Decoupling Capacitance Design Strategies for Power Delivery Networks with Power Gating

Abstract

Power gating is a widely used leakage power saving strategy in modern chip designs. However, power gating introduces unique power integrity issues and trade-offs between switching and rush current (wake-up) supply noises. At the same time, the amount of power saving intrinsically trades off with power integrity. In addition, these trade-offs significantly vary with supply voltage. In this article, we propose systemic decoupling capacitors (decaps) optimization strategies that optimally trade-off between power integrity and leakage saving. Specially, new global decap and reroutable decap design concepts are proposed to relax the tight interaction between power integrity and leakage saving of power gated PDNs with a single supply voltage level. Furthermore, we propose a flexible decap allocation technique to deal with the design trade-offs under multiple supply voltage levels. The proposed strategies are implemented in an automatic design flow for choosing the optimal amount of local decaps, global decaps and reroutable decaps. The conducted experiments demonstrate that leakage saving can be increased significantly compared with the conventional PDN design approach with a single supply voltage level using the proposed techniques without jeopardizing power integrity. For PDN designs operating at two supply voltage levels, the optimal performance is achieved at each voltage level.