A 9.7-nTᵣₘₛ, 704-ms Magnetic Biosensor Front-End for Detecting Magneto-Relaxation

This article reports a low-noise magnetic sensor front-end with an 18-bit Zoom ADC for detecting temporal magnetic nanoparticle (MNP) relaxation. Techniques such as dynamic element matching (DEM) and magnetoresistive correlated double sampling (MRCDS) are proposed to remove the sensor and analog front-end (AFE) 1/
${f}$
noise while a fast-settling Miller compensation (FSMC) technique is proposed to reduce the amplifier power. Collectively, these result in state-of-the-art input-referred noise performance (9.7 nT
_rms
) and a figure-of-merit (FoM) that is 6.6
$\times $
and 210
$\times $
better than previously reported magnetic sensor and relaxation-based AFEs, respectively. A relaxation-based magnetic immunoassay (MIA) was performed to demonstrate the concept. This design is implemented in a 0.18-
$\mu \text{m}$
CMOS process and consumes 4.32 mW from a 1.8-V supply.