Linearized Sigma–Delta-Based Direct Digital Converter for GMR Sensors

Abstract

A direct digital converter, based on the sigma-delta modulation principle, is proposed in this article for giant magnetoresistance (GMR) sensors. The proposed converter intelligently integrates the GMR sensors with an improved sigma-delta modulator and provides a linear digital indication of the input magnetic field. The digital output is obtained directly, without using any analog-to-digital converter modules. Some additional merits of the proposed interface are: 1) requirement of a single reference voltage; 2) easy-to-use facility to tune/enhance the overall sensitivity; 3) low conversion time etc. The modulator circuit is followed by a digital filter and decimation circuit, implemented in a microcontroller unit. This sigma-delta converter is validated extensively using simulation and emulation studies. The results from these studies corroborate well, and the maximum nonlinearity is found to be less than 0.12%. Finally, an experimental prototype is developed with a GMR sensor, and the functionality of the converter is tested for static and time-varying field inputs. The experimental nonlinearity of 0.69% shows the better performance of the proposed scheme with respect to other digital digitizer circuits present in the literature.