Development on Linearizing Front End and Amplification Structure for Commercial GMR Sensor-based Cardiorespiratory...

Magnetoplethysmogram (MPG) is typically acquired by placing a giant magnetoresistance sensor (GMR)-magnet system in a blood vessel's (e.g., radial artery) vicinity. This brief analyzed multiple linearizing front ends for the GMR-magnet system. GMR based analog front end's (AFE) gain requirement is derived through COMSOL and MATLAB-based simulation considering the raw signal data. After that, we designed a fully differential difference amplifier (FDDA) in 0.18 µm, 1.8 V process using the SPICE environment for amplification of MPG signals. An automatic calibration method is used for compensating the GMR sensor's offset and lowering it to a few µV level during constant current excitation. This proposed GMR-magnet system is a stepping stone towards noninvasive arterial pulse waveform (APW) detection using the MPG principle, with or without direct skin contact. The DDA achieves open and closed-loop gain of 102 dB and 32 dB, phase margin of 62^◦, an IRN of 1.8µV, and a unity-gain frequency of 32kHz, resulting in a closed-loop bandwidth of 800 Hz while dissipating 1.2 µA from a 1.8-V supply.