A 13nW temperature-to-digital converter utilizing sub-threshold MOSFET operation at sub-thermal drain voltage

A new principle of temperature sensing based on a sub-threshold MOSFET operation at sub-thermal drain voltage is proposed. The proposed external-reference-free temperature-to-digital converter with on-chip proportional-to-absolute-temperature (PTAT) digital output achieves the lowest power consumption of 13nW at 0.8V. The proposed principle takes the ratio of two sub-threshold currents with different drain voltages. The principle is implemented using op-amp-free current generators and relaxation oscillator based current-to-frequency converters for ultra-low power operation. Measurement results from 8 chips fabricated in a 180-nm CMOS process achieve 110mK resolution and -0.7/+1.3°C inaccuracy over a temperature range of -20°C to 80°C.