A 162nW, 0.845pJ/step Resistance-to-Digital Converter for Miniature Battery-Powered Sensing Systems.

This paper proposes a 162nW resistance-to-digital converter (RDC) for miniature battery-powered sensing systems. The RDC first converts input resistance to a pulse by charging a capacitor to a threshold voltage with a current proportional to the resistance. It compensates temperature sensitivity of the charging current by generating the threshold voltage with the same temperature dependency. Then, the circuit digitizes the pulse using an up-down counter that cancels temperaturedependent delay and offset of the low-power comparator in a digital Correlated Double Sampling (CDS) style. Designed in a 180 nm CMOS process, the proposed circuit achieves a figureof-merit (FoM) of 0.845pJ/c.s. in simulation, with a conversion time of 50 ms for input resistance from 50k Omega to 1M Omega, while consuming 162nW at a supply voltage of 900 mV. Also, it obtains a temperature sensitivity of 26.9ppm/degrees C from -40 to 100 degrees C. Compared with the state-of-the-art RDCs, this work improves the FoM and temperature sensitivity by 42.91% and 11.52%, respectively.