A Multi-Ratio Helical Ladder Switched-Capacitor DC-DC Converter for Low Power Sensor Nodes

This brief presents a highly efficient helical ladder switched capacitor (HLSC) converter derived from a conventional ladder switched capacitor (CLSC) converter. In the proposed switched-capacitor converter (SCC), the large charge-carrying flying capacitors (Cfly) of the CLSC are identified and reconfigured to reduce the charge flow. This reduction in the charge flow reduced the charge sharing loss and improved the overall efficiency of the proposed HLSC without changing the total Cfly. A systematic process is shown to develop an HLSC architecture for the 2/5 voltage conversion ratio (VCR) of CLSC. The fully integrated HLSC and CLSC converters prototype is fabricated and compared for 1/4, 3/4 VCRs in 180 nm CMOS. The measurement results show that HLSC achieved peak efficiency (ηpeak) of 81% and maximum power density (PD) of 7.56 mW/mm with load currents up to 2.3 mA. Further, HLSC shows 27% efficiency improvement than CLSC at VOUT=0.4 V in 1/4 VCR configuration.