An Interface Circuit for Low-Voltage Low-Current Energy Harvesting Systems

In this paper, we present an interface circuit designed to match low-power and low-voltage harvesters to generic electronic loads. The interface circuit consists of a power management unit, a supply regulation unit, and an energy storage module. The electric power delivered by the harvester is stored in a low leakage capacitor, converted to match the load electrical characteristics, and used cyclically to supply the load during fixed time-windows. The interface circuit is compatible with dc harvesters with a current of at least 2 $\mu$ A at 0.5 V and exhibits an efficiency of 65% in the 1 $\mu$ W$-$1 mW range. The supply regulation unit is a two-stage, self-starting boost circuit that steps-up the 0.5-V input voltage to 3 V. To test the interface circuit, an autonomous wireless sensor node has been realized; it exploits the little electric power delivered by a 385 $\mu$m $\times$ 245 $\mu$m photovoltaic harvester to sense and transmit information about the environment wirelessly. The harvester is implemented with a custom 0.35- $\mu$m BCD SOI chip. The system has been designed to be low cost, fully autonomous and smaller of 9 cm$^{3}$.