An 11-nW CMOS Temperature-to-Digital Converter Utilizing Sub-Threshold Current at Sub-Thermal Drain Voltage

A fully integrated CMOS temperature-to-digital converter utilizing MOSFETs in the sub-threshold region is proposed. The temperature-to-digital converter achieves the ultra-low power operation required for Internet of Things (IoT) nodes. The proposed principle takes the ratio of the sub-threshold currents of two nMOSFETs whose drain voltages are maintained well above and well below the thermal voltage, respectively. The proposed circuit implementation of the temperature-to-digital converter achieves ultra-low power consumption of 11 nW at room temperature of 25 °C. Measurement results of the proposed temperature sensor fabricated in a 180-nm CMOS process show -0.9/+1.2 °C peak-to-peak inaccuracy over a temperature range of -20 °C to 80 °C after a two-point calibration while achieving a resolution of 145 mK.