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EEG Signal aquisition Design Help?

Question asked by sanket.kulkarni on Dec 5, 2016
Latest reply on Mar 16, 2017 by christoliver

I Have designed a circuit to acquire the EEG signal from electrode within 0-20 microvolt. My design consists of AD620 (gain = 2), -> LPF (4th order G=2.515, Fc= 0-40Hz),-> HPF (4th order G=2.515, Fc = 0.1 to 40 Hz), -> Two stage amplifier with G=180. But I am getting a constant output at AD620 of 1.28V without or with  input connected. And the output after LPF filter HPF, and two stage amplifier  is found to be 4.78V constantly. 

          I am not getting why  this error persists. I have checked my PCB and it is ok connection wise. So it will be of great help if you can tell me the error?  

         I want to acquire EEG signal to make it in acceptible limit of ADC of 0-5V.

       I want to give the acquired EEG signal to 24 ADC and then toARM Cortex M3 for further processing.