Recent advances in various fields like high speed wireless communication links, big data processing etc., has enabled the implementation of large distributed sensor systems. And with the onset of the era of Internet of Things (IoT), demand for self-sustaining and efficient sensors is ever growing. Consequently, due to their economical and complex integration benefits, CMOS based sensors have gained a lot of attention in implementations of distributed sensor systems for vast number of applications.

Applications of wireless distributed temperature sensor systems (WDTS) are often limited by the power consumed and area occupied by each sensor node. Recent works in building ultra-low power high temperature sensors has enabled the sensor core to operate on powers of the order of tens of µW to few hundred nW and occupy an area on the order of mm2. In this work, we propose a new ring oscillator based temperature sensor in 0.18µm CMOS SOI process is developed. A high resistive NOT gate is used as a single stage of the proposed ring oscillator to minimize the power consumed by the oscillator. The proposed oscillator generates oscillations of frequencies from 0.222 KHz to 13.089 KHz over a temperature range of 130°C to 260°C and consumes a maximum power of 2.052nW of power at 260°C.

Also a low power custom SRAM with control digital circuitry is designed to be integrated with the sensor and energy harvesting blocks to develop a complete wireless temperature sensor node for geothermal reservoirs.