An integrated CMOS micro search‑coil magnetometer with on‑chip calibration and a low‑noise amplifier

This paper presents a fully CMOS‑integrated micro search‑coil magnetometer (µSCM) that achieves a NEMI of 2.1 nT/√Hz at 1 kHz while consuming only 364 µW, approximately a tenfold improvement over previous CMOS search‑coil magnetometers (SCMs). The system integrates a low‑noise instrumentation amplifier (INA) and on‑chip calibration, optimized for operation from 1 Hz to 1 kHz. Implemented in a standard TSMC 180 nm CMOS process, it uses an Integrated‑within‑Aperture layout that places the INA entirely inside the planar spiral inductor's inner diameter, maximizing area efficiency. A dedicated theoretical framework is used to determine the critical line width (w_c) and inner diameter (D_ic) to minimize the noise equivalent magnetic induction (NEMI). 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. Additional features, including a Hall‑effect sensor for DC magnetic field measurements and a temperature sensor, 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.