Hi All,
First of all I want to tell you that I successfully designed 24-channel EEG mobile device using three ADS1299 IC's. I've modifier you bias driver (Driven Right Leg circuit) and I've achieved CMRR of 143dB on amplification of the 24. I've tested it using EEG simulator device: Differential signal sin, 5uV amplitude and frequency of 3Hz, and common mode signal sin 2.5V, of frequency 50Hz.
The idea is to increase common mode amplification and in that way to increase CMRR. The modification is next: on schematic on figure 52 (SBAS499A PDF - PDF about ADS1299), you have RC circuit on pins BIASINV and BIASREF (Cext - 1.5nF and Rext - 1M). I've removed that components. Now you have open loop BIAS-amp, but the loop is closed over patien. The only thing that you must to do is to put serial resistor of 1M on BIASOUT pin to limit maximum current that may flow to the patient. With this configuration, you will get CMRR of 143dB and will have great EEG recordings without using Notch filter of 50/60Hz.
I've wanted to share my experience with all.
Best regards,
Vojin Ilic
