Direct Digital Frequency Synthesis (DDFS) is a method of producing an analog waveform by generating a time-varying signal in digital form, succeeded by digital-to-analog reconstruction. At behavioral level the bit products with specified weights are used to generate the sine wave. In representation of a sine wave both positive and negative weights are generated. Since negative weights are not desired in design, the negative weights are transformed to positive weights. To reduce the number of current sources and control signals, bit product signals of those current sources which cannot be switched on simultaneously and have equal weights are shared. After sharing weights, the control signals are reduced to from 59 to 43 and current sources from 207 to 145. Different control words are used by the DDFS system in order to generate different frequencies. The control word is successively added to the previous value in a 20-bit accumulator. Nine most significant bits out of these twenty bits are used for the DAC. Since the Current Steering DAC architecture is suitable for high speed and high resolution purposes, so a 9-bit nonlinear current steering DAC is used to convert the output of bit products to the analog sine wave. Seven bits are used to generate one quarter of the sine wave. Eighth and ninth bits are used to generate the full sine wave. HCMOS 9 (130 nm) ST Microelectronics process is used by employing high speed NMOS and PMOS transistors. The bit products (control signals) are computed by using complementary static CMOS logic which then act as control signals for the current sources after passing through D-flip flops. Practical design issues of current sources and parts of digital logic were studied and implemented using the Cadence full-custom design environment.

The resistor ladder (R/2R) digital-to-analogue converter (DAC) architecture is often used in high performance audio solutions due to its low-noise performance. Even high-end R/2R DACs suffer from static nonlinearity distortions. It was suspected that compensating for these nonlinearities would be possible. It was also suspected that this could improve audio quality in audio systems using R/2R DACs for digital-to-analogue (A/D) conversion. Through the use of models of the resistor ladder architecture a way of characterizing and measuring the faults in the R/2R DAC was created. A compensation algorithm was developed in order to compensate for the nonlinearities. The performance of the algorithm was simulated and an implementation of it was evaluated using an audio evaluation instrument. The results presented show that it is possible to increase linearity in R/2R DACs by compensating for static nonlinearity distortions. The increase in linearity can be quite significant and audible for the trained ear.

This thesis is one part of a overall task of designing a module for frequency shift keying (FSK) to be used in an Ultra Wide Band (UWB) system. The FSK system has a Direct Digital Synthesizer (DDS) and Digital-to-Analog (DAC). The DACs differential current signals are directly fed to a RF (Radio Frequency) unit that generates the UWB RF signal. The focus of this thesis is on DAC while the DDS is developed in VHDL as another thesis work. This thesis demonstrates a low-power, ultra wide band 10 bit DAC with an update frequency of 24 MSPS(Mega Samples Per Second). The DAC uses a L-fold linear interpolation architecture. It includes a 16-tap voltage controlled delay line and a 10 bit binary-weighted DAC with a time interleaved structure. The linear interpolation technique improves the attenuation of mirror components and also reduces the glitch. This helps to relax the analog filter requirements and sometimes an off chip capacitor is enough as low pass filter. The attenuation of image components is doubled in decibels(dB) compared with that of conventional DAC. In this work various DAC architectures are studied. The current-steering DAC is chosen due to its high speed and high resolution. A binary weighted architecture is chosen to reduce the digital circuits. This helped in reducing the power consumption. The design and simulation is done with help of Cadence. The layout is done in Cadence Virtuoso and the DDS is integrated with the DAC. The chip is to be manufactured in 130 nm CMOS process.

Den här högskoleavhandlingen beskriver framtagningen av en modell för en kombinerad styr- och mätutrustning. Syftet med utrustningen är att använda denna för att underlätta vidare utveckling av organisk elektronik vilket är ett av Acreo AB:s forskningsområden. Istället för att till varje ny komponent eller system utveckla ett nytt testsystem kan denna modell användas på ett generellt sätt, vilket sparar värdefull utvecklingstid. I avhandlingen presenteras först de krav som utrustningen ska uppfylla följt av några förslag på lösningar. Därefter väljs ett av förslagen och en grundläggande implementering genomförs med hänsyn mot kraven. Slutligen innehåller rapporten förslag på hur vidare arbete med modellen kan ske. / This bachelor thesis describes the developing of a model for combined steering and measuring equipment. The purpose is to ease further developing of organic electronics, which is one of Acreo AB’s research areas. A test system is needed for every new component or system developed. Instead of constructing a new test environment for every case this equipment will be a general solution that will save valuable developing time. This thesis will first present the requirements followed by some proposal solutions. Thereafter one proposal will be chosen and an essential implementation will be done with consideration of the requirements. Finally the thesis contains suggestions on how to further develop the model.

Στην παρούσα Διπλωματική Εργασία μελετάται η δομή και τα χαρακτηριστικά, ενός καινοτόμου Μετατροπέα Ψηφιακού Σήματος σε Αναλογικό (Digital to Analog Converter - DAC) που αναπτύχθηκε στο Εργαστήριο Ηλεκτρονικών Εφαρμογών του Πανεπιστημίου Πατρών. Η δομή του συγκεκριμένου DAC βασίζεται στην τοπολογία του γνωστού R-2R Ladder και παρ’ όλο που υλοποιείται με αντιστάσεις μικρής σχετικά ακρίβειας, επιτυγχάνει τελικά πολύ υψηλές επιδόσεις σε γραμμικότητα, κατανάλωση αλλά και επιφάνεια υλοποίησης. Στα πλαίσια της παρούσας Διπλωματικής Εργασίας χρησιμοποιήθηκε το ‘κατά κοινή ομολογία’ καλύτερο λογισμικό σχεδίασης και εξομοίωσης ολοκληρωμένων ηλεκτρονικών κυκλωμάτων, το Cadence. Με τη βοήθεια αυτού του Cadence εξομοιώσαμε την νέα τοπολογία DAC και ελέγξαμε την δυνατότητα προσέγγισης της υψηλής γραμμικότητας που παρουσιάζεται στις ερευνητικές εργασίες που βασιστήκαμε. Επιπλέον, έγινε και μία υλοποίηση σε φυσικό επίπεδο με τη χρήση του λογισμικού Cadence, δηλαδή σχεδιάστηκε η τοπολογία του κυκλώματος στο πυρίτιο για τη δημιουργία ολοκληρωμένου συστήματος (system on chip). / This Diploma Thesis studies on an innovative Digital to Analog Converter (DAC) structure developed in the Applied Electronics Laboratory of the Electrical and Computer Engineering Department, University of Patras. This new DAC structure is based on the well-known R-2R Ladder, and is capable to achieve very high linearity on high resolution DAC without requiring resistances of high accuracy, while preserving at the same time the good characteristics of the conventional R-2R ladder in terms of speed, power consumption and implementation area. The state of the art EDA tool, Cadence was employed in the framework of this Diploma Thesis in order to simulate the behavior of the DAC and to certify its enhanced characteristics regarding the linearity. Additionally, the same EDA tool was employed for designing the DAC topology on a silicon chip.

p. 1-79 / Submitted by Antonio Geraldo Couto Barreto (ppgms@ufba.br) on 2013-10-02T17:02:51Z No. of bitstreams: 1 TESE_Consuêlo Padilha-1.pdf: 9442449 bytes, checksum: 72ab1d2cb912c235e58236ec944e7b16 (MD5) / Approved for entry into archive by Patricia Barroso (pbarroso@ufba.br) on 2013-10-30T19:36:47Z (GMT) No. of bitstreams: 1 TESE_Consuêlo Padilha-1.pdf: 9442449 bytes, checksum: 72ab1d2cb912c235e58236ec944e7b16 (MD5) / Made available in DSpace on 2013-10-30T19:36:47Z (GMT). No. of bitstreams: 1 TESE_Consuêlo Padilha-1.pdf: 9442449 bytes, checksum: 72ab1d2cb912c235e58236ec944e7b16 (MD5) Previous issue date: 2013 / A Doença Hepática Gordurosa Não Alcoólica (DHGNA) representa a causa mais comum de doença do fígado na atualidade. Está associada com síndrome metabólica e, mais recentemente, às doenças cardiovasculares. Objetivo: avaliar a associação entre DHGNA e doença arterial coronariana (DAC) e os fatores preditivos desta associação em indivíduos submetidos à cineangiocoronariografia (CAG). Metodologia: Foi realizado estudo transversal, que avaliou indivíduos submetidos à CAG com suspeita de DAC. Os pacientes realizaram avaliação clínico–laboratorial e ultrassonografia abdominal (USAB). Critérios para DAC: presença de lesão obstrutiva em artérias coronárias epicárdicas ou seus principais ramos. Critérios para DHGNA: presença de esteatose na USAB; ingestão alcoólica ≤20 g/dia; ausência de outras doenças hepáticas. As variáveis contínuas foram avaliadas pelos testes t de Student ou teste de Mann-Whitney e as categóricas pelo teste do qui-quadrado com nível de significância (p) < 0,05. Análise de regressão mediu a força da relação entre os fatores de risco e a presença concomitante de DAC e DHGNA. Resultados: Foram estudados 244 pacientes com média de idade de 61,5±9,3 anos. A DAC foi observada em 63,5%, e a DHGNA, em 42,2% dos pacientes. Aqueles com DAC eram, predominantemente, do gênero masculino (p<0,01); diabéticos (p<0,05) e tabagistas (p=0,045), e 43,9% deles tinham DHGNA. A DHGNA esteve associada à DM2, resistência insulínica, síndrome metabólica, obesidade central, índice de massa corpórea, triglicérides e alanina aminotransferase (p<0,05). A ocorrência concomitante de DAC e DHGNA foi positivamente correlacionada a sobrepeso/obesidade e HOMA-IR ≥3,0. Conclusões: A amostra teve elevada frequência de ambas, DAC e DHGNA; DHGNA foi mais elevada em pacientes com DAC, porém não houve associação estatisticamente significante entre as duas doenças; pacientes com associação DAC e DHGNA apresentavam sobrepeso/obesidade, e resistência insulínica. Os resultados sugerem a relevância clínica de investigar a DHGNA em pacientes com DAC, no sentido de diminuir a morbimortalidade desses pacientes. / Salvador

abstract: High speed current-steering DACs with high linearity are needed in today's applications such as wired and wireless communications, instrumentation, radar, and other direct digital synthesis (DDS) applications. However, a trade-off exists between the speed and resolution of Nyquist rate current-steering DACs. As the resolution increases, more transistor area is required to meet matching requirements for optimal linearity and thus, the overall speed of the DAC is limited. In this thesis work, a 12-bit current-steering DAC was designed with current sources scaled below the required matching size to decrease the area and increase the overall speed of the DAC. By scaling the current sources, however, errors due to random mismatch between current sources will arise and additional calibration hardware is necessary to ensure 12-bit linearity. This work presents how to implement a self-calibration DAC that works to fix amplitude errors while maintaining a lower overall area. Additionally, the DAC designed in this thesis investigates the implementation feasibility of a data-interleaved architecture. Data interleaving can increase the total bandwidth of the DACs by 2 with an increase in SQNR by an additional 3 dB. The final results show that the calibration method can effectively improve the linearity of the DAC. The DAC is able to run up to 400 MSPS frequencies with a 75 dB SFDR performance and above 87 dB SFDR performance at update rates of 200 MSPS. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014

Hydrogen can be an unlimited source of clean energy for future because of its very high energy density compared to the conventional fuels like gasoline. An efficient and safer way of storing hydrogen is in metals and alloys as hydrides. Light metal hydrides, alanates and borohydrides have very good hydrogen storage capacity, but high operation temperatures hinder their application. Improvement of thermodynamic properties of these hydrides is important for their commercial use as a source of energy. Application of pressure on materials can have influence on their properties favoring hydrogen storage. Hydrogen desorption in many complex hydrides occurs above the transition temperature. Therefore, it is important to study the physical properties of the hydride compounds at ambient and high pressure and/or high temperature conditions, which can assist in the design of suitable storage materials with desired thermodynamic properties. The high pressure-temperature phase diagram, thermal expansion and compressibility have only been evaluated for a limited number of hydrides so far. This situation serves as a main motivation for studying such properties of a number of technologically important hydrides. Focus of this dissertation was on X-ray diffraction and Raman spectroscopy studies of Mg2FeH6, Ca(BH4)2, Mg(BH4)2, NaBH4, NaAlH4, LiAlH4, LiNH2BH3 and mixture of MgH2 with AlH3 or Si, at different conditions of pressure and temperature, to obtain their bulk modulus and thermal expansion coefficient. These data are potential source of information regarding inter-atomic forces and also serve as a basis for developing theoretical models. Some high pressure phases were identified for the complex hydrides in this study which may have better hydrogen storage properties than the ambient phase. The results showed that the highly compressible B-H or Al-H bonds and the associated bond disordering under pressure is responsible for phase transitions observed in brorohydrides or alanates. Complex hydrides exhibited very high compressibility suggesting possibility to destabilize them with pressure. With high capacity and favorable thermodynamics, complex hydrides are suitable for reversible storage. Further studies are required to overcome the kinetic barriers in complex hydrides by catalytic addition. A comparative study of the hydride properties with that of the constituting metal, and their inter relationships were carried out with many interesting features.

La vaporisation rapide du sodium liquide surchauffé est supposée être à l’origine des arrêts automatiques pour réactivité négative du réacteur Phénix.Un dispositif expérimental a été mis en œuvre pour reproduire la détente d'un gaz pressurisé, repoussant un liquide dans un canal de section rectangulaire très allongée.L’interface qui sépare les deux fluides, initialement plate, ondule du fait d'instabilités de Rayleigh-Taylor dont le caractère 2D est garanti par le rapport d'aspect de la section du canal. L’aire interfaciale augmente d'un facteur 50.L’expansion du gaz peut être divisée en deux phases principales : une phase dite « de Rayleigh-Taylor » (linéaire et non-linéaire) et une phase dite « à multi-structures » (transitionnelle et chaotique). La première est caractérisée par la dynamique de l'interface et l’aire interfaciale qui en résulte est proportionnelle à l’amplitude des ondulations. La deuxième est influencée par le comportement des structures liquides, dispersées dans la matrice gazeuse et l’aire interfaciale est alors proportionnelle au nombre de structures.La distribution de fraction volumique suggère un modèle d’écoulement composé de trois régions : une région où la frontière des bulles est clairement définie et régulière, une région compartimentée par des membranes liquides issues des frontières des bulles, une région diphasique formée de la queue de ces structures. L’analyse de sensibilité à la tension superficielle confirme que plus la tension est faible, plus les interfaces sont instables. Les ondes sont plus prononcées et plus de structures sont produites, ce qui conduit à une majoration du taux de production de l’aire interfaciale. / The sharp vaporization of superheated liquid sodium is investigated. It is suspected to be at the origin of the automatic shutdown for negative reactivity, occurred in the Phénix reactor at the end of the eighties.An experimental apparatus has been designed and operated to reproduce the expansion of overpressurized air, superposed to water in a narrow vertical rectangular section channel.When expansion begins, the initial flat interface separating the two fluids becomes corrugated under the development of two-dimensional Rayleigh-Taylor instabilities. The interface area increases significantly and becomes even 50 times larger than the initial value. Since the channel is very narrow, instabilities along the channel depth do not develop.The gas expansion in a narrow channel can be divided into two main phases: Rayleigh-Taylor (linear and non-linear) and multi-structures (transition and chaotic) phases. The former is characterized by the dynamic of corrugated profile and the interface area results proportional to the amplitude of corrugation The latter is influenced by the behavior of the liquid structures dispersed in gas matrix and the interface area is mainly proportional to the number of liquid structures.The distribution of volume fraction suggests a model of channel flow consisting of three regions: the regular profile of peaks, the spike region and the structures tails. The analysis of sensibility to surface tension confirms that, with a lower surface tension, the fluids configuration is more unstable. The interface corrugations are more pronounced and more structures are produced, leading to a higher increment of the interface area.

The growing digitalization of the world’s economy and the further integration of the EU:s internal market, combined with aggressive tax schemes becoming more and more sophisticated, has caused a growing need for unionwide effort to prevent aggressive tax-panning practises. The Council Directive (EU) 208/822 often referred to as DAC-6 is but the latest step in the European Union’s ongoing work to fulfil that need. The directive which to a large degree is built on the OECD:s BEPS project action 12, aims to provide early information to tax agencies within the union about potentially harmful tax-arrangements, at an early stage. The hope is that armed with that information can member states intervene in an early stage and protect the tax base. The directive is not uncontroversial and has faced criticism and ongoing legal action[1] for being vague, infringing on the rights guaranteed in the EU charter of fundamental rights and potentially the four freedoms. Whenever the union choses to use its competence to enact legislation, it must abide by the principles of proportionality and subsidiarity, and questions have been made if the directive has gone unproportionally far to combat tax evasion. The vague implementation and use of the main benefit test have also been criticised for possibly being contra productive in combating aggressive tax practises and causing European enterprises to become less competitive due to mounting administrative costs.  [1] Se C-694/20.