Equivalent Noise Analysis and Modeling for a Magnetic Tunnel Junction Magnetometer with In Situ Magnetic Feedback

Magnetic tunnel junction (MTJ) sensors have been one of the excellent candidates for magnetic field detection due to their high sensitivity and compact size. In this paper, we design a magnetometer with in situ magnetic feedback consisting of an MTJ sensor. To analyze and evaluate the detectivity of the MTJ magnetometer, a noise model of the MTJ sensor in the magnetometer without magnetic feedback is first developed. Then, the noise model of the MTJ magnetometer with in situ magnetic feedback is also established, including the noises of the MTJ sensor and the signal conditioning circuit, as well as the feedback circuit. The equivalent noise model of the MTJ magnetometer with in situ magnetic feedback is evaluated through nonlinear fitting for the noise voltage spectrum. Although the noise generated by the MTJ sensor is much greater than that of the signal conditioning circuit, the noise introduced by the feedback coils into the MTJ sensor is slightly more than twice that generated by the MTJ sensor itself. The measurement results show that the detectivity of the MTJ magnetometer with in situ magnetic feedback reaches 526 pT/Hz1/2 at 10 Hz. The equivalent noise analysis method presented in this paper is suitable for the detectivity analysis of magnetometers with magnetic feedback.