A 310 nW Temperature Sensor Achieving 9.8 mK Resolution Using a DFLL-Based Readout Circuit

This paper reports a high-performance, low-power temperature sensor suitable for wireless IoT devices/RFID tags. The system utilizes a mostly digital approach to achieve energy-efficient, sub-μW operation with a resistor-based temperature sensor. A sampled, incomplete-settling, switched-capacitor-based Wheatstone bridge is read out using a digital frequency-locked loop (DFLL) while harnessing the quasi-periodic limit cycles to reduce in-band noise. Implemented in a 65 nm CMOS process, it consumes 310 nW and achieves 9.8 mK resolution in a 10 ms conversion time. This results in a 297 fJ∙K2 figure-of-merit (FoM) and low energy (3.1 nJ/meas.).