A 3.11 μW 40 nV/ √Hz Instrumentation Amplifier for Bio-Impedance Sensors Exploiting Positive-Feedback-Assisted Gain Boosting

This paper presents a low-power and low-noise instrumentation amplifier (IA) for bio-impedance sensing ap-plications. To solve the loop gain reduction problem when the input resistor in a transconductance (TC) stage decreases as low as
$< 10\mathrm{k}\Omega$
, two positive-feedback-based gain boosting techniques are applied to the flipped voltage follower circuit: (1) a super gain casco de current mirror and (2) a current mirror amplifier with local positive feedback. Simulated in a 65 nm CMOS process, the designed IA ensures a 70 dB DC loop gain within the TC stage while achieving 40
$\mathbf{nV}/\sqrt{\mathbf{Hz}}$
input referred noise floor and a 369kHz bandwidth at 3.11
$\mu \mathrm{W}$
power consumption, 1 V supply. The enhanced loop gain leads to only a 0.04 dB (0.46%) IA gain deviation over the PVT variations.