Bo olean Analysis of MOS Circuits
Randal E Bryant
Computer Science Department
Carnegie Mellon University
Pittsburgh PA
February
Abstract
The switch level mo del represents a digital metal oxide semiconductor MOS cir
cuit as a network of charge storage no des connected by resistive transistor switches
The functionality of such a network can b e expressed as a series of systems of Bo olean
equations Solving these equations symb olically yields a set of Bo olean formulas that
describ e the mapping from input and current state to the new network state This
analysis supp orts the same class of networks as the switch level simulator MOSSIM I I
and provides the same functionality including the handling of bidirectional e ects and
indeterminate X logic values In the worst case the analysis of an n no de network
can yield a set of formulas containing a total of O n op erations However all but
a limited set of dense pass transistor networks give formulas with O n total op era
tions The analysis can serve as the basis of e cient programs for a varietyoflogic
design tasks including logic simulation on b oth conventional and sp ecial purp ose
computers fault simulation test generation and symb olic veri cation
Keywords and phrases switch level networks symb olic analysis logic simulation fault
simulation simulation accelerators