A 0.67 V-IIRN super-T-Z_IN17.5W/Ch Active Electrode With In-Channel Boosted CMRR for Distributed EEG Monitoring

We present the design, development, and experimental characterization of an active electrode (AE) IC for wear able ambulatory EEG recording. The proposed architecture features in-AE double common-mode (CM) rejection, making the recording's CMRR independent of typically-significant AE-to-AE gain variations. Thanks to being DC coupled and needless of chopper stabilization for flicker noise suppression, the architecture yields asuper-T Omega input impedance. Such a large input impedance makes the AE's CMRR practically immune to electrode-skin inter face impedance variations across different recording channels, a critical feature for dry-electrode ambulatory systems. Signal quantization and serialization are also performed in-AE, which enablesa distributed system in which all AEs use a single data bus for data/command communication to the backend module, thus sig-nificantly improving the system's scalability. Additionally, the pre-sented AE hosts auxiliary modules for (i) detection of an unstable electrode-skin connection through continuous interface impedance monitoring, (ii) dynamic measurement and adjustment of input DC level, and(iii)a CM feedback loop for further CMRR enhancement. The article also presents the development of printed (extrusion)tattoo electrodes and their experimental characterization results with the proposed AE architecture. Besides bio-compatibility, low-cost, pattern flexibility, and quick fabrication process, the printe delectrodes offer a very stable electrode-skin connection, conform to scalp shape, and exhibit consistent performance under variousbending curvatures. Analog circuit blocks of the presented A Earchitecture are designed and fabricated using a standard 180 nm CMOS technology, and the 1x1.3 mm2IC is integrated with off-chip low-power digital modules on a PCB to form the A E.Our measurement results show a CMRR of 82.2 dB (at 60 Hz),amplification voltage gain of 52.8 dB, a bandwidth of 0.2-400 Hz,+/- 500 mV input DC off set tolerance, An input impedance>1T Omega,and 0.67 mu VRMSintegrated input referred noise (0.5-100 Hz),while consuming 17.5 mu W per channel. All auxiliary modules are tested experimentally, and the entire system is validated in-vivo, for both ECG and EEG recording.