A Wearable 8-Channel Active-Electrode EEG/ETI Acquisition System for Body Area Networks

This paper describes an 8-channel gel-free EEG/electrode-tissue impedance (ETI) acquisition system, consisting of nine active electrodes (AEs) and one back-end (BE) analog signal processor. The AEs amplify the weak EEG signals, while their low output impedance suppresses cable-motion artifacts and 50/60 Hz mains interference. A common-mode feed-forward (CMFF) scheme boosts the CMRR of the AE pairs by 25 dB. The BE post-processes and digitizes the analog outputs of the AEs, it also can configure them via a single-wire pulse width modulation (PWM) protocol. Together, the AEs and BE are capable of recording 8-channel EEG and ETI signals. With EEG recording enabled, ETIs of up to 60 k Omega can be measured, which increases to 550 k Omega when EEG recording is disabled. Each EEG channel has a 1.2 G Omega input impedance (at 20 Hz), 1.75 mu Vrms (0.5-100 Hz) input-referred noise, 84 dB CMRR and +/- 250 mV electrode offset rejection capability. The EEG acquisition system was implemented in a standard 0.18 mu m CMOS process, and dissipates less than 700 mu W from a 1.8 V supply.