Decoupling capacitor design strategy for minimizing supply noise of ultra low voltage circuits

Supply noise is a critical problem for the robust operation of integrated circuits at ultra low voltage regimes. Although decoupling capacitance is a traditional solution, the reduction of gate capacitance at subthreshold voltage can cause area overhead. In this paper, we propose a decoupling capacitor design strategy to reduce area overhead. The strategy consists of two parts: 1) enhancing gate capacitance through circuit optimizations and 2) using remote decoupling capacitors. Remote decoupling capacitors, which can be placed far from the block to compensate, can minimize the area overhead of the capacitance-enhancing optimizations. They also exploit less utilizable silicon area. The proposed strategy improves the capacitance density by 6.1× without extra process steps, compared to the conventional approach. The gained robustness may be traded off for higher energy efficiency.