Digital Interface for Short-Span Resistive Sensors Using SAR Technology

This paper presents a digitizing interface circuit suitable for resistive sensors with a relatively short output span. The scheme employs an improved successive approximation register (SAR)-based technique for digitization. The proposed architecture offers good performance for short-span sensors while retaining the inherent advantages of the SAR method. The mathematical methodology of the circuit solution is detailed and analyzed. Simulation studies are conducted to verify the effectiveness of the scheme. Results show that the scheme provides a low nonlinearity error (0.07%) when interfaced with a sensor having a base resistance of 5 k Ω and a span of 500 Ω. Further, experimental evaluation of the circuit is carried out with both a synthesized resistive sensor and a commercial magnetoresistance (MR) sensor. The practicality of the scheme is established through these tests. Results indicate that the scheme can serve as an effective linearizing interface for low-field MR-based magnetometers.