Este trabalho apresenta o desenvolvimento de uma plataforma para o estudo teórico e experimental de dispositivos amplificadores de micro-ondas do tipo válvula de ondas progressivas (TWT). A plataforma é composta por um modelo matemático e uma bancada de testes. O modelo matemático descreve a TWT como uma linha de transmissão acoplada a um feixe eletrônico unidimensional, onde as forças de carga espacial AC e DC são calculadas auto consistentemente, eliminando-se a necessidade de um cálculo separado para o fator de redução de carga espacial. O modelo matemático deu origem a dois códigos para a simulação da TWT. Ambos foram comparados com resultados experimentais e teóricos disponíveis na literatura especializada para uma pré-validação. O nível de concordância entre os presentes resultados e aqueles de referência foi acima de 90%, o que atendeu as expectativas de exatidão do modelo, tendo em vista que nem todos os parâmetros de entrada estavam disponíveis na referência. A bancada de testes construída é composta por uma TWT com banda de operação de 6,0 a 18 GHz e potência saturada máxima em torno de 55 dBm (316 W) em 13 GHz, um circuito de polarização para a mesma e a instrumentação necessária para a realização das medidas pertinentes aos amplificadores de potência. A TWT em questão foi caracterizada segundo seu comportamento mono-sinal e multi-sinal. As curvas de ganho e potência foram obtidas em função da frequência utilizando a voltagem de aceleração do feixe eletrônico e a potência de entrada como parâmetros. As curvas de transferência de potência, de fase e compressão de ganho foram obtidas para frequências escolhidas ao longo da banda, tendo novamente a voltagem de aceleração como parâmetro. Adicionalmente, a produção de produtos de intermodulação de terceira ordem foi caracterizada no ponto de 1 dB de compressão de ganho ao longo da banda analisada. Um teste de linearização por injeção de sinais, que estava previsto no plano de trabalho, não apresentou o desempenho esperado devido a problemas no funcionamento do circuito linearizador. Esses problemas foram analisados e listou-se uma série de passos para saná-los. / This work deals with the development of a platform for theoretical and experimental investigations of microwave amplifiers devices of the type traveling-wave tube (TWT). The platform consists of a mathematical model and a test bench. The mathematical model describes the TWT as a transmission line coupled to a onedimensional electron beam, in which the AC and DC space charge forces are calculated self-consistently, eliminating the need for a separate calculation for the space charge reduction factor. The mathematical model gave rise to two codes for the simulation of TWTs. Both codes were validated against experimental and theoretical results available in the literature. The overall level of agreement between the present results and those from the reference was above 90%, which was considered satisfactory since not all input parameters were available in the reference. The test bench consists of a wideband TWT operating from 6.0 to 18 GHz and maximum saturated power around 55 dBm (316 W) at 13 GHz, a biasing circuit, and the instrumentation needed to perform the relevant measurements to the power amplifier. The TWT in question was characterized according to its mono-signal and multi-signal behavior. The gain and power curves were obtained as a function of the frequency using the beam voltage and the input power as parameters. The curves of power transfer, phase transfer and gain compression were obtained for selected frequencies along the operating band, again, using the beam voltage as a parameter. Furthermore, the production of third-order intermodulation products was measured at the 1 dB gain compression point over the band analyzed. A linearization test applying the signal injection technique, which was part of the initial work plan, presented inadequate performance due to problems in the linearizer circuit operation. These problems were analyzed and a guide to solve them was provided.

Accurate linear and nonlinear models for devices and components are essential for successful RF/microwave computer aided engineering (CAE). The modeling techniques can be categorized in different levels based on the abstraction of the model as well as the application of the models at various design phases. This dissertation deals with behavioral modeling techniques for nonlinear RF components, especially amplifiers. There is an increasing demand for accurate behavioral models of RF and microwave components, or integrated circuit (IC) blocks used in wireless system designs. Accurate behavioral models help designers evaluate and select the appropriate components at simulation phase, thereby cutting development cost. However, there isnt a practical (or flexible) solution for accurate and effective behavioral model generation. This dissertation tries to tackle this problem. Power amplifiers and devices are the main components studied in this dissertation. The primary focus is on the characterization of the loadpull performance of power amplifiers and devices. Major contributions of this dissertation include development of advanced loadpull measurement procedures, large-signal load-aware behavioral model, and a load-aware behavioral model with memory-effect capabilities. There are two advanced loadpull measurements documented in this dissertation: the AM-PM loadpull measurement and the digital demodulation loadpull measurement. These two measurements may have been used internally by some research groups, however, according to the best knowledge of the author, they havent received much attention in the literature. This is the first published work on these two topics. It is shown in this work that the AM-PM performance can be strongly dependent on the load conditions. This property provides important information about the nonlinearities of power amplifiers and is used herein to create better behavioral models. This newly developed digital demodulation loadpull measurement procedure enables system designers to evaluate power amplifiers directly against digital communication system parameters such as error vector magnitude (EVM). Two example measurements are given to demonstrate the measurement system setup and the correlations between traditional nonlinear figure-of-merits and system metrics. A new behavioral modeling technique / procedure is developed based on loadpull AM-AM and AM-PM measurements. The large-signal scattering function theory is applied in the technique to formulate the model. The created model is able to automatically detect the load impedance and generate corresponding nonlinear properties. Three example models are presented to demonstrate the capability of this technique to predict accurately the output power contours, 50 ohm large-signal S21, and 3rd order intermodulation products (through additional file-based model). Finally, a modeling technique is demonstrated to enable predicting the linear memory effect within a varying load condition. The nonlinear block used in the traditional two-box model structure is replaced with the large-signal loadpull model mentioned above. By adding this new feature, the resulting model is able to predict the load-related AM-AM and AM-PM properties, which will improve the accuracy of ACPR prediction.

In the development of a nonlinear transistor model, several measurements are used to extract equivalent circuit parameters. The current-voltage (IV) characteristic of a transistor is one of the measurement data sets that allows the nonlinear model parameters to be extracted. The accuracy of the IV measurement greatly influences the accuracy of the large-signal model. Numerous works have reported the inadequacy of traditional static DC IV measurements to accurately predict radio-frequency (RF) behavior for many devices. This inaccuracy results from slow processes in the device that do not have time to completely respond to the quick changes in terminal conditions when the device is operating at high frequencies; however, these slow processes respond fully to reach a new steady-state condition in the DC sweep measurement. The two dominant processes are self-heating of the device and changes in trap occupancy. One method of allowing the thermal and trap conditions to remain in a state comparable to that of RF operation is to perform pulsed IV measurements to obtain the IV curves. In addition, thermal correction can be used to adjust the IV curves to compensate for self-heating in the case that the predominant effect in the device is thermal. To gain a better understanding of pulsed IV measurement techniques, measurement waveforms of a commercially available pulsed IV analyzer are examined in the time domain. In addition, the use of bias tees with pulsed IV measurement is explored; such a setup may be desired to maintain stability or to enable simultaneous pulsed S-parameter and pulsed IV measurement. In measurements with bias tees, the pulse length setting must be long enough to allow the voltage across the inductor to change before the measurement is made. In many circumstances, it is beneficial to compare different sets of IV curves for a device. The comparison of pulsed and static IV measurements, measured and modeled IV measurements, as well as two measurements with identical settings on the same instrument (to ascertain instrument repeatability) can be performed using the proposed normalized difference unit (NDU). This unit provides a comparison that equally weights the two sets of data to be compared. Due to the normalization factor used, the value of the NDU is independent of the size of the device for which the IV curves are compared. The variety of comparisons for which this unit can be used and its ability to present differences quantitatively allow it to be used as a robust metric for comparing IV curves. Examples of the use of the NDU shown include determination of measurement repeatability, comparison of pulsed and static IV data, and a comparison of model fits. The NDU can also be used to isolate thermal and trapping processes and to give the maximum pulse length that can be used for pulsed IV measurement without contamination by each of these processes. Plotting the NDU comparing static and pulsed IV data versus pulse length shows this maximum pulse length that can be used for each effect, while a plot of the NDU comparing pulsed IV data for two quiescent bias points of equal power dissipation reveals only differences due to trapping effects. In this way, trapping effects can be distinguished from thermal effects. Electrothermal modeling has arisen as a method of correcting for self-heating processes in a device with predominantly thermal effects. A parallel RC circuit is used to model channel temperature as a function of ambient temperature and power dissipated in the channel or junction. A technique is proposed for thermal resistance measurement and compared with a technique found in the literature. It is demonstrated that the thermal time constant can be measured from a plot of the NDU versus pulse length, and the thermal capacitance is then obtained using the thermal resistance and time constant. Finally, the results obtained through the thermal resistance measurement procedures are used to thermally correct static IV curves. Because trapping effects are negligible, it is shown that IV curves corresponding to different quiescent bias points for a Si LDMOSFET can be synthesized from three sets of static IV data taken at different ambient temperatures. The results obtained from this correction process for two quiescent bias points are compared to the pulsed IV results for these quiescent bias points and found to be quite accurate. Use of the methods presented in this work for obtaining more accurate transistor IV data data should assist in allowing more accurate nonlinear models to be obtained.

In this Thesis a Unified Discrete State-Space Model for power converters in CCM is presented. Two main approaches to arriving at the discrete model are used. The first approach involves an impulse function approximation of the duty cycle modulations of the converter switches , and this approach results in a small signal discrete model. The Second approach is direct and does not involve any approximation of the modulations , this approach yields both a large signal nonlinear discrete model and a linear small signal model. Harmonic analysis of the converter states at steady-state is done for steady-state waveform acquisition , which increases the accuracy of the model especially for finding the control to inductor current frequency response. Finally the Discrete model is verified for the Half-Bridge DC/DC topology for its three main control schemes (Asymmetric , Symmetric , DCS). A GUI platform in MATLAB is presented as a wrapper that utilizes the models and analysis presented in this thesis.

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This work focuses on the safe and stable operation of an autonomous power system interconnecting an AC source with various types of power electronic loads. The stability of these systems is a challenge due to the inherent nonlinearity of the circuits involved. Traditionally, the stability analysis in this type of power systems has been approached by means of small-signal methodology derived from the Nyquist stability criterion. The small-signal analysis combined with physical insight and the adoption of safety margins is sufficient, in many cases, to achieve a stable operation with an acceptable system performance. Nonetheless, in many cases, the margins adopted result in conservative measures and consequent system over designs. This work studies the system stability under large-perturbations by means of three different tools, namely parameter space mapping, energy functions, and time domain simulations. The developed parameters space mapping determines the region of the state and parameter space where the system operation is locally stable. In this way stability margins in terms of physical parameters can be established. Moreover, the boundaries of the identified stability region represent bifurcations of the system where typical nonlinear behavior appears. The second approach, based on the Lyapunov direct method, attempts to determine the region of attraction of an equilibrium point, defined by an operation condition. For this a Lyapunov function based on linear matrix inequalities was constructed and tested on a simplified autonomous system model. In Addition, the third approach simulates the system behavior on a computer using a detailed system model. The higher level of model detail allows identifying unstable behavior difficult to observe when simpler models are used. Because the stability of the autonomous power system is strongly associated with the characteristics of the energy source, an improved voltage controller for the generator is also presented. The generator of an autonomous power system must provide a good performance under a wide variety of regimes. Under these conditions a model based controller is a good solution because it naturally adapts to the changing requirements. To this extent a controller based on the model of a variable frequency synchronous generator has been developed and tested. The results obtained show a considerable improvement performance when compared to previous practices. / Ph. D.

Résumé: Parmi les technologies du 21e siècle en pleine expansion, la télécommunication sans-fil constitue une dimension fondamentale pour les réseaux mobiles, l’aéronautique, les applications spatiales et les systèmes de positionnement par satellites. Les nouveaux défis à surmonter sont à la fois l’augmentation des distances de transmission associée à l’accroissement des quantités de données véhiculées ainsi que la miniaturisation, la réduction du coût de production, la moindre consommation énergétique et la fiabilité de la solution technologique employée pour la chaîne de transmission. Dans ce sens, l’exploitation de bandes de plus hautes fréquences et la multiplication des canaux de transmission sont activement visées par les travaux de recherches actuels. Les technologies à l’étude reposent sur l’utilisation de systèmes intégrés pour répondre aux considérations de coûts de fabrication et d’encombrement. L’élément de base de ces systèmes, le transistor, établit largement la performance du dispositif final en termes de montée en fréquence, de fiabilité et de consommation. Afin de répondre aux défis présents et futurs, des alternatives à la filière silicium sont clairement envisagées. À ce jour, la filière nitrure de gallium est présentée comme la plus prometteuse pour l’amplification de puissance en bande Ka et W au vu de ses caractéristiques physiques et électriques, des performances atteintes par les prototypes réalisés et des premiers produits commerciaux (off-the-shelf) disponibles. L’exploitation de cette technologie à son plein potentiel s’appuie particulièrement sur la maîtrise des étapes de fabrication, de caractérisation et de modélisation du transistor. Ce travail de thèse a pour objectif le déploiement d’une méthodologie permettant la modélisation semi-physique de transistors fabriqués expérimentalement et démontrant des performances à l’état de l’art. Une partie conséquente de ce travail portera sur la caractérisation thermique du dispositif en fonctionnement ainsi que sur la modélisation d’éléments secondaires (éléments passifs) pour la conception d’un circuit amplificateur hyperfréquence. / Abstract: Amongst the emerging and developing technologies of the 21st century, wireless transmission is a fundamental aspect for mobile networks, aeronautics, spatial applications and global positioning systems. Concerning the associated technological solutions, the new challenges to overcome are both the performance increases in terms of data quantity as well as the associated device features in terms of size, production costs, energetic consumption and reliability. In that sense, the use of higher frequency bandwidths and increase of transmission channels are aimed by various current research works. Investigated technologies are based upon integrated systems to meet the criteria of devices costs and size. As the cornerstone of such devices, the transistor largely accounts for the final system performance in terms of working frequency, reliability and consumption. To respond to the challenges of today and tomorrow challenges, alternatives to the dominant current silicon process are clearly considered. To date, gallium nitride based technology is found to be the most promising for hyperfrequency power amplification for Ka and W bands given the associated physical and electrical characteristics, prototypes performance and first commercial “off-the-shelf” products. Exploitation of this technology to its full potential requires controlling and mastering the involved fabrication, characterization and modeling steps related to the transistor. This work aims at establishing a methodology enabling a semi-physical modeling of experimental transistors which exhibit state-of-the-art performance. A significant part of this work will also focus on thermal characterization of devices under test and on modeling of secondary elements (passive elements) suited for the design of hyperfrequency amplifiers.

This dissertation presents a novel large signal modeling approach which can be used to accurately model CMOS transistors used in millimeter-wave CMOS power amplifiers. The large signal model presented in this work is classified as an empirical compact device model which incorporates temperature-dependency and device periphery scaling. These added features allow for efficient design of multi-stage CMOS power amplifiers by virtue of the process-scalability. Prior to the presentation of the details of the model development, background is given regarding the 90nm CMOS process, device test structures, de-embedding methods and device measurements, all of which are necessary preliminary steps for any device modeling methodology. Following discussion of model development, the design of multi-stage 60GHz Class AB CMOS power amplifiers using the developed model is shown, providing further model validation. The body of research concludes with an investigation into designing a CMOS power amplifier operating at frequencies close to the millimeter-wave range with a potentially higher-efficiency class of power amplifier operation. Specifically, a 24GHz 130nm CMOS Inverse Class F power amplifier is simulated using a modified version of the device model, fabricated and compared with simulations. This further demonstrates the robustness of this device modeling method.

L'objectif de ce travail est d'étudier les transistors à effet de champ à haute mobilité électronique (HEMT) réalisés en Nitrure de Gallium par des mesures en bruit basse fréquence et de réaliser un oscillateur à faible bruit de phase en bande-X. Dans la première partie, nous décrivons succinctement les propriétés du matériau, le transistor ainsi que les sources de bruit basses susceptibles d'êtres présentes dans une structure de type HEMT. La méthodologie de mesure et le banc de bruit basse fréquence sont présentés. Une étude comparative est réalisée sur les comportements en bruit basse fréquence des composants épitaxiés sur différents substrats (Si, SiC, Al2O3). Enfin, une les variations de l'index de fréquence g du bruit en 1/fg relevées sur certains composants sont corrélées au mécanisme de transport des électrons dans la structure : pour cela, nous avons confronté les mesures en bruit basse fréquence avec des simulations physiques. La seconde partie s'intéresse aux composants épitaxiés sur un substrat de Carbure de Silicium. Une méthodologie d'extraction de composantes mathématiques du spectre de bruit basse fréquence est présentée puis validée. Des études en fonction de la polarisation et de la température ont permis de découvrir l'origine des pièges et de les localiser. Enfin, une corrélation avec une étude physique (SIMS) est présentée. Dans la troisième partie, nous développons un modèle large signal afin de réaliser un démonstrateur en bande X. Les performances à l'état de l'art de l'oscillateur sont ensuite présentées (POUT=20dBm, Lf(100kHz)=-105 dBc/Hz à 10 GHz).

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