Digital interface circuits using sigma-delta modulation for integrated micro-fluxgate magnetic sensors

This paper presents a high-resolution micro fluxgate magnetic sensor interface circuit based on 2nd-order sigma-delta modulation. The fluxgate sensing element is placed in the modulation loop. This technique allows us to realize pulse negative feedback in the magnetic flux domain, and the instability due to the use of a ferromagnetic core can be reduced. As one of the integrators, a continuous-time integrator is used, and that is also used for the multi-aliasing filter for phase sensitive detector output. The oversampling A/D conversion using 2nd-order sigma-delta modulation results in the high-precision detection of extremely weak magnetic field in the order of sub-nanotesla. The interface circuit chip is designed and evaluated by circuit simulation and behavior-level simulation