A 0.6v/0.9v 26.6-To-119.3 Mu W Delta Sigma-Based Bio-Impedance Readout Ic With 101.9db Snr And < 0.1hz 1/F Corner

Bio-impedance (BioZ) is an important physiological parameter in wearable healthcare sensing. Besides the inherent cardiac and respiratory information, BioZ can be also used for other emerging applications such as non-invasive blood status sensing [1]. A conventiona14-e1ectrode (4E) setup eliminates the effect of electrode-tissue impedance (ETI) at the expense of user comfort, system complexity, and cost. On the other hand, a 2-electrode (2E) setup avoids short-falls of 4E but can only capture relative changes of Bi0Z instead of its absolute value. In addition, a readout front-end (RFE) with wide dynamic range (DR) and high signal-to-noise ratio (SNR) is needed to deal with small BioZ variation (0.1$\\sim10\\Omega$) as well as large baseline resistance (\u003e10k$\\Omega$). A conventional RFE architecture employing an instrumentation amplifier (IA) and ADC has to trade-off between resolution, DR and noise [2, 3]. Although flicker noise in the current generator (CG) is mitigated through dynamic element matching (DEM) [2], the reference current (IREF) noise issue remains unaddressed. In [5], digital-assisted baseline cancellation and IREF correlated noise cancellation are proposed, which help eliminate IREF noise and input-dependent noise [4] due to the large signal in the current-balance instrumentation amplifier (CBIA). Nevertheless, larger noise is still observed due to the finite residual current $(I_{res})$ from the baseline cancellation.