Design of a VCO based ADC in a 180 nm CMOS process for use in positron emission tomography

116 Pages·2010·4.91 MB·English

2010:069 CIV
M A S T E R ' S T H E S I S
Design of a VCO based ADC in a
180 nm CMOS Process for use
in Positron Emission Tomography
Joakim Bergs
Luleå University of Technology
MSc Programmes in Engineering
Arena, Media, Music and Technology
Department of Computer Science and Electrical Engineering
Division of EISLAB
2010:069 CIV - ISSN: 1402-1617 - ISRN: LTU-EX--10/069--SE

Design of a VCO based ADC in a
180 nm CMOS process for use in
Positron Emission Tomography
Joakim Bergs
Fraunhofer IIS - Erlangen, Germany
Dept. of Analog and Mixed-Mode IC design
August 2009 - January 2010

A
BSTRACT
AVoltage-ControlledOscillator(VCO)-basedAnalog-to-DigitalConverter(ADC)foruse
in Positron Emission Tomography has been designed in a 180 nm CMOS process. The
VCO-based ADC is a time-based architecture with a first-order noise shaping ability.
The ADC designed in this thesis utilizes a five-element current-starved VCO-core and a
new counter architecture. The work deals with the theory and limitations for designing
and evaluate these ADC architectures. The ADC sampling frequency is set to 50 MHz
with an input signal bandwidth of 500 kHz. Thus, an oversampling ratio (OSR) of 50.
The ADC achieves a peak Signal-to-Noise Ratio (SNR) of 88 dB or approximately 14.3
bitwhiledissipatingonly1.18mWfroma1.8Vsupplyandoccupyinganactivechip-area
of <0.01 mm2.
The work was carried out at the Fraunhofer - Institut fu¨r Integrierte Schaltungen (IIS),
in Erlangen, Germany under a time period of approximately five months. A part of the
thesis was also to take part in the patent application process for a new counter architec-
ture, described in this thesis.
Keywords: VCO-Based ADC, Data Converter, Analog-to-Digital, Time-Based, VCO-
Quantizer, FSDM
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P
REFACE
While writing the last lines of words in this thesis, I have also come to the end of my
education to become an electrical engineer. But before I period this thesis and graduate,
I would like to take the opportunity to say thanks to a couple of guys.
First I would like to thank my supervisor Matthias Vo¨lker and all the colleagues in
the ICDA group at Fraunhofer IIS, especially Harald Neubauer for the great barbecues.
Then I also take the opportunity to express gratitude to Jonny Johansson at Lule˚a Uni-
versity of Technology. You have been the most inspiring and motivating lecturer under
my time at the university. He pushed me to not give up under the hardest part of this
thesis. I would also like to thank my internal supervisor Johan Borg. Thanks also to all
my wonderful friends, both old and new ones that I have meet, often in the mountains
freeride skiing or at the students sports club. Thanks Genesis and Dream Theater for
filling my life with brilliant music.
Finally but most important, my family. Without your support I would not have been
able to be so successful under my time at the University. There are no words to express
my gratitude. I dedicate this thesis to my family and my beloved girlfriend.
Live it and Love it!
G¨oteborg, March 2010
Joakim Bergs
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A
BBREVIATIONS
AAF Anti-Aliasing Filter
ADC Analog-to-Digital Converter
CC Cross-coupled
CS Current-starved
CT Continues -Time
FDSM Frequency Delta-Sigma Modulator
FFT Fast-Fourier Transform
FIFO First In First Out
LSB Least Significant Bit
NTF Noise Transfer Function
OSR Oversampling Ratio
PET Positron Emission Tomography
PSD Power Spectral Density
PSRR Power Supply Rejection Ratio
SAFF Sense-Amplifier based Flip-Flop
SFDR Spurious Free Dynamic Range
SNDR Signal-to-Noise and Distortion Ratio
SNR Signal-to-Noise Ratio
THD Total Harmonic Distortion
VCO Voltage-Controlled Oscillator
VCVS Voltage Controlled Voltage Source
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