Abstract-The work presents the principle and the complete characterization of a single-chip unit formed by MEMS magnetometers to sense the 3D magnetic field vector, and a Tang resonator. The three sensors, nominally with the same resonance frequency, are operated 200 Hz off-resonance through an AC current whose reference frequency is provided by the resonator, embedded in an oscillating circuit. The sensors gain is increased by adopting a current recirculation strategy using metal strips directly deposited on the structural polysilicon. At a driving value of 100 µArms flowing in series through the three devices, the magnetometers show a sub 185 nT/ √ Hz resolution with a selectable bandwidth up to 50 Hz. Over a ± 5 mT full-scale range, the sensitivity curves show linearity errors lower than 0.2%, with high cross-axis rejection and immunity to external accelerations. Under temperature changes, stability of the 200-Hz difference between the magnetometers and the resonator frequency is within 55 ppm/K. Offset is trimmed down to the µT range, with an overall measured Allan stability of about 100 nT at 20 s observation time.