Self-oscillating multilevel switched-capacitor DC/DC converter for energy harvesting

Abstract

This paper presents three self-oscillating multilevel time-interleaved switched-capacitor DC/DC converters implemented and taped-out in 0.18-μm CMOS targeting microwatt power levels. Two of the converters are step-up with ratios of 1:2, 1:3, and 1:4, and one is a step-down with ratios of 2:1, 3:1, and 4:1. They all regulate the output voltage towards a targeted reference removing the need for a separate regulator. Aimed for use in vibration energy harvesting systems, the converters have a wide combined input voltage range of 450 mV to 20 V. The low voltage step-up converter operates from an input voltage of 475 mV and has a peak measured power efficiency of 82.2% with an area of 0.62 mm ² . The medium voltage step-up converter operates from an input voltage of 700 mV and has a peak power efficiency of 74.5% and an area of 0.53 mm ² . Lastly, the step-down converter works with input voltages up to 20 V and achieves a peak power efficiency of 68.7% with an area of 0.55 mm ² .