Clock buffer polarity assignment considering capacitive load

Abstract

A clock buffer polarity assignment method is proposed that considers the impact of capacitive load on the peak current. It is shown that the peak current on the supply rails of a buffer is a monotonically increasing function of its driving capacitance. Consequently, the polarity of a clock buffer is assigned based on its capacitive load. The proposed method can be applied to assign buffer polarity on any number of levels of the clock tree. In experiments, the peak current on the clock tree in each local area is reduced by 36.3% on average. The worse case peak current of all the local areas are reduced by 35.7% on average. The proposed method is implemented with a pseudo-polynomial dynamic programming scheme demonstrating runtimes under a minute.