A 65-nm CMOS 0.4 V 49.6 nW Voltage Monitor for Small-Form-Factor Biomedical IoT Applications

This paper presents a low-power voltage monitor for small-form-factor, low-sample-rate biomedical Internet of Things (IoT) applications aiming to convert the analog output voltage 0–0.2 V of a biosensor into digital code. This design consists of 3 oscillators and a periphery logic circuit. A reference oscillator that can provide stable output frequency even supply voltage floats range of 0.35–0.45 V. Two sensitive oscillators which the output frequency will change rapidly due to the output voltage from biosensors. A resistive input stage is used in each sensitive oscillator to improve the linearity of the output. The SPICE simulation performed in 65-nm CMOS technology shows that the nonlinearity error is within −1.56 mV/+1.19 mV when the input voltage is 0–0.2 V, much lower than previous works. The power consumption of this design is 49.6 nW when the voltage supply is 0.4 V.