High Speed Oversampling Data Converters

Professor David Johns,
University of Toronto, Canada

ABSTRACT: Analog-to-digital converters (ADC) are one of the most crucial building blocks in integrated circuits. They are used to interface real world signals with digital signal processing in practically all electronics applications with some examples being ethernet, wireless networks, ultrasonic imaging, audio and video processing, and xdsl communications. The main specifications for an ADC are clock rate, dynamic range, silicon area and power consumption. Two main classes of ADCs are Nyquist-rate converters and oversampling converters. Nyquist-rate converters generally operate at a clock rate that is equal to twice the input signal bandwidth. On the other hand, oversampling converters operate with a clock rate that is higher than twice the input signal bandwidth.

This talk will discuss architectures for oversampling converters with a particular emphasis on those that are well suited for wider input signal bandwidths. The first part of the talk will describe the basic operation of oversampling converters and describe some of the advantages and disadvantages of using an oversampling converter. In addition, the benefits of a multi-bit converter over a single-bit converter will be presented. Following this introduction, architecture and circuit choices for converters having wide input signal bandwidths will be discussed. First, the use of a feedforward path will be presented that reduces non-ideal opamp effects. Next, continuous-time oversampled converters will be discussed as well as a technique to increase their clock frequency due to excess loop delay. In addition, a technique for time-interleaving oversampling converters will be presented. Finally, experimental results for some recent work at the University of Toronto will be presented describing a continuous-time time-interleaved oversampling converter with a 20MHz input signal bandwidth as well as a continuous-time lowpass converter with a complex signal bandwidth from 0-23MHz.

BIO: David A. Johns received the BA Sc., MA Sc., and PhD degrees from the University of Toronto, Canada, in 1980, 1983, and 1989, respectively. In 1988, he was hired at the University of Toronto where he is currently a full professor. He has ongoing research programs in the general area of analog integrated circuits. His research work has resulted in more than 80 publications as well as the 1999 IEEE Darlington Award and the 2005 ISSCC Design Contest award. Together with academic experience, he also has spent a number of years in the semiconductor industry and is a co-founder of Snowbush Microelectronics. He served as a guest editor of the IEEE Journal of Solid-State Circuits and an associate editor for IEEE Trans. on Circuits and Systems and was elected to Adcom for SSCS in 2002. His homepage is located at http://www.eecg.toronto.edu/~johns.