In this thesis, digital controller design methods for sampled-data nonlinear systems are considered. Although sampled-data nonlinear control has attracted much attention in recent years, the controller design methods for sampled-data nonlinear systems are still limited. Therefore, a range of controller design methods for sampled-data nonlinear systems are developed such as backstepping, adaptive and robust backstepping, reduced-order observer-based output feedback controller design methods based on the Euler approximate model. These controllers are designed to compensate the effects of the discrepancy between the Euler approximate model and exact discrete time model, parameter estimation error in adaptive control and observer error in output feedback control which behave as disturbance. A dual-rate control scheme is presented for output-feedback stabilization of sampled-data nonlinear systems. It is shown that the designed controllers semiglobally practically asymptotically (SPA) stabilize the closed-loop sampled-data nonlinear system. Moreover, various applications of these methods are given and their performances are analyzed with simulations.

Large phased array antennas are widely used in many military and commercial applications. The analysis of large arrays containing many antenna or frequency-selective (FSS) surface elements is inefficient or intractable when brute force numerical methods are used. For the efficient analysis of such structures hybrid methods (analytic and numerical, numerical and numerical) can be used. In this thesis, a hybrid method combining the uniform geometrical theory of diffraction (UTD) and the moment method (MoM) used for the analysis of large, finite arrays is modified for the efficient yet accurate analysis of large printed dipole arrays. In the present hybrid UTD-MoM approach, the number of unknowns to be solved is drastically reduced as compared to the conventional MoM approach, which provides a great efficiency on the computational cost. This extreme reduction in the number of MoM unknowns is carried out by introducing a few UTD-ray type global basis functions for the unknown array element currents. In this study, this hybrid UTD-MoM method is applied to the analysis of a finite, planar periodic array of printed dipoles on a grounded dielectric substrate. The efficiency and accuracy of this hybrid method are demonstrated with some numerical results.

Making a robot autonomous has been a common challenge to be overcome since the very beginning. To be an autonomous system, the robot should collect environmental data, interpret them, and act accordingly. In order to accomplish these, some resource management should be conducted. That is, the resources, which are time, and computation power in our case, should be allocated to more important areas. Existing researches and approaches, however, are not always human like. Indeed they don&rsquo / t give enough importance on this. Starting from this point of view, the system proposed in this thesis supplies the resource management trying to be more &rsquo / human like&rsquo / . It directs the focus of attention to where higher resolution algorithms are really needed. This &rsquo / real need&rsquo / is determined by the visual features of the scene, and current importance levels (or weight values) of each of these features. As a further attempt, the proposed system is compared with human subjects&rsquo / characteristics. With unbiased subjects, a set of parameters which resembles a normal human is obtained. Then, in order to see the effect of the guidance, the subjects are asked to concentrate on a single predetermined feature. Finally, an artificial neural network based learning mechanism is added to learn to mimic a single human or a group of humans. The system can be used as a preattentive stage module, or some more feature channels can be introduced for better performance in the future.

In this thesis nonlinear control method techniques are investigated to control the attitude of Low Earth Orbit satellites. Nonlinear control methods are compared with linear control methods. Simulations are done using Matlab and Simulink software and BILSAT-1 parameters are used in the simulations. Reaction wheels are used as the actuator.

In nanotechnology, Carbon Nanotubes systems are studied with Molecular Dynamics Simulation software programs investigating the properties of molecular structure. Computational loads are very complex in these kinds of software programs. Especially in three body simulations, it takes a couple of weeks for small number of atoms. Researchers use supercomputers to study more complex systems. In recent years, by the development of sophisticated Field Programmable Gate Array (FPGA) Technology, researchers design special purpose co-processor to accelerate their simulations. Ongoing researches show that using application specific digital circuits will have better performance with respect to an ordinary computer. In this thesis, a new special co-processor, called TERSOFF2, is designed and implemented. Resulting design is a low cost, low power and high performance computing solution. It can solve same computation problem 1000 times faster. Moreover, an optimized digital mathematical elementary functions library is designed and implemented through thesis study. All of the work about digital circuits and architecture of co-processor will be given in the related chapter. Performance achievements will be at the end of thesis.

Advanced digital modulation schemes used in the wireless applications, result in the modulated RF signals with high peak to average power ratio which requires linear amplification. On the other hand, the demand for a longer talk time with less battery volume and weight, especially in hand-held radio units, necessitate more power efficient methods to be utilized in power amplifier design. But improved linearity and efficiency have always been contradicting requirements demanding innovative power amplifier and linearizer design techniques. Dynamically varying the load impedance and bias point of a transistor according to the varying envelope of the incoming RF signal also known as Dynamic Load Modulation (DLM) and Dynamic Supply Modulation (DSM), respectively, are two separate methods for improving the efficiency in power amplifier design. In this dissertation, a combination of both variable gate bias and tunable load concepts is applied in an amplifier structure consisting of two transistors in parallel. A novel computer aided design methodology is proposed for careful selection of the load and biasing points of the individual transistors. The method which is based on load-pull analysis performs sweeps on the gate bias voltages of the active devices and input drive level of the amplifier in order to obtain ranges of biases that result in the generation of IMD sweet spots. Following that, the amplifier is designed employing the load line theory and bias switching at the same time in order to enhance the efficiency in reduced drive levels while extending the output 1 dB compression point to higher values at higher drives. Tunable matching networks are implemented utilizing varactor stacks in a &Pi / con

Advanced digital modulation schemes used in the wireless applications, result in the modulated RF signals with high peak to average power ratio which requires linear amplification. On the other hand, the demand for a longer talk time with less battery volume and weight, especially in hand-held radio units, necessitate more power efficient methods to be utilized in power amplifier design. But improved linearity and efficiency have always been contradicting requirements demanding innovative power ampli

Medical imaging modalities provide effective information for anatomic or metabolic activity of tissues and organs in the body. Therefore, medical imaging technology is a critical component in diagnosis and treatment of various illnesses. Medical image segmentation plays an important role in converting medical images into anatomically, functionally or surgically identifiable structures, and is used in various applications. In this study, some of the major medical image segmentation methods are examined and applied to 2D CT images of upper torso for segmentation of heart, lungs, bones, and muscle and fat tissues. The implemented medical image segmentation methods are thresholding, region growing, watershed transformation, deformable models and a hybrid method / watershed transformation and region merging. Moreover, a comparative analysis is performed among these methods to obtain the most efficient segmentation method for each tissue and organ in torso. Some improvements are proposed for increasing accuracy of some image segmentation methods.

This thesis reports the development of high performance readout electronics for resistive microbolometer detector arrays that are used for uncooled infrared imaging. Three different readout chips are designed and fabricated by using a standard 0.6 &micro / m CMOS process. Fabricated chips include a conventional capacitive transimpedance amplifier (CTIA) type readout circuit, a novel readout circuit with dynamic resistance nonuniformity compensation capability, and a new improved version of the CTIA circuit. The fabricated CTIA type readout circuit uses two digital-to-analog converters (DACs) with multiple analog buses which compensate the resistance nonuniformity by adjusting the bias currents of detector and reference resistors. Compensated detector current is integrated by a switched capacitor integrator with offset cancellation capability followed by a sample-and-hold circuit. The measured detector referred current noise is 47.2 pA in an electrical bandwidth of 2.6 KHz, corresponding to an expected SNR of 530. The dynamic nonuniformity compensation circuit uses a feedback structure that dynamically changes the bias currents of the reference and detector resistors. A special feature of the circuit is that it provides continuous compensation for the detector and reference resistances due to temperature changes over time. Test results of the fabricated circuit show that the circuit reduces the offset current due to resistance nonuniformity 42.5 times. However, the calculated detector referred current noise is 360 pA, which limits the circuit SNR to 70. The improved CTIA type readout circuit introduces a new detector biasing method by using an additional auxiliary biasing transistor for better current controllability. The improved readout circuit alleviates the need for high resolution compensation DACs, which drastically decreases the circuit area. The circuit occupies an area of one seventh of the first design. According to test results, the current compensation ratio is 170, and the detector referred current noise is 48.6 pA in a 2.6 KHz bandwidth.

This thesis presents the development of electrochemical etch-stop techniques (ECES) to achieve high precision 3-dimensional integrated MEMS sensors with wet anisotropic etching by applying proper voltages to various regions in silicon. The anisotropic etchant is selected as tetra methyl ammonium hydroxide, TMAH, considering its high silicon etch rate, selectivity towards SiO2, and CMOS compatibility, especially during front-side etching of the chip/wafer. A number of parameters affecting the etching are investigated, including the effect of temperature, illumination, and concentration of the etchant over the etch rate of silicon, surface roughness, and biasing voltages. The biasing voltages for passivating the n-well and enhancing the etching reactions on p-substrate are determined as -0.5V and -1.6V, respectively, after a series of current-voltage characteristic experiments. The surface roughness due to TMAH etching is prevented with the addition of ammonium peroxodisulfate, AP. A proper etching process is achieved using a 10wt.% TMAH at 85&deg / C with 10gr/lt. AP. Different silicon etch samples are produced in METU-MET facilities to understand and optimize ECES parameters that can be used for CMOS microbolometers. The etch samples are fabricated using various processes, including thermal oxidation, boron and phosphorus diffusions, aluminum and silicon nitride layer deposition processes. Etching with the prepared samples shows the dependency of the depletion layer between p-substrate and n&amp / #8209 / well, explaining the reason of the previous failures during post-CMOS etching of CMOS microbolometers from the front side. Succesfully etched CMOS microbolometers are achieved with back side etching in 6M KOH at 90 &deg / C, where &amp / #8209 / 3.5V and 1.5V are applied to the p-substrate and n-well. In summary, this study provides an extensive understanding of the ECES process for successful implementations of integrated MEMS sensors.