A 763 pW 230 pJ/Conversion Fully Integrated CMOS Temperature-to-Digital Converter With+0.81 °C/-0.75 °C Inaccuracy

A sub-nW fully integrated temperature sensor is presented that digitizes temperature via a capacitive charging time feedback loop controlled by a least significant bit (LSB)-first algorithm. Specifically, an ultra-low-power current reference generator charges two metal-insulator-metal (MIM) capacitors Ctop and Cbot, generating Vramp, top and Vramp, bot which are then compared to a constant with temperature (CWT) voltage and a proportional to absolute temperature (PTAT) voltage, respectively. Temperature is then digitized by matching the charging time between the Vramp, top and Vramp, bot via feedback tuning of Ctop driven by an energy-efficient digital processing unit (DPU) for direct ultra-low-power digital readout. The design is fabricated in 65 nm complementary metal-oxide-semiconductor, and measurement from 12 samples reveals a maximum temperature error of +1.61 degrees C/-1.53 degrees C (+ 0.86 degrees C/-0.83 degrees C) and + 0.81 degrees C/-0.75 degrees C when operating from 0 degrees C to 100 degrees C after two-point (three-point) calibration without and with trimming, respectively. Operating from a 0.5 V supply, the 12 samples consumed an average power of 763 pW at 20 degrees C, which after a 0.3 s conversion time results in 230 pJ/conversion.