21.1 A single-cycle MPPT charge-pump energy harvester using a thyristor-based VCO without storage capacitor

The switched-capacitor power converter, also called a charge pump (CP), features no off-chip components and is suitable for the monolithic smart nodes in the internet of everything (IoE) [1]. To reduce the inevitable charge-redistribution loss (CRL) from a fixed conversion ratio (CR), reconfigurable CPs have been proposed to dynamically change their CRs for optimized harvesting efficiency [2,3]. However, they lacked the startup and self-sustaining capability [4], which are vital to the power-management unit for IoE. The clock generator of an energy harvester should oscillate with the initial low harvesting voltage. To realize the self-sustaining capability, the controller should rely on the harvested power of the CP, which implies an ultra-low power consumption. The conventional current-starved ring oscillator is not suitable for this microwatt power budget due to its correlated nature between speed, slew rate, and power consumption.