ELECTRON DEVICE NONLINEAR MODELLING FOR MICROWAVE CIRCUIT DESIGN

The electron device modelling is a research topic of great relevance, since the performances required to devices are continuously increasing in terms of frequency, power and linearity: new technologies are affirming themselves, bringing new challenges for the modelling community. In addition, the use of monolithic microwave integrated circuits (MMIC) is also increasing, making necessary the availability, in the circuit design phase, of models which are computationally efficient and at the same more and more accurate. The importance of modelling is even more evident by thinking at the wide area covered by microwave systems: terrestrial broadband, satellite communications, automotive applications, but also military industry, emergency prevention systems or medical instrumentations. This work contains a review of the empirical modelling approach, providing the description of some well-known equivalent-circuit and black-box models. In addition, an original modelling approach is described in details, together with the various possible applications: modelling of nonquasi-static phenomena as well as of low-frequency dispersive effects. A wide experimental validation is provided, for GaAs- and GaN-based devices. Other modelling issues are faced up, like the extraction of accurate models for Cold-FET or the more convenient choice of the data-interpolator in table-based models. Finally, the device degradation is also treated: a new measurement setup will be presented, aimed to the characterization of the device breakdown walkout under actual operating conditions for power amplifiers

Mecanismos de geração da distorção não-linear em amplificadores Doherty

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

Continuous Mode High Efficiency Power Amplifier Design for X Band

This thesis is focused on the investigation and implementation of novel techniques for the design of X band (8 - 12GHz) power amplifiers. One of the main topics is the expansion and novel implementation of continuous mode theory, with the intention of improving the bandwidth and efficiency of X band power amplifiers. This work builds upon the Class B/J continuous mode theory to incorporate cases where <[ZF0] 6= RL, not described by the original Class B/J theory, with a tool called the “clipping contour”. The clipping contour tool shows a graphical representation on the Smith chart of the boundary between impedances generating a voltage waveform which will modulate or “clip” the current waveform, and a voltage waveform which will leave the current waveform unaltered. This non-clipping space is shown, with measured load pull and amplifier data, to represent the maximum efficiency case for a given ZF0, thus the clipping contour tool thus gives designers the ability to predict the areas of highest efficiency and power given any ZF0, without the need to use costly, time consuming multi harmonic load pull techniques. Push pull amplifiers using quarter wave coupled line baluns are proposed as an ideal matching topology to exploit this new tool. Various balun topologies are studied using a novel extended transmission line model. This model is shown to predict accurately and explain the “trace separation” effect seen in planar baluns and not their 3D coaxial cable equivalents. It also forms the basis of analysis which results in a powerful new equation capable of guaranteeing the elimination of trace separation completely, without compromising performance. This equation is used to design an optimal balun which possesses the largest fractional bandwidth (130%) of any balun ever published on single layer thin film Alumina, whilst simultaneously eliminating trace separation. The optimised Alumina baluns are used to construct push pull output demonstrator circuits which show efficiencies of 40% over greater than an octave bandwidth, a significant advancement of any other comparable published work. These techniques demonstrate the potential to exceed double octave bandwidths with efficiencies greater than 40% once optimised. Initial investigations on MMIC and 2.5D processes show the potential to replicate the Alumina performance over octave and decade bandwidths respectively

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

New non-linear microwave network parameters with application to gallium nitride high electron mobility transistor modeling with x-parameters

High power amplifiers have been receiving increasing attention as key components responsible for a sizable portion of base station cost in wireless communication systems. Higher performance and lower cost can be achieved on a device technology and a circuit design. On the device technology, Gallium Nitride (GaN) technology brings unparalleled performance in efficiency and linearity thanks to its higher energy bandgap, higher breakdown electric field, higher electron velocity and higher operating temperature. Large- and small- signal modeling of GaN HEMTs, which is the aim of our work, is an important step for high power amplifier designer. In general, most of the published models are accurate only in linear mode since they rely on DC and multi-bias S-parameters measurements for model parameters extraction. The availability of X-parameters measurements and their benefits compared to S-parameters presents an opportunity for incorporating non-linear data directly in the modeling process. The main objective of this research is how to exploit X-parameters to more accurately and quickly build a nonlinear device model that captures the device behavior at the fundamental and harmonic frequencies. Nonlinear network Z-, Y-, ABCD-, T-, G- and H-parameters are essential to extract and validate large-signal model based on X-parameters. The expression of nonlinear impedances, admittances, ABCD-, T-, G- and H- are derived from X-parameters. Moreover, standard conversion rules between these nonlinear network parameters are established. The nonlinear network parameters can describe any topology of pure linear or nonlinear or a mix of linear and nonlinear components. In this work, a new equivalent circuit modeling technique based on X-parameters measurements was proposed. The new model is subdivided into extrinsic and intrinsic parts. Extrinsic elements are extracted with a technique based on de-embedding open structure fabricated on the same wafer of the device under test and forward measurements. Xparameters of the intrinsic part are determined thanks to X-parameters de-embedding technique. The intrinsic part is modeled as a modified Pi-Network of nonlinear characteristic impedances modeling the drain-to-source, gate-to-source, drain-to-gate and gate-to-drain junctions

Power Efficiency Enhancement and Linearization Techniques for Power Amplifiers in Wireless Communications

Wireless communication systems require Power Amplifiers (PAs) for signal transmissions. The trade-off between power efficiency and nonlinear distortion in PAs degrades the communication performance. Thus, power efficiency and nonlinearity are two main concerns of operating PAs in communication systems. Nonlinear behavioral models are typically used to quantify and mitigate the distortion effects of PAs on communication systems. This dissertation presents an estimation approach for modeling and linearizing the PA Amplitude-to-Amplitude (AM/AM) nonlinearity using the design specifications of PAs, such as gain, the third-order intercept point, and 1dB compression point. Furthermore, an enhanced approach for modeling solid-state power amplifiers is developed by modifying the Saleh empirical model. The Envelope Tracking (ET) technique for PAs has been a popular power efficiency enhancement in modern cellular systems. However, the time-varying effects of the supply voltage impacts the PA linearity. Therefore, an accurate behavioral model for PA with ET has become an important research effort to characterize the effect of dynamic supply voltage on both the amplitude and phase nonlinearities. Furthermore, the empirical models of ET PAs are widely used to improve PAs linearity by using Digital Predistortion (DPD). This dissertation develops an extended modeling approach to characterize the AM/AM and Amplitude-to-Phase (AM/PM) conversions as well as account for the impact of the time-varying supply voltage on the ET PAs. Memory effects, due to energy storage elements (e.g. capacitors and inductors) in ET PA circuits in addition to the temperature variation of integrated circuit, are modeled using digital filters (finite impulse-response filters) in series with the static AM/AM and static AM/PM nonlinearities. A least-squares approach is mathematically derived for estimating the model coefficients of ET PAs. The model identification of many coefficients requires high computational cost in Float Point Operations (FLOPS), such as multipliers and adders. In addition, the computational cost in FLOPs of a complex number is equivalent to (2-6) times the cost of real numbers. The estimation complexity of the ET PAs model in this work requires around half the number of FLOPS compared to the state-of-the-art behavioral models. This is because the modeling approach in this work consists of real coefficients and a lower number of model parameters. A DPD model is derived in this dissertation to compensate for both the AM/AM and AM/PM nonlinear distortions in ET PAs. A dual-input single-output function architecture is calculated for the DPD model to compensate for the nonlinearities in the AM/AM and AM/PM conversions contributed by the time-varying supply voltage in the ET system. Both the proposed AM/AM and AM/PM DPD models exhibit lower numbers of coefficients, which result in reduction of the identification complexity compared to the state-of-the-art DPD models. The proposed behavioral models of the ET PA and DPD are both evaluated in the time and frequency domains, as well as compared to the state-of-the-art models in terms of model accuracy and estimation complexity

Design and Control of Power Converters for High Power-Quality Interface with Utility and Aviation Grids

Power electronics as a subject integrating power devices, electric and electronic circuits, control, and thermal and mechanic design, requires not only knowledge and engineering insight for each subarea, but also understanding of interface issues when incorporating these different areas into high performance converter design.Addressing these fundamental questions, the dissertation studies design and control issues in three types of power converters applied in low-frequency high-power transmission, medium-frequency converter emulated grid, and high-frequency high-density aviation grid, respectively, with the focus on discovering, understanding, and mitigating interface issues to improve power quality and converter performance, and to reduce the noise emission.For hybrid ac/dc power transmission,• Analyze the interface transformer saturation issue between ac and dc power flow under line unbalances.• Proposed both passive transformer design and active hybrid-line-impedance-conditioner to suppress this issue.For transmission line emulator,• Propose general transmission line emulation schemes with extension capability.• Analyze and actively suppress the effects of sensing/sampling bias and PWM ripple on emulation considering interfaced grid impedance.• Analyze the stability issue caused by interaction of the emulator and its interfaced impedance. A criterion that determines the stability and impedance boundary of the emulator is proposed.For aircraft battery charger,• Investigate architectures for dual-input and dual-output battery charger, and a three-level integrated topology using GaN devices is proposed to achieve high density.• Identify and analyze the mechanisms and impacts of high switching frequency, di/dt, dv/dt on sensing and power quality control; mitigate solutions are proposed.• Model and compensate the distortion due to charging transition of device junction capacitances in three-level converters.• Find the previously overlooked device junction capacitance of the nonactive devices in three-level converters, and analyze the impacts on switching loss, device stress, and current distortion. A loss calculation method is proposed using the data from the conventional double pulse tester.• Establish fundamental knowledge on performance degradation of EMI filters. The impacts and mechanisms of both inductive and capacitive coupling on different filter structures are understood. Characterization methodology including measuring, modeling, and prediction of filter insertion loss is proposed. Mitigation solutions are proposed to reduce inter-component coupling and self-parasitics

Design and Linearization of Energy Efficiency Power Amplifier in Nonlinear OFDM Transmitter for LTE-5G Applications. Simulation and measurements of energy efficiency power amplifier in the presence of nonlinear OFDM transmitter system and digital predistortion based on Hammerstein-Wiener method

This research work has made an effort to understand a novel line of radio frequency power amplifiers (RFPAs) that address initiatives for efficiency enhancement and linearity compensation to harmonize the fifth generation (5G) campaign. The objective is to enhance the performance of an orthogonal frequency division multiplexing-long term evolution (OFDM-LTE) transmitter by reducing the nonlinear distortion of the RFPA. The first part of this work explores the design and implementation of 15.5 W class AB RF power amplifier, adopting a balanced technique to stimulate efficiency enhancement and redeeming exhibition of excessive power in the transmitter. Consequently, this work goes beyond improving efficiency over a linear RF power amplifier design; in which a comprehensive investigation on the fundamental and harmonic components of class F RF power amplifier using a load-pull approach to realise an optimum load impedance and the matching network is presented. The frequency bandwidth for both amplifiers was allocated to operate in the 2.620-2.690 GHz of mobile LTE applications. The second part explores the development of the behavioural model for the class AB power amplifier. A particular novel, Hammerstein-Wiener based model is proposed to describe the dynamic nonlinear behaviour of the power amplifier. The RF power amplifier nonlinear distortion is approximated using a new linear parameter approximation approach. The first and second-order Hammerstein-Wiener using the Normalised Least Mean Square Error (NLMSE) algorithm is used with the aim of easing the complexity of filtering process during linear memory cancellation. Moreover, an enhanced adaptive Wiener model is proposed to explore the nonlinear memory effect in the system. The proposed approach is able to balance between convergence speed and high-level accuracy when compared with behavioural modelling algorithms that are more complex in computation. Finally, the adaptive predistorter technique is implemented and verified in the OFDM transceiver test-bed. The results were compared against the computed one from MATLAB simulation for OFDM and 5G modulation transmitters. The results have confirmed the reliability of the model and the effectiveness of the proposed predistorter.Fundacão para a Ciência e a Tecnologia, Portugal, under European Union’s Horizon 2020 research and innovation programme ... grant agreement H2020-MSCA-ITN- 2016 SECRET-722424 I also acknowledge the role of the National Space Research and Development Agency (NASRDA) Sokoto State Government Petroleum Technology Trust Fund (PTDF