CMOS temperature sensor with built-in ADC

Abstract

An area efficient temperature sensor using Ring Oscillator (RO) is proposed. It is basically implemented with two ROs, one being temperature-sensitive and the other temperature-insensitive. Temperature measurement is done in two steps. Initially, temperature-to-time conversion is performed when temperature-sensitive RO is enabled and then time-to-digital conversion is performed when temperature-insensitive RO is enabled. This two step process optimizes the area because only one counter is sufficient. The feedback provision enables only one RO at once, providing low dynamic power dissipation. A True Single-Phase Clock (TSPC) based high speed counter is employed to meet the requirement. It is designed using UMC 0.18 μm CMOS technology with the supply votage of 1.8 V and the simulation results are presented. The proposed sensor is capable of measuring the temperatures from -55° C to 125° C with the resolution of 5.68 LSB/°C. It dissipates 650 μW with the conversion rate of 300K Samples/S and occupying 10.05 μm2.