A Frontend for Magnetoresistive Sensors With a 2.2-pA/√Hz Low-Noise Current Source

In this letter, we present an integrated readout chip for magnetoresistive (MR) sensors consisting of a readout chain that comprises a dc-coupled fully differential difference amplifier (FDDA) followed by a programmable gain amplifier (PGA), as well as a low-noise current biasing scheme for the MR sensor. The current bias scheme features a 10-bit digital-to-analog converter (DAC) to compensate for process variations of the MR sensing element as well as to calibrate for variations in the dc bias field of the sensor. The bias current source achieves a very low current noise floor of 2.2 pA/
$\sqrt {\mathrm {Hz}}$
for bias currents up to 1 mA. The readout chip is manufactured in 180-nm SOI CMOS and consumes a total power of 38 mW. The letter is an extended version of (Mohamed
et al.
, 2021) incorporating additional modeling details and measurement results.