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 C
_top
and C
_bot
, generating V
_ramp,top
and V
_ramp,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 V
_ramp,top
and V
_ramp,bot
via feedback tuning of C
_top
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 °C/-1.53 °C (+0.86 °C/-0.83 °C) and +0.81 °C/-0.75 °C when operating from 0 °C to 100 °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 °C, which after a 0.3 s conversion time results in 230 pJ/conversion.