Efficient self‐powered convertor with digitally controlled oscillator‐based adaptive maximum power point tracking and RF kick‐start for ultralow‐voltage thermoelectric energy harvesting

Abstract

A self-powered convertor for thermoelectric energy harvesting in body sensor nodes (BSNs) is designed to boost extremely low voltage to the typical supply voltage of BSNs. An adaptive maximum power point tracking (MPPT) based on digitally controlled oscillator (DCO) is achieved by adjusting the switching frequency according to the relation between the half open-circuit voltage of thermoelectric generator and the equivalent voltage. DCO exhibits small line sensitivity and temperature coefficient (TC). Radio frequency (RF) kick-start based on a self-synchronous rectifier is introduced to achieve the no-battery effect. A modified zero current switching based on the common-gate comparator is utilised to decrease the power dissipation of power metal–oxide–semiconductor field-effect transistors. In addition, the power dissipation of the main blocks is reduced by discontinuing the clocked and common-gate comparators after comparison in each cycle, and by making most transistors of DCO and the complementary metal-oxide-semiconductor (CMOS) voltage reference work in the weak inversion or linear region. The zero TC principle of the CMOS voltage reference is extended to all process. The novel convertor is designed and verified in Central Semiconductor Manufacturing Corporation CMOS 0.18 µm process. The results reveal that it achieves adaptive MPPT without battery and exhibits a peak end-to-end efficiency of about 63%.