An all-digital CMOS temperature sensor with a wide supply voltage range

Abstract

This paper proposes a MOSFET-based all-digital temperature sensor fabricated in a standard 55-nm CMOS process. The temperature sensing elements of the sensor are composed of ring oscillators, which convert temperature information into frequency information. The frequency ratio's proportional to absolute temperature (PTAT) feature is generated by using two separate frequency oscillators with varied temperature sensitivity. The frequency-to-digital converter (FDC) converts frequency information into digital representation without introducing any overhead reference clock. A die area of 1915 µm 2 is occupied, owing to the all-digital architecture. After two-point calibration, the proposed sensor achieves an error of −0.4 • C∼+0.6 • C throughout a temperature range of −40 • C∼125 • C. With the help of class-adjustable oscillators, the sensor can function in a wide supply voltage range from 0.5 V to 1.2 V. It obtains a resolution of 0.166 • C at room temperature with a dissipation of 2.5 µW.