The Research of Prof. Willy Sansen: An Overview

The author discusses his relationship with Willy Sansen, whom he first met in 1969 when Sansen came to the Electrical Engineering and Computer Science (EECS) Department of the University of California, Berkeley, as a new Ph.D. candidate. The author supervised his Ph.D. research in the field of analog integrated circuit (IC) design for the next three years and got to know him well. Sansen arrived at Berkeley at an exciting time in the development of ICs. Silicon ICs were rapidly taking over commercial digital applications and were making major inroads in the analog circuits field as well. Sansen quickly realized that to make progress on both the theoretical analysis and computer simulation of these circuits, he would need to simultaneously tackle the problem of device characterization for IC processes. The state of the art in device modeling at the time was quite crude, particularly with regard to the parasitic elements associated with bipolar transistors, the dominant active devices then in widespread use. Sansen’s research on this topic was described in a 1972 paper that has been widely referenced over the years. He then applied this modeling expertise to the characterization of signal distortion in bipolar transistor VGAs. He combined closed-form analytical expressions with computer simulation that, for the first time, enabled circuit designers to quickly predict the nonlinear behavior of this important class of circuits. This work then led to the realization of methods of maximizing the dynamic range of VGAs. This research required inclusion of VGA device electrical noise processes in the analysis and explained for the first time a number of aspects of VGA noise performance that had been observed empirically but were not well understood. New circuit design ideas such as bleed-current injection to the common-emitter points of the main differential pairs were introduced, and these techniques are being used today in a wide range of circuit applications in a number of different IC technologies at frequencies as high as 75 GHz.