A Sub-10 mV Power Converter With Fully Integrated Self-Start, MPPT, and ZCS Control for Thermoelectric Energy Harvesting

An inductive power converter for thermoelectric generator (TEG) is presented in this paper. A novel redundant inverter ring oscillator is proposed to self-oscillate in a very low supply voltage down to 45 mV. An additional self-start assist circuit with a differential clock booster and an exponential charge pump is implemented in the power converter to achieve lower self-start voltage. Boundary continuous-conduction mode, zero current switch (ZCS), and maximum power point tracking (MPPT) features have been incorporated into the power converter. Selective turn-ON dynamical-comparators have been used in ZCS and MPPT circuits to save power and achieve minimum operating supply voltage. Fabricated in 65-nm CMOS process, the chip can self-start at 210 mV. After self-start, only 7-mV input voltage is needed to sustain the power converter operation. With a TEG open circuit voltage of 80 mV and internal resistance of 5 Ω, the chip can provide a maximum output power of 229 μW with end-to-end efficiency of 71.5%.