BIAS. Why do I need it?

asantesanaasantesana
in Electrodes

I'm trying to understand the need for the BIAS electrode when taking EEG measurements. 

If I’m not
mistaken, in the default operation mode the ADS1299 amplifies the voltage
difference between any channel and the SRB2 pin, digitalizes it and sends it
over to the computer. My question is: If this
process only takes into account the voltage difference between two electrodes,
why is it so important to have an additional electrode connected to the BIAS
pin?


Comments

  • wjcroftwjcroft Mount Shasta, CA
    Asante, hi.

    All EEG and biosignal amplifiers have a Ground (or Bias) lead connection to the subject. This can serve two functions: to center the highly sensitive differential amps used on each channel. And in the case of 'Bias' (sometimes called RLD, Right Leg Drive), to also inject back into the subject, a reverse phase low amplitude signal to help in cancelling common-mode mains noise.

    William
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