A fully-integrated dual-mode switched-capacitor DC-DC converter with 75% efficiency for ultra-low-power biosensor systems

This paper presents a fully-integrated dual-mode switchedcapacitor (SC) DC-DC converter to supply always-on wake-up timer in biosensor systems. To balance chip area and conversion efficiency, optimal sizes of power switches, flying capacitor (C_fly) and output capacitor (C_out) in SC cell are determined through power loss analysis method. Power-on and self-powered modes (dual modes) under two voltage domains and an on-chip ultra-low-power (ULP) bias circuit are proposed to further improve the conversion efficiency. Furthermore, a hybrid self-biased current (HSBC) scheme is utilized to achieve low output voltage ripple. Implemented with a 40-nm CMOS process, this DC-DC converter can realize the voltage conversion from 1.8V to 0.4V. Measurement results show that the peak conversion efficiency reaches 75% at average load arriving 3µA, while the voltage ripple is below 12mV over 10 nA-5µA load range.