24 research outputs found
Analysis of Current Conveyor based Switched Capacitor Circuits for Application in ∆Σ Modulators
The reduction in supply voltage, loss of dynamic range and increased noise prevent the analog circuits from taking advantage of advanced technologies. Therefore the trend is to move all signal processing tasks to digital domain where advantages of technology scaling can be used. Due to this, there exists a need for data converters with large signal bandwidths, higher speeds and greater dynamic range to act as an interface between real world analog and digital signals.
The Delta Sigma (∆Σ) modulator is a data converter that makes use of large sampling rates and noise shaping techniques to achieve high resolution in the band of interest. The modulator consists of analog integrators and comparators which create a modulated digital bit stream whose average represents the input value. Due to their simplicity, they are popular in narrow band receivers, medical and sensor applications.
However Operational Amplifiers (Op-Amps) or Operational Transconductance Amplifiers (OTAs), which are commonly used in data converters, present a bottleneck. Due to low supply voltages, designers rely on folded cascode, multistage cascade and bulk driven topologies for their designs. Although the two stage or multistage cascade topologies offer good gain and bandwidth, they suffer from stability problems due to multiple stages and feedback requiring large compensation capacitors. Therefore other low voltage Switched-Capacitor (SC) circuit techniques were developed to overcome these problems, based on inverters, comparators and unity gain buffers.
In this thesis we present an alternative approach to design of ∆Σ modulators using Second Generation Current Conveyors (CCIIs). The important feature of these modulators is the replacement of the traditional Op-Amp based SC integrators with CCII based SC integrators. The main design issues such as the effect of the non-idealities in the CCIIs are considered in the operation of SC circuits and solutions are proposed to cancel them. Design tradeoffs and guidelines for various components of the circuit are presented through analysis of existing and the proposed SC circuits. A two step adaptive calibration technique is presented which uses few additional components to measure the integrator input output characteristic and linearize it for providing optimum performance over a wide range of sampling frequencies while maintaining low power and area.
The presented CCII integrator and calibration circuit are used in the design of a 4th order (2-2 cascade) ∆Σ modulator which has been fabricated in UMC 90nm/1V technology through Europractice. Experimental values for Signal to Noise+Distortion Ratio (SNDR), Dynamic Range (DR) and Figure Of Merit (FOM) show that the modulator can compete with state of art reconfigurable Discrete-Time (DT) architectures while using lower gain stages and less design complexity
Automatic calibration of modulated fractional-N frequency synthesizers
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (p. 145-148).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.The focus of this research has been the development of a low power, radio frequency transmitter architecture. Specifically, a technique for in service automatic calibration of a modulated phase locked loop (PLL) frequency synthesizer has been developed. Phase/frequency modulation is accomplished by modulating the feedback divide value in a phase locked loop frequency synthesizer. A digital precompensation filter is used to extend the modulation bandwidth by canceling the low-pass transfer function of the PLL. The automatic calibration circuit maintains accurate matching between the digital precompensation filter and the analog PLL transfer function across process and temperature variations. The automatic calibration circuit, which is the main contribution of this thesis, operates while the transmitter is in service. This online calibration eliminates the need for production calibration and periodic down time for calibration cycles.(cont.) In addition the calibration circuitry provides greater accuracy in the modulation than what is possible via offline methods of calibration. The calibration circuit works with M-ary GFSK as well as 2 level GFSK. The automatic calibration circuit has been implemented in two forms to prove its operation. The first version is a circuit board level implementation with a center frequency of around 60 MHz. The second implementation of the system is in a full custom 0.6 ,Lm BiCMOS integrated circuit. The integrated circuit contains the complete synthesizer with automatic calibration and operates in the 1.88 GHz frequency band used by the Digital European Cordless Telephone (DECT) standard. A data rate of 2.5 Mbps using 2 level GFSK and 5.0 Mbps using 4 level GFSK has been achieved with a power consumption of 78 mW.by Daniel R. McMahill.Ph.D
Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)
Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression
Design and optimization of optical routing techniques and devices
Doutoramento em Engenharia ElectrotécnicaEste trabalho apresenta três estudos principais acerca do desenvolvimento e
aplicação de sistemas de monitorização óptica avançados com base na
análise de histogramas assíncronos, conversão de comprimento de onda de
sinais de débito elevado e o impacto das não-linearidades das fibra ópticas em
sistemas utilizando técnicas avançadas de transmissão. Mostra-se que a
comparação de histogramas assíncronos com histogramas de referência pode
ser usada para extrair informação a respeito da qualidade e do ruído que
afecta o sinal em análise. O método proposto é validado através de simulação
numérica e experiência.
Um modelo analítico para a computação das limitações em frequência da
modulação cruzada de fase (XPM) em conversores de comprimento de onda
de fibra é proposto e validado através de simulação numérica até frequências
de modulação acima de 1 THz. O modelo proposto permite a derivação de
regras de engenharia para o dimensionamento de conversores de
comprimento de onda compostos por espelhos de fibra não linear. O
dimensionamento de um novo filtro para a optimização da conversão da XPM
em modulação de intensidado é proposto e validado por simulação numérica.
O impacto das não-linearidades na transmissão em fibra óptica de sinais de
banda lateral única a 10 Gb/s com compensação de dispersão concentrada é
avaliado através de simulação numérica. Mostra-se que as não-linearidades
intra-canal levam a severa degradação do desempenho. A degradação de
sinais de chaveamento por desvio diferencial de fase (DPSK) a 40 Gb/s devida
a XPM com sinais de chaveamento por desvio de amplitude herdados de
sistemas anteriores é também analisada. Uma análise bomba-sonda mostra
que a degradação do sinal resulta da modulação de intensidade induzida por
XPM. Este resultado permite a derivação de um modelo para estimar a
probabilidade de erro dos sinais DPSK degradados por XPM. Finalmente, é
apresentada uma abordagem analítica baseada em pequenas perturbações
para o estudo de não linearidades intra-canal em fibra óptica em sinais com
razão de extinção finita. Este estudo permite a identificação de duas novas
formas de degradação tomando a forma de impulsos entre diferentes símbolos
e fluctuações temporais e de amplitude.This work presents three main studies regarding the development and
application of advanced optical monitoring systems based on the analysis of
asynchronous amplitude histograms, the wavelength conversion of ultra-high
bit-rate signals, and the impact of fiber nonlinearities in systems employing
advanced transmission techniques. It is shown that asynchronous amplitude
histograms may be numerically compared with reference histograms to extract
information regarding quality and the noise degrading the signal under analysis.
The proposed method is validated through numerical simulation and
experiment.
An analytical model to compute the frequency limitations of cross-phase
modulation (XPM) in all-optical fiber wavelength converters is proposed and
validated using numerical simulation at modulation frequencies exceeding 1
THz. The proposed model allows deriving engineering rules for the
dimensioning of wavelength converters using nonlinear optical loop mirrors. A
novel filter design to optimize the conversion of XPM-induced phase
modulation in intensity modulation is proposed and validated using numerical
simulation.
Numerical simulation is used to evaluate the impact of fiber nonlinearities in the
transmission of 10 Gb/s single sideband signals in links using concentrated
electrical or optical dispersion compensation. It is shown that, intra-channel
fiber nonlinearities severely degrade the performance. The degradation of 40
Gb/s differential phase-shift-keying (DPSK) signals due to XPM with legacy
amplitude-shift keying signals is also analyzed. Pump-probe analysis show that
the signal degradation results from XPM-induced intensity modulation. This
allows deriving and validating a novel analytical model to estimate the bit-error
probability of the XPM-degraded DPSK signals. Finally, an analytical smallperturbations
approach to the study of intra-channel fiber nonlinearities in
signals with finite extinction ratio is presented. It allows the identification of two
new forms of degradation taking the form of impulses between symbols and
amplitude and temporal jitter
Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)
Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial cellular communications services. While the first and second International Mobile Satellite Conferences (IMSC) mostly concentrated on technical advances, this Third IMSC also focuses on the increasing worldwide commercial activities in Mobile Satellite Services. Because of the large service areas provided by such systems, it is important to consider political and regulatory issues in addition to technical and user requirements issues. Topics covered include: the direct broadcast of audio programming from satellites; spacecraft technology; regulatory and policy considerations; advanced system concepts and analysis; propagation; and user requirements and applications
Faculty of Engineering and Design. Research Review
STUDENTS AND ACADEMICS - This publication introduces you to the department or school and then each faculty member’s research areas, research applications, and their most recent activities. A comprehensive index can be found at the back of this publication to help guide you by specific areas of interest, as well as point out interdisciplinary topics and researchers.
INDUSTRY LEADERS - This publication includes information regarding specific facilities, labs, and research areas of departments and
schools as well as individual faculty members and researchers. A comprehensive index can be found at the back of this publication to help guide you by specific areas of interest, as well as point out interdisciplinary topics and researchers
High efficiency wide-band line drivers in low voltage CMOS using Class-D techniques
In this thesis, the applicability of Class-D amplifiers to integrated wide-band
communication line driver applications is studied. While Class-D techniques
can address some of the efficiency limitations of linear amplifier structures
and have shown promising results in low frequency applications, the low
frequency techniques and knowledge need further development in order to
improve their practicality for wide band systems.
New structures and techniques to extend the application of Class-D to
wide-band communication systems, in particular the HomePlug AV wire-
line communication standard, will be proposed. Additionally, the digital
processing requirements of these wide-band systems drives rapid movement
towards nanometer technology nodes and presents new challenges which will
be addressed, and new opportunities which will be exploited, for wide-band
integrated Class-D line drivers.
There are three main contributions of this research. First, a model of Class-D
efficiency degradation mechanisms is created, which allows the impact of
high-level design choices such as supply voltage, process technology and
operating frequency to be assessed. The outcome of this section is a strategy
for pushing the high efficiency of Class-D to wide band communication
applications, with switching frequencies up to many hundreds of Megahertz.
A second part of this research considers the design of efficient, fast and
high power Class-D output stages, as these are the major efficiency and
bandwidth bottleneck in wide-band applications. A novel NMOS-only totem
pole output stage with a fast, integrated drive structure will be proposed.
In a third section, a complete wide-band Class-D line driver is designed in a
0.13μm digital CMOS process. The line driver is systematically designed
using a rigorous development methodology and the aims are to maximise
the achievable signal bandwidth while minimising power dissipation. Novel
circuits and circuit structures are proposed as part of this section and the
resulting fabricated Class-D line driver test chip shows an efficiency of 15%
while driving a 30MHz wide signal with an MTPR of 22dB, at 33mW injected
power
Space Communications: Theory and Applications. Volume 3: Information Processing and Advanced Techniques. A Bibliography, 1958 - 1963
Annotated bibliography on information processing and advanced communication techniques - theory and applications of space communication
Data Acquisition Applications
Data acquisition systems have numerous applications. This book has a total of 13 chapters and is divided into three sections: Industrial applications, Medical applications and Scientific experiments. The chapters are written by experts from around the world, while the targeted audience for this book includes professionals who are designers or researchers in the field of data acquisition systems. Faculty members and graduate students could also benefit from the book