Flat Bandwidth Expansion for Spin-Valve GMR Magnetic Field Sensors

A magnetic field sensing system based on the combination of giant magnetoresistance (GMR) sensors driven by different schemes is investigated to achieve a high flat bandwidth. The system utilized a summing amplifier to combine the high-frequency (HF) and low-frequency (LF) sensors of unified sensitivity. The field modulated GMR, which is non-hysteretic and highly linear, is used as the LF sensor, while the GMR sensor operated with a dc bias field serves as the HF sensor. It is found that the total sensitivity of the combined system is constant at 4398 V/T when the second-order low-pass and high-pass filters are used. A -3 dB flat bandwidth of sensitivity is as high as 100 kHz for the second-order system, but the phase angle turns over at the transition frequency of 100 Hz. The first-order system has a moderate flat bandwidth of 40 kHz while the phase lag is less than 9.4° up to 100 Hz. The proposed systems are useful in measurement of dc and transient magnetic fields as well as non-contact monitoring of static and alternating electric currents.