A Duty-Cycled Integrated-Fluxgate Magnetometer for Current Sensing

This article presents a duty-cycled integrated-fluxgate (IFG) magnetic-to-digital converter for contactless current 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\times $ 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.