RADIO-FREQUENCY CONVERSION AND SYNTHESIS (FOR A 115 MILLIWATT GPS RECEIVER) (CMOS MIXERS, FREQUENCY SYNTHESIZERS)

SHAHANI, ARVIN RAMESH STANFORD UNIVERSITY 1999 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Recently, there has been a proliferation of wireless devices and services. These services have evolved from simple paging functions to voice applications (i.e., cellular telephony). One system that is poised to make an impact in the wireless arena is the Global Positioning System (GPS). In addition to position information, GPS also provides an accurate time reference. Both types of information are valuable not only to a mobile user, but also in the design and operation of other wireless systems. The work in this dissertation is part of a complete front-end for a GPS receiver that was fabricated in a 0.5 <math> <f> <g>m</g></f> </math>m CMOS process. The focus of this project is on CMOS hardware techniques that are low power and suitable for radio-frequency integrated circuits. Thus, not only are the architectures that we present well-suited for a GPS receiver, they are also applicable to other systems that require low-power, radio-frequency circuits. The two front-end functions highlighted in this work are frequency conversion and synthesis. The CMOS voltage mixer takes advantage of good voltage switches in the form of CMOS transistors, as well as the mixer's integrated environment. This voltage-domain passive mixer operates on a negligible amount of power, while achieving noise figures that are lower than any alternative CMOS mixer architecture. It additionally possesses excellent linearity. The new phase-locked loop (PLL) architecture synthesizes a gigahertz; local oscillator (LO) from a low-frequency reference without using a divide-by-N block in the PLL's feedback loop. In doing so, the power consumption of the loop is substantially lower than that of conventional techniques. The power consumption can be reduced even further if a power-efficient voltage-controlled oscillator (VCO) is used. A further benefit of removing the divider is the reduction of on-chip interference caused by the divider's large high-speed transistions. The tradeoff with this architecture is greater acquisition complexity in exchange for the lower power consumption and reduced interference in lock.

Things rich and strange: Economies of encounter and exchange in early modern drama

Shahani, Gitanjali G Emory University 2007 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

In the late sixteenth and seventeenth centuries, as England embarked on a series of expansionary ventures across the globe, English drama began to grapple with both foreign subjects and foreign objects. A variety of "rich and strange" things from the world over, found their way onto the English stage. The "life" of these alien things, their intricate trajectories across geographical boundaries, and their complex representations in the drama of this period collectively form the subject of this dissertation. In "Things Rich and Strange," I look at the staging of global commerce and intercourse in the early modern English theater. Specifically, I consider how objects that travel through cultural and economic circuits of transnational exchange are represented in the work of dramatists like William Shakespeare, Ben Jonson, Thomas Heywood, Thomas Middleton, John Fletcher, and Philip Massinger. My project is structured around four kinds of objects---spices, textiles, gifts, and gold---that fundamentally determined the course of England's early imperial and mercantile expeditions in different parts of Asia, Africa, and the New World. I am particularly interested in the animate form that these inanimate objects took in the early modern theater, where they came to be personified as simultaneously alluring and dangerous incarnations of the cultural others that produced them. I argue that in the dramatic invocation of these foreign bodies we see new imaginings of racial, cultural, and religious alterity that are necessarily interwoven with emergent discourses of trade, travel, and ethnography in early modern England. Thus while focusing on the portrayal of foreign bodies in plays like A Midsummer Night's Dream, The Fair Maid of the West, and The Sea Voyage, I also draw on genres such as travelogues, mercantile treatises, recipe books, and ethnographies that are similarly invested in depicting and deciphering alien peoples, places, and things. Combining textual analysis, historicist interpretation, and archival research, my work engages with key debates in Renaissance studies about whether and how the early modern intersects with the early colonial, or what has come to be called the "proto-colonial.".

Interfacial Evolution in Four Dimensions: Growth and Coarsening in Highly Anisotropic Systems

Shahani, Ashwin J Northwestern University ProQuest Dissertations & T 2016 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Experimental studies into the morphological evolution of highly faceted systems have been performed in an effort to gain a more fundamental understanding of the role of anisotropy during growth and coarsening. The interfacial dynamics in solid-liquid mixtures were examined using four dimensional (i.e., space and time resolved), synchrotron-based X-ray tomography. The following three phenomena were investigated using this novel approach: (1) the coarsening of Si particles in Al-Si(-Cu) liquids; (2) the growth of Si particles in Al-Si-Cu; and (3) eutectic growth in Al-Ge. Initially, the isothermal coarsening process of hyper-eutectic Al-Si samples was analyzed via ex situ X-ray tomography. The results show that the inverse surface area per unit volume increases with the cube root of time despite the lack of microstructural self-similarity and highly anisotropic particle morphology. More specifically, the Si particles evolve from mostly faceted domains to a more isotropic structure that is not given by the fully-faceted Wulff shape of the crystal [198]. These trends can be rationalized by the presence of twin defects that intersect the particle edges and that may provide the kink sites necessary for interfacial propagation, thus leading to a more isotropic structure. Qualitatively, the same behavior was observed for Si particles in an Al-Si-Cu liquid, studied via in situ X-ray tomography [199]; this suggests that the thermal cycling in the ex situ experiment has negligible influence on the coarsening dynamics. Twin-mediated crystal growth has long been a mystery due to the lack of four dimensional experiments. To shed light on the mechanism by which twin defects facilitate growth, we probe the real-time interfacial dynamics of polycrystalline Si particles growing from an Al-Si-Cu liquid. Our analysis of the time evolution of the interfacial normals allows us to quantify unambiguously the habit plane and grain boundary orientations during growth [197]. This, when combined with direct measurements of the interfacial morphology, provide the first three dimensional confirmation of twin-mediated growth, proposed over 50 years ago by Wagner, Hamilton and Seidensticker [85, 237]. Lastly, we track the solidification of an irregular eutectic via in situ X-ray tomography. One example of an irregular eutectic alloy is Al-Ge, in which the Ge phase is faceted, and the Al phase is non-faceted. The faceted phase does not change direction easily due to its atomic structure and defect-mediated growth mechanism; as a result, the microstructure is non-periodic with varying interphase spacing. Our results show that the eutectic morphology in Al-Ge is markedly different from previously employed model systems and theories based upon the ex situ analysis of microstructure [200]. In particular, defects play a critical role in the growth process, in which pockets of the non-faceted phase engulf the exposed facets and control the growth rate of the eutectic colonies.