An Energy-Efficient and Reconfigurable Sensor IC for Bio-Impedance Spectroscopy and ECG Recording

This paper presents a low power reconfigurable IC for wearable health devices that perform bio-impedance (BioZ) spectroscopy, respiration, and ECG signals measurement. The IC consists of a broadband excitation current source (I-DAC) and a power efficient readout circuit (RO). Both are highly scalable to mitigate the tradeoff among noise, dynamic range, speed, power, and safe current limits. On circuit level, the I-DAC supports two broadband excitation modes based on maximum length sequence (MLS), a flexible selection of frequency points, bandwidth, and current magnitude. The RO employs a low noise instrumentation amplifier and a reconfigurable 8-to-12 bit ADC for flexible sensitivity, dynamic range and speed with an automatic scaling of the power consumption. On system level, calibration of the entire circuit chain, oversampling and MLS averaging further improve the bandwidth, accuracy and sensitivity of BioZ spectroscopy beyond the intrinsic circuit performance. As a result, the BioZ sensor IC achieves 2
$\text{m}\Omega $
sensitivity within 3.3
$\text{m}\Omega $
–
$100~\Omega $
range and
$0.6~\Omega $
sensitivity within
$3.3~\Omega $
–100
$\text{k}\Omega $
range. The BioZ spectroscopy spans up to 125 kHz while consuming
$155~\mu \text{W}$
. Furthermore, this IC can measure respiration and ECG simultaneously at a lower sampling rate of 20 kS/s while consuming
$31~\mu \text{W}$
. Compared to prior art, to the best of our knowledge, this IC is the only work that can measure BioZ and ECG simultaneously with a single readout channel while consuming the lowest power and offering the highest flexibility in performance, application range, and power consumption.