A Practical Approach for the Evaluation of Noise in Oscillator-Based Resistive Sensor Interfaces

Controlled oscillators are a leading option for sensor interfaces when high input dynamic range (DR) is needed. This is often met in applications like gas, temperature and strain sensing where the low level measurand is embedded in a high DC common-mode signal. Aiming for high DR and high accuracy, with low energy use, challenges the interface linearity and signal-to-noise ratio. Such performance requires the use of specific analytical tools for the design of the interface. In this article a methodology for the quantification of noise-related uncertainty in oscillator-based resistive sensor interfaces is presented. A time-domain analysis of the output oscillation is performed with the aid of classical period jitter tools and long-term stability is assessed with the Allan variance. Finally, an energetic evaluation constrained by the output requirements is carried out. As an application case, the methodology is used to evaluate the performance of a gas sensor interface confirming the need and usefulness of the proposed approach to achieve best accuracy.