A Simple Digital Interface Circuit for Giant Magneto-Resistance Sensors

Giant Magneto-Resistance (GMR) sensor-elements are usually configured in a Wheatstone bridge form. In this work, a new simple interface circuit with a microcontroller is proposed to identify the fractional-resistance change of GMR sensor using the discharge times of the capacitor. An Op-amp is used to avoid the effect of the mismatch of unshielded-resistance of the GMR sensor. This method just uses three conversion modes to make the output immune to the pin-resistance of the microcontroller. Simulation and emulation studies of the proposed interface are performed. A worst-case nonlinearity of 0.35% is observed. A hardware model of the interface is tested with the GMR sensor and the associated results are also reported in this paper.