1,720,959 research outputs found
Ultra-Low Noise Oscillators enabling Frequency Generation for Radar Systems in Scaled CMOS Technologies
Full text linkIn those systems where it is important to synthesize a precise frequency signal, such as the carrier of a transmission system, phase noise is certainly one of the most important aspects that define the performance. Because of the ever increasing data rate in modern communication systems (5G), the interest of low phase noise frequency synthesizer is high. Radar systems are another example in which the phase noise has an important role: by exploiting the Doppler effect, informations on distance and speed of the target are obtained by comparing the frequency of the transmitted and received signal. Radar systems are precise but also expensive due to their complexity. As an example, radar are used in air plane to detect perturbations. In recent years, however, radar systems have also been spreading in the automotive field, as advanced driving assistance systems (ADAS). Although this is not new: the first car to have a radar system appeared in the market in 1990, only luxury models were employing radar. Nowadays, ultrascaled CMOS technology has made the widespread deployment of radar on low-cost cars economically advantageous. The challenge is to obtain good performances comparable with bipolar technology. For this reason, oscillators, which are the heart of a frequency synthesizer, in CMOS technology, are the main topic of this thesis. After a brief introduction about the operating principle of a typical car radar, we enter into the merits of the design of an analog circuit by developing a methodology to identify the optimum oscillation frequency, that is, the frequency that allows us to obtain the best performance. Then the designs of two oscillator topologies are described, both operating at 20GHz: the first is a hybrid class B/D oscillator, while the second one a class C. The latter in particular proves to be effective in reducing the contribution of the flicker noise from the active devices, one of the biggest imitations of modern CMOS technologies. Finally, a method to extract the fourth harmonic from the class C oscillator is presented. This allows to employ the class C oscillator for automotive radar application, as described by regulations.In qualunque sistema in cui sia necessario generare una segnale di frequenza preciso, come ad esempio la portante di un sistema di trasmissione, il rumore di fase è certamente uno degli aspetti più importanti che definiscono le prestazioni dell’apparato. L’interesse per sistemi a basso rumore di fase è al giorno d’oggi grande vista la diffusione di sistemi di comunicazione 5G. Un’altra applicazione in cui questo è importante è nei sistemi radar, dove sfruttando l’effetto Doppler, le informazioni su distanza e velocita del bersaglio vengono ottenute dal confronto tra frequenza del segnale trasmesso e ricevuto. Il radar è un apparato di misura preciso ma anche complesso e perciò costoso; in ambito civile trova applicazione soprattutto a bordo di aerei per individuare, ad esempio, perturbazioni meteo. Negli ultimi anni però, si sta assistendo alla diffusione di sistemi radar anche nel campo automibilistico, come sistemi di aiuto alla guida, i così detti ADAS. Per quanto questo non sia nuovo, la prima auto ad avere un sistema radar è comparsa nel mercato nel 1990, solo modelli di lusso montavano questi sistemi. Ora la tecnologia CMOS ha raggiunto una maturità tale da rendere econimicamente vantaggiosa la diffusione su larga scala di radar anche su auto a basso costo. La sfida è quella di ottenere prestazioni da tecnologie digitali CMOS comparabili a quelle a bipolari. Per questo motivo, questa tesi, tratta di oscillatori, che sono il cuore di un sintetizzatore di frequenza, realizzati in tecnologia CMOS. Dopo una breve introduzione su quello che è il principio di funzionamento di un tipico radar per auto, si entra nel merito del design di un circuito analogico sviluppando una metodologia per individuare la frequenza di oscillazione ottima, cioè quella frequenza che consente di ottenere le prestazioni migliori. Dopodiché vengono descritti i design di due topologie di oscillatori entrambi operanti a 20GHz: il primo è un ibrido classe B/D, il secondo un classe C. Quest’ultimo in particolare si dimostra essere efficace a ridurre il contributo del rumore flicker dei dispostivi attivi, uno dei più grossi limiti delle tecnologie CMOS moderne. Infine viene mostrato un metodo per estrarre una componente di quarta armonica, ovvero a 80 GHz, dall’oscillatore in classe C cosicché il radar possa operare a frequenze concesse dalle normative
A 19.5-GHz 28-nm Class-C CMOS VCO, With a Reasonably Rigorous Result on 1/f Noise Upconversion Caused by Short-Channel Effects
No full textClass-C operation is leveraged to implement a K-band CMOS voltage-controlled oscillator (VCO) where the upconversion of 1/f current noise from the cross-coupled transistors in the oscillator core is robustly contained at a very low level. Implemented in a bulk 28-nm CMOS technology, the 12%-tuning-range VCO shows a phase noise as low as -112 dBc/Hz at 1-MHz offset (-86 dBc/Hz at 100 kHz offset) from a 19.5 GHz carrier while consuming 20.7 mW, achieving a figure of merit (FoM) of -185 dBc/Hz. The design is complemented by a theoretical investigation of 1/f noise upconversion caused by short-channel effects in the cross-coupled transistors, obtaining the first instance of a closed-form phase noise expression in the 1/f3 region
On the Optimal Operation Frequency to Minimize Phase Noise in Integrated Harmonic Oscillators
No full textThis brief aims at finding the most appropriate frequency of operation of an integrated harmonic oscillator in order to maximize its spectral purity. To achieve this, a simple, yet accurate, scalable model is developed for the LC tank, that tracks the dependence of the parasitics on the inductance value. Using an ultra-scaled CMOS digital technology as a case study, the frequencies around 5 GHz are singled out as the sweet spot to minimize the phase noise
A 19.5 GHz 28 nm CMOS class-C VCO with reduced 1/f noise upconversion
No full textClass-C operation is leveraged to implement a K-band CMOS VCO where the upconversion of the 1/f noise from the core transistors is robustly contained at a minimal level. Implemented in a bulk 28 nm CMOS technology,the VCO shows a phase noise as low as -108.5 dBc/Hz at 1 MHz offset (-83 dBc/Hz at 100 kHz offset) from the 19.5 GHz carrier,while consuming 14.4 mW and featuring a 12% tuning range
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
- …
