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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
211

A wide dynamic range high-q high-frequency bandpass filter with an automatic quality factor tuning scheme

Kumar, Ajay 09 January 2009 (has links)
An 80 MHz bandpass filter with a tunable quality factor of 16∼44 using an improved transconductor circuit is presented. A noise optimized biquad structure for high-Q, high- frequency bandpass filter is proposed. The quality factor of the filter is tuned using a new quality factor locked loop algorithm. It was shown that a second-order quality factor locked loop is necessary and sufficient to tune the quality factor of a bandpass filter with zero steady state error. The accuracy, mismatch, and sensitivty analysis of the new tuning scheme was performed and analyzed. Based on the proposed noise optimized filter structure and new quality factor tuning scheme, a biquad filter was designed and fabricated in 0.25 μm BiCMOS process. The measured results show that the biquad filter achieves a SNR of 45 dB at IMD of 40 dB. The P-1dB compression point and IIP3 of the filter are -10 dBm and -2.68 dBm, respectively. The proposed biquad filter and quality factor tuning scheme consumes 58mW and 13 mW of power at 3.3 V supply.
212

Pathways of paternal antigen presentation to initiate antigen-specific immune responses in pregnancy.

Moldenhauer, Lachlan January 2008 (has links)
The fetus and its placenta, collectively called the conceptus, are semi-allogeneic to the mother, as they express transplantation antigens of paternal origin. Foreign tissues generally experience immunological rejection by the host immune system; however in a normal healthy pregnancy the conceptus does not undergo immune attack. Emerging evidence indicates the conceptus avoids rejection through a number of mechanisms including the induction of active maternal immune tolerance specific for paternal antigens. However, the mechanisms responsible for establishing this tolerance remain undefined, including the timing of the first encounter with paternal antigen and the cellular processes by which paternal antigen is presented to the maternal immune system. Exposure to paternal transplantation antigens occurs in two waves: initially in the context of male seminal fluid at conception, and secondly after placental trophoblast invasion of maternal tissues in mid-gestation pregnancy. Therefore the aim of this research was to evaluate the female immune response to paternal antigens in seminal fluid and those associated with the conceptus. The mechanisms of antigen presentation, the impact of the cytokine environment and the consequences of T cell activation on pregnancy were also investigated. A transgenic system using ovalbumin (OVA) as the model paternal antigen was established. The transgenic Act-mOVA mouse expresses OVA constitutively and ubiquitously under a B-actin promoter and OVA was shown to be present in seminal fluid and in the fetal and placental tissue of sired progeny. The OVA-reactive CD8+ OT-I and CD4+ OT-II T cells were employed to gauge the relative amount of OVA antigen presented, with the strength of the maternal immune response quantified based upon the extent of T cell proliferation, as assessed by CFSE dye-dilution. Utilising bone marrow chimeric mice, it was demonstrated that upon insemination by an Act-mOVA male, seminal fluid-derived OVA was processed and indirectly presented by maternal bone marrow-derived antigen presenting cells to induce activation and proliferation of the CD8+ OT-I T cells within the uterinedraining para-aortic lymph nodes of the female. Likewise, OT-II T cells were responsive to MHC class II-restricted presentation of seminal fluid OVA. Post-implantation conceptus-derived OVA was detected within peripheral lymph nodes and the spleen where it was presented via the MHC class I and class II-restricted pathways to induce systemic proliferation of both OT-I and OT-II T cells. Furthermore, as gestation advanced the extent of OVA presentation and hence T cell proliferation intensified. Conceptus-derived OVA was still presented systemically until 20 days pp. The impact of the uterine cytokine environment was assessed to determine its influence on seminal OVA antigen processing and presentation. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a key factor in regulating the leukocyte population of the female reproductive tract. GM-CSF-deficient female mice were unable to process and present seminal fluid OVA as effectively or efficiently as their wildtype counterparts, as assessed by their reduced capacity to drive OT-I and OT-II T cell proliferation following insemination by an Act-mOVA male. Finally, with highly-reactive OVA-specific T cells activated in response to seminal and conceptus OVA antigen, it was of interest to determine the effect of OT-I T cell activation on fetal survival and pregnancy success. It was found that OT-I T cells activated in vivo to paternal OVA antigen in the context of seminal fluid and pregnancy were not deleterious to pregnancy outcomes. However the transfer of cytotoxic OT-I T cells generated in vitro in the presence of an IL-2 into female mice carrying OVA-expressing conceptuses was detrimental to fetal survival. Collectively these experiments demonstrated that the initial exposure to paternal antigen, and hence the first opportunity to develop paternal antigen-specific tolerance, occurs at insemination. Paternal antigen is presented to the maternal T cell repertoire throughout gestation and may play a role in maintaining immune tolerance during pregnancy. The processing and presentation of paternal-derived antigen is chiefly performed by female bone marrow-derived antigen presenting cells. The cytokine environment of the mated female reproductive tract is critical in allowing optimal antigen processing and presentation, to generate an immune response consistent with maternal immune tolerance of the conceptus. / Thesis (Ph.D.) - University of Adelaide, School of Paediatrics and Reproductive Health, 2008
213

Immune regulation in mouse models of allergic asthma

Su, Yung-Chang, University of New South Wales & Garvan Institute of Medical Research. St. Vincent's Clinical School, UNSW January 2006 (has links)
Allergic asthma is an immunological disease, mediated by CD4+ Th2 cells, and its prevalence has increased over recent decades. Features of allergic asthma include airway hyperresponsiveness (AHR), airway eosinophilia, excessive airway mucus production, and increased IgE and Th2 cytokine levels. Airway remodeling with pulmonary fibrosis is noted in the progress of asthma. In this thesis, a murine model of allergic asthma was used to investigate the effect of cyclophosphamide (CY) on asthma and the involvement of regulatory T cells (Treg), and the role of Granulocyte-macrophage colony stimulating-factor (GM-CSF) in allergic asthma by using GM-CSF knockout mice. CY is a cytotoxic agent, which paradoxically augments several immune responses. The first part of this thesis was aimed to study the effects of CY in a murine model of allergic airway inflammation. BALB/c mice were immunized with ovalbumin (OVA) on days 0 and 14, and challenged with aerosolized OVA from days 21 to 27. Some mice additionally received CY on days -2 and 12. In the CY-treated animals, pronounced worsening of inflammatory features was noted, including increases in eosinophil infiltration, epithelial thickness, mucus occlusion and eosinophil numbers in bronchoalveolar lavage fluid (BALF). Increased total and OVA-specific serum IgE were also noted in the CY-treated animals. In cell cultures from peritracheal lymph nodes, the Th2 cytokines IL-4 and IL-5 were elevated in animals treated with CY. It was hypothesized that the effects of CY could be caused by reduced immunosuppression mediated by Treg. mRNA expression of the immunosuppressive cytokines IL-10 and TGF-beta was reduced in the lungs of CY-treated mice. The expression of FoxP3, a marker of naturally occurring Treg, was significantly reduced in spleens, thymuses and peritracheal lymph nodes after the second injection of CY, and in the lung tissue after allergen challenge in CY-treated mice. Furthermore, lung IL-10-producing CD4+ T cells and CTLA-4+-bearing CD4+ T cells were reduced after allergen aerosol challenge in CY-treated mice. Thus CY worsened the features of allergic pulmonary inflammation in this model, in association with increased production of IgE and Th2 cytokines. The reduction in expression of FoxP3 and immunosuppressive cytokines by CY suggests that toxicity to Treg may contribute to the increased inflammation. GM-CSF plays a role in the growth, development, and maturation of bone marrow hemopoietic cells into mature blood cells, and has been proposed to be involved in potentiating the function of inflammatory cells in allergic inflammation. In the second part of this thesis, GM-CSF knockout (KO) mice were used to investigate the role of GM-CSF. In allergic KO mice, airway eosinophils were only shown in the perivascular, but not peribronchial areas in the lung, compared to the allergic wild-type (WT) mice in which eosinophil infiltration appeared in both areas. Eosinophil numbers were drastically reduced in the bronchoalveolar lavage fluid (BALF) of KO mice. IL-5 production in the lung tissue and BALF in allergic KO mice was reduced; similar results were also found in peritracheal draining lymph nodes after in vitro stimulation assays. However, IL-4 and IL-13 production, airway hyperresponsiveness (AHR), and serum IgE production were not affected in allergic KO mice. Surprisingly, lung IFN-gamma mRNA and BALF levels were increased in allergic KO mice. Lung mRNA levels of CCR3, a key chemokine receptor on eosinophils, were significantly reduced in allergic KO mice, whereas expression of the chemokines eotaxin and RANTES were at similar levels in allergic KO and WT mice. Lung mRNA levels of the IFN-gamma-inducible chemokines Mig (CXCL9) and IP-10 (CXCL10), which are antagonists of CCR3, and their receptor CXCR3 were increased in allergic KO mice, compared with allergic WT mice. Data obtained from flow cytometry showed more eosinophils survived in the lung of WT mice than KO mice. Another allergy model, a peritoneal allergy model was performed to investigate inflammation in a different model. Leukocyte subpopulations such as neutrophils, eosinophils, macrophages, and lymphocytes were reduced in the peritoneal lavage fluid of allergic KO mice. The findings revealed that GM-CSF is essential for IL-5 production, pulmonary airway eosinophilia and eosinophil survival. In the absence of GM-CSF, over-production of IFN-???? may induce chemokines, including Mig and IP-10, which are antagonists for CCR3 and may reduce airway eosinophil infiltration. In this thesis, a murine model of allergic asthma has been used to obtain novel findings on the regulation of allergic inflammation. The results with CY are relevant to the treatment of asthma patients with CY and other cytotoxic agents. The findings in the GM-CSF KO mice suggest that GM-CSF is a potential therapeutic target in asthma, and that in assessment of new therapeutic agents for asthma, effects on GM-CSF should be considered.
214

Ett Färgat Köpbeteende : En studie om färgers påverkan på konsumenters uppfattning av märkning / A Colorful Consumer Behavior

Myhrman, Martin, Uppman, Robin January 2015 (has links)
Titel: Ett Färgat Köpbeteende Nivå: C-uppsats i ämnet företagsekonomi Författare: Martin Myhrman & Robin Uppman Handledare: Jonas KågströmDatum: 2015 - 05 Syfte: Bakgrunden till att vi har utfört denna studie är att forskning om färgers påverkan på beslutsfattande inom ämnet marknadsföring är begränsad, tidigare forskning har även pekat på att vidare forskning borde beröra vilka faktorer som skulle kunna påverka konsumenters uppfattning om genmodifierade produkter. Således är vårt syfte:“Syftet med denna uppsats är att undersöka hur färgkodad märkning kan kompensera för den negativa uppfattningen som kan råda kring genmodifierade livsmedel.” Metod: För att besvara vårt syfte har vi valt att utföra ett experiment. Studien genomfördes på 120 respondenter på en högskola i Sverige, testpersonerna utförde ett smaktest där de tre olika betingelserna var märkta med olika färger (röd, blå och grön). Den data vi fick in analyserades sedan med hjälp av statistikprogrammet IBM SPSS Statistics 22, därefter har vi tolkat och diskuterat resultaten. Resultat & Slutsats: Vårt huvudsakliga fynd är att röd färg på negativ märkning genererar lägre betalningsvilja än grön och blå färg, vårt resultat korroborerar tidigare forskning som bland annat menar att röd färg bidrar till en aggressivare sinnesstämning och ett mer analytiskt tänkande. I övrigt har vi sett tendenser till att färgen på märkningen inte påverkat varken smakupplevelsen eller hälsouppfattning. Förslag till vidare forskning: Flertalet av våra resultat har inte uppnått statistisk signifikans, vilket troligtvis beror på att vårt urval har varit för litet, vidare forskning borde replikera vår studie på ett större urval. Utöver detta förslag till framtida forskning anser vi att följande bör undersökas:- Hur påverkar färgmärkning uppfattningen om andra GMO-produkter?- Hur blir köpbeteendet påverkat av olika färgnyanser?- Hur förhåller sig varumärke och färg till varandra i köpbeslut? Uppsatsens bidrag: Vår studie har bidragit till att branschen bör tänka på att använda färger med viss försiktighet när det kommer till märkning. Vidare har vi visat att färger påverkar kunders betalningsvilja, vilket är vårt bidrag till ämnet marknadsföring. / Title: A Colorful Consumer Behavior Level: Final assignment for Bachelor Degree in Business Administration Author: Martin Myhrman & Robin Uppman Supervisor: Jonas KågströmDate: 2015 – 05 Aim: The background of our study was grounded in the fact that the research of colors impact are limited in the field of marketing. Studies have also shown that future research should examine which factors that affect consumer’s perception of genetically modified products. The aim of our study is as follows: “The aim of this study is to examine how colored labeling might compensate for the negative perception of genetically modified products.” Method: In this study we have performed an experiment. The experiment took place at a University in Sweden and we had 120 respondent commits. The respondents were asked to perform a taste test in which the color of a label was manipulated between three test groups (red, blue and green). The collected data was analyzed with IBM SPSS Statistics 22, further the results were interpreted and discussed. Result & Conclusions: Our main finding is that the color red on a negative label generated a lower willingness to pay than both blue and green. This result confirms previous research which among other things says that the color red trigger an aggressive mindset and encourage analytical thinking. Furthermore we have seen trends that indicate that colors do not affect the taste and health perception. Suggestions for future research: Many of our results have not been statistically significant, which probably depends on our relatively limited sample, further research should replicate our study with a wider sample. In addition to this suggestion we would like to see further research concerning:- Colors impact on the perception of other GMO products.- The impact of color shades on consumer behavior.- The relation between brands and colors in buying decisions. Contribution of the thesis: Our contribution to people working with marketing is that they should be aware that colored labels may affect the consumer perception. Furthermore we have shown that colors affect consumer’s willingness to pay, which is our contribution to the field of marketing.
215

Grammatiska metaforer i elevtexter : En studie av högstadieelevers användning av grammatiska metaforer

Polat, Rumeysa January 2018 (has links)
Syftet med denna undersökning är att studera förekomsten av grammatiska metaforer (GM) i form av nominaliseringar i elevtexter från det nationella provet i svenska och svenska som andraspråk i årskurs nio. Begreppet GM avser icke-typiska realiseringar av betydelser där GM till exempel kan vara en nominalisering – en process som uttrycks som ett substantiv (ex: tävling, trygghet) istället för ett verb (ex: tävla) eller ett adjektiv (ex: trygg). Vid användning av GM blir texter mer informationstäta och abstrakta eftersom språket packas ihop. Studiens teoretiska utgångspunkt är systemisk-funktionell grammatik, i vilken GM spelar en viktig roll. Materialet utgörs av 60 elevtexter, fördelat på 30 elevtexter i svenska och 30 elevtexter i svenska som andraspråk. Av dessa 30 texter har 15 tilldelats betyget E och resterande hälft betyget B. I texterna undersöks fördelningen av GM av typen nominalisering av process och nominalisering av egenskap, förekomsten av GM i förhållande till betyg och ämne samt de mest använda GM. Resultatet visar att det förekommer betydligt fler GM av typen nominalisering av process än egenskap och att elevtexter som bedömts betyget B innehåller högre andel GM än elevtexter som tilldelats betyget E. Vidare visar resultatet att förekomsten av GM i förhållande till ämne är jämnt fördelat, med endast en GM i skillnad. Vad gäller de mest använda GM visar undersökningen att det finns 12 olika ord som är frekvent återkommande i elevtexterna, vilket förklaras genom provuppgiftens utformning och instruktioner.
216

A formação contínua de professores para o ensino fundamental regular noturno de jovens e adultos na Escola GM : ações, tensões e contradições de uma política pública municipal

Dresch, Nelton Luis January 2001 (has links)
A presente Dissertação conta uma breve história acerca do cotidiano de um programa de formação contínua de professores municipais, na periferia da Grande Porto Alegre, que iniciaram a lecionar no SEJA –Serviço de Educação de Jovens e Adultos- proposta político-pedagógica de Ensino Fundamental Regular de Jovens e Adultos. O pesquisador, aceito como partícipe reflexivo pelo grupo de professores de uma escola, desenvolveu uma modalidade de Pesquisa-Ação buscando contribuir na identificação e solução das situações-problemáticas que surgiram ao longo do referido programa de formação. A dissertação teoriza alguns saberes emergentes e vivenciados na pes-quisa-em-campo : concepção de currículo, prática docente e política de forma-ção contínua de professores para o Ensino Fundamental Regular de Jovens e Adultos; bem como, concepção de pesquisa educacional na escola. Durante a pesquisa-em-campo, o pesquisador-em-ação assumiu um po-sicionamento político de “parceria crítica” com o grupo de professores frente aos conflitos políticos surgidos nas relações destes com a respectiva Secretaria de Educação, gerando , por sua vez, outros conflitos devidamente discutidos no texto. Em função desses conflitos e demais circunstâncias a pesquisa sofreu alterações no seu objeto inicial de estudo, bem como nos respectivos procedi-mentos específicos, seguindo, portanto, a flexibilidade metodológica inerente à Pesquisa-Ação. São propostos princípios político-pedagógicos para as políticas públicas de formação contínua de professores para o Ensino Fundamental Regular de Jovens e Adultos. No relato reflexivo dessa caminhada o pesquisador encontrou seu pró-prio processo de aprendizagem, suas lacunas e limites de formação – vivência aproveitada em sua prática docente acadêmica.
217

A formação contínua de professores para o ensino fundamental regular noturno de jovens e adultos na Escola GM : ações, tensões e contradições de uma política pública municipal

Dresch, Nelton Luis January 2001 (has links)
A presente Dissertação conta uma breve história acerca do cotidiano de um programa de formação contínua de professores municipais, na periferia da Grande Porto Alegre, que iniciaram a lecionar no SEJA –Serviço de Educação de Jovens e Adultos- proposta político-pedagógica de Ensino Fundamental Regular de Jovens e Adultos. O pesquisador, aceito como partícipe reflexivo pelo grupo de professores de uma escola, desenvolveu uma modalidade de Pesquisa-Ação buscando contribuir na identificação e solução das situações-problemáticas que surgiram ao longo do referido programa de formação. A dissertação teoriza alguns saberes emergentes e vivenciados na pes-quisa-em-campo : concepção de currículo, prática docente e política de forma-ção contínua de professores para o Ensino Fundamental Regular de Jovens e Adultos; bem como, concepção de pesquisa educacional na escola. Durante a pesquisa-em-campo, o pesquisador-em-ação assumiu um po-sicionamento político de “parceria crítica” com o grupo de professores frente aos conflitos políticos surgidos nas relações destes com a respectiva Secretaria de Educação, gerando , por sua vez, outros conflitos devidamente discutidos no texto. Em função desses conflitos e demais circunstâncias a pesquisa sofreu alterações no seu objeto inicial de estudo, bem como nos respectivos procedi-mentos específicos, seguindo, portanto, a flexibilidade metodológica inerente à Pesquisa-Ação. São propostos princípios político-pedagógicos para as políticas públicas de formação contínua de professores para o Ensino Fundamental Regular de Jovens e Adultos. No relato reflexivo dessa caminhada o pesquisador encontrou seu pró-prio processo de aprendizagem, suas lacunas e limites de formação – vivência aproveitada em sua prática docente acadêmica.
218

Socioecological Transformation and the History of Indian Cotton, Gujarat, Western India

SIM, JUYEON January 2018 (has links)
Landscape management is often referred to as a holistic concept, which deals with large-scale processes and multidisciplinary manners in regards to natural resource use with ecological and livelihood considerations. Seen in this light, landscape transformation should be understood within the context of the human-nature relationship, viewing human activities and their institutions as an essential part of the system rather than as external agents. When it comes to the landscape planning and management related to cotton farming in Gujarat, there has been diversity of interest groups such as local communities, governments, corporations and non-governmental organisations. In the present study, I examine two case studies of cotton production pertaining to the Gujarat region in order to study the opportunities and challenges faced by local farmers in the process of developing agriculture. In the first case study on Cotton Improvement Program in the nineteenth century, I highlight the socioecological consequences of the colonial cotton project and how it relates to the social dynamics of networks and agricultural landscape management. The second case study examines current debates regarding the social, economic and environmental impacts of genetically modified (GM) cotton on India’s social and natural landscape. This thesis emphasises that there are recursive motifs between the two case studies in terms of the local resistances, power relations and possible environmental effects, which can be explained through the state of ‘global core’ and ‘periphery’, and partly the framework of ecologically unequal exchange. The analysis of recurring patterns concludes that exploring the narratives of local experiences offers a number of significant details that show complex power dynamics manifested through constant struggles and resistances by ‘peripheral agent’.
219

Mecanismos de identificação de soja não geneticamente modificada no sistema agroindustrial da soja: um estudo multi-caso.

Leonelli, Fabiana Cunha Viana 20 December 2001 (has links)
Made available in DSpace on 2016-06-02T19:51:26Z (GMT). No. of bitstreams: 1 DissFCVL.pdf: 804823 bytes, checksum: 48e645ad54e3430addcbcd601ba1ef0c (MD5) Previous issue date: 2001-12-20 / Financiadora de Estudos e Projetos / The present thesis investigated the role of coordination and management supply chain in face of identifies no-GM crops and the need to preserve the identity of grains. This change traverses the entire productive chain, from the seeds industry to the final consumer, ever more demanding in terms of issues related to food safety. A new arrangement in the system (Strictly Co-ordination) will be linked to the capacity of the various agents of the agroindustrial systems to coordinate and manage these relationships, mainly by means of the development of mechanisms of incentives and control, including efficient forms of identity preservation (IP), traceability and certification of the product throughout the chain. The latter will play a fundamental role in diminishing the information asymmetry between producers and consumers and valuated agri-food products. The theoretic framework utilized was Transaction Cost Economics, which allowed the foundation and systematization of the analysis, validated by case studies that involved situations of Identity Preservation in Brazil. Thus, four firms that work with non-GM soybeans and utilized segregation systems, incentives and monitoring of crops production were analyzed. It was verified that, indeed, the trend toward product segregation involves the need for adaptations and alteration in the predominating governance form. Identity preservation also involves increased costs, which permeate all phases of the productive chain. These costs are identifiable and have a strong relationship to the characteristics of the transactions and to the attributes of the product one wishes to segregate. The thesis also identified that incentive and monitoring strategies are fundamental for the success of the identity preserved (IP) system. The other relevant aspect was about reputation of the certificated entity. / O presente trabalho investigou o papel da coordenação e gerenciamento da cadeia de suprimentos em face à necessidade de identificação de não-GM e adoção de mecanismos de preservação de identidade para a exploração de oportunidades de mercado no sistema agroindustrial da soja. Devida à necessidade de garantir a credibilidade da informação, faz-se necessário gerenciar e controlar as relações entre diferentes agentes da cadeia produtiva, desde a indústria de sementes até o consumidor final. Para exercer tal controle, a adoção de um novo arranjo do sistema produtivo (SAGs estritamente coordenados), está vinculada à capacidade de coordenação da cadeia produtiva no desenvolvimento de mecanismos de incentivo e controle entre os elos da cadeia, incluindo a adoção de sistemas de preservação de identidade (PI), rastreabilidade e certificação ao longo da cadeia produtiva. O arcabouço teórico utilizado Economia de Custos de Transação (ECT) permitiu a fundamentação e sistematização da análise empírica, validada pela abordagem qualitativa de estudos de casos. Foram analisadas quatro empresas que exploram oportunidades comerciais advindas da soja não-GM e utilizam sistemas de identidade preservada, segregação de grãos, incentivos e monitoramento para a coordenação dos sistemas produtivos. Verificou-se que a exploração deste segmento de mercado implica adaptações de processo que alteram a forma de governança predominante no SAG genérico da soja, cuja adoção de sistemas de preservação de identidade (PI) corroboraram o pressuposto inicial da necessidade de um novo arranjo produtivo (SAGs estritamente coordenados). Além disso, foi constatado que a preservação de identidade também implica aumento nos custos, que permeiam todas as fases da cadeia produtiva. Esses custos são identificáveis e têm forte relação com as características das transações. Outro aspecto que se mostrou relevante diz respeito à reputação da entidade certificadora contratada para auditoria do processo produtivo.
220

Projeto de um modulador sigma-delta de baixo consumo para sinais de áudio / Low power audio sigma delta modulator design

Heiner Grover Alarcón Cubas 23 May 2013 (has links)
Este trabalho descreve o projeto de um modulador Analógico-Digital (A/D) Sigma-Delta de 16 bits (98 dB de SNR) de baixo consumo em tecnologia CMOS para a aquisição de sinais de áudio. Para projetar o modulador foi utilizada a metodologia top down, a qual consiste em projetar desde o nível de sistema até os blocos básicos em nível de transistores. O sistema foi analizado e projetado utilizando equacões e modelos comportamentais para obter as especificações de cada bloco do modulador. Considerando um baixo consumo de potência foi escolhida a topologia CIFF (do inglês Chain of Integrator with FeedForward) de terceira ordem e quatro bits implementado com capacitores chaveados. O modulador projetado é composto por três integradores chaveados, um somador analógico, um weigthed DAC e um quantizador de quatro bits. A técnica de Chopper é incluida no modulador para diminuir o ruído Flicker na entrada do modulador. Os blocos de maior consumo dentro do modulador são as OTAs. Por esta razão eles são projetados utilizando a metodologia gm/ID reduzindo assim o consumo de potência. O projeto foi realizado na tecnologia IBM 0,18 \'mü\'m sendo utilizado o simulador spectre do Cadence. O modulador Sigma-Delta atinge um SNR de 98 dB para uma banda de 20 kHz e um consumo de potência de 2,4 mW para uma fonte de alimentação de 1,8 V. / This work describes the design of a 16 bits low power Sigma-Delta modulator (98 dB SNR) in a CMOS technology for the acquisition of audio signals. To design the modulator it was used the top-down methodology, which consists on the design from system level to the transistor-level basic blocks. The system was analyzed and designed using behavioral models and equations to obtain the specifications of each block of the modulator. Considering a low power consumption it was chosen a third-order four bits CIFF topology (Chain Integrator with feedforward) implemented with switched capacitors. The modulator is composed by three integrators, one analog adder, one weigthed DAC and one four bit quantizer. The Chopper technique is included in the modulator to reduce the Flicker noise at the input of the modulator. The blocks of higher consumption within the modulator are the OTAs. Hence, they was designed using the methodology gm/ID to reduce power consumption. It was designed on the 0.18 \'mü\'m IBM technology and using the Cadence Spectre simulator. The Sigma-Delta modulator achieves a SNR of 98 dB for a bandwidth of 20 kHz and a power consumption of 2.4 mW with a 1.8 V power supply.

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