05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
Browse
20 results
Search Results
Item Open Access Active electronic loads for radiometric calibration(2017) Weissbrodt, Ernst; Kallfass, Ingmar (Prof. Dr.)Although radiometer systems are widely applied in very different fields, they all have one important requirement in common: They require a thorough radiometric calibration. Various conventional calibration references are well established, but their bulkiness, high power consumption, and complexity are limiting the expanding fields of application. Since novel industrial applications such as passive millimeter-wave imaging emerge, the requirements for calibration references have increased drastically. But also in scientific fields like radio astronomy, cosmology or environmental monitoring, modern remote sensing radiometers do not rely only on conventional references anymore. In this work, millimeter-wave monolithic integrated circuits (MMICs) based on metamorphic high electron mobility transistors (mHEMT) were designed to be used as active electronic loads for radiometric calibration. These novel references have not only the outstanding property, that they can be directly integrated on chip-level into the radiometer front-end, but also, that they can exhibit cold as well as hot reference noise temperatures. Since this is achieved without any physical cooling or heating, the power consumption is notably reduced. By monolithic integration of field effect transistor (FET) switches, theses multiple references can internally be routed to the receiver input without any mechanical wear. As a result, laborious external references can be omitted and the repetition rate of the calibration procedure increased, which results in a higher radiometric accuracy and allows a more compact and cost-effective design of modern radiometer systems. This work presents the first radiometric calibration front-end that allows to internally switch between active electronic cold and active electronic hot loads, as well as a passive ambient load. All components are integrated on a single MMIC, and a patent was granted for this innovation. To predict the achievable noise temperatures of active cold loads (ACLs), different simulation approaches were previously published. This work evaluates and adapts these existing approaches to design and manufacture several W-band loads. But the required design-flow was found to be very time-consuming because multiple iterations are necessary to successively design and optimize the input- and output matching networks, and to finally achieve the desired low noise temperature. Therefore, a novel simulation approach is introduced that makes efficiently use of modern optimization algorithms and the very accurate model library of the mHEMT technology and the passive structures. With this novel simulation method, the first active hot loads (AHLs) were designed as well as state-of-the-art ACLs up to 140 GHz. However, the characterization of low-noise one-port devices is particularly challenging, especially at such high frequencies. Hence, a substantial part of this work is to investigate the reliability of different noise measurement setups and the repeatability of noise temperature results. Dedicated setups in W- and D-band are used to characterize all manufactured active loads and some selected results are cross-checked by measuring the same circuits with independently designed measurement systems of other research facilities. The discrepant results are discussed, concluding that high variations in measured one-port noise temperature do not allow to rely on one single measurement setup. At the same time, this thorough investigation and comparison permits to establish an accuracy range within which the results of the manufactured active electronic loads are reliable, whereas other previously published ACLs are typically only measured with one measurement setup.Item Open Access Radiation mitigation techniques for EIVE satellite mission payload computer(2022) Bischof, TobiasDie Satellitenmission ’Exploratory In-orbit Verification of an E/W-band link’ (EIVE) demonstriert die breitbandige Datenübertragung von der niedrigen Erdumlaufbahn zur Erde mit Datenraten von bis zu 15 Gbits−1.Umden korrekten Betrieb des EIVE-Satelliten sicherzustellen und die Strahlungseinwirkungen auf die Schaltung von EIVE zu reduzieren, sind Strahlungsminderungstechniken für den Nutzlastcomputer erforderlich. Daher untersucht diese Arbeit die Strahlungsminderungstechniken, Mechanismen für den Schutz des FPGA-Konfigurationsspeichers und implementiert robuste Kodierungsmechanismen der E/W-Band-Validierungsdateien. Die Untersuchungen und die implementierten Ansätze stehen dabei im Einklang mit den Leistungsbeschränkungen der Mission.Item Open Access Digital self-interference cancellation using FPGA for in-band full-duplex radios(2023) Roge, Swapnil SunilConventionally, the transmission and the reception of signals in a particular wireless communication system is performed using the half-duplex method, wherein the transmitter and the receiver signals are either time-multiplexed or frequency-multiplexed. However, in case of an in-band full-duplex system, the bidirectional communication of signals is performed simultaneously in the same frequency band, which improves the spectral efficiency of these systems by a factor of two as compared to the traditional half-duplex systems. Therefore, the in-band full-duplex communication systems can double the data rate provided by the half-duplex communication systems, thereby making the former a matter of interest across the wireless research community. However, the in-band full-duplex systems have theirownset of disadvantages. The major challenge is the self-interference imposed by the high-power transmitter signal on the incoming low-power receiver signal, which further degrades the latter and negatively impacts its estimation. Out of the various methodologies to mitigate the self-interference from the receiver signal, this work focuses on the digital self-interference cancellation techniques. In this thesis, the effects of the self-interference signal on the receiver signal are examined. Furthermore, the different digital self-interference cancellation methods employed for suppressing the self-interference are comparatively analysed. Finally, the field-programmable gate array based implementation of the various digital self-interference cancellation algorithms and their respective performance results are presented as well.Item Open Access Novel characterization techniques for the study of the dynamic behavior of silicon carbide power MOSFETs(2022) Salcines, Cristino; Kallfass, Ingmar (Prof. Dr.-Ing.)This dissertation provides insight into the dynamic behavior of SiC power MOSFETs from their inherent static IV and CV characteristics. While conventional dynamic measurements extracted from a DPT or a similar dynamic test-bench yield accurate quantitative data, the static IV and CV characteristics of a power semiconductor device offer more qualitative information to delve into the root mechanisms responsible for its dynamic behavior. Conventional characterization techniques are limited to power levels way below those which the power device withstands in the application. As a result, the static IV and CV characteristics attained by available measurement solutions are reduced to a limited scope of bias conditions insufficient to infer information about the dynamic behavior of the power device. This work tackles this gap and proposes novel measurement techniques that enable the characterization of the static IV and CV characteristics of SiC power MOSFETs at the full range of bias conditions the power device goes through in the application. Iso-thermal IV characteristics of a commercially available SiC power MOSFET are measured up to 40 kW power (instantaneous 50 A and 800 V) at junction temperatures ranging from 25°C to 175 °C. The CV characteristics are mapped at drain-source and gate-source bias combinations of VDS = 0 - 40 V and VGS = 0 - 20 V, respectively, at junction temperatures ranging from 25°C to 150 °C. The results of these measurements reveal unique insights into the electrical characteristics of SiC power MOSFETs which impact their performance in the application and explain unclear phenomena observed in their dynamic behavior. On the one hand, the intrinsic capacitances of the SiC power MOSFET extend their non-linearity, function of both VGS and VDS, to the saturation region of the power device. Moreover, they are also affected by the junction temperature of the power device. The impact of these in the voltage commutation speed of the device under different switching conditions is thoroughly analyzed in the thesis. On the other hand, the IV characteristics of the SiC power MOSFET reveal the existence of short channel effects that drastically affect the transconductance of the power device in its high voltage saturation region. Furthermore, the measurements show a positive temperature coefficient of the drain current in the high voltage saturation region of the SiC power device, attributed to the density of trap energy states in the SiC/SiO2 interface. These effects effectively lower the plateau voltage of the device and lead to faster current commutation speeds in the application than those expected from the datasheet values. The insights revealed by the proposed characterization techniques are intended to help fine-tune semiconductor technology processes and improve the accuracy of simulation models to achieve a higher grade of optimization in the design of future SiC-based energy conversion circuits.Item Open Access FPGA implementation of an energy-efficient real-time image compression algorithm for the EIVE satellite mission(2021) Wiewel, FlorianIn this thesis three commonly used image compression algorithms are analyzed in terms of computational complexity, rate-distortion performance and execution time in order to find the most suitable basis for the implementation of an energy-efficient and real time image compression algorithm for the EIVE satellite mission. The selected algorithm is than modified to reduce its complexity while keeping its performance at a comparable level to the base algorithm. Afterwards the algorithm is implemented in the programmable logic part of a Xilinx Zynq UltraScale+ MPSoC device. Finally, the performance of the algorithm implemented on hardware is determined and compared to the performance of an implementation using a high-level scripting language and the performance of its base algorithm.Item Open Access Design of frequency-converting monolithic integrated circuits for millimeter-wave applications(2022) Grötsch, Christopher; Kallfass, Ingmar (Prof. Dr.-Ing.)This thesis focuses on how to efficiently utilize the low terahertz spectrum in the frequency range from 220 to 325 GHz, also called H-band. This work presents an introduction on several techniques necessary for designing frequency-converting monolithic millimeter-wave integrated circuits for this frequency range. Six different frequency-converter MMICs in a 35 nm gate-length InGaAs mHEMT technology are presented: a nonlinear resistance up- and down-converter, a dual-gate up and down-converter, a gate-pumped transconductance up-converter and a half Gilbert cell up-converter. Each design is explained in detail, their advantages and their disadvantages are evaluated. Three examples will be given where a selection of the frequency-converter architectures are integrated with other functional stages like frequency multipliers and amplifiers to form a millimeter-wave transceiver: a highly linear FMCW radar receiver with a 50 GHz bandwidth, a heterodyne communication receiver facilitating multi-channel transmissions with carrier aggregation at W-band and a homodyne communication receiver with an integrated antenna for low-cost assembly on a PCB. Thereby, this thesis provides insight into the design considerations of terahertz frequency converters, the trade-off of different circuit architectures and topologies for certain applications, the obstacles that can occur during their development and approaches to overcome them.Item Open Access Sensorfusion auf Basis maschinellen Lernens zur Bestimmung der Sperrschichttemperatur(2024) Kuderna Melgar, DiegoDie genaue Bestimmung der Sperrschichttemperatur spielt eine elementare Rolle bei der Optimierung der Leistungsfähigkeiten sowie der Zuverlässigkeit von SiC (Silicon Carbide)-Leistungsmodulen. Im Rahmen der indirekten Bestimmung der Sperrschichttemperatur lassen sich Temperature Sensitive Electrical Parameters (TSEPs) einsetzen, die jedoch neben der Sperrschichttemperatur weitere Abhängigkeiten von elektrischen Größen aufweisen. Dies kann zu einer ungenauen Schätzung der Sperrschichttemperatur führen, weshalb diese Bestimmung robuster gestaltet werden muss. Ein Ansatz, um dies zu erreichen, stellt die Kombination mehrerer TSEPs dar, die im Anschluss mithilfe einer KI auf einem Mikrocontroller verarbeitet werden. In dieser Arbeit werden zwei unterschiedliche Ansätze aufgezeigt, um anhand von maschinellen Lernens die Sperrschichttemperatur eines Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) auf Basis von TSEPs zu bestimmen. Hierzu werden die Werkzeuge NanoEdgeAI Studio sowie X-CUBE-AI eingesetzt, um die entwickelten Modelle auf einem STM32 Mikrocontroller zu implementieren. Ein Vergleich beider Ansätze zeigt, dass NanoEdgeAI Studio Modelle mit effizienterer Nutzung der Ressourcen des Mikrocontrollers ermöglicht. Im Gegensatz dazu erreichen in Python entwickelte Modelle in Kombination mit X-CUBE-AI ohne Quantisierung präzisere Schätzungen bei größerem Speicherbedarf. Im Kontext der Arbeit werden diverse Untersuchungen durchgeführt, um die Schätzgenauigkeit der betrachteten Modelle zu maximieren. Dazu gehören Ensemblebildung und Trainingsprozesse mit unterschiedlich großen Datensätzen sowie die Variation der Anzahl der Eingabesignale. So lässt sich zeigen, dass sich durch Bildung von Ensembles der R-Squared-Wert bei gleichzeitiger Reduktion des maximalen Fehlers erhöhen lässt. Durch Vergrößerung des Datensatzes lässt sich dieser Wert ebenfalls anheben und eine Steigerung durch die Kombination von TSEPs ist beobachtbar. Die realisierten Algorithmen erzielen unabhängig von der Qualität der gemessenen Signale höhere R-Squared-Werte als der traditionelle Ansatz, der lediglich einen elektrischen Parameter für die Schätzung der Sperrschichttemperatur einsetzt. Dieser beträgt 97,9% und der maximale Fehler weist einen Wert von 14K auf. So lässt sich durch die Kombination sämtlicher TSEPs ein Random Forest in NanoEdgeAI Studio entwickeln, der einen R-Squared-Wert von 99,03% erzielt, was einem Zuwachs von 1,13 Prozentpunkten entspricht. Überdies bemisst der maximale Fehler 8K, was 6K unter dem maximalen Fehlers des konventionellen Ansatzes liegt. Zusätzlich ermöglicht dieses Vorgehen die Bestimmung weiterer Parameter, exemplarisch lässt sich der Laststrom nennen.Item Open Access A comparison of system architectures for wireless links in the terahertz band(2022) Dan, Iulia; Kallfass, Ingmar (Prof. Dr.-Ing.)This thesis shows an in-depth analysis of two system architecures used for future terahertz communication systems. For each architecture wireless data transmissions are carried out based on analog frontend devices that use that particular architecuture. The performance of the links is compared and the structure of the wireless links is described in detail and analyzed.Item Open Access Evaluation and characterization of a reduced-bandwidth sampling system for predistorting broadband E-Band communication links(2021) Bleickert, SimonToday’s communication link modulation formats, such as 5G New Radio or wideband Code Division Multiple Access (CDMA), require highly linear Radio Frequency (RF) front-ends to allow for sufficient bandwidth and efficient transmissions. Power Amplifiers (PAs) are the communication link’s predominant nonlinear component. To avoid nonlinear behavior, PAs have to be operated in back-off in terms of PA input power. However, limiting the PA’s input power reduces the available bandwidth and leads to PA inefficiency. If PA’s linear amplification region would be higher, efficiency could be improved. One approach to compensate for PA nonlinearity is Digital Predistortion (DP). However, broadband DP puts high demands on the Analog-to-Digital Converters (ADCs) in terms of sampling rate. Therefore, costly broadband ADCs are required. To address this issue, the Institute of Robust Power Semiconductor Systems (Institut für Robuste Leistungshalbleitersysteme, ILH) developed a low-cost Printed Circuit Board (PCB) that claims to be suitable for sampling 2.5GHz baseband signals and therefore allowing for DP. This is achieved by downconverting and by sampling the broadband input signal in individual and narrowband frequency windows using a frequency mixer. In this study, it was investigated, whether the new PCB is capable of downconverting and sampling of 2.5GHz bandwidths for a satellite communication link. During testing, it was found that the hardware is not capable of sampling broadband signals due to a missing filter. Nevertheless, it was possible to sample a bandwidth of 700MHz by adding filters manually. This implies, that the concept of sampling a broadband signal using low-cost components works. However, in this thesis only the PCB and its sampling capabilities were examined and no DP was performed. Future studies might successfully develop and verify DP using low-cost, broadband downconverting and sampling PCBs. Such PCBs could be beneficial in predistorting broadband satellite communication links.Item Open Access Search algorithm for the ground station antenna of the EIVE satellite(2023) Erdogan, Mustafa EfeSatellite technologies have rapidly become integral to modern life, used for broadcasting, navigation, communication, and Earth observation. As technology advances, satellites generate increasingly large volumes of data, presenting hardware challenges in terms of data storage and transmission due to limited power sources. To meet the escalating demand for high-capacity channels with high data rates, the EIVE project was initiated to explore the feasibility of using E-band frequencies (71-76 GHz) for satellite communication. EIVE, led by the University of Stuttgart in collaboration with various partners, aims to test data transfer capabilities in this uncharted frequency range. A key challenge is the establishment of a communication link between a ground station antenna and the LEO satellite in the EIVE project. This task is compounded by the ground station’s Cassegrain antenna with a narrow HPBW of 0.23° and a low achieved scanning area because of the LEO. To address these challenges, this research thesis introduces a CONSCAN based search algorithm, which expands the antenna’s scanning area by executing conical patterns around the satellite’s estimated trajectory. By using quaternion rotations and the Orekit library for trajectory estimation, this algorithm significantly enhances the search capabilities, increasing the scanning area in the sky. Furthermore, the research highlights the importance of continuous signal acquisition from the satellite for the planned data transfers. To tackle this issue, the groundwork for a tracking algorithm based on theMMTmethod is introduced to provide precise measurements of the satellite’s position, combining the MMT method with Kalman filters and GPS based methods. This novel method promises the improvement of the accuracy and stability of the system.