Automatic Mode-Selected Energy Harvesting Interface with >80% Power Efficiency over 200 nW to 10 mW

This paper proposes a dual-mode digital buck converter with an automatic mode-select feature in a 0.18-μm CMOS for self-powered Internet-of-Things applications. The proposed converter combines the digital pulsewidth modulation and the proposed predetermined pulse-frequency modulation (PPFM) techniques to achieve both a high conversion efficiency and a wide output power range. The proposed PPFM technique calculates the appropriate OFF time of the power transistor in advance, eliminating the additional power budget requirement of the conventional zero-crossing detection circuit. From the results, it can be seen that the conversion efficiency improves by 21% under ultralight-load conditions. The available input voltage (VIN) ranges from 0.55 to 1.8 V for a wide variety of energy harvesters, and the output voltage (V_OUT) ranges from 0.3 to 0.55 V to power the energy-efficient CMOS digital circuits. The proposed dual-mode digital buck converter achieves a maximum conversion efficiency of 90.5%, with an output power ranging from 25 nW to 10 mW. Owing to the proposed PPFM technique, the converter achieves a power conversion efficiency of more than 80%, with an output power of 200 nW to 10 mW.