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.