A 0.6V$-$1.8V Compact Temperature Sensor with 0.24°C Resolution, $\pm$1.4°C Inaccuracy and 1.06nJ per Conversion

Abstract: This paper presents a fully-integrated CMOS temperature sensor for densely-distributed thermal monitoring in systems on chip supporting dynamic voltage and frequency scaling. The sensor front-end exploits a sub-threshold PMOS-based circuit to convert the local temperature into two biasing currents. These are then used to define two oscillation frequencies, whose ratio is proportional to absolute-temperature. Finally, the sensor back-end translates such frequency ratio into the digital temperature code. Thanks to its low-complexity architecture, the proposed design achieves a very compact footprint along with low-power consumption and high accuracy in a wide temperature range. Moreover, thanks to a simple embedded line regulation mechanism, our sensor supports voltage-scalability. The design was prototyped in a 180nm CMOS technology with a 0{\deg}C $-$ 100{\deg}C temperature detection range, a very wide supply voltage operating range from 0.6V up to 1.8V and very small silicon area occupation of just 0.021$mm^2$. Experimental measurements performed on 20 test chips have shown very competitive figures of merit, including a resolution of 0.24{\deg}C, an inaccuracy of $\pm$1.4{\deg}C, a sampling rate of about 1.5kHz and an energy per conversion of 1.06nJ at 30{\deg}C.