20.8 A 500nW batteryless integrated electrostatic energy harvester interface based on a DC-DC converter with 60V maximum input voltage and operating from 1μW available power, including MPPT and cold start

Battery life is a major concern in wireless sensing applications, as it causes a trade-off between system size and power consumption of the electronic circuits connected to it. Even if electronic circuit power consumption is steadily decreasing, the energy density of common energy storage systems is still extremely low in space-constrained applications. In this scenario, energy harvesting is a valuable solution to extend, in theory indefinitely, the autonomy of ubiquitous sensing systems. In particular, vibrational energy harvesters are an excellent solution to power sensors in industrial and automotive applications. This paper presents an electrostatic energy harvester (EEH) interface. Recently, electret-based EEHs have attracted considerable attention because of their capability to generate large powers, even at low accelerations [1]. Unfortunately, these devices are characterized by extremely high internal impedances and their interfacing circuits need to be simultaneously ultra-low-power and capable of working reliably with several tens of Volts applied to the input. To the best of our knowledge, only one solution has been proposed to efficiently interface high-voltage energy harvesters [2]. However, that circuit did not allow fully autonomous battery-less operation and did not work under 25μW available power.