Ultra-Low-Power Circuits for Energy Harvesting Applications

Abstract

Recent advancements in integrated circuit (IC) technology and design methodologies, particularly in the realm of ultra-low power circuits, have facilitated the fast expansion of fully integrated and portable electronics inside Internet of Things (IoT) smart nodes and wearable sensor systems on chip (SoC). IoT applications, such as biomedical sensors, body area networks, and wireless sensors, have leveraged this advancement. However, with the rising demands of individuals, several components must be included into the IoT SoC. Therefore, a small, efficient, and self-sustaining power management circuit (PMC) with a prolonged lifespan design is essential for IoT SoC. Consequently, energy scavengers, including solar cells (PV), thermoelectric generators (TEG), and electrostatic harvesters, provide an appealing approach for powering the PMC, enabling self-sustaining and extended lifespan systems.        
The switched capacitor charge pump (SCCP) combined with low dropout (LDO) regulators is an effective solution for power management circuits (PMC) in energy harvesting systems (EHS) due to their on-chip integrability, eliminating the need for cumbersome off-chip inductors, particularly in implantable biomedical applications. Nevertheless, these regulators must be managed using a maximum power point tracking (MPPT) system to optimize energy harvesting and ensure optimal storage. The MPPT regulates whether to optimize power transmission according to load demand or to configure the regulator to extract the maximum available power from the energy harvester. Numerous MPPTs have been created to identify the maximum power point, hence enhancing tracking efficiency and/or conversion efficiency. Several criteria to be fulfilled include extensive input voltage handling, broad output load range coverage, output voltage control, and ultra-low power consumption. The latter is of significant significance to optimize the overall efficiency of the EHS and prolong its lifespan in the context of battery-powered PMCs.