Power gating scheduling for power/ground noise reduction

Power gating is a technique for efficiently reducing leakage power by disconnecting idle blocks from the power grid. When gated blocks are woken up, large amounts of switching currents are drawn in a short period of time that may introduce severe noise on the power delivery mesh. In this paper, we propose a GA-based approach to schedule power gating considering power/ground noise. We introduce a simulation-based method to accurately and efficiently estimate the worst case noise, taking all the current sources, inductance and decaps' effects into consideration. We also present an incremental scheduling procedure considering the dynamic changes of decap configuration. Experimental results show that by optimally scheduling the wake-up order under time constraints, our technique can reduce noise up to 50% compared to waking gated blocks simultaneously. The quality of results depends upon the total wake-up time constraint, locations of gated blocks, current densities of gated blocks, and decap distribution.