A PNP-Based Temperature Sensor With Continuous-Time Readout and ±0.1 °C (3σ) Inaccuracy From-55 °C to 125 °C

This article describes a PNP-based temperature sensor that achieves both high energy efficiency and accuracy. Two resistors convert the CTAT and PTAT voltages generated by a PNP-based front-end into two currents whose ratio is then digitized by a continuous-time (CT) Delta Sigma -modulator. Chopping and dynamic-element-matching (DEM) are used to mitigate the effects of component mismatch and 1/f noise, while the spread in VBE and in the ratio of the two resistors is digitally trimmed at room temperature (RT). Fabricated in a 0.18 mu m CMOS process, the sensor occupies 0.12 mm2, and draws 9.5 mu A from a supply voltage ranging from 1.7 to 2.2 V. Measurements on 40 samples from one batch show that it achieves an inaccuracy of +/- 0.1 degrees C ( 3 sigma ) from -55 degrees C to 125 degrees C, and a commensurate supply sensitivity of only 0.01 degrees C/V. Furthermore, it achieves high energy efficiency, with a resolution Figure of Merit (FoM) of 0.85 pJ center dot K-2.