Voltage drop reduction for on-chip power delivery considering leakage current variations

Abstract

In this paper, we propose a novel on-chip voltage drop reduction technique for on-chip power delivery networks of VLSI systems in the presence of variational leakage current sources. The new method inserts decoupling capacitors (decaps) into the power grid networks to reduce the voltage fluctuation. The optimization is based on sensitivity-based conjugate gradientmethod and sequence of linear programming approach. Different from existing power grid noise reduction methods, the new approach considers the impacts of inter-die and intra-die variational leakage current sources due to unavoidable process variability during the decap optimization process for the first time. Leakage currents, which although are static in nature typically, can still add to the total voltage drops and dynamic voltage reduction thus must consider the leakage-induced voltage variations. The proposed algorithm exploits the relative constant variations for different decap configurations of power grid circuits to speed up the statistical optimization process. Decaps can be inserted in such a way that the resulting circuits have much higher probability to meet the voltage drop constraints in the presence of leakage current variations. Experimental results demonstrate the effectiveness of the proposed approach and show that the new method has 100X to 1,000X of speedup over the Monte Carlo based statistical decap optimization method.