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Este documento visa apoiar o estudo da resposta em frequência de amplificadores com transístores bipolares (BJT). Considera-se um amplificador baseado no BJT NPN BC 108-B polarizado por uma fonte de tensão de 10 V, através de uma malha de polarização estabilizada, com condenadores de acoplamento para estabilização do ponto de funcionamento em repouso (PFR) e para aplicação do sinal à carga. Do ponto de vista de sinal, a montagem é do tipo emissor comum (EC), com degeneração de emissor (o emissor liga a GND através de resistências no emissor). Os exemplos são simulados no software de uso livre TINA-TI ( http://www.ti.com/tool/tina-ti ).
Na avaliação da resposta em frequência consideram-se três casos distintos: o amplificador apenas com condensadores de acoplamento; amplificador com condensador de acoplamento e com condensador de contorno (bypass) numa das resistências de emissor; a influência do valor da resistência de carga no ganho em tensão. Em qualquer dos casos apresentam-se os gráficos dos diagramas de Bode de resposta em frequência.
This paper proposes a video codec based on the discrete wavelet transform (DWT). The video sequences are first splitted in groups of frames(GOF). Each GOF is then decomposed in the time domain, and in the spatial domain (for each frame) by applying the DWT. We use the lifting scheme to compute the DWT coefficients. The coefficients of the 3D structure resulting from both DWT (in time and space domain) are than coded througth the extension of EZW coding to 3D and the bitstream is finnaly passed through a Huffman coder, to achieve better compression ratios. The structure of the video codec and some experimental results are presented. Experimental results evaluate the quality of the codec images and compression ratio achieved with the proposed codec.
Neste artigo apresenta-se um codificador de vídeo baseado na transformada de ôndulas, com interface do tipo
Windows®, desenvolvido em Borland C++ Builder v5.0. O codificador tira partido das características da estrutura
hierárquica 3D de coeficientes da DWT, resultante da sua aplicação no domínio do tempo e do espaço. O utilizador
escolhe a sequência a codificar (armazenada em ficheiro), o número de tramas, o nível de decisão, e a ôndula a
considerar na DWT no espaço, podendo obter resultados do desempenho do codificador, e guardar esses valores em
ficheiros compatíveis com Microsoft® Excel. Pode, também, visualizar alguns resultados intermédios do processo de
codificação, nomeadamente a decomposição por aplicação da DWT no tempo e no espaço, conferindo a este trabalho,
também, um cariz didáctico.
This paper presents some project themes
proposed by the authors and the methodology adopted in its supervision, in a transdisciplinary approach. We describe the projects and discuss the most relevant
aspects of this approach, from the technical and pedagogical points of view. The stronger points of this methodology are some similarities with the
environment that recent graduated students might find
in the employment market. Balancing the pros and
cons we conclude that due to the project
interdependencies, benefits are mainly on technical
skills improvement and in mutual responsibilities to
accomplish tasks on schedule.
This paper addresses the most relevant aspects of lossy image coding techniques, and presents an
evaluation study on this subject, using several transforms and different methods in the transform domain. We
developed different transform based image coders/decoders (codecs) using different transforms, such as the
discrete cosine transform, the discrete wavelet transform and the S transform. Besides JPEG Baseline, we also
use other techniques and methods in the transform domain such as a DWT based JPEG-like (JPEG DWT), a
JPEG DWT with visual threshold (JPEG-VT), a JPEG–like coder based on the ST, and an EZW coder. The
codecs were programmed in MATLAB™, using custom and built-in functions. The structures of the codecs
are presented, also as some experimental results which allow us evaluate them, and support this study.
This paper presents a comparative study on image coders using the discrete cosine transform and the discrete wavelet transform, addressing in particular the JPEG-like and the EZW based image coders. We compare and evaluate the JPEG Baseline Image coder (using the DCT), a JPEG-like image coder based on the DWT, and an EZW coder, which is also based on the DWT. Taking into account the differences on the architecture of the coders, we compare them by using the same test images, for approximately the same conditions and characteristics, namely the approximately equal compression ratio.
In this paper decomposition techniques are applied to derivative operators, used for image edge detection. It is shown that the application of decomposition techniques to common edge detectors can result in substantial savings in computing time. For a 25x25 Laplacian of Gaussian, mask, an improvement of six times less arithmetic operations is achieved when decomposition techniques are applied.We also show that these techniques are advantageous for hardware realization of the filters. The memory required to a 2-D (nxn)-th order FIR filter direct realization with distributed arithmetic is O(2(n+1) ) while the worst case for the decomposed filter is O(n x 2n).
Tese de mestrado em Engenharia Electrotécnica e de Computadores, IST, 2002
Neste trabalho foi desenvolvido um codificador/descodificador (CoDec) de vídeo de ritmo
binário variável, baseado na decomposição 3D por transformada de ôndulas, sendo o cálculo
das transformadas de ôndulas, e das transformadas inversas, realizado através do esquema
progressivo (lifting scheme).
Analisa-se a aplicação à codificação de vídeo da decomposição de sinais 1D e 2D por bancos
de filtros de ôndulas, a sua relação com a análise multiresolução, e as relações de dependência
hierárquica dos coeficientes da estrutura resultante da decomposição. Apresenta-se, também, a
associação do esquema progressivo aos bancos de filtros e a obtenção dos algoritmos das
transformadas pela factorização segundo o esquema progressivo.
Implementaram-se as transformadas (pelo esquema progressivo), para a ôndula Daubechies 2 e
para as ôndulas biortogonais (4,4), para explorar a redundância espacial e temporal, aplicando-
as à codificação de vídeo.
Apresentam-se resultados experimentais obtidos com o codificador desenvolvido, com base
em sequências de vídeo de teste, nomeadamente o factor de compressção, a relação sinal/ruído
entre as imagens recuperadas e as imagens originais e a qualidade subjectiva das imagens
recuperadas. Discutem-se os resultados obtidos e o tempo necessário para processar as
sequências. Propõem-se soluções para melhorar a eficiência do codificador, no que diz respeito
ao tempo de processamento e ao factor de compressão. Implementaram-se, também, as
transformadas de ôndula num processador digital de sinal com arquitectura VLIW, analisando-
se a aceleração de processamento obtida, tendo em vista a codificação de vídeo em tempo real.
This chapter focuses on the analysis and characterization of the vibrations produced by switched reluctance actuators. The emphasis stands on the linear configuration of this type of machine. The complexity of the mechanical system and the
materials is used to define the modal frequencies. Moreover, the power controller
topology, the excitation regimes, and the switching frequency used for the actuator
operation can excite the natural modes and put restrictions on its usage. The analysis
considers both numerical and experimental methodologies. The numerical technique
relies on the finite element method (FEM) using the 3D model of the actuator to find
its natural frequencies up to 1.3 kHz. The experimental characterization counts on
the operational modal responses and the acoustic noise emitted. We identify the
regions of interest to measure the local accelerations and collect data for postprocessing and record the audible noise emitted for signal analysis. The popular
discrete Fourier transform and the joint wavelet-Fourier analysis are used for signal
analysis. The reliability and the suitability of this approach are verified comparing
both the numerical and the experimental outcomes and support the identification of
the switching frequencies with high potential to excite the natural modes under the
regular operation of the machine and to choose the proper control strategy.
Contém referências bibliográficas
This paper proposes a simple scheme for audio
coding that does not use perceptual models. The audio coder
is based on the discrete wavelet transform to decorrelate
signals, computed through the lifting scheme, and followed by
Huffman coding. The evaluation of the coding scheme is
presented by using some .wav audio test files, coded for
different conditions, and also includes subjective evaluation.
Experimental results show the compression ratios achieved,
the degradation of the signals expressed as values of signal to
noise ratio and the changes in spectrum information.
Neste artigo apresenta-se uma ferramenta computacional para síntese automática de filtros digitais, com
interface do tipo Windows®, desenvolvida em MATLAB™. Os filtros sintetizados podem ser posteriormente
implementados em DSPs da família TMS320 da Texas Instruments, nomeadamente, nos DSPs TMS320C50 e
TMS320C6201. Os filtros foram testados num sistema baseado no DSP C6201, recorrendo a sinais áudio
digitais armazenados em ficheiro (*.wav) enquanto no sistema com o DSP C50 se efectua a filtragem de sinais
analógicos. Através da interface gráfica, o utilizador define o tipo de filtro (FIR ou IIR) e as suas especificações
(com base na resposta em frequência), sendo a geração do código e a implementação realizadas de forma
totalmente automática.
This paper addresses the problem of vibrations produced by switched reluctance actuators, focusing on the linear configuration of this type of machines, aiming at its characterization regarding the structural vibrations. The complexity of the mechanical system and the number of parts used put serious restrictions on the effectiveness of analytical approaches. We build the 3D model of the actuator and use finite element method (FEM) to find its natural frequencies. The focus is on frequencies within the range up to
nearly 1.2 kHz which is considered relevant, based on preliminary simulations and experiments. Spectral analysis results of audio
signals from experimental modal excitation are also shown and discussed. The obtained data support the characterization of the
linear actuator regarding the excited modes, its vibration frequencies, and mode shapes, with high potential of excitation due to the regular operation regimes of the machine. The results reveal abundant modes and harmonics and the symmetry characteristics of the actuator, showing that the vibration modes can be excited for different configurations of the actuator. The identification of the most critical modes is of great significance for the actuator’s control strategies. This analysis also provides significant information to adopt solutions to reduce the vibrations at the design.
