Prof. Dr. Abdullah Atalar danışmanlığındaki tezler
39 tez · İhsan Doğramacı Bilkent University
GaN tabanlı yüksek kazançlı güç yükselteç tasarımı
RF power amplifiers remain a vital element of space, airborne, and radar applications. Modern systems require high power and gain while maintaining high efficiency. However, obtaining these features with a compact design brings challenges. Monolithic Microwave Integrated Circuits (MMIC) provide flexibility and enhanced performance while operating at higher frequencies. Among other transistor technologies, GaN on SiC based high electron mobility transistors (HEMTs) provide extraordinary performance with high power density, thermal conductivity, and high band gap. In this thesis, we present a three-stage X-Band MMIC power amplifier (PA) based on NANOTAM 250 nm GaN-on-SiC process technology. The characterization steps of the transistors are discussed to extract process parameters for the design. The amplifier is designed on the Keysight ADS environment. The design is realized on a 3-inch GaN-on-SiC wafer. In the 8.5–10.5 GHz frequency band, measurements show that the PA achieves a 40 dB small signal gain, PAE higher than 40%, and average 20 W output power under 28 V, 100 mA/mm pulsed biasing conditions at room temperature. The MMIC occupies 10.26 mm2 area and has 1.96 W/mm2 power density.
Üç fazlı invertör için gelişmiş direkt dörtlü kontrol uygulaması
Power electronics is widely utilized in various fields, such as the military, daily life, and industry. The efficiency of power conversion applications is important. Three-phase inverters are primarily used in motors and UPS systems. However, the design of a three-phase inverter requires advanced knowledge of software, hardware, and algorithms. The digital control of the three-phase inverter provides flexibility for the adjustment of output voltage and frequency. The combination of Sinusoidal Pulse Width Modulation (SPWM) and Direct Quadrature (DQ) control increases the stability of output voltage. In this thesis, we present an implementation of a three-phase voltage source inverter using the Digital Signal Processor (DSP) based controller of TMS320F28379D. There are three electronic cards in the system. The first card includes Switched-Mode Power Supplies (SMPS), current sense circuits, and three half-bridges using discrete MOSFETs. The second card comprises of a low-loss filter and a voltage sensing circuit. The input voltage of the three-phase inverter is 30 V, and the output is a three-phase inverter with an output voltage that can be adjusted up to 12 V with an output frequency of 50 Hz. The maximum power of the inverter is 98.5 W. The efficiency of the inverter is 90.72 % at the full load.
3 T manyetik rezonans görüntüleme sistemleri için düşük gürültü ve düşük güç tüketimli amplifikatörün tasarımı ve uygulaması
Magnetic Resonance Imaging (MRI) is a vital diagnostic tool in modern medicine due to its high spatial resolution, excellent soft tissue contrast, and non-invasive nature. The signal quality in MRI systems is primarily determined by the signal-to-noise ratio (SNR), which is crucial in high-field MRI systems like 3 T scanners. This thesis presents the design and implementation of a low-noise amplifier (LNA) operating at 123 MHz, corresponding to the Larmor frequency of hydrogen nuclei at 3 T. The LNA, based on a single-stage common-source topology using a GaAs pHEMT transistor, achieves a measured gain of 14.5 dB, a noise figure (NF) of 0.64 dB, an input reflection coefficient (S11) of -0.28 dB, and a 1 dB compression input power (P_in1dB) of -10.75 dBm. These results were validated against simulations, where the design showed high performance, with a power consumption of only 12.6 mW. The amplifier meets the requirements for MRI receiver systems, ensuring low noise and power consumption. Additionally, another version was implemented with input protection diodes for safe operation. This version achieves a measured gain of 14.9 dB, a noise figure (NF) of 0.79 dB, an input reflection coefficient (S11) of -0.32 dB, and a 1 dB compression input power (P_in1dB) of -9.65 dBm. This version also achieved 3.5 μs recovery time after 14 dBm of input power was applied for 1 ms. Key challenges such as impedance matching to short circuit, bias network, and input protection circuit are addressed in the design.
Kapasitif mikro işlemli sensör sürülmesi için Dickson şarj pompası devrelerinin tasarım, gerçekleme, üretim ve ölçümleri
This work presents the design and testing process of Dickson charge pump circuits for micromachined sensor biasing. Necessary blocks of different types of circuits with different functions are examined such as inverters, diode connected MOSFETs, ring oscillators, bond PADs, charge pump stages. Layouts for these circuits are designed and simulated using extracted parameters. The designed circuits are operating using a 5 Volts supply to generate output voltage levels of 12-15 Volts. Finalized layouts are placed on a chip using 0.35µm process. Designed chip is manufactured and bonded on a test PCB for verification. Measurement results are given and analyzed. Layout and circuit design improvements are proposed and simulated for proof. Steps for future improved designs and precautions are provided. This work enables the way for better functioning charge pump topologies and designs in the future.
Mekanik ayarlama ile Ku-Bant gömülü dalga kılavuzu bant geçiren filtre tasarımı
Substrate integrated waveguide (SIW) filters are widely used due to their easy fabrication techniques and relatively high quality factor. In microwave frequencies, manufacturing tolerances become comparable with wavelength and affect filter performance. Tuning resonator center frequencies and couplings between resonators allow correcting the errors that are caused by imperfections. An iris bandpass filter is designed in Ku-band using coupling matrix approach which relates mathematical coupling values to physical dimensions. SIW tuning is usually done by adding varactors to the circuit. This introduces nonlinearities which may be undesirable while also requiring external control voltages. A mechanical tuning method for SIW, similar to tuning screws that are used in waveguide filters, is analyzed for resonators and couplings. It is modified by using small surface mount resistors to achieve a more compact structure. Tuning mechanisms are inserted to designed filter and fabricated on a low loss substrate. Time domain method for tuning coupled filters is introduced as a tuning algorithm. Using mechanical tuners, SIW filter is tuned to desired filter performance.
Milimetre-dalga uygulamaları için geliştirilmiş Wilkinson güç bölücü yapıları
Communication systems, radars, electronic warfare and space applications desire integrated circuits with higher operating frequencies. Working at the millimeter-wave region increases data rates, provides a more efficient use of the spectrum and enables smaller products. Power dividers are used as building blocks for such applications to split and combine RF signals. Wilkinson power divider is one of the most commonly used topology, providing high return loss and isolation with low insertion loss. However, it occupies valuable chip area, has a limited bandwidth, requires accurate modeling and precise fabrication. In addition, the layout becomes complicated for three or more outputs and cannot be realized on a planar circuit. This work presents three techniques to address the drawbacks of the original Wilkinson divider. The first structure achieves a compact size without bandwidth degradation and provides additional physical isolation at the output. The second divider improves the bandwidth of operation and increases tolerance to sheet resistance variance, enabling robustness and higher yields. The third technique simplifies the layout of three-way dividers and allows a planar fabrication technology. The proposed structures are analyzed using even-odd mode analysis and design equations are derived. Three high performance dividers with 30 GHz center frequency are designed employing the developed methods. The circuits are realized using GaN based coplanar waveguide and microstrip monolithic microwave integrated circuit technology. Experimental results demonstrate good agreement with theory and simulations, proving that the presented improvements could be useful in future millimeter-wave RF applications.
EKG'de aritmi tespiti için bir analog nöromorfik tanımlayıcı çip
Following Moore's Law, the increase in the availability of more processing power alongside the development of algorithms that can use this power, electrocardiogram (ECG) systems are now becoming a part of our daily lives. The analytical detection of irregularities within the ECG scan, arrhythmias, is tricky due to the variations in the signals that differ from people to people due to physiological reasons. In order to overcome this problem, a two stage machine-learning based time-domain algorithm is first developed and tested on MatLab using data-sets from the MIT - BIH Arrhythmia Database. The algorithm begins with the preprocessing stage where seven features are extracted from the input ECG waveform. These features are then moved onto the second classification stage where a perceptron classifies the features as arrhythmic or normal. The algorithm was then converted into an analog CMOS circuit using the XFAB XC06M3 fabrication process on Cadence Virtuoso. Most of the operations in the preprocessing stage were completed using operational transconductance amplifiers (OTAs). For the classifier, the circuit uses analog floating gate metal oxide semiconductor transistors (FGMOS) to store the weights of the perceptron and a winner-take-all current comparator for the activation function. Simulation results show that the circuit works as intended with a power consumption of 290 μW.
Yük modülasyonlu dengeli yükselteçlerin analitik modeli ve tasarımı
RF power amplifiers (PA) with high efficiency and linearity are in high demand for modern communication systems. Modulated signals having a high peak-to-average power ratio (PAPR) require PA's to maintain these features in the output-back-off (OBO) region. Since higher linearity always brings the trade-off in the form of lower efficiency, a PA having both high efficiency and linearity is challenging requirement for RF designers. Load modulation is one of the promising techniques offering good efficiency-linearity trade-off under OBO conditions for conventional PAs. This work presents an analytical model for the load modulated balanced amplifier (LMBA) using the recently introduced analytical non-linear model of a RF power transistor. We show that it is possible to predict the efficiency and nonlinearity of the LMBA reasonably well using this simple transistor model having only a small number of parameters. To test the performance of the analytical model, we designed an LMBA using three identical discrete RF transistors and 3-dB hybrid couplers. The model parameters of the 5-W GaAs PHEMT are determined from the I-V characteristics and load-pull measurements. LMBA works at 1.7~GHz with a peak output power of 37.5~dBm and with a peak efficiency of 53\%. The efficiency is measured to be 47\% at 6~dB output-back-off.
Zarf takip metodu radyo frekans güç yükselteci tasarımı
In modern wireless communication systems, the requirement of achieving high data rates results in non-constant envelope signals with high peak to average power ratio (PAPR). However, the operation of conventional power amplifiers (PAs) at back-off power levels creates significant degradation in efficiency. Since efficiency is a critical design consideration for PAs to avoid high power consumption and heating problems, several techniques were introduced to maintain the high efficiency for a wide range of power levels. We designed an envelope tracking power amplifier (ETPA) that uses the supply modulation technique which is a promising solution to the efficiency degradation problem. In ETPA, the high efficiency is maintained at back-of levels by adjusting the supply voltage in accordance with the time varying signal envelope. The supply voltage was efficiently generated by using a synchronous buck converter operating at 10 MHz switching frequency. The converter was integrated to the designed class-AB PA by using a proper low pass filter. In order to improve the signal bandwidth that can be tracked, an envelope bandwidth elimination algorithm was used. The efficiency of the resulting ETPA system was measured as 26% for the signal that has 3 MHz bandwidth and 12 dB PAPR. The system has an efficiency of 20% with the signal that has 5 MHz bandwidth and 13 dB PAPR.
Manyetik rezonans görüntüleme için düşük güç tüketimli ve küçük boyutlu optik bağlantılı işaret alma sistemi
In Magnetic Resonance Imaging (MRI) systems echo signals received by a coil are sampled and subjected to digital signal processing. The physical link between the sampling system and the signal processor is coaxial cables in conventional applications. However, coaxial cables possess risks and limitations when placed in gradient and radio frequency fields, both of which are present in an MRI system. The complexity of issues related to coaxial cables increases rapidly as the number of channels scales up in parallel imaging applications. To overcome the drawbacks of coaxial cables, systems that employ fiber optic cables for the transmission of the analog signal have been proposed. In this work, we designed a system which transmits sampled and digitized analog signal through fiber optic cables, while the power required to perform acquisition and conversion operations is also delivered to the module using an optical link. To increase the number of channels that can be placed in a typical birdcage compartment, dimensions of the module are kept as small as possible. The module is designed to be used in a project with a 10.5 Tesla MRI system operating at 447 MHz which is currently available only at the University of Minnesota. The circuit design for one of the proposed approaches is completed at both the schematic and the layout levels to perform feasibility analysis. Theoretical estimations show that the power consumption is 263 mW and occupied cross-sectional area is 900 mm^2 per channel while attaining more than 95 dBFS SNR figure using 65 MSPS sampling rate.
X-bandında çalışan çapraz bağlı cmos gerilim kontrollü osilatörler
Voltage controlled oscillators (VCOs) are electronic devices whose oscillation frequencies can be tuned by applying an external control input. A widely preferred topology is the cross-coupled VCO topology, which offers easy implementation inside integrated circuits. VCO designers take certain performance metrics into account for their designs, with the most prominent ones being the frequency tuning range and the output phase noise. These two metrics often require trading off from one another; as introducing more networks for tunability increases the overall noise within the device. With the aim of observing this trade-off between the tuning range and phase noise, four VCOs have been designed and fabricated in a single die with a 0.18 µm CMOS process. They are designed to operate in the X-band, at almost the same oscillation frequencies, to allow for easier comparison. Each VCO in the IC offers either more tunability with more tuning circuits or better phase noise performance with simpler circuits. Measurement results verify this hypothesis; a decrease in output phase noise is observed in the tested VCOs that contained simpler tuning network. With center frequencies of oscillation at approximately 12 GHz in the VCOs, tuning ranges as high as 25% are achieved in the VCO with most tunability, while phase noises as low as -106 dBm/Hz (at a 1 MHz offset) were achieved in the one with no tunability.
PHEMT teknolojisi kullanarak yüksek güçlü MMIC yükselteç tasarımı
Power amplifiers are regarded as the one of the most important part of the radar and communication systems. In order to satisfy the system specifications, the power amplifiers must provide high output power and high efficiency at the same time. AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors (PHEMT) provide significant advantages offering high output power and high gain at RF and microwave frequencies. Considering the electrical performance, cost and the reliability issues, PHEMT monolithic microwave integrated circuit (MMIC) high power amplifiers are preferable at Ku-band frequencies (12-18 GHz portion of the electromagnetic spectrum in the microwave range of frequencies). In this thesis, a three-stage AlGaAs/InGaAs/GaAs pHEMT MMIC high power amplifier is developed which operates between 16-17.5 GHz. Based on 0.25 μm gate-length pHEMT process, the MMIC is fabricated on 4-mil thick wafer with the size of 5.5 x 5.7 mm^2. Under 8V drain voltage operation, 26.5-24 dB small signal gain, 10-W (40 dBm) continuous-wave mode output power at 3 dB compression with %25-30 drain efficiency is achieved when the base temperature of the chip is 85°C.
Ultra geniş bantlı güç bölücü birleştirici
Many typologies like the designs of Wilkinson Power Divider and Gysel Power Divider have been worked and improved through the years. Each design targets a higher bandwidth, a better isolation and a higher power handling capacity or smaller size. The basic analysis of every structure begins with the even mode and the odd mode models. The tapered lines are ultra wideband matching structures that are used to match real impedances. The only limitation of tapered line is the size, which has to be the half wavelength of the lower frequency limit. The tapered lines do not have any upper frequency cut-o . Because of the limitations in sizes, tapered lines have not been able to be used very commonly. The proposed new topology has a new taper topology with a single capacitor at the input side to decrease the lower frequency limit of the tapered line. The even mode structure of the proposed power divider/combiner is constructed of these improved tapered lines. In the odd mode analysis, the N section Wilkinson power divider/combiner design has been used. In order to determine the isolation resistor values, four di erent methods have been proposed. The proposed structure uses the surface resistive materials to implement these resistors. It has been observed that continuity of the isolation resistors between transmission lines causes some loss in the even mode. In order to solve this problem, the width of the resistors should be as small as possible to prevent the even mode loss.
Yeni saçılım parametresi ilişkilerini kullanarak performansı geliştirilmiş güç bölücüler ve yönlü bağlaçlar tasarlamak için yeni teknikler
Wide bandwidth provides with several benefits in RF applications such as enabling high data rates for communication applications, enhancing the multi tread avoiding capabilities of the jamming systems, improving the effectiveness of spread spectrum techniques. Operation in a wide bandwidth requires either broadband components or multiple narrow band components together with sophisticated multiplexing methods. There are several trivial methods to increase the bandwidth of the RF components. For instance the bandwidth of a power divider can be increased by increasing the number of sections which directly increases the insertion loss and circuit size, burdening a big trade off for the designer. The methods avoiding such a trade off are life savers in most of the applications. Such methods require new design approaches. This work aims to develop such methods with a special focus on improving the bandwidth and performance of the power dividers and directional couplers. We derive new scattering parameter relations and show that the relations require tricky design guidelines. S-parameter relations for a number of power divider types and directional coupler schemes are investigated. The derived equations have significant usages. One of the equations is used to design the optimal isolation network for the Wilkinson power divider. A number of equations imply a reduction in the number of the optimization parameters in the design of n-section or n-way dividers. Another equation is used to increase the directivity of microstrip directional couplers in a wide bandwidth. Experimental results are presented verifying the theoretical work.
Elektriksel uzunluğu kısa anten için tampon amfiler
Professional direction finding applications cover broad bandwidth of one to two decades and performance of the radiative element is of fundamental importance for such receiver oriented applications. It is important to optimize radiative element, i.e, antenna, for the bandwidth of interest. However, portability and weight concerns for the system limits radiator dimensions and eventually restricts the antenna design. Such antennas with their limitations are referred as electrically small antennas. For the application, utilization of a single electrically small monopole antenna that is capable of recovering the electromagnetic signal within a bandwith more than a decade is considered. Due to electrically small radiator, the antenna has a large reactance and small resistance as its input impedance, making it strictly narrowband. For wideband applications, presence of highly reactive impedance of the antenna implies significant reflection loss. This work is based on buffering an electrically small monopole receiver antenna that is to be used by a compact direction finding system. In the bandwidth of operation (20MHz-1GHz), the antenna is not suitable for passive matching, therefore a buffer amplifier is considered. Transferring the power directly to the receiver is not possible due to input impedance of the antenna. Alternatively, the approach is to probe the antenna output voltage by the active circuit with a high input impedance. This implies antenna voltage is taken without any reduction, then reference voltage is buffered to the output while providing a constant output impedance. Two types of buffer amplifiers for the monopole are designed, simulated and tested combined with the antenna.
Kapasitif mikroişlenmiş ultrasonik çeviriciler için transempedans yükseltiçi
In this thesis a design of a CMOS transimpedance amplifier (TIA) for a capacitive micro-machined ultrasonic transducer (CMUT) is presented. CMUT's have a high electrical impedance when used as receivers. Any capacitance between the CMUT and a high impedance amplifier will degrade the frequency response. So, we need to amplify the current rather than the voltage. This approach requires a transimpedance amplifier. The designed TIA has a 30 MHz bandwidth and 400 kohm transimpedance gain. The total input referred current noise of the TIA is 270fA/sqrt(Hz) at 10 MHz. The noise figure of the TIA is 2.7 dB at 10 MHz when connected to the CMUT with 200 kohm source resistance. The power consumption of the TIA is 10.5 mW and the size of the TIA layout is 133um x 45um. The TIA chip will be fabricated in AMS C35B4C3 0.35um process.
Geniş bantlı değiştirilmiş Gysel güç bölücüsü
Power dividers/combiners are one of the essential and crucial components of the modern RF communication systems since dividing makes RF power ampli cation easier to handle. As the data rates of the systems increase, the demand for wide bandwidth devices become more urgent and essential. Also, wide bandwidth systems show broadband performance in electronic warfare applications such as jamming. However, for RF power combiners/dividers increasing the bandwidth comes along with an engineering trade-off ; the isolation of the divider decreases signi cantly. There are several studies in literature that o er various types of trivial solutions for improving both the bandwidth and the isolation performance of generic Wilkinson and Gysel power divider structures. This work concentrates on the conventional Gysel power divider structure since for high-power applications Gysel divider is preferred mainly for the feasibility of external isolation resistors. We propose a modi ed Gysel divider structure with a series LC circuit resonant at the center frequency to correct the impedance at the output and the isolation ports and the generic transmission line impedances optimized to adapt to this modifi cation. We both show the interrelations of the capacitor and inductor values and also their relations to the scattering parameters and off er a guideline to choose the appropriate fi lter for the required application. The experimental results are presented to verify the proposed Gysel divider structure.
Çok modlu dikdörtgen boşluk rezonatörü tabanlı kompakt Ka-bant filtre uygulamaları
Filters based on multiple mode cavity resonator technique have the advantage of realizing a given fi lter function in a reduced volume and weight with the drawback of increased complexity. In order to decrease the dependence on electromagnetic analysis software and to gain a better insight on the physics of the structure, the multiple mode single rectangular cavity fi lter structure is investigated with an analytical approach. Expressions are obtained for the modal frequency shifts and for the intermodal coupling due to various types of corner cuts. An algorithm is proposed predicting the physical dimensions of the final structure given the corresponding coupling matrix. Example designs are realized. The algorithm is able to determine the physical dimensions of the second and third-order filters within a few percent. The classical triple mode rectangular cavity filter structure is altered to form a triplet. The new triplet structure can be arranged to result in either a lower or higher sideband transmission zero. An example Ka-Band design is fabricated with both machining and a novel 3D printing technology. The results are in agreement with the expectations. The filter structure is further tailored to allow integration to Ka-Band waveguide output microwave modules without signifi cant increase in the module's volume requirement.
Dengeli yükselteçlerde kazanç varyasyonu ve gürültü figürü kötüleşmesi
Although using balanced amplifiers in modern wireless communication systems has many advantages, the output and the noise response of the balanced amplifiers may vary from the expected value considerably due to the imperfections in the amplifier and the divider/combiner sections. First, we analyze the variation in the total gain of the balanced amplifiers using 2-way 0° power dividers and 90° couplers. In this context, mathematical analyses are made and analytical expressions are obtained to compare the two topologies. Analytical expressions show that the uncertainty in the total gain is more if the 90° coupler is used in the balanced structure as opposed to a 2-way 0° power divider for the same return loss/isolation values. Then, we present exact and approximate analytical results for the noise figure and noise parameters of the balanced amplifier in divider topology by using the noise waves. By the help of the noise wave approach, the output noise powers generated by each element in the balanced amplifier are derived. Y-parameters are used to determine the noise waves and the correlation matrix of the divider whereas the noise parameters are used to write the noise waves of the amplifier. Balanced amplifiers suffer in the noise figure performance in comparison to a stand-alone amplifier even with an ideal input divider. The noise parameters degrade further with an imperfect divider. Not only the nonzero return loss and the isolation but also the ohmic loss, amplitude and phase imbalances are considered. Besides, non-zero optimal source impedance affects the noise parameters of the balanced amplifier. Measurement results are also presented as a verification.
94-GHZ SiGe BiCMOS teknolojisinde faz evireci-değiştirilebilir kazançlı yükselteç
Phased array radar systems are capable of steering the beam of radio waves electronically by adjusting the gain and phase of each antenna element as desired. In order to achieve that, each element has to have gain/phase control and these parameters have to be controlled separately. In W-Band designs, constant gain-360 degree phase control is difficult to achieve due to parasitic effects of high frequencies which may quickly differ across different settings. Dividing the phase control task into different blocks in system eases the design difficulties. A well developed W-Band technology SiGe BiCMOS is also crucial to achieve high frequencies and system control. In this thesis, a 94-GHz SiGe BiCMOS phase inverter with variable gain amplifier is developed. Single bit-180 degree phase inversion enables to use multiple bit-180 degree phase shifter which is easier to design in W-Band. In addition to that, variable gain ampli er allows to use this circuit in phased array systems for amplitude tapering to achieve desired beam forming.
Mikroişlenmiş basınç sensörü
Capacitive Micromachined Ultrasonic Transducer (CMUT) is a microelectromechanical device that is basically formed by a moving top electrode, a stable bottom electrode and a gap in between. In spite of its this simple mass-spring construction, CMUT is a nonlinear device and its working principles have been formulated. According to these studies, the top electrode can be set in motion by the applied pressure on it and by depending on the amount of that pressure, the resonant frequency of the CMUT can be altered. Therefore, it is possible to use CMUT to obtain a pressure sensor. In this respect, what we have to do is keep tracking of its resonant frequency to deduce the pressure. The most effective way of doing it, on the other hand, is using an oscillator circuit which also provides us the capability of tracking the resonant frequency in real time. Also, to design an integrated circuit that works with the CMUT, the best way is utilizing a Colpitts oscillator. In this thesis, we design a pressure sensor with CMUT based Colpitts oscillator.
FFT ve FHT algorıtmaları için uygulamaya özgü komut kümeli işlemci tasarımı
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier trans-mission technique which is used in many digital communication systems. Inthis technique, Fast Fourier Transformation (FFT) and inverse FFT (IFFT) arekernel processing blocks which are used for data modulation and demodulationrespectively. Another algorithm which can be used for multi-carrier transmissionis the Fast Hartley Transform algorithm. The FHT is a real valued transforma-tion and can give signiï¬cantly better results than FFT algorithm in terms ofenergy eï¬ciency, speed and die area. This thesis presents Application Speciï¬cInstruction Set Processors (ASIP) for the FFT and FHT algorithms. ASIPscombine the ï¬exibility of general purpose processors and eï¬ciency of applicationspeciï¬c integrated circuits (ASIC). Programmability makes the processor ï¬exibleand special instructions, memory architecture and pipeline makes the processoreï¬cient.In order to design a low power processor we have selected the recently pro-posed cached FFT algorithm which outperforms standard FFT. For the cachedFFT algorithm we have designed two ASIPs one having a single execution unitiiiand the other having four execution units. For the FHT algorithm we havederived the cached FHT algorithm and designed two ASIPs; one for the FHTand one for the cached FHT algorithm. We have modeled these processors withan Architecture Description Language (ADL) called Language of Instruction SetArchitectures (LISA). The LISATek processor designer, generates the softwaretool chain (assembler, linker and instruction set simulator) and HDL code of theprocessor from the model in LISA automatically. The generated HDL code isfurther synthesized into gate-level description by Synopsis Design Compiler with0.13 micron technology library and then power simulations are performed. Thesingle execution unit cached FFT processor have been shown to save 25% of en-ergy consumption as compared to an FFT ASIP. The four execution unit cachedFFT processor on the other hand runs faster up to 186%. The ASIP designedfor the developed cached FHT algorithm runs almost two times faster than theASIP for the FHT algorithm.Keywords: FFT, cached FFT, FHT, cached FHT, Applicattion Speciï¬c Instruc-tion Set Processor, OFDMiv
Önbozulum yolu ile güç yükselteci doğrusallaştırması
Power ampliï¬ers are important elements in communication systems but they areinherently nonlinear. This nonlinearity shows itself in the form of amplitude andphase distortion. One way to get rid of this nonlinear behaviour is to applybackoï¬ which means to operate the ampliï¬er at an output power smaller thanits saturated output power. As the backoï¬ is increased, the ampliï¬er will behavemore linearly. But this will also reduce the eï¬ciency of the ampliï¬er, which isundesirable. This tradeoï¬ between eï¬ciency and linearity is solved by lineariza-tion techniques. By using linearization techniques, the ampliï¬er can be operatednear to saturation with good eï¬ciency and linearity.This thesis focuses on polar polynomial predistortion and polar look-up tablepredistortion, which are popular linearization techniques. A polar polynomialpredistorter and a polar look-up table predistorter are implemented and testedwith simulations in software. The implementation and testing is done by us-ing IT++ which is a C++ library of mathematical, signal processing, speechprocessing, and communications classes and functions. The testing of the predis-torters is done by using a baseband system model which consists of a 16-QAMmodulator, an upsampler, a raised cosine ï¬lter, the predistorter and a basebandiiibehavioural ampliï¬er model. The performance of the predistorters is evaluatedin terms of adjacent channel power ratio, AM/AM & AM/PM responses andBER under AWGN. Simulation results show that the predistorters have goodperformance. In the simulations, the polar polynomial predistorter achieved 20dB reduction and the polar look-up table predistorter achieved 25 dB reductionin adjacent channel power ratio. The eï¬ect of polynomial order and table sizeon the performance of the predistorters is investigated. Furthermore, the eï¬ectof lowpass ï¬ltering on the performance of the predistorters is also investigatedby placing a lowpass ï¬lter after the predistorters in the system model. It is ob-served that as the ratio of the bandwidth of the lowpass ï¬lter to the bandwidthof the raised cosine ï¬lter decreases, the negative eï¬ect of the lowpass ï¬lter onthe performance of the predistorters increases.Keywords: polar polynomial predistortion, polar look-up table predis-tortion, linearization, AM/AM distortion, AM/PM distortion, ampli-ï¬er nonlinearity.iv
Çift ikili turbo kod analizi ve kod çözücü uygulaması
Classical Turbo Code presented in 1993 by Berrau et al. received great attention due to its near Shannon Limit decoding performance. Double Binary Circular Turbo Code is an improvement on Classical Turbo Code and widely used in today?s communication standards, such as IEEE 802.16 (WIMAX) and DVB-RSC. Compared to Classical Turbo Codes, DB-CTC has better error-correcting capability but more computational complexity for the decoder scheme. In this work, various methods, offered to decrease the computational complexity and memory requirements of DB-CTC decoder in the literature, are analyzed to find the optimum solution for the FPGA implementation of the decoder. IEEE 802.16 standard is taken into account for all simulations presented in this work and different simulations are performed according to the specifications given in the standard. An efficient DB-CTC decoder is implemented on an FPGA board and compared with other implementations in the literature.