A 5V, 33-kHz, OJ-μW pulse generation circuit for ultra-low-power boost charging energy harvesters

Abstract

This paper presents a ultra-low-power oscillator and pulse-width modulator circuits for a boost-converter-based energy harvester that is capable of collecting net energy even when the input power is less than 2μW. While the previously published leakage-based relaxation oscillators demonstrated 0.42μW at 3.2-MHz, their voltage swings were limited to 0.45V to prevent crowbar currents in the crossing detector stages. New crossing detector circuits that limit the crowbar current to a sub-threshold leakage level enables both the ultra-low-power oscillator and pulse-width modulator even when they are operating at a 5V supply. Fabricated in a 0.25μm CMOS, the prototype oscillator dissipates only 10nW~50μW while generating a 10-Hz to 20-MHz clock at 5V swing. The energy harvester switching at 33-kHz keeps the efficiency above 59% even when the input power level from photovoltaic cells drops to 2μW.