Electrical – Amplifiers for EEG and Resistor Values


AD620 is commonly used for DIY EEG/EC/EMG projects. I've seen an instrumentation amplifier that is designed by using 3x TL081 opamp for EEG project.

For example : enter image description here

I've checked that AD620's input offset voltage is in uV and TL081's in mV. As you know input signals are in the range of micro volts for EEG.

1) Do you think using the figure above as instrumentation amplifier would just work fine or would have high error level ?

2) How can I choose what resistor value is best for me ? In the figure Rg = 220 ohm, for example. What would occur if Rg was 3.3k ?

3) As known, high and low pass filters are used in EEG project and those filters have opamp inside. What should be the gain value for them ?

Thanks in advance for your help.
Have a nice day.

Best Answer

To start with, the TL081 is far from the best op amp to use. Take a look at the Open EEG Project, specifically the schematics