65,256 research outputs found
When self-consistency makes a difference
Compound semiconductor power RF and microwave device modeling requires, in many cases, the use of selfconsistent electrothermal equivalent circuits. The slow thermal dynamics and the thermal nonlinearity should be accurately included in the model; otherwise, some response features subtly related to the detailed frequency behavior of the slow thermal dynamics would be inaccurately reproduced or completely distorted. In this contribution we show two examples, concerning current collapse in HBTs and modeling of IMPs in GaN HEMTs. Accurate thermal modeling is proved to be be made compatible with circuit-oriented CAD tools through a proper choice of system-level approximations; in the discussion we exploit a Wiener approach, but of course the strategy should be tailored to the specific problem under consideratio
Metodologia Per la Caratterizzazione di amplificatori a basso rumore per UMTS
In questo lavoro si presenta una metodologia di
progettazione elettronica a livello di sistema,
affrontando il problema della caratterizzazione dello spazio di progetto dell' amplificatore a basso rumore costituente il primo stadio di un front end a conversione diretta per UMTS realizzato in tecnologia CMOS con lunghezza di canale .18u. La metodologia è sviluppata al fine di valutare in modo quantititativo le specifiche ottime di sistema per il front-end stesso e si basa sul concetto di Piattaforma Analogica, che prevede la costruzione di un modello di prestazioni per il blocco analogico basato su
campionamento statistico di indici di prestazioni del blocco stesso, misurati tramite simulazione di dimensionamenti dei componenti attivi e passivi soddisfacenti un set di equazioni specifico della topologia circuitale. Gli indici di prestazioni vengono successivamente ulizzati per parametrizzare modelli comportamentali utilizzati nelle fasi di ottimizzazione a livello di sistema. Modelli comportamentali atti a rappresentare i sistemi RF sono stati pertanto studiati per ottimizzare la scelta delle metriche di prestazioni. L'ottimizzazione dei set di
equazioni atti a selezionare le configurazione di
interesse per il campionamento ha al tempo stesso richiesto l'approfondimento dei modelli di dispositivi attivi validi in tutte le regioni di funzionamento, e lo studio dettagliato della progettazione degli amplificatori a basso rumore basati su degenerazione induttiva. Inoltre,
il problema della modellizzazione a livello di sistema degli effetti della comunicazione tra LNA e Mixer è stato affrontato proponendo e analizzando diverse soluzioni. Il lavoro ha permesso di condurre un'ottimizzazione del front-end UMTS, giungendo a specifiche ottime a livello di sistema per l'amplificatore stesso
Wavelet-Based High-Order Adaptive Modeling of Lossy Interconnects
Abstract—This paper presents a numerical-modeling strategy for simulation of fast transients in lossy electrical interconnects. The proposed algorithm makes use of wavelet representations of voltages and currents along the structure, with the aim of reducing the computational complexity of standard time-domain solvers. A special weak procedure for the implementation of possibly dynamic and nonlinear boundary conditions allows to preserve stability as well as a high approximation order, thus leading to very accurate schemes. On the other hand, the wavelet expansion allows the computation of the solution by using few significant coefficients which are automatically determined at each time step. A dynamically refinable mesh is then used to perform a sparse time-stepping. Several numerical results illustrate the high efficiency of the proposed algorithm, which has been tuned and optimized for best performance in fast digital applications typically found on modern PCB structures. Index Terms—Finite difference methods, time-domain analysis, transmission lines, wavelet transforms. I
Stochastic macromodeling of nonlinear systems via polynomial chaos expansion and transfer function trajectories
A novel approach is presented to perform stochastic variability analysis of nonlinear systems. The versatility of the method makes it suitable for the analysis of complex nonlinear electronic systems. The proposed technique is a variation-aware extension of the Transfer Function Trajectory method by means of the Polynomial Chaos expansion. The accuracy with respect to the classical Monte Carlo analysis is verified by means of a relevant numerical example showing a simulation speedup of 1777 X
Composite load spectra for select space propulsion structural components
The objective of this program is to develop generic load models with multiple levels of progressive sophistication to simulate the composite (combined) load spectra that are induced in space propulsion system components, representative of Space Shuttle Main Engines (SSME), such as transfer ducts, turbine blades, and liquid oxygen posts and system ducting. The first approach will consist of using state of the art probabilistic methods to describe the individual loading conditions and combinations of these loading conditions to synthesize the composite load spectra simulation. The second approach will consist of developing coupled models for composite load spectra simulation which combine the deterministic models for composite load dynamic, acoustic, high pressure, and high rotational speed, etc., load simulation using statistically varying coefficients. These coefficients will then be determined using advanced probabilistic simulation methods with and without strategically selected experimental data
The Coyote Universe III: Simulation Suite and Precision Emulator for the Nonlinear Matter Power Spectrum
Many of the most exciting questions in astrophysics and cosmology, including
the majority of observational probes of dark energy, rely on an understanding
of the nonlinear regime of structure formation. In order to fully exploit the
information available from this regime and to extract cosmological constraints,
accurate theoretical predictions are needed. Currently such predictions can
only be obtained from costly, precision numerical simulations. This paper is
the third in a series aimed at constructing an accurate calibration of the
nonlinear mass power spectrum on Mpc scales for a wide range of currently
viable cosmological models, including dark energy. The first two papers
addressed the numerical challenges, and the scheme by which an interpolator was
built from a carefully chosen set of cosmological models. In this paper we
introduce the "Coyote Univers"' simulation suite which comprises nearly 1,000
N-body simulations at different force and mass resolutions, spanning 38 wCDM
cosmologies. This large simulation suite enables us to construct a prediction
scheme, or emulator, for the nonlinear matter power spectrum accurate at the
percent level out to k~1 h/Mpc. We describe the construction of the emulator,
explain the tests performed to ensure its accuracy, and discuss how the central
ideas may be extended to a wider range of cosmological models and applications.
A power spectrum emulator code is released publicly as part of this paper.Comment: 10 pages, 10 figures, minor changes to address referee report,
version v1.1 of the power spectrum emulator code can be downloaded at
http://www.hep.anl.gov/cosmology/CosmicEmu/emu.html, includes now fortran
wrapper and choice of any redshift between z=0 and z=1 (note: webpage now
maintained at Argonne National Laboratory
Swarm Intelligence Based Multi-phase OPF For Peak Power Loss Reduction In A Smart Grid
Recently there has been increasing interest in improving smart grids
efficiency using computational intelligence. A key challenge in future smart
grid is designing Optimal Power Flow tool to solve important planning problems
including optimal DG capacities. Although, a number of OPF tools exists for
balanced networks there is a lack of research for unbalanced multi-phase
distribution networks. In this paper, a new OPF technique has been proposed for
the DG capacity planning of a smart grid. During the formulation of the
proposed algorithm, multi-phase power distribution system is considered which
has unbalanced loadings, voltage control and reactive power compensation
devices. The proposed algorithm is built upon a co-simulation framework that
optimizes the objective by adapting a constriction factor Particle Swarm
optimization. The proposed multi-phase OPF technique is validated using IEEE
8500-node benchmark distribution system.Comment: IEEE PES GM 2014, Washington DC, US
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