腦部神經活動的綜合變化所產生之電訊號稱作腦電波(Electroencephalogram、EEG)。由於腦波和人類的意識活動有某種程度的對應，因而引起許多研究者的興趣。 腦電波在經過頭顱衰減後便的十分微弱，且容易受到市電等外來雜訊的干擾，因此量測上並不容易。由於腦波訊號十分微弱，而皮膚與電極間的阻抗也不小，為了降低負載效應對量測的影響，需要使用一個具有高輸入阻抗的系統。 一般電路都會受到零件誤差的影響而與原本設計上有所出入，在本系統中以陷波濾波器最容易受到影響，零件的誤差會使的陷波濾波器的效果大幅降低，所以希望以電路設計與調整可變電阻來改善零件誤差所造成的影響。 本研究設計一個應用於視覺又發電位之腦波人機介面的腦波量測系統，包含類比放大電路、低通濾波器、陷波濾波器及傳輸與電腦介面，頻寬在10Hz-50Hz，具有高增益，高輸入阻抗的特性，並且能調整可變電阻來改善零件誤差所帶來之問題，並加入無線傳輸系統使攜帶更方便。 The signal, compositive changes produced by cerebration, is called electroencephalogram (EEG). Researchers are interested in EEG because EEG relates consciousness of human. After going though the skull, EEG signal is very weak. Moreover, it is easily interfered with noise. Therefore, it is difficult to measure. Furthermore, because the brain wave is very feeble and electrode-skin impedance is high, the measurement system should have high impedance to reduce the loading effect. Due to the uncertainties of electric elements, circuits are not ideal, especially the notch filter. This study designs an effective circuit only by adjusting a variable resistance of the circuit. This study proposes a brain wave measure and amplifier circuit for a visual evoked potentials (VEPs) brain computer interface (BCI) system. The proposed brain wave measurement system includes a preamplifier, a three order low pass filter (LPF), a two order high pass filter (HPF), a notch filter and a wireless transmission module. The designed circuit has not only high gain but also high input impedance. The system can adjust variable resistance to overcome the non-ideal situation of the circuit. In addition, the circuit combination with a wireless transmission module and battery makes the proposed system being portable.
