Design and Experimental Verification of A 2.1 nW 0.018 mm² Slope ADC-Based Supply Voltage Monitor for Biofuel-Cell-Powered Supply-Sensing Systems in 180-nm CMOS

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This brief presents a slope analog-digital converter (ADC)-based supply voltage monitor (SVM) for biofuel-cell-powered supply-sensing systems operating in a supply voltage range of 0.18-0.35 V. The proposed SVM is designed to utilize the output of energy harvester extracting power from biological reactions, realizing energy-autonomous sensor interfaces. A burst pulse generator uses a dynamic leakage suppression logic oscillator to generate a stable clock signal under the subthreshold region for pulse counting. A slope-based voltage-to-time converter is employed to generate a pulse width proportional to the supply voltage with high linearity. The test chip of the proposed SVM is implemented in 180-nm CMOS technology with an active area of 0.018 mm². It consumes 2.1 nW at 0.3 V and achieves a conversion time of 117-673 ms at 0.18-0.35 V with a nonlinearity error of -5.5/+8.3 mV, achieving an energy-efficient biosensing frontend.