ETD system

Electronic theses and dissertations repository


Tesi etd-04272020-095107

Thesis type
Tesi di dottorato di ricerca
Design of high-performance, application-specific Analog-to-Digital Converters
Settore scientifico disciplinare
Corso di studi
tutor Prof. Bruschi, Paolo
tutor Prof. Piotto, Massimo
Parole chiave
  • adc
  • cmos
  • design
  • microeletronics
  • chopper
  • cryocmos
  • low-power
Data inizio appello
Data di rilascio
Riassunto analitico
From the birth of the first digital computers, Analog-to-Digital Converters (ADCs)
have gained more and more importance in every fields of electronics. From very
high-speed digitizers required for wireless and wired data link, to very highresolution
converters for environmental sensor interfacing, ADCs with very high performances
must be designed. It is possible to divide the world of the Analog-to-Digital
Converters according to requirements of the target applications, basically high-speed
and high-resolution. Different architectures have been developed and different parameters
are used to evaluate their performances, depending on the specific fields of interest.
From the examples that will be described, it will look evident how general-purpose solutions
cannot fulfil so different design spaces in an efficient way. Data acquisition systems
for sensor interfacing, as requested in wireless sensor networks for environmental
monitoring, must be very accurate, keeping low power and area consumptions. The
ADC is one of the most pivotal blocks in the acquisition chain. Its presence is essential
due to the need to process, storage or transmit the information: all operations that
can be realized very efficiently only in the digital world. The design of electronics for
sensor nodes powered by energy harvesters or for wearable devices can be even more
challenging, due to the need to keep the power consumption as low as possible, often
working with supply voltage domain of few hundreds of millivolts. Extreme environments
as dilution fridges, where physical experiments on qubits for quantum computing
applications, can also host classical electronics, so that specific design techniques must
be employed for the design of analog-mixed electronics, including analog-to-digital
In this work of thesis, a full description of the design of three different Analog-to-
Digital Converters will be presented. The different target specifications will require
different architectures and specific solutions that will be deeply analysed. First, a
Delta-Sigma (DS) Analog-to-Digital Converter optimized for low-frequency signals
has been developed. A complete description of the high-level and transistor-level design
allows a full comprehension of the complex challenges for the fulfilment of high-accuracy
and high-resolution specifications, as typically required for sensor interfacing.
In particular, offset and low-frequency noise could be especially detrimental due to the
bandwidth of interest of the input signals, in the range from the dc to few kilohertz. A
system-level chopper stabilization technique has been fully analysed and implemented.
Thanks to this technique, it has been possible to reach an offset on the order of few
microvolts and a rms noise voltage of tens of microvolts.
Looking at the high demanding of low-power and low-voltage electronics for wireless
sensor networks, possibly powered by energy harvesting devices, a DS converter
capable of working with supply voltage as low as 200 mV has been realized. Typical
issues of low amplifier dc-gain and low-headroom for MOSFET devices are faced by
means of a novel switched-capacitor, inverter-based integrator. The ultra-low power
and ultra-low voltage converter has been simulated, showing good performances, as
summarised by the figure-of-merit of 42.4 fJ/conv with Vdd = 0:3V . To prove the effectiveness
of the proposed inverter-based integrator, a simple single-order DS modulator
has been designed with the 0.18 μm CMOS process. Measurements on a test chip
show the functionality of the converter with supply voltage as low as 0.2 V, with very
low power consumptions.
Finally, the design of an high-speed Successive Approximation Register (SAR) converter
for extreme environment applications is proposed. It has been optimized for
quantum computing application, more precisely for radio-frequency reflectometry interface
for spin qubit readout. A new challenge in the design of classical electronics for
quantum computing is the compatibility with cryogenic temperatures (4 K), in order to
improve the scalability of the actual quantum computers. A ping-pong SAR converter
with a maximum sampling frequency of 1 GHz and a resolution of 6 has been developed.
Additional programmability allowed the increasing of the converter resolution
up to 9 bit, at the cost of some speed penalties. Novel techniques in the converter topology
and in the switching algorithm scheme have been developed in order to face the
changing of MOSFET behaviour at cryogenic temperatures.