Operational transconductance amplifier-based nonlinear function syntheses

It is shown that the operational transconductance amplifier, as the active element in basic building blocks, can be efficiently used for programmable nonlinear continuous-time function synthesis. Two efficient nonlinear function synthesis approaches are presented. The first approach is a rational approximation, and the second is a piecewise-linear approach. Test circuits have been fabricated using a 3- mu m p-well CMOS process. The flexibility of the designed and tested circuits was confirme

Generalised sensor linearisation and calibration

The aim of this work was to conduct a survey of current sensor measurement technologies and investigate sensor linearisation, cahbration and compensation methods m order to determine the methods most suitable for generic embedded sensor implementation. The thesis contains a comprehensive survey of sensor technologies and their interfacing requirements as a prerequisite for determining modules required by the generic embedded sensor interface. Different linearisation and calibration techmques are investigated and the most promising techniques, curve fitting and progressive polynomial calibration method, are then examined in greater detail and simulations performed to compare their performance. The fundamental limitations and trade offs in design and implementation on the microprocessor of these methods are studied. The design of the compensation module is also presented and its implementation on the microprocessor m the form of the C code is described. All methods are tested and implemented on a PIC microcontroller as a part of linearisation, cahbration and compensation module of the generic embedded sensor interface

Impacto e compensação da largura de banda vídeo em amplificadores de potência de elevado rendimento

The aim of this work is to determine, quantify and model the performance degradation of wideband power amplifiers when subject to concurrent multiband excitation, with a particular focus on the average efficiency variation. The origins of this degradation are traced to two main transistor properties: the output baseband current generation by the nonlinear transconductance, and the input baseband current generation by the nonlinear gate-source capacitance variation. Each mechanism is analised separately, first by providing a qualitative and intuitive explanation of the processes that lead to the observed efficiency degradation, and then by deriving models that allow the prediction of the average efficiency dependence with the input signal bandwidth. The resulting knowledge was used to improve matching network design, in order to optimize baseband impedance terminations and prevent the efficiency degradation. The derived models were experimentally validated with several PA prototypes implemented with Gallium Nitride HEMT devices, using both conventional and optimized baseband impedance matching networks, achieving over 400MHz instantaneous bandwidth with uncompromised efficiency. The consolidation of the wideband degradation mechanisms described in this work are an important step for modelling and design of wideband, high-efficiency power amplifiers in current and future concurrent multi-band communication systems.O objetivo deste trabalho é determinar, quantificar e modelar a degradação do desempenho de amplificadores de banda-larga quando submetidos a excitação multi-banda concorrente, com particular ênfase na variação do rendimento energético. As origens desta degradação são devidas a duas das principais propriedades do transístor: a geração de corrente em banda-base na saída pela variação não-linear da transcondutância, e a geração de corrente de banda-base na entrada pela variação não-linear da capacidade interna porta-fonte. Cada um destes mecanismos é analisado isoladamente, primeiro por uma explicação qualitativa e intuitiva dos processos que levam à degradação de eficiência observada e, em seguida, através da derivação de modelos que permitem a previsão da degradação do rendimento médio em função da largura de banda do sinal de entrada. O conhecimento resultante foi utilizado para melhorar o desenvolvimento de malhas de adaptação, por forma a otimizar as terminações de impedância em banda-base e prevenir a degradação do rendimento. Os modelos desenvolvidos foram validados experimentalmente em vários amplificadores de potência implementados com transístores de tecnologia GaN HEMT, utilizando malhas de adaptação convencionais e otimizadas, onde se obteve 400MHz de largura de banda instantânea sem degradação do rendimento. A consolidação dos mecanismos de degradação descritos neste trabalho são um importante passo para a modelação e projeto de amplificadores de elevado rendimento e largura-debanda para os sistemas de comunicação multi-banda concorrente convencionais e do futuro.Programa Doutoral em Engenharia Eletrotécnic

Integrated Heart - Coupling multiscale and multiphysics models for the simulation of the cardiac function

Mathematical modelling of the human heart and its function can expand our understanding of various cardiac diseases, which remain the most common cause of death in the developed world. Like other physiological systems, the heart can be understood as a complex multiscale system involving interacting phenomena at the molecular, cellular, tissue, and organ levels. This article addresses the numerical modelling of many aspects of heart function, including the interaction of the cardiac electrophysiology system with contractile muscle tissue, the sub-cellular activation-contraction mechanisms, as well as the hemodynamics inside the heart chambers. Resolution of each of these sub-systems requires separate mathematical analysis and specially developed numerical algorithms, which we review in detail. By using specific sub-systems as examples, we also look at systemic stability, and explain for example how physiological concepts such as microscopic force generation in cardiac muscle cells, translate to coupled systems of differential equations, and how their stability properties influence the choice of numerical coupling algorithms. Several numerical examples illustrate three fundamental challenges of developing multiphysics and multiscale numerical models for simulating heart function, namely: (i) the correct upscaling from single-cell models to the entire cardiac muscle, (ii) the proper coupling of electrophysiology and tissue mechanics to simulate electromechanical feedback, and (iii) the stable simulation of ventricular hemodynamics during rapid valve opening and closure

Estimation and control of non-linear and hybrid systems with applications to air-to-air guidance

Issued as Progress report, and Final report, Project no. E-21-67

Non-Uniform Cellular Neural Network and its Applications

セルラーニューラルネットワーク(CNN)には連続時間的な ものと，離散時間的なものがあり，本研究は主に後者について議論 する. CNNは1988年にカリフォルニア大学バークレ校のL.O.Chua 教授らによって提案され，現在，アメリカ，ヨーロッパを中心に盛 んに研究が進められている. CNNは従来のニューラルネットワー クと異なり，近傍のセルとのみ結合しているため集積回路としての 実現が容易であり，画像処理用CNNとして注目されている. 第一章では，ニューラルネットワークに関する研究の動向，お よび，人間の目と同様な処理機能を持つ連続時間CNNに関する研 究の動向と，この論文で議論している離散時間CNNの背景につい て簡単に述べている.　 第二章では，離散時間的な非均一CNNとして，二相同期信号 の回路モデルを提案し，その安定性等について議論してある. この モデルは各セルについて二相同期信号1個で実現できるため，VLS1 の実現が容易であると云う特徴がある. まず，モデルの動作原理か ら状態電圧，出力電圧の動作領域を明かにした. このことは物理的 に実現可能なCNNを設計するために重要である.つぎに，安定性 を議論するためにエネルギ一関数からリアフノフ関数を定義し，そ の関数の時間単調減少の条件を利用して，大域的な安定性を持つ離 散時間CNNの設計方法を明らかにした. 第三章では，非線形システムにおける平衡点の求解法について 議論している.連想記憶に用いられるCNNは多くの平衡点をもち， 入力信号によってどの平衡点に到達するかが決定せられる. ロバス トな連想記憶用CNNを設計するためには，このような平衡点を調 べることが必要である. ここでは，解曲線追跡法に基づいた複数解 の求解アルゴリズムを提案している. このアルゴリズムは急激な解 曲線の変化を効率よく追跡できるように，エルミー卜予測子とBDF 積分公式に基づいている. また，大規模系に適用できるようにニュ ートン・ラフソン法の代わりにブラウンの反復法を採用している. このようなアルゴリズを採用することによりロバストなCNNの設 計が可能となる. 第四章では， 離散時間CNNによる連想記憶について述べてい る. 連想記憶は人間の脳の基本的な機能であり，ニューラルネット ワーク応用研究の一つとして古くから盛んに研究されている.本章 では， 離散的なCNNを用いた外積学習アルゴリズムと中点写像ア ルゴリズムの2種類の記憶方式を提案し，その性質を解明している. まず，前者は，入力パターンに対して，エネルギー関数の値が最少 になるようにニューロン間の接続を表す重み行列を設定しようと云 うものであり，これはHebbの理論に基づいている. また，上のよう な手法で学習されたパターンを連想記憶できる条件について議論し た.中点写像アルゴリズムは重み行列の設定方法に対して， いま考 えている中心セルからの近傍を定義し，近傍に存在するセルの状態、 をベクトル表示する.これを全てパターンについて実行し，このよ うにして決定された行列によって写像されるセルのパターンが，元 の中心セルと同一のパターンを持つように重み行列を設定しようと いうもので，数学的には一般化逆行列の理論に基づいている.この ような学習方法の特徴は入力された画像が全て連想されると云うこ とである. 本章では，さらに，このことを応用例によって実証した. 第五章では，画像処理への応用として，輪郭抽出，雑音除去， 視覚パターンの認識に対する離散的なCNNについて述べている. 多くの結果から処理時間は従来のものと比較して極端に短縮される ことが分かった. また，不均一離散時間CNNによって，一つ画面 中に多数の異なる視覚パターンを同時に認識できることも分かった。 第六章では，不均一離散的なCNNの特徴と今後の問題点につ いて述べている

A mathematical framework for the analysis and modelling of memristor nanodevices

This work presents a set of mathematical tools for the analysis and modelling of memristor devices. The mathematical framework takes advantage of the compliance of the memristor's output dynamics with the family of Bernoulli differential equations which can always be linearised under an appropriate transformation. Based on this property, a set of conditionally solvable general solutions are defined for obtaining analytically the output for all possible types of ideal memristors. To demonstrate its usefulness, the framework is applied on HP's memristor model for obtaining analytical expressions describing its output for a set of different input signals. It is shown that the output expressions can lead to the identification of a parameter which represents the collective effect of all the model's parameters on the nonlinearity of the memristor's response. The corresponding conclusions are presented for series and parallel networks of memristors as well. The analytic output expressions enable also the study of several device properties of memristors. In particular, the hysteresis of the current-voltage response and the harmonic distortion introduced by the device are investigated and both interlinked with the nonlinearity of the system. Moreover, the reciprocity principle, a property form classical circuit theory, is shown to hold for ideal memristors under specific conditions. Based on the insights gained through the analysis of the ideal element, this work takes a step further into the modelling of memristive devices in an effort to improve some of the macroscopic models currently used. In particular, a method is proposed for extracting the window function directly from experimentally acquired input-output measurements. The method is based on a simple mathematical transformation which relates window to sigmoidal functions and a set of assumptions which allow the mapping of the sigmoidal to current-voltage measurements. The equivalence between the two representations is demonstrated through a new generalised window function and several existing sigmoidals and windows. The proposed method is applied on three sets of experimental measurements which demonstrate the usefulness of the window modelling approach and the newly proposed window function. Based on this method the extracted windows are tailored to the device under investigation. The analysis also reveals a set of non-idealities which lead to the introduction of a new model for memristive devices whose response cannot be captured by the window-based approach.Open Acces

Simulating and optimizing electrical current flow and neuronal activation in retinal implants

© 2018 Dr Timothy Bede Esler[Abstract Withheld