A1 0f J ·K2 Wheatstone Bridge Temperature Sensor With a Tail-Resistor-Linearized OTA

Abstract

This article describes a highly energy-efficient Wheatstone bridge temperature se nsor. To maximize sensitivity, the bridge is made from resistors with positive (silicided diffusion) and negative (poly) temperature coefficients. The bridge is bal- anced by a resistive (poly) FIR-DAC, which is part of a 2nd-order continuous-time delta-sigma modulator (CT 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 μW from a 1.8-V supply and achieves a resolution of 150 μK rms in an 8-ms conversion time. This translates into a state-of-the-art resolution figure-of- merit (FoM) of 10 fJ ·K 2. Furthermore, the sensor achieves an inaccuracy of ±0.4 ◦C( 3 σ) from −55 ◦C to 125 ◦C after a ratio-based one-point trim and systematic non-linearity removal, which improves to ±0.1 ◦C( 3σ) after a 1st-order fit.