A time-based energy-efficient analog-to-digital converter

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (leaves 123-129).Dual-slope converters use time to perform analog-to-digital conversion but require 2N+1 clock cycles to achieve N bits of precision. We describe a novel algorithm that also uses time to perform analog-to-digital conversion but requires 5N clock cycles to achieve N bits of precision via a successive sub-ranging technique. The algorithm requires one asynchronous comparator, two capacitors, one current source, and a state machine. Amplification of two is achieved without the use of an explicit amplifier by simply doing things twice in time. The use of alternating Voltage-to-Time and Time-to-Voltage conversions provides natural error cancellation of comparator offset and delay, 1/f noise, and switching charge-injection. The use of few components and an effcient mechanism for amplification and error cancellation allow for energy-effcient operation: In a 0.35 [mu]m implementation, we were able to achieve 12 bits of DNL limited precision or 11 bits of thermal noise-limited precision at a sampling frequency of 31.25kHz with 75 [mu] W of total analog and digital power consumption. These numbers yield a thermal noise-limited energy-efficiency of 1.17pJ per quantization level making it one of the most energy-effcient converters to date in the 10 to 12 bit precision range.(cont.) This converter could be useful in low-power hearing aids after analog gain control has been performed on a microphone front-end. An 8 bit audio version of our converter in a 0.18 [mu] m process consumes 960nW and yields an energy-efficiency of 0.12pJ per quantization level, perhaps the lowest ever reported. This converter may be useful in biomedical and sensor-network applications where energy-efficiency is paramount. Our algorithm has inherent advantages in time-to-digital conversion. It can be generalized to easily digitize power-law functions of its input, and it can be used in an interleaved architecture if higher speed is desired.by Heemin Yi Yang.Ph.D

Advanced prognosis and health management of aircraft and spacecraft subsystems

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (p. 89).Beacon Exception Analysis for Maintenance (BEAM) has the potential to be an efficient and effective model in detection and diagnosis of nominal and anomalous activity in both spacecraft and aircraft systems. The main goals of BEAM are to classify events from abstract metrics, reduce the telemetry requirements during normal and abnormal flight operations, and to detect and diagnose major system-wide changes. This thesis explores the mathematical foundations behind the BEAM process and analyzes its performance on an experimental dataset. Furthermore, BEAM's performance is compared to analysis done with principal component transforms. Metrics are established where accurate reduction of observable telemetry and detection of system-wide activities are stressed. Experiments show that BEAM is able to detect critical and yet subtle changes in system performance while principal component analysis proves to lack the sensitivity and at the same time requires more computation and subjective user inputs. More importantly, BEAM can be implemented as a real-time process in a more efficient manner.by Heemin Yi Yang.M.Eng