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1
Postma, Marius. „Air-fuel ratio control in spark ignition internal combustion engines using switching LPV techniques“. Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/30499.
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The Three-Way Catalytic Converter (TWC) is a critical component for the mitigation of tailpipe emissions of modern Internal Combustion (IC) engines. Because the TWC operates effectively only when a stoichiometric ratio of air and fuel is combusted in the engine, accurate control of the air-fuel ratio is required. To track the desired ratio, a switching Linear Parameter Varying (LPV) air-fuel ratio feedback controller, scheduled based on engine speed and air flow, and providing guaranteed L2 performance, is introduced. The controller measures the air-fuel ratio in the exhaust flow using a Universal Exhaust Gas Oxygen (UEGO) sensor and adjusts the amount of fuel injected accordingly.
A detailed model of the air-fuel ratio control problem is developed to demonstrate the non-linear and parameter-dependent nature of the plant, as well as the presence of pure delays. The model’s dynamics vary considerably with engine speed and air flow. A simplified model, widely used in literature and known as a First Order Plus Dead Time (FOPDT) model, is then derived. It effectively captures the control problem using a model which is linear but parameter-varying with engine speed and air flow.
Large variation of the FOPDT model across the engine’s operating range has led to conservative LPV controllers in previous literature. For this reason, the operating range is divided into smaller subregions, and an individual LPV controller is designed for each subregion. The LPV controllers are then switched based on the current engine speed and air flow and are collectively referred to as a switching LPV controller. The controller design problem is expressed as a Linear Matrix Inequality (LMI ) convex optimization problem which can be efficiently solved using available LMI techniques.
Simulations are performed and the air-fuel ratio tracking performance of the switching LPV controller is compared with that of conventional controllers including, H∞ and LPV, as well as a novel adaptive controller. The switching LPV controller achieves improved performance over the complete operating range of the engine.
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Parsons, Teresa Camille. „Effects of Concurrent Fixed Interval-fixed Ratio Schedules of Reinforcement on Human Responding“. Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc4846/.
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The present study contributes an apparatus and research paradigm useful in generating human performances sensitive to concurrent schedules of reinforcement. Five participants produced performances observed to be under temporal and ratio control of concurrent fixed interval-fixed ratio schedules. Two aspects of interaction between FI and FR schedules were distinguishable in the data. First, interaction between two schedules was observed in that changes in the value of one schedule affected behavior reinforced on another schedule. Second, switching from one pattern to the other functioned as an operant unit, showing stability during schedule maintenance conditions and sensitivity to extinction. These effects are discussed in the context of current views on behavior under concurrent schedules of reinforcement, and some implications for the conceptualization, measurement, analysis, and treatment of complex behavior are presented.
3
Kolks, Giacomo, und Jürgen Weber. „Electro-hydrostatic compact drives with variable transmission ratio“. Technische Universität Dresden, 2020. https://tud.qucosa.de/id/qucosa%3A71209.
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Electro-hydrostatic compact drives are an emerging technology within a range of industrially available translational drive solutions, combining the specific advantages of hydraulic and electromechanical screw drives. Compared to electromechanical screw drives, hydrostatic drives can vary their transmission ratio with comparably little effort, giving them the key advantage of downsizing the electric drive components for a given load cycle. This paper provides a guideline on how to calculate the downsizing potential of electric motors and inverters arising from variable transmission ratio based on the load regime of a given application. Furthermore, a comprehensive systematisation of the actual switching process is described for systems that are switched by means of switching valves. The presented set of methodology is applied to demonstrators in order to validate the general findings.
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Radić, Aleksandar. „Comparative analysis of high input voltage and high voltage conversion ratio step-down converters equipped with silicon carbide and ultrafast silicon diodes“. Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/861.
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DC to DC step-down applications with high input voltage and high voltage conversion ratio operational requirements, such as photovoltaic battery chargers, are subject to high conduction losses, high switching losses and substantial reverse-recovery losses when minority carrier principle diodes are used. The recent introduction of silicon carbide diodes with high breakdown voltages has made possible the elimination of reverse-recovery losses at high voltage levels and as such has sparked interest in their use due to the potential efficiency improvements.
This report presents the results of a comprehensive analysis on the use of silicon carbide diodes and their counterparts, ultrafast silicon diodes, in conventional buck converters and isolated current-fed buck converters in high input voltage and high voltage conversion ratio step-down applications. The analysis illustrates both theoretically, with the use of steady-state average models, and experimentally the substantial efficiency benefits of the use of reverse-recovery free silicon carbide diodes in the conventional buck converter and the small but significant improvement in the efficiency of the isolated current-fed buck converter. The improvements of the conventional buck converter paired with silicon carbide diodes are shown to be significant enough to grant the variant the most efficient position for power levels below 1 kW. In addition, the four variants are categorized based on their cost and performance; therefore, providing engineers with a convenient guide to aid their selection of the appropriate converter depending on the operational requirements.
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Dowell, Margaret Anne. „Influence of three-tier cost sharing on patient compliance with and switching of cardiovascular medications“. Columbus, Ohio : Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1030118543.
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Thesis (M.S.--Ohio State University, 2002.Title from first page of PDF file. Document formatted into pages; contains xvi, 173 p.: ill. Includes abstract and vita. Co-advisors: Craig A. Pedersen, Dept. of Pharmacy; Anne Scheck McAlearney, School of Public Health. Includes bibliographical references (p. 169-173).
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Duan, Quiyi. „Autonomous and Intelligent Radio Switching“. BYU ScholarsArchive, 2008. https://scholarsarchive.byu.edu/etd/1835.
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With the proliferation of mobile applications and the abundance of wireless devices, it is increasingly common for devices to support multiple radios. When two devices are communicating they should choose the best available radio based on user preference and application requirements. This type of “radio switching” should happen automatically, so that the system optimizes performance dynamically. To achieve this objective, we design an Autonomous and Intelligent Radio Switching (AIRS) system to leverage the radio heterogeneity common in today's wireless devices. The AIRS system consists of three key components. First, we design a radio preference evaluation module to dynamically select the best radio according to users' preference, application's QoS requirements, and the device battery usage. Second, we propose a link quality measurement and prediction module to predict the radio quality under a variety of mobility and interference conditions. Third, we present a radio switching decision making module to switch to the preferred available radio intelligently, based on the preference and link quality evaluations. The AIRS system maintains connectivity, as well as improves link quality, via dynamic and intelligent radio switching, regardless of interference or collisions from the interfaces of other devices. The radio preference evaluation module is able to generate and adjust a preference list dynamically. Multiple users' requirements are satisfied in a mutually beneficial manner and the selected radio is Pareto optimal. The link prediction module is able to achieve an accuracy above 90% under a variety of mobility and interference conditions. The module can dynamically increase the link measurement interval and significantly reduce its power consumption, without sacrificing accuracy. The decision algorithm uses several parameters to avoid switching radios too frequently, and is able to provide dynamic, but stable radio switching, while balancing the competing objectives of high throughput and low power consumption. Overall, the AIRS system is able to achieve high goodput (application level throughput) and long battery life as applied to handoff management in a frequently changing mobile environment.
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Kim, David Storm. „Hybrid free-space and radio frequency switching“. College Park, Md.: University of Maryland, 2008. http://hdl.handle.net/1903/8913.
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Thesis (M.S.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of Electrical and Computer Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Dileseigres, Angeline. „Diarylethenes used as molecular switches for the connection of gold nanoparticles“. Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS014.
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Les molécules de diaryléthène utilisées comme interrupteurs moléculaires sont envisagées comme composants de dispositifs électroniques moléculaires. Ces molécules photochromiques présentent une stabilité thermique, une résistance à la fatigue et une efficacité de commutation élevées. Néanmoins, la commutation de la plupart des diaryléthènes (DAEs) est asymétrique : leur réaction de photocycloréversion possède un rendement quantique bien inférieur à celui de leur réaction de photocyclisation. Une stratégie pour résoudre ce problème de commutation asymétrique a été testée, elle consistait à connecter les molécules de diaryléthène à des nanoparticules d'or (AuNPs). En effet, les nanoparticules d'or présentent à la fois une résonance plasmonique de surface localisée (LSPR), très utile pour le suivi de l'adsorption des DAEs à la surface des AuNPs, et un effet de nanoantenne plasmonique. Cet effet de nanoantenne, générant une importante amplification du champ électromagnétique au voisinage immédiat de la nanoparticule, devait augmenter l'efficacité de la réaction de photocycloréversion (son rendement quantique), conduisant à une commutation plus symétrique. La commutation des molécules de dithiényléthène (DTE) a d'abord été caractérisée pour les molécules seules en solution. Ensuite, la fonctionnalisation de nanoparticules d'or de 28 nm déposées sur ITO par les molécules de DTE a été suivie in situ par spectroscopie UV-visible. Les mesures de commutation sur les échantillons ITO/AuNPs/DTE ont été réalisées par spectroscopie UV-visible combinée à un dispositif d'irradiation. Il en est résulté que pour les molécules de diaryléthène choisies pour cette étude connectées à des AuNPs de 28 nm, bien que la capacité de commutation ait été préservée lors du greffage sur les AuNPs, le piégeage (« quenching ») était largement dominant. Par conséquent, un ralentissement des réactions photo-induites a été provoqué et non une accélération. Les nanoparticules d'or ont également été étudiées à l'échelle de la nanoparticule unique par AFM et hypermicroscopie (microscopie en champ sombre couplée à la spectroscopie UV-visible). D'une part, la fonctionnalisation de nanoparticules d'or individuelles de 51 nm a été suivie par hypermicroscopie. Des mesures de commutation ont ensuite été effectuées sur les molécules de diaryléthènes portées par les AuNPs uniques, révélant que cette commutation était comparable à celle précédemment mesurée à une échelle plus globale. D'autre part, des dimères plasmoniques asymétriques constitués d'un AuNP de 51 nm et d'un AuNP de 28 nm ont été préparés et caractérisésDiarylethene molecules used as molecular switches are envisioned as components of molecular electronic devices. These photochromic molecules exhibit high thermal stability, resistance to fatigue, and switching efficiency. Nevertheless, the switching of most diarylethenes (DAEs) is asymmetric: their photocycloreversion reaction possessing a much lower quantum yield than that of their photocyclization reaction. A strategy to solve that asymmetric switching issue was tested, it consisted in connecting the diarylethene molecules to gold nanoparticles (AuNPs). Indeed, gold nanoparticles exhibit both a localized surface plasmon resonance (LSPR), very useful for the monitoring of the adsorption of the DAEs at the surface of the AuNPs, and a plasmonic nanoantenna effect. This nanoantenna effect, generating a large enhancement of the electromagnetic field in the close vicinity of the nanoparticle, was expected to increase the efficiency of the photocycloreversion reaction (its quantum yield), leading to a more symmetric switching. The switching of the dithienylethene (DTE) molecules was first characterized for the molecules alone in solution. Then, the functionalization of 28 nm gold nanoparticles deposited on ITO by the DTE molecules was monitored in situ by UV-visible spectroscopy. Switching measurement on the samples ITO/AuNPs/DTE were performed by UV-visible spectroscopy combined with an irradiation set-up. It resulted that for the diarylethene molecules chosen for this study connected to 28 nm AuNPs, although the switching capacity was preserved upon grafting on the AuNPs, the quenching was largely dominant. As a consequence, a slowing of the photo-induced reactions was caused and not an acceleration. Gold nanoparticles were also studied at the unique nanoparticle scale by AFM and hypermicroscopy (dark field microscopy coupled to UV-visible spectroscopy). On the one hand, the functionalization of individual 51 nm gold nanoparticles was monitored by hypermicroscopy. Switching measurements were then conducted on the diarylethenes molecules beard by single AuNPs, revealing that this switching was comparable to the one previously measured on a more global scale. On the other hand, asymmetric plasmonic dimers made of a 51 nm AuNP and a 28 nm AuNP were prepared and characterized
9
Lundberg, Oscar. „Channel Characteristics Variations from Switching Between Narrow Beams“. Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-65628.
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The demand for higher throughput and lower latency in telecommunication systems is growing. Upcoming telecommunication systems will operate at higher frequencies (above 15 GHz) compared with previous systems (below 6 GHz). Antenna arrays will be employed in upcoming systems for increased link budget (coverage) and multiple input multiple output channels. This implies that narrow beams will be used. Beam tracking and beam steering is necessary to follow the user equipment. It is hypothesised that changing beam direction changes the channel condition for the communication link. In this work beam changes in data gathered with a 5G testbed is analysed at both 15 GHz and 28 GHz. The results show that the channel is indeed affected by beam changes. Statistical results of the conducted analysis are presented followed by specific examples on how the channel is affected by the beam changes. Knowledge on how the channel is affected by beam changes is of interest when designing systems for beam selection. The results show a nearly threefold increase of rank changes immediately after a beam change at 15 GHz. The probability for a rank change up or down is found to be equal. At 28 GHz the metric used for channel richness is singular value ratio. The statistical results show that the difference in singular value ratio before and after a beam change is increased by a factor 2. It is also shown that grating lobes may have a significant effect on the channel richness when changing beam direction.
10
Lam, Wai, und 林蔚. „Code switching and code mixing in the broadcasts of Commercial Radio Hong Kong (CRHK)“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/192985.
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Being a British colony for more than a century, Hong Kong has been influenced by the western culture in multiple aspects. One of the prominent western footprints is the ubiquitous Cantonese-English code switching and code mixing behavior which permeates all walks of life in this bilingual community. Though having seen its pervasiveness in different domains, limited studies from the sociolinguistic perspective have been conducted in the broadcasting domain, especially within the radio broadcast domain. This research gap prompts a study idea to unravel the sociolinguistic motivations behind the Cantonese-English code switching and code mixing behavior in Hong Kong radio broadcasts. Instances of code-switched and code-mixed which happened during the conversations among radio hosts were transcribed from the broadcasts of Commercial Radio Hong Kong (CRHK) between April 26th and May 24th 2013 for exploratory analysis.
The language alternation behavior was investigated through a communicative discourse context. In essence, the reasons motivating code switching and code mixing behavior among radio hosts include ‘principle of economy’, ‘generality/ specificity’, ‘euphemism’ and ‘emotional buffer’. Code switching/ code mixing also serves as a purposeful communicative strategy in tone switching or creating comical effect to enhance the entertainment value of the programs. It also helps the speakers to portray a particular social orientation or specifically, to project a western image. By code switching/ code mixing, the hosts also take into consideration of the societal preference of codes. The ideas of ‘we-code’, ‘they-code’, and ‘social distance’ are also applicable in exploring the social meaning of code switching/ code mixing within the Hong Kong radio broadcasts.published_or_final_version
English Studies
Master
Master of Arts
11
Yildirim, Recep Ali. „Mmse Based Iterative Turbo Equalization For Antenna Switching Systems“. Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612480/index.pdf.
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In this thesis, we study the performance of an antenna switching (AS) system in comparison to an Alamouti coded system. We analyze the outage probabilities and propose minimum mean-squared error based iterative equalizers for both systems. We see from the outage probability analysis of both systems that the AS system may achieve the same diversity order of the Alamouti coded scheme contingent on the transmission rate and constellation size. In the proposed receiver, MMSE equalization and channel decoding are jointly carried out in an iterative fashion. We use both hard and soft decision channel decoders in our simulations. It is observed that the Alamouti based scheme performs better when the channel state information is perfect. The Alamouti scheme also performs better than the AS scheme when the channel state information is imperfect in hard decision channel decoder case and a random interleaver is used. On the other hand, if a random interleaver is not used, AS scheme performs remarkably better than the Alamouti scheme in hard decision channel decoder case. In a soft decision channel decoder case, when the channel state information is imperfect, the AS scheme performs approximately a 2 dB better than the Alamouti scheme. Moreover, there is approximately a 3 dB performance gain if a soft decision channel decoder is used instead of hard decision.
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Babur, Ozgur. „A Simulation Study Of Scheduling Algorithms For Packet Switching Networks“. Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/2/1219336/index.pdf.
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A scheduling algorithm has the primary role in implementing the quality of service guaranteed to each flow by managing buffer space and selecting which packet to send next with a fair share of network. In this thesis, some scheduling algorithms for packet switching networks are studied. For evaluating their delay, jitter and throughput performances, a discrete event simulator has been developed. It has been
seen that fair scheduling provides, fair allocation of bandwidth, lower delay for sources using less than their full share of bandwidth and protection from ill-behaved
resources.
13
Roth, David C. „An analysis of alternative data communications networks for the Federal Aviation Administration's weather message switching center replacement“. Thesis, Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/50085.
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The design and life cycle cost of commercially available data communication networks for the Federal Aviation Administration’s Weather Message Switching Center Replacement (WMSCR) were analyzed. Only existing commercial networks large enough to handle the WMSCR traffic load were considered.
The recommendation is to proceed into a full and open competitive government procurement. In a competitive environment, this type of procurement will allow the government to receive the lowest possible life cycle cost.
A description of the existing system, the end-state system, the interim network design, the commercial networks analyzed, and their associated life cycle costs are included.Master of Science
incomplete_metadata
14
Gibson, Richard Samuel. „Reduction of variable speed drive IGBT switching loss, utilising the IGBT gate drive, without increasing radio frequency radiated emissions“. Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/2427.
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Radio frequency radiated emission from a variable speed drive must be limited below defined limits to avoid interference with electronic equipment. It is possible to comply with the international standards however, the current state of the art methods such as large gate drive resistance and output filters significantly reduce the efficiency or increase the cost of the products. It is known that the main source of emissions emanate from the switching transients associated with the output power semiconductors, however the exact mechanisms and specific sources are unknown. This thesis examines the interaction of power devices during the switching transient identifying features which can be controlled by a sophisticated gate drive design. Analysis of the frequency content of the signals is presented together with methods to minimise power losses while maintaining compliance with radiated emission standards. A research program has been undertaken to identify the sources responsible for radiated emissions and predict a figure of merit as an indication of compliance. Measuring radio frequency content on high voltage and current signals is difficult and several techniques to accurately achieve this are presented. Simple passive gate drive solutions which can be easily implemented are examined along with a discussion on more complicated optimised solutions.
15
Prys, Myfryr. „Style in the vernacular and on the radio : code-switching and mutation as stylistic and social markers in Welsh“. Thesis, Bangor University, 2016. https://research.bangor.ac.uk/portal/en/theses/style-in-the-vernacular-and-on-the-radio-codeswitching-and-mutation-as-stylistic-and-social-markers-in-welsh(952270df-9881-48b5-9193-85b0b8c4eecd).html.
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This thesis seeks to analyse two types of linguistic features of Welsh, code-switching and mutation, as sociolinguistic variables: features which encode social information about the speaker and/or stylistic meaning. Developing a study design that incorporates an analysis of code-switching and mutation in naturalistic speech has demanded a relatively novel methodological approach. The study combined a variationist analysis of the vernacular use of both variables in the 40-hour Siarad corpus (Deuchar 2014) with a technique that ranks radio programmes in order of formality through the use of channel cues and other criteria (Ball et al 1988). This allows for a comparison of the use of code-switching and mutation in multiple stylistic contexts, each of which show varying degrees of emotional engagement and self-monitoring by speakers. The analysis found that code-switching was strongly correlated with the level of formality of each radio programme, and that at least one aspirate mutation trigger, (a), also patterned in a similar way. Some other mutation triggers, most notably including the nasal possessive trigger (fy), seemed to be primarily affected by the speakers’ backgrounds and their relative ages in particular. A qualitative analysis of the type of discourse found in each radio programme made further links between the institutional style of each programme and their use of the stylistically controlled ‘marker’ variables, with non-standard variants appearing to be indexical of solidarity, subversion and irony, while standard variants indexed prestige, authority and earnestness.
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Barnes, Simon Daniel. „Cognitive radio performance optimisation through spectrum availability prediction“. Diss., University of Pretoria, 2012. http://hdl.handle.net/2263/25908.
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The federal communications commission (FCC) has predicted that, under the current regulatory environment, a spectrum shortage may be faced in the near future. This impending spectrum shortage is in part due to a rapidly increasing demand for wireless services and in part due to inefficient usage of currently licensed bands. A new paradigm pertaining to wireless spectrum allocation, known as cognitive radio (CR), has been proposed as a potential solution to this problem. This dissertation seeks to contribute to research in the field of CR through an investigation into the effect that a primary user (PU) channel occupancy model will have on the performance of a secondary user (SU) in a CR network. The model assumes that PU channel occupancy can be described as a binary process and a two state Hidden Markov Model (HMM) was thus chosen for this investigation. Traditional algorithms for training the model were compared with certain evolutionary-based training algorithms in terms of their resulting prediction accuracy and computational complexity. The performance of this model is important since it provides SUs with a basis for channel switching and future channel allocations. A CR simulation platform was developed and the results gained illustrated the effect that the model had on channel switching and the subsequently achievable performance of a SU operating within a CR network. Performance with regard to achievable SU data throughput, PU disruption rate and SU power consumption, were examined for both theoretical test data as well as data obtained from real world spectrum measurements (taken in Pretoria, South Africa). The results show that a trade-off exists between the achievable SU throughput and the average PU disruption rate. Significant SU performance improvements were observed when prediction modelling was employed and it was found that the performance and complexity of the model were influenced by the algorithm employed to train it. SU performance was also affected by the length of the quick sensing interval employed. Results obtained from measured occupancy data were comparable with those obtained from theoretical occupancy data with an average percentage similarity score of 96% for prediction accuracy (using the Viterbi training algorithm), 90% for SU throughput, 83% for SU power consumption and 71% for PU disruption rate.Dissertation (MEng)--University of Pretoria, 2012.
Electrical, Electronic and Computer Engineering
unrestricted
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Goken, Burcu. „Investigation Of Gmpls Applications In Optical Systems“. Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/2/12606571/index.pdf.
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In this study, possible applications of label switching in large area, fully optical
networks are investigated. The objective was to design a label assignment method
by using Generalized Multi-Protocol Label Switching (GMPLS) concept to get an
efficient optical network operation. In order to fulfill this objective, two new
approaches were proposed: a label assignment method and a concatenated label
structure.
Label assignment method was designed to provide an efficient utilization of
resources. Concatenated label structure aimed handling the label in optical
domain. Mainly, the lambda switch capable GMPLS networks were investigated.
In order to verify the performance of label assignment method, a simulator was
developed.
The results of simulation have clearly indicated that the proposed approaches
could be beneficial in an optical network operation.
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Hietakangas, S. (Simo). „Design methods and considerations of supply modulated switched RF power amplifiers“. Doctoral thesis, Oulun yliopisto, 2012. http://urn.fi/urn:isbn:9789514298363.
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Abstract This thesis studies the design methods and properties of supply-modulated switch-mode radio frequency power amplifiers. Besides simulation based studies and theory review, two amplifiers were designed: a discrete MESFET class E amplifier (0.5 W at 1 GHz), and an integrated pHEMT class E-1 amplifier (2.0 W at 1.6 GHz) with an on-chip resonator. The existing design methods of the resonant output network of switching amplifiers were reviewed and some extensions on the handling of nonlinear capacitances were proposed. The effects of varying supply voltage were studied and suggestions were given to minimize Vdd / AM and Vdd / PM distortion in supply modulated amplifiers. The implementation of the bias feed was also discussed resulting in proposing a combination of a short transmission line and a small inductor, which provides both fast supply modulation and little effect on harmonic impedances. The main contributions are related to the study of the input impedance of a class E power amplifier, where the effects of supply dependent input impedance and timing skew generated by injected harmonic distortion were analyzed. The stabilization of the amplifier was also discussed. Based on the findings, a push-pull class E amplifier with extra cross-coupled feedback capacitors and second harmonic traps at the gates appears to be a very good starting point for a further studyTiivistelmä Tämä väitöstyö käsittelee radiotaajuuksilla toimivien käyttöjännitemoduloitujen kytkintehovahvistimien ominaisuuksia ja suunnittelumenetelmiä. Suunnittelumenetelmiin liittyvän katsauksen ja simulaatioihin perustuvan tutkimusten lisäksi kaksi vahvistinta toteutettiin väitöstutkimuksen aikana: diskreettikomponentein toteutettu E-luokan vahvistin (MESFET, 0.5 W ja 1 GHz) ja integroituna piirinä toteutettu käänteinen E-luokan vahvistin (pHEMT, 2.0 W ja 1.6 GHz), jonka lähdön resonaattoripiiri sisällytettiin integroituun piiriin. Kytkinvahvistimien suunnittelumenetelmiä verrattiin ja kehitettiin edelleen siten, että suunnitteluvaiheessa voidaan ottaa huomioon esim. transistoripiirin takaisinkytkennässä olevan kapasitanssin epälineaarisuus. Työssä tutkittiin myös käyttöjännitemodulaation vaikutusta kytkinvahvistimien toimintaan, ja tutkimuksen tuloksena annettiin muutamia ehdotuksia käyttöjänniteriippuvan amplitudi- (Vdd / AM) ja vaihemodulaation (Vdd / PM) vähentämiseksi. Lähdön biasointipiirin toteutukseen suositeltiin pienen kelan ja siirtolinjan yhdistelmää. Yhdistelmän avulla pyritään maksimoimaan modulaationopeus ja minimoimaan vaikutukset harmonisiin impedansseihin. Pääkohtina väitöksessä ovat E-luokan kytkinvahvistimesta saadut tutkimus- ja mittaushavainnot käyttöjännitteen funktiona muuttuvasta transistorin tuloimpedanssista sekä suurikokoisen transistorin tuloissa tapahtuvan, säröytymisen aiheuttaman tulosignaalien ajoitusvirheen analyysi. Näiden lisäksi vahvistimen stabiilisuuteen kiinnitettiin huomiota. Saatujen havaintojen perusteella voimme todeta, että push-pull -tyyppinen E-luokan vahvistin olisi mielenkiintoinen valinta jatkotutkimuksille
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Nchai, Tlali Pius. „The comprehension by factory workers of English technical terms in Ministry of Employment and Labour Radio Broadcasts in Lesotho“. Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/18062.
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Thesis (MPhil )--Stellenbosch University, 2011.ENGLISH ABSTRACT: With the advent of the information age, government ministries in Lesotho, as well as nongovernmental agencies, are trying to gain publicity in terms of services they offer to the general public. The Ministry of Employment and Labour (MEL), for example, resorted to using radio programmes in order to inform the public about the services it offers. These range from career guidance and counselling, pre- and post-employment advice, information about occupational health and safety and HIV/AIDS, providing facts about what type of vacancies are available locally and internationally, to instilling the spirit of dialogue among relevant stakeholders in matters related to labour, employers and employees. During various weekly radio presentations, presented in Sesotho, several departments are able to go on-air and present services that their departments offer to the general public and what the public can do in the event they are given a disservice by the concerned department. In the process of doing so, many technical terms are used. These often take the form of code switches into English, translations from English into Sesotho and borrowings from English. The purpose of this thesis is to examine whether the use of code switching, translation and borrowing makes it possible for factory workers in Lesotho to understand the message that is being delivered to them in a clear and unmistakable manner that will influence a change of behaviour on the part of factory workers. In order to ascertain the level of comprehension of technical terms, participants completed a questionnaire in which they gave their understanding of various technical terms selected from transcribed MEL radio broadcasts. The findings of this study show that the use of code switching, translation and borrowing from English limit the understanding of what is being communicated, making the radio broadcasts less effective in disseminating information on matters related to HIV/AIDS, the plight of factory workers according to the ratified conventions of the International Labour Organization (ILO), legal terms related to contracts of employment, their commencement and termination, conditions of work, the level of the unemployed versus the employed, skills needed to venture into the country’s labour market and occupational health and safety guidelines as reflected in the Labour Code of Lesotho.
AFRIKAANSE OPSOMMING: Met die aanbreek van die inligtingsera probeer staatsministeries in Lesotho, asook nieregeringsorganisasies, om publisiteit te verkry vir die openbare dienste wat hul lewer. Die Ministerie van Werksverskaffing en Arbeid (MWA) het byvoorbeeld besluit om gebruik te maak van radioprogramme om die publiek in te lig aangaande sy dienste. Hierdie dienste wissel van beroepsvoorligting en -berading, voor- en na-indiensnemingsadvies, inligting oor bedryfsgesondheid en -veiligheid en HIV/VIGS, die verskaffing van feite oor beskikbare plaaslike en internasionale vakaturetipes, tot die kweek van ’n dialoog-gees onder relevante belanghebbendes in arbeid-, werkgewer- en werknemersake. Tydens verskeie weeklikse radio-aanbiedings, aangebied in Sesotho, kan ’n aantal departemente hulle openbare dienste adverteer, asook die prosedure wat gevolg kan word deur lede van die publiek wat veronreg is deur die gegewe departement. Hierdie boodskappe bevat verskeie tegniese terme, dikwels aangebied in die vorm van kodewisselings na Engels, vertalings uit Engels na Sesotho, asook Engelse leenwoorde. Die doel van hierdie tesis is om vas te stel of die gebruik van kodewisseling, vertaling en woordleen fabriekswerkers in Lesotho daartoe in staat stel om die boodskap wat gekommunikeer word te verstaan in ’n duidelike, ondubbelsinnige wyse wat tot ’n gedragsverandering onder die fabriekswerkers sal lei. Ten einde die begripsvlak vir tegniese terme vas te stel, het deelnemers ’n vraelys voltooi waarin hulle hul begrip van verskeie tegniese terme (geselekteer uit getranskribeerde MWA-radiouitsendings), weergegee het. Die bevindinge van hierdie studie dui daarop dat die gebruik van kodewisseling, vertaling en woordleen uit Engels die begrip van wat gekommunikeer word, beperk. Dít maak die radiouitsendings minder effektief in die verspreiding van inligting oor HIV/VIGS; die saak van fabriekwerkers (met inagname van die gesanksioneerde konvensies van die Internasionale Arbeidsorganisasie); regsterme wat verband hou met arbeidskontrakte, spesifiek hul aanvang en terminasie, asook werksomstandighede; die vlak van werkloses teenoor werkendes; die vaardighede wat benodig word om die land se arbeidsmark te betree; en bedryfsgesondheid en –veiligheidsriglyne, soos gereflekteer in die Arbeidswet van Lesotho.
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Aruchamy, Logabharathi. „Analysis of Radio Access Network Buffer Filling Based on Real Network Data“. Thesis, Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-6063.
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The 3G and 4G networks have drastically improved availability and quality in data transmission for bandwidth hungry services such as video streaming and location-based services. As 3G networks are very widely deployed, there exists increased capacity requirement and transport channel allocation to simultaneous users under a particular cell. Due to this reason, adequate resources are not available, which in turn degrades both service quality and user experienced quality. This research aims at understanding the characteristics of buffer filling during dedicated channel (DCH) transmission under fixed bit-rate assumptions on a per-user level taking different services into consideration. Furthermore, the resource utilisation in terms of empty buffer durations and user throughput achieved during dedicated channel transmission are also analysed for different data services existing in the mobile networks. The traces are collected from a real network and characteristics of the traffic are analysed prior to understanding its buffer filling in Radio Network Controller (RNC) during downlink data transmission. Furthermore, the buffer is modelled with some series of assumptions on channel bit-rates and simulations are performed taking single user scenario into consideration, for different services with the help of obtained traces as input to the buffer. This research is helpful in understanding the RNC buffer filling for different services, in turn yielding possible understanding on the existing transport channel switching scenario. With the help of analysing the buffer filling for different services and transport channel utilisation, we learn that most of the data services show low DCH utilisation of approximately around 20% and also found to have 80% of the total DCH session duration with empty buffer, causing sub-optimal radio resource utilization.
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Gurakan, Berk. „Cfar Processing With Multiple Exponential Smoothers For Nonhomogeneous Environments“. Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612719/index.pdf.
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Conventional methods of CFAR detection always use windowing, in the sense that some number of cells are investigated and the target present/absent decision is made according to the composition of the cells in that window. The most commonly used versions of CFAR detection algorithms are cell averaging CFAR, smallest of cell averaging CFAR, greatest of cell averaging CFAR and order-statistics CFAR. These methods all use windowing to set the decision threshold. In this thesis, rather than using windowed CFAR algorithms, a new method of estimating the background threshold is presented, analyzed and simulated. This new method is called the Switching IIR CFAR algorithm and uses two IIR filters to accurately estimate the background threshold. Then, using a comparison procedure, one of the filters is selected as the current threshold estimate and used. The results are seen to be satisfactory and comparable to conventional CFAR methods. The basic advantages of using the SIIR CFAR method are computational simplicity, small memory requirement and acceptable performance under clutter edges and multiple targets.
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Masoud, Khalid Hasan. „Circuits and controls for grid-connected inverters“. Thesis, Queensland University of Technology, 2002.
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Hoefel, Roger Pierre Fabris. „CDMA/PRMA : um mecanismo de controle de acesso ao meio para transmissão de pacotes em sistemas sem fio de terceira geração“. [s.n.], 2000. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260670.
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Orientador: Celso de AlmeidaTese (doutorado) - Umiversidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-17T06:29:22Z (GMT). No. of bitstreams: 1 Hoefel_RogerPierreFabris_D.pdf: 16131215 bytes, checksum: 8d67fff6992c05fd8d2eac683e4a1f9e (MD5) Previous issue date: 2000
Resumo: O objetivo deste trabalho é o de analisar, caracterizar e apresentar soluções para o excitante desafio de projetar protocolos de acesso para o transporte de pacotes multimídia no enlace reverso de sistemas celulares terrestres que empregam interface do ar do tipo TD/DS-CDMA (Time Division/Direct Sequence Code Division Multiple Access). Os estudos relativos aos aspectos inerentes à transmissão de pacotes em sistemas TD/DS-CDMA são particularizados na análise dos protocolos CDMA/PRMA (Code Division Multiple Access/ Packet Reservation Multiple Access) e Slotted CDMA/ALOHA. CDMA/PRMA é um protocolo de múltiplo acesso híbrido, no qual se aplicam os conceitos de multiplexação no tempo~por código e de alocação de recursos por meio de reserva. O acesso controlado ao canal do protocolo CDMA/PRMA permite a redução da variação da carga instantânea do canal e, conseqüentemente, redução da interferência de múltiplo acesso em relação ao protocolo Slotted CDMA/ ALOHA, onde os terminais acessam no próximo slot de tempo tão logo tenham pacotes a transmitir. Utiliza-se simulação computacional de maneira intensiva para à obtenção de resultados concernentes ao desempenho dos protocolos CDMA/PRMA e Slotted CDMA/ ALOHA em distintas condições operacionais. Estes resultados são validados por análises numéricas. Entre outros aspectos deste trabalho, destaca-se: (i) o modelo do ponto de equilíbrio proposto para os protocolos CDMA/PRMA e Slotted CDMA/ ALOHA; (ii) as expressões numéricas propostas para uma análise de desempenho do protocolo CDMA/PRMA; (iii) o desenvolvimento de um simulador de rede de pacotes para a investigação dos efeitos da interferência externa nas redes de pacotes CDMA/PRMA e Slotted CDMA/ ALOHA; (iv) efeitos dos parâmetros de projeto no desempenho dos protocolos CDMA/PRMA e Slotted CDMA/ ALORA; (v) estudo do desempenho dos protocolos CDMA/PRMA e Slotted CDMA/ ALORA com tráfego de vídeo com taxa variável e tráfego de dados WWW; (vi) a investigação dos efeitos do controle de potência, do desvanecimento rápido e do desvanecimento lento no desempenho dos protocolos CDMA/PRMA e Slotted CDMA/ ALORA com tráfego multimídia; (vii) o projeto integrado do protocolo CDMA/PRMA com receptor de detecção conjunta descorrelacionadora
Abstract: This thesis has the objective of to analyze, to characterize and to propose solutions to the challenge of design medium access control protocols for transmission of multimedia packets over the reverse channel of land mobile cellular systems based on TD/DS-CDMA (Time Division/Direct Sequence Code Division Multiple Access) air interface. Some inherent aspects of packet transmission over the reverse link of TD/DS-CDMA systems are particularized in the analysis of the CDMA/PRMA (Code Division Multiple Access/Packet Reservation Multiple Access) and Slotted CDMA/ ALOHA protocols. The joint CDMA/PRMA protocol is a hybrid multiple-access technique that combines time-division, code-division and Reservation ALOHA concepts. The CDMA/PRMA medium access control brings to reduction of the users variance on the channel, so a larger capacity is obtained in relation to the Slotted CDMA/ ALOHA protocol, where a mobile station accesses a time slot as soon as it has packets to transmit. It is used intensely computational simulation techniques to obtain some performance results concerning to CDMA/PRMA Slotted and CDMA/ ALOHA behavior over distinct operational conditions. It is utilized numerical techniques to validate some of obtained results. It is emphasized the following aspects of this Thesis: (i) a equilibrium point analysis model for the CDMA/PRMA and Slotted CDMA/ ALOHA protocols; (ii) some numerical expressions that permits to analyze the CDMA/PRMA behavior on voice-only traffic; (iii) a system level network simulator developed to assess and to compare the intercell interference effects on the CDMA/PRMA and Slotted CDMA/ ALOHA protocols performance; (iv) the design parameters effects on the performance of CDMA/PRMA and Slotted CDMA/ALOHA systems; (v) some studies of CDMA/PRMA and Slotted CDMA/ALOHA behavior on mixed voice/variable bit rate video and voice/WWW browsing traffic; (vi) some analysis of the imperfect power control effects, slow and fast fading effects on the capacity of CDMA/PRMA and Slotted CDMA/ ALOHA protocols; (vii) a integrated design of CDMA/PRMA protocol and a multiuser decorrelator detector
Doutorado
Telecomunicações e Telemática
Doutor em Engenharia Elétrica
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Sahu, Biranchinath. „Integrated, Dynamically Adaptive Supplies for Linear RF Power Amplifiers in Portable Applications“. Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/7607.
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Energy-efficient radio frequency (RF) power amplifiers (PAs) are critical and paramount to achieve longer battery life in state-of-the-art portable systems because they typically determine and dominate the power consumption of such devices. In this dissertation, a high-efficiency, linear RF PA with a dynamically adaptive supply and bias current control for code division multiple access (CDMA) and wideband CDMA (WCDMA) is conceived, simulated, and experimentally demonstrated with a discrete PCB-level design and in integrated circuit (IC) form. The PA efficiency is improved by dynamically adjusting both its supply voltage and bias current, there by minimizing its quiescent power dissipation. The PA supply voltage is derived from the battery by a noninverting, synchronous buck-boost switching regulator because of its flexible functionality and high efficiency. Adjusting the PA supply voltage and bias current by tracking the output power, instead of following the complete envelope in large baseband bandwidth wireless applications, is achieved by a converter with a lower switching frequency and consequently higher light-load efficiency, which translates to prolonged battery life.
A discrete PCB-level prototype of the proposed system with 915 MHz center frequency, CDMA IS-95 signal having 27-dBm peak-output power resulted in more than four times improvement in the average efficiency compared to a fixed-supply class-AB PA while meeting the required performance specifications. In the IC solution fabricated in AMIs 0.5-micron CMOS process through MOSIS, a dual-mode, buck-boost converter with pulse-width modulation (PWM) control for high power and pulse-frequency modulation (PFM) for low power is designed and implemented to improve the PA efficiency during active and standby operation, respectively. The performance of the dynamically adaptive supply and bias control IC was validated by realizing a 25-dBm, 1.96 GHz center frequency, WCDMA PA over an input supply range of 1.4 4.2 V. The PA with dual-mode power supply and bias control IC showed an average-efficiency improvement of seven times compared to a fixed-supply class-AB PA, which translates to five times improvement in battery life assuming the PA is active for 2 % of the total time and in standby mode otherwise.
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Ghasemi, Negareh. „Improving ultrasound excitation systems using a flexible power supply with adjustable voltage and frequency to drive piezoelectric transducers“. Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/61091/1/Negareh_Ghasemi_Thesis.pdf.
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The ability of a piezoelectric transducer in energy conversion is rapidly expanding in several applications. Some of the industrial applications for which a high power ultrasound transducer can be used are surface cleaning, water treatment, plastic welding and food sterilization. Also, a high power ultrasound transducer plays a great role in biomedical applications such as diagnostic and therapeutic applications. An ultrasound transducer is usually applied to convert electrical energy to mechanical energy and vice versa. In some high power ultrasound system, ultrasound transducers are applied as a transmitter, as a receiver or both. As a transmitter, it converts electrical energy to mechanical energy while a receiver converts mechanical energy to electrical energy as a sensor for control system. Once a piezoelectric transducer is excited by electrical signal, piezoelectric material starts to vibrate and generates ultrasound waves. A portion of the ultrasound waves which passes through the medium will be sensed by the receiver and converted to electrical energy. To drive an ultrasound transducer, an excitation signal should be properly designed otherwise undesired signal (low quality) can deteriorate the performance of the transducer (energy conversion) and increase power consumption in the system. For instance, some portion of generated power may be delivered in unwanted frequency which is not acceptable for some applications especially for biomedical applications.
To achieve better performance of the transducer, along with the quality of the excitation signal, the characteristics of the high power ultrasound transducer should be taken into consideration as well. In this regard, several simulation and experimental tests are carried out in this research to model high power ultrasound transducers and systems. During these experiments, high power ultrasound transducers are excited by several excitation signals with different amplitudes and frequencies, using a network analyser, a signal generator, a high power amplifier and a multilevel converter. Also, to analyse the behaviour of the ultrasound system, the voltage ratio of the system is measured in different tests. The voltage across transmitter is measured as an input voltage then divided by the output voltage which is measured across receiver. The results of the transducer characteristics and the ultrasound system behaviour are discussed in chapter 4 and 5 of this thesis.
Each piezoelectric transducer has several resonance frequencies in which its impedance has lower magnitude as compared to non-resonance frequencies. Among these resonance frequencies, just at one of those frequencies, the magnitude of the impedance is minimum. This resonance frequency is known as the main resonance frequency of the transducer. To attain higher efficiency and deliver more power to the ultrasound system, the transducer is usually excited at the main resonance frequency. Therefore, it is important to find out this frequency and other resonance frequencies. Hereof, a frequency detection method is proposed in this research which is discussed in chapter 2.
An extended electrical model of the ultrasound transducer with multiple resonance frequencies consists of several RLC legs in parallel with a capacitor. Each RLC leg represents one of the resonance frequencies of the ultrasound transducer. At resonance frequency the inductor reactance and capacitor reactance cancel out each other and the resistor of this leg represents power conversion of the system at that frequency. This concept is shown in simulation and test results presented in chapter 4.
To excite a high power ultrasound transducer, a high power signal is required. Multilevel converters are usually applied to generate a high power signal but the drawback of this signal is low quality in comparison with a sinusoidal signal. In some applications like ultrasound, it is extensively important to generate a high quality signal. Several control and modulation techniques are introduced in different papers to control the output voltage of the multilevel converters. One of those techniques is harmonic elimination technique. In this technique, switching angles are chosen in such way to reduce harmonic contents in the output side. It is undeniable that increasing the number of the switching angles results in more harmonic reduction. But to have more switching angles, more output voltage levels are required which increase the number of components and cost of the converter. To improve the quality of the output voltage signal with no more components, a new harmonic elimination technique is proposed in this research. Based on this new technique, more variables (DC voltage levels and switching angles) are chosen to eliminate more low order harmonics compared to conventional harmonic elimination techniques. In conventional harmonic elimination method, DC voltage levels are same and only switching angles are calculated to eliminate harmonics. Therefore, the number of eliminated harmonic is limited by the number of switching cycles. In the proposed modulation technique, the switching angles and the DC voltage levels are calculated off-line to eliminate more harmonics. Therefore, the DC voltage levels are not equal and should be regulated. To achieve this aim, a DC/DC converter is applied to adjust the DC link voltages with several capacitors. The effect of the new harmonic elimination technique on the output quality of several single phase multilevel converters is explained in chapter 3 and 6 of this thesis.
According to the electrical model of high power ultrasound transducer, this device can be modelled as parallel combinations of RLC legs with a main capacitor. The impedance diagram of the transducer in frequency domain shows it has capacitive characteristics in almost all frequencies. Therefore, using a voltage source converter to drive a high power ultrasound transducer can create significant leakage current through the transducer. It happens due to significant voltage stress (dv/dt) across the transducer. To remedy this problem, LC filters are applied in some applications. For some applications such as ultrasound, using a LC filter can deteriorate the performance of the transducer by changing its characteristics and displacing the resonance frequency of the transducer. For such a case a current source converter could be a suitable choice to overcome this problem. In this regard, a current source converter is implemented and applied to excite the high power ultrasound transducer. To control the output current and voltage, a hysteresis control and unipolar modulation are used respectively. The results of this test are explained in chapter 7.
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Csipkes, Gabor-Laszlo. „Integrated realizations of reconfigurable low pass and band pass filters for wide band multi-mode receivers“. Doctoral thesis, [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=979677483.
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Csipkes, Gabor-Laszlo. „Integrated realizations of reconfigurable low pass and band pass filters for wide band multi-mode receivers“. Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1145345696511-52655.
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With the explosive development of wireless communication systems the specifications of the supporting hardware platforms have become more and more demanding. According to the long term goals of the industry, future communications systems should integrate a wide variety of standards. This leads to the idea of software defined radio, implemented on fully reconfigurable hardware.Among other reconfigurable hardware blocks, suitable for the software radio concept, an outstanding importance belongs to the reconfigurable filters that are responsible for the selectivity of the system. The problematic of filtering is strictly connected to the architecture chosen for a multi-mode receiver realization. According to the chosen architecture, the filters can exhibit low pass or band pass frequency responses.The idea of reconfigurable frequency parameters has been introduced since the beginning of modern filtering applications due to the required precision of the frequency response. However, the reconfiguration of the parameters was usually done in a limited range around ideal values. The purpose of the presented research is to transform the classical filter structures with simple self-correction into fully reconfigurable filters over a wide range of frequencies. The ideal variation of the frequency parameters is continuous and consequently difficult to implement in real circuits. Therefore, it is usually sufficient to use a discrete programming template with reasonably small steps.There are several methods to implement variable frequency parameters. The most often used programming templates employ resistor and capacitor arrays, switched according to a given code. The low pass filter implementation proposed in this work uses a special switching template, optimized for a quasi-linear frequency variation over logarithmic axes. The template also includes the possibility to compensate errors caused by component tolerances and temperature. Another important topic concerns the implementation of programmable band pass filters, suitable for IF sampling receivers. The discussion is centered on the feasibility and the flexibility of different band pass filter architectures. Due to the high frequency requirements, the emphasis lays on filters that employ transconductance amplifiers and capacitorsDie rasch fortschreitende Entwicklung drahtloser Kommunikationssysteme führt zu immer anspruchsvolleren Spezifikationen der diese Systeme unterstützenden Hardwareplattformen. Zukünftige Kommunikationssysteme sollen übereinstimmend mit den längerfristigen Zielen der Industrie verschiedene Standards integrieren. Dies führt zu der Idee von vollständig rekonfigurierbarer Hardware, welche mittels Software gesteuert wird.Inmitten anderer rekonfigurierbarer Hardwareblöcke, die für das Software Radio Konzept geeignet sind, besitzen die steuerbaren Filter, welche wesentlichen Einfluss auf die Selektivität des Systems haben, eine enorme Bedeutung. Die Filterproblematik ist eng mit der gewählten Architektur der standardübergreifenden Empfängerrealisierung verknüpft. Die Filter können entsprechend der ausgesuchten Architektur Tiefpass- oder Bandpasscharakter annehmen.Die Idee rekonfigurierbarer Frequenzparameter wurde bereits mit Beginn moderner Filteranwendungen auf Grund geforderter Frequenzganggenauigkeit umgesetzt. Jedoch wurde die Parameterrekonfiguration üblicherweise nur in einem begrenzten Bereich um die Idealwerte herum vorgenommen. Das Ziel der vorgestellten Forschungsarbeit ist es, diese klassischen Filterstrukturen mit einfacher Selbstkorrektur in über große Frequenzbereiche voll rekonfigurierbare Filter zu transformieren. Idealerweise werden die Frequenzparameter kontinuierlich variiert weswegen sich die Implementierung in reellen Schaltkreisen als schwierig erweist. Deshalb ist es üblicherweise ausreichend, ein diskretes Steuerschema mit kleinen Schrittweiten zu verwenden.Es gibt verschiedene Methoden, variable Frequenzparameter zu implementieren. Die meisten Schemata verwenden Widerstands- und Kondensatorfelder, die entsprechend eines Kodes geschaltet werden. Die in dieser Arbeit vorgestellte Implementierung eines Tiefpassfilters nutzt ein spezielles Umschaltschema, welches für die quasi-lineare Frequenzvariation bei Darstellung über logarithmischen Axen optimiert wurde. Es beinhaltet weiterhin die Möglichkeit, Fehler zu kompensieren, die durch Bauelementtoleranzen und Temperaturschwankungen hervorgerufen werden.Ein weiteres interessantes Thema betrifft die Implementierung steuerbarer Bandpassfilter, die für Empfänger mit Zwischenfrequenzabtastung geeignet sind. Die Betrachtung beschränkt sich hierbei auf die Durchführbarkeit und Flexibilität verschiedener Bandpassfilterarchitekturen. Auf Grund hoher Frequenzanforderungen liegt der Schwerpunkt auf Filtern, die auf Transkonduktanzverstärkern und Kondensatoren basieren
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Ducarouge, Benoît. „Conception et caractérisation de micro-commutateurs électromécaniques hyperfréquences de puissance : application à un circuit de commutation d'émission/réception large bande“. Toulouse 3, 2005. http://www.theses.fr/2005TOU30172.
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L'introduction des technologies MEMS ("Micro Electro Mechanical Systems") dans les modules hyperfréquences répond au besoin croissant en systèmes de communications intégrables, reconfigurables et présentant d'excellentes performances électriques jusqu'aux fréquences millimétriques. Le développement de nouvelles architectures intelligentes jusque là inaccessibles aux technologies traditionnelles est également envisageable grâce à ces composants. Cela dit, la conception multi-physique de ces circuits alliant des aspects électrostatiques, mécaniques et électromagnétiques reste difficile à mettre en œuvre et complique leur optimisation. De plus, peu de recherches se sont focalisées sur la tenue en puissance de ces composants, pourtant primordiale pour envisager leur intégration dans des chaînes d'émission radio fréquences. Nos travaux de thèse ont porté sur la conception et la caractérisation de micro-interrupteurs MEMS de puissance et de circuits hyperfréquences les intégrant et opérant en bande X (10GHz). Le premier chapitre présente une méthodologie multi-physique de conception de commutateurs MEMS RF électrostatiques à contact capacitif réalisés au Laboratoire d'Analyse et d'Architecture des Systèmes. Cette méthodologie, associée à une topologie optimale de micro-commutateurs, a permis un prototypage efficace de commutateurs MEMS et a été validée expérimentalement grâce à des structures montrant d'excellentes performances hyperfréquences. Le second chapitre s'intéresse à l'optimisation en puissance de commutateurs MEMS RF. Nous avons développé une méthodologie de prédiction de la puissance maximale de fonctionnement pour ces composants. Cette méthodologie a été ensuite utilisée pour l'optimisation en puissance du commutateur développé dans le chapitre 1. Un dimensionnement ainsi que l'ensemble des résultats de simulations sont présentés et validés expérimentalement. Enfin le dernier chapitre présente la mise en application des méthodologies décrites aux deux premiers chapitres pour la conception d'un circuit de commutation de puissance large bande 6-18 GHz basé sur des topologies série et parallèle d'interrupteurs MEMS. Les structures ont ainsi été optimisées, fabriquées et mesurées. Elles présentent d'excellentes performances RF sur une large gamme de fréquenceMEMS ("Micro Electro Mechanical Systems") technologies have been successfully introduced in the past decade in order to develop smart micro-systems exhibiting high integration level, new functionalities such as reconfigurability (to switch over different standards) or self repairing ability, and high electrical performances up to millimeterwave frequencies. Moreover, new system architectures can be implemented thanks to these devices, which demonstrate the potentialities of MEMS technologies in future wireless systems. In the meantime, their multi-physic design dealing with electrostatic, mechanical and electromagnetical concerns, translates into a long and complex optimization of the MEMS-based circuits slowing their industrial use. Moreover, few studies are available on the power handling capabilities of these components, which is the key parameter to improve their integration into front-end networks. Our work, made in LAAS-CNRS, concentrates on the design and characterisation of power RF-MEMS switches and their integration into a broadband single pole double throw circuit, for front-end duplexer operating in X band. The first chapter will be dedicated to a multi-physic design methodology for capacitive electrostaticaly actuated RF-MEMS switches design. This methodology, associated with an optimized topology, enables an efficient development of MEMS components and circuits. Demonstrators have been measured and demonstrate outstanding RF performances which validate the proposed methodology. The second part of this work points out the power optimization of RF MEMS switches. A power handling prediction methodology has been proposed and used to optimize the switch described in the first chapter. Simulations have been confirmed by measurements which validate our prediction method. The measured RF MEMS power handling demonstrates the ability of this technology to be used in front-end circuits and systems. Finally, the third chapter deals with an application using the methodologies described above: a broadband (6-18 GHz) power switching circuit for front-end duplexer. This circuit has been optimized, realized and characterized and exhibits state of the art microwave and power performances over a broad frequency band
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Hsieh, Chia-Ming, und 謝家銘. „A study on the demand switching ratio for multiple products“. Thesis, 2008. http://ndltd.ncl.edu.tw/handle/71325357979073523335.
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碩士國立中興大學
科技管理研究所
96
In many business management policies, the inventory management and decision - makings have been the very important of the business administration. Variability of products’ demand frequently attracts managers’ attention because of its costly implications. By carrying high inventory levels, firms may satisfy customers’ orders and materialize high revenue in periods when demand is high, but often end up with excess inventory in periods when demand is low. On the other hand, carrying low inventory levels to avoid the costs of excess inventory may result in a poor service level and loss of potential profit. We already know that using a framework with demand reshape to take advantage of the risk-pooling effect, with the required level of safety stock that the parent company sets to satisfy the quality of its services. It is demonstrated that a company can improve its profit by encouraging some of its customers, who intended to purchase one product to switch to another. The risk-pooling effect has been documented to benefit inventory systems by reducing the need for safety stock and consequently lowering costs such as inventory holding and shortage penalty. In this research we use the above framework for companies that provide multiple products. In this study, we consider scenarios to do the demand switching by different ratio. We point out the influence of the demand switching in profit of the companies and provide an optima decision for the manager. At last, a numerical study is used to demonstrate the impact of demand reshape for multi-products.
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Lin, Shih-Cian, und 林詩倩. „Analyzing the Loss Ratio in Taiwan''s Property-Casualty Reinsurance by Markov-Switching model“. Thesis, 2009. http://ndltd.ncl.edu.tw/handle/61455548343171811002.
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碩士國立高雄第一科技大學
風險管理與保險所
97
This study discusses whether the Property-Casualty Reinsurance in Taiwan has the underwriting cycle. At first, we use AR(2) model developed by Venezian (1985) to ascertain the underwriting cycle in Taiwan’s reinsurance market, and then construct two regime switching regressions from Markov-Switching model developed by Hamilton (1989) to identify what the key factors have impacts on loss ratio of reinsurance. The empirical results indicate that there is no obvious underwriting cycle in Taiwan’s reinsurance market even through we further examine the reinsurance of the Automobile, the Fire, the Goods Traffic and The Others. As for the Markov-Switching regressions, in first regime (Soft Market) the loss ratio of the overall reinsurance market is positively affected by the jobless rate (JR), however in second regime (Hard Market) it’s positively affected by economical growth rate (GR), foreign exchange rate (FER), interest rate (R), securities investment (S).In addition, while using the above five factors to compare different kinds of reinsurance, we can find that the overall reinsurance market has a similar result with The Others, and a widely divergent result with the Fire. In sum, the economical growth rate has the greatest impact on the reinsurance market and also implies that it is the key factor to influence the reinsurance market.
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YEH, CHIEN-CHENG, und 葉千正. „Novel Highly Stable Electrochromic Polyamides with High Contrast Ratio, Multicolor and Low-Switching Voltage“. Thesis, 2011. http://ndltd.ncl.edu.tw/handle/04825011694940206739.
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碩士國立臺灣科技大學
化學工程系
99
Three series of new polyamides based on triphenylamine showing anodically electrochromic characteristic were synthesized from the polycondensation reaction of three diamine monomers, 2,6-bis(N,N-(4-aminophenyl-4’-methoxyphenyl)amino) naphthalene(2), 1,6-bis(N,N-(4-aminophenyl-4’-methoxyphenyl)amino)pyrene(5), and N,N’-bis(4-methoxyplenyl)-N,N’-bis[4-(4-aminophenyl-4’- methoxyphenylamino)phenyl]-p-phenylenediamine(8) with various commercially available aromatic dicarboxylic acids, respectively. All the polyamides were amorphous with good solubility in many organic solvents, such as N-methyl-2-prrolidinone(NMP) and N,N-dimethyl-acetamide(DMAC). These aromatic polyamides had good thermal stability associated with their high glass-transition temperatures(204~308℃), and 10% weight-loss temperatures in excess of 420℃. The polyamides (3) derived from the diamine 2 showed reversible electrochemical oxidation accompanied by strong color change with high coloration efficiency(CE), high contrast ratio, and rapid switching time. The optical transmittance change (△T%) at 888 nm between the neutral state and the fully oxidized state is up to 98.9%, and the coloration efficiency is as high as ca. 313 cm2/C. The polyamides 6 derived from the diamine 5 showed reversible electrochemical oxidation accompanied by strong color change with high contrast ratio, and rapid switching time. The optical transmittance change (△T%) at 1031 nm between the neutral state and the fully oxidized state is up to 89%. In addition, the dilute NMP solutions of these polyamides exhibited fluorescence maxima around 536~541 nm with quantum yields up to 40.6%. The polyamides 9 derived from the diamine 8 showed reversible electrochemical oxidation with high contrast ratio both in the visible range and NIR region, which also exhibited high coloration efficiency, and high stability for long-term electrochromic operation. At the first oxidation stage, the polyamide film 9a revealed high coloration efficiency in visible(CE=272 cm2/C) and NIR(CE=305 cm2/C) region with reversible electrochemical cycling stability(over 14000 times within 4.32% loss relative to its initial CE). As the dication radical form of second oxidation stage, the polymer film still exhibited excellent electrochromic/electroactive stability(more than 8000 cyclic swithes) with enhaced contrast ration of 87.8%.
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Yang, Min-Sen, und 楊閔森. „An Interleaved High Conversion Voltage Ratio Converter with Soft-Switching Using a Single Auxiliary Switch“. Thesis, 2013. http://ndltd.ncl.edu.tw/handle/31178706032686173970.
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碩士國立勤益科技大學
電機工程系
101
This thesis presents an interleaved high voltage conversion ratio converter with soft-switching by means of a single auxiliary switch. As a voltage step-up converter, it successfully performs zero voltage switching (ZVS) and zero current switching (ZCS) operations on the main switches therein through the manipulation of the single auxiliary switch. In so doing, the switching loss as well as the switching stress suffered by the main switches can be reduced significantly, that is, the conversion efficiency of the converter can be elevated considerably. Furthermore, the aim of ZVS and ZCS is reached merely by use of a resonant branch in parallel with an existing converter. Hence, this work presents a simple structured and easy to implement converter. This proposed soft switching converter not merely boosts the output voltage of a fuel cell to a high level, that is applied to a high voltage DC link or a DC load, but also reduces the current stress in main switches, the input current and the output voltage ripples. In the end, this work is applied to fuel cells and validated by some simulation and experimental results.
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CHANG, CHIAO-WEI, und 張巧薇. „A Discussion on the Hedge Performance of the Minimum Variance Dynamic Hedge Ratio Model with Markov Switching“. Thesis, 2013. http://ndltd.ncl.edu.tw/handle/69282651551124989841.
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碩士國立臺北大學
統計學系
101
Nowadays, there are many financial commodities provided by several globalized financial markets. In the meantime, the volatility of financial market also causes a relative of the investor exposure to potential risk. The financial market in Taiwan is especially vulnerable to the disturbance of national and/or international political and economic situation which will conducts a higher investment risk. The types of risk can be divided into systemic risk and non-systematic risk. Non-systematic risk can be diversification by diversifying investment. The system risk is primarily attributed to general economic and political situation. To avoid the system risk, investors may use derivatives to divert the risk to the adventurers. In order to offer the demand of investors to avoid the price volatility of financial assets, some derivatives such as options and futures are also provided by the market. The high correlation of price variations between spots and derivatives can be applied to the hedge operation and the derivatives will be good hedging instruments for stock investors. This research mainly applies the correlation between spots and futures of Taiwan Weighted Index to establish a vector autoregression model and a dynamic conditional correlation GARCH model with Markov regime switching. The hedge ratios of each model at different regimes are also calculated. Finally, the hedging performances of two hedge models were compared according to the hedge ratios.
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Zhuo, Fan. „Essays on regime switching and DSGE models with applications to U.S. business cycle“. Thesis, 2016. https://hdl.handle.net/2144/19564.
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This dissertation studies various issues related to regime switching and DSGE models. The methods developed are used to study U.S. business cycles.
Chapter one considers and derives the limit distributions of likelihood ratio based tests for Markov regime switching in multiple parameters in the context of a general class of nonlinear models. The analysis simultaneously addresses three difficulties: (1) some nuisance parameters are unidentified under the null hypothesis, (2) the null hypothesis yields a local optimum, and (3) the conditional regime probabilities follow stochastic processes that can only be represented recursively. When applied to US quarterly real GDP growth rates, the tests suggest strong evidence favoring the regime switching specification over a range of sample periods.
Chapter two develops a modified likelihood ratio (MLR) test to detect regime switching in state space models. I apply the filtering algorithm introduced in Gordon and Smith (1988) to construct a modified likelihood function under the alternative hypothesis of two regimes and I extend the analysis in Chapter one to establish the asymptotic distribution of the MLR statistic under the null hypothesis of a single regime. I also apply the test to a simple model of the U.S. unemployment rate. This contribution is the first to develop a test based on the likelihood ratio principle to detect regime switching in state space models.
The final chapter estimates a search and matching model of the aggregate labor market with sticky price and staggered wage negotiation. It starts with a partial equilibrium search and matching model and expands into a general equilibrium model with sticky price and staggered wage. I study the quantitative implications of the model. The results show that (1) the price stickiness and staggered wage structure are quantitatively important for the search and matching model of the aggregate labor market; (2) relatively high outside option payments to the workers, such as unemployment insurance payments, are needed to match the data; and (3) workers have lower bargaining power relative to firms, which contrasts with the assumption in the literature that workers and firms share equally the surplus generated from their employment relationship.
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„Code-Switching in the Radio“. Master's thesis, 2012. http://hdl.handle.net/2286/R.I.14999.
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abstract: ABSTRACT This thesis analyzes the Spanish (SPA) and English (ENG) code-switching (CS) at Latino Vibe (LV), a bilingual radio station in Phoenix; Arizona from a sociolinguistic perspective. Using Gumperz's (1982) Conversational Functions of CS, Myers-Scotton's (1993) Markedness Model, and Bell's (1984) Audience Design model, this thesis intends to evaluate which one of these sociolinguistic models is the most accurate to explain the SPA-ENG CS at LV. In January 2009, the data were collected in a two week period of programming of the show "José y Tina en la mañana" (José and Tina in the morning), and then transcribed. This qualitative study consisted in analyzing the same subset of the data, corresponding to ten days. The model with the greater predictably of the types of CS and their causes would be considered the most appropriate for the data studied. The results show that CS is common and that codeswitched utterances are the most representative at LV. The conclusion also states that out of the three models, Gumperz's accounts better for the data than the other two. It explains more clearly the reasons why LV announcers code-switch in particular social contexts, and the important role of these switches during their interaction in this bilingual radio station. KEYWORDS: Code-switching, bilingual radio, Spanish-EnglishDissertation/Thesis
M.A. Spanish 2012
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Ho, Hsiang-Terh, und 何祥德. „Fast Switching Frequency Synthesizers for Mobile Radio Communications“. Thesis, 1995. http://ndltd.ncl.edu.tw/handle/38988225956340774124.
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碩士國立交通大學
電信研究所
83
As personal communication service (PCS) rapidly grows up, system and circuit design problems for mobile radio communications are overwhelming studied in recent years. In RF design, the key components, frequency synthesizers, must have faster speed, lower power, and higher operation frequency requirements. This thesis begins with a discussion of the conventional single-loop PLL synthesizer. In the following, we review the fast switching techniques that have been developed in the last two decades. Moreover, the frequency detector aided PLL synthesizer will be further explored. Finally, we introduce a method which uses the digital adaptive delta modulation technique in the frequency acquisition process in order to improve the fast switching speed requirements. In additional, we present some design rules from viewpoints of engineering experience for designing fast switching frequency synthesizers. In the last chapter, we also provide technical directions for improving frequency synthesizer switching speed in the future.
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Wei, Yang Tsung, und 楊宗瑋. „The discussion of regime switching model and optimal hedge ratios“. Thesis, 2006. http://ndltd.ncl.edu.tw/handle/12548088372396583329.
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碩士南台科技大學
財務金融系
94
This research primarily uses Markov Regime Switching model to investigate the optimal hedge ratio between Taiwan Stock Index and Taiwan Future Exchange (TAIFEX). In the past researches, when it comes to hedge ratio between spot and future markets, Bivariate-GARCH model is often used. This is because that Bivariate-GARCH model is able to catch the interaction between these two markets.On the other hand, Alizadeh and Nomikos（2004）claimed that there may be different regimes in the interaction between stock index and index future. Therefore, hedge ratios may depend on different regimes. Also, Sarno and Valente（2000）found Regime Switching Model outperforms OLS when investigating the relationship between stock index and index futures price. Thus, this research examines the optimal hedge ration in TAIFEX with Markov Regime Switching model.This research also takes Random Coefficient Autoregressive model (RCAR) and other models into consideration, such as Bivariate GARCH model, OLS, and Naïve, to compare the hedge efficiency between all models. Finally, the empirical result shows: RCAR outperforms other models in-sample, and MRS model is next to it; asymmetric Bivariate GARCH has better out-of-sample performance than other models, and RCAR Model is only second to it. Therefore, this research suggests that investors will be able to enhance efficiency in hedge strategy if they could take account of different regimes.
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Hu, Chih-Min, und 胡智閔. „High-Voltage LDMOSFET Radio Frequency Characteristics and its Switching Circuit Applications“. Thesis, 2011. http://ndltd.ncl.edu.tw/handle/15136625001405251378.
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39
Chen, Yu-Yu, und 陳宥毓. „A Study on the Code-Switching of Taiwanese in Mandarin Radio Programs“. Thesis, 2005. http://ndltd.ncl.edu.tw/handle/15570106140655117387.
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碩士國立成功大學
外國語文學系碩博士班
93
This study investigated the switches from Mandarin to Taiwanese in the present Taiwanese society. The data used here were collected from a female broadcaster’s and her two interviewees’ remarks. The broadcaster broadcasts the Mandarin radio program “Wonderful Life” of Kaohsiung Broadcasting Station on FM 94.3. According to the data analyses and the commonalities of the broadcaster’s and the two interviewees’ use of the Taiwanese language, four phenomena of Taiwanese use in public settings are observed, and they are listed as follows: 1. Taiwanese use is cultural as well as practical. 2. The choice of language may be influenced by the participant. In addition, after taking into the ailable evidence in the current conversation, the speaker rationally makes code choices. Code-switching demonstrates the speaker’s rational calculation. 3. For Taiwanese people, their Mandarin talks mixed with Taiwanese codes indicate that code-switching has become a very common and normal communication. It also reveals that no language is worse than any other language. 4. Multilingualism can help the speaker express his/her thoughts more precisely, more attractively, and more creatively. In conclusion, the switching from Mandarin to Taiwanese in Taiwan has become a very common and usual communication. It also presents that language is dynamic. In the sociolinguistic aspect, the code-switching from Mandarin to Taiwanese in Taiwan responds to people’s mother tongue applied more often in public settings governed by Mandarin, the social multicultural spirit, and a language style peculiar to a certain society at a certain time.
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Wei, Chang Jin, und 張晉維. „A Study on Applying Radio Techniques to Switching Control of the Capacitor Banks“. Thesis, 2000. http://ndltd.ncl.edu.tw/handle/43367533861546527419.
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碩士國立臺北科技大學
機電整合研究所
88
The theme of this thesis is to investigate the feasibility of applying radio techniques to switching control of the capacitor banks. It will be shown in this thesis that the spread spectrum radio networks is utilized as the communication networks for the feeder automation system. The technical feasibility as well as the system characteristics are investigated. Routing methodologies of different types of spread spectrum radio networks are also investigated. Based on the routing methodologies, computer simulation programs are designed to evaluate the communication delays in the radio networks. Taking Tu-Cheng Secondary substation of Taiwan Power Company’s Southern North District Office as the planning site, radio field test is conducted to design the radio communication routes and determine the appropriate installation sites of radio transceivers. The affects of voltage and power factor on the feeders due to the control of any capacitor on the feeder are also studied through site measurement and computer simulations. Finally, two control strategies to automatically control the switching of capacitors on the feeders are proposed in this thesis. The former one is based on the power factor prediction while the other one is based on the inference techniques by Artificial Neural Networks. Two proposed control strategies are both verified through computer simulations based on the load model of Tu-Cheng Secondary substation.
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Rezanezhad, Gatabi Iman. „Tunnel MOS Heterostructure Field Effect Transistor for RF Switching Applications“. Thesis, 2013. http://hdl.handle.net/1969.1/151047.
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GaN RF switches are widely used in today’s communication systems. With digital communications getting more and more popular nowadays, the need for improving the performance of involved RF switches is inevitable. Designing low ON-state resistance GaN switches are exceedingly important to improve the switch insertion loss, isolation and power loss. Moreover, considerations need to be taken into account to improve the switching speed of the involved GaN HEMTs.
In this dissertation, a new GaN HEMT structure called “Tunnel MOS Heterostructure FET (TMOSHFET)” is introduced which has lower ON-state resistance and faster switching speed compared to conventional AlGaN/GaN HEMTs. In the switch ON process, the channel of this device is charged up by electron tunneling from a layer underneath the channel as opposed to typical AlGaN/GaN HEMTs in which electron injection from the source is charging up the channel. The tunneling nature of this process together with the shorter travel distance of electrons in TMOSHFET provide for a faster switching speed.
In order to understand the tunneling mechanisms in TMOSHFET, the fabrication of AlGaN/GaN Schottky Barrier Diodes (SBDs) with various AlGaN thicknesses is demonstrated on Si (111) substrate. The impacts of SF6 dry etching on the trap density and trap state energy of AlGaN surface are investigated using the GP/w- w method. Various tunneling mechanisms at different biases are then characterized in samples and compared with each other.
To improve the source and drain resistances in TMOSHFET, a model is generated to optimize the 2DEG density and electric field in AlGaN/GaN heterostructure based on Al mole fraction, AlGaN thickness and the thickness of SiN passivation layer and it is experimentally verified by non-contact Hall 2DEG density measurements. The spontaneous and piezoelectric polarizations together with strain relaxation have been implemented into the model, taking into account the annealing effects. From the experimental data on obtained parameters, the operation and device parameterization of the TMOSHFET is outlined and design considerations to improve the device R_(ON)-V_(BR) figure of merit are discussed.
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Sewnath, Gajadhar. „A packet radio system for an industrial data network“. Thesis, 1992. http://hdl.handle.net/10413/6898.
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This project was undertaken for a commercial electronics company,
CONTROL LOGIC (CONLOG) which is involved in the research, design,
development and manufacture of data acquisition, control, energy
management and automotive equipment. Currently CONLOG uses an inhouse token passing local area network CONET for industrial data
communications.The need had arisen to provide a means of data communication amongst widely geographically distributed remote terminal units (RTUs) generating demands at a very low duty cycle. A need for communications between RTUs and a centralised controller was also required. In addition to this, multihop communications between the RTUs was required. Packet switching using a broadcast radio network provides
an efficient means of achieving this. An investigation into to the various media access control protocols and contention techniques using packet radio was carried out. The various media access techniques were compared with respect to throughput and normalised delay. This led to the selection of a media
access scheme for the packet radio network using RTUs. A protocol specification control is centralised or Interconnect Organisation.The switching protocol (OSI) for the packet radio network, in which distributed, was done. The architechure of specified adheres to the Open Systems model of the International Standards.An experimental packet switching radio network was implemented using the protocol specification defined above. The packet radio network (PACNET) uses existing off the shelf radios and purpose built hardware for the remote terminal units. The thesis describes methods of data communications suitable for widely dispersed industrial data communications, the selection of the packet switching media access methods and control protocols, and the design and implementation of the prototype system.Thesis (M.Sc.Eng.)-University of Natal, 1992.
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Hsieh, Chung-Chi, und 謝仲啟. „Design of Radio Frequency Identification Circularly Polarized Reader Antennas and Varactor-Controlled Beam-Switching Printed Antenna Array“. Thesis, 2005. http://ndltd.ncl.edu.tw/handle/60378282435521179988.
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碩士國立交通大學
電信工程系所
93
Design of circularly polarized reader antennas suitable for 915MHz radio frequency identification system is proposed in the first half of this thesis. We discuss the techniques and limits to realize circularly polarized microstrip antennas by dual feed and single feed structure separately. By means of increase the height and change the feeding structure to let the design antennas can conform to this system bandwidth requirement. In wireless communication, we often hope we can change the direction and shape of the antennas beams to improve the signal gain and propagate distance, and diminish the unnecessary interference and decrease the percentage of occurrence. Varactor-controlled bam-switching antennas which can be realized by planar printed circuit board is proposed in the second half of this thesis, in order to lower hardware fabrication cost and reduce antenna size to conform to the trend of wireless communication:light,thin,short,and small. In this thesis, Ansoft HFSS is used to simulate and design every kind of antenna structure.
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WU, CHAO-CHENG, und 吳朝成. „Design and studies of a switching Dc-Dc converter with wide conversion range without extremely duty ratios“. Thesis, 1993. http://ndltd.ncl.edu.tw/handle/51017175119240307912.
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Mahajan, Mehak. „Charge Density Wave-driven Carrier Transport in Layered Heterostructures“. Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5850.
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Metal-based electronics remain one of the longstanding goals of researchers to achieve ultra-fast and radiation-hard electronic circuits. Generally, metals are primarily used as passive conductors in modern electronics and do not play an active role. Nanoscale materials with distinctive size-dependent properties provide opportunities to achieve new device functionalities. Ta-based di-chalcogenides, particularly 1T-TaS2 and 2H-TaSe2, which form layered structures and exhibit charge density waves (CDW), are promising in this context. CDW is a macroscopic state shown by materials with reduced dimensions, for example, one-dimensional and layered two-dimensional crystals. It results from the modulation in the electronic charge arising due to a periodic modulation in the crystal lattice.
1T-TaS2 exhibits one of the strongest known CDW characteristics enabling temperature-dependent distinct resistivity phases. The nearly commensurate (NC) to the incommensurate (IC) CDW phase transition that usually occurs at 353 K and can be driven electrically at room temperature is of high practical interest. However, resistivity switching during this phase transition is weak (< 2) and cannot be modulated by an external gate voltage – limiting its widespread usage. Using a back-gated 1T-TaS2/2H-MoS2 heterojunction, we show resistivity switching up to 17.3, which is ~14.5-fold higher than standalone TaS2. We demonstrate a low barrier electrical contact between a TaS2 source and a MoS2 channel, promising “all-2D” flexible electronics. Additionally, we show that the usual resistivity switching in TaS2 due to different phase transitions is accompanied by a surprisingly strong modulation in the Schottky barrier height (SBH) at the TaS2/MoS2 interface – providing an additional knob to control the degree of the phase-transition-driven resistivity switching by an external gate voltage. In particular, the commensurate (C) to triclinic (T) CDW phase transition increases the SBH owing to a collapse of the Mott gap in TaS2. The change in SBH allows us to estimate an electrical Mott gap opening of ~71 ± 7 meV in the C phase of TaS2. The results show a promising pathway to externally control and amplify the CDW induced resistivity switching.
Further, we achieve gate- and light-controlled negative differential resistance (NDR) characteristics in an asymmetric 1T-TaS2/2H-MoS2 T-junction by exploiting the electrically driven CDW phase transition of TaS2. The device operation is purely governed by majority charge carriers, making it distinct from typical tunneling-based NDR devices, thus avoiding the bottleneck of weak tunneling efficiency in van der Waals heterojunctions. Consequently, we achieve a peak current density over 10^5 nA μm^(-2), which is about two orders of magnitude higher than that obtained in typical layered material-based NDR implementations. An external gate voltage and photo-gating can effectively tune the peak current density. The device characteristics show a peak-to-valley current ratio (PVCR) of 1.06 at 290 K, increasing to 1.59 at 180 K. To exploit the low thermal conductivity of 1T-TaS2 and 2H-TaSe2 in a local heater structure, we insert 2H-TaSe2 in between TaS2 and MoS2 layers, thereby forming a triple-layered 1T-TaS2/2H-TaSe2/2H-MoS2 T-junction. TaSe2 acts as a buffer layer preventing the CDW-induced SBH modulation at TaS2/MoS2 interface. This will allow efficient thermionic switching of carriers resulting from sharp temperature rise in the junction due to electrically driven TaS2 phase transitions. Interestingly, the device can toggle between the current increment and NDR characteristics by simply changing the biasing conditions. At TaS2 biasing, the heterostructure device shows a current increment by a factor of 3 at 300 K, which gets enhanced up to ~10^3 at 77 K, beneficial for various switching circuits and sensing applications. However, under TaSe2 biasing, the device exhibits NDR characteristics with a PVCR of 1.04 and 1.10 at 300 K and 77 K, respectively. The external back-gate voltage can effectively tune the current enhancement factor and NDR. The devices mentioned above are robust against ambiance-induced degradation, and the characteristics repeat in multiple measurements over more than six months.
Conventional metals, in general, do not exhibit strong photoluminescence. However, we found that 2H-TaSe2 exhibits a surprisingly strong optical absorption and photoluminescence resulting from inter-band transitions. We use this perfect combination of electrical and optical properties in several optoelectronic applications. We show a seven-fold enhancement in the photoluminescence intensity of otherwise weakly luminescent multi-layer MoS2 through non-radiative resonant energy transfer from TaSe2 transition dipoles. Using a combination of scanning photocurrent and time-resolved photoluminescence measurements, we also show that the hot electrons generated by light absorption in TaSe2 have a relatively long lifetime, unlike conventional metals, making TaSe2 an excellent hot-electron injector. Finally, we show a vertical TaSe2/MoS2/graphene photodetector demonstrating a responsivity greater than 10 AW^(-1) at 0.1 MHz - one of the fastest reported photodetectors using MoS2.
The findings will boost device applications that exploit CDW phase transitions, such as ultra-broadband photodetection, negative differential conductance, thermal sensors, fast oscillator, and threshold switching in neuromorphic chips. These functionalities will enable the implementation of active metal-based circuits.
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Variar, Harsha B. „Device-Circuit Reliability Co-Design in High voltage and Power devices“. Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5875.
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For the last four decades, silicon CMOS technology has captured a significant share in IC, smart power IC, SoC, and the power device market. But there is aggressive research on other materials such as graphene & similar 2D materials and wideband gap materials. But, several aspects, including the fabrication process to improve device performance [7,9,12,13], understanding the device reliability physics [8,10,11], interconnection and packaging, need to be matured before these compound materials take the limelight. Besides these, a fab set-up for large scale production requires high NRE capital. On the other hand, Silicon had been through a great degree of maturity. Moreover, for intelligent power applications, Silicon has superior reliability. Therefore, Silicon is predicted to capture the power device market till the other materials gain perfection.
Besides the commercial market, the requirement for discrete and integrated power device technology within the strategic sector is enormous. Discrete power switching devices (often power MOS or IGBT switch) and power RF devices are used in numerous onboard power electronic and power RF applications. The first part of this work strives to bridge the device-circuit co-design gap that has severely limited predictive modelling of circuits for high power applications such as Radio Frequency Power Amplifiers (RF PAs) using high power devices LDMOSs and GaN HEMTs. A correlation between the device’s intrinsic parameters and PA performance is explored, and the iterative process aims to provide a high-performing circuit.
LDMOS is one of the prominent power devices which adopts CMOS processing and easy integration. The lateral double diffused MOSFET (LDMOS) is the predominant power device in implementing Power integrated circuits PICs because of its attractive electrical characteristics such as low on-resistance, high breakdown voltage, high input impedance and fast switching frequency. To obtain high breakdown voltage with low on-resistance for LDMOS, RESURF technology is used, in which the vertical p-n junction depletion layer between the n-type drift region and p-type epitaxial region and its interaction with lateral p-n junction depletion between the p-type channel and n-type drift region is optimised to reduce the surface electric field to obtain high breakdown voltage. A field plate (FP) on top of the gate and a drain field plate on top of the drift region is introduced to improve breakdown voltage further. These field plates help reduce feedback capacitance (Cgd) and increase the breakdown voltage FP LDMOS.
This work explores optimising the field plates for achieving breakdown characteristics above 900V without altering the on-resistance of the devices [2]. It covers major classical power devices from conventional design to non-conventional device designs. Conventional devices without field plates show 30% lower breakdown voltages than those with field plates. It can be concluded that field plates play a vital role in enhancing the breakdown characteristics of the device. Taking optimised design further, the field plates are introduced into non-conventional devices, where RESURF and SOI-based devices are explored. Along with the performance studies, the reliability of these structures is also explored. Regarding reliability, RESURF based devices show a higher tendency of deviation/degradation when stressed, up to 20% higher than the breakdown condition like that of the conventional devices without Fp. Further, the role of each field plate individually under the ESD condition is explored [3]. It was clearly understood that field plates at the source side play a significant role in distributing the junction electric field, while field relaxation at the drain side helps in improving the failure threshold. Gate and Source field plates improve the trigger voltage characteristics up to 54%, while drain field plate improves the failure threshold up to 60%.
Power semiconductor device industries are aggressively looking for system-on-chip (SOC) solutions for power amplifier (PA) circuits and are exploring different technologies, including gallium arsenide (GaAs), to more recent and intriguing gallium nitride (GaN) technologies, for power transistors with Radio Frequency (RF) applications. The advantage of silicon technology for RF applications lies mature fabrication process at low cost and their easy integration capability with the CMOS technology. Applications that require radio frequency power amplifiers such as broadcast, ISM (industrial, scientific, and medical), avionics, radar, wideband communications, telecom & satellite communications, RF heating applications, etc. Among them, the 50V RF LDMOS device is mainly used in wireless broadcast, ISM, and radar, which requires a higher breakdown voltage and power density. For 50V RF LDMOS with 0.35µm CMOS technology, the breakdown voltage must be higher than 100 V to guarantee a reliable operation. RESURF technology and the introduction of field plates have improved the breakdown voltage to 114V. Both DC and RF performance of various designs of FP RF LDMOS are evaluated, and results show that industry-leading performance is achieved [1]. Electrostatic Discharge (ESD) robustness was studied for the FP RF LDMOS designs as ESD has been identified as a source of damage to unprotected devices. Hot Carrier Injection (HCI) reliability was also investigated to address the complete reliability of these devices.
Though Silicon-based transistors have the advantage of mature technology, the requirement for high power and high-frequency devices demands transistors based on semiconductor materials with large breakdown voltage and high electron velocity. GaN is an attractive candidate for power amplifier applications because of several superior qualities in amplifier applications achieved due to its semiconductor properties. The wide bandgap in Gallium Nitride based transistors results in higher breakdown voltages because the ultimate breakdown field is the field required for band-to-band impact ionisation. Also, its high electron saturation velocities allow high-frequency operation. GaN can be used to fabricate high electron mobility transistors (HEMTs), which have high carrier concentration and higher electron mobility due to reduced ionised impurity scattering. A rigorous device-circuit co-design investigation of AlN/GaN HEMT to explore its feasibility for power amplifier operation at frequencies > 1THz. Both class A and class AB operations were invested. A novel device-circuit co-design methodology was adopted [4], which involves (i) device design optimisation using a well-calibrated TCAD setup, (ii) careful extraction of large-signal model cards with I-V, C-V & S-parameter matching, and finally (iii) source-load pull-based power amplifier design/exploration, for every device design investigated. For PA operation, both class A and class AB operations were invested while exploring PA gain, output power, efficiency at 1dB compression point, and linearity through dual-tone (IMD3) investigations. Besides, a complete range of device design parameters was investigated to explore the ultimate scalability limit and narrow down the device design window that can enable THz operation.
The last two decades have witnessed significant scaling in MOS technology from sub-micron to sub-nm level. To achieve devices with good performance at a small dimension, it was essential to explore new device architectures which could offer subthreshold swing (SS) values below 60 mV/dec. Several CMOS-like structures were designed, such as Fin-FETs, Nanowire Gate All Around (GAA) MOSFETs, Carbon nanotube FETs, Tunnel FETs, etc., which could lower the leakage current at small dimensions. Among these, TFET could achieve SS less than 60 mV/dec attributed to a fundamentally different mechanism for carrier injection. Hence, TFET is considered a future on the roadmap. A prediction of reliability is essential in choosing a device for a particular application. Therefore, it is necessary to understand the reliability of devices at the design stage itself. As technologies advance towards the deep submicron, the ESD (Electrostatic Discharge) protection design issues have become more critical. The second part of this work tries to understand the ESD robustness of a couple of novel Tunnel FET architectures.
A novel Fin-enabled vertical or area-scaled tunnelling FET is proposed for sub- 10-nm channel length operation. This device enables a smooth transition from FinFET technology to Fin-based vertical TFETs, while enjoying the benefits of FinFET architecture. To make this device commercial, it’s essential to understand the reliability performance of this device. This work explores the reliability physics of this device with detailed physical insight into the device’s operation and failure under ESD stress conditions [5]. The proposed device has a deep N+ implant underneath the P+ source, like adding a pocket between the source and gate for the ESD protection applications. Early avalanche assisted BTBT at the source-pocket junction, in addition to the drain-substrate junction, causes the device to turn on at lower voltages, lower self-heating resulting in improved failure current in the proposed device with less area overhead.
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Swart, Arthur James. „Design and development of a high frequency Mosfet driver“. Thesis, 2004. http://hdl.handle.net/10352/253.
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Thesis (M. Tech. Engineering: Electrical--Vaal University of TechnologyA high-power Mosfet was incorporated as a switching device into the efficient Class E configuration, where the switching device switches current through itself either completely on or completely off at high frequencies. The first objective of this project was to demonstrate the effectiveness of a phase-lock loop circuit in generating stable high frequencies when connected in an indirect frequency synthesizer configuration. The indirect frequency synthesizer has established itself as a versatile frequency generator capable of generating high frequencies based on a lower stable reference frequency. The frequency generation stage incorporates a phaselock loop circuit, a frequency divider and a stable reference frequency section. The phase-lock loop section incorporates the TTL based 74HC 4046 that is based upon the common CMOS 4046 integrated circuit. The frequency divider section is built around the CMOS-based 4526 whilst the reference frequency section incorporates the CMOS-based 4060. The frequency synthesizer produced a range of frequencies from 50 kHz to 8 MHz in 50 kHz steps. The output voltage was constant at 5,5 V. The second objective was to show that the complementary emitter follower is indeed a worthy Mosfet gate drive circuit at high frequencies. The Mosfet driver stage produced a voltage signal of at least 11 V, being able to source and sink relatively high peaks of current, especially at high frequencies. Voltage amplification occurred through the use of multiple CMOS-based 40106 inverters. The complementary emitter follower, known for its low output impedance and its ability to source and sink large amounts of current, was an important component in the final Mosfet gate section.
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Frebrowski, Daniel Jordan. „Investigation of Time Domain Modulation and Switching-Mode Power Amplifiers Suitable for Digitally-Assisted Transmitters“. Thesis, 2010. http://hdl.handle.net/10012/5492.
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Innovation in wireless communication has resulted in accelerating demand for smartphones using multiple communications protocols such as WiFi, Bluetooth and the many cellular standards deployed around the world. The variety of frequency, bandwidth and power requirements associated with each standard typically calls for the implementation of separate radio frequency (RF) front end hardware for each standard. This is a less-than-ideal solution in terms of cost and device area. Software-defined radio (SDR) promises to solve this problem by allowing the RF hardware to be digitally reconfigurable to adapt to any wireless standard. The application of machine learning and cognition algorithms to SDR will enable cognitive radios and cognitive wireless networks, which will be able to intelligently adapt to user needs and surrounding radio spectrum conditions.
The challenge of fully reconfigurable transceivers is in implementing digitally-controlled RF circuits which have comparable performance to their fixed-frequency counterparts. Switching-mode power amplifiers (SMPA) are likely to be an important part of fully reconfigurable transmitters since their switching operation provides inherent compatibility with digital circuits, with the added benefit of very high efficiency. As a step to understanding the RF requirements of high efficiency and switching PAs, an inverse class F PA in push-pull configuration is implemented. This configuration is chosen for its similarity to the current mode class D (CMCD) topology. The fabricated PA achieves a peak drain efficiency of over 75% with 42.7 dBm (18.6 W) output power at 2.46 GHz.
Since SMPAs cannot directly provide the linearity required by current and future wireless communications standards, amplitude information must be encoded into the RF signal in a different way. Given the superior time resolution of digital integrated circuit (IC) technology, a logical solution is to encode this information into the timing of the signal. The two most common techniques for doing so are pulse width modulation and delta-sigma modulation. However, the design of delta-sigma modulators requires simulation as part of the design process due to the lack of closed-form relationships between modulator parameters (such as resolution and oversampling) and performance figures (such as coding efficiency and signal quality). In particular, the coding efficiency is often ignored although it is an important part of ensuring transmitter efficiency with respect to the desired signal. A study of these relationships is carried out to observe the tradeoffs between them. It is found that increasing the speed or complexity of a DS modulated system does not necessarily translate to performance benefits as one might expect. These observations can have a strong impact on design choices at the system level.
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Nam, Haewoon. „Joint diversity combining technique and adaptive modulation in wireless communications“. Thesis, 2006. http://hdl.handle.net/2152/3460.
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Rodrigues, Ricardo Filipe Soares. „Design of a Class-D RF power amplifier in CMOS technology“. Master's thesis, 2016. http://hdl.handle.net/10362/20513.
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In this thesis an RF Class-D Power Amplifier is presented. The analysis of the Class-D
amplifier considering ideal components has shown that the drain efficiency of 100% can
be achieved. The output power and the drain efficiency are degraded by the internal
resistance of each component. A driver is used to drive the gate capacitances of the Class-D amplifier. Both driver and amplifier are implemented with CMOS inverters. The size of the inverters in the driver is scaled down by a factor of 3 relatively to the preceding stage.
The first being the inverter of the Class-D amplifier. At the output a 3rd order Butterworth bandpass filter is implemented. A non-ideal analysis of the Class-D amplifier is performed to create a base model which is used to aid in the design of the circuit.
The RF Class-D Power Amplifier with the operation frequency of 2.4GHz was implemented with standard 130 nm CMOS technology. Two simulations were taken into
account considering ideal and pre-layout components in the output filter. The following
results were obtained when using ideal components: the output power of 6.91 dBm, the
drain efficiency of 40% and the overall efficiency of 23%. Using pre-layout components the results were the following: the output power of 0.317 dBm the drain and overall efficiency of 8.6% and 4.9%, respectively.