Low-power CMOS digital-pixel Imagers for high-speed uncooled PbSe IR applications

This PhD dissertation describes the research and development of a new low-cost medium wavelength infrared MWIR monolithic imager technology for high-speed uncooled industrial applications. It takes the baton on the latest technological advances in the field of vapour phase deposition (VPD) PbSe-based medium wavelength IR (MWIR) detection accomplished by the industrial partner NIT S.L., adding fundamental knowledge on the investigation of novel VLSI analog and mixed-signal design techniques at circuit and system levels for the development of the readout integrated device attached to the detector. The work supports on the hypothesis that, by the use of the preceding design techniques, current standard inexpensive CMOS technologies fulfill all operational requirements of the VPD PbSe detector in terms of connectivity, reliability, functionality and scalability to integrate the device. The resulting monolithic PbSe-CMOS camera must consume very low power, operate at kHz frequencies, exhibit good uniformity and fit the CMOS read-out active pixels in the compact pitch of the focal plane, all while addressing the particular characteristics of the MWIR detector: high dark-to-signal ratios, large input parasitic capacitance values and remarkable mismatching in PbSe integration. In order to achieve these demands, this thesis proposes null inter-pixel crosstalk vision sensor architectures based on a digital-only focal plane array (FPA) of configurable pixel sensors. Each digital pixel sensor (DPS) cell is equipped with fast communication modules, self-biasing, offset cancellation, analog-to-digital converter (ADC) and fixed pattern noise (FPN) correction. In-pixel power consumption is minimized by the use of comprehensive MOSFET subthreshold operation. The main aim is to potentiate the integration of PbSe-based infra-red (IR)-image sensing technologies so as to widen its use, not only in distinct scenarios, but also at different stages of PbSe-CMOS integration maturity. For this purpose, we posit to investigate a comprehensive set of functional blocks distributed in two parallel approaches: • Frame-based “Smart” MWIR imaging based on new DPS circuit topologies with gain and offset FPN correction capabilities. This research line exploits the detector pitch to offer fully-digital programmability at pixel level and complete functionality with input parasitic capacitance compensation and internal frame memory. • Frame-free “Compact”-pitch MWIR vision based on a novel DPS lossless analog integrator and configurable temporal difference, combined with asynchronous communication protocols inside the focal plane. This strategy is conceived to allow extensive pitch compaction and readout speed increase by the suppression of in-pixel digital filtering, and the use of dynamic bandwidth allocation in each pixel of the FPA. In order make the electrical validation of first prototypes independent of the expensive PbSe deposition processes at wafer level, investigation is extended as well to the development of affordable sensor emulation strategies and integrated test platforms specifically oriented to image read-out integrated circuits. DPS cells, imagers and test chips have been fabricated and characterized in standard 0.15μm 1P6M, 0.35μm 2P4M and 2.5μm 2P1M CMOS technologies, all as part of research projects with industrial partnership. The research has led to the first high-speed uncooled frame-based IR quantum imager monolithically fabricated in a standard VLSI CMOS technology, and has given rise to the Tachyon series [1], a new line of commercial IR cameras used in real-time industrial, environmental and transportation control systems. The frame-free architectures investigated in this work represent a firm step forward to push further pixel pitch and system bandwidth up to the limits imposed by the evolving PbSe detector in future generations of the device.La present tesi doctoral descriu la recerca i el desenvolupament d'una nova tecnologia monolítica d'imatgeria infraroja de longitud d'ona mitja (MWIR), no refrigerada i de baix cost, per a usos industrials d'alta velocitat. El treball pren el relleu dels últims avenços assolits pel soci industrial NIT S.L. en el camp dels detectors MWIR de PbSe depositats en fase vapor (VPD), afegint-hi coneixement fonamental en la investigació de noves tècniques de disseny de circuits VLSI analògics i mixtes pel desenvolupament del dispositiu integrat de lectura unit al detector pixelat. Es parteix de la hipòtesi que, mitjançant l'ús de les esmentades tècniques de disseny, les tecnologies CMOS estàndard satisfan tots els requeriments operacionals del detector VPD PbSe respecte a connectivitat, fiabilitat, funcionalitat i escalabilitat per integrar de forma econòmica el dispositiu. La càmera PbSe-CMOS resultant ha de consumir molt baixa potència, operar a freqüències de kHz, exhibir bona uniformitat, i encabir els píxels actius CMOS de lectura en el pitch compacte del pla focal de la imatge, tot atenent a les particulars característiques del detector: altes relacions de corrent d'obscuritat a senyal, elevats valors de capacitat paràsita a l'entrada i dispersions importants en el procés de fabricació. Amb la finalitat de complir amb els requisits previs, es proposen arquitectures de sensors de visió de molt baix acoblament interpíxel basades en l'ús d'una matriu de pla focal (FPA) de píxels actius exclusivament digitals. Cada píxel sensor digital (DPS) està equipat amb mòduls de comunicació d'alta velocitat, autopolarització, cancel·lació de l'offset, conversió analògica-digital (ADC) i correcció del soroll de patró fixe (FPN). El consum en cada cel·la es minimitza fent un ús exhaustiu del MOSFET operant en subllindar. L'objectiu últim és potenciar la integració de les tecnologies de sensat d'imatge infraroja (IR) basades en PbSe per expandir-ne el seu ús, no només a diferents escenaris, sinó també en diferents estadis de maduresa de la integració PbSe-CMOS. En aquest sentit, es proposa investigar un conjunt complet de blocs funcionals distribuïts en dos enfocs paral·lels: - Dispositius d'imatgeria MWIR "Smart" basats en frames utilitzant noves topologies de circuit DPS amb correcció de l'FPN en guany i offset. Aquesta línia de recerca exprimeix el pitch del detector per oferir una programabilitat completament digital a nivell de píxel i plena funcionalitat amb compensació de la capacitat paràsita d'entrada i memòria interna de fotograma. - Dispositius de visió MWIR "Compact"-pitch "frame-free" en base a un novedós esquema d'integració analògica en el DPS i diferenciació temporal configurable, combinats amb protocols de comunicació asíncrons dins del pla focal. Aquesta estratègia es concep per permetre una alta compactació del pitch i un increment de la velocitat de lectura, mitjançant la supressió del filtrat digital intern i l'assignació dinàmica de l'ample de banda a cada píxel de l'FPA. Per tal d'independitzar la validació elèctrica dels primers prototips respecte a costosos processos de deposició del PbSe sensor a nivell d'oblia, la recerca s'amplia també al desenvolupament de noves estratègies d'emulació del detector d'IR i plataformes de test integrades especialment orientades a circuits integrats de lectura d'imatge. Cel·les DPS, dispositius d'imatge i xips de test s'han fabricat i caracteritzat, respectivament, en tecnologies CMOS estàndard 0.15 micres 1P6M, 0.35 micres 2P4M i 2.5 micres 2P1M, tots dins el marc de projectes de recerca amb socis industrials. Aquest treball ha conduït a la fabricació del primer dispositiu quàntic d'imatgeria IR d'alta velocitat, no refrigerat, basat en frames, i monolíticament fabricat en tecnologia VLSI CMOS estàndard, i ha donat lloc a Tachyon, una nova línia de càmeres IR comercials emprades en sistemes de control industrial, mediambiental i de transport en temps real.Postprint (published version

The LLAB model for quantifying colour appearance

A reliable colour appearance model is desired by industry to achieve high colour fidelity between images produced using a range of different imaging devices. The aim of this study was to derive a reliable colour appearance model capable of predicting the change of perceived attributes of colour appearance under a wide range of media/viewing conditions. The research was divided into three parts: characterising imaging devices, conducting a psychophysical experiment, and developing a colour appearance model. Various imaging devices were characterised including a graphic art scanner, a Cromalin proofing system, an IRIS ink jet printer, and a Barco Calibrator. For the former three devices, each colour is described by four primaries: cyan (C), magenta (M), yellow (Y), and black (K). Three set of characterisation samples (120 and 31 black printer, and cube data sets) were produced and measured for deriving and testing the printing characterisation models. Four black printer algorithms (BPA), were derived. Each included both forward and reverse processes. A 2nd BPA printing model taking into account additivity failure, grey component replacement (GCR) algorithm gave the most accurate prediction to the characterisation data set than the other BPA models. The PLCC (Piecewise Linear interpolation assuming Constant Chromaticity coordinates) monitor model was also implemented to characterise the Barco monitor. The psychophysical experiment was conducted to compare Cromalin hardcopy images viewed in a viewing cabinet and softcopy images presented on a monitor under a wide range of illuminants (white points) including: D93, D65, D50 and A. Two scaling methods: category judgement and paired comparison, were employed by viewing a pair of images. Three classes of colour models were evaluated: uniform colour spaces, colour appearance models and chromatic adaptation transforms. Six images were selected and processed via each colour model. The results indicated that the BFD chromatic transform gave the most accurate predictions of the visual results. Finally, a colour appearance model, LLAB, was developed. It is a combination of the BFD chromatic transform and a modified version of CIELAB uniform colour space to fit the LUTCRI Colour Appearance Data previously accumulated. The form of the LLAB model is much simpler and its performance is more precise to fit experimental data than those of the other models

Investigation into the applications of genetic algorithms to control engineering

Bibliography: pages 117-120.This thesis report presents the results of a study carried out to determine possible uses of genetic algorithms to problems in control engineering. This thesis reviewed the literature on the subject of genetics and genetic algorithms and applied the algorithms to the problems of systems parameter identification and Pl/D controller tuning. More specifically, the study had the following objectives: To investigate possible uses of genetic algorithms to the task of system identification and Pl/D controller tuning. To do an in depth comparison of the proposed uses with orthodox traditional engineering thinking which is based on mathematical optimisation and empirical studies. To draw conclusions and present the findings in the form of a thesis. Genetic algorithms are a class of artificial intelligence methods inspired by the Darwinian principles of natural selection and survival of the fittest. The algorithm encodes potential solutions into chromosome-like data structures that. are evolved using genetic ·operators to determine the optimal solution of the problem. Fundamentally, the evolutionary nature of the algorithm is introduced through the operators called crossover and mutation. Crossover fundamentally takes two strings, selects a crossing point randomly and swaps segments of the strings on either side of the crossover point to create two new individuals. There are three variations of crossover which were considered in this thesis: single point crossover, two point crossover and uniform crossover. It was important that these be given careful consideration since much of the outcome of the algorithm is influenced by both the choice and the amount with which they are applied

Discrimination and control in stochastic neuron models

Major topics of great interest in neuroscience involve understanding the brain function in stimuli coding, perceptive discrimination, and movement control through neuronal activities. Many researchers are designing biophysical and psychological experiments to study the activities of neurons in the presence of various stimuli. People have also been trying to link the neural responses to human perceptual and behavioral level. In addition, mathematical models and neural networks have been developed to investigate how neurons respond and communicate with each other. In this thesis, my aim is to understand how the central nervous system performs discrimination tasks and achieves precise control of movement, using noisy neural signals. I have studied, both through experimental and modelling approaches, how neurons respond to external stimuli. I worked in three aspects in details. The first is the neuronal coding mechanism of input stimuli with different temporal frequencies. Intracellular recordings of single neurons were performed with patch-clamp techniques to study the neural activities in rats somatosensory cortices in vitro, and the simplest possible neural model—integrate-and-fire model—was used to simulate the observations. The results obtained from the simulation were very consistent with that in the experiments. Another focus of this work is the link between the psychophysical response and its simultaneous neural discharges. I derived that under a widely accepted psychophysical law (Weber’s law), the neural activities were less variable than a Poisson process (which is often used to describe the neuron spiking process). My work shows how psychophysical behaviour reflects intrinsic neural activities quantitatively. Finally, the focus is on the control of movements by neural signals. A generalized approach to solve optimal movement control problems is proposed in my work, where pulses are used as neural signals to achieve a precise control. The simulation results clearly illustrate the advantage of this generalized control. In this thesis, I have raised novel, insightful yet simple approaches to study and explain the underlying mechanism behind the complexity of neural system, from three examples on sensory discrimination and neural movement control

Development and evaluation of a haptic framework supporting telerehabilitation robotics and group interaction

Telerehabilitation robotics has grown remarkably in the past few years. It can provide intensive training to people with special needs remotely while facilitating therapists to observe the whole process. Telerehabilitation robotics is a promising solution supporting routine care which can help to transform face-to-face and one-on-one treatment sessions that require not only intensive human resource but are also restricted to some specialised care centres to treatments that are technology-based (less human involvement) and easy to access remotely from anywhere. However, there are some limitations such as network latency, jitter, and delay of the internet that can affect negatively user experience and quality of the treatment session. Moreover, the lack of social interaction since all treatments are performed over the internet can reduce motivation of the patients. As a result, these limitations are making it very difficult to deliver an efficient recovery plan. This thesis developed and evaluated a new framework designed to facilitate telerehabilitation robotics. The framework integrates multiple cutting-edge technologies to generate playful activities that involve group interaction with binaural audio, visual, and haptic feedback with robot interaction in a variety of environments. The research questions asked were: 1) Can activity mediated by technology motivate and influence the behaviour of users, so that they engage in the activity and sustain a good level of motivation? 2) Will working as a group enhance users’ motivation and interaction? 3) Can we transfer real life activity involving group interaction to virtual domain and deliver it reliably via the internet? There were three goals in this work: first was to compare people’s behaviours and motivations while doing the task in a group and on their own; second was to determine whether group interaction in virtual and reala environments was different from each other in terms of performance, engagement and strategy to complete the task; finally was to test out the effectiveness of the framework based on the benchmarks generated from socially assistive robotics literature. Three studies have been conducted to achieve the first goal, two with healthy participants and one with seven autistic children. The first study observed how people react in a challenging group task while the other two studies compared group and individual interactions. The results obtained from these studies showed that the group interactions were more enjoyable than individual interactions and most likely had more positive effects in terms of user behaviours. This suggests that the group interaction approach has the potential to motivate individuals to make more movements and be more active and could be applied in the future for more serious therapy. Another study has been conducted to measure group interaction’s performance in virtual and real environments and pointed out which aspect influences users’ strategy for dealing with the task. The results from this study helped to form a better understanding to predict a user’s behaviour in a collaborative task. A simulation has been run to compare the results generated from the predictor and the real data. It has shown that, with an appropriate training method, the predictor can perform very well. This thesis has demonstrated the feasibility of group interaction via the internet using robotic technology which could be beneficial for people who require social interaction (e.g. stroke patients and autistic children) in their treatments without regular visits to the clinical centres

Low-Power Integrated Circuits For Biomedical Applications

With thousands new cases of spinal cord injury reported everyday, many people suffer from paralysis and loss of sensation in both legs. Beside the healthcare costs, such a state severely deteriorates the patients' quality of life and may even lead to additional medical conditions. Therefore, there is a growing need for cyber-physical systems to restore the walking ability through bypassing the damaged spinal cord. This goal can be achieved by monitoring and processing patient's brain signals to enable brain-directed control of prosthetic legs. Among several existing methods to record brain signals, electrocorticography (ECoG) has gained popularity due to being robust to motion artifacts, having high spatial resolution and signal to noise ratio, being moderately invasive and the possibility of chronic implantation of recording grids with no or minor scar tissue formation. The latest property is of particular importance for the whole system to be a viable fully implantable solution. Furthermore, the implanted system has to operate independently with no or minimal need of external hardware (e.g. a bulky personal computer) to be individually and socially accepted. To implement a fully implantable system, low-power and miniaturized electronics are needed to reduced heat generation, increase battery life-time and be minimally intrusive. These requirements indicate that many of the system's components should be custom-designed to integrated as much functionality as possible in a given real estate. This thesis presents silicon tested prototypes of several building blocks for the envisioned system, namely, ultra low-power brain signal acquisition front-ends, a low-power and inductorless MedRadio transceiver, and a fast start-up crystal oscillator. Brain signal acquisition front-ends provide low noise amplification of weak ECoG biosignals. MedRadio transceiver enables communication between the implant and end effectors or base station (e.g. prosthetic legs or desktop computer). Crystal oscillator generates the reference signal for other system's components such as analog to digital converter. Novel techniques to improve important performance parameters (power consumption, low noise operation and interference resilience) have been introduced. Electrical, in-vitro and in-vivo experimental measurements have verified the functionality and performance of each design