AN INHERENTLY LINEAR TRANSDUCER USING THERMAL SIGMA-DELTA MODULATOR

The aim of this article is to describe a feedback circuit with thermoresistive sensor based on thermal sigma-delta modulator. The circuit uses 1-bit first order sigma-delta modulator in which a considerable part of conversion functions is performed by the sensor. This transducer circuit is able to measure digital physical quantities that interact with the sensor: temperature, thermal radiation and fluid velocity. In this study, it is used to measure environment temperature, on which digital output is linearly dependent. Equations that support circuit behaviour, simulation results and experimental results are shown. Two architectures are presented, one completely analogue and other with some parts digitally implemented using microcontroller. In addition, it is presented a thermal radiation architecture version in which digital output is intrinsically linear to the thermal radiation measure.