An Accurate BJT-Based CMOS Temperature Sensor With Duty-Cycle-Modulated Output

This paper describes the design of a precision bipolar junction transistor based temperature sensor implemented in standard 0.7-mu m CMOS technology. It employs substrate p-n-ps as sensing elements, which makes it insensitive to the effects of mechanical (packaging) stress and facilitates the use of low-cost packaging technologies. The sensor outputs a duty-cycle-modulated signal, which can easily be interfaced to the digital world and, after low-pass filtering, to the analog world. In order to eliminate the errors caused by the component mismatch, chopping and dynamic element matching (DEM) techniques have been applied. The required component shuffling was done concurrently rather than sequentially, resulting in a fast DEM scheme that saves energy without degrading accuracy. After a single-temperature trim, the sensor's inaccuracy is +/- 0.1 degrees C (-20 to 60 degrees C) and +/- 0.3 degrees C (-45 to 130 degrees C), respectively. Measurements of sensors in different packages show that the package-induced shift is less than 0.1 degrees C. Measurements of eight sensors over 367 days show that their output drift is less than 6 mK. While dissipating only 200 mu W, the sensor achieves a resolution of 3 mK (rms) in a 1.8-ms measurement time, and a state-of-the-art resolution figure of merit of 3.2 pJK(2). This combination of high accuracy, high resolution, high speed, and low-energy consumption makes this sensor suited for commercial and industrial applications.