A PFM Boost Harvester With System-Level Self-Tuned Maximum Power Point Tracking

This article presents a low-overhead energy harvesting and delivery system (EHDS) with pulse frequency modulated (PFM) integrated voltage regulator (IVR) power conversion and self-tuned maximization of system output power. A novel load-inclusive time-based maximum power point tracking (LI-TB-MPPT) is developed to provide centralized tuning of PFM-IVR operation based on both source capabilities and load demand on-the-fly, and a configurable fractional sample and hold circuit provides adaptive harvesting window control. The proposed EHDS enables robust harvesting while relieving the use of high passives, with over two orders of magnitude reduction, at the cost of only slight decrease in end-to-end efficiency compared to prior works. Furthermore, a low-overhead wake-up assist circuit utilizes cold-configuration of harvesting sources for efficient and accelerated cold-start. The proposed EHDS is demonstrated in a 65 nm CMOS process with commercial photovoltaic energy harvesting modules. Using only 1.2 and 1
$\mu$
H of passives, measured results show a peak 74.9% end-to-end efficiency (simulated up to 85% at 47
$\mu$
H) and a fast startup time of 3.8 ms. Up to 15% increase in conversion efficiency against load and input voltage variations is achieved with LI-TB-MPPT. The results demonstrate a compact solution for self-sustained cost-restricted stand-alone systems.