ADS1299: ADS1299 FE PDK IMPEDANCE REPEATABILITY AND GETTING ECG SIGNAL BUT NOT EEG SIGNAL

Hello TI team

I have been in contact with TI experts from past 4 months. It was really helpful to have an informative discussion regarding ADS1299 8 Channel EEG device development. We are at close to finalizing the development of the device. We got ECG signal and external impedance testing. I have queries regarding simultaneous impedance check using all channels and unable to get alpha wave or EEG signal.

Question 1. While connecting all channels using SINGLE ENDED CONFIGURATION with common REFERENCE (J6 pin-6) and BIAS (J6 pin-2) routed to negative terminals of all channels, with LEAD OFF DETECTION  current 24 micro Amp at 31.25 HZ, we are getting two standards of value randomly as following

Details of the analysis has been given below. By increasing gain value, real value is multiplied by gain. Conclusion are as following:

• With multiple channels there are two possibilism of values
• First is True value within 10% range
• Second is 65% of true value
• Technical reason still in doubts

LOFF INJECTION CURRENT 31.25 HZ AND 24 MICRO AMP

EXTERNAL CIRCUIT

EXP1 EXP4 EXP5 EXP6

QUESTION.2  We are getting ECG but unable to get EEG signal or ALPHA wave. What would be the possible reasons?

• Suggest the quality of electrodes to get EEG if any recommendations?
• It would be limitation of GAIN value 24 ? Because ECG can be seen successfully