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Original question:

ADS1299-4: Regarding measurement of EEG using ADS1299 AFE

ADS1299-4: Question about ADS1299-4

Lumina Gui
Expert 2975 points
Part Number: ADS1299-4
Other Parts Discussed in Thread: ADS1299

Hi TI Teams,

We have some question about the application of ADS1299-4, the details are shown as below:

Design Description:

As shown in the below picture, ADS1299-4 is used to collect EEG signals.

1)IN1P-IN4P is used as the input for the EEG electrode, and IN1N-IN4N is routed to the REF reference electrode through SRB1. The driving electrode uses an internal operational amplifier;

2)Using a single power supply, AVDD is+5V, AVSS is 0V, and the reference power supply uses internal 4.5V and digital power supply+3.3V.

Question:

1)Is it possible to use ADS1299-4 to continuously detect 4-channel EEG signals and 4-channel electrodes at the same time?

2)According to the instructions on pages 10 and 36 of the ADS1299 data sheet, if fDR/4 is used, can 4-channel EEG signals and 4-channel human contact impedances be continuously detected at the same time?

3)Our current EEG acquisition DATA RATE is 250Hz, so fDR/4=62.5Hz, the collected EEG data contains 62.5Hz AC signal, through the upper computer processing, respectively extract EEG signal and AC impedance signal, is it feasible?

4)Are the in-band and out of band mentioned on page 36 of the ADS1299 specification divided relative to the frequency range of EEG? out of band ac current source or sink must be implemented using an external current source or can it be implemented using an ac source of fDR/4 inside the ADS1299-4? If an external current source must be used, is there a recommended current source?

page 10

page 36

Thanks,

Kind Regards

  • 0
    TI__Mastermind 19815 points

    Hi,
    Would you please let me know the customer? If not allowed to disclose in public, please let me know. I will reach out to you via email.

    1. For "continuously detect 4-channel EEG signals and 4-channel electrodes at the same time?"
    I understand "detect 4-channel EEG signals", yes, it's possible. But I don't understand what you mean by "4-channel electrodes"? Were you trying to se lead or electrode off detection?

    2) So, are you referring to AC lead off detection? By the way, page 10 or 36 doesn't show any instruction. Could you clarify?
    The continuous mainly refer/affix to DC lead off detection. If it affix to AC lead off detection, it means that the AC excitation is running, the result/outcome may not be considered.

    2) and 3) AC lead off detection is described in page 31 9.3.2.4.3.2 AC Lead-Off (One Time or Periodic). And, datasheet doesn't not suggest to use AC lead off detection continuously while the EEG signal is being acquired. The suggested usage for AC lead off detection is for occasionally check not continuously. Also, if customer MUST and really want to use AC lead off detection, customers will need to do experiments, tests, data collection&analysis to develop DSP and/or algorithms to distinguish the AC lead off detection. In other words, AC lead off detection is not as straight forward/simple as DC lead off detection.
    Also, customers may need to pay attention to any RC circuit along the signal path while using AC lead off detection as any RC circuit could have effect to attenuate the AC lead off detection excitation signals, customers again will need to do experiments, tests, data collection&analysis to determine/decide which RC circuit they want to use based on/with respect to their signal of interest as well as the AC lead off detection excitation frequency.

    4) We leave the current source option to customers, we don't have any suggested current sources.

    Thanks

  • 0 in reply to ChienChun Yang
    Expert 2975 points

    Hi Chienchun,

    You can email to 12qq34er56@163.com , and maybe we can communicate through the email directly. For your question, the answer is as below:

    1) Answer: Yes, what I mean is that both EEG signals and and human contact impedance signals can be collected simultaneously (using internal AC Lead-Off ac current source).

    2)Answer: We will testing based on your suggestions, but we also found a post that is similar to my question as follows.

    https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/238755/ads1299-lead-off-detection

    Now, we have found a new problem about the core MCU communicating with the ADS1299-4. The board is always powered on, the program will reset the ADS1299-4 after each run, then send the comand SDATAC to the ADS1299-4 to stop the continuous reading mode, delay 10ms and then send the instruction RREG to read the ID or other registers, but the read value is always 0. Can you help to check the reason for this problem?

    Thanks,

    Kind Regards

  • 0 in reply to Lumina Gui
    TI__Mastermind 19815 points

    Hi,

    Thanks.

    I will reach out to you via email.