An Automatic Loop Gain Enhancement Technique in Magnetoimpedance-Based Magnetometer

Abstract

A low-power, low-noise, and high-bandwidth mag- netometer that utilizes the magnetoimpedance (MI) element as a sensor head is presented. The MI element has a high sensitivity, and it can be implemented in the mm-scale through the MEMS process. The analog front-end (AFE) circuit of the magnetometer includes a digital calibration scheme that automatically enhances the loop gain of the system, resulting in high bandwidth and low-noise characteristics. The AFE circuit is designed based on a switched-capacitor (SC) approach, and its dedicated switching scheme can suppress the folded noise of an amplifier. A single- coil magnetic negative feedback architecture with correlated double sampling (CDS) enables to achieve a high dynamic range (DR) and stable passband gain in addition to simplifying the structure of the MI element. The AFE chip of the magnetometer is implemented in a 0.18- µm CMOS process, and it achieves an 8-pT/√Hz noise floor within a 31-kHz bandwidth and the DR of 96 dB, where the power consumption is 1.97 mW.