Sharif Digital Repository

iN This thesis, Design and implementation of a low voltage, low power Delta-Sigma Modulator (DSM) is presented. System level considerations have been discussed thoroughly. In addition a systematic design flow in the context of continuous time delta sigma modulators is provided. While voltage-domain signal processing becomes more difficult in deep sub-micron processes, a finer time resolution is achievable. Time-domain quantizers can ameliorate the design challenges of flash quantizers which arises from lower supply voltages and higher fraction of comparator metastable region. VCO based quantizer such as voltage to frequency and voltage to phase considered as time domain quantizers can be a... 

In this research, modal incremental dynamic analysis (MIDA) has been investigated on three-dimensional structures with irregular plans. The MIDA method is an incremental static analysis that considers higher modes of the structure. In fact, it is a combination of modal pushover (MPO) and incremental dynamic analysis (IDA) methods that incorporate the advantages of both and is much faster than the IDA method. Compared to constant analyses, incremental analysis is more extensive in terms of results and response to earthquakes. Due to the uncertainties in the nature of future earthquakes, engineers use the IDA method to achieve a broader view of the structure's response under potential... 

The matrix converter is an array of controlled bidirectional semi-conductor switches that allows direct ac–ac conversion without an intermediate dc link. This converter has several attractive features that have been investigated in the last two decades. Multilevel converter technology has become increasingly popular in recent years due to high power quality,high-voltage capability, low switching losses and low EMI issues.This paper is concerned with applying multilevel techniques to direct ac–ac power converters and concentrates on developing the concepts of space vector modulation for a multilevel matrix converter. The common-mode voltage produced by a modern power converter has been... 

Wideband mm-wave radars are gaining popularity in automotive applications due to their superiority in harsh weather conditions, high distance resolution, precise velocity measurement, and superior spatial resolution. The primary purpose of this thesis is to design and implement a voltage-controlled oscillator for 77GHz automotive radar applications.Phase noise -as one of the most crucial specifications in VCO design- Phase noise improvement techniques as well as harmonic engineering methods are delineated. Also, an Ocean-based code for ISF simulation is introduced and developed to obviate the need for additional signal processing software so that simulation speed increases... 

It is generally accepted that Electronic Warfare has three distinct components: (1) electronic support (ES), (2) electronic attack (EA), and (3) electronic protect (EP). ES is included those measures taken to collect information about an adversary by intercepting radiated emissions. EA refers to attempting to deny adversaries access to their information by radiating energy into their receivers. EP includes activities under taken to prevent an adversary from successfully conducting ES or EA on friendly forces.
The function of Electronic Support Measurement (ESM) System is considered as a part of the first component (i.e. ES). After receiving emitted signals from various radars by ESM... 

In this work we have investigated the methods of providing quality of service in cognitive radio networks. At first, we have explained the various algorithms of providing BER quality of service in wireless networks. Especially we have explained those algorithms which are known as the distributed power control algorithms. Then we have introduced methods of using adaptive modulation and we have used this kind of modulation to provide delay quality of service in cognitive radio networks. We have done this by maximizing the sum of effective capacities of secondary links under the power constraints and also the interference constraints set by the primary receivers. Finally, we have introduced... 

Optical impairments, as a challenging obstacle in optical communication systems, have been under deep attention of optical engineers in recent years. These impairments can be divided into two categories of linear and nonlinear impairments. Dispersion is a significant linear impairment leads to broadening of the optical signal and interference between transmitted symbols during detection. Nonlinear impairments such as cross-phase modulation (XPM) and self-phase modulation (SPM) also distort the transmitted signal through the fiber, causing interference at the receiver and degrading the system's performance. An appropriate solution for compensating optical fiber impairments is to utilize... 

Nowadays, radiation therapy is one of the most common methods for the cancer treatment. Intensity Modulated Radiation Therapy(IMRT) is a novel technique of radiation therapy that aims to delivere sufficient dose to cancerous tissues while sparing healthy organs. There are various uncertainties in radiation therapy problems, including uncertainty about device setup, device errors, interfraction and intrafraction motions. One of the most important uncertainties is the movement of the tumor during the treatment process(intrafraction motion), as this displacement may cause the cancer tissue to not receive sufficient dose and also to damage the healthy tissue due to a violation of their dose... 

The use of protons and charged particles such as carbon in the treatment of cancerous tumors is one of the new methods of external radiation therapy. Proton therapy can achieve almost the same tumor dose coverage as traditional photon therapy with a greatly reduced dose to the normal organ. The radiation deviations caused by the magnetic field are an effective factor in reducing the dose of vital organs without sacrificing the dose coverage of tumors; Therefore, a new method of proton therapy, called magnetic field-modulated proton therapy, has been proposed, in which the Bragg peak positions of proton beams can be modulated under the cover of predesigned magnetic fields inside cancer... 

Delta-Sigma Analog-to-Digital converters have been positioned themselves as robust reliable converters so far. The magic Of extracting high resolutions from low bit ADC has made them popular between designers. Previously, the noise-shaping magic was used in high-resolution applications such as high-quality audio signal converters. However, as the technology scales and proceeds, these converters are approaching RF applications, too. Power and OSR trade-off limits this progress. To increase OSR in bandpass delta-sigma modulators, more power should be consumed to increase the quality factor of loop filters. In this thesis, a systematic approach has been utilized. An n-path filter is employed... 

Reduction of power converters’ cost is one of the most important efforts to improve machines control systems. In this way, some new topologies for power electronic converters have been proposed. Among various topologies, four switch three phase inverter (FSTPI) thanks to the simple circuit, low cost, minimized conduction and switching losses and high reliability has attracted much attention recently. In this thesis, direct torque control (DTC) method is utilized to control of four switch inverter fed induction motor. In this way, in order to decrease flux and torque ripple and achieving constant switching frequency, a new Discrete Space Vector Modulation (DSVM) method have been proposed in... 

Dye-sensitized solar cells (DSSCs) are emerging as low-cost alternatives to conventional, solid-state, silicon solar cells. A porous network of a nanosize semiconductor material with a wide band-gaps usually TiO2, serves as charge transport medium. A monolayer of dye is chemically adsorbed on this material. Photoexcitation of dye causes injection of electrons into the conduction band of TiO2 from where they diffuse towards a transparent conducting oxide (TCO) substrate. The dye is regenerated through receiving electrons from a redox couple dissolved in the electrolyte. After passing through a desired load, the electrons enter the cell through a counter electrode to reduce the redox ions and... 

In this thesis we study the possibility of unidirectional transmission of light using reciprocal and nonreciprocal elements. Unidirectional transmission will allow us to separate the coupling of light into and out of resonators and design unidirectional waveguides. We start by studying the effects of one-sided modulations of dielectric constant of reciprocal structures. One-sided modulation will satisfy the phase matching condition for the coupling of two waves only in one direction. Using coupled mode theory, we study one sided modulation in layered media. Next, we find the exact solution to such strucures using transfer matrix method and analyze one-sided modulation in waveguide... 

set V = {1; : : : ; n}. Let K be a field and let S be the polynomial ring K[x1; : : : ; xn].The edge ideal I(G), associated to G, is the ideal of S generated by the set of squarefree monomials xi xj so that i is adjacent to j. The graph G is Cohen–Macaulay over K if S=I(G) is a Cohen–Macaulay ring. In this project we will explain Herzog-Hibi’s classification of all Cohen–Macaulay bipartite graphs  

The use of wind energy and wind generators as an inexpensive type of renewable energy sources is increasing. Wind farms and distributed wind generators connected to the power transmission and distribution systems and microgrids, and wind generators in standalone mode of operation affect the stability and power quality of the grid. In this thesis, the performance of a matrix converter in grid connection of variable speed PMSG–driven wind turbine is improved. In this way, by transferring the matrix converter modulation matrix into the synchronous reference frame and decomposing it into the singular values, a new general method is proposed for analysis, modelling and modulation of a matrix... 

In this thesis, pulsed power structures containing a step up high voltage transformer with large transformer ratio are investigated. In pulsed power applications, a step up pulse transformer is a proper choice in the cases in which a low primary voltage is available. The noticeable advantage of employing these transformers is the ability to use several modules in the primary side of the transformer. However, it should be noticed that the primary side current of the transformer is large. So to solve this problem, the number of primary windings could be increased and the primary large current can be shared between these windings. In this thesis, the sharing methods are investigated and the... 

Nowadays, power electronics converters with pulse width modulation (PWM) are widely used in different power circuits. Operation of semi-conductive switches during on and off conditions causes switching dissipation and consequently decreases the efficiency of the PWMs. Recently, by increasing the required power for power electronics applications, quasi-resonant converters attract attentions. Quasi-resonant converters, by adding resonant circuits to the PWM converters causes the soft switching operation (switching with zero current or voltage) and decreases the energy loss. In conventional control methods of these converters, the nonlinear average circuit model is linearized around the... 

converters, the different configurations for matrix converters are proposed. In this thesis, a one-phase to three-phase matrix converter is used to control in three-phase induction motor. Different control methods are proposed to control the induction motor. The novel control methods include close loop speed and converter output current controls of induction motor are proposed based on SPWM. The structure of indirect matrix converter for the mentioned application also investigated. Moreover, three usual method of control of induction motor: DTC (Direct Torque Control), FOC (Field Oriented Control) and Space Vector Modulation are applied to the single to three- phase matrix converter. Each of... 

In this Mater thesis, we o?er a general Prime Ideal Principle for proving that certain ideals in a commutative ring are prime. This leads to a direct and uniformtreatment of a number of standard results on prime ideals in commutative algebra,due to Krull, Cohen, Kaplansky, Herstein, Isaacs, McAdam, D.D. Anderson, andothers. More signi?cantly, the simple nature of this Prime Ideal Principle enablesus to generate a large number of hitherto unknown results of the “maximal impliesprime” variety. The key notions used in our uniform approach to such prime idealproblems are those of Oka families and Ako families of ideals in a commutative ring.In chapter 2, we amplify this study by developing... 

High-definition video streaming, multimedia file sharing, cloud computing, mobile networks and online gaming, all together, will increase the network traffic enormously every year.Long-haul optical fiber networks form the backbone of the Internet and scaling to higher throughput and lower cost per bit is essential to ensure continued growth of information technologies. For four decades, optical networks have exploited significant progress in physical technologies, including low-loss single-mode fibers (SMFs), high-performance lasers and modulators, and low-noise optical amplifiers. In parallel, communication methods have evolved to multiplex information in various physical dimensions in...