A Duty-Cycled Integrated-Fluxgate Magnetometer for

Abstract

This article presents a duty-cycled integrated- fluxgate (IFG) magnetic-to-digital converter for contactless cur- rent sensing. While previous works have proven high linearity, low noise, and low offset capabilities of fluxgate sensing, this work focuses on low energy operation. The mixed-signal front-end design enables energy-efficient duty cycling with a 13-bit digital integrator to retain the last converged output during sleep mode and resume searching in its vicinity upon wake up. The system achieves a ±2.4 mT measured range of magnetic fields for indirect current measurement. The hierarchical search modes achieve 10× faster convergence than analog implementations. The faster readout with a peak sampling rate of 770 kS/s translates to lower compensation energy per sample. The 3-dB bandwidth of 125 kHz is 67% higher than prior IFG art, with competitive 500-nT rms noise. The test chip fabricated in 250-nm CMOS technology consumes the lowest power of known IFG works. It can be duty-cycled to save energy in low-bandwidth applications or run at peak bandwidth for low latency.