A Bioimpedance Sensing Interface IC With Current Matching and Common-Mode Suppressing Loop for Wearable Health Monitoring

This letter presents a bioimpedance (Bio-Z) sensing interface IC with a current matching and common-mode suppressing (CMCS) loop for long-term health monitoring applications. The CMCS loop eliminates the mismatch between the source and sink stimulation currents of the current generator (CG), while reducing the area of the CG by half. Furthermore, the CMCS loop reuses the common-mode feedback loop of the Bio-Z instrumentation amplifier to substantially enhance the common-mode rejection ratio (CMRR) of the interface with reduced power consumption and area overhead. The proposed Bio-Z interface is designed in 130-nm CMOS technology. By employing the CMCS loop, it achieves a CMRR of 127 dB, exhibits a 3.84-mΩ/√Hz input-referred impedance noise, occupies an area of 0.07 mm ² , and consumes a power of 10.4 µW for the readout front end and 12.9–122.7 µW for the CG.