A Pipeline-TDC-Based CMOS Temperature Sensor with a 48 fJ·K² Resolution FoM

An energy-efficient temperature sensor is important for temperature monitoring in Biomedical Internet-of-things (BIoT) applications. This article presents a time-domain temperature sensor with a pipeline time-to-digital converter (TDC). A programmable-gain time amplifier (PGTA) with high linearity and wide linear range is proposed to improve the resolution of the sensor and to reduce the chip area. The conversion time of the sensor is reduced by the fast TDC that only needs ~26 ns/conversion, which means the sensor is suitable for BIoT applications that commonly use duty cycling mode. Fabricated in a 40 nm standard CMOS technology, the sensor consumes 7.6 μA at a 0.6 V supply and achieves a resolution of 90 mK and a sensitivity of 0.62%/°C in a 1.3 μs conversion time. This translates into a resolution figure-of-merit of 48 fJ·K2. The sensor achieves an inaccuracy of 0.39 °C from −20 °C to 80 °C after two-point calibration. Duty cycling the sensor results in an even lower average power: ~18.6 nW at 10 conversions/s