An acquisition circuit for electroencephalogram detection device

• Main Author: Mo, Yanfei
• Other Authors: Goh Wang Ling
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: http://hdl.handle.net/10356/78848
• Institution: Nanyang Technological University

The brain wave signal is derived from the synaptic potential caused by the synchronization of many neurons, reflecting the electrophysiological activity of brain neurons, which carries a large amount of biological information. The information contained in EEG has important research and application value, especially it can provide an important basis for clinical diagnosis and treatment. However, it is not easy to detect EEG signal. The EEG signal is very weak, generally only about 50 μV, and the amplitude range is 5 μV~100 µV. EEG signal scalp and skull usually have a resistance of several thousand ohms, so the front part has a high input impedance. The frequency, generally 0.1~100 Hz, of the EEG signal is low, and EEG signal acquisition in the normal environment is affected by common mode interference such as power frequency interference, since the signal-to-noise ratio is usually lower than -10 dB. Therefore, when we design the acquisition circuit, higher amplification gain, greater input impedance and low-pass filter are the required technical indexes. In general, EEG signal is enlarged by about 20,000 times, the input impedance is greater than 10 MΩ to improve the EEG signal acquisition ability. Besides, the amplifier in circuit is required to have a high common mode rejection ratio (CMRR), which is generally greater than 120 dB, because power frequency interference mainly exists in the form of common mode, and the amplitude is on the order of mV. To satisfy the requirements of EEG signal acquisition circuit, ICL7650 chip is employed in the design, since it has some good characteristics such as high gain, high CMRR, low offset and so on. After accessing information online, a suitable structure of the acquisition circuit based on ICL7650 is determined. Then to verify the function of each module in the circuit. We used Multisim to perform the simulation of circuit. According to the resulted waveforms, the circuit can execute the amplifying and filtering function normally.