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Archived Theses
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DOIs Assigned
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Archived Theses
Design of low power continuous time σ − ∆ analog to digital converters
A second order CT Σ − ∆ modulator for audio frequency sensory systems in 180nm TSMC CMOS process is presented. The design incorporates a C-gm based current mode structure with 2nd order noise shaping, a 25 kHz bandwidth, a sampling frequency of 12.8 MHz marking an OSR of 256 and a total power consumption of 5.9$\mu$W. Consequently the proposed loop achieves a FOM of 2.8fJ/conv. The overall power consumption is distributed evenly among segments of the loop to attain adequate number of bits without the need to sacrifice power. Two representations of overall design, a robust Voltage input circuit and a high precision current input modulator, are introduced.
RF-mikrodalga frekans aralığındaki elektromanyetik dalgaların biyolojik dokular üzerine etkisinin FDTD simülasyonu
Günümüzde en sık görülen hastalık türlerinden biri olan kanseri tedavi etmek amacıyla elektromanyetik dalgaların kullanımı ve kablosuz haberleşme teknolojilerinin insan sağlığı üzerindeki etkileri elektromanyetik dalga-doku etkileşimlerinin analizini gerektirmektedir. Tez çalışmasında farklı elektrik ve manyetik özelliklere sahip biyolojik dokulara uygulanan elektromanyetik dalganın doku ile etkileşiminin analizi için ilk olarak mikrodalga-radyofrekans aralığındaki elektromanyetik dalgaların biyolojik dokuda ilerlediği mesafe doğrultusunda özgül güç yoğunluğu, emilen elektromanyetik radyasyon dozu ve sıcaklık artışı için analitik çözüm yapılarak sonuçlar değerlendirilmiştir. Daha sonra aplikatör (kaynak) ışınımının artan özgül güç yoğunluğu ve artan uygulama sürelerinde mesafeye bağlı sıcaklık artışları yorumlanmıştır. Tezin sonraki kısmında Pennes biyo-ısı denkleminden yararlanılarak zaman domeninde sonlu farklar metodu (FDTD) ile MATLAB ortamında hipertermi için simülasyon modeli geliştirilmiştir. Simülasyonlarda 6.8 GHz frekans büyüklüğünde noktasal mikrodalga kaynağı kullanılarak biyolojik dokuların basit modellemelerinin ve daha sonra gerçek insan vücudunun bilgisayarlı tomografi kesitleri üzerinde elektromanyetik dalganın elektrik alan, manyetik alanlar, özgül soğurma oranı (Spesific Absorbtion Rate-SAR) ve elektromanyetik dalganın biyolojik dokuya aktardığı ısı enerjisi dağılımları incelenmiştir. Tek boyutlu dağılımlarda elde edilen elektrik alan sinyallerin dalgacık (wavelet) analizi yapılarak sonuçlar değerlendirilmiştir. Son olarak ise basit modelde noktasal kaynak cildin üstüne, cilt içine ve yağ dokusunun içine yerleştirilerek meydana gelen SAR değişimleri analiz edilmiştir. Simülasyonlarda tüm dokularda meydana gelen SAR ve ısı artışları gözlenmiştir. Bu durum Radyofrekans-Mikrodalga frekans aralığında elektromanyetik dalgaların biyolojik dokular üzerine etkisinin bir bütün olarak değerlendirilmesini sağlamıştır. ANAHTAR KELİMELER: Hipertermi, elektromanyetik dalga, SAR, ısı enerjisi
HF/UHF dual mode RFID transponder antenna and HF range extension via wireless power transmission
A novel HF/UHF compatible RFID transponder antenna is designed, simulated and measured for dual band operation and HF range increase. Dual mode compatible RFID transponder antenna enjoys the benefits of each mode and eliminates the disadvantages of single mode operation. The transponder antenna can easily be configured for either HF mode, or UHF mode only, or HF mode with UHF range extension mode.Limited range of HF RFID systems can be overcome if more power can be delivered to the transponder antenna which could not be achieved in HF band due to near-field strength regulations set by the standards. However, using UHF band, wireless power can be delivered by the reader to the HF transponder. To achieve such operation, the transponder antenna must be dual band. The rectify circuit for wireless power transmission at UHF band must also be optimized for maximum efficiency and we obtained about 63% system efficiency when measured from end-to-end. The influence of coexistence of HF and UHF antennas on the same structure are well characterized and measured to corroborate simulation results.Even though UHF RFID has benefit in having better read/write range capability, these tags can get easily affected by the surroundings or application environment such as on/near metal and plastics. When tags are placed in such environments, tag impedance can change and detune easily, and also radiation characteristics may change considerably, which, in turn, makes the UHF tag less reliable. Therefore, there is a need for an UHF RFID tag that is less sensitive to environment and is capable of preserving radiation characteristics in such environments. Although several studies which address this issue have been reported in the literature, they are all limited to dipole-like or slot dipole-like structures. We propose a microstrip antenna where its ground serves as isolation to its surroundings such that its main electrical performance metrics do not change drastically when placed on or near metallic structures. The performance of the designed antenna has been compared to that of a Texas Instruments transponder antenna, which has widespread use for many UHF applications. We prove that our transponder antenna behaves much better than TI?s antenna under a variety of typical RFID applications.
A video surveillance system based on interacting multiple models
The video-based surveillance systems are becoming widespread due to the increasing security needs. Consequently, these systems bring huge volumes of visual data to be analyzed. The automated systems are developed to assist human operators in time-consuming scene analysis. Besides, they enhance the surveillance efficiency by tracking interesting moving objects and interpreting the tracking results for potentially dangerous situations or suspicious activities.In this thesis, we present an automated visual surveillance system with real-time and robust tracking capabilities. The system detects moving objects under changing background conditions by an adaptive Mixture of Gaussians method. The detected objects in the consecutive video frames are properly associated with each other by means of data validation and association algorithms. The tracking algorithm makes use of the prediction and estimation results of the Interactive Multiple Modal (IMM) estimator operating on constant velocity and coordinated turn motion models simultaneously. The system has been used to analyze PETS 2001 datasets which provide a unique test environment for the objective evaluation of the tracking algorithms.
Modelling of indoor wireless propagation and comparing the results with FEKO
In this work, indoor wireless propagation is studied. It is hard to solve indoor wireless propagation problems by analytical methods. In order to solve this problem, an office room is modelled; and simulation and experimental results are compared to each other. The model was constructed like a real office room and suitable for the electromagnetic theory.The practical study is divided into three parts. First part is free office room (without furniture), second part is furniture located in the office, which is made of cartoon (cartoons dielectric properties similar to the wood). Third part is cartoon furniture located in the office, which is covered by aluminum foil. Also at the second and third parts, there exist two water bottles as a model of human and child, which is filled with sea water and drinking water mixtures. All the measurements are made both by using Transverse Electric and Transverse Magnetic modes.In conclusion, with simulation program the modelled same office room is analyzed to compare with the measurement results of free office room, office room filled with cartoon furniture and office room filled metal furniture. It is observed that practical solutions can not be the same with simulation results.
6-bit flash analog-to-digital converter
The purpose of this thesis is to design a converter with low power consumption andhigh sampling rate using a different structure from conventional flash analog-to-digitalconverters. The designed novel voltage comparator circuit and the following structureenable to overcome the speed problems of conventional voltage comparators. Moreover,the ROM can be driven without encoder circuit with the help of decision circuit.As in conventional Flash ADC designs, voltage comparator circuits compare inputvoltages against reference voltages in this designed Flash ADC. However, instead ofproducing a digital signal, voltage comparators produce a current at the output. The currenthas the highest value in only one voltage comparator. This current is detected by a currentcomparator which produces a digital ?1?. The outputs of voltage comparators can havevery close values at the boundaries of reference voltages. Therefore, two currentcomparators can produce ?1? at the same time. In this situation, decision circuit determinesthe highest current by the help of latch circuit. The ROM circuit can be driven withoutproducing thermometer code and encoder circuit.As a result, 6-bit, 1GS/s Flash ADC is designed in TSMC 180nm CMOS for 1.8Voperation. This converter is arranged to operate between -40° and 120°. All designsteps and details are shown in this thesis. Verification of designed circuits and all systemhas been carried out by simulations. Also, this work is compared against some of the FlashADC converters which have same technology and similar specifications, the results arepresented in this thesis.
Design of dual aperture coupled antenna and offset slot fed aperture coupled microstrip antenna
DESIGN OF DUAL APERTURE COUPLED ANTENNA AND OFFSETSLOT FED APERTURE COUPLED MICROSTRIP ANTENNAMicrostrip patch antennas play a very important role in the field of wireless communications because of their advantages such as low-profile, low-cost, easy fabrication of various types. Microstrip patch antennas are versatile in terms of various possible geometries that make them applicable to many different applications. In this thesis, two different coupled stacked microstrip patch antennas have been designed at Ku band.Our frequency spectrum is between 10.8 GHz and 12.75 GHz. The gains of the antennas are more than 9 dBi and VSWR is less than 2 for all frequency bands. The slot length isless than /4 for containing all frequency intervals.And hourglass shaped aperture is usedbecause it gives maximum coupling. The patch on the substrate is the radiating elementand the slot in the ground plane couples the energy from the microstrip feed line to thepatch and parasitic patch on the topmost substrate is used to increase bandwidth. Themicrostrip patches in the structure have dimensions nearly resonant dimensions ( ) atcenter frequency of operating band 11.9 GHz. The parasitic patch a little smaller thanradiating element.In Chapter 2 the beam controllable antenna which is the name of `Dual Aperture CoupledAntenna Design? has been designed. Also, its array synthesis and feed network design hasbeen presented. Simulations and measurements results have been displayed. In Chapter 3the main beam tilted antenna which is the name of `Offset Slot Fed Aperture CoupledMicrostrip Antenna? has been designed. Its array synthesis and feed network design hasbeen presented. Simulations and measurements results have been displayed.
Elektronik ticaret sistemleri ve geliştirilen B2C uygulamasının performans artırımına yönelik yapılan analizler ile sunulan yeni yaklaşımlar
Son dönemlerde çoğu yazılım projesi web teknolojileri kullanılarak İnternet üzerinde çalışacak şekilde geliştirilmektedir. Bu eğilimin temel nedenleri olarak web projelerinin çoklu kullanıcı yapısına uygun olması, uygulama üzerinde yapılan değişikliklerin aynı anda sisteme yansıması, uygulamaya ulaşmak için sadece bir İnternet tarayıcısına ihtiyaç duyulması ve dünyanın herhangi bir noktasından ulaşılabilmesi gösterilebilir.Bu tez çalışmasında şirket tüketici arası elektronik ticaret yapısının seçilmiş olmasının nedenleri popüler bir eğilim olmasının ötesinde, çoklu kullanıcı yapısına tamamen uygun olması, giriş gerektirmeksizin kullanıcılar tarafından görüntülenebiliyor olması ve çoğu web teknolojisinin kullanılmasına elverişli olmasıdır. Tez kapsamında sadece bir elektronik ticaret uygulaması oluşturulmamış, aynı zamanda uygulama oluşturulurken sistem aşamalara ayrılarak bir yazılım proje yönetimi uygulanmıştır. Projenin analiz aşamasından sonra titiz bir görsel çalışma yapılmıştır. Projenin kodlanması aşamasında performans artışı sağlanması amacıyla hazır kod oluşturucu programlar kullanılmamış, yoğun bir içerik ve veritabanı sorgulamasına sahip sayfalara yönelik yapılan performans analizleri doğrultusunda yeni bir çözüm sunulmuştur. Uygulama dışında tez çalışması içerisinde temel olarak proje kapsamında kullanılan web teknolojilerinin özellikleri, elektronik ticaret kavramı ana hatlarıyla irdelenmiş, ayrıca geliştirilen uygulama içerisinde yer alan tüm fonksiyonlar açıklanmıştır. Elektronik ticaret uygulaması geliştirilirken seçilen teknolojilerin standart olarak kabul edilmiş olmasına, uygulamanın görüntüleneceği İnternet tarayıcıları arasında farklı sonuçlar göstermemesine ve akademik bir çalışma olması nedeniyle açık kaynak kodlu teknolojilerin seçilmesine özen gösterilmiştir.Anahtar Kelimeler: Elektronik Ticaret, B2C, Web, Performans
Computer aided design of the biquadratic filters using memristors
This thesis presents new circuit topologies realized by using the fourth passive element memristor. The terminal equations and the properties of memristor are given and its SPICE model is simulated.Some active circuit applications such as biquadratic active filters, frequency dependent negative resistor realization oscillator design are given employing the memristors instead of capacitors. The fully integrated circuit configurations are derived and their terminal relations are calculated.The gain curves of the proposed filters, i-v characteristics of the frequency dependent negative resistor, the oscillation wave form of oscillator are plotted using SPICE simulator.
Relative intensity noise of mode-locked lasers utilizing sinusoidally chirped fiber bragg grating
The relative intensity noise (RIN) of a mode-locked hybrid soliton pulse source (HSPS) utilizing a sinusoidally chirped fiber Bragg grating (FBG) is investigated using the time-domain solution of coupled wave equations and rate equations which include both spontaneous and carrier density noise. The effect of some laser diode and grating parameters on the RIN of the HSPS are also described. The numerical results show that most of the parameters affect the system operation even without noise. However, noise increases with increasing linewidth enhancement factor, gain saturation parameter, spontaneous coupling factor and field coupling factor. Noise is also extremely sensitive to the RF and DC currents. RIN reduction at the fundamental frequency (2.5 GHz) is possible in a mode-locked HSPS utilizing a sinusoidally chirped Gaussian apodized FBG when compared with a HSPS with linearly chirped gratings. 9.64 dB noise reductions are obtained when the standard parameters are used. Furthermore, it is also shown that a HSPS utilizing a sinusoidally chirped FBG produces shorter pulses than linearly chirped FBG with and without noise.