Design For Eeg Data Acquisition System Used In Brain-computer Interface

Electroencephalogram(EEG) signal is the sum of the electric potential generated by the cerebral cortex neuron synapse group that is recorded from the scalp. It is a very typical biological signal which contains a lot of physiological and pathological information. In order to explore the mysteries of the human brain, it is necessary to establish a direct communication channel between the brain and the external environment. Therefore, the Brain-Computer Interface(BCI) has been proposed. Through the study of BCI, we can understand the relationship between the electrical activity in nerve cells and people’s psychological and physical activity. It is of great significance in the field of clinical medicine.The first premise of research on BCI is to obtain the right EEG. This kind of signal is the feature of weak low frequency and strong background noise. It is belong to non-stationary random physiological signal. In view of the characteristics of the signal, and in order to extract and obtain effective EEG, we use the steady state VEP(SSVEP) to induced EEG. We amplify, sample and digital filter the EEG and then through the signal power spectrum analysis and identification methods to identify the effective EEG for saving it. At present, although abroad there are many EEG acquisition systems used in brain-machine interface, the price is very expensive. And domestic EEG acquisition systems are mainly used in clinical study. The volume is too big and the price is also very expensive. Therefore, they are not good used in the study of BCI. According to the above problems, this paper on the basis of in-depth study of EEG characteristics designs a EEG acquisition system which can be used to BCI. And it has reached the purpose of small volume, low cost and gain adjustable. Here is an illustration of the main research contents.(1) By taking a detailed research and analysis for the feature classification, generation method, electric lead system, electrode placement of the EEG signal processing system, a clear understanding for the research and design background of the EEG acquisition system is gained.(2) The analog amplifier circuit for the EEG acquisition system, especially the AD8222 instrumentation amplifier is analyzed exhaustively. And take into account the characteristics of the EEG, such as weak and vulnerable to interference, a high performance amplifier circuit with low noise and high common mode rejection ratio(CMRR) is designed.(3) The digital controlling part of the EEG acquisition system is studied. And a digital controlling circuit system is designed. The TMS320C6747 DSP processer is used and acts as the controller of the acquisition system. The AD1178 AD converter deployed for the converting of the amplified EEG signal. The AD(Analog-to-Digital) sampling circuit and the UART(Universal Asynchronous Receiver/Transmitter) serial communication circuit are included in the system. Thus, the robustness of the communication between the sampling system and the DSP/PC can be guaranteed.(4) By study the post DSP processing of the digitalized EEG signal in the acquisition system, the software system is designed. The 50 Hz digital band-stop filter and the 200 Hz digital low-pass filter are adopted for filtering the acquired digital signal. After the filtering, the valid EEG signal is gained after identification in power spectrum analysis. The serial communication ports of the DSP system are performed as the communication interface to the PC.(5) The software for communication control between DSP and PC is designed. The acquired rough signal, the digitalized signal and the identified EEG signal are being transmitted to the PC. The PC can display and store the signal data. And the EEG signal acquisition system is controlled by the PC.