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Renate Gorre D-78465
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Series in
Signal and Information Processing, Vol. 24
edited by Hans-Andrea Loeliger
Jonas Biveroni
On A/D Converters with Low-Precision Analog
Circuits
and Digital Post-Correction.
1. Auflage/1st
edition 2013, XIV, 140 Seiten/pages, € 64,00.
ISBN 3-86628-452-7,
978-3-86628-452-4
Progress in the fabrication of integrated
circuits (ICs) enables smaller and smaller minimum feature sizes, so that more
and more transistors can be realized per chip area. Digital circuits greatly
benefit from the miniaturization. By contrast, analog circuits suffer from
reduced precision when component sizes are decreased, because for decreased
component sizes, the respective component values increasingly deviate from
their nominal values in a non-deterministic manner. Some of the resulting
precision errors can be corrected by digital processing. Thus, a promising
approach to mixed-signal circuit design is using small low-precision analog
circuits and applying digital correction, such that the system as a whole is sufficiently
precise.
In this thesis, we apply the above-mentioned
approach to analog-to-digital converters (ADCs), as they combine analog and
digital circuits. ADCs are key building blocks of modern electronic devices
which process physical quantities digitally. Examples of such devices are
mobile phones, digital cameras or measurement devices such as digital
voltmeters. Such devices often contain several ADCs which convert radio
signals, touchscreen information, optical image data or plain voltage values into
digital signals.
Specifically, we consider ADCs using
low-precision analog circuits and digital post-correction. We mostly consider
static characteristics, ignoring dynamical issues like noise, sampling or
settling. The thesis presents a few studies and ideas on the topic.
We study the static accuracy of various ash-type
ADCs with low-precision components and digital correction. We model the key
analog components and assess the static accuracy using Monte Carlo simulations.
Similarly, we extend the discussion of the static accuracy to sequential ADCs
based on beta expansions (“radix < 2” conversion). We conclude that both
ash-type ADCs and sequential ADCs using low-precision analog circuits are
useful with proper digital correction.
After fabrication, the static characteristics of
the ADC's low-precision analog part are not known exactly. However, proper
digital correction requires the static characteristics to be known. We thus
elaborate a calibration method, which is suited for a built-in self-test (BIST).
The method includes a test signal generator circuit and algorithms which
estimate the static characteristics using measurement data of the test signals.
The algorithms are based on Gaussian message passing on a graphical model
(factor graph) of the system. In simulations, we achieve very accurate
estimations of the static characteristics using the presented method.
Finally, we design and manufacture an
experimental pipeline ADC in a 0:13 µm CMOS process. The circuit implements the
beta-expansion principle using simple analog low-precision sub-circuits.
Keywords: Analog-to-digital
converter, ash ADC, sequential ADC, low-precision analog circuits, digital
post-correction, static accuracy, calibration, factor graph, message-passing
algorithms, integrated circuit design.
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