Ring Oscillator Based Smart Temperature Sensor Using All-Digital Sigma-Delta Modulator

In this work, an on-chip smart temperature sensor is presented. The design is based on a bias circuit providing two bias currents, two ring oscillators, an up/dow $n$ counter, and a simple binary counter. One bias current has a positive temperature coefficient (PTAT), while the other bias current has a negative temperature coefficient (CTAT). The two currents bias the ring oscillators, producing the PTAT and the CTAT frequency clocks. The outputs of the two oscillators are combined and further processed using the all-digital implementation of time domain Sigma-Delta $(\Sigma\triangle)$ converter. The architecture is designed in 180-nm technology, and the nominal simulation results are presented, together with Monte Carlo analysis. The achieved accuracy $(3\sigma)$ is $\pm 5.4^{\circ}\mathrm{C}$ , within the temperature range from $-40^{\circ}\mathrm{C}$ to $125^{\circ}\mathrm{C}$ , and the mean resolution is $0.293^{\circ}\mathrm{C}$ .