Interface Circuit for Low-Resistance Sensors Based on Noise Cancelling Technique

A resistive sensor is conventionally biased by a voltage divider or a Wheatstone bridge. Applying a precise bias on a low-resistance sensor with these conventional approaches, however, necessarily requires calibration of the components, which is time-consuming and costly for mass production. In this paper, we propose an analog front-end circuit for low-resistance sensors, based on a closed-loop bias circuit with high-impedance output, which does not require any calibration. In addition, after a comprehensive analysis of the bias noise, we introduce a noise canceling technique, which allows more than 25 dB reduction of the bias noise in the complete interface circuit, even in the presence of gain mismatches as large as 5%.