A CMOS Smart Temperature Sensor with One Homogeneous Delay Line and Curvature Compensation

Abstract

A CMOS time-domain smart temperature sensor with one homogeneous delay line and curvature compensation is presented for accuracy improvement. For temperature sensing, a temperature-sensing delay line was used to generate a thermal pulse with a width (tp) proportional to absolute temperature. However, a curvature exists on the temperature-to-time transfer curve of the delay line to seriously affect the output linearity. By adding a thermal-compensated circuit on the pulse-shrinking unit, the pulse-shrinking amount (i.e., time resolution, R) can correct the curvature of the thermal-sensing time tp to generate a linearized output so as to improve the sensor accuracy. The cyclic homogeneous delay line is constructed by all identical NAND gates to eliminate undesirable pulse-shrinking amount for further accuracy enhancement and to improve the thermal sensitivity of tp for area saving. The proposed sensor only occupied 0.022 mm2 in a 0.35-μm CMOS process. The inaccuracy is reduced from -1.6∼1.1°C to ±0.7°C in a range of 0∼100°C. To the best of our knowledge, the circuit area is the best among the related works.