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 switched-capacitor (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 (Cfly) and output capacitor (Cout) 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 1.8 V to 0.4 V. Measurement results show that the peak conversion efficiency reaches 75 % at average load arriving 3 µA, while the voltage ripple is below 12 mV over 10 nA-5 µA load range.