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Grounding problems: ADS1298, INA114 and human test subject

Komal Mariam
Prodigy 130 points
Other Parts Discussed in Thread: ADS1299, ADS1298, INA114

Hello,

I am working on acquiring the EEG signals from a human test subject using ADS1298 (due to certain time constraints ADS1299 is not an available option).

Currently I am trying to pick up an eye blink signal from two electrodes, pass it through a pre-amplification stage (made up of TI's INA114) and then into the ADS1298ECG-FE PDK board.

My question is that how do I ensure that all the three parts of my system (human body, INA114 circuit and ADS1298) are operating at the same ground level.

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    TI__Mastermind 38745 points
    Hey Komal,
    Great question! Are the two electrodes that you are using both signal carrying electrodes? Or is one of them a bias electrode? If one of them is a bias electrode, connect that electrode to the output of the RLD amplifier on the ADS1298. The RLD amplifier will produce a patient drive signal that will establish a common mode voltage on the patient. A detailed description of its functionality can be found in the ADS1298 datasheet.
    If both electrodes are measurement electrodes, you will want to AC couple your inputs by placing a DC blocking capacitor in series with the inputs in front of the instrumentation amplifier. However, you can still use the RLD amplifier on the ADS1298 to provide a buffered common mode voltage to bias the inputs through large value resistors. Then since the RLD output will be the effective signal ground (and has a very low output impedance), you can connect it to the REF node on the instrumentation amplifier.
    Regards,
    Brian Pisani