Clock Buffer Polarity Assignment Considering Capacitive Load

Jianchao Lu and Baris Taskin
Drexel University


A clock buffer polarity assignment method is proposed that considers the impact of capacitive load on peak current. It is shown that the peak current on the supply rails of a buffer is proportional to 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 in each local area is reduced by 28.6% on average. The worse case peak current of all the local areas are reduced by 22.7% on average. The proposed method is implemented with a pseudo-polynomial dynamic programming scheme demonstrating runtimes under a minute.