Smart Temperature Sensor Using Ring Oscillators and All‐Digital Sigma‐Delta Modulator in 180‐nm Technology

ABSTRACT A ratiometric time‐domain temperature sensor is presented in this work. The front‐end of the sensor generates two temperature‐dependent currents: proportional to absolute temperature (PTAT) and complementary to absolute temperature (CTAT), which bias two ring oscillators, the first of which generates the PTAT clock and the second the CTAT clock. The clocks are combined within an all‐digital sigma–delta converter consisting of an up/down counter, a Flip‐Flop, and a 12‐bit counter. The sensor occupies an area of only 0.019 mm 2 , which gives it an advantage over the vast majority of smart temperature sensors in 180‐nm technology, including some sensors in lower nodes. The min/max accuracies of the measured 12 parts are −0.6/+6.6°C achieved with the 1‐point and −2.7/+2.3°C achieved with the 2‐point trimming. The nominal resolution of the sensor is 0.3°C (effective resolution is 0.37°C and ENOB is 8.8 bits) and the measuring range is −40 to 125°C.