Wednesday, September 8, 2004
Hewlett Packard Auditorium, 306 Soda Hall
4:00-5:00 p.m.

Professor Bernhard Boser

Electrical Engineering and Computer Sciences Department
U. C. Berkeley

Digitally Assisted Analog Circuits

Abstract:

Continued technology scaling is resulting in an exponentially growing relative performance gap between analog and digital functions. Over the last two decades, the relative performance of microprocessors outpaced performance enhancements of analog-to-digital converters by more than two orders-of-magnitude. The reasons are unique constraints by analog circuits on electronic noise and distortion performance that do not benefit from scaling. Reduced supply voltage and lower intrinsic device gain exacerbate this problem and result in a scaling penalty for common analog functions such as high-gain amplifiers. Typical solutions include technology additions such as multiple supply voltages and gate oxide thicknesses. Aside from increased processing complexity, these techniques are not taking advantage of the intrinsically higher speed and power efficiency of technology scaling, thus resulting in suboptimal overall performance.

Digitally assisted analog circuits avoid the problem by shifting analog circuit challenges to the digital domain. Removing linearity and accuracy constraints from analog building blocks increases circuit speed and lowers power dissipation. The resulting errors are compensated with a digital pre- or post-processor that benefits fully from continued technology advances. A proof-of-concept realization consisting of a 12-Bit ADC fabricated in a 0.35um CMOS process employs inaccurate openloop amplification and digital calibration to achieve a 60% reduction in power dissipation in its critical first amplification stage while adding negligible digital processing overhead. The device uses a stochastic background calibration technique to continuously track analog circuit imperfections. Much more significant performance and power advantages are possible with shorter channel length and lower supply voltage processes and by including additional analog functions such as filtering and power amplification in the calibration process.

Bernhard E. Boser received the Diploma in Electrical Engineering from the Swiss Federal Institute of Technology in 1984 and the M.S. and Ph.D. from Stanford University in 1985 and 1988. From 1988 he was a Member of Technical Staff in the Adaptive Systems Department at AT&T Bell Laboratories. In 1992 he joined the faculty in the Department of Electrical Engineering and Computer Sciences at the University of California, Berkeley where he also serves as a Director of the Berkeley Sensor & Actuator Center. Dr. Boser's research is in the area of analog and mixed signal circuits, with special emphasis on on analog-digital interface circuits and micromechanical sensors and actuators. He has served on the program committees of the International Solid-State Circuits Conference, the Transducers Conference, the VLSI Symposium, and was the Editor of the IEEE Journal of Solid-State Circuits.