Achieving Low-Noise, High-Bandwidth, Nanoscale-Resolution Position Sensing with GMR Sensors

This article presents a low-noise high-bandwidth giant magnetoresistance (GMR) sensor-readout circuit for nanometer resolution position sensing, critical requirement in several precision applications such as Atomic Force Microscopy (AFM). The main impediment to performance is the GMR sensor’s significantly higher 1/f noise extending over large bandwidths, thereby limiting achievable SNR. Therefore, sensing system needs be designed at level order minimize excess intrinsic generation and transmission, well external pickup. characteristics of sensor its readout components, their effect on SNR, are investigated analytically experimentally. A general process designing circuit, applicable not just sensors but also other high-1/f-noise sensors, presented. 2.5 nm bandwidth 100 kHz demonstrated an AFM nanopositioner, ten-fold improvement previously reported comparable state-of-the-art, more complex, capacitive sensors. scheme simple implement using COTS components easily extendable even unlike schemes, modulation/demodulation, where increasingly carrier frequencies renders further improvements impractical.