A 10 fJ.K2 Wheatstone Bridge Temperature Sensor With a Tail-Resistor-Linearized OTA

This article describes a highly energy-efficient Wheatstone bridge temperature sensor. To maximize sensitivity, the bridge is made from resistors with positive (silicided diffusion) and negative (poly) temperature coefficients. The bridge is balanced by a resistive (poly) FIR-DAC, which is part of a 2nd-order continuous-time delta-sigma modulator (CT Delta Sigma M). Each stage of the modulator is based on an energy-efficient current-reuse OTA. To efficiently suppress quantization noise foldback, the 1st stage OTA employs a tail-resistor linearization scheme. Sensor accuracy is enhanced by realizing the poly arms of the bridge and the DAC from identical unit elements. Fabricated in a 180-nm CMOS technology, the sensor draws 55 mu W from a 1.8-V supply and achieves a resolution of 150 mu K-rms in an 8-ms conversion time. This translates into a state-of-the-art resolution figure-ofmerit (FoM) of 10 fJ.K-2. Furthermore, the sensor achieves an inaccuracy of +/- 0.4 degrees C (3 sigma) from -55 degrees C to 125 degrees C after a ratio-based one-point trim and systematic non-linearity removal, which improves to +/- 0.1 degrees C (3 sigma) after a 1st-order fit.

Automated summary

This article presents a highly energy-efficient Wheatstone bridge temperature sensor with improved sensitivity and accuracy achieved through the use of specialized resistors and DAC. The sensor demonstrates high resolution and precision with improved accuracy across different temperature ranges after calibration and non-linear processing.