CMOS temperature sensor using a current starved ring oscillator for low power and low leakage IOT applications

This paper presents a CMOS temperature sensor working at sub-threshold voltage (Sub-VTh) for ultra low power applications. The sensor consists of a proportional-to-absolute-temperature (PTAT) current element that starves a current starved ring oscillator (CSRO). Since the circuit is designed in Sub-VTh, it enables ultra low power applications. But at the same time it becomes highly vulnerable to variations due to changes in process thereby resulting circuit currents to vary from die to die. An architecture is proposed where a bit-weighted current mirror (BWCM) is incorporated with CSRO to mitigate the effect due to process variations in the PTAT current. Lastly we have integrated the CSRO with a frequency to digital converter that converts the oscillator output signal into digital bits. Designing of the temperature sensor system is done in 180nm CMOS technology. The output frequency of the CSRO was found to be 50 Mhz. The sensor is operated at a VDD of 0.2V and the power consumed is 3.75 pW.