VCO Design

183 Pages·2014·3.78 MB·English

by  Pedro Pereira

Pedro Miguel Ribeiro Pereira

Mestre

Optimization Based Design of
LC Voltage Controlled Oscillators

Dissertação para obtenção do Grau de Doutor em
Engenharia Electrotécnica e de Computadores

Orientador: Prof. Doutora Maria Helena Fino, Professora
Auxiliar, Faculdade de Ciências e Tecnologia da
Universidade Nova de Lisboa
Co-orientador: Prof. Doutor Mário Ventim Neves, Professor
Auxiliar, Faculdade de Ciências e Tecnologia da
Universidade Nova de Lisboa

Júri:
Presidente: Prof. Doutor Paulo da Costa Luís da Fonseca Pinto
Arguentes: Prof. Doutor Francisco Vidal Fernández Fernández
Prof. Doutor João Manuel Torres Caldinhas Simões Vaz
Vogais: Prof. Doutor Mourad Fahkfahk
Prof. Doutor Fernando José Almeida Vieira Coito

Maio, 2013

Optimization Based Design of LC Voltage Controlled Oscillators

Copyright © Pedro Miguel Ribeiro Pereira, Faculdade de Ciências e Tecnologia, Univer-
sidade Nova de Lisboa.

A Faculdade de Ciências e Tecnologia e a Universidade Nova de Lisboa têm o direito,
perpétuo e sem limites geográficos, de arquivar e publicar esta dissertação através de exem-
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right, perpetual and without geographical limits, of filing and publishing this dissertation
through printed examples reproduced in paper or in the digital form, or for any other known
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Acknowledgments
I would like to take this opportunity to remember, in an informal way, those who in
many different ways have supported me during the long years that I took to complete this
work.
Sincerely, I am deeply grateful to my supervisor, Professor Helena Fino, for her support,
guidance, professionalism, patience and knowledge, both scientific and intellectual. Without her
enthusiasm and insights, priceless comments and discussions, probably most of this work
would not have been possible. I will be forever grateful.
I would like to thanks to my co-supervisor, Professor Ventim-Neves, for his useful ad-
vices when I faced less optimistic moments. I will never forget some of his history lessons
during countless enjoyable lunches.
I also would like to express my sincere thanks to Professor Fernando Coito, for his
valuable comments throughout some periods of my research. The joint work that has resulted
from our close collaboration, was fruitful.
A special word of appreciation goes to Professor Leão Rodrigues, for opening me the
door of the academic world, but mostly for his delightful lectures and teachings during my time
as student, that have made me embrace this career. To him, my most sincere recognition.
I wish to express my sincere thanks to Professor Mourad Fakhfakh, Amin Sallem and
Mouna Kotti, from University of Sfax – Tunisia, for their collaboration through this last years,
and for their valuable input on my research.
I would like to say “thanks” to all the colleagues of my group. Those who daily knocked
on my office door, inviting me for a coffee or just for five minutes of talking, deserve a special
word of appreciation. Many thanks to João (Pina), who has a great sense of humour that im-
proves a lot the working environment. Day by day, he became more than a colleague. A big
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thanks to Anabela, who started as my teacher and over time became a good friend – I would
like to thank her for her support and friendship. The other João (Martins), the most recent
member of the group, but rapidly has proved to be a cool fellow. To him, my genuine friend-
ship. Last, I would like to mention David, for his friendship and support.
There are friends that no matter where they are, we can count on them. Fortunately, I
have two of those friends: Raquel and Agostinho. I am forever grateful for their patience lis-
tening me.
A special thanks to my family. Without their love, support and encouragement during
this path would have been harder. I would like to say sorry to little Diogo, for all the time and
patience that at times I did not have for him. Although, he has always been present when I
needed him. Thanks for every smile.
Finally, I would like to acknowledge the financial support from the Portuguese National
Funding Agency through the Fundação para a Ciência e Tecnologia (FCT - Science and
Technology Foundation) PEst-OE/EEI/UI0066/2011 project.
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Abstract
As result of the progress in technology development and the use of submicron CMOS
processes, digital circuits have become faster and more precise, and with decreased imple-
mentation area. This technological improvement enforces more restricted specifications in
terms of gain, phase noise and size for the analog/RF counterparts.
Due to the high-density integration needs as well as to low cost fabrication, fully inte-
grated LC-VCOs applied to RF applications, such as clock generation, frequency synthesizers
or timing-recovery circuits are usually implemented in CMOS technology. Thus, nowadays the
challenge of analog/RF design task is to design a circuit to accomplish very stringent design
specifications in terms of phase-noise, power consumption or area, among others, must be
attained, leading to the necessity of finding design solutions where technology is pushed to-
wards its limits.
Nonetheless, the technology scaling has lead to a decrease in the supply voltage, thus
making the analogue design more challenging, since neither a wide range of linearity nor full
output voltage swing are easily guaranteed. In the particular case of LC-VCOs, since their
design involves some trade-offs and relies on the estimation of several parameters, which can
be correlated. Traditional hand-calculation design methods are not an option when CMOS
submicrometer technology is being used. Moreover, simulation based optimization, which is
generally the most accurate design procedure, can become prohibitive, since is an extremely
time consuming process. To cope with the complexity of the design, optimization based meth-
odologies must be adopted. For the efficiency of the design process, analytical models for
both passive and active devices must be considered.
To accomplish the goal proposed for this thesis, emphasis is placed on identifying the
most suitable analytical models that accurately characterize the behaviour of each single ele-
ment in the LC-VCO. These models, which must rely on technological parameters, in opposi-
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tion to those based in fitting parameters supported by an exhaustive simulation process, are a
fundamental key for an optimization based design procedure, that aims to be simulation inde-
pendent. Such kind of analytical models, allow to understand the device physics and to apply
it successfully for the analog/RF design purposes.
To achieve the LC-VCO design optimization goals, evolutionary algorithms, namely the
genetic algorithms, are used. Due to the different kind of nature of the problem under analy-
sis, the optimization process is able to deal with discrete and continuous variables as well as
constrained search space. Moreover, this optimization technique help designers dealing with
design trade-offs, such as phase noise and power consumption, in an intuitive way, avoiding
the blind believe in simulators.
The performance of the LC voltage controlled oscillator, designed by the proposed opti-
mization-based design tool, gives fairly acceptable results when compared with those obtained
through commercial simulators. It proves that the proposed tool is a good design instrument
for a first approach design, as intended to be.

Keywords: LC-VCO; Accurate device models; Design methodology; Discrete-Variable
Optimization; Genetic Algorithms
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