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ADS1299 not getting EEG or ECG signal

mustafa guner
Prodigy 40 points
Other Parts Discussed in Thread: ADS1299, ADS1298

Hello Dear friends!  I have problem with getting eeg or ecg signals via my board that I designed for my thesis project. firstly I must mention about my board. it contains stm32f4 mcu, ADS1299 adc and peripheral units such as uSdCard, accelerometer, bluetooth. I got inspired from OpenBCI while desinging my board and I brought it to certain ground. but the board cant read eeg or ecg signals. I dont have a problem with SPI comm. because I m able to read the internal test signals or Register Values modestly but regarding get eeg or ecg signals I m getting oscillations. I have tried to solve my problem so much but  there is no my chance.  if you could help me it would be appreciated! I attached images below which contain circuit diagram, internal test signal and oscillation signal.

I get those eeg signals in uV level when connecting electrodes to the brain surface and I suspect those signals to be noise???

Here is my ads1299 schematic and Lowpass Filter which contains 2.2k res. and 1uF cap each per chan.

  • 0
    TI__Mastermind 38745 points

    Hello mustafa,

    You are seeing significant utility frequency interference. This is becuase the RC filter you have is subject to component tolerance. Subsequently, any common mode signal applied to the inputs is filtered slighly differently so it is a differential signal by the time it reaches the ADS1299. One way to mitigate this problem is to decrease the size of the capacitors significantly thus making the cutoff frequency much larger. You should not be very concerned about anti-aliasing since the ADS1299 is a delta-sigma ADC. Delta-sigmas have digital filters which remove a lot of out-of-band noise.

    In addition, are you using the BIAS_SENS feature of the bias amplifier on this device? This application note describes how to use this function in the ADS1298, but the operation is the same in the ADS1299: Improving Common-Mode Rejection Using the Right-Leg Drive Amplifier.

    Brian

  • 0 in reply to Brian Pisani
    Prodigy 40 points

    Hello Brian!

         Thank you so much for your quick reply!  actually I m a software developer and newbie to circuit design. I dont know currently whether I have what kind of design glitches or big failure but I will investigate my board again & compute my cap's vals correctly. additionally I will try BIAS_SENS feature and I will post the results I got here.                                                  

                                                                                                                                                                                                                                                                           Best Regards.