A Low Power Fully-Digital Multi-Level Voltage Monitor Operating in a Wide Voltage Range for Energy Harvesting IoT

IoT devices operating on harvested energy from the environment need to deal with the variability of the available energy and consequently adapt the application workload. To support this adaptivity, this paper presents a fully-digital multi-level voltage monitor, operating from an unregulated supply voltage down to sub-threshold. The proposed fully-digital voltage monitor eliminates the overhead of analog components and additional power supplies. The proposed design is based on frequency variation with supply voltage of two specifically designed ring oscillators leveraging the dynamic leakage suppression logic. Simulation results of process variations including corners and random mismatch show a maximum standard deviation of 30 mV over a supply voltage range from 0.3 V to 0.9 V after one-point calibration. The simulation results also indicate a maximum of 0.3%/°C relative voltage deviation over a temperature range from 0°C to 90°C. The total power consumption of the proposed voltage monitor is 7 nW at 0.5V, designed in a 28-nm FDSOI technology. The designed digital voltage monitor results in the smallest chip area of 293 2, as compared to the state-of-the-art.