Efficiency Optimization of a Step-Down Switched Capacitor Converter for Subthreshold

In this brief, an efficient voltage scalable switched capacitor converter (SCC) for 1.1 V battery-powered digital system is presented. The SCC employs a binary resolution technique to preserve high efficiency at load voltages down to sub-200 mV while keeping the efficiency high. The proposed converter can be configured into four topologies to support subthreshold output levels of 0.18-0.6 V. The converter is designed in a standard lowpower 40-nm CMOS TSMC process. Simulation results show that the efficiency of the SCC can be improved by 10%-11% in the vicinity of VDD=200 mV as compared to one using a conventional approach. An optimization strategy for designing multi-topology SCC is presented to improve the effectiveness of the circuit and to preserve efficiency over large load voltages.