A Low-Power Battery Charge and Discharge Protection Circuit for Bio-Implantable Sensors in 65nm CMOS

This paper proposes an ultra-low power complete battery protection circuit with key four features to avoid battery malfunction and damage during charging and discharging modes for bio-implantable battery-powered sensors. The protection circuit is complemented by a recovery capability managed by a biasing approach in charging and discharging mode, ensuring the recovery of a fully depleted battery and disconnected protection circuits for cold start conditions. The charger part of the circuit connects the battery to the energy harvester while avoiding over-voltage and under-voltage charging by providing a safe narrow charging window of 4 V to 4.2 V and consuming only 460 pW in 65 nm standard CMOS technology in post-layout simulation. The low-power discharge protection circuits, consuming 520 pW, disconnect the battery from both continuous and switching loads to avoid full depletion of the battery. The fourth protective feature is provided by an ultra-low power, 80 pW, deep-sleep protection circuit extending the integrated battery-powered sensor storage time from a week to a month avoiding battery replacement after a long period of inactivity.