Studies on Linearizing Direct-Digital Converter Schemes for Thermistors

This paper discusses direct-microcontroller technique based linearizing digital circuits for thermistors. The methodology of a basic digitizer, based on a single mode linearization topology, is discussed first. An improved digital converter with less non-linearity, equipped with dual mode linearization, is then proposed. The resistor parameters of these converters are optimized for non-linearity, using a differential evolution approach. This algorithm converts the inherent constrained optimization problem to an unconstrained one, and arrives at resistor parameters for achieving best linearity. The performance of both (single mode and dual mode) digitizers have been studied using simulation and experimental studies over multiple temperature ranges. Results show that dual mode digitizer provide lower non-linearity than single mode counterpart. The measured non-linearity of dual mode digitizer is 0.47% for 5 degrees C to 45 degrees C and 3.45% for an extended range of 0 degrees C to 120 degrees C.