• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 96
  • 54
  • 24
  • 14
  • 8
  • 6
  • 5
  • 3
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 242
  • 44
  • 35
  • 29
  • 28
  • 28
  • 28
  • 26
  • 22
  • 21
  • 20
  • 20
  • 19
  • 19
  • 19
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
231

Using eye tracking to optimise the usability of content rich e-learning material / Optimising the usability of content rich e-learning material: an eye tracking experiment

Mpofu, Bongeka 11 1900 (has links)
This research was aimed at the optimisation of the usability of content-rich computer and mobile based e-learning material. The goal was to preserve the advantages of paper based material in designing optimised modules that were mobile and computer-based, but at the same time avoiding the pitfalls of converting traditional paper based learning material for use on screen. A mobile eye tracker was used to analyse how students studied similar course content on paper, and on mobile device. Screen based eye tracking was also used to analyse how participants studied corresponding content on a desktop screen. Eye movements which were recorded by an eye tracker revealed the sequences of fixations and saccades on the text that was read by each participant. By analysing and comparing the eye gaze patterns of students reading the same content on three different delivery platforms, the differences between these platforms were identified in terms of their delivery of content rich, text based study material. The results showed that more students read online content on a computer screen than on mobile devices. The inferential analysis revealed that the differences in reading duration, comprehension, linearity and fixation count on the three platforms were insignificant. There were significant differences in saccade length. This analysis was used to identify strong aspects of the respective platforms and consequently derive guidelines for using these aspects optimally to design content rich material for delivery on computer screen and mobile device. The limitations of each platform were revealed and guidelines for avoiding these were derived / Computing / M. Sc. (Computing)
232

Characterisation of an Additively Manufactured Self-Sensing Material Using Carbon Fibre Sensors

Williamson, Alain January 2023 (has links)
Increasing demand for structural health monitoring in space highlights the need to make the creation of these systems more accessible. This study investigates the potential of additive manufacturing to achieve this goal by characterizing a self-sensing material made of a commercially available 3D-printed continuous carbon fibre filament. The results demonstrate the feasibility of converting the filament into a strain sensor with improved sensitivity compared to conventional foil strain gauges. Mechanical and electromechanical properties of the self-sensing material were characterized, including an ultimate tensile strength of 45.09 ± 3.45 MPa, a failure strain of 38.93 ± 3.41%, and a base resistance of 759.11Ω. The tensile gauge factor was calculated to be 467.06 ± 375.90 within the strain range of 0% to 3.8% with a linearity (R2) of 0.93. For the first time, a systematic literature review compares mechanical and electromechanical properties to enable material selection for mechanical design incorporating self-sensing material. The study highlights that the spread of material properties in a group of materials indicates how well-developed a material is for self-sensing purposes. This study advances our understanding of the feasibility of using additive manufacturing to create self-sensing materials for structural health monitoring systems and opens up new avenues for further research.
233

PCBA verification and fault detection using a low-frequency GMR-based near-field probe with magnetic closed-loop feedback compensation : A non-contact alternative to physical probing / Verifiering och feldetektering av kretskort mha en lågfrekvent närfältssond baserad på en GMR-sensor med magnetisk återkopplingskrets med sluten kompensationsslinga : Ett kontaktlöst alternativ till fysisk sondering

Sundh, Joacim January 2022 (has links)
As electronics are getting both smaller and more advanced, the need to verify and validate remains and the means are getting more complex the more functions and components are added. Traditionally, in-circuit tests (ICTs) are performed by probing dedicated test points on the Printed Circuit Board Assembly (PCBA) in a test sequence that is unique to each product. But as the density of components increases, the choice between component and test point must be considered. Instead of decreasing the reliability during verification by having to remove less system-critical test points, this thesis suggests the use of a near-field probe (NFP) based around a Giant Magneto-Resistance (GMR) sensor to possibly replace the need for a physical test point by instead performing contactless testing. The use of a GMR sensor allows for bandwidth from 0 Hz up to the MHz range, whereas commercial NFPs are based on a different technique and are operational from the MHz range and up. The goal of this project was to improve the non-linearity of typically 15% present in the AAH002-02 model from NVE by the use of an analogue closed-loop magnetic feedback circuit. The project successfully improved the linearity to 99.8% by the use of an instrumentation amplifier, a subtractor and a push-pull amplifier in conjunction with a 3x30 turn planar coil embedded in a PCB, located beneath the sensor Integrated Circuit (IC). The resulting linearity was verified by a Helmholtz coil where a uniform magnetic field was produced with linearly increased field strength, and calculated using the R2 value from a linear regression analysis on the acquired data. In the future, the data acquired from this kind of NFP could be used together with a Machine Learning (ML) model to remove the manual labour required when constructing these product-unique test sequences. / Dagens elektronik blir både mindre och mer avancerad, men behovet av verifiering och validering av dessa kvarstår och metoderna för detta ökar i komplexitet ju fler funktioner och komponenter som läggs till. Dagens kretskortstester genomförs genom att sondera dedikerade testpunkter strategiskt utplacerade på kretskortet enligt en testsekvens som är unikt skapad för varje produkt. Men med att densiteten av komponenter ökar måste valet mellan komponent och testpunkt tas i beaktning. Instället för att minska tillförlitligheten vid validering genom att ta bort mindre kritiska testpunkter föreslår denna avhandling användandet av en närfältssond baserad runt en Giant Magneto-Resistance (GMR)-sensor för att möjligen ersätta behovet av en fysisk testpunkt genom att istället genomföra kontaktlös testning. Användandet av en GMR-sensor tillåter en bandbredd från 0 Hz upp till MHzområdet, där kommersiella närfältssonder är baserade på annan teknik och är funktionsdugliga från MHz-området och uppåt. Målet med detta projekt var att förbättra olinjäriteten på typiskt 15% som är närvarande hos en sensor av modell AAH002-02 från NVE genom en analog magnetisk återkopplingskrets med sluten slinga. Projektet lyckades förbättra linjäriteten till 99.8% genom användandet av en intrumentförstärkare, en subtraherare och en push-pull-förstärkare i samverkan med en plan spole på 3x30 varv inbyggd i ett mönsterkort placerd under sensorns integrerade krets. Den resulterande linjäriteten validerades med hjälp av en Helmholtz-spole där ett uniformt magnetfält producerades med linjärt ökande fältstyrka och beräknades genom R2 -värdet från en linjär regression-analys på den inhämtade datan. I framtiden kan datan som inhämtats från den här sortens närfältssond kunna användas tillsammans med en maskininlärningsmodell för att ersätta det manuella arbetet som idag krävs för att konstruera dessa produktunika testsekvenser
234

Vad är god praxis för kalibrering och funktionskontroller av vågar inom läkemedelsindustrin / What is the best practice for calibration and routine testing of balances in the pharmaceutical industry

Gourie, Roberto January 2022 (has links)
I denna studie så ville AstraZenecas dispenseringsfunktion, som arbetar med att finfördelamaterial från sin bulkförpackning undersöka hur och med vilka frekvenser kalibreringar ochfunktionskontroller för deras vågar bör göras. Detta i hopp om att harmonisera en uppdateradoch förbättrad standard mellan siterna Gärtuna och Snäckviken. Standarder inom mätningslära är inget som läkemedelsföretag själva investerar resurser i, utanföljer det som farmakopéerna världen över publicerar i sina böcker. Däri återfinns allt som kantänkas behövas för tillverkning och utformning av läkemedel. Syftet med att kalibrera ochgenomföra funktionskontroller så ofta som AstraZeneca gör i dagsläget är för att vara förenligamed regelverk för att bli godkända vid inspektioner. Däremot finns risken attfunktionskontroller och kalibreringar genomförs med högre eller lägre frekvens än vad de bordegöras samt att irrelevanta tester vid dessa kontroller får alltför hög prioritering för att påvisa envågs förmåga att fungera som den ska. För att undersöka detta genomfördes det en kartläggning av hur AstraZeneca arbetar idag medvågkalibreringar och funktionskontroller. Denna behandlade både hur arbetet sker internt viaegna funktioner, men också externt via vågtillverkaren och valideringsfirmor. Dennainformation tillsammans med vad farmakopéerna och vågtillverkaren själva påstår är korrektarbetssätt blev ett tydligt och effektivt sätt att sålla bort överflödiga och i vissa fall irrelevantametoder som används på AstraZeneca idag. Utöver dessa finns det fenomen såsommätosäkerhet och störningselement som kan påverka varje vägning till den grad där resultatenär fullständigt missvisande, och i läkemedelsindustrins fall är dessa oacceptabla. Vid studiens slut kunde flera systematiska brister identifieras och rekommendationer för attmotverka eller lösa dessa gavs i enlighet med syftet om att nå god praxis för våganvändningen isamband med dispenseringsprocessen. Framtida förbättringsarbeten hade förenklats ocheffektiviserats till stor del om en fullständig digitalisering och övervakning avstörningselementen möjliggörs. / In this study that was commissioned by AstraZeneca's dispensing function that worksmainly by sub-dividing materials from its bulk packaging. They wanted to investigatehow and with what frequencies calibrations and routine testing for their balances shouldbe performed. This, with the purpose of harmonizing an updated and improvedstandard between the sites Gärtuna and Snäckviken. Measurement theory standards are not something that pharmaceutical companiesthemselves invest resources in but rather follow what pharmacopoeias around the worldpublish in their books. The books contain everything that may be needed for themanufacturing and design of medicines. The purpose of calibrating and performingroutine testing as often as AstraZeneca does today is to comply with regulations to beapproved during inspections. However, there is a risk that routine testing andcalibrations are performed at a higher or lower frequency than they should be, and thatirrelevant tests at these routine tests are given too high a priority to demonstrate abalances ability to function properly. To investigate this, a survey was conducted of how AstraZeneca works today withbalance calibrations and routine testing. The survey considered both how the work isdone internally via AstraZeneca’s own employees, but also externally via the balancemanufacturer and validation companies. This information, in combination with whatthe pharmacopoeias and the balance manufacturer themselves claim is the correct wayof operating, became a clear and effective way of sifting away superfluous and in somecases irrelevant methods used in AstraZeneca today. In addition to these, there arephenomena such as measurement uncertainty and external disturbance elements thatcan affect any weighing to the extent that the results are completely misleading, and inthe case of the pharmaceutical industry, such results would be unacceptable. At the end of the study, several systematic flaws or shortcomings could be identified andrecommendations to counteract or solve these were given in accordance with the aim ofachieving best practice for the use of balances in connection with the dispensingprocess. Future improvement work would have been greatly simplified and streamlinedif complete digitization and monitoring of the disturbance elements were made possible.
235

La santé publique globalisée

Lapaige, Véronique January 2007 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.
236

Conception d'amplificateur faible bruit reconfigurable en technologie CMOS pour applications de type radio adaptative / Digitally controlled CMOS low noise amplifier for adaptative radio

De Souza, Marcelo 15 December 2016 (has links)
Les systèmes de communication mobiles permettent l’utilisation de l’information en environnements complexes grâce à des dispositifs portables qui ont comme principale restriction la durée de leurs batteries. Des nombreux efforts se sont focalisés sur la réduction de la consommation d’énergie des circuits électroniques de ces systèmes, une fois que le développent des technologies des batteries ne avance pas au rythme nécessaire. En outre, les systèmes RF sont généralement conçus pour fonctionner de manière fixe, spécifiés pour le pire cas du lien de communication. Toutefois, ce scénario peut se produire dans une petite partie du temps, entraînant ainsi en perte d’énergie dans le reste du temps. La recherche des circuits RF adaptatifs, pour adapter le niveau du signal d'entrée pour réduire la consommation d'énergie est donc d'un grand intérêt et de l'importance. Dans la chaîne de réception radiofréquence, l'amplificateur à faible bruit (LNA) se montre un composant essentiel, autant pour les performances de la chaîne que pour la consommation d'énergie. Au cours des dernières décennies, des techniques pour la conception de LNAs reconfigurables ont été proposées et mises en oeuvre. Cependant, la plupart d'entre elles s’applique seulement au contrôle du gain, sans exploiter Le réglage de la linéarité et du bruit envisageant l'économie d'énergie. De plus,ces circuits occupent une grande surface de silicium, ce qui entraîne un coût élevé, ou NE correspondent pas aux nouvelles technologies CMOS à faible coût. L'objectif de cette étude est de démontrer la faisabilité et les avantages de l'utilisation d'un LNA reconfigurable numériquement dans une chaîne de réception radiofréquence, du point de vue de la consommation d'énergie et de coût de fabrication. / Mobile communication systems allow exploring information in complex environments by means of portable devices, whose main restriction is battery life. Once battery development does not follow market expectations, several efforts have been made in order to reduce energy consumption of those systems. Furthermore, radio-frequency systems are generally designed to operate as fixed circuits, specified for RF link worst-case scenario. However, this scenario may occur in a small amount of time, leading to energy waste in the remaining periods. The research of adaptive radio-frequency circuits and systems, which can configure themselves in response to input signal level in order to reduce power consumption, is of interest and importance. In a RF receiver chain, Low Noise Amplifier (LNA) stand as critical elements, both on the chain performance or power consumption. In the past some techniques for reconfigurable LNA design were proposed and applied. Nevertheless, the majority of them are applied to gain control, ignoring the possibility of linearity and noise figure adjustment, in order to save power. In addition, those circuits consume great area, resulting in high production costs, or they do not scale well with CMOS. The goal of this work is demonstrate the feasibility and advantages in using a digitally controlled LNA in a receiver chain in order to save area and power. / Os sistemas de comunicação móveis permitem a exploração da informação em ambientes complexos através dos dispositivos portáteis que possuem como principal restrição a duração de suas baterias. Como o desenvolvimento da tecnologia de baterias não ocorre na velocidade esperada pelo mercado, muitos esforços se voltam à redução do consumo de energia dos circuitos eletrônicos destes sistemas. Além disso, os sistemas de radiofrequência são em geral projetados para funcionarem de forma fixa, especificados para o cenário de pior caso do link de comunicação. No entanto, este cenário pode ocorrer em uma pequena porção de tempo, resultando assim no restante do tempo em desperdício de energia. A investigação de sistemas e circuitos de radiofrequência adaptativos, que se ajustem ao nível de sinal de entrada a fim de reduzir o consumo de energia é assim de grande interesse e importância. Dentro de cadeia de recepção de radiofrequência, os Amplificadores de Baixo Ruído (LNA) se destacam como elementos críticos, tanto para o desempenho da cadeia como para o consumo de potência. No passado algumas técnicas para o projeto de LNA reconfiguráveis foram propostas e aplicadas. Contudo, a maioria delas só se aplica ao controle do ganho, deixando de explorar o ajuste da linearidade e da figura de ruído com fins de economia de energia. Além disso, estes circuitos ocupam grande área de silício, resultando em alto custo, ou então não se adaptam as novas tecnologias CMOS de baixo custo. O objetivo deste trabalho é demonstrar a viabilidade e as vantagens do uso de um LNA digitalmente configurável em uma cadeia de recepção de radiofrequência do ponto de vista de custo e consumo de potência.
237

La santé publique globalisée

Lapaige, Véronique January 2007 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal
238

MEMS-Laser-Display-System / MEMS Laser Display System

Specht, Hendrik 19 October 2011 (has links) (PDF)
In der vorliegenden Arbeit werden die im Zusammenhang mit der Strahlablenkung stehenden Systemaspekte der auf MEMS-Scanner basierenden Laser-Display-Technologie theoretisch analysiert und aus den Ergebnissen die praktische Implementierung eines Laser-Display-Systems als Testplattform vorgenommen. Dabei werden mit einem Ansatz auf Basis zweier 1D-Scanner und einem weiteren Ansatz mit einem 2D-Scanner zwei Varianten realisiert. Darüber hinaus erfolgt die Entwicklung eines bildbasierten Multiparametertestverfahrens, welches sowohl für den Test komplettierter Strahlablenkeinheiten bzw. Projektionsmodule als auch zum umfassenden und zeiteffizienten Test von MEMS-Scannern auf Wafer-Level geeignet ist. Mit diesem Verfahren erfolgt eine Charakterisierung der zwei realisierten Varianten des Laser-Displays. Ausgehend von den Eigenschaften des menschlichen visuellen Systems und den daraus resultierenden Anforderungen an das Bild sowie einer systemtheoretischen Betrachtung des mechanischen Verhaltens von MEMS-Scannern bildet die Ansteuersignalerzeugung für den resonanten Betrieb der schnellen und den quasistatischen Betrieb der langsamen Achse einen Schwerpunkt. Neben dem reinen digitalen Regler- bzw. Filterentwurf sowie mehreren Linearisierungsmaßnahmen beinhaltet dieser auch die Herleitung einer FPGA-basierten Videosignalverarbeitung zur Konvertierung von Scannpattern, Zeitregime und Auflösung mit einer entsprechenden Synchronisierung von Strahlablenkung und Lasermodulation. Auf Grundlage der daraus resultierenden Erkenntnisse über den Zusammenhang zwischen Scanner-/Systemparametern und Bildparametern werden Testbild-Bildverarbeitungsalgorithmus-Kombinationen entwickelt und diese, angeordnet in einer Sequenz, mit einem Kalibrierverfahren zu einem Testverfahren für MEMS-Scanner vervollständigt. Die Ergebnisse dieser Arbeit entstanden im Rahmen von industriell beauftragten F&E-Projekten und fließen in die andauernde Fortführung des Themas beim Auftraggeber ein.
239

[pt] ESTUDO DE VIGAS DE AÇO COM ABERTURAS DE ALMA TIPO ALVEOLAR, LITZKA E VIGAS EXPANDIDAS EM ALTURA / [en] STUDY OF STEEL BEAMS WITH WEB OPENINGS INCLUDING CELLULAR, LITZKA AND DEPTH-EXPANDED BEAMS

JORGE AUGUSTO WISSMANN 30 October 2017 (has links)
[pt] Estruturas cada vez mais esbeltas têm sido usadas para otimizar edifícios de grande porte e reduzir custos, inclui-se nisto o pé-direito das edificações e portanto a altura das vigas. Grandes vãos são cada vez mais comuns, principalmente quando se utiliza aço em edificações, gerando então amplos espaços de serviço em uma direção, mas obstáculos na outra pela continuidade das vigas. A utilização de aberturas na alma das vigas para passagem de tubulações de ar-condicionado, incêndio, etc., evita um acréscimo na altura. Em consequência há uma grande diminuição da capacidade resistente nestes elementos estruturais que dependem diretamente da forma, do tamanho e da posição destas aberturas. A presente dissertação descreve alguns métodos construtivos de aberturas em almas de vigas de aço, cálculos de dimensionamentos e normas relacionadas. Alguns estudos numéricos com aplicações do método dos elementos finitos foram realizados investigando: angulação de aberturas hexagonais, vigas com três aberturas nos terços médios, vigas casteladas (tipo Litzka, com quantidades diferentes de aberturas), vigas expandidas em altura e uma viga Litzka Expandida. Para tal, utilizou-se de seis perfis de uso prático e comparando-os entre estas alternativas descritas. A viga Litzka Expandida se destacou em resistência quando comparada com outros métodos de fabricação, como também pelo menor peso linear, praticidade na fabricação e posicionamento das aberturas. / [en] More slender structures are used in order to reduce costs, floors depht and floor to ceiling clear heights. Steel construction and composite construction for buildings often employs long spans for beams and girders, offering service room between beams in one direction only. The use of web openings for passage of service ducts avoids increasing the depth of construction. Beams with web openings have reductions on flexural and shear resistances depending on the geometry, size and position of such openings on the beam. This dissertation presents some construction methods of beam web openings, analysis and design recommendations, related standards and codes. Some numerical studies by the finite elements method were carried out and results are presented for: type of openings, number and spacing of openings, castelled beams (Litzka type and nonuniform distribution of openings) and expanded in depth beams. For this purpose, six commonly used profiles were used for testing the described web openings solutions. Some comparison results are presented. The Litzka type of web expanded beam presented the best performance in terms of strength, easy of fabrication and reduction of material costs.
240

Σχεδίαση και ανάπτυξη ολοκληρωμένων κυκλωμάτων για συστήματα υπερευρείας ζώνης με έμφαση στα κυκλώματα του πομπού / Design and development of integrated circuits for ultra wideband systems, with emphasis on the transmitter circuits

Παπαμιχαήλ, Μιχαήλ 14 May 2012 (has links)
Η πληθώρα των εφαρμογών που μπορεί να εξυπηρετήσει η τεχνολογία Υπερευρείας Ζώνης (UWB), από τα ασύρματα προσωπικά δίκτυα υψηλών ταχυτήτων, μέχρι τα ασύρματα δίκτυα αισθητήρων με δυνατότητες ακριβούς εντοπισμού θέσης, και τα ασύρματα δίκτυα ιατρικών αισθητήρων, έχει προκαλέσει έντονο ερευνητικό ενδιαφέρον γύρω από τις υλοποιήσεις UWB συστημάτων. Η ασυνήθιστα μεγάλη περιοχή συχνοτήτων που έχει ανατεθεί στο UWB, από τα 3.1-10.6 GHz, επιτρέπει την επίτευξη υψηλών ταχυτήτων με απλά σχήματα διαμόρφωσης, ωστόσο, λόγω της διαμοίρασης του φάσματος με τις υφιστάμενες τεχνολογίες ασύρματης δικτύωσης, οι UWB εκπομπές πρέπει να περιορίζονται σε ισχύ κάτω από το κατώφλι των -41.3 dBm/MHz, ικανοποιώντας πολύ αυστηρές μάσκες εκπομπής που εισάγουν έντονες προκλήσεις στη σχεδίαση των πομπών. Η υλοποίηση αναδιατάξιμων UWB πομπών σε σύγχρονες CMOS τεχνολογίες, με υψηλή φασματική ευελιξία, ταχύτητα και ποιότητα διαμόρφωσης, καθώς και με χαμηλή κατανάλωση, αποτέλεσε το αντικείμενο της συγκεκριμένης διατριβής. Υιοθετώντας την αρχιτεκτονική Multi-Band Impulse-Radio (MB-IR) σε συνδυασμό με την τεχνική Direct Sequence BPSK, η έρευνα προσανατολίστηκε προς την ανάπτυξη καινοτόμων μονάδων βασικής ζώνης, με στόχο την ενεργειακά αποδοτική αντιστροφή Γκαουσιανών μορφοποιημένων παλμών υψηλής ποιότητας φάσματος και διάρκειας μικρότερης ακόμα και από 1 nsec. Προς αυτή την κατεύθυνση, αναπτύχθηκε μια καινοτόμα γεννήτρια Γκαουσιανών παλμών με πολύ χαμηλούς πλευρικούς λοβούς στο φάσμα, τυπικά κάτω από -40 dB, ώστε να υποστηρίζονται οι αυστηρότερες μάσκες εκπομπής ή και μελλοντικές. Η σχεδίασης της προτεινόμενης γεννήτριας είχε ως κριτήριο την ευέλικτη ρύθμιση της διάρκειας των παραγόμενων παλμών, και αξιοποίησε τη χαρακτηριστική μεταφοράς τάσης ενός ωμικά φορτωμένου, ασύμμετρου CMOS αντιστροφέα. Η γεννήτρια βασίζεται κυρίως σε ψηφιακά κυκλώματα πολύ χαμηλής τάσης και, σε σύγκριση με τις υφιστάμενες υλοποιήσεις, παρουσιάζει σημαντικό προβάδισμα στον τομέα της ταχύτητας, καθώς και στο πλάτος εξόδου, η μεγάλη τιμή του οποίου χαλαρώνει σημαντικά τη σχεδίαση του RF front end. Η γεννήτρια μελετήθηκε διεξοδικά, διεξήχθη ανάλυση κλιμάκωσης, έγινε εξαγωγή σχεδιαστικών εξισώσεων και αναπτύχθηκαν εργαλεία λογισμικού για την αυτοματοποιημένη σχεδίασή της. Για περαιτέρω αύξηση της ταχύτητας των παλμικών σημάτων εφαρμόσθηκε ειδική σχεδίαση, η οποία αντιπραγματεύεται την ταχύτητα με το επίπεδο των λοβών του φάσματος. Για την αποδοτική BSPK διαμόρφωση των Γκαουσιανών παλμών αναπτύχθηκε ειδική τοπολογία “Μεταγωγής Σήματος Πυροδότησης Πλήρους Ισορροπίας με Up-Conversion”. Η τοπολογία αυτή, σε αντίθεση με τις ανταγωνιστικές τοπολογίες, αποφεύγει την αντιστροφή του παλμού με αναλογικά κυκλώματα υψηλής κατανάλωσης, αλλά και την αναλογική μεταγωγή, καθώς η διαμόρφωση λαμβάνει χώρα πριν από την παραγωγή των παλμών. Παράλληλα, επιτυγχάνονται υψηλοί ρυθμοί, καθώς και υψηλή ποιότητα διαμόρφωσης λόγω των ισορροπημένων μονοπατιών της τοπολογίας. Η γεννήτρια μαζί με το διαμορφωτή αποτελούν τις καινοτόμες παρεμβάσεις στη μονάδα Βασικής Ζώνης του προτεινόμενου πομπού. Για την ολοκλήρωση της λειτουργικότητας του πομπού, αναπτύχθηκε ένα RF front end, το οποίο αποτελείται από έναν διπλά ισορροπημένο μίκτη, έναν LO buffer, ένα μετατροπέα διαφορικού σήματος σε απλό, και έναν ενισχυτή ισχύος, ο οποίος είναι προσαρμοσμένος στα 50 Ohms, χωρίς να απαιτεί κανένα εξωτερικό στοιχείο. Το RF front end ολοκληρώθηκε μαζί με τη μονάδα βασικής ζώνης, και ο ολοκληρωμένος πομπός κατασκευάστηκε σε τεχνολογία CMOS 130 nm. Το ολοκληρωμένο προσαρτήθηκε στην RF πλακέτα συστήματος με την τεχνική Chip on Board. Για την επιτυχία του συστήματος με την πρώτη προσπάθεια έγινε συσχεδίαση σε επίπεδο IC-Package-PCB, δίνοντας ιδιαίτερη έμφαση στα ζητήματα Signal/Power Integrity. Ο πομπός παρουσίασε την υψηλότερη ταχύτητα από τις ανταγωνιστικές MB-IR UWB υλοποιήσεις, ίση με 1.5 Gbps, με αντίστοιχη ενεργειακή αποδοτικότητα 21 pJoule/bit και μέτρο διανυσματικού σφάλματος 5.5%. Ο πομπός βελτίωσε τους πλευρικούς λοβούς στο φάσμα περισσότερο από 10 dB, ενώ η διατριβή, εκμεταλλευόμενη την αναδιαταξιμότητα του πομπού, παρουσιάζει, επιπλέον, τις πρώτες μετρήσεις σε ταχύτητες εκατοντάδων Mbps για ικανοποίηση της χαμηλής ζώνης της πρόσφατα θεσμοθετημένης, και εξαιρετικά αυστηρής, ευρωπαϊκής μάσκας εκπομπής. / The multitude of applications that Ultra-Wideband (UWB) technology can serve, from high-speed Wireless Personal Area Networks, to Wireless Sensor Networks with precision Geolocation abilities, and Wireless Medical Networks, has attracted intense research interest in the implementation of UWB systems. The unusually wide range of frequencies assigned to UWB, from 3.1-10.6 GHz, allows UWB systems employing low order modulation schemes to enjoy high throughput at low power consumption. However, since UWB shares the spectrum with existing wireless networking technologies, UWB emissions must be limited to a power spectral density below the threshold of -41.3 dBm/MHz, satisfying very stringent emission masks and introducing great challenges in the design of UWB transmitters. The subject of this thesis is the design of low power, fully integrated, reconfigurable CMOS UWB transmitters, with high spectral flexibility, high speed and high modulation quality. Adopting the Multi-Band Impulse-Radio architecture, in conjunction with the Direct Sequence BPSK modulation, the research focused on the development of a baseband unit, able to precisely invert Gaussian shaped, subnanosecond pulses. The key contributions of this thesis are a CMOS Gaussian Pulse Generator and a BSPK modulation topology, which jointly constitute the proposed baseband unit. The Pulse Generator (PG) is based on non-linear shaping, so as to facilitate the configurability of the output pulse duration, and exploits the voltage transfer characteristic of a Resistive Loaded Asymmetrical CMOS Inverter, which results in spectral sidelobes typically better than -40 dB. The PG incorporates mostly-digital low voltage circuits, while the MOSFET devices that undertake the pulse shaping avoid exclusive operation in weak inversion, in contrast to previous implementations. Consequently, the proposed CMOS PG is able to support higher throughput, as well as higher output amplitude, which relaxes considerably the design of the RF front end. This thesis presents a systematic design procedure and a scaling analysis of the non-linear pulse shaper. Moreover, in order to further increase the speed, a special PRF boost technique is proposed, which trades off speed and spectral efficiency for the spectral sidelobes level. Regarding the BPSK modulator, this work introduces the “Trigger Switching Fully Balanced Up-Conversion” topology, which avoids the use of power-hungry and distortion-prone analog circuits for the accurate inversion of the subnanosecond shaped pulses, as well as avoids the application of analog waveform switching to the baseband pulses, since the baseband modulation takes place before the generation of the pulses. The digital nature of the switching lends itself to high data rates, while the balanced paths of the topology ensure high modulation quality with minimal design effort. Wafer probing measurements confirmed the high performance of the baseband unit. The functionality of the transmitter was completed by the development of an RF front end which consists of a double balanced mixer, an LO buffer, a differential to single-ended (DtoSE) converter, and a power amplifier which is ready to drive a 50 Ohms load without requiring any off-chip components. The integrated transmitter, which incorporates the proposed baseband unit and the RF front end, was fabricated in 130 nm CMOS technology. The transmitter RFIC was directly attached to the system RF PCB using the Chip-on-Board packaging option. The First-Pass success of the system was ensured by paying particular attention to Signal/Power Integrity issues and following an IC-Package-PCB co-design procedure. The transmitter was measured up to 1.5 Gbps, which, to the author’s knowledge, was the highest speed amongst the competitive Multi-Band Impulse-Radio UWB implementations in the literature. The corresponding energy efficiency was 21 pJoule/bit and the Error Vector Magnitude (EVM) 5.5%, while the proposed transmitter improved the spectral sidelobes by over 10 dB. Exploiting the reconfigurability of the transmitter, this thesis presents the first measurements at multi-Mbps speeds that completely meet the final version of the European spectrum emission mask.

Page generated in 0.0759 seconds