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

Abstract

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 kΩ can be measured, which increases to 550 kΩ when EEG recording is disabled. Each EEG channel has a 1.2 GΩ input impedance (at 20 Hz), 1.75 µVrms (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 µm CMOS process, and dissipates less than 700 µW from a 1.8 V supply.

Active Electrodes for Wearable EEG Acquisition: Review and Electronics Design Methodology

“…Alternatively, non-inverting amplifiers can utilize capacitive feedback [38] (Fig. 7b) to mitigate resistor noise.…”

“…The 1/f 2 noise has been observed in other chopper amplifier architectures, such as a non-inverting chopper amplifier [38], inverting chopper amplifiers [30] [56], and a chopper amplifier equipped with an external floating high-pass filter (HPF) [44]. The common problem of these amplifiers is that chopping was always performed at very high-impedance node (in GΩ range).…”

“…The CMFF can be integrated into a non-inverting amplifier with a resistive feedback [37] or a capacitive feedback (Fig. 24) [38]. In both cases, the CMFF is realized by connecting the AEs' reference inputs together to null the common mode input current.…”

Soft, Comfortable Polymer Dry Electrodes for high Quality ECG and EEG Recording

“…The amplitude of EEG signals is in the µV range, so an active circuit next to the polymer dry electrode is needed to compensate for the high impedance of our electrode [32,33]. Such a so-called "active electrode setup" helps reduce the interference from the environment, such as 50 Hz noise and signal disturbance caused by cable movement.…”

Class AB two stage and folded cascode OpAmps based on a squaring circuit

“…The ever-increasing demand for portable, wearable and/or biomedical devices has driven low-power design today [1]. Nonetheless, the lowering of power consumption has a significant impact on the signal handling capabilities of operational amplifiers (OpAmps), thus establishing stringent demands with regard to their design [2], [3].…”