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ADS1299 EEG-FE

Marc Hoof
Prodigy 45 points
Other Parts Discussed in Thread: ADS1299, INA121

We are looking to test the evaluation board for a Auditory Brainstem Evoked potential, EEG or ECG. We have trouble connecting the electrodes and configuring the software with which it is supplied (ADS1299EEGFE-PDK Version 1.0.2).

Could someone from experience give us some pointers how to configure the settings and connect the electrodes to the board (reference, ground and electrodes (+/-)) for a simple proof of principal?

  • 0
    Prodigy 40 points

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  • 0 in reply to Daniel Weiss
    Intellectual 270 points
    Oh, I have the similar problem now. :(
  • 0 in reply to Heejin Kim
    Prodigy 60 points
    According to the literature, the signal should be filtered between 30 to 3000 Hz. Should it be an analog filter or a digital filter?. If that is an analog filter, how the filter shold be connected to the differential PGA in ADS1299. on the other hand, is there any embedded filters with amplifiers in any DAC Chips?
  • 0 in reply to Afsheen JInan
    TI__Mastermind 38745 points
    Hey Afsheen,

    Do you have a signal that will be between 30 and 3000 Hz and you need to filter it to that band? The ADS1299 has a digital filter which will could provide the low-pass portion of your filter. The high pass portion could be done in analog or in digital. An analog filter could just be an RC passive filter on each of the differential inputs.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 60 points
    Dear Brian,

    Thank you for the reply

    Further the signal needs to be amplified x 100,000 as the signal amplitude is 100 - 500 nV. But the PGA has a limited gain of 24.
    Should I have to use an Instrumentation amplifier (with high gain) before feeding the signal into the PGA.
    In that case the PGA works as a normal amplifier (Hence the built-in RLD Biasing circuit cannot be used).
    But if I use the PGA as a differential amplifier I would get a signal with low SNR (the gain of PGA is small).
    I need suggestion in the above case.

    Could you please suggest me an embedded ADC with an amplifier which has got high gain (may contain filters and/or Inverting/non-inverting amplifiers) to increase SNR before Digital signal Processing.
    Then the filtering can be done in digital domain.
    (I suggested filtering in analog domain to avoid saturation)

    Also please suggest me if there is any low noise amplifier to extract ABR signals. (as the signal amplitude is 100 - 500 nV).

    Thanks and Regards,
    Afsheen
  • 0 in reply to Afsheen JInan
    TI__Mastermind 38745 points
    Hey Afsheen,

    You will definitely need another gain stage since the signal you wish to measure has a magnitude lower than the input referred noise of the ADS1299. You can certainly still use the Bias amplifier to bias the patient, however. I don't see an issue with that.

    Unfortunately we do not have any ADCs at the moment with gains larger than 24. I recommend you use the INA121. This amplifier uses bipolar supplies, has low-noise, adjustable gain, and a MOSFET gate input which will keep the input current extremely low. You can connect the output of the INA121 to the input of the ADS1299 and use the PGA gain on the ADS1299 to amplify the signal further. It is not uncommon for this ADC to measure signal that are just a few mV RMS since it has such a large dynamic range.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 60 points

    Dear Brian,

    Thank you for the reply

    You answered my question.

    Regards,

    Afsheen

  • 0 in reply to Brian Pisani
    Prodigy 90 points
    Hi ，Engineer

    Sorry，I don't understand the word of “You can certainly still use the Bias amplifier to bias the patient, however. I don't see an issue with that.” .As you said, the common mode voltage is from tow amplifier(first amplifier and the one in ADS1299) but not only the first amplifier.Because the amplifier in ads1299 is in single end input mode，the
    the common mode voltage could really works？

    And,how could I use the function of electrode-off detection and impedance measurement ,if I add a preamplifier？？

    Sincerely
  • 0 in reply to Zhang jian
    TI__Mastermind 38745 points
    Hello Zhang,

    You can still use the bias amplifier output connected to a bias electrode to maintain the patient's common-mode voltage within the limits of the INA. Otherwise, you'd have to ac couple the inputs. The ADS1299's PGA can not be configured in a "single-ended mode" as it is always a fully differential amplifier. However, you could fix one of it inputs to a DC voltage (perhaps using the RLD output) from which respect all other voltages will be measured.

    You will not be able to detect electrode-off conditions using the ADS1299's internal circuitry if you use a amplifier stage before the ADS1299. However, you could place a very large pull-up or pull-down resistor on the inputs and then use the ADS1299's internal lead-off detection comparators to see if the voltage level of any singular input ever exceeds one of the set thresholds.

    Regards,
    Brian