Sizing and placement of charge recycling transistors in MTCMOS circuits

A downside of using Multi-Threshold CMOS (MTCMOS) technique for leakage reduction is the energy consumption during transitions between sleep and active modes. Previously, a charge recycling (CR) MTCMOS architecture was proposed to reduce the large amount of energy consumption that occurs during the mode transitions in power-gated circuits. Considering the RC parasitics of the virtual ground and VDD lines, proper sizing and placement of charge-recycling transistors is key to achieving the maximum power saving. In this paper, we show that the sizing and placement problems of charge-recycling transistors in CR-MTCMOS can be formulated as a linear programming problem, and hence, can be efficiently solved using standard mathematical programming packages. The proposed sizing and placement techniques allow us to employ the CR-MTCMOS solution in large row-based standard cell layouts while achieving nearly the full potential of this power-gating architecture, i.e., we achieve 44% saving in switching energy due to the mode transition in CR-MTCMOS compared to standard MTCMOS.