Novel Σ-Δ-Based Direct Digitizers for Single-Element Resistive Sensors With Considerations on Lead-Wire Compensation

Abstract

This work proposes the design and performance studies of two sigma-delta modulation-based direct-digital converters (DDCs) for single-element resistive sensors. Both the interfaces produce linear digital output, without using a separate analog-to-digital converter. The first of the two designs is a simple direct-digital interface that can be used in all applications where the lead wires, connecting the sensor element to the modulator interface, possess negligible resistance. The second DDC circuit is an enhanced version of the first design and produces digital output, independent of error due to lead-wire resistance. Thus, this improved modulator interface can be efficiently used in remote measurement applications. Moreover, both interfaces possess further useful features, such as output-span enhancement facility, fast conversion rate, use of single regulated voltage source, and relatively low implementation cost. Performances of the proposed interfaces are studied comprehensively through simulation and experimental validation. The maximum experimental nonlinearities, in the two designs, are found to be around 0.25%. This proves the primary efficacy of the schemes in producing linear output characteristics. Moreover, the enhanced sigma-delta digitizer exhibits a maximum error of just 0.1% for variations in lead-wire resistance. A detailed comparison study brings out efficacies of the proposed interfaces.