With the rise of wireless sensor networks and the internet of things, many sensors are being developed to help us monitor our environment. Sensor applications from marine animal tracking to implantable healthcare monitoring require small and non-invasive methods of powering, for which purpose traditional batteries are considered too bulky and unreasonable. If appropriately designed, energy harvesting devices can be a viable solution. Solar and wind energy are good candidates of power but require constant exposure to their sources, which may not be feasible for in-vivo and underwater applications. Mechanical energy, however, is available underwater (the motion of the waves) and inside our bodies (the beating of the heart). These vibrations are normally low in frequency and amplitude, thus resulting in a low voltage once converted into electrical signals using conventional mechanical harvesters. These mechanical harvesters also suffer from narrow bandwidth, which limits their efficient operation to a small range of frequencies. Thus, there is a need for a mechanical energy harvester to convert mechanical energy into electrical energy with enhanced output voltage and for a wide range of frequencies. In this thesis, a new mechanical harvester is introduced, and two different methods of rectifying it are investigated. The designed harvester enhances the output voltage and extends the bandwidth of operation using a mechanical frequency up-convertor. This is implemented using magnetic forces to convert low-frequency vibrations to high-frequency pulses with the help of a piezoelectric material to generate high output voltage. The results show a 48.9% increase in the output voltage at 12.2Hz at an acceleration of 1.0g, and a bandwidth increase from 0.23Hz to 11.4Hz. For the rectification, mechanical rectifiers are discussed, which would obviate the need for electrical rectification, thus preventing the losses normally caused by the threshold voltage of electronics. Two designs of mechanical rectifiers are investigated and implemented on the frequency up-converter: a static rectifier and a rotating rectifier. The results show a voltage rectification, which required a sacrifice in the bandwidth and boosted voltage.

The constant endeavor to measure and record neural signals from the human brain and anticipate the results to figure out the mechanism which governs the functionality of our brain and its true behavior is the major driving force behind this thesis. Neural recording integrated circuits (ICs) are often inserted directly into the brain, with a set of probes for sensing these action potentials (and local field potentials), and appropriate circuitry for amplifying the neural signals (Pre-Amp), sampling and converting the analog signals to digital (ADC) and transmitting the resulting digital signal (Transmitter) to a nearby reader instrument (Receiver). Action potentials are comprised of signals typically looking like spikes having a peak voltage of 1-2mV, whereas local field potentials are continuous signals generally having an amplitude of around 100-200μV often with a dc component of several mV. Fourier analysis of action potentials and local field potentials show frequency components in the range of 0.1 Hz up to 10kHz. This thesis proposes a low-power 5-bit algorithmic A/D converter to feed a 5-stage serial shift register for use in sampling and converting a presumed neuron action potential signal at the rate of 20k samples/sec. In addition to that, a low-power preamp with at least 40dB gain and a low-pass type spectrum having a unity-gain frequency of at least 20MHz is used to amplify the input signal. The algorithmic A/D converter includes a sample-and-hold circuit for sampling the analog action potential spike at a rate of 20kHz. The ADC utilizes an X2 gain circuit based on a capacitive redistribution technique. A less complex circuit in terms of dependency on Capacitor sizing and their non-ideal effects is the key factor for selecting this type of ADC which can be used for neural recording applications. All the circuits are designed based on the IBM/Global Foundries 8HP 130nm BiCMOS technology.

Massive MIMO (Multiple-Input Multiple-Output) base stations have proven, both in theory and in practice, to possess many of the qualities that future wireless communication systems will require.  They can provide equally high data rates throughout their coverage area and can concurrently serve multiple low-end handsets without requiring wider spectrum, denser base station deployment or significantly more power than current base stations.  The main challenge of massive MIMO is the immense hardware complexity and cost of the base station—each element in the large antenna array needs to be individually controllable and therefore requires its own radio chain.  To make massive MIMO commercially viable, the base station has to be built from inexpensive simple hardware.  In this thesis, it is investigated how the use of low-end power amplifiers and analog-to-digital converters (ADCs) affects the performance of massive MIMO.  In the study of the signal distortion from low-end amplifiers, it is shown that in-band distortion is negligible in massive MIMO and that out-of-band radiation is the limiting factor that decides what power efficiency the amplifiers can be operated at.  A precoder that produces transmit signals for the downlink with constant envelope in continuous time is presented to allow for highly power efficient low-end amplifiers.  Further, it is found that the out-of-band radiation is isotropic when the channel is frequency selective and when multiple users are served; and that it can be beamformed when the channel is frequency flat and when few users are served.  Since a massive MIMO base station radiates less power than today's base stations, isotropic out-of-band radiation means that low-end hardware with poorer linearity than required today can be used in massive MIMO.  It is also shown that using one-bit ADCs—the simplest and least power-hungry ADCs—at the base station only degrades the signal-to-interference-and-noise ratio of the system by approximately 4 dB when proper power allocation among users is done, which indicates that massive MIMO is resistant against coarse quantization and that low-end ADCs can be used. / Massiv-MIMO-basstationer (eng: Multiple-Input Multiple-Output) har visats, både i teori och praktik, besitta många av de egenskaper som framtida trådlösa kommunikationssystem kommer att behöva.  De kan tillhandahålla enhetligt höga datatakter i hela täckningsområdet och simultant betjäna flera enkla mobilenheter utan att använda bredare spektrum, tätare basstationsplacering eller betydligt mer effekt än dagens basstationer.  Huvudutmaningen med massiv MIMO är basstationens enorma hårdvarukomplexitet och -kostnad – varje element i den stora gruppantennen skall kunna kontrolleras individuellt och kräver sålunda sin egen radiokedja.  För att massiv MIMO skall bli kommersiellt attraktiv, måste basstationen byggas av billig, enkel hårdvara.  I denna avhandling undersöks hur enkla effektförstärkare och analog-till-digital-omvandlare (AD-omvandlare) påverkar massiv-MIMO-systemets prestanda.  I studien av signaldistorsionen från enkla förstärkare visas det att inband-distorsionen är försumbar i massiv MIMO och att utombandsstrålningen är den begränsande faktorn som bestämmer vid vilken verkningsgrad förstärkarna kan arbeta.  En förkodare som åstadkommer nerlänks-sändsignaler som har konstant envelopp i kontinuerlig tid presenteras för att möjliggöra användandet av enkla förstärkare med hög verkningsgrad.  Vidare konstateras det att utombandsstrålningen är isotrop när kanalen är frekvensselektiv och när flera användare betjänas; och att den kan lobformas när kanalen är frekvensflat och när få användare betjänas.  Eftersom en massiv-MIMO-basstation utstrålar mindre effekt än dagens basstationer, betyder isotrop utombandsstrålning att enkel hårdvara med sämre linearitet än vad som krävs idag kan användas i massiv MIMO.  Det visas även att användandet av enbits-AD-omvandlare – de enklaste och mest strömsnåla AD-omvandlarna – i basstationen endast minskar signal-till-interferens-och-brus-förhållandet med 4 dB när tillbörlig effektallokering mellan användarna utförs, vilket indikerar att massiv MIMO är motståndskraftig mot grov kvantisering och att enkla AD-omvandlare kan användas. / 大規模多輸入多輸出基站，無論從理論上或實際上，皆已經證明具有許多未來無線通訊系統所需的特質。比如：在其整個覆蓋區域均一地提供高數據傳輸速率、在同一時間頻率資源上服務多個簡單的終端設備，而無需佔用更多頻譜資源或更密集地部署基站，亦無需提高基站的功耗。實現大規模多入多出系统的主要挑戰在於硬件複雜度及基站成本——大規模天線陣列中的每一個天線元必須單獨可控，因此需要其自身的射頻鏈路。爲使大規模多入多出基站有商業吸引力，基站必須以簡單低成本的硬件來建造。本論文探討簡單的功率放大器與模擬數字轉換器對大規模多入多出性能的影響。對低端功放信號失真的研究表明，帶內失真對大規模多入多出的性能影響幾乎可以忽略，而帶外泄露是限制功放效率的決定因素。爲使用高功率效率低端功放，本文提出能產生具有恆定包絡連續時間信號的預編碼。本文指出，在頻率選擇性衰落信道上服務多個用戶時，帶外泄露呈現各向同性；而在平坦衰落信道上服務少數用戶時，帶外泄露可呈現波束賦形。由於大規模多入多出基站比現用基站輻射較少功率，帶外泄露各向同性意味著大規模多入多出基站可使用低端硬件，其線性要求不比現有基站的高。另外表明，如果進行合理的多用戶功率分配，基站使用單比特模擬數字轉換器——最簡單低耗的轉換器——僅使系統的信干噪比降低約４分貝。以此可見，大規模多入多出系統對非精確量比較穩定，低端模擬數字轉換器可於此類系統中使用。

Les lasers à fibre optique délivrant des impulsions femtoseconde sont aujourd'hui utilisés dans de nombreuses applications scientifiques ou industrielles. Pour étendre l'éventail de ces applications, l'augmentation des performances en termes de durée, énergie par impulsion, et puissance moyenne délivrée par ces sources a fait l'objet de nombreux développements. Ce travail a pour objectif d'utiliser l'idée de combinaison cohérente d'impulsions femtoseconde dans le but de poursuivre l'amélioration des caractéristiques des amplificateurs à fibre ultrabrefs selon deux axes.La première partie est consacrée à la montée en énergie en utilisant des architectures de combinaison cohérente passives, c'est à dire ne nécessitant pas de boucle de contrôle de la phase optique entre les impulsions à combiner. Ces systèmes exploitent à la fois le domaine spatial, (combinaison de faisceaux) et le domaine temporel (combinaison de répliques de l'impulsion initiale décalées dans le temps). Nous démontrons que ces techniques permettent effectivement la montée en énergie, et étudions les limites de leur utilisation liées aux non-linéarités optiques et à la saturation du gain des amplificateurs. Nous proposons également des perspectives pour outrepasser ces limites.La deuxième partie du manuscrit est dédiée à la réduction de la durée des impulsion émises par ces sources à fibre. Nous utilisons dans un premier temps la combinaison cohérente active de deux impulsions femtoseconde amplifiées ayant des contenus spectraux différents et décalés. Ainsi, une impulsion plus courte que chacune des impulsions individuelles est synthétisée. Une autre approche consistant à sculpter le contenu spectral de l'impulsion à amplifier afin de compenser le profil de gain de l'amplificateur est également étudiée. Enfin, nous appliquons les architectures de combinaison cohérente passive étudiées dans la première partie à des systèmes de compression temporelle non-linéaire afin d'outrepasser leurs limites en énergie. / Optical fiber-based ultrafast laser sources are nowadays used in numerous scientific and industrial applications. To extend further the number of possible applications, it is essential to improve their performances in terms of pulsewidth, energy per pulse, and average power. Extensive research work has been performed over the last years on this area. The work described in this manuscript is a contribution to these research efforts, and aims at improving ultrafast fiber laser sources by using coherent combination of several femtosecond pulses.The first part is devoted to energy scaling by using passive coherent combining architectures, that do not require a feedback control loop of the relative optical phase between pulses to be combined. This idea is used both in the space (combining beams) and time (combining replicas of the pulse at different delays) domains. We demonstrate that these techniques allow energy scaling and study their limitations related to optical nonlinearities and gain saturation in the amplifiers. We also propose ways to circumvent these limitations.In the second part, we study various ways of decreasing the output pulsewidth of fiber-amplified femtosecond sources. First, we implement an active coherent combining system that performs combination of two amplified femtosecond pulses with different, shifted spectral content. This allows the synthesis of a pulse that is shorter than any of the individual pulses to be combined. Another studied approach consists in tailoring the spectrum of input pulses to precompensate the spectral gain shape of the amplifier. Finally, by using passive combining architectures described in the first part, we demonstrate energy scaling of temporal nonlinear compression setups.

Les lasers à impulsions ultra-courtes (< 10 ps) ont largement démontré leur intérêt pour de nombreuses applications scientifiques, industrielles ou encore médicales. Le domaine du micro-usinage par impulsions laser est l'un des domaines les plus actifs du moment. Les dernières avancées en la matière privilégient deux axes de recherche, l'augmentation du taux de répétition associé à de fortes puissances moyennes et une montée en énergie. Nos travaux s'inscrivent dans ce contexte et visent à développer des amplificateurs d'impulsions ultracourtes innovants à base de fibres cristallines Yb:YAG délivrant de fortes puissances moyennes et de fortes énergies en régime de polarisation cylindrique. Les sources développées sont destinées à être intégrées au sein de systèmes de micro-usinage laser aux performances inédites développés dans le cadre du projet européen Razipol. Celles-ci joueront le rôle de préamplificateur fort gain au sein d'une architecture MOPA composé d'un oscillateur ultra-rapide à base de cristal d'Yb:KYW et d'un amplificateur final à base de disque mince Yb:YAG. Pour répondre à la problématique des dégradations spatiales liées à la montée en puissance moyenne dans les architectures à laser solide pompé par diode, une architecture en cascade composée de trois étages d'amplification permettant de réduire la charge thermique a d'abord été réalisée. Grâce à une fine optimisation de l’ensemble des paramètres spectroscopiques (taux de dopage des cristaux, longueur d'onde de pompe...) et géométriques (longueur des cristaux, tailles de faisceaux...) a permis d'amplifier des impulsions femtosecondes (750 fs) jusqu'à des puissances moyennes de 100 et 85 W, respectivement obtenues en polarisation linéaire et cylindrique, à la cadence de 20 MHz. Un amplificateur picoseconde de forte énergie à également été réalisé. Intégrant un dispositif de combinaison cohérente à division temporelle à 4 ou 8 répliques visant à réduire les effets non-linéaires, la source développée délivre des énergies remarquablement élevées pour ce type de système à amplification directe. Il délivre des énergies de 1 et 2 mJ à des cadences inférieures à 20 kHz. Ces résultats ont fait l'objet de 2 publications dans des revues internationales à comité de lecture. Par ailleurs les deux amplificateurs développés ont été intégrés sous la forme de systèmes compactes et robustes, utilisables par les membres du projet européen Razipol. Ces travaux ont également inspirée une nouvelle ligne de produits désormais commercialisés la société Fibercryst. / In the last decade ultra-short pulse laser (< 10 ps) have sparked increasing interest for many industrial and scientific applications. Among the geometries used so far for high-power Yb-doped diode-pumped solid-state lasers as slabs, rods and thin disks, the single crystal fiber (SCF) technology was recently shown to have a high potential for the amplification of ultrashort pulses thanks to a very efficient thermal management and high optical efficiencies. This technology combined with the cubic crystal structure of Yb:YAG offers a cylindrical symmetry of the optical and thermo-mechanical properties. Yb:YAG SCFs are therefore well suited for the amplification of cylindrically polarized beams. In the context of a European Project called RAZIPOL, we have developed new laser amplifier architectures using SCF to directly amplify femtosecond pulses to achieve high energy and high average power pulses with radial and azimuthal polarizations without any stretching and recompression of the pulses.We first demonstrate a three-stage diode-pumped Yb:YAG single-crystal-fiber amplifier to generate femtosecond pulses at high average powers with linear or cylindrical (i.e., radial or azimuthal) polarization. At a repetition rate of 20 MHz, 750 fs pulses were obtained at an average power of 85 W in cylindrical polarization and at 100 W in linear polarization. Investigations on the use of Yb:YAG single-crystal fibers with different length/doping ratios and the zero-phonon pumping at a wavelength of 969 nm were conducted in order to optimize the performances of the amplifiers.The second part of the project is focused on pulse energy scaling. In this sense, we demonstrate a two-stage Yb:YAG single-crystal-fiber amplifier designed for high peak power to significantly increase the pulse energy of a low power picosecond laser. The first amplifier stage has been designed for high gain. Using a gain medium optimized in terms of doping concentration and length an optical gain of 32dB has been demonstrated. The second amplifier stage designed for high energy using divided pulse technique allows to generate recombined output pulse energy of 2mJ at 12.5 kHz with a pulse duration of 6 ps corresponding to a peak power 320MW. Average powers ranging from 25W to 55W with repetition rates varying from 12.5 kHz to 500 kHz have been demonstrated.This results has led to the publication of 2 articles in international peer-reviewed journals and have been presented in 7 conferences. Finally this work has inspired the launch of a new line of industrial products by Fibercryst.

abstract: This dissertation focuses on three different efficiency enhancement methods that are applicable to handset applications. These proposed designs are based on three critical requirements for handset application: 1) Small form factor, 2) CMOS compatibility and 3) high power handling. The three presented methodologies are listed below: 1) A transformer-based power combiner architecture for out-phasing transmitters 2) A current steering DAC-based average power tracking circuit for on-chip power amplifiers (PA) 3) A CMOS-based driver stage for GaN-based switched-mode power amplifiers applicable to fully digital transmitters This thesis highlights the trends in wireless handsets, the motivates the need for fully-integrated CMOS power amplifier solutions and presents the three novel techniques for reconfigurable and digital CMOS-based PAs. Chapter 3, presents the transformer-based power combiner for out-phasing transmitters. The simulation results reveal that this technique is able to shrink the power combiner area, which is one of the largest parts of the transmitter, by about 50% and as a result, enhances the output power density by 3dB. The average power tracking technique (APT) integrated with an on-chip CMOS-based power amplifier is explained in Chapter 4. This system is able to achieve up to 32dBm saturated output power with a linear power gain of 20dB in a 45nm CMOS SOI process. The maximum efficiency improvement is about ∆η=15% compared to the same PA without APT. Measurement results show that the proposed method is able to amplify an enhanced-EDGE modulated input signal with a data rate of 70.83kb/sec and generate more than 27dBm of average output power with EVM<5%. Although small form factor, high battery lifetime, and high volume integration motivate the need for fully digital CMOS transmitters, the output power generated by this type of transmitter is not high enough to satisfy the communication standards. As a result, compound materials such as GaN or GaAs are usually being used in handset applications to increase the output power. Chapter 5 focuses on the analysis and design of two CMOS based driver architectures (cascode and house of cards) for driving a GaN power amplifier. The presented results show that the drivers are able to generate ∆Vout=5V, which is required by the compound transistor, and operate up to 2GHz. Since the CMOS driver is expected to drive an off-chip capacitive load, the interface components, such as bond wires, and decoupling and pad capacitors, play a critical role in the output transient response. Therefore, extensive analysis and simulation results have been done on the interface circuits to investigate their effects on RF transmitter performance. The presented results show that the maximum operating frequency when the driver is connected to a 4pF capacitive load is about 2GHz, which is perfectly matched with the reported values in prior literature. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2019

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No description available.

Silicon (Si) and silicon nitride (Si3N4) have become the dominant photonic integrated circuit (PIC) material platforms, due to their low-cost, wafer-scale production of high-performance circuits. However, novel materials can offer additional functionalities that cannot be easily accessed in Si and Si3N4, such as light emission. Tellurium oxide (TeO2) is a novel material of interest because of its large linear and non-linear refractive indices, low material losses and large rare-earth dopant solubility, with applications including compact low-loss waveguides and on-chip light sources and amplifiers. This thesis investigates the post-processing integration of TeO2 devices onto standardized Si and Si3N4 chips to incorporate TeO2 material advantages into high-performance PICs. Chapter 1 introduces the state-of-the-art functionality for various integrated photonic materials as well as methods for integrating multiple materials onto single chips. Chapter 2 presents the development of a high-quality TeO2 thin film fabrication process by reactive RF sputtering, with material refractive indices of 2.07 and optical propagation losses of <0.1 dB/cm at 1550 nm. Chapter 3 investigates a conformally coated TeO2-Si3N4 waveguide platform capable of large TeO2 optical confinement and tight bending radii, characterizing fiber-chip edge couplers down to ~5 dB/facet, waveguide propagation losses of <0.5 dB/cm, directional couplers with 100% cross-over ratio, and microresonators with internal Q factors of 7.3 × 105. In Chapter 4 a spectroscopic study of TeO2:Er3+-coated Si3N4 waveguide amplifiers was undertaken, with internal net gains of up to 1.4 dB/cm in a 2.2-cm-long waveguide and 5 dB total in a 6.7-cm-long sample demonstrated, predicted to reach >10 dB could 150 mW of pump power be launched based on a developed rate-equation model. Chapter 5 demonstrates TeO2-coated microtrench resonators coupled to silicon waveguides, with internal Q factors of up to 2.1×105 and investigates environmental sensing metrics of devices. Chapter 6 summarizes the thesis and provides avenues for future work. / Thesis / Doctor of Philosophy (PhD)

<p>Sal/Hall D, Forum, KTH-ICT, Isafjordsgatan 39, Kista</p>