Amid the blizzard of design-automation technologies, the analytical MOSFET models (and their
associated model parameter sets) receive scant attention from the design community. However,
these models and parameter sets are fundamental to the design process, since they represent the
critical "communication link" between a design group and its wafer foundry. Particularly for
analog design, there is a need for the models to be more than a “black box;” the models should
provide the ability to support modern analog design methodologies.
The first part of this tutorial will examine the present "infrastructure" of MOS modeling for
circuit simulation, with particular emphasis on how history has played a role at least as large as
that of engineering. In recent years, the entire structure of MOS models has been evolving into
continually more complicated and empirical forms, opening up a "reality gap" between a model's
mathematical structure and circuit design usage. Among the many severe consequences of the
present situation, the MOS models have become completely removed from good circuit design
practices, particularly for analog design; many common analog circuits cannot even be simulated
properly using "modern" MOS models!
The second part of this tutorial will make the connection between MOS modeling and a modern
approach to designing analog and digital integrated circuits. Transistor-level analog CMOS
design is greatly complicated since, at a given MOSFET drain current, there are two independent
degrees of design freedom: inversion level and channel length. The methodology allows
management of the tradeoffs in circuit bandwidth, transconductance, output conductance, DC
gain, DC matching, linearity, white noise, flicker noise, and layout area resulting from the
selection of inversion level and channel length. This permits MOSFET sizing for optimal
bandwidth, optimal DC matching, balanced compromises in bandwidth and DC matching, and
other combinations of circuit performance. The methodology permits operation anywhere in the
continuum of MOSFET operation - weak, moderate, or strong inversion.
About the Presenters:
Daniel Foty is the Founder and President of Gilgamesh Associates in Fletcher, Vermont, an
Adjunct Associate Professor of Electrical Engineering at the University of Tennessee, and the
Director of Design Methodologies at Nanopower Technologies in Newport Beach, California.