A Low Noise CMOS Sensor Frontend for a TMR-based Biosensing Platform

In this paper, we propose a low noise CMOS frontend for a Point-of-Care (PoC) biosensing platform based on tunnel magnetoresistance (TMR) as sensors. The integration of a low noise and low power integrated circuit (IC) with the TMR sensors reduces power consumption compared to a realization with discrete electronics, and thereby paves the way towards a portable diagnostic system. The proposed chip uses a DCcoupled fully differential difference amplifier (FDDA) to amplify the minute signals generated by magnetic nanotags (MNTs) that will be used as biomarkers in the target biosensing application. The FDDA features a gain of around 60dB with a suitable offset calibration scheme to deal with the large DC offsets caused by TMR and/or magnetic field variations. The ability to deal with changing DC fields is crucial for a portable setup that is intended to be used in unshielded environments outside the lab. The offset cancellation is achieved by two on-chip current steering DACs that can accommodate TMR resistances between 535 Ω and 4.7kΩ. The presented chip is manufactured in a 180nm SOI CMOS technology and features a thermal noise floor of 7 nV/√Hz. It consumes a total of 7.7 mA from a 1.8V supply.