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Ch Active Electrode with In-Channel Boosted CMRR for Distributed EEG Monitoring
  • Alireza Dabbaghian ,
  • Hossein Kassiri
Alireza Dabbaghian
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Hossein Kassiri
York University

Corresponding Author:[email protected]

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Abstract

We present the design, development, and experimental characterization of an active electrode (AE) IC for wearable 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 a super-TOhm input impedance. Such a large input impedance makes the AE’s CMRR practically immune to electrode-skin interface impedance variations across different recording channels, a critical feature for dry-electrode ambulatory systems. Signal quantization and serialization are also performed in-AE, which enables a distributed system in which all AEs use a single data bus for data/command communication to the backend module, thus significantly improving the system’s scalability. Additionally, the presented 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 paper also presents the development of printed (extrusion) tattoo electrodes and their experimental characterization results with the proposed AE architecture. Besides bio-compatibility, lowcost, pattern flexibility, and quick fabrication process, the printed electrodes offer a very stable electrode-skin connection, conform to scalp shape, and exhibit consistent performance under various bending curvatures. Analog circuit blocks of the presented AE architecture are designed and fabricated using a standard 180nm CMOS technology, and the 1 x 1.3mm2 IC is integrated with off-chip low-power digital modules on a PCB to form the AE. Our measurement results show a CMRR of 82.2dB (at 60Hz), amplification voltage gain of 52.8dB, a bandwidth of 0.2-400Hz, +-500mv input DC offset tolerance, An input impedance > 1TOhm, and 0.66uV integrated input referred noise (0.5-100Hz), while consuming 17.5uW per channel. All auxiliary modules are tested experimentally, and the entire system is validated in vivo , for both ECG and EEG recording.