Forum Post: RE: On Reference/Bias electrode of ADS1299 EEG-FE

Hi Xinling,

Thanks for your questions. While we are not experts in EEG, I think I can provide some guidance here:

1. Typically, your frontal electrodes would both be referenced with respect to a common reference point on the body. I'm assuming this is the intention of the earlobe electrode, correct? There are two options for routing the reference:
   1. Use the appropriate pins on J6 to route the reference to AINxN.
   2. Use REF_ELEC and route the reference through SRB1, which connects to all AINxN inputs internally. This option allows you to buffer the reference through U4, if desired.
2. AIN1 was not intended for the reference electrode. It is just another way to input signals to the positive channels inputs.
3. The BIAS_ELEC is an output from the ADS1299 that is intended to set the common-mode point of the patient. This also helps to improve common-mode rejection in your measurements. This is very similar to the Right Leg Drive technique used in ECG applications.

Does this help clarify the EVM connections?

Regards,