An Integrated CMOS Micro Search Coil Magnetometer with On-Chip Calibration and Low-Noise Amplifier

This paper presents a fully CMOS-integrated micro search coil magnetometer (µSCM) with an integrated low-noise instrumentation amplifier (INA) and on-chip calibration capability, optimized for low-frequency magnetic field measurements (1 Hz–1 kHz). The µSCM is implemented using the TSMC 180 nm CMOS process, with a novel layout that maximizes on-chip area efficiency by placing the INA within the critical inner diameter of the planar spiral inductor. The µSCM design is optimized for minimal Noise Equivalent Magnetic Induction (NEMI) through a comprehensive theoretical analysis of key parameters, including line width, line spacing, and inner diameter. The integrated INA employs a nested-chopped current-feedback architecture to mitigate flicker noise, achieving a significant reduction in input-referred noise from 73.45 nV/√Hz to 36.92 nV/√Hz at 100 Hz. Experimental results validate the µSCM’s superior sensitivity, achieving a NEMI of 2.1 nT/√Hz at 1 kHz while consuming only 364 µW, which is more than one order of magnitude better than commercially available CMOS magnetic sensors and previous works. Additional features, including a Hall effect sensor for DC magnetic field measurements and a temperature sensor for compensation, further enhance the system's versatility. This compact, energy-efficient solution is ideal for precision applications such as biomedical diagnostics, environmental monitoring, and energy-efficient systems.