Phase optimization in technology mapping

Though tree covering is an efficient algorithm for technology mapping, phase assignments on tree boundaries are not taken into consideration. Several inverter minimization algorithms have been proposed so far, but they do phase optimization before or after technology mapping, and their cost function is not to minimize the total area but to minimize the number of inverters. This paper describes a new formulation of phase optimization problem aiming to minimize the total area during the technology mapping. Cost function representing area according to each phase assignment is introduced, and tree covering algorithm is modified to handle that cost function. Edge-Valued Binary Decision Diagram is used to represent the function implicitly. Experimental results show that proposed method reduces about 10% area on average compared with a state-of-the-art logic synthesis system sis.