IEEE Trans Biomed Circuits Syst. 2011 Dec;5(6):555-67. doi: 10.1109/TBCAS.2011.2170985.
This paper presents an active electrode system for gel-free biopotential EEG signal acquisition. The system consists of front-end chopper amplifiers and a back-end common-mode feedback (CMFB) circuit. The front-end AC-coupled chopper amplifier employs input impedance boosting and digitally-assisted offset trimming. The former increases the input impedance of the active electrode to 2 GΩ at 1 Hz and the latter limits the chopping induced output ripple and residual offset to 2 mV and 20 mV, respectively. Thanks to chopper stabilization, the active electrode achieves 0.8 μVrms (0.5-100 Hz) input referred noise. The use of a back-end CMFB circuit further improves the CMRR of the active electrode readout to 82 dB at 50 Hz. Both front-end and back-end circuits are implemented in a 0.18 μm CMOS process and the total current consumption of an 8-channel readout system is 88 μA from 1.8 V supply. EEG measurements using the proposed active electrode system demonstrate its benefits compared to passive electrode systems, namely reduced sensitivity to cable motion artifacts and mains interference.
本文提出了一种用于无凝胶生物电势 EEG 信号采集的有源电极系统。该系统由前端斩波放大器和后端共模反馈 (CMFB) 电路组成。前端交流耦合斩波放大器采用输入阻抗提升和数字辅助失调调整。前者将有源电极的输入阻抗在 1 Hz 时提升至 2 GΩ，后者将斩波引起的输出纹波和残余失调限制在 2 mV 和 20 mV 以内。得益于斩波稳定，有源电极实现了 0.8 μVrms（0.5-100 Hz）的输入参考噪声。后端 CMFB 电路的使用进一步将有源电极读出的 CMRR 提高到 82 dB，在 50 Hz 时。前端和后端电路均采用 0.18 μm CMOS 工艺实现，8 通道读出系统的总电流消耗为 1.8 V 电源下的 88 μA。使用所提出的有源电极系统进行 EEG 测量证明了它与无源电极系统相比的优势，即降低了对电缆运动伪影和市电干扰的敏感性。
