EEG (Electroencephalography) is a measurement of electrical activity of the brain from different positions on the scalp. Main objective of this project is to design an EEG instrumentation system with low cost. This instrumentation part of EEG system mainly carries of three major blocks Instrumentation amplifier, High pass filter and Low pass filter.
Instrumentation amplifier is mainly responsible for extracting the AC signal; it also rejects the common mode noise and differential DC voltage. Bio electric signal needs a CMRR (Common Mode Rejection ratio) greater than 80 dB. In this project to reduce the cost we design a three op-amp instrumentation amplifier with a gain of 200 using discrete components instead of using Instrumentation amplifier IC.With our design we have obtained a CMRR of 97.6 dB, it is sufficient to eliminate DC signals and common mode noise.
EEG signal occurs between 1-70 Hz, it is done with the help of second order High pass filter and 6th order Low pass filter. Both filters were designed using sallen-key architecture. Notch filter is used to remove the power-line (50/60 Hz) noise. Due to the high impedance of electrode-tissue interface, we add a voltage follower before the instrumentation amplifier. Then the signal is passed to driver amplifier which strengthens the weak signal and finally the output of our system is viewed through Digital storage oscilloscope (DSO).