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EEG Amplifier


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Guys, for my project work I need to make an EEG amplifier. Hope you all know what an EEG signal is (Electro Encephalogram), which for my greatest sorrow, is an extrmely small signal, something around 10 to 50 microvolts, which is very small compared to the noise signals that I will encounter. By amplifier I mean any differential amplifier which can amplify such a small signal at the same time reject the common noise signal. I expect an output of about 3 - 4.5 V.
Can you guys suggest something.
Thankyou. ???

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I know nothing about EEG, but in instrumentation it is common to convert the voltage to current and read the current or even convert it back to a voltage in order to keep the noise level to a minimum.
Hope it helps you a little. Another thought is that fiber optics are pretty much immune to noise.

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The following link might be an excellent building block to get you started. It is a low voltage (0-1V) voltage to current converter with single supply rail. See Fig. 1 for the schematic.


Happy soldering!


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  • 1 month later...

Probably best to use an instrumentation amplifier. These can be a bit spendy, but one can be cobbled from three opamps (and they'd best be from a quad for better device matching). From that a current loop driver would be good, and an optoisolator too. I'll try to find an illustration I have laying about this afternoon, but I'm off to work in a few minutes.

Okay, I'm a day later than I promised. The image is from page 1-19 of Designer's Handbook of Integrated Circuits by Arthur B. Williams. The relevant text indicates that the gain will be [2(R2/R1) + 1](R3/R4). "Resistor values should be kept low to minimize DC offset." Another illustration shows 10k in positions R2, R3, and R4. The gain can be varied with R1 alone. Pretty neat, I think I'll use it on something. I hope this helps.


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