Alternative control strategies for rule-based transistor placement in CMOS VLSI design

A CMOS leaf cell may be regarded as a grid of elements, each of which is a p-type or n-type transistor. An arbitrary placement may be improved by swapping particular transistor pairs. Nine rules have been devised, each of which proposes candidate pairs to be swapped. The number of possible swaps for a given leaf cell is large and a complete exploration of the search space is not computationally feasible. The authors consider the effectiveness of four possible iterative algorithms for the selection of transistor swaps proposed by the rule set and compare them with an algorithm for constructive placement