A Design Of 64-Channel Electroencephalography Amplifier

The brain,composed of tens of billions of neurons,is the most complex organ of the human body.The EEG signal is the direct manifestation of electrophysiological activity carried out by each neuron at its specific location.The EEG signals are very weak and easily interfered by external noise(such as power frequency interference)and other bioelectric signals(EEG signals,EMG signals,and ECG signals).So,it is necessary to use high-performance EEG amplifiers to collect EEG signals.This paper has designed a high-performance EEG amplifier with 64 channels.The EEG amplifier designed in this thesis has consisted of three parts: the analog circuit part,the digital circuit part,and the computer software acquisition part.Among them,the circuit part has used a stacked design scheme of 8 analog boards and 1 digital board.In order to accurately collect the EEG signal,the EEG amplifier needs to reduce the sources' impedance,which means reducing the contact impedance between the electrode and the scalp.This paper has used a commonly used non-invasive Ag/AgCl wet electrode.The electrodes have transmitted the collected EEG signal to the analog circuit part through the shielded line.The analog circuit has performed the processes of amplifying,filtering,single-ended to differential and analog-to-digital conversion of the received EEG signal.At the same time,in order to make ensure the safety of the electrical.The electrical isolation scheme was adopted in the analog circuit part which contacts the human body and the digital circuit part which does not touch the human body.And the analog circuit part has added a dial switch to facilitate the replacement of the analog board.The digital part has consisted of two parts.The first part of the EEG amplifier is the controller part that has controlled the whole amplifier and encoded the received EEG signals and flag signals.The FPGA chip used in this circuit is the EP4CE6E22C8 of Altera's Cyclone IV series.The second part is the USB interface circuit part,which is responsible for the communication between the amplifier and the computer.The USB chip used in this circuit is the CY7C68013 of Cypress' s chip.The computer software acquisition part has integrated the digital signals received via USB and displayed and saved the data in real time.This paper has designed a 64-channel EEG amplifier with a sampling rate of 1 KHz,a bandwidth of 0.5 Hz-100 Hz,an analog-to-digital converter resolution of 24 bits,and more than 110 dB of the system common mode suppression ratio.In order to verify the feasibility of the EEG amplifier,the performance test and EEG test have been carried out separately in this paper.The performance test part has included a common mode suppression ratio test and noise test.The verification part of the EEG experiment included spontaneous EEG experiment,stability state visual evoked potential experiment,oddball experimental paradigm experiment,and unilateral preparatory potential experiment.The experimental results have shown that the 64-channel EEG amplifier designed in this paper can meet the requirements of national standards and be applied to medical and scientific research fields.