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The false lock characteristics of a sampled-data phase lock loop containing a phase detector with a sawtooth characteristic are investigated. The ideal processor of data operated on by such a phase detector nonlinearity is derived in open-loop form. A second system is proposed which is shown to approximate the operation of the ideal system with increasing accuracy for decreasing noise variance. The operation of the approximate system is interpreted in geometric terms. This geometric interpretation is used to place a lower bound on the probability of false lock of the ideal system. A suboptimal system which uses feedback and a time-varying linear filter is analyzed. It was necessary to use a computer to perform the integration leading to the probability distribution of the error of this system. The bound on the probability of false lock for the ideal system is compared with the probability of a similar error for the suboptimal system. It is concluded that this bound is a conservative one. / Ph. D.

The objective of this research is to develop and implement a method for fault simulation that considers bridging faults in CMOS circuits that are tested using supply current monitoring. The discussion is restricted to single fault detection in CMOS combinational circuits. A CMOS circuit is represented by a two-level hierarchy. At the higher level, the circuit is partitioned into modules based on the circuit layout. Each module is represented at the lower level by a switch-level graph. This representation has the advantage of structural accuracy at the lower level and efficient logic propagation at the higher level. Based on a module's switch-level graph, an exhaustive list of bridging faults corresponding to certain physical defects can be derived. Fault collapsing techniques are used to optimize the exhaustive fault list. There are two major processes in this bridging fault simulation program, logic simulation and fault sensitization at switch level. The simulation program uses preprocessing and bit-wise parallelism to minimize computation time. At the end of fault simulation, a fault coverage and fault matrices suitable for test grading and fault diagnosis are produced for each test set. This research also identifies types of CMOS modules and uses them to analyze test generation for bridging faults. The completeness and minimality of switch-level test sets are considered for general series-parallel (GSP) modules. Finally, several single-module circuits are simulated using gate-level, switch-level and random test sets, and their effectiveness is compared. / Master of Science

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The Phase Locked Loops (PLLs) are widely used in contemporary electronic systems for frequency synthesis, clock recovery, frequency multiplication and other purposes. Because of continuous increase in operating frequency of clocking systems the requirements on the clock spectral purity and low jitter became very demanding and are one of major designers' concerns.Frequency synthesizers used in microprocessors are integrated on the same substrate as the rest of the circuit and thus suffer from a substantial switching noise injected into global supply and ground busses. Usually when the reference signal comes from a crystal oscillator, VCO becomes a main source of phase noise. A designer of VCO needs to determine the best circuit structure by considering different prototypical perturbations scenarios and predicting the worst case and jitter response when the perturbation signals are switched on and off. Therefore the time efficient estimation of the jitter effects resulting from many shapes, frequencies and phases of perturbation is critical.The presented dissertation demonstrates simulation methodology for rapid estimation of jitter in oscillators, particularly in VCOs, caused by perturbation sources such as power supply and substrate couplings. The methodology is also extended to these types of PLLs in which the VCO instability is a main contributor to the output timing jitter.Simulation of oscillatory circuits is strongly effected by the round-off errors. Special technique was developed to eliminate these effects.The technique is applicable for predicting timing non-idealities for arbitrary perturbation shapes, frequencies and phases. Different jitter metrics can be easily extracted for all important perturbation scenarios.The methodology utilizes the new concept of the transient multi-cycle Voltage Impulse Sensitivity Function (VISF), which has been developed in the dissertation. It contains information about sensitivity of oscillator to noise injection and also allows for efficient prediction of the transient effects caused by switching on and off the perturbation sources. The methodology offers efficiency and great simplicity of use, which frees designers from complicated, time consuming analysis of data generated by a simulator. The very involved postprocessing of simulation data can be fully automated.

The capability of measuring surface temperatures of hybrid circuits at the Virginia Tech Hybrid Microelectronics Laboratory has been established. This capability provides a quantitative method for effectively evaluating thermal design software. Surface operating temperatures were measured and predicted for an operating hybrid circuit. The temperatures were measured using an infrared thermal imaging system, which measures surface temperatures by detecting the infrared radiation emitted and reflected. The accuracy of the measurements has been quantified for variations in surface emissivity, convective cooling condition, and operating temperature range. The most accurate temperature measurement of a one-resistor circuit was compared to the operating temperature predicted by a lumped-parameter one-dimensional heat transfer analysis. The comparison agreed within the expected limits for this simple analysis and identified areas for possible improvement both of the model and the experimental technique. Thermal design of a circuit is critical because excessive temperatures are a common cause of circuit failure. Circuit designers rely on computer programs to predict circuit component temperatures because of the high cost of prototype experimentation. Accurate thermal design software that is currently available is too complicated for occasional use by circuit designers. Simple, yet accurate, thermal design software is essential for this type of design, so that circuit layouts can be quickly and easily optimized. / M.S.

A study has been carried out to investigate the use of "real-time" radiography as a method of automated inspection of through-hole electronic circuit board solder joints. By evaluating five major solder defects it has been found that film radiography employing high contrast film results in a definite distinction between a good solder joint and a defective solder joint. The same five defects were also found to be distinguishable from a good solder joint when evaluated by a real-time radiographic inspection unit using digital image processing. Although the type of defect being investigated was not discernible, the ability to distinguish a good solder joint from a defective solder joint is a major step in the implementation of automated solder joint inspection for military electronics.

The present paper introduces one very efficient and flexible time-domain analysis technique to predict the kinds of reflections and crosstalk. Numerical results show that this technique is indeed efficient and accurate in the transient analysis of a general multiple line system. Furthermore, this algorithm can be eventually coded in a form of a subroutine compatible with any standard CAD program, such as SPICE.

M.Ing. / In this investigation charge balancing will be investigated from an Electro-Magnetic- Compatibility perspective. The primary sources of common mode Electro-Magnetic- Interference in switching converters are the switching nodes. This is mainly due to the parasitic capacitance between the switching node and the reference earth. Filtering components that are currently used take up a lot of valuable space resulting in the products overall size and cost to increase. Combating common mode current at the source will drastically reduce the size or the need for these large filters. This investigation will focus on a simple method of reducing common mode noise (produced by the switching node), of a two wire system, at the source by making use of a compensating winding which requires very little or no additional space; a buck converter will be used to illustrate the concept. The investigation will start with an overview of Electro-Magnetic-Interference and its components (common and differential mode noise). This investigation will deal with the measurement of common and differential mode noise as well as general Electro-Magnetic-Interference measurement. A design of the buck converter and its drive circuit will also be presented. Reducing the common mode noise by making use of charge balancing using planar inductors will then be presented. This investigation contains the theoretical analysis as well as experimental results to validate the theory. The experiments show encouraging results in using this technique to minimise common mode noise in switched-mode-power-supplies.

Apresentamos cálculos de primeiros princípios da geometria atômica, energia de formação e estrutura eletrônica para as impurezas substitucionais de oxigênio e nitrogênio em GaAs (\'O IND. aS1\'\'N IND.As \'e \'N IND. Ga\'). Também estudamos a geometria atômica e estrutura eletrônica dos complexos neutros formados pelas mesmas impurezas substitucionais e átomos de hidrogênio intersticial (\'O IND. As-H\',\'N IND. As-H\',\'N IND. Ga-H\', \'N IND. As-H IND.2\' e \'N IND. Ga-H IND 2\'). Nossos resultados para os centros \'O IND. As\'e \'N IND. Ga\', em diferentes estados de carga, mostram distorções Jahn-Teller as quais induzem estados de carga não estáveis, observando-se um comportamento U-negativo para cada centro. Entretanto para o centro \'N IND. As\' não foram observadas distorções. Em todos os sistemas estudados, as impurezas introduzem níveis profundos no gap. Para os complexos O-H e N-H foram encontradas várias configurações metaestáveis, correspondentes a diferentes posições de equilíbrio do átomo de hidrogênio, as quais apresentam energias entre 0.5 e 2.5 e V relativas à configuração estável. Na configuração estável do complexo \'O IND. As-H\', oxigênio não interage diretamente com hidrogênio, ligando-se a três gálios primeiros vizinhos. Entretanto para os complexos \'N IND. As-H\' e \'N IND. Ga\'-Hg\' é observada a formação de um dímero NH ligado à rede. Para os complexos N-\'H IND. 2\' também são encontradas várias configurações metaestáveis. O complexo\'N IND. As\'-\'H IND. 2\' apresenta uma configuração estável onde um dos hidrogênios forma o dímero NH, enquanto que o segundo fica ligado a um gálio primeiro vizinho, em simetria \'C IND. 3 v\'. Para o complexo \'N IND. Ga\'-\'H IND.2\' é observada a formação de uma molécula do tipo N\'H IND.2\', a qual também se liga à rede. As propriedades passivadora e ativadora do átomo de hidrogênio, como também sua interação com os níveis no gap, são discutidas para cada complexo / We report first-principles calculations of the electronic structure, atomic geometry and formation energy for the isolated oxygen and nitrogen substitutional impurities in GaAs (OA, NA, and Naa)· Also we performed electronic structure and atomic geometry calculations for the neutra! complexes formed by the same substitutional impurities and interstitial hydrogen atoms (O A,-H,NA,-H, Naa-H, Nk,-H2 and Naa-H2). Our results for the O ko and Naa centers for different charge states show Jahn-Telier distortions which induce unstable charge states, implying in a nega tive-U behaviour for each center. The NA-< center remains on-site for ali the charge states studied. Ali the substitutional impurity give rise deep leveis in the gap. For the 0-H and N-H complexes we found severa! metastable configurations related to different hydrogen equilibrium positions, with energies ranging from 0.5 to 2.5 eV relative to the stable configuration. The stable configuration for the O A,-H complex shows a weak interaction between oxygen and hydrogen, while for the NA,-H and Naa-H complexes it shows the formation of a N H dimer which is bonded to the lattice. For the N-H2 complexes we also found severa! metastable configuration. The stable configuration for the Nk,-H2 complex shows one H atom fonning a N H dimer wit.h nitrogen, while the second one bonds with a nearestneighbour Ga atom, in C3, symmetry. For the Naa·H2 complex we observed the formation o f a N H T like molecule ais o bonded to the lattice. The passivation and activation properties related to hydrogen atom and their interaction with the gap leveis are discussed.