A 7.5-mV-Input Boost Converter for Thermal Energy Harvesting With 11-mV Self-Startup

A DC-DC boost converter for ultra-low-voltage thermal energy harvesting is presented herein. The focus of this brief is to provide both self-startup and efficient conversion at ultra-low input voltages. The converter startup is achieved through the use of a cold starter based on an ultra-low-voltage oscillator and a charge pump. The inductive boost converter architecture uses two low-side switches in order to independently optimize the low-voltage startup and the steady-state conversion efficiency. The model of the developed converter allows optimization of the boost switches as a function of the TEG internal resistance and input voltage. A zero current switching circuit with accurate detection for low input voltages is designed and implemented. The prototype fabricated in 130 nm standard CMOS technology achieves startup for an input voltage of 11 mV and, once started, the system can perform the boost operation for input voltages as low as 7.3 mV, delivering 50% of end-to-end efficiency at 10.5 mV and peak end-to-end efficiency of 85% at 140 mV.