Design and Experimental Verification of 0.9-2.6pW 0.1-0.25V 22nm 2-bit Supply-to-Digital Converter Using Always-Activated Supply-Controlled Oscillator and Supply-Dependent-Activation Buffers for Bio-Fuel-Cell-Powered-and-Sensed Time-Stamped Bio-Recording

The sensor with low power consumption, small area and low operational voltage is particularly important for power-limited, area-limited sensors such as in-body sensors. This paper presents a low power supply-to-digital converter (SDC) for bio-recording system where bio-fuel-cell provides both power and sensing data. It is achieved by a supply-controlled oscillator, supply-dependent activation buffers (SDAB) with different V-thresholds, and an encoder. A prototype chip was fabricated using 22nm CMOS ULL and exhibits its feasibility with a power of 0.9-2.6 pW under 0.1-0.25 V. The chip size reached 0.00028 mm2. Design methodologies for minimizing power consumption and controlling buffer V-threshold of SDAB, which is the keys in this work, are introduced.