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S

Series in
Signal and Information Processing, Vol. 24
edited by HansAndrea Loeliger
Jonas Biveroni
On A/D Converters with LowPrecision Analog
Circuits
and Digital PostCorrection.
1. Auflage/1st
edition 2013, XIV, 140 Seiten/pages, € 64,00.
ISBN 3866284527,
9783866284524
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 nondeterministic manner. Some of the resulting
precision errors can be corrected by digital processing. Thus, a promising
approach to mixedsignal circuit design is using small lowprecision analog
circuits and applying digital correction, such that the system as a whole is sufficiently
precise.
In this thesis, we apply the abovementioned
approach to analogtodigital 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
lowprecision analog circuits and digital postcorrection. 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 ashtype
ADCs with lowprecision 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
ashtype ADCs and sequential ADCs using lowprecision analog circuits are
useful with proper digital correction.
After fabrication, the static characteristics of
the ADC's lowprecision 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 builtin selftest (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
betaexpansion principle using simple analog lowprecision subcircuits.
Keywords: Analogtodigital
converter, ash ADC, sequential ADC, lowprecision analog circuits, digital
postcorrection, static accuracy, calibration, factor graph, messagepassing
algorithms, integrated circuit design.
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