High-precision biomagnetic measurement system based on tunnel magneto-resistive effect

This paper presents a novel low-noise and high-precision readout circuit for tunnelling magnetoresistive (TMR) array to evaluate the suitability of biomagnetic measurement platform for detection of weak biomagnetic fields. We propose a three operational-amplifier architecture with a high input impedance and an adjustable gain for the fabricated TMR sensor that is highly miniaturized and can be operated at room temperature. The proposed system was designed using standard 0.18 µm CMOS technology and achieved a good performance with regard to gain, linearity, power consumption, and noise by employing a chopper stabilization technique and common mode feedback. The gain can reach 80 dB through adjusting two 5-bit programmable resistors and the input-referred noise voltage only has 44.6 nV/vHz with 10 nA input bias over a wide range of frequency. Moreover, the whole readout dissipates 58 µW of power with a 1.8 V supply voltage. Benefiting from the CMOS compatibility of the TMR sensor, it offers monolithic integration directly on a silicon substrate as a TMR-on-chip sensing system. This will enable a new scientific and engineering paradigm to revitalize the biomagnetism field as an alternative way to understand the underlying mechanism of the human body.