ENIDH – EEM - Comunicações, Congressos, Seminários, Encontros, etc.
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- A 1.1 µA voltage reference circuit with high PSRR and temperature compensationPublication . Pereira, M. Silva; Costa, João E. N.; Santos, M.; Vaz, J. CaldinhasThis paper presents a low-power and a low output voltage CMOS Bandgap Reference Generator topology with high PSRR and a novel temperature curvature compensation method. The proposed design was implemented in a standard 0.13 μm CMOS process. The main circuit is based in an opamp based β-multiplier bandgap circuit with resistive division. The compensation method cancels out up to 2nd order non-linear terms of the BJT voltage by using the MOSFET leakage current effect. The performance of the circuit was verified by post-layout simulations. Simulated results have shown temperature coefficients as low as -4.4 ppm/°C over a temperature range of 140°C (-40°C to 100°C). In addition the circuit demonstrated a PSSR of -100 dB at low frequencies and -73 dB at 1 MHz. The current consumption is 1.1 μA at 27°C.
- Computing Repairs from Active Integrity ConstraintsPublication . Cruz-Filipe, L.; Engrácia, P.; Nunes, I.; Gaspar, G.Repairing an inconsistent knowledge base is a well known problem for which several solutions have been proposed and implemented in the past. In this paper, we start by looking at databases with active integrity constraints - consistency requirements that also indicate how the database should be updated when they are not met - as introduced by Caroprese et al.We show that the different kinds of repairs considered by those authors can be effectively computed by searching for leaves of specific kinds of trees. Although these computations are in general not very efficient (deciding the existence of a repair for a given database with active integrity constraints is NP-complete), on average the algorithms we present make significant reductions on the number of nodes in the search tree. Finally, these algorithms also give an operational characterization of different kinds of repairs that can be used when we extend the concept of active integrity constraints to the more general setting of knowledge bases.
- Description logics, rules and multi‐context systemsPublication . L. Cruz‐Filipe, l.; Henriques, R.; Nunes, I.The combination of rules and ontologies has been a fertile topic of research in the last years, with the proposal of several different systems that achieve this goal. In this paper, we look at two of these formalisms, Mdl-programs and multi-context systems, which address different aspects of this combination, and include different, incomparable programming constructs. Despite this, we show that every Mdl-program can be transformed in a multi-context system, and this transformation relates the different semantics for each paradigm in a natural way. As an application, we show how a set of design patterns for multi-context systems can be obtained from previous work on Mdl-programs.
- Dynamic Voltage-Combiners Biased OTA for Low-Power High-Speed SC CircuitsPublication . Póvoa, R.; Canelas, A.; Martins, R.; Lourenço, N.; Horta, N.; Goes, J.his paper presents the design of a fully-dynamic voltage-combiners biased CMOS operational transconductance amplifier, for low-power high-speed analog-to-digital converters and high-performance switched-capacitor filters, using the UMC 130nm node. The biasing is controlled by switched-capacitors and simulation results of an optimized solution using AIDA-C, a state-of-the-art multi-objective multi-constraint IC optimization tool, present a DC gain of 60.9dB, a gain-bandwidth product of 155.1MHz for a 6pF load and a current consumption of 0.69mArms for a sampling clock frequency of 100MHz.
- Effect of Fused Filament Fabrication Processing Parameters on The Mechanical Properties of PLA ComponentsPublication . Marat-Mendes, R.; Guedes, M.; Leite, M.; Baptista, R.This paper studies the influence of Fused Filament Fabrication processing parameters upon mechanical properties and microstructural features of processed PLA parts. The effect of extrusion temperature and raster angle were tested upon two PLA filaments of different trademarks, DoWire and BQ, using a commercial fused deposition extruder. The filling density, layer thickness and velocity were kept constant at 60 %, 0.2 mm and 40 mm/s, respectively. Results allowed to determine fused filament fabrication parameters resulting in increased mechanical performance of manufactured parts. Mechanical performance is higher when material is stored under controlled atmosphere before use, and when material deposition direction is aligned with applied load. Increasing the extrusion temperature also increases performance, by increasing deformation ability of PLA molecules. Obtained results contribute to accumulation of a property database and provide design guidance to the procurement of additive manufacturing products with enhanced mechanical strength.
- Efficient Yield Optimization Method using a Variable K-Means Algorithm for Analog IC SizingPublication . Canelas, A.; Martins, R.; Póvoa, R.; Lourenço, N.; Horta, N.This paper presents the study and implementation of a new efficient yield optimization technique for multi-objective optimization-based automatic analog integrated circuit sizing. The approach uses a commercial electrical simulator and standard process design kit (PDK) models to perform, during the optimization process, the same Monte Carlo (MC) simulations that designers use. The proposed yield estimation technique reduces the number of required MC simulations by using the k-means algorithm, with a variable number of clusters, to select only a handful potential solutions where the MC simulations are performed. Due to the use of a commercial simulator tool and foundry supplied PDK models the developed methodology provides the most accurate and reliable results, and also, the variable k-means algorithm is able to achieve 91% reduction in the total number of the MC simulations required for an optimization, when considering MC simulations for all solutions. Moreover, this new approach presents a 50% increase in speed performance when comparing to a previous yield optimization technique also using k-means and MC simulations.
- Experimental and Numerical Characterization of Stress-Strain Fields on Sandwich Beams, Subjected to 3PB and 4PBPublication . Marat-Mendes, R.; Martins, R.; Reis, L.
- Features of the European Maritime ClustersPublication . Simões, Abel; Salvador, Regina; Soares, Carlos GuedesThe paper analyses the national and regional European maritime clusters according to the sea basin division proposed by the European Union Integrated Maritime Policy: Atlantic and Arctic oceans; Baltic, Black, Mediterranean and North seas. In line with Wijnolst, Jensen & Sødal (2003) that propose a maritime sector benchmarking - the “Global Maritime Benchmarking” – which should allow evaluating the maritime clusters evolution and strength - the paper start to estimate nine indicators: 1. structural indicators (no. of clusters, no. of companies, no. of employees, no. of sectors, technological level, location); 2. economic indicators (Gross Added Value, production, productivity, profit and rentability rates); 3. internationalisation (exports and imports, major clients and suppliers, international average prices, EU and third countries markets shares); 4. critical mass (agglomerations and scale economies by maritime sector) and leader firms; 5. level playing-field (free-competition, monopolistic, oligopolistic markets); 6. innovation (major universities and R&D centres, no. patents, regional innovation systems); 7. institutional framework (governance, connection with regional and national governments)and business networks; 8. labour market (unemployment rate, average wages) and education (major schools and courses by different grades, training centres); and 9. Image and communication. The comparison between sea basins will allow characterizing “Maritime Europe’, identifying the location of the main excellence centres and the major beneficiaries of the Integrated Maritime Policy decisions. The paper also suggest public strategies that would support clusters development – or “cluster enablers” – that include, among others, the definition of an industrial policy, strengthening of demand pull sectors or the promotion of innovation, R&D and leader firms. The needed conditions in order that Europe could organise itself has a “vast continental maritime cluster” are also under scrutiny
- Indoor Position Method Using Wi-FiPublication . Fernandes, Luís; Barata, Fábio; Chaves, PauloThe main objective of this paper is to present an indoor position method, developed for museums and hospitals, in order to known the position of persons and equipments. The method is composed by a particle filter algorithm to be embedded in smartphones or tags. The main goal is to develop a light method to run by not very powerful microprocessors, energized by batteries. The position method presented is based on a Wi-Fi structure, to lighten the use of the communication network, the position is generated by each device from raw data received locally.
- Layout-Aware Challenges and a Solution for the Automatic Synthesis of RadioFrequency IC BlocksPublication . Martins, R.; Lourenço, N.; Póvoa, R.; Canelas, A.; Horta, N.; Passos, F.; Castro López, R.; Roca, E.; Fernández, F.In this paper, the major methodologies proposed in the last years to speed-up the synthesis of radio-frequency integrated circuits blocks are overviewed. The challenges to automate this task are discussed, and, to avoid non-systematic iterations between circuit and layout design steps, the architecture of an innovative solution is proposed. The proposed tool exploits the full capabilities of most established computer-aided design tools available nowadays, i.e., off-the-shelf circuit simulator, electromagnetic simulator and layout extractor. The approach intends to bypass the two major bottlenecks of RF-design: the design of reliable integrated inductors and accurate layout parasitic estimates since the early stages of design process.
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