An Inaccuracy of +/- 0.5 degrees C Digital Temperature Sensor From-40 degrees C to 125 degrees C With Curvature Correction

This paper proposes an all-digital and MOSFET-based temperature sensor which is fabricated in 110-nm CMOS process. The sensor utilizes ring oscillators as temperature sensing elements which convert temperature information to frequency information. The proportional to absolute temperature (PTAT) characteristic of the frequency ratio is obtained by using two different frequencies which perform different temperature sensitivities. The frequency information is digitalized by the frequency-to-digital converter (FDC) without introducing overhead reference clock. Furthermore, different frequencies are generated from different threshold voltages of transistors due to the effect of reverse narrow width and the effect of reverse short channel. An area of only 3355 um(2) is occupied benefited from the all-digital architecture. Moreover, in order to obtain a satisfactory accuracy, the polynomial fitting is adopted and the quantization error induced by asynchronous oscillators is optimized The presented sensor achieves an inaccuracy of +/- 0.5 degrees C after two-point calibration which operates from -40 degrees C to 125 degrees C. The sensor obtains a resolution of 0.14 degrees C and a resolution figure of merit (FOM) of 0.1 nJK(2).