Estimation of maximum power-up current

Power gating is emerging as a viable solution to reduction of leakage current. However, power gated circuits are different from the conventional designs in the sense that a power-gated circuit must be brought to a valid state from the power-off state, when all nodes in the circuit are at logic zero state, before useful computation can begin. Thus, estimation of the maximum current in a power gated circuit must determine the maximum of all possible power-up and normal switching current. In this paper we propose a cluster-based ATPG algorithm to estimate the maximum power-up current for combinational circuits. Our method achieves substantial improvement over simulation-based methods and also over the previously proposed ATPG-based methods. Further we also formulate the sequential circuit maximum current problem as a combinational ATPG problem, and solve it using the cluster-based estimation algorithm. Experimental results show that the maximum power-up current for sequential circuits can be up to 73% larger than the maximum normal switching current