A High-Efficiency Dual-Polarity Thermoelectric Energy-Harvesting Interface Circuit With Cold Startup and Fast-Searching ZCD

This article presents an auto-polarity thermoelectric energy-harvesting interface circuit based on a single-inductor boost/buck–boost hybrid converter. The power stage is configured automatically as a boost converter for a positive input voltage or a buck–boost converter for a negative input voltage. A collaborative efficiency-improving scheme of frequency selection and maximum power point tracking (MPPT) is implemented for input power ranging from 1 to 800 $\mu \text{W}$ . An improved digital zero-current detection (ZCD) technique with fast searching is proposed to turn off power switches accurately. Dual-polarity cold startup is realized with the aid of a pair of cross-coupled Dickson charge pumps. This work is fabricated with a 0.13- $\mu \text{m}$ CMOS process. From the measured results, the interface starts up from a 140- or −160-mV thermoelectric generator (TEG) voltage. It boosts input voltages ranging from 10 mV to 0.4 V and from −10 mV to −0.4 V to a 1.2-V output voltage. It achieves a peak end-to-end efficiency of 90% with a 0.3-V input voltage or 88% with a −0.4-V input voltage. Moreover, end-to-end efficiencies are higher than 80% for input voltages from 90 mV to 0.4 V and from −110 mV to −0.4 V.