Systementwicklung und Optimierung eines hochempfindlichen digitalen Magnetfeldsensors

Measurements of extremely weak magnetic fields in unshielded environments require mobile sensors providing a high dynamic range and slew rate. At present, analog Superconducting Quantum Interference Devices (DC-SQUIDs) are favored for applications necessitating a flux resolution within the fT-range. Due to the periodic voltage-flux characteristics those devices exhibit, a flux locked loop is required to keep the sensor in its operation point. The additional electronics lead to a limitation of the dynamic field change (slew rate) and thus of mobility. The present work deals with the Digital-SQUID as an alternative concept to the analog solutions. The sensor works as a counter of magnetic flux quanta. It is based on a delta modulation scheme thus exhibiting a theoretically infinite dynamic range. During this work, a measurement system was developed embedding the integrated circuit that had been designed by Reich/Ortlepp. The measurement system was evaluated using approaches from signal and system theory. The main focus was put on the analysis and optimization of linearity and dynamic range taking into account the effects of noise and non-linear distortion. The reasons for the practical limitation of the dynamic range could hence be identified. Furthermore, the parameters influencing the required properties as well as their mutual interdependence were derived. The comprehensive experimental part of the work validates the theory on the cause-effect relationships. The knowledge gained was used to derive design rules permitting to optimize the system with regard to the required parameters. In addition, further steps necessary for running the sensor in magnetically unshielded environment were introduced and discussed. First measures were already implemented in an improved circuit design. The results of the presented work make an important contribution to the transfer of a laboratory-based magnetic field sensor concept into a measurement system for mobile applications with extremely high sensitivity in magnetically unshielded environments.Hochauflösende mobile Magnetfeldmessungen im unabgeschirmten Erdmagnetfeld stellen hohe Anforderungen an Bandbreite und Dynamikbereich des verwendeten Sensorsystems. Die in Biomedizin und Geoexploration derzeit eingesetzten supraleitendenQuanteninterferometer (DC-SQUID) erreichen eine Auflösung im fT-Bereich, müssen jedoch aufgrund ihrer periodischen Kennlinie mit Hilfe einer Flussregelschleife in ihrem Arbeitspunkt gehalten werden, was zu einer Begrenzung der maximalen Feldänderung und damit der erlaubten Bewegungsgeschwindigkeit führt. Die vorliegende Arbeit beschäftigt sich mit dem alternativen Konzept des Digital-SQUIDs, eines als Flussquantenzähler arbeitenden Magnetfeldsensors, welcher als Delta-Modulator einen theoretisch unbegrenzten Dynamikbereich besitzt. Das von Reich/Ortlepp entwickelte Schaltungskonzept wurde in ein selbst entwickeltes Messsystem eingebettet und unter Zuhilfenahme von Ansätzen aus Systemtheorie und Signalverarbeitung evaluiert. Der Schwerpunkt wurde hierbei auf die Analyse und Optimierung von Linearität und Dynamikbereich unter Berücksichtigung von Rauscheinflüssen und Nichtlinearitäten gelegt. Die Ursachen für die praktische Begrenzung von Auflösung und Dynamikbereich wurden abgeleitet. Des Weiteren wurden die Einflussparameter auf diese Kenngrößen sowie ihre komplexen Wirkzusammenhänge identifiziert und Schlussfolgerungen unter den gegebenen technologischen Rahmenbedingungen gezogen. Der umfangreiche experimentelle Teil der Arbeit bestätigt die erarbeitete Theorie. Aus den gewonnenen Erkenntnissen wurden Entwurfsregeln abgeleitet, welche zur Optimierung des Systems hinsichtlich der geforderten Kenngrößen führen. Darüber hinaus wurden Maßnahmen aufgezeigt und diskutiert, welche für einen Einsatz des Systems im unabgeschirmten Erdmagnetfeld erforderlich sind. Erste Maßnahmen wurden in einem neuen Entwurf bereits implementiert. Das Ergebnis der Arbeit ist ein wichtiger Beitrag zur Überführung des vorliegenden Schaltungskonzepts in ein praktisches hochauflösendes Messsystem zum mobilen Einsatz im Freifeld.Auch im Buchhandel erhältlich: Systementwicklung und Optimierung eines hochempfindlichen digitalen Magnetfeldsensor / Imke Haverkamp Ilmenau : ISLE 2013. -VIII, 120 S. ISBN 978-3-938843-76-

Defect-based testing of LTS digital circuits

A Defect-Based Test (DBT) methodology for Superconductor Electronics (SCE) is presented in this thesis, so that commercial production and efficient testing of systems can be implemented in this technology in the future. In the first chapter, the features and prospects for SCE have been presented. The motivation for this research and the outline of the thesis were also described in Chapter 1. It has been shown that high-end applications such as Software-Defined Radio (SDR) and petaflop computers which are extremely difficult to implement in top-of-the-art semiconductor technologies can be realised using SCE. But, a systematic structural test methodology had yet to be developed for SCE and has been addressed in this thesis. A detailed introduction to Rapid Single-Flux Quantum (RSFQ) circuits was presented in Chapter 2. A Josephson Junction (JJ) was described with associated theory behind its operation. The JJ model used in the simulator used in this research work was also presented. RSFQ logic with logic protocols as well as the design and implementation of an example D-type flip-flop (DFF) was also introduced. Finally, advantages and disadvantages of RSFQ circuits have been discussed with focus on the latest developments in the field. Various techniques for testing RSFQ circuits were discussed in Chapter 3. A Process Defect Monitor (PDM) approach was presented for fabrication process analysis. The presented defect-monitor structures were used to gather measurement data, to find the probability of the occurrence of defects in the process which forms the first step for Inductive Fault Analysis (IFA). Results from measurements on these structures were used to create a database for defects. This information can be used as input for performing IFA. "Defect-sprinkling" over a fault-free circuit can be carried out according to the measured defect densities over various layers. After layout extraction and extensive fault simulation, the resulting information will indicate realistic faults. In addition, possible Design-for-Testability (DfT) schemes for monitoring Single-Flux Quantum (SFQ) pulses within an RSFQ circuit has also been discussed in Chapter 3. The requirement for a DfT scheme is inevitable for RSFQ circuits because of their very high frequency of operation and very low operating temperature. It was demonstrated how SFQ pulses can be monitored at an internal node of an SCE circuit, introducing observability using Test-Point Insertion (TPI). Various techniques were discussed for the introduction of DfT and to avoid the delay introduced by the DfT structure if it is required. The available features in the proposed design for customising the detector make it attractive for a detailed DBT of RSFQ circuits. The control of internal nodes has also been illustrated using TPI. The test structures that were designed and implemented to determine the occurrence of defects in the processes can also be used to locate the position for the insertion of the above mentioned DfT structures