The most accurate method for performing analog signal processing in MOS (metal-oxide-semiconductor) integrated circuits is through the use of switched-capacitor circuits. A switched-capacitor circuit operates as a discrete-time signal processor. These circuits have been used in a variety of applications, such as filters, gain stages, voltage-controlled oscillators, and modulators. A switched-capacitor circuit contains operational amplifiers (opamps), capacitators, switches, and a clock generator. Capacitors are used to define the state variables of a system. They store charges for a defined time interval, and determine the state variables as voltage differences. Switches are used to direct the flow of charges and to enable the charging and discharging of capacitors. Nonoverlapping clock signals control the switches and allow charge transfer between the capacitors. Opamps are used in order to perform high-accuracy charge transfer from one capacitor to another. The goal of this research is to design and explore future low-voltage switched-capacitor circuits, which are crucial for portable devices. Low-voltage operation is needed for two reasons: making reliable and accurate systems compatible with the submicron CMOS technology and reducing power consumption of the digital circuits. To this end, three different switched-capacitor integrators are proposed, which function with very low supply voltages. One of these configurations is used to design a lowpass ����� modulator for digital-audio applications. This modulator is fabricated and tested demonstrating 80 dB dynamic range with a 1-V supply voltage. The second part of this research is to show that these low-voltage circuits are suitable for modern wireless communication applications, where the clock and signal frequencies are very high. This part of the research has focused on bandpass analog-to-digital converters. Bandpass analog-to-digital converters are among the key components in wireless communication systems. They are used to digitize the received analog signal at an intermediate center frequency. Such converters are used for digital FM or AM radio applications and for portable communication devices, such as cellular phones. The main block, in these converters, is the resonator, which is tuned to a particular center frequency. A resonator must be designed such that it has a sharp peak at a specific center frequency. However, because of circuit imperfections, the resonant peak gain and/or the center frequency are degraded in existing architectures. Two novel switched-capacitor resonators were invented during the second part of this research. These resonators demonstrate superior performance as compared to previous architectures. A fourth-order low-voltage bandpass ����� modulator, using one of these resonators, has been designed. / Graduation date: 2002

Electroabsorption is the physical phenomenon by which the absorption of light in a medium can be controlled by applying an electric field. The Quantum–Confined Stark Effect, which makes the absorption band–edge in quantum wells very field–dependent, together with the strong absorption peak provided by excitons, are the physical foundations for the success of electroabsorption modulators based on quantum well structures in telecommunication networks. This thesis describes the design and fabrication of surface–normal electroabsorption modulation devices. The techniques needed to understand the design and fabrication of surface–normal multiple quantum well optical modulators are introduced, as are the various characterisation techniques used during and after the fabrication. Devices for several types of applications have been designed, fabricated, characterised and in some cases integrated into optical systems: – Two–dimensional arrays of 128´128 pixel amplitude modulators grown on GaAs substrates have been fabricated and characterised. Speeds of up to 11700 frames per second were demonstrated, limited by the output electronics of the computer interface. – Large–area modulators grown on GaAs substrates for free–space optical communication were developed, with an active area of 2cm2 and a modulation speed of several megahertz. Contrast ratios up to 5:1 on full modulator areas were measured. Problems limiting the yield and modulation speed of such devices have been studied, and solutions to overcome them have been demonstrated. – Large–area devices grown on InP substrates for free–space optical communication have been developed. Contrast ratios of up to 2:1 for transmissive types have been demonstrated. – Devices consisting of two rows of pixels, grown on GaAs substrates, with an active area of 22mm´5mm, divided into 64 or 128 pixels per row have been developed. These amplitude modulation devices were designed for optical signal processing applications. – One variant of these optical signal processing devices was also characterised as a ternary, binary amplitude and binary phase modulator array. – The use of GaAs multiple quantum well optical modulators in a free–space optical retro–communication system has been studied. An opto–mechanical design for a modulating retro–reflector is described, allowing a large field of view in one direction using reflecting, resonant–cavity modulators for high contrast ratios. / QC 20100802

Delta-Sigma Modulator-based Analog-to-Digital converter design is an active area of research. New topologies require extensive simulations to verify their performance. A series of improvements were made to an existing circuit simulation package in order to speed the simulation process for the designer. Various examples of these improvements are presented in typical applications. / Graduation date: 1992

Switching frequency modulation techniques, an inductor current sensing circuit for fast switching converter, and a dual converter are proposed, and the simulation results and experimental results are drawn. The experimental results for monotonic and pseudo-random modulation techniques show that the switching noise peak was effectively reduced as much as -19 dBc. The inductor current sensing circuit accurately tracks the output current of the switching converter that switches up to 30MHz. This current sensing circuit is used to drive the slow converter in the dual converter. The dual converter consists of a fast converter and a slow converter. The fast converter provides only the high frequency conponents in the output current, and the slow converter provides the majority portion of the output current with a higher efficiency. Therefore, the dual converter can have a fast transient response without sacrificing its efficiency. All chips are fabricated in a standard CMOS 0.18um process.

No description available.

In this thesis, studies on the applications of digital micro-mirror devices (DMD) to enhancement of digital optical microscope images are presented. This involves adaptation of the fast switching capability and high optical efficiency of DMD to control the spatial illumination of the specimen. The first study focuses on a method of using DMD to enhance the dynamic range of a digital optical microscope. Our adaptive feedback illumination control method generates a high dynamic range image through an algorithm that combines the DMD-to-camera pixel geometrical mapping and a feedback operation. The feedback process automatically generates an illumination pattern in an iterative fashion that spatially modulates the DMD array elements on a pixel-by-pixel level. Via experiment, we demonstrate a transmitted-light microscope system that uses precise DMD control of a DMD-based projector to enhance the dynamic range ideally by a factor of 573. Results are presented showing approximately 5 times the camera dynamic range, enabling visualization over a wide range of specimen characteristics. The second study presents a technique for programming the source of the spherical reference illumination in a digital in-line holographic microscope using DMD. The programmable point source is achieved by individually addressing the elements of a DMD to spatially control the illumination of the object located at some distance from the source of the spherical reference field. Translation of the ON-state DMD mirror element changes the spatial location of the point source and consequently generates a sequence of translated holograms of the object. The experimental results obtained through numerical reconstruction of translated holograms of Latex microspheres shows the possibility of expanding the field of view by about 263% and also extracting depth information between features in an object volume. The common challenges associated with the use of DMD in coherent and broadband illumination control in both studies are discussed.

Optical electroabsorption modulators (EAMs) that utilize quantum wells (QWs) are known to exhibit high modulation sensitivity, which is required for the analog optical fiber link application, compared to other types of optical modulators. QW-EAMs utilize the change of absorption coefficients that depends on the change of electric field across the QW for the optical intensity modulation. This dissertation focuses on the theoretical analysis of the optical properties of asymmetric double QWs (ADQWs) and the systematic optimization of modulation sensitivity in low-voltage EAMs that incorporate ADQWs. In this structure, the accurate calculation of excitons is especially important because the excitonic as well as the band-to-band optical transitions dominate the optical properties at the operating wavelength. The complex linear optical susceptibility was calculated within the density matrix approach in the quasi-equilibrium regime for the low excitation power and through a thorough treatment of line broadening. Transition strengths were calculated in the wavevector space, which effectively includes valence subband mixing with the warping of the subbands, excitonic mixing effects, and possible optical selection rules (e.g., light polarization, spin of excitons). The calculated transmission properties of the waveguide EAMs were almost identical to the experimental data at the device operating bias range. The mixing of excitons in ADQWs was analyzed in detail in momentum space, which was demonstrated to be very important in the process of structural optimization of ADQWs. The optimization of the structural parameters revealed that at an adequate barrier position and well width, the barrier thickness affects the modulation efficiency the most. Subsequently, in InGaAsP-based waveguide type QW-EAMs that operate at 1550 nm, the optimization of only one variable the thickness of the coupling barrier of the ADQWs shows 380 % enhancement in the modulation sensitivity at a much lower bias field (70->35 kV/cm) compared with that of single-QW structures. This enhancement is found to be caused by the strong mixing of the two exciton states originating in different subband pairs.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 4 uppsatser.

La résistance à de multiples drogues anticancéreuses (Multidrug Resistance ou MDR) est actuellement un problème majeur dans le cas de nombreuses chimiothérapies. Parmi les mécanismes à l'origine de la MDR, la surexpression de protéines membranaires de type ABC est le plus étudié. Les deux protéines ABCG2 et MRP1 sont parmi les protéines membranaires impliquées. Ces transporteurs sont capables d'induire un efflux massif des agents anticancéreux hors des cellules cancéreuses, réduisant ainsi leur concentration intracellulaire et donc leur efficacité thérapeutique. Afin de contrecarrer cette chimiorésistance, notre objectif s'est concentré sur le développement de nouveaux modulateurs d'ABCG2 et de MRP1. Dans ce cadre, de nouveaux inhibiteurs d'ABCG2, dérivés de chromones, ont été conçus afin de restaurer la sensibilité des cellules cancéreuses aux agents anticancéreux. De plus, la modélisation de modèles pharmacophores nous a permis d'obtenir de nouvelles informations quant aux interactions ABCG2-ligands. Les nouveaux modulateurs de MRP1, dérivés de flavonoïdes, sont capables quant à eux d'induire un efflux massif de glutathion cellulaire via MRP1, sans être transportés eux même, entraînant l'apoptose sélective des cellules cancéreuses surexprimant le transporteur. / Resistance to chemotherapeutic agents (Multidrug Resistance or MDR) is a major hurdle for anticancer chemotherapy. Among different mechanisms involved in MDR, the overexpression of membrane proteins belonging to ABC family is the most relevant one. Among such proteins, ABCG2 and MRP1 are considered to play an important role. These transporters are able to induce a massive efflux of anticancer agents out of the cancer cells, reducing their intracellular concentration and their therapeutic potency. In order to overcome this resistance, novel modulators of ABCG2 and MRP1 were designed, synthetized and tested biologically. In this context, new derivatives of chromones as inhibitors of ABCG2 were developed in order to restore sensitivity of cancer cells to chemotherapeutic agents. In addition, molecular modelling of new pharmacophores allowed us to gather new data exploring ABCG2-ligand interactions. New modulators of MRP1, derivatives of flavonoids, are able to induce a massive efflux of intracellular glutathione that is mediated by the protein, without being transported and causing selective apoptosis of cancer cells overexpressing MRP1.