A Low-Power, Variable-Resolution Analog- to-Digital Converter

(Abstract) Analog-to-digital converters (ADCs) are used to convert analog signals to the digital domain in digital communications systems. An ADC used in wireless communications should meet the necessary requirements for the worst-case channel condition. However, the worst-case scenario rarely occurs. As a consequence, a high-resolution and subsequently high power ADC designed for the worst case is not required for most operating conditions. A solution to reduce the power dissipation of ADCs in wireless digital communications systems is to detect the current channel condition and to dynamically vary the resolution of the ADC according to the given channel condition. In this thesis, we investigated an ADC that can change its resolution dynamically and, consequently, its power dissipation. Our ADC is a switched-current, redundant signed-digit (RSD) cyclic implementation that easily incorporates variable resolution. Furthermore, the RSD cyclic algorithm is insensitive to offsets, allowing simple, low-power comparators. Our ADC is implemented in a 0.35 µm CMOS technology with a single-ended 3.3 V power supply. Our ADC has a maximum power dissipation of 6.35 mW for a 12-bit resolution and dissipates an average of 10 percent less power when the resolution is decreased by two bits. Simulation results indicate our ADC achieves a bit rate of 1.7 MHz and has a SNR of 84 dB for the maximum input frequency of 8.3 kHz. iii Acknowledgements I am indebted to my committee chairman and advisor Dr. Dong S. Ha for giving me the opportunity to work with him. Without his insightful guidance and help, I could not have completed this work. I would also like to express my appreciation to Dr. Peter M. Athanas and Dr. Jeffrey H. Reed for participating in my examination committee. I greatly appreciate the computing resources provided by VISC (Virginia Tech Information Systems Center). Without these resources, this work could not have been conducted. All the members of the VTVT (Virginia Tech VLSI for Telecommunications) team have been a great help. I would like to thank Hanbin Kim, Sulistyo of the VTVT team. I am very grateful to my family and my fiancé, Douglas H. Cox. Without their encouragement, help, and understanding, completing this work would have been a much more difficult task.