The convergence of sensory signals plays an important role in perception. Two cases of convergence are examined in this thesis by means of modelling; the case when the converging signals are congruent, which leads to combination and an enhancement of perception, and the case when they are incongruent.The former modelling experiment considers the integration of phonemes and letters. Based on a series of reports on different aspects of letter-phoneme integration that has been presented from the Department of Cognitive Neuroscience at Maastricht University in the Netherlands we have developed a model for simulating some features of this course of events. Our model, the Artificial Cortical Network (ACN), is an artificial neural network whose essential parts are two types of modules, each employing its own learning law, none requiring manual intervention. The particular ACN architecture used in this thesis consists of three modules which are interconnected, where each module processes one of three different types of pre-processed stimuli: letters, phonemes and the bimodal combination of these. Modules of this architecture contain one or more neural lattices and inter-module information exchange is carried out using the coordinates of the neurons that respond the strongest to the inputs. The model is generally useful; it is, for example, equally suitable for modelling the integration of different features in a single modality, and the ideas behind it are new. The main features modelled using the architecture, are the combination of unimodal signals at the bimodal module and feedback from the bimodal to the auditory module. Simulation results of the architecture show the same characteristics as corresponding results from psychology and neuroscience. One important result is the qualitative enhancement of the response to a noise-perturbed sensory signal in one modality using a congruent one from a complementary modality. This is what happens at the opera when the libretto is shown above the scene: one better perceives what is sung. Another is the ability to use input to one modality as support for distinguishing the relevant signal from a collection of signals in another modality. This mechanism is most probably active when having a conversation at a cocktail, on the bus or in the subway. In these situations the (possibly unconscious) monitoring of the communicating peer's mouth movements may improve comprehension. The latter modelling experiment considers a case when integration "fails" due to irreconcilable incoming signals. The particular phenomenon under examination is that of binocular rivalry: the alternating periods of dominance and suppression occasioned by stimulation of corresponding retinal areas with dissimilar monocular stimuli. Typically an observer only "sees" one stimulus at a time and the rate of recurrence is about 1-2 seconds on average. The switching that occurs has some well established properties; such as a skewed unimodal distribution of dominance times and an increase of switching speed with stimulus contrast. In this thesis an artificial neural network model of a cortical area in which competition between populations of neurons that should not be co-active is presented. The focus of the model is for it to be able to simulate key properties of binocular rivalry; the skewed unimodal distribution of dominance times, and three other well-known properties of binocular rivalry. These properties are Levelt's second and fourth proposition and the "flipped" case of Levelt's second proposition. The essential driving forces in this architecture are fatigue and noise. Simulation results obtained from the model are in fair quantitative agreement with psychophysical experiments in all four aspects, using the same model parameters.

For millions of visually impaired individuals worldwide, independent navigation is a major challenge. The white cane can be used to avoid obstacles close-by, but it does not aid in navigation as it is difficult to get a large-scale view of the environment. Technological aids have been developed, notably ones based on GPS, but they have not been widely adopted. This thesis approaches the problem from different perspectives. Firstly, current navigation aids are examined from a user-interaction perspective, leading to some design guidelines on how to present spatial information non-visually. Secondly, a prototype of a new navigation aid (the Virtual White Cane) is proposed, and a field trial with visually impaired participants is described. The idea behind the Virtual White Cane is to utilise the intuitive way humans avoid obstacles by touch, and specifically to leverage the experience white cane users already have. This is accomplished by scanning the environment with a laser rangefinder, and presenting the range information using a haptic interface. The regular white cane is easy to use because it behaves like an extended arm, and so does the Virtual White Cane, albeit working at a much greater distance than the regular cane. A field trial with six experienced white cane users was conducted to assess the feasibility of this kind of interaction. The participants carried out a trial procedure where they traversed a prepared environment using the Virtual White Cane. They did not receive extensive training prior to the trial, the point being that if the Virtual White Cane behaves like a regular one, it should be quick to learn for a white cane user. The results show that spatial information can be feasibly conveyed using a haptic interface. This is demonstrated by the ease with which the field trial participants familiarised themselves with the system, notably adopting a similar usage pattern. In interviews that were conducted following the trial procedures, the participants expressed interest in the idea and thought that being a white cane user helped them use the Virtual White Cane. Despite knowing how to operate the system, the participants found locating objects to be difficult. An extended training period would likely have made this easier, but this problem could also be lessened by understanding what model parameters (such as the length of the virtual cane) should be used. / Seende rullstol

Brains and computers represent and process sensory information in different ways. Bridgingthat gap is essential for managing and exploiting the deluge of unprocessed andcomplex data in modern information systems. The development of brain-like computersthat learn from experience and process information in a non-numeric cognitive way willopen up new possibilities in the design and operation of both sensor and informationcommunication systems.This thesis presents a set of simple computational principles with cognitive qualities,which can enable computers to learn interesting relationships in large amounts of datastreaming from complex and changing real-world environments. More specifically, thiswork focuses on the construction of a computational model for analogical mapping andthe development of a method for semantic analysis with high-dimensional arrays.A key function of cognitive systems is the ability to make analogies. A computationalmodel of analogical mapping that learns to generalize from experience is presented in thisthesis. This model is based on high-dimensional random distributed representations anda sparse distributed associative memory. The model has a one-shot learning process andan ability to recall distinct mappings. After learning a few similar mapping examplesthe model generalizes and performs analogical mapping of novel inputs. As a majorimprovement over related models, the proposed model uses associative memory to learnmultiple analogical mappings in a coherent way.Random Indexing (RI) is a brain-inspired dimension reduction method that was developedfor natural language processing to identify semantic relationships in text. Ageneralized mathematical formulation of RI is presented, which enables N-way RandomIndexing (NRI) of multidimensional arrays. NRI is an approximate, incremental, scalable,and lightweight dimension reduction method for large non-sparse arrays. In addition, itprovides low and predictable storage requirements, and also enables the range of arrayindices to be further extended without modification of the data representation. Numericalsimulations of two-way and ordinary one-way RI are presented that illustrate whenthe approach is feasible. In conclusion, it is suggested that NRI can be used as a tool tomanage and exploit Big Data, for instance in data mining, information retrieval, socialnetwork analysis, and other machine learning applications.

The usage of Global Navigation Satellite Systems (GNSS) in general and the American GPS in particular increases everyday and so does the number of applications where it is used. The GNSS receivers relies on receiving signals from satellites orbiting the earth at an altitude of about 20 000 km and the signals received by the receiver are signicantly weaker then the background noise. Due to the weak signals it is fairly easy to intentionally or accidentally make it very hard or even impossible for a receiver to detect and track the satellites.With this in mind there is a need to develop cost eective methods to detect and localize interference so that appropriate counter measures can be taken. A number of methods have been proposed to detect and localize these sources. The complexity of these methods ranges from requiring future cellphones to contain software to monitor the GNSS environment to dedicated systems with multiple antennas and complicated hardware. In this thesis, two complementary methods will be presented which can detect and also localize interference in the GNSS bands using minimum amount of equipment. The equipment is based around a type of GNSS "receiver" that only samples the GNSS frequency so that it can be processed using a software dened GNSS eceiver. It will be shown that it is capable of detecting and localizing interference sources while also be cost eective and easily deployable. The rst technique is based on measuring the received power level. Since the GNSS signals are below the noise oor, the number of visible satellites will not aect the received power level. Instead the received power level will be aected by changes in the spectrum and changes in the receiver hardware. The GNSS signal is fairly robust against interference so an interferer usually has to have a signicantly higher signal power than the received power from the satellites in order to cause problems for the receiver. By monitoring the received signal power using multiple receivers it is possible to both detect interference and estimate the position of the transmitter. This method requires very little bandwidth but since the signal is measured in the analog domain it is sensitive to process variations between dierent receivers. Also, the nonlinear behaviour of the analog components in the receiver limits the accuracy of the position estimations. To improve the accuracy of the interference localization, a second method has been evaluated. In this method the GNSS samples recorded by dierent receivers at different locations is compared. When a GNSS receiver calculates a position it is actually calculating the time it takes for the signals to travel from the satellite to the receiver. This made it possible to synchronize data from multiple independent receivers both in time and frequency and then estimate the time dierence of arrival of the interfering signal between the dierent receivers. Both localization methods were evaluated during experiments done with assistance from the Swedish armed forces research agency (FOI). It will be shown that the signal power measurement can be used as a detector for interference and that the GPS signal can be used to synchronize data from independent stations so that the dierence in distance to a wideband transmitter can be estimated. To determine the amount of interference in the GPS L1 band two measurement campaigns were made. The rst campaign, measured where interference might be present in an urban area using a car mounted receiver. The other campaign took place at two airports in the summer and fall of 2011 and measured the interference level from xed antennas over an extended period of time.All research was done using the GPS L1 signal but the methods can easily be applied to other GNSS signals as well.

Because failures in power electronics can cause production stops and unnecessary damage to interconnected equipment, monitoring schemes that are able to predict such failures provide various economic and safety benefits. The primary motivation for this thesis is that such monitoring schemes can increase the reliability of energy production plants. Power semiconductors are crucial components in power electronics, and monitoring their temperatures yields information that can be used to predict incipient failures.This thesis presents a system concept for wireless, single-chip, high-temperature monitoring of power semiconductors. A wireless single-chip solution is both cost effective and easy to integrate with existing power semiconductor modules. However, the concept presents two major challenges: the implementation of wireless power and communication, and the low-power design of the temperature sensors. Thus, the feasibility of using on-chip coils to provide communication with and obtain power from an external reader coil is assessed, and a low-power, high-temperature bandgap temperature sensor is developed. The sensor is capable of operating in the high-temperature range, allowing it to be useful for detecting incipient faults, particularly solder faults, at up to 230 °C. This is achieved by compensating for leakage currents that arise in hot reverse-biased p-n junctions, which become significant at these high temperatures.A single-chip, on-chip coil solution provides the combined advantages of galvanic isolation from the power device and simplicity of integration in existing modules. However, as the use of a wireless design with a small on-chip coil will limit the amount of available power, it incurs the disadvantage of requiring a low-power design for the sensor. Initial experiments have been performed on a prototype on-chip coil to assess the feasibility of this concept and provide insight into the challenges of on-chip coil design.In this thesis, focus is placed on the challenge of how to handle large leakage currents in low-power integrated silicon circuits. At high temperatures, these leakage currents can approach or even surpass the level of the circuit's quiescent current. Earlier work on leakage current compensation techniques is examined, compared to and combined with a compensation technique designed to compensate for collector-base leakage in the main bipolar pair of a Brokaw bandgap reference. Experiments show that fully analogue sensors operating at up to 228 °C with an accuracy of 10 °C that consume only 8.2 µW are feasible. If a higher accuracy, such as 3 °C, is required, then a temperature range of up to 200 °C can be achieved with a power consumption of 2.3 µW.It is likely that the high temperature range and low power consumption of the sensors presented in this thesis, in combination with on-chip coils, will make them suitable for use in solder fault prediction in power semiconductor modules.

The three-dimensional view of the world is something that we often take for granted, a phenomenon that has proven challenging for machine vision applications in which description of the environment requires the relative position and motion of different objects in the scene. Currently, range imaging (RIM) measurements are based on digital imaging technology and are merged with the ability to measure the distance to the corresponding object point in each pixel. The distance measurement is based on either the direct or indirect time-of-flight principle. The distance to the corresponding object point in each pixel is directly correlated with time-resolved imaging concerning the measurement of the photon arrival time. This time-resolved image generates a distance image by using the direct time-of-flight technique. This distance image is much more useful than an ordinary picture in regard to measuring and controlling anything, including in the process industry, obstacle detection for automotive safety, navigation, and path planning. The time resolved imaging system consists of two essential building blocks: 1) a photon detector capable of sensing single photons and 2) a fast time resolver or time-to-digital converter that can measure the time of light to picosecond resolution. To address emerging applications, a miniaturized time resolver with acceptable performance and a low cost must be designed that could be integrated with an array of single photon detectors. The goal of this thesis is therefore to investigate, design, and layout a time-to-digital converter to achieve an acceptable cm-level resolution for a range of 10-15 meters. In this thesis, two ideas have been selected for investigation based on their appealing attributes, including their improved resolution, area, and power consumption: 1) an on-pixel time stretcher based on analog time expansion and 2) the combination of the on-pixel time stretcher with a global gated ring oscillator-based time-to-digital converter. Both ideas have been used in conjunction to demonstrate a new architecture for a time-to-digital converter for 3-D time-of-flight measurements. The time stretcher uses analogue time expansion, where the time interval to be measured is stretched by a factor k. This is achieved by charging a capacitor with a constant current I, followed by discharging the capacitor by a current I/k . To achieve an acceptable linearity and constant current generation, wide swing cascode current source/sinks have been used. An idea to build precisely matched current mirror as a time stretcher has also been addressed. The final time-to-digital conversion is performed by the gated ring oscillator-based time-to-digital converter. The multiphase gated ring oscillator, which is the heart of time-to-digital converter, is capable of measuring the stretched time interval by counting the full clock cycles and determining the timing positions within the clock cycle. The work has been discussed in light of the previous research by designing circuits, performing layouts, simulating and conducting parasitic extractions in a 0.35 μm CMOS process. Based on simulations and results, a prototype of an integrated time-to-digital can be built to achieve a cm-level distance error.

At present, induction motors are controlled via the so-called variable-frequency drives (VFD) that allow to control the speed for the motors. The purpose of this PhD thesis is to improve electromagnetic modeling techniques for the study of conducted electromagnetic emissions in variable-frequency drives, with the aim of enhancing their reliability in energy production plants. Pulse-width-modulated voltage converters are used to feed an AC motor, and they are considered to be the primary reason for high-frequency effects in both the motor and the supply grid. In particular, high-frequency currents, known as common mode currents, flow between all energized components and the ground and travel via low-resistance and low-inductance interconnects such as the power cable between the inverter and the motor.Electrically long power cables are commonly used in VFD installations, and require particular attention. Accurate models can be obtained using the theory of multiconductor transmission lines. In the case of nonlinear terminations, such as an inverter, only time-domain analysis is possible. In recent years, several techniques have been proposed. Some of these techniques include the lumped-element equivalent circuit method, the method of characteristics (MoC) and its generalizations, and the Pad´e approach. In this context, a modeling technique based on Green’s functions has been proposed. The input/output impedance matrix is expressed as a rational series, whose poles and their residues are identified by solving algebraic equations. The primary disadvantage of this method lies in the large number of poles that is typically necessary to model the dynamics of the system, especially when electrically long interconnectsare considered. To overcome this limitation, we have proposed the Delay-Rational Green’s-Function-based Method, abbreviated as DeRaG. In this method, the line delay is extracted and, by virtue of suitable mathematical manipulation of the rational series, is incorporated through hyperbolic functions. The delay extraction enables the use of a reduced number of poles and improves the accuracy of the model in general, avoiding any ringing effects in the time-domain response. The primary advantage of the proposed method compared with other well-known techniques lies in the delayed state-space representation. The obtained model can be computed regardless of the terminations and/or sources, and the terminal conditions can be immediately and essentially incorporated.The next step will be to simulate the entire inverter-cable-motor system. The partial element equivalent circuit (PEEC) technique will be used to model the interconnects as well as the discontinuities in the power cable that can be caused, for example, by switch disconnectors. The theoretical results will be verified against experimental measurements. The final objective is to provide new techniques for modeling the electrodynamics of variable-frequency drives to allow their complete EMC assessment as early as the design stage and to enable the planning of corrective actions in advance. / Frekvensomriktares funktion i beredskapskritiska system

Radio frequency identification (RFID) technology is used today in a number of differentareas, such as logistics, supply chain management, access control and environmentalmonitoring. The ability to store information electronically in small tags that can be readwirelessly has great potential. Recently, research on RFID technology has focused onsensor-tags, localization techniques, antennas and propagation, data security, communicationprotocols and circuit design for the tags and the readers.In a typical RFID system, a passive tag is powered up remotely by a radio frequencysignal sent from a reader unit. The RF signal received by the tag antenna is convertedto a DC-supply voltage in the rectifier in the analog front-end of the tag. To avoid lossin the rectifying operation, low-voltage Schottky diodes are often used in a multi-stagerectifier. However, using Schottky diodes is not cost-efficient because these diodes mustbe designed in advanced semiconductor processes. Because one of the demands on futureRFID technology is to reduce the cost, efficient rectifiers that can be integrated in alow cost semiconductor process is highly desirable. For this reason, different rectifiers instandard CMOS has been proposed.This thesis discuss recent work as well as present new ideas on rectifiers in CMOSthat have the potential to replace Schottky diodes in low-power, multistage rectifiers formagnetically coupled RFID systems. As a brief summary of this thesis, Part I includesa theoretical analysis of the RF to DC generation block. The analysis illustrates howdifferent properties, such as voltage and power conversion efficiency of the rectifier, the Qfactor of the resonance circuit and coupling coefficient between coil antennas, affect thetag DC generation. In Part II, paper A discusses the limitations with the CMOS crossconnectedbridge rectifier and proposes a modified bridge with active diodes to improverectifier performance. The proposed bridge was manufactured, and an evaluation ofthe chip show good agrement between simulated and measured performance. Paper Bpresents a theoretical model for diode connected MOS transistors with internal thresholdcancelation (ITC), as well as a design procedure that describes how to optimize a rectifierbased on MOS ITC diodes. In Paper C a highly efficient active MOS diode is presentedthat can be used in multi-stage low-power rectifiers. In addition, this study shows thatactive diodes in CMOS can be designed to have a diode voltage drop below 100 mV thatconsumes a small amount of μW. These results are promising in the improvement andcost reduction of inductively coupled RFID systems.The work in this thesis has shown that highly efficient RF to DC conversion can beachieved in CMOS rectifiers for low power applications. New techniques in CMOS havebeen demonstrated with the potential to replace Schottky diodes in RFID rectifiers. / ESIS

Printed Wiring Board (PWB) and Printed Circuit Board Assembly (PCBA) testing aims to ensure an error free board after the etching and the assembly processes. After the etching process, several types of errors might occur such as opens and bridges, which are already, showstoppers in Direct Current (DC) applications. Mouse bites, spurs and others such as weak traces, which can be problematic in Radio Frequency (RF) and high-speed signals applications. Loading expensive component on defective boards can be economically catastrophic especially for high volume production. The rule of ten which has been reported by the production experts says that the defect costs ten times when detected in the next testing phase. Bare board also needs to be tested for the characteristic impedance correctness due to the process variations and the compounding raw material tolerances that can cause characteristic impedance mismatches. Although testing the characteristic impedance is not in interest in some application, sampling the characteristic impedance for a specific design is one way to test the manufacturing process stability for better tuning, otherwise PWBs might differ from each other even within the same batch. In addition to the possibility of defective PWB, the assembly process is never perfect to achieve 100 % of PCBA yield due to the possible errors in the process steps such as paste application, pick and place operations and soldering process which might lead to bridges, opens, wrong or miss oriented components.For low volume production, flying probes test technology is cost efficient as compared to bed-of-nails. The performance of the flying probes system depends on the test algorithm, the mechanical speed and the number of probes. To reduce the initial and maintenance costs of the probing technology and to accelerate the test time, Paper A introduces a new indirect method to test PWB continuity and isolation testing using a single probe for testing both continuity and isolation at the same time. RF signal is injected into the trace under test, instead of a DC current. The phase shift between the incident and the reflected signals is measured as it carries the information about the correctness of the trace when compared with a reference value of the same trace in the correct board. The method shown an important capability for detecting PWB defects such as as opens, DC and RF bridges, exceeded and different width lines. The margin in the measurement between a defective and a correct board, which depends on the type of the defect, is about 7 % to 68 %. Applying this approach to PCBA testing led to significant margins between correct and defective interconnect. The test cases in paper C shown 40 % and 33 %. Moreover, this margin has been proven to be important even for short microstrip line, which intended to connect two typical IC pins. This technique is strongly recommended to be applied to PCBA testing where probing is feasible. The approach can be applied to the complete layout testing or to boost a test strategy whose test solutions are not covering 100 % of the possible defects.By applying this test solution to bed-of-nails equipment, 50 % of the probes will be reduced, on the other hand, for a given design with NI isolated traces and NA adjacent pairs, employing this solution to flying probes system with two probes, leads to the reduction of the number of tests from (NI+NA) tests to NI tests as isolation and continuity are performed in one go. Flying probes system involves mechanical movements, which dominate the test time, reducing the number of the mechanical movements increases dramatically the test throughput. On the other hand, this method is believed to be extremely fast to test the correctness of the characteristic impedance which is prone to variations due to the instability of the PWB manufacturing process, in the same time one could employ the method to evaluate the process stability by checking after each batch of PWBs. Paper B and D provide insight into the impact of the PWB manufacturing variations on the characteristic impedance. Moreover single probe approach is believed to have a good potential for Sequential Build-Up (SBU) interconnects testing where connections between component pads and the upper layers are often impossible to test with the current test technologies.

The pulp and paper industry of today is facing a highly competitive market where manufacturers are constantly seeking ways to reduce costs as well as to improve product specifications and quality. On-line quality control is one of many areas being actively developed, from the wood delivered to the plant to the fibers in the finished product. In general, on-line property measurements are best utilized by establishing an understanding of the underlying physics and using that knowledge in an optimal way to determine the parameter or property sought for. One specific area of development is to determine fiber orientation in a paper sheet. The fiber orientation is set by the production Process and is an important parameter since it defines e.g. strength and Optical properties of the paper. In the paper mill today, improvements can be made if the fiber orientation could be determined on-line and in real time. One way of doing this is to use non-contact, full-optical techniques to determine the light scattering pattern in a paper sheet. The objective of this work is to determine the properties of light scattering in paper and how this knowledge could be utilized in extracting information on the properties of paper.A numerical model utilizing light scattering in a sphere-cylinder medium is presented. The simulated medium can represent scattering in both wood pulp and paper. Wood fibers are represented as long, straight cylinders and smaller particles, like fines, are represented as small spherical particles. Scattering from fibers are determined by an analytical solution of Maxwell’s equations for scattering on infinitely long cylinders. The small spherical particles are described by Mie theory. Fibers can have random orientation as in the case of pulp, or aligned orientation as in paper. The layer-like anisotropic microstructure in paper is considered in the model. The model also employ the Stokes-Mueller formalism for the scattering particles, making the state of polarization possible to track.The effects of varying volume concentration and size of the scattering components on reflection, transmission and polarization of the incident light are investigated. The findings on the differences in depolarization and its spatial distribution opens for techniques that enables the relative proportions of fibers and fines in pulp to be determined.For aligned fiber structures it is shown both theoretically and experimentally that spatially resolved reflectance and transmittance exhibits directional dependence. This information could possibly be used in a robust, rapid and cheap device for on-line characterization in the paper production process.