Useful-skew clock optimization for multi-power mode designs

Instead of minimizing clock skew, skew can be useful to improve circuit performance. However, it is difficult to apply useful skew to a design with complicated power modes. With only one clock tree, useful skew in one power mode may be harmful in another power mode. In this paper, we propose to use adjustable delay buffers (ADBs) to construct a tunable clock tree so that useful skew can be assigned for different power modes. Assuming positions of ADBs are determined, we assign delays of ADBs for each power mode by LP. Then a speedup theorem is proposed to greatly reduce LP inequalities. We also propose an efficient method to select positions of ADBs. Our experimental results show that average 99.45% inequities are decreased and an average performance improvement of 27.35% is obtained compared with commercial tool SOC Encounter™.