Simple and Efficient Relaxation-Oscillator-Based Digital Techniques for Resistive Sensors — Design and Performance Evaluation

This article proposes simple relaxation-oscillator-based digital interfacing schemes for resistive sensors in single-element and quarter-bridge forms. The proposed interfaces, equipped with novel compensation techniques, render a direct-digital output proportional to sensor resistance. These interfaces offer many meritorious features, such as simplicity of design, nonrequirement of the reference voltage, lower execution time, and negligible influences from circuit nonidealities. The methodology of the interfaces and their design criteria and error analysis are described in this article. The first two interfaces are suitable for nonremote resistive sensors, while the third interface has been developed for remotely located resistive sensors. The functionality of the proposed interfaces has been verified using simulation as well as detailed experimental studies. The developed interfaces provide a linear direct-digital output, and the maximum experimental nonlinearity is merely 0.08%. Later, a representative sensor based on the giant magnetoresistance (GMR) phenomenon is selected, characterized, and tested with the developed interfaces. The complete instrumentation system is shown to act as a linear digital magnetometer. Finally, the performance of the developed interfaces is compared and shown to be better/comparable with respect to the existing works.