Design of an Ultra-Low Power Start-up Circuit for Micro-Power Management Units in Energy Harvesting Applications

In the last decades, the Internet of Things paradigm has been bringing the vision of ubiquitous smart sensor networks closer to reality. However, the battery-powered devices suffer from recharging and environmental issues. In this context, energy harvesting, particularly from RF sources, is an effective solution to power smart sensors on-demand. In this paper, an integrated Start-Up (SU) circuit for a RF-powered micro-power management unit (MPMU) is presented. In power-constrained applications, the SU circuit needs to self-start from the low voltages and powers, and with the high output source resistances typical of rectennas, accumulating enough energy to kickstart the main converter. The circuit is designed in a STMicroelectronics 110-nm technology, and simulations show operation from 0.5μW and 125 mV in the typical corner, reaching an output voltage of 1.2 V.