Resolution enhancement in measuring low-frequency magnetic field of tunnel magnetoresistance sensors with AC-bias polarity technique

The noise analysis is an indispensable investigation to find out the appropriate solutions for the enhancing resolution in the magnetic sensor developments. Especially, the tunneling magnetoresistance (TMR) sensor, which is one type of resistive sensors, is a promising candidate for biomedical applications and security detections. However, these applications have the magnetic field radiations in the dc or very low-frequency regimes, where the low-frequency noise (1/f noise) component is dominant. To suppress the 1/f noise, an AC-bias circuit for TMR-bridge sensor was investigated and implemented. The obtained experimental results and designed driving circuit showed a significant reduction of the 1/f noise. The intrinsic noise of TMR2102 sensor at 1 Hz (∼9 nT/√Hz@1Hz) was eliminated by a factor of 5. By applying the AC-bias technique the field noise level was reduced down to ∼1.7 nT/√Hz@1Hz. The angular response of the TMR sensor using the proposed read-out circuit was also demonstrated in the measuring Earth magnetic field with a magnetic deviation was less than 0.1 µT. The TMR bridge sensor driven by an AC biased voltage is a promising approach for lessening the noise disturbances. Especially, it is the 1/f noise component in the weak magnetic field measurements. The proposed circuit could be applied for improving the resolution of the other resistive sensor types in the measuring low-frequency applications, such as strain gauges, load cells, and pressure sensors.