Study And Design Of Multi-Channel EEG Acquisition System

EEG,as an external manifestation of human brain activity,can directly reflect the activities of various regions of the cerebral cortex.EEG can not only be used to monitor the physiological and psychological state,but also can provide reliable diagnostic basis for dementia,tumors,epilepsy and other encephalopathy.With the development of medicine,the current 16-channel EEG acquisition system has been unable to meet epilepsy,tumors and other brain diseases' need in accurately locating.On the other hand,the rapid development of BCI(brain-computer interface)also requires more integration of EEG acquisition channel in order to obtain more closely brain parts' information for algorithm analysis.In view of the above situation,this article studies and designs a multi-channel EEG acquisition system.The multi-channel EEG acquisition system can be divided into multi-channel analog front-end amplifier circuit and supporting Multi-channel acquisition's digital circuit.The multi-channel analog front-end amplifying circuit comprises an instrument amplifying circuit,a Driven-Right-Leg circuit,a high gain amplifying circuit,a multi-channel multiplexing circuit and an analog-to-digital conversion circuit.Supporting Multi-channel acquisition's digital circuit mainly include FPGA chips,four DDR3 chips,two Gigabit Ethernet PHY chip.EEG signal is amplified and analog-digital transformed firstly,and then the digital circuit sent it to the computer for save and restore.The design of the Driven-Right-Leg circuit has been improved.By improving the buffer amplifier's gain,so as to enhance Driven-Right-Leg circuit's gain on the power-frequency signal amplification by 20 dB,and thus better suppression of power frequency interference.By adding advance compensation to the buffer circuit to increase the phase margin of the feedback loop.To achieve a multi-channel acquisition,we add multi-channel multiplexing circuit to this system.By adding this circuit,it is also possible to expand the number of the acquisition circuit' channel by a factor while does not significantly increase the cost.To support the expansion of channels and the increase in sampling rate,we design a digital board that can support acquisition system which is 500 ksps sampling rate,24 bit,256 acquisition channels.The parameters of the system are as follows: sampling rate is 50 ksps,quantization precision is 16 bits,number of channels is 64 channels(expandable),and the communicaiton rate between digital circuit and PC can reach gigabits per second.This project is prospective study,the actual test based on the existing 16-channel EEG caps.When the state of the tested personnel is stable,the output signal of the multi-channel analog front-end amplification circuit is observed by the oscilloscope,which proves that the multi-channel analog front-end amplification circuit is working normally.After the data were transformed into the computer via the digital circuit board,the data were analyzed by MATLAB software.The results showed that the frequency of the signal was mainly below 30 Hz,which was consistent with the frequency of EEG signal when the human body was quiet,thus verifying the feasibility of the acquisition system.