Symmetric Response Magnetoresistance Sensor With Low 1/f Noise by Using an Antiphase AC Modulation Bridge

S Shirotori,Y Higashi,Y Kurosaki,H Iwasaki,A Kikitsu

doi:10.1109/tmag.2020.3012655

S Shirotori, Y Higashi + Show 3 more

Open Access

https://doi.org/10.1109/tmag.2020.3012655

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Journal: IEEE transactions on magnetics	Publication Date: Jul 30, 2020
Citations: 19	License type: CC BY 4.0

Affiliation: Toshiba (Japan)

Abstract

A new high-sensitive magnetic sensor which is referred to a symmetric response magnetoresistance (SRMR) sensor is proposed. This sensor uses giant magnetoresistance (GMR) elements which have symmetric field response. An ac magnetic field with frequency f is applied to the GMR elements in order to modulate a small detecting magnetic field. Due to the symmetric response of the MR element, a carrier signal of the ac magnetic field is converted to 2f and the detecting signal is converted to f . By using a full bridge circuit, where two pairs of GMR elements have opposite phase of the applied ac field, the 2f components can be eliminated at the differential output terminal of the bridge. Since this system converts the frequency range of the detecting magnetic field to higher one, its noise level, which is dominated by the 1/f noise, can be decreased. In this study, the SRMR sensor with the antiphase ac modulation bridge was fabricated and investigated. The effect of noise reduction and carrier signal suppression were confirmed by a circuit simulation based on the fabricated GMR element. A full-bridge circuit using four dual-spin-valve GMR elements was fabricated. It was confirmed that the carrier signal (2f components) was reduced to less than the signal level (f components). An increase in the noise level was found at the frequency range near f, which may be due to slight asymmetry shown in the magnetoresistance (MR) response.

Highlights

H IGH-SENSITIVITY magnetic sensors have attracted much attention for the detection of weak magnetic field from the human body [1]
Suppressing the influence of huge 1/ f noise is important because the signal in the above applications lies in the frequency range of less than 100 Hz
The Hooge-like parameter α, which is related to the 1/ f noise level, was defined 2 × 10−12 by the following power spectrum density equation [23]: Sv = α × V 2 (2)

Summary

INTRODUCTION

H IGH-SENSITIVITY magnetic sensors have attracted much attention for the detection of weak magnetic field from the human body [1]. In order to resolve the signal distinguishing problem in the ac modulation method, a high-sensitive MR sensor named symmetric response MR (SRMR) is developed. It uses ac modulation of the response of MR elements, but the detected signal and the ac carrier signal are converted to different frequencies by employing MR elements with a response of the even function. A concept of the SRMR sensor system and the antiphase ac modulation bridge is explained Basic functionality of this method, that is, the reduction of the noise level and the elimination of the carrier signal is investigated by a circuit simulation. Experimental results based on the fabricated sample using four dual-pinned type spin valve MR elements are demonstrated

CONCEPT OF THE SRMR SENSOR WITH ANTIPHASE AC MODULATION BRIDGE

SIMULATION RESULTS

EXPERIMENTAL RESULTS

CONCLUSION