A 26.6–119.3-μW 101.9-dB SNR Direct Digitization Bio-Impedance Readout IC

This article presents a direct digitization bio-impedance (BioZ) readout IC with high power-to-noise efficiency over a wide input impedance range. This design features a delta-sigma (
$\Delta \Sigma$
)-based BioZ readout topology with the first-order noise shaping and a feedback current-steering digital-to-analog converter (IDAC) that minimizes the residual current to suppress the input-dependent noise modulation in current balancing instrumentation amplifier (CBIA). Furthermore, various dynamic element matching (DEM) techniques are applied to mitigate the impact of 1/
$f$
noise and switching noise during analog to digital conversion. The proposed BioZ readout circuit was implemented in a standard 40-nm CMOS process. Measurement results showed 101.9-dB SNR within 4-Hz bandwidth with lower than 0.1-Hz 1/
$f$
noise corner and 152.6-dB figure-of-merit (FoM) for
$I$
path.