Modelling, Analysis and Design of Optimised Electronic Circuits for Visible Light Communication Systems

This thesis explores new circuit design techniques and topologies to extend the bandwidth of visible light communication (VLC) transmitters and receivers, by ameliorating the bandwidth-limiting effects of commonly used optoelectronic devices. The thesis contains detailed literature review of transmitter and receiver designs, which inspired two directions of work. The first proposes new designs of optically lossless light emitting diode (LED) bandwidth extension technique that utilises a negative capacitance circuit to offset the diode’s bandwidth-limiting capacitance. The negative capacitance circuit was studied and verified through newly developed mathematical analysis, modelling and experimental demonstration. The bandwidth advantage of the proposed technique was demonstrated through measurements in conjunction with several colour LEDs, demonstrating up to 500% bandwidth extension with no loss of optical power. The second direction of work enhances the bandwidth of VLC receivers through new designs of ultra-low input impedance transimpedance amplifiers (TIAs), designed to be insensitive to the high photodiode capacitances (Cpd) of large area detectors. Moreover, the thesis proposes a new circuit, which modifies the traditional regulated cascode (RGC) circuit to enhance its bandwidth and gain. The modified RGC amplifier efficiently treats significant RGC inherent bandwidth limitations and is shown, through mathematical analysis, modelling and experimental measurements to extend the bandwidth further by up to 200%. The bandwidth advantage of such receivers was demonstrated in measurements, using several large area photodiodes of area up to 600 mm^2, resulting in a substantial bandwidth improvement of up to 1000%, relative to a standard 50 Ω termination. An inherent limitation of large area photodiodes, associated with internal resistive elements, was identified and ameliorated, through the design of negative resistance circuits. Altogether, this research resulted in a set of design methods and practical circuits, which will hopefully contribute to wider adoption of VLC systems and may be applied in areas beyond VLC

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

SIMPLIS efficiency model for a synchronous multiphase buck converter

In this master’s thesis, an efficiency model was developed for the synchronous multiphase buck converters of the TPS6594x-Q1 integrated circuit using SIMPLIS simulator. The model includes internal losses occurring in power stage transistors, power stage drivers and bondwires. Modeled external losses include printed circuit board resistance and inductance, inductor direct and alternating current characteristics as well as capacitor nonidealities. Internal loss modeling was mostly based on Cadence simulations. Power stage transistors especially were thoroughly modeled. The capacitances of the power stage transistors were extracted by integrating gate and drain currents during the transistor on and off transitions. Charging of the parasitic capacitances followed the theory in turn-off and turn-on transitions and therefore the capacitance extraction was fairly simple. Nonlinearities of the parasitic capacitors were modeled in SIMPLIS with multiple linear approximations. Transistor gate drivers were very rough approximations of the real drivers but good enough for the simulation model. Drivers were modeled to match the gate currents simulated in Cadence, which were then combined the accurate switching transistor models in order to accurately model the switching characteristics. External loss models were based on measurements and simulations. Printed circuit board losses were based on Ansys simulations in which the printed circuit board inductances and resistances were solved from the geometry of the printed circuit board. Inductors were modeled to match the datasheet impedance and resistance graphs and the model was verified against the measurements done in the laboratory. An automated measurement testbench was done for the inductor measurements using LabVIEW and the results were parsed using Matlab. A ladder topology with resistances and inductances was used in the final inductor model to model the frequency characteristics of the inductor. The effect of direct current on inductance was also investigated but the inductance reduction did not have any significant impact on efficiency. Other external components such as capacitors also cause some external losses and they were modeled based on the capacitor datasheets. The simulation model was compared against single- and two-phase efficiency measurements with multiple different input and output voltages which were chosen to match the most common use cases. Efficiency curves were drawn for each configuration using the implemented simulation model and over 300 different comparison points were compared in total. A post processing script that was launched after a simulation completes had to be written with the programming language SIMPLIS supports to draw the efficiency graph from the simulated data. Using the script allowed to run the efficiency simulation without any additional licenses other than the SIMPLIS license. The final model achieved an average error of under 1 % between all the measured and simulated efficiency curves. The most accurate results were obtained with lower switching frequency and larger inductance. Apart from accuracy, the simulator had to be practical and therefore the simulation time had to be considered. Simulation time was attempted to be kept at minimum by simplifying the schematic in as many ways as possible without losing accuracy. For example, reducing the point of the linear approximations in the power stage transistors from 79 points to 17 points saved nearly 50 seconds in single-phase simulations without significant changes in simulation accuracy

New Approaches in Automation and Robotics

The book New Approaches in Automation and Robotics offers in 22 chapters a collection of recent developments in automation, robotics as well as control theory. It is dedicated to researchers in science and industry, students, and practicing engineers, who wish to update and enhance their knowledge on modern methods and innovative applications. The authors and editor of this book wish to motivate people, especially under-graduate students, to get involved with the interesting field of robotics and mechatronics. We hope that the ideas and concepts presented in this book are useful for your own work and could contribute to problem solving in similar applications as well. It is clear, however, that the wide area of automation and robotics can only be highlighted at several spots but not completely covered by a single book

A review of advances in pixel detectors for experiments with high rate and radiation

The Large Hadron Collider (LHC) experiments ATLAS and CMS have established hybrid pixel detectors as the instrument of choice for particle tracking and vertexing in high rate and radiation environments, as they operate close to the LHC interaction points. With the High Luminosity-LHC upgrade now in sight, for which the tracking detectors will be completely replaced, new generations of pixel detectors are being devised. They have to address enormous challenges in terms of data throughput and radiation levels, ionizing and non-ionizing, that harm the sensing and readout parts of pixel detectors alike. Advances in microelectronics and microprocessing technologies now enable large scale detector designs with unprecedented performance in measurement precision (space and time), radiation hard sensors and readout chips, hybridization techniques, lightweight supports, and fully monolithic approaches to meet these challenges. This paper reviews the world-wide effort on these developments.Comment: 84 pages with 46 figures. Review article.For submission to Rep. Prog. Phy

Design and manufacture of a universal mechanical human joint simulator

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.The work performed in this thesis involves the study of human hip joint kinematics and load analysis. Such analyses are very useful for investigating mobility and natural functionality as well as the variation in motion due to replacement implants. The objective of this study is to design, build and testing of a universal human joint simulator that is configurable to hold several human joints and easily programmable to create the required motion. This was performed by creating a Stewart Platform, which is capable of moving in all six degrees of freedom; the maximum number needed by any human joint. Many specific human joint simulators are available on the market for simulating all major human limbs. These are used for wear testing replacement joints by using high load repetitive motion. These systems have a predetermined limit degree of movement and are very expensive; if one wanted to emulate another joint, one would have to purchase a whole new system. This novel system compromises of a three-phase power supply, Control Area Network with six actuators and drivers, a force reading clamp with strain gauges and data logger. A user friendly computer program was developed that is able to derive joint movement data from two inputs and replicating the movement by driving the platform, as well as recording force and displacement data from the joint. The product would be marketed towards biomechanical researchers and implant designers. Verification of this system was performed by simulating the human hip joint. A known combination of kinematic and force data were inputted into the system for nine different types of activities. The resultant force and joint centre displacement was then compared to see how well the system perform in comparison to the inputted data from a previous study. The outcome of this project is a fully functional machine and configurable program that can create movement data at varying speeds and body weights; which is also able to drive the human joint simulator. The design also costs a fraction of any industrial joint simulator. It is hoped that the simulator will allow easier study of both the kinematics and load analysis within the human joints, with the intent on aiding investigation into mobility and functionality; as well as variation in motion caused by a replacement implant

Advanced High Efficiency Architectures for Next Generation Wireless Communications

L'abstract è presente nell'allegato / the abstract is in the attachmen

Design and fabrication of a long-life Stirling cycle cooler for space application. Phase 3: Prototype model

A second-generation, Stirling-cycle cryocooler (cryogenic refrigerator) for space applications, with a cooling capacity of 5 watts at 65 K, was recently completed. The refrigerator, called the Prototype Model, was designed with a goal of 5 year life with no degradation in cooling performance. The free displacer and free piston of the refrigerator are driven directly by moving-magnet linear motors with the moving elements supported by active magnetic bearings. The use of clearance seals and the absence of outgassing material in the working volume of the refrigerator enable long-life operation with no deterioration in performance. Fiber-optic sensors detect the radial position of the shafts and provide a control signal for the magnetic bearings. The frequency, phase, stroke, and offset of the compressor and expander are controlled by signals from precision linear position sensors (LVDTs). The vibration generated by the compressor and expander is cancelled by an active counter balance which also uses a moving-magnet linear motor and magnetic bearings. The driving signal for the counter balance is derived from the compressor and expander position sensors which have wide bandwidth for suppression of harmonic vibrations. The efficiency of the three active members, which operate in a resonant mode, is enhanced by a magnetic spring in the expander and by gas springs in the compressor and counterbalance. The cooling was achieved with a total motor input power of 139 watts. The magnetic-bearing stiffness was significantly increased from the first-generation cooler to accommodate shuttle launch vibrations