93 research outputs found

    Mecanismos de geração da distorção não-linear em amplificadores Doherty

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    Doutoramento em Engenharia ElectrotécnicaNowadays, wireless communications systems demand for greater mobility and higher data rates. Moreover, the need for spectral efficiency requires the use of non-constant envelope modulation schemes. Hence, power amplifier designers have to build highly efficient, broadband and linear amplifiers. In order to fulfil these strict requirements, the practical Doherty amplifier seems to be the most promising technique. However, due to its complex operation, its nonlinear distortion generation mechanisms are not yet fully understood. Currently, only heuristic interpretations are being used to justify the observed phenomena. Therefore, the main objective of this work is to provide a model capable of describing the Doherty power amplifier nonlinear distortion generation mechanisms, allowing the optimization of its design according to linearity and efficiency criteria. Besides that, this approach will allow a bridge between two different worlds: power amplifier design and digital pre-distortion since the knowledge gathered from the Doherty operation will serve to select the most suitable pre-distortion models.Presentemente, os sistemas de comunicações sem fios exigem uma maior mobilidade e elevadas taxas de transferência. Para além disso, a necessidade de eficiência espectral obriga ao uso de esquemas de modulação de envolvente variável. Consequentemente, o desenvolvimento de amplificadores de elevada eficiência, com uma elevada largura de banda e, ao mesmo tempo, lineares, tornou-se num dos maiores desafios para os engenheiros de projeto de amplificadores de potência. Por forma a cumprir estes requisitos muito rigorosos, o amplificador em configuração Doherty parece ser a técnica mais promissora. Contudo, devido à sua complexa operação, os seus mecanismos de geração de distorção não linear não são ainda completamente conhecidos. Atualmente, apenas interpretações heurísticas estão a ser usadas para justificar os fenómenos observados. Nesse sentido, o principal objetivo deste trabalho é desenvolver um modelo capaz de descrever os mecanismos de geração da distorção não linear em amplificadores Doherty, permitindo assim, a optimização do seu projeto, tendo em conta as especificações de linearidade e eficiência. Para além disso, esta abordagem permitirá uma ponte entre dois mundos diferentes: projecto de amplificadores de potência e pré-distorção digital, uma vez que o conhecimento recolhido da operação do Doherty ajudará na escolha de modelos de pré-distorção mais adequados

    Design Considerations, Modeling And Characterization Of Gan Hemts And Design Of High Frequency And High Power Mmic Amplifiers

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    Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2011Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2011Yüksek kapasiteli kablosuz veri iletimi, cep telefonu, kişisel iletişim ve mikrodalga erişim için dünya çapında birlikte çalışabilirlik (WiMAX) gibi gelişmiş haberleşme sistemlerinin pazarları hergeçen gün daha da geliştikçe, yüksek güçlü ve yüksek hızlı transistor ve yükselteçler üzerine ilgi de artmaktadır. Yüksek frekanslı güç elektroniği alanında meydana gelen hızlı gelişim, şu anki yarıiletken teknolojirinin performanslarında önemli bir gelişme olmayacağından yüksek çıkış gücü, yüksek çalışma gerilimi ve yüksek giriş empedancı özelliklerine sahip geniş enerji bant aralığına sahipuygu bir malzemenin tanıtılmasını gerektirmiştir. Galyum nitrat (GaN) HEMT teknolojisi diğer III-V grubu yarıiletken malzemelerle karşılaştırıldığında sahip olduğu yüksek enerji bant aralığı, yüksek ısıl iletkenlik, yüksek kırılma alanı ve yüksek doyma hızı gibi özelliklere sahiptir ve bu özellikleri sayesinde daha yüksek güç ve yüksek hız performansları vaat eder. Bu özellikleriden dolayı GaN HEMT teknolojisini yüksek güçlü ve yüksek hızlı MMIC yükselteçler için uygundur. Bu çalışmada ilk olarak yüksek güçlü ve yüksek hızlı GaN HEMT transistorlarının tasarımlarının önemli noktaları açıklanmıştır. Bu özelliklere dayanarak termal olarak daha verimli bir güç HEMT transistoru tasarımı yapılmıştır. Daha sonra ise HEMT transistorlar için mikrofabrikasyon adımları ve karakterizasyon methodları verilmiştir. Buna göre, 8x100 µm büyüklüğündeki bir GaN HEMT transistorundan 1.1 A/mm savak akım yoğunluğu, 37.5 GHz akım kazancı kesim frekansı, 48.5 GHz güç kazancı kesim frekansı ve 10 GHz frekansında 1.25 W/mm çıkış güç yoğunluğu elde edilmiştir. Sonra 4x75 µm büyüklüğünde bir GaN transistorun büyük işaret modeli elde edilmiştir. Bu model kullanılarak 20 GHz de GaN MMIC tasarlanmış ve üretilmiştir. Bu MMIC’e ait ölçüm sonuçlarına göre ise 20 GHz de 603 mW çıkış gücü ve 19.2 GHz de 9 dB küçük işaret kazancı elde edilmiştir. Son olarak ise WiMAX uygulamaları için Cree GaN HEMT tasarım modelleri kullanılarak S bandında iki adet GaN MMIC PA tasarımı yapılmıştır. İlk PA 3.5 GHz de 42.6 dBm çıkış gücü ve %55 güç ilaveli verim (PAE) ile 3.2-3.8 GHz frekans aralığında 16 dB küçük işaret kazancına sahiptir. İkinci PA ise ilk PA nın dışardan Lange-coupler tekniği kullanılarak parallellenmesi yöntemine dayanmaktadır ve 3.5 GHz de 45.3 dBm çıkış gücü ve %45 PAE ile 3.3-3.8 GHz frekansında 0.2 dB den küçük kazanç dalgalanması ile 16 dB küçük işaret kazancı elde edilmiştir. Bu çalışma 13-20 Ağustos 2011 tarihlerinde İstanbul’da düzenlenecek olan The XXX General Assembly and Scientific Symposium of the International Union of Radio Science (Union Radio Scientifique Internationale-URSI) tarafından kabul edilmiştir.As the market for advanced telecommunication systems such as high capacity wireless data transferring, cellular, personal communication and worldwide interoperability for microwave access (WiMAX) coming closer to reality, high power and high frequency microwave transistors and amplifiers have attracted great attention. The rapid development of the radio frequency (RF) power electronics requires the introduction of wide bandgap material due to its potential in high output power density, high operation voltage and high input impedance, since there will be no significant performance improvements regarding to this problem in present semiconductor technologies. Gallium nitride (GaN) HEMT technology provides some specific material characteristics including wide bandgap, high breakdown field, high thermal conductivity, and high saturated velocity and promises better high power and high frequency performances compared to other III-V semiconductor materials. These features make GaN HEMT technology suitable for high frequency and high power monolithic microwave integrated circuit (MMIC) power amplifiers (PAs). Firstly, high power and high frequency design considerations of GaN HEMT transistors were explained in this work. A thermally efficient power HEMT design was introduced based on these considerations. Then, micro fabrication steps and characterization methods of these HEMTs were given. Moreover, 1.1A/mm drain current density, 37.5 GHz of fT, 48.5 GHz of fmax and 1.25 W/mm output power density at 10 GHz are achieved from a fabricated 8x100 µm GaN HEMT device. Next, large signal nonlinear modeling was performed for a 4x75 µm GaN HEMT transistor. By using this nonlinear model, a GaN MMIC PA was designed at 20 GHz and fabricated. According to measurement results, 603 mW output power obtained at 20.1 GHz with 9 dB small signal gain at 19.2 GHz. Finally, two S band GaN MMIC PAs were designed for WiMAX applications by using Cree GaN HEMT design kit. First PA has a 42.6 dBm output power with a 55%PAE @ 3.5 GHz and 16 dB small signal gain in the 3.2-3.8 GHz frequency range. When two of these MMICs were combined by using off-chip Lange Couplers, 45.3 dBm output power with a 45%PAE @3.5Ghz and 16 dB small signal gain were obtained with less than 0.2 dB gain ripple in the 3.3-3.8 GHz frequency range. This work was accepted by The XXX General Assembly and Scientific Symposium of the International Union of Radio Science (Union Radio Scientifique Internationale-URSI) which will be held at Istanbul, Turkey on August 13-20, 2011.Yüksek LisansM.Sc

    CHARACTERIZATION AND MODELING OF III-V TRANSISTORS FOR MICROWAVE CIRCUIT DESIGN

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    New mobile communication technologies have given a boost to innova-tions in electronic for telecommunications and microwave electronics. It’s clear that the increasing request for mobile data availability, as proved by the growth of 69% of mobile data traffic in 2014, poses great challenges to indus-tries and researchers in this field. From this point of view a rapid diffusion of wireless mobile broadband network data standards, like LTE/4G, should be seen, which requests a state-of-the-art transceiver (i.e., transmitter/receiver) electronics. It will be mandato-ry to use higher frequencies, with wider bandwidth and excellent efficiency, to improve battery duration of mobile phones and reduce the energy consump-tion of the network infrastructures (i.e. base stations). Moreover, the microwave electronics is ubiquitous in satellite systems. As an example the GPS-GLONASS systems, developed respectively by United-States and Russian Federation for geo-spatial positioning, now are commonly used as navigation support for planes, ships, trains, automobiles, and even people. Other interesting applications are the earth-observation satellites, like the Italian system COSMO-SkyMed: a constellation of four satellites developed for the observation of the entire planet. These systems are able to produce a detailed image of the earth surface exploiting a microwave synthetic aperture radar, with the possibility to observe an area even by night or with bad weather conditions. Clearly these features are impossible for traditional opti-cal systems. Even if a lot of electronic applications are focused on the system architec-ture, in microwave electronics the single transistor still plays a key role. In-deed, the number of transistors in high-frequency circuits is low and wide ar-eas are occupied by numerous passive elements, required to optimize the sys-tem performance. There is a lot of interest in finding the optimum transistor operating condition for the application of interest, because the high-frequency electron-device technologies are relatively young and often still in develop-ment, so the transistor performance is generally poor. As a matter of fact, transistor characterization plays a very important role: various measurement systems, developed for this purpose, have been pro-posed in literature, with different approaches and application fields. Moreover, a meticulous characterization of the transistor is the basis for the identification of accurate models. These models, allowing to predict the tran-sistor response under very different operating conditions, represent a funda-mental tool for microwave circuit designers. This thesis will resume three years of research in microwave electronics, where I have collaborated in research activities on transistor characterization and modelling oriented to microwave amplifier design. As various kinds of amplifiers (i.e., low-noise amplifier, power amplifier) have been developed, various characterization techniques have been exploited. In the first chapter, after a presentation of the most common large-signal characterization systems, a low-frequency large-signal characterization setup, oriented to transistor low-frequency dispersion analysis and power amplifier design, will be described as well as the development of the control algorithm of the measurement system and its application to the design of a Gallium-Nitride class-F power-amplifier, operating at 2.4 GHz with 5.5 W of output power and 81% efficiency. Another application of the proposed setup for fast-trap characterization in III-V devices is then reported. Successively, an exten-sion of the setup to very low frequencies will be presented. In the second chapter, small-signal characterization techniques will be dealt with, focusing on noise measurement systems and their applications. Af-ter a brief introduction on the most relevant small-signal measurement system (i.e., the vector network analyzer), an innovative formulation will be intro-duced which is useful to analyze the small-signal response of Gallium-Arsenide and Gallium-Nitride transistors at very low frequencies. Successive-ly, the application of neural network to model the low-frequency small signal response of a Gallium-Arsenide HEMT will be investigated. The third and last chapter will deal with the EM-based characterization of Gallium-Nitride transistor parasitic structures and its usage, combined with small-signal and noise measurements, for developing a transistor model ori-ented to low-noise amplifiers design. In particular, the design of a three stages low-noise amplifier with more than 20 dB of gain and less than 1.8 dB of noise figure operating in Ku-band will be described

    Contributing to Second Harmonic Manipulated Continuum Mode Power Amplifiers and On-Chip Flux Concentrators

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    The current cellular network consumes a staggering 100 TWh of energy every year. In the coming years, millions of devices will be added to the existing network to realize the Internet of Things (IoT), further increasing its power consumption. An RF power amplifier typically consumes a large proportion of the DC power in a wireless transceiver, improving its efficiency has the largest impact on the overall system. Additionally, amplifiers need to demonstrate high linearity and bandwidth to adhere to constraints imposed by wireless standards and to reduce the number of amplifiers required as an amplifier with a broader bandwidth can potentially replace several narrowband amplifiers. A typical approach to improve efficiency is to present an appropriate load at the harmonics generated by the transistor. Recently proposed continuous modes based on harmonic manipulation, such as class B/J continuum, continuous class F (CCF) and continuous class F-1 (CCF-1), have shown the capability of achieving counteracting requirements viz., high efficiency, high linearity, and broad bandwidth (with a fractional bandwidth greater than 30%). In these classes of amplifiers, the second harmonic is manipulated by placing a reactive second harmonic load and the reactive component of the fundamental load is adjusted while keeping a fixed resistive component of the fundamental load. The first contribution of this work is to investigate the reason for amplifiers designed in classes B/J continuum and CCF to achieve high efficiency at back-off and 1dB compression. In this thesis, we demonstrate that the variation of the phase of the current through the non-linear intrinsic capacitances due to the variation of the phase in the continuum of drain voltage waveforms in Class B/J/J* continuum leads to either a reduction or enhancement of intrinsic drain current. Consequently, a subset of voltage waveforms of the class B/J/J* continuum can be used to design amplifiers with higher P1dB, and efficiency at P1dB than in Class B. A simple choice of this subset is demonstrated with a 2.6GHz Class B/J/J* amplifier, achieving a P1dB of 38.1dBm and PAE at P1dB of 54.7%, the highest output power and efficiency at P1dB amongst narrowband linear amplifiers using the CGH40010 reported to date, at a comparable peak PAE of 72%. Secondly, we propose a new formulation for high-efficiency modes of power amplifiers in which both the in-phase and out-of-phase components of the second harmonic of the current are varied, in addition to the second harmonic component of the voltage. A reduction of the in-phase component of the second harmonic of current allows reduction of the phase difference between the voltage and current waveforms, thereby increasing the power factor and efficiency. Our proposed waveforms offer a continuous design space between class B/J continuum and continuous F-1 achieving an efficiency of up to 91% in theory, but over a wider set of load impedances than continuous class F-1. These waveforms require a short at third and higher harmonic impedances, which are easier to achieve at a higher frequency. The load impedances at the second harmonic are reactive and can be of any value between -j∞ and j∞, easing the amplifier design. A trade-off between linearity and efficiency exists in the newly proposed broadband design space, but we demonstrate inherent broadband capability. The fabricated narrowband amplifier using a GaN HEMT CGH40010F demonstrates 75.9% PAE and 42.2 dBm output power at 2.6 GHz, demonstrating a comparable frequency weighted efficiency for this device to that reported in the literature. IoT devices may be deployed in critical applications such as radar or 5G transceivers of an autonomous vehicle and hence need to operate free of failure. Monitoring the drain current of the RF GaN MMIC would allow to optimize the device performance and protect it from surges in its supply current. Galvanic current sensors rely on the magnetic field generated by the current as a non-invasive method of current sensing. In this thesis, our third major contribution is a planar on-chip magnetic flux concentrator, is enhance the magnetic field at the current sensor, thereby improving the current detection capability of a current sensor. Our layout utilizes a discontinuity in a magnetic via, resulting in penetration of the magnetic field into the substrate. The proposed concentrator has a magnetic gain x1.8 in comparison to air. The permeability of the magnetic core required is 500, much lower than that reported in off-chip concentrators, resulting in a significant easing of the specifications of the material properties of the core. Additionally, we explore a novel three-dimensional spiral-shaped magnetic flux concentrator. It is predicted via simulations that this geometry becomes a necessity to enhance the magnetic field for increased form factor as the magnetic field from a single planar concentrator deteriorates as its size increases

    Wide Bandgap Based Devices

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    Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era. SiC- and GaN-based devices are starting to become more commercially available. Smaller, faster, and more efficient than their counterpart Si-based components, these WBG devices also offer greater expected reliability in tougher operating conditions. Furthermore, in this frame, a new class of microelectronic-grade semiconducting materials that have an even larger bandgap than the previously established wide bandgap semiconductors, such as GaN and SiC, have been created, and are thus referred to as “ultra-wide bandgap” materials. These materials, which include AlGaN, AlN, diamond, Ga2O3, and BN, offer theoretically superior properties, including a higher critical breakdown field, higher temperature operation, and potentially higher radiation tolerance. These attributes, in turn, make it possible to use revolutionary new devices for extreme environments, such as high-efficiency power transistors, because of the improved Baliga figure of merit, ultra-high voltage pulsed power switches, high-efficiency UV-LEDs, and electronics. This Special Issue aims to collect high quality research papers, short communications, and review articles that focus on wide bandgap device design, fabrication, and advanced characterization. The Special Issue will also publish selected papers from the 43rd Workshop on Compound Semiconductor Devices and Integrated Circuits, held in France (WOCSDICE 2019), which brings together scientists and engineers working in the area of III–V, and other compound semiconductor devices and integrated circuits

    DESIGN TECHNIQUES FOR HIGH-EFFICIENCY MICROWAVE POWER AMPLIFIERS

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    The increasingly diffusion of wireless devices during the last years has established a sort of “second youth” of analog electronics related to telecommunication systems. Nowadays, in fact, electronic equipments for wireless communication are exploited not only for niche sectors as strategic applications (e.g., military, satellite and so on): as a matter of fact, a large number of commercial devices exploit wireless transmitting systems operating at RF and microwave frequencies. As a consequence, increasing interest has been focused by academic and industrial communities on RF and microwave circuits and in particular on power amplifiers, that represent the core of a wireless transmitting system. In this context, more and more challenging performance are demanded to such a kind of circuit, especially in terms of output power, bandwidth and efficiency. The present thesis work has been focused on RF and microwave power amplifier design that, as said before, represents one of most actual and attractive research theme. Several aspects of such topic have been covered, from the analysis of different design techniques available in literature to the development of an innovative design approach, providing many experimental results related to realized power amplifiers. Particular emphasis has been given to high-efficiency power amplifier classes of operation, that represent an hot issue in a world more and more devoted to the energy conservation. Moreover, electron device degradation phenomena were investigated, that although not directly accounted for, represent a key issue in microwave power amplifier design. In particular, the first chapter of this thesis provides an overview of commonly adopted design methodologies for microwave power amplifier, analyzing the advantages and the critical aspects of such approaches. Moreover, nonlinear device modeling issues oriented to microwave power amplifier design have been dealt with. In the second chapter, an innovative design technique is presented. It is based on experimental electron device nonlinear characterization, carried out by means of a low-frequency large signal measurement setup, in conjunction with the modeling of high-frequency nonlinear dynamic phenomena. Several design examples have been carried out by exploiting the proposed approach that confirm the effectiveness of the design technique. In the third chapter, the proposed design methodology has been applied to high-efficiency power amplifier classes of operations, that need to control the device terminations not only at the fundamental frequency, but also at harmonics. Two high-efficiency power amplifiers have been realized by adopting such a technique, demonstrating performance in terms of output power and efficiency comparable with the state of the art. Finally, in chapter four an important power amplifier design aspect has been dealt with, related to degradation and performance limitation of microwave electron devices. Several experimental results have been carried out by exploiting a new measurement setup, oriented to the characterization of degradation phenomena of microwave electron devices
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