An energy-efficient BJT-based temperature sensor with a continuous-time readout

Abstract

This thesis presents an energy-efficient high-accuracy temperature sensor that combines a BJT front-end with a continuous-time readout circuit. Its front-end is based on PNP transistors, which, compared to NPNs, are more widely available in CMOS processes and less sensitive to stress. In this design, proportional-to-absolute-temperature (PTAT) and complementary-toabsolute-temperature (CTAT) currents are created by forcing ΔVBE and VBE over two resistors
of the same type, after which their ratio is digitized by a continuous-time Delta-Sigma Modulator (CTDSM). As a result, the sampling noise present in traditional switched-capacitor (SC) modulators is eliminated, which improves the sensor’s energy efficiency. High accuracy is achieved by the liberal use of chopping and dynamic element matching techniques. Fabricated in a 0.18µm CMOS process, the sensor achieves a 0.15°C (3σ) inaccuracy over the industrial temperature range (-45°C to 85°C) after a 1-point temperature calibration. It also achieves a 1.24mK resolution in 56.3ms, while consuming only 16µW. This corresponds to a state-of-theart resolution Figure-of-Merit (FoM) of 1.4pJ°C2.