioria dos sistemas. Esta tese de doutoramento propõe e avalia novas arquiteturas para transmissores completamente digitais, bem como novas técnicas de processamento de sinal que possam beneficiar das tecnologias de implementação existentes (e.g. FPGAs) por forma a construir novos transmissores digitais de forma eficiente e flexível. O objetivo desta tese é reduzir as limitações atuais ainda presentes neste tipo de transmissores, nomeadamente as relacionadas com a eficiência, largura de banda, cancelamento de ruído e falta de flexibilidade. Na parte inicial desta tese é realizada a revisão do estado da arte das diversas topologias de transmissores digitais bem como as suas principais vantagens e limitações técnicas. É também feita uma análise comparativa das diversas técnicas apresentadas em termos da sua eficiência energética, flexibilidade, desempenho e custo. De seguida, é apresentado o trabalho desenvolvido no contexto desta tese de doutoramento, seguindo-se uma discussão focada na resolução das atuais limitações deste tipo de transmissores. A primeira parte foca-se no uso de técnicas de processamento paralelo de sinal, por forma a suportar sinais de largura de banda mais elevada que os reportados no atual estado da arte. O trabalho desenvolvido e publicado baseia-se no uso de arquiteturas implementadas em FPGA que contribuíram para um aumento da largura de banda num fator de aproximadamente dez vezes. Outra das contribuições fundamentais desta tese consiste no aumento da eficiência do sistema através da melhoria da eficiência de codificação do sinal pulsado produzido. Com base no uso de múltiplos transmissores pulsados, e apresentado um esquema de combinação construtiva e destrutiva de sinais para a redução do ruído de quantização proveniente das técnicas de processamento de sinal pulsado usadas. Este trabalho resultou em duas importantes publicações que mostram que a melhoria da eficiência de codificação do sinal pode ser utilizada de forma a obter uma maior eficiência energética do transmissor. Por ultimo, são apresentadas diversas técnicas para a conversão dos sinais banda-base em sinais RF pulsados. As propostas apresentadas permitem o uso de uma arquitetura de hardware simplista, mas configurável por software, o que a torna bastante flexível. Com o uso desta arquitetura e possível alterar em pleno funcionamento a frequência central bem como a largura de banda e resposta do conversor pulsado. O trabalho apresentado nesta tese demonstra alguns dos melhoramentos no estado da arte para transmissores r adio completamente digitais, baseando os resultados obtidos não apenas em simulações mas também na implementação e medidas realizadas sobre protótipos laboratoriais. O trabalho desenvolvido no âmbito desta tese contribuiu com avanços na implementação de transmissores ageis, eficientes, com maior largura de banda e capazes de transmissão em múltiplas bandas com recurso a múltiplos protocolos, abrindo caminho para o desenvolvimento de novos rádios cognitivos e definidos por softwareFCT, FSEPrograma Doutoral em Engenharia Eletrotécnic

The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

Chip-scale optical frequency comb sources for terabit communications

To keep up with the ever-increasing data transmission speed needs, data center interconnects are scaling up to provide multi-Tbit/s connectivity. These links require a high number of WDM channels, while the associated transceivers should be compact and energy efficient. Scaling the number of channels, however, is still limited by the lack of adequate optical sources. In this book, we investigate novel chip-scale frequency comb generators as multi-wavelength light sources for Tbit/s WDM links

Chip-scale optical frequency comb sources for terabit communications

The number of devices connected to the internet and the required data transmission speeds are increasing exponentially. To keep up with this trend, data center interconnects should scale up to provide multi-Tbit/s connectivity. With typical distances from a few kilometers to 100 km, these links require the use of a high number of WDM channels. The associated transceivers should have low cost and footprint. The scalability of the number of channels, however, is still limited by the lack of adequate optical sources. In this book, we investigate novel chip-scale frequency comb generators as multi-wavelength light sources in WDM links. With a holistic model, we estimate the performance of comb-based WDM links, and we compare the transmission performance of different comb generator types, namely a quantum-dash mode-locked laser diode and a microresonator-based Kerr comb generator. We characterize their potential for massively-parallel WDM transmission with various transmission experiments. Combined with photonic integrated circuits, these comb sources offer a path towards highly scalable, compact, and energy-efficient Tbit/s transceivers

Novel MRI Technologies for Structural and Functional Imaging of Tissues with Ultra-short T₂ Values

Conventional MRI has several limitations such as long scan durations, motion artifacts, very loud acoustic noise, signal loss due to short relaxation times, and RF induced heating of electrically conducting objects. The goals of this work are to evaluate and improve the state-of-the-art methods for MRI of tissue with short T₂, to prove the feasibility of in vivo Concurrent Excitation and Acquisition, and to introduce simultaneous electroglottography measurement during functional lung MRI