Matching Items (124)
Description
In thesis, a test time reduction (a low cost test) methodology for digitally-calibrated pipeline analog-to-digital converters (ADCs) is presented. A long calibration time is required in the final test to validate performance of these designs. To reduce total test time, optimized calibration technique and calibrated effective number of bits (ENOB) prediction from calibration coefficient will be presented. With the prediction technique, failed devices can be identified only without actual calibration. This technique reduces significant amount of time for the total test time.
ContributorsKim, Kibeom (Author) / Ozev, Sule (Thesis advisor) / Kitchen, Jennifer (Committee member) / Barnaby, Hugh (Committee member) / Arizona State University (Publisher)
Created2013
Description
This study focuses on implementing probabilistic nature of material properties (Kevlar® 49) to the existing deterministic finite element analysis (FEA) of fabric based engine containment system through Monte Carlo simulations (MCS) and implementation of probabilistic analysis in engineering designs through Reliability Based Design Optimization (RBDO). First, the emphasis is on experimental data analysis focusing on probabilistic distribution models which characterize the randomness associated with the experimental data. The material properties of Kevlar® 49 are modeled using experimental data analysis and implemented along with an existing spiral modeling scheme (SMS) and user defined constitutive model (UMAT) for fabric based engine containment simulations in LS-DYNA. MCS of the model are performed to observe the failure pattern and exit velocities of the models. Then the solutions are compared with NASA experimental tests and deterministic results. MCS with probabilistic material data give a good prospective on results rather than a single deterministic simulation results. The next part of research is to implement the probabilistic material properties in engineering designs. The main aim of structural design is to obtain optimal solutions. In any case, in a deterministic optimization problem even though the structures are cost effective, it becomes highly unreliable if the uncertainty that may be associated with the system (material properties, loading etc.) is not represented or considered in the solution process. Reliable and optimal solution can be obtained by performing reliability optimization along with the deterministic optimization, which is RBDO. In RBDO problem formulation, in addition to structural performance constraints, reliability constraints are also considered. This part of research starts with introduction to reliability analysis such as first order reliability analysis, second order reliability analysis followed by simulation technique that are performed to obtain probability of failure and reliability of structures. Next, decoupled RBDO procedure is proposed with a new reliability analysis formulation with sensitivity analysis, which is performed to remove the highly reliable constraints in the RBDO, thereby reducing the computational time and function evaluations. Followed by implementation of the reliability analysis concepts and RBDO in finite element 2D truss problems and a planar beam problem are presented and discussed.
ContributorsDeivanayagam, Arumugam (Author) / Rajan, Subramaniam D. (Thesis advisor) / Mobasher, Barzin (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2012
Description
During the last decades the development of the transistor and its continuous down-scaling allowed the appearance of cost effective wireless communication systems. New generation wideband wireless mobile systems demand high linearity, low power consumption and the low cost devices. Traditional RF systems are mainly analog-based circuitry. Contrary to digital circuits, the technology scaling results in reduction on the maximum voltage swing which makes RF design very challenging. Pushing the interface between the digital and analog boundary of the RF systems closer to the antenna becomes an attractive trend for modern RF devices. In order to take full advantages of the deep submicron CMOS technologies and digital signal processing (DSP), there is a strong trend towards the development of digital transmitter where the RF upconversion is part of the digital-to-analog conversion (DAC). This thesis presents a new digital intermediate frequency (IF) to RF transmitter for 2GHz wideband code division multiple access (W-CDMA). The proposed transmitter integrates a 3-level digital IF current-steering cell, an up-conversion mixer with a tuned load and an RF variable gain amplifier (RF VGA) with an embedded finite impulse response (FIR) reconstruction filter in the up-conversion path. A 4th-order 1.5-bit IF bandpass sigma delta modulator (BP SDM) is designed to support in-band SNR while the out-of-band quantization noise due to the noise shaping is suppressed by the embedded reconstruction filter to meet spectrum emission mask and ACPR requirements. The RF VGA provides 50dB power scaling in 10-dB steps with less than 1dB gain error. The design is fabricated in a 0.18um CMOS technology with a total core area of 0.8 x 1.6 mm2. The IC delivers 0dBm output power at 2GHz and it draws approximately 120mA from a 1.8V DC supply at the maximum output power. The measurement results proved that a digital-intensive digital IF to RF converter architecture can be successfully employed for WCDMA transmitter application.
ContributorsHan, Yongping (Author) / Kiaei, Sayfe (Thesis advisor) / Yu, Hongyu (Committee member) / Bakkaloglu, Bertan (Committee member) / Aberle, James T., 1961- (Committee member) / Barnaby, Hugh (Committee member) / Arizona State University (Publisher)
Created2012
Description
Concrete design has recently seen a shift in focus from prescriptive specifications to performance based specifications with increasing demands for sustainable products. Fiber reinforced composites (FRC) provides unique properties to a material that is very weak under tensile loads. The addition of fibers to a concrete mix provides additional ductility and reduces the propagation of cracks in the concrete structure. It is the fibers that bridge the crack and dissipate the incurred strain energy in the form of a fiber-pullout mechanism. The addition of fibers plays an important role in tunnel lining systems and in reducing shrinkage cracking in high performance concretes. The interest in most design situations is the load where cracking first takes place. Typically the post crack response will exhibit either a load bearing increase as deflection continues, or a load bearing decrease as deflection continues. These behaviors are referred to as strain hardening and strain softening respectively. A strain softening or hardening response is used to model the behavior of different types of fiber reinforced concrete and simulate the experimental flexural response. Closed form equations for moment-curvature response of rectangular beams under four and three point loading in conjunction with crack localization rules are utilized. As a result, the stress distribution that considers a shifting neutral axis can be simulated which provides a more accurate representation of the residual strength of the fiber cement composites. The use of typical residual strength parameters by standards organizations ASTM, JCI and RILEM are examined to be incorrect in their linear elastic assumption of FRC behavior. Finite element models were implemented to study the effects and simulate the load defection response of fiber reinforced shotcrete round discrete panels (RDP's) tested in accordance with ASTM C-1550. The back-calculated material properties from the flexural tests were used as a basis for the FEM material models. Further development of FEM beams were also used to provide additional comparisons in residual strengths of early age samples. A correlation between the RDP and flexural beam test was generated based a relationship between normalized toughness with respect to the newly generated crack surfaces. A set of design equations are proposed using a residual strength correction factor generated by the model and produce the design moment based on specified concrete slab geometry.
ContributorsBarsby, Christopher (Author) / Mobasher, Barzin (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2011
Description
In today's world there is a great need for sensing methods as tools to provide critical information to solve today's problems in security applications. Real time detection of trace chemicals, such as explosives, in a complex environment containing various interferents using a portable device that can be reliably deployed in a field has been a difficult challenge. A hybrid nanosensor based on the electrochemical reduction of trinitrotoluene (TNT) and the interaction of the reduction products with conducting polymer nanojunctions in an ionic liquid was fabricated. The sensor simultaneously measures the electrochemical current from the reduction of TNT and the conductance change of the polymer nanojunction caused from the reduction product. The hybrid detection mechanism, together with the unique selective preconcentration capability of the ionic liquid, provides a selective, fast, and sensitive detection of TNT. The sensor, in its current form, is capable of detecting parts per trillion level TNT in the presence of various interferents within a few minutes. A novel hybrid electrochemical-colorimetric (EC-C) sensing platform was also designed and fabricated to meet these challenges. The hybrid sensor is based on electrochemical reactions of trace explosives, colorimetric detection of the reaction products, and unique properties of the explosives in an ionic liquid (IL). This approach affords not only increased sensitivity but also selectivity as evident from the demonstrated null rate of false positives and low detection limits. Using an inexpensive webcam a detection limit of part per billion in volume (ppbV) has been achieved and demonstrated selective detection of explosives in the presence of common interferences (perfumes, mouth wash, cleaners, petroleum products, etc.). The works presented in this dissertation, were published in the Journal of the American Chemical Society (JACS, 2009) and Nano Letters (2010), won first place in the National Defense Research contest in (2009) and has been granted a patent (WO 2010/030874 A1). In addition, other work related to conductive polymer junctions and their sensing capabilities has been published in Applied Physics Letters (2005) and IEEE sensors journal (2008).
ContributorsDiaz Aguilar, Alvaro (Author) / Tao, Nongjian (Thesis advisor) / Tsui, Raymond (Committee member) / Barnaby, Hugh (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2012
Description
The front end of almost all ADCs consists of a Sample and Hold Circuit in order to make sure a constant analog value is digitized at the end of ADC. The design of Track and Hold Circuit (THA) mainly focuses on following parameters: Input frequency, Sampling frequency, dynamic Range, hold pedestal, feed through error. This thesis will discuss the importance of these parameters of a THA to the ADCs and commonly used architectures of THA. A new architecture with SiGe HBT transistors in BiCMOS 130 nm technology is presented here. The proposed topology without complicated circuitry achieves high Spurious Free Dynamic Range(SFDR) and Total Harmonic Distortion (THD).These are important figure of merits for any THA which gives a measure of non-linearity of the circuit. The proposed topology is implemented in IBM8HP 130 nm BiCMOS process combines typical emitter follower switch in bipolar THAs and output steering technique proposed in the previous work. With these techniques and the cascode transistor in the input which is used to isolate the switch from the input during the hold mode, better results have been achieved. The THA is designed to work with maximum input frequency of 250 MHz at sampling frequency of 500 MHz with input currents not more than 5mA achieving an SFDR of 78.49 dB. Simulation and results are presented, illustrating the advantages and trade-offs of the proposed topology.
ContributorsRao, Nishita Ramakrishna (Author) / Barnaby, Hugh (Thesis advisor) / Bakkaloglu, Bertan (Committee member) / Christen, Jennifer Blain (Committee member) / Arizona State University (Publisher)
Created2012
Description
The non-quasi-static (NQS) description of device behavior is useful in fast switching and high frequency circuit applications. Hence, it is necessary to develop a fast and accurate compact NQS model for both large-signal and small-signal simulations. A new relaxation-time-approximation based NQS MOSFET model, consistent between transient and small-signal simulations, has been developed for surface-potential-based MOSFET compact models. The new model is valid for all regions of operation and is compatible with, and at low frequencies recovers, the quasi-static (QS) description of the MOSFET. The model is implemented in two widely used circuit simulators and tested for speed and convergence. It is verified by comparison with technology computer aided design (TCAD) simulations and experimental data, and by application of a recently developed benchmark test for NQS MOSFET models. In addition, a new and simple technique to characterize NQS and gate resistance, Rgate, MOS model parameters from measured data has been presented. In the process of experimental model verification, the effects of bulk resistance on MOSFET characteristics is investigated both theoretically and experimentally to separate it from the NQS effects.
ContributorsZhu, Zeqin (Author) / Gildenblat, Gennady (Thesis advisor) / Bakkaloglu, Bertan (Committee member) / Barnaby, Hugh (Committee member) / Mcandrew, Colin C (Committee member) / Arizona State University (Publisher)
Created2012
Description
Ultra-concealable multi-threat body armor used by law-enforcement is a multi-purpose armor that protects against attacks from knife, spikes, and small caliber rounds. The design of this type of armor involves fiber-resin composite materials that are flexible, light, are not unduly affected by environmental conditions, and perform as required. The National Institute of Justice (NIJ) characterizes this type of armor as low-level protection armor. NIJ also specifies the geometry of the knife and spike as well as the strike energy levels required for this level of protection. The biggest challenges are to design a thin, lightweight and ultra-concealable armor that can be worn under street clothes. In this study, several fundamental tasks involved in the design of such armor are addressed. First, the roles of design of experiments and regression analysis in experimental testing and finite element analysis are presented. Second, off-the-shelf materials available from international material manufacturers are characterized via laboratory experiments. Third, the calibration process required for a constitutive model is explained through the use of experimental data and computer software. Various material models in LS-DYNA for use in the finite element model are discussed. Numerical results are generated via finite element simulations and are compared against experimental data thus establishing the foundation for optimizing the design.
ContributorsVokshi, Erblina (Author) / Rajan, Subramaniam D. (Thesis advisor) / Neithalath, Narayanan (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2012
Description
The current method of measuring thermal conductivity requires flat plates. For most common civil engineering materials, creating or extracting such samples is difficult. A prototype thermal conductivity experiment had been developed at Arizona State University (ASU) to test cylindrical specimens but proved difficult for repeated testing. In this study, enhancements to both testing methods were made. Additionally, test results of cylindrical testing were correlated with the results from identical materials tested by the Guarded Hot&ndashPlate; method, which uses flat plate specimens. In validating the enhancements made to the Guarded Hot&ndashPlate; and Cylindrical Specimen methods, 23 tests were ran on five different materials. The percent difference shown for the Guarded Hot&ndashPlate; method was less than 1%. This gives strong evidence that the enhanced Guarded Hot-Plate apparatus in itself is now more accurate for measuring thermal conductivity. The correlation between the thermal conductivity values of the Guarded Hot&ndashPlate; to those of the enhanced Cylindrical Specimen method was excellent. The conventional concrete mixture, due to much higher thermal conductivity values compared to the other mixtures, yielded a P&ndashvalue; of 0.600 which provided confidence in the performance of the enhanced Cylindrical Specimen Apparatus. Several recommendations were made for the future implementation of both test methods. The work in this study fulfills the research community and industry desire for a more streamlined, cost effective, and inexpensive means to determine the thermal conductivity of various civil engineering materials.
ContributorsMorris, Derek (Author) / Kaloush, Kamil (Thesis advisor) / Mobasher, Barzin (Committee member) / Phelan, Patrick E (Committee member) / Arizona State University (Publisher)
Created2011
Description
Lateral Double-diffused (LDMOS) transistors are commonly used in power management, high voltage/current, and RF circuits. Their characteristics include high breakdown voltage, low on-resistance, and compatibility with standard CMOS and BiCMOS manufacturing processes. As with other semiconductor devices, an accurate and physical compact model is critical for LDMOS-based circuit design. The goal of this research work is to advance the state-of-the-art by developing a physics-based scalable compact model of LDMOS transistors. The new model, SP-HV, is constructed from a surface-potential-based bulk MOSFET model, PSP, and a nonlinear resistor model, R3. The use of independently verified and mature sub-models leads to increased accuracy and robustness of an overall LDMOS model. Improved geometry scaling and simplified statistical modeling are other useful and practical consequences of the approach. Extensions are made to both PSP and R3 for improved modeling of LDMOS devices, and one internal node is introduced to connect the two component models. The presence of the lightly-doped drift region in LDMOS transistors causes some characteristic device effects which are usually not observed in conventional MOSFETs. These include quasi-saturation, a sharp peak in transconductance at low VD, gate capacitance exceeding oxide capacitance at positive VD, negative transcapacitances CBG and CGB at positive VD, a "double-hump" IB(VG) current and expansion effects. SP-HV models these effects accurately. It also includes a scalable self-heating model which is important to model the geometry dependence of the expansion effect. SP-HV, including its scalability, is verified extensively by comparison both to TCAD simulations and experimental data. The close agreement confirms the validity of the model structure. Circuit simulation examples are presented to demonstrate its convergence.
ContributorsYao, Wei (Author) / Gildenblat, Gennady (Thesis advisor) / Barnaby, Hugh (Committee member) / Cao, Yu (Committee member) / McAndrew, Colin (Committee member) / Arizona State University (Publisher)
Created2012