Optimal Allocation of LDOs and Decoupling Capacitors within a Distributed On-Chip Power Grid

Abstract

Parallel on-chip voltage regulation, where multiple regulators are connected to the same power grid, has recently attracted significant attention with the proliferation of small on-chip voltage regulators. In this article, the number, size, and location of parallel low-dropout (LDO) regulators and intentional decoupling capacitors are optimized using mixed integer non-linear programming formulation. The proposed optimization function concurrently considers multiple objectives such as area, power noise, and overall power consumption. Certain objectives are optimized by putting constraints on the other objectives with the proposed technique. Additional constraints have been added to avoid the overlap of LDOs and decoupling capacitors in the optimization process. The results of an optimized LDO allocation in the POWER8 chip is compared with the recent LDO allocation in the same IBM chip in a case study where a 20% reduction in the noise is achieved. The results of the proposed multi-criteria objective function under a different area, power, and noise constraints are also evaluated with a sample ISPD’11 benchmark circuits in another case study.