Hi Melanie,
Thanks for the explanation!
Therefore, a single-ended measurement should use the REF_ELEC as the negative input to all of input channels. This can be done by routing REF_ELEC to the SRB1 pin and setting the appropriate registers in the ADS1299.
Another alternative to route REF_ELEC to the negative channel inputs is to remove the jumper on (1-2) of JP25, and tie REF_ELEC to pin 1 only. Then, place a jumper on the appropriate pins of J6 (9-10, 13-14, 17-18, 21-22, 25-26, 29-30, 33-34). One advantage to doing this is to improve common-mode rejection as both the (+) and (-) inputs to each channel should see nearly the same input impedance to the ADS1299.
For the BIAS_ELEC, the intention behind this feature is to drive patient to a known potential, similar to the way the bias potential known as "Right Leg Drive" sets the common-mode of the patient in an ECG application. The BIAS_ELEC is generated internally and set to mid-supply. JP25 on the ADS1299 EVM allows you to route this bias potential to the (+) inputs (shorting 3-4), or the (-) inputs (shorting 1-2). If (5-6) are shorted, this BIAS_ELEC is shorted to the REF_ELEC and fed back into SRB1 pin of the device.
Since you are planning to use your own reference signal from the REF electrode in your diagram, you simply need to disconnect (5-6) on JP25, and connect your reference electrode in either of the two methods I described earlier.
Do you plan to bias the patient as well?
Regards,