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Analysis and Design of a Wide-Bandwidth Low Power Sigma-Delta ADC in CMOS Technology
Full text linkThe evolution of the CMOS technology brings many challenges to analog designers.
The scaling-down of the transistor feature size has a big impact on analog circuit design, because it considerably degrades the performance of an analog circuit. For instance, the reduced supply voltage and the degraded device characteristics are inevitable problems for CMOS designers. As an interface between the analog circuit and the digital circuit, the Analog-to-Digital Converter (ADC) is moving into scaled nanometer CMOS technologies due to the advantages for the digital circuit. This put increasingly difficult demands on the design ADCs.
Sigma-Delta ADCs are promising candidates for the Analog-To-Digital (A/D) conversion. The reason for that is twofold. One the one hand, unlike the other converters that need accurate building blocks to obtain high resolution, Sigma-Delta converters show low sensitivity to the imperfections of their building blocks. This is achieved thanks to the extensive use of digital circuitry, which is preferred in CMOS technologies due to their low power and high density characteristics. On the other hand, the number of applications with industrial interest has also grown. In fact, starting from the earliest in the audio band, we can find Sigma-Delta converters in a large variety of A/D interfaces, ranging from instrumentation to communications.
Despite the fact that Sigma-Delta is a mature subject, there are still many unanswered questions. Due to the incorporation of a highly non-linear element (the quantizer) in the feedback loop, the exact analysis of Sigma-Delta modulation is a very challenging task.
In this thesis the circuit level approach and the system level approach are presented for low-power, low-voltage Sigma-Delta ADC design in nanometer CMOS technologies. In the first part of this work, a full-feedforward Sigma-Delta topology suitable for the Sigma-Delta ADC design in nanometer CMOS technologies is introduced. The most important feature of this topology is that the signal transfer function is unity, which is fairly indipendent of the building block characteristics. A detailed analysis is presented in this text, leading to optimized system-level parameters. Also a new digital circuitry is presented in order to extend the usage of Sigma-Delta modulators at higher signal bandwidths.
The second part of the thesis is dedicated to the circuital design. The main achievement is a 65nm CMOS Sigma-Delta modulator with 94dB Dynamic Range (DR). The power dissipation is 407uW in a 500kHz signal bandwidth under a 1.2V power supply voltage. This design proves that the feedforward Sigma-Delta topology is an excellent topology for low-power, high bandwidth and high resolution Sigma-Delta ADC designs in nanometer CMOS technologies.L’evoluzione delle tecnologie CMOS ha portato a molte sfide per i designer di circuiti analogici. La riduzione delle dimensioni dei transistor ha un grande impatto sul design del circuito analogico, in quanto ne degrada in modo considerevole le performance.
Ad esempio, la ridotta tensione di alimentazione e la degradazione delle caratteristiche dei dispositivi sono problemi inevitabili per i designer di dispositivi CMOS. In quanto interfaccia tra i circuiti analogici e quelli digitali, il convertitore Analogico Digitale (ADC) si sta muovendo verso tecnologie CMOS ultra-scalate al fine di godere dei vantaggi che lo scaling tecnologico porta sulla circuiteria digitale. Questo pone una crescente difficoltà nel design degli ADC. I convertitori Sigma-Delta sono dei promettenti candidati per la conversione analogico-digitale (A/D). La ragione di ciò è duplice. Da un lato, a differenza degli altri convertitori che necessitano di elementi molto performanti per ottenere risoluzioni elevate, i convertitori Sigma-Delta mostrano una elevata robustezza alle imperfezioni dei blocchi che li compongono. Questo è ottenuto grazie ad un esteso utilizzo di cricuiteria digitale, che nelle tecnologie CMOS scalate risulta preferibile grazie al suo basso consumo di potenza e all’elevata densità. D’altra parte, anche il numero di applicazioni industriali è cresciuto. Infatti, a cominciare dalle prime applicazioni in campo audio, possiamo trovare convertitori Sigma-Delta in una gran varietà di interfacce A/D, come strumentazioni biomediche fino al campo delle comunicazioni.
Nonostante l’architettura Sigma-Delta sia un soggetto ormai maturo, ci sono tutt’ora diverse questioni irrisolte. A causa della presenza di un elemento fortemente non lineare, il quantizzatore, all’interno del loop di feedback, l’analisi esatta della modulazione Sigma-Delta risulta complicata. In questa tesi, un approccio a livello circuitale e a livello di sistema viene presentato per il design di un convertitore ADC a bassa potenza e a bassa tensione di alimentazione in tecnologia nanometrica CMOS. Nella prima parte di questo lavoro, viene introdotta una particolare topologia Sigma-Delta adatta al design di convertitori in tecnologia nanometrica. La caratteristica piú portante di questa topologia è la funzione di trasferimento tra ingresso e uscita unitaria. Viene presentata un’analisi dettagliata, portando alla scelta ottimizata di parametri di sistema. Viene inoltre presentata una nuova circuiteria digitale per estendere l’uso del modulatore Sigma-Delta a bande più elevate.
La seconda parte di questa tesi è dedicata al design circuitale. Il principale raggiungimento di questo lavoro è un modulatore Sigma-Delta in tecnologia 65nm con un range dinamico di 94dB. Il consumo di potenza è 407uW in un banda di 500kHz con una tensione di alimentazione di 1.2V. Questo design dimostra che la topologia Sigma-Delta feedforward è una scelta eccellente per il design di ADC a bassa potenza, elevata banda ed elevata risoluzione in tecnologie nanometriche CMOS
Optimal DWA design in scaled CMOS technologies for mismatch cancellation in multibit ΣΔ ADCs
No full textA built-in self-testing framework for asynchronous bundled-data NoC switches resilient to delay variations
No full textMost multi- and many-core integrated systems are currently designed by following a globally asynchronous locally synchronous paradigm. Asynchronous interconnection networks are promising candidates to interconnect IP cores operating at potentially different frequencies. Nevertheless, post-fabrication testing is a big challenge to bring asynchronous NoCs to the market due to a lack of testing methodologies and support for them. In particular, the unpredictable delay variability introduced by the manufacturing process may differentiate the delay of nominally-balanced I/O timing paths, thus making the order of the input patterns unpredictable and precluding the correct behaviour of signature-based test compactors. This paper tackles this challenge by proposing a testing framework for asynchronous NoCs which works effectively despite delay variations in and across timing paths of the NoC under test. Moreover, in order to mitigate the growing test application costs in modern ICs, we come up with a built-in self-testing infrastructure which automatically controls and delivers the outcome of the testing process without the intervention of an external automatic test equipment (ATE)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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