• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 46 subscribers
  • Views 1103 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Four questions about ADS1298 for EEG

Taichi Noda
Expert 1350 points
Other Parts Discussed in Thread: ADS1298

Hello.

  1. In the case of setting Vref from external electric source,how much is Vref setting range?Vref means voltage between VrerP and VrefN.
  2. Writing Input-Referred Noise:4uVpp on features of ADS1298 datasheets Page1,this means that output digital value has noise?
  3. In the case of setting Amp on former ADS1298,can we use RLD,Lead-Off detection?And if impossible,can we turn off those functions?
  4. Writing APPLICATIONS are Medical Instrumentation(ECG,EMG and EEG) on ADS1298 datasheets Page1,input voltage of EEG is very small so I think that ADS1298 unfitted for EEG.Which are developers of ADS1298 thinking that this device fits for an instrument measure skin directly or indirectly?(I’m sorry for an ambiguous question.)

ADS1298 datasheets：http://www.tij.co.jp/product/jp/ads1298 

Best regards.

  • 0
    Expert 1350 points

    Hi,All

    I found out some my questions by myself.

    The answer for no.1 question
    ⇒
    The settable voltage of external Vref is only 2.5[V] and 4.0[V].

    The answer for no.2 question
    ⇒
    Input-Referred noise emanate from Amp and Low Pass Filter.
    And input-referred noise doesn't mean digital output noise.

    If my answer is wrong,please advise me.


    I can't find out questions for No.3 and No.4 yet.
    Please teach me answers for No.3 and No.4.

    Best Regards.

  • 0 in reply to Taichi Noda
    Expert 1350 points

    Hi,All.

    In the case of setting Vref from external source,how muchi is Vref setting range?

     

    Page5 on ADS1298 datasheet is written down following.

    External Reference

    Reference input voltage

      3V supply Vref = (VrefP – Vref N):2.5V

      5V supply Vref = (VrefP – Vref N):4.0V

    Page6 on ADS1298 datasheet is written down following

    Power-Supply Reqquirements

    Analog supply:2.7 to 5.25V

     

    I think  that Vref Range is a bit larger  than a range 2.5 to 4.0V,but I don't know correct Vref setting range.Please tell me how much is correct external Vref setting range.

    I don't get a reply for now. Please stay out of other questions.

    Best Regards.

     

     

     

  • 0 in reply to Taichi Noda
    TI__Guru 57366 points

    Hello Taichi-san, 

    Thank you for your questions. I will address your question about VREF first and then share my thoughts on your original questions if you still need clarification.

    When providing an external reference, the negative input (VREFN) is equal to AVSS and the positive input (VREFP) can be as large as AVDD.


    Best Regards,

  • 0 in reply to Ryan Andrews
    Expert 1350 points

    Hello Mr.Ryan

    Thank you for reply.

    I'm sorry for my confusing question.

     

    Example,In the case of setting Vref 24mV from external source,can we reduce input range to ±4mV?

    Please teach me Vref settable range .

     

    I was asked above question from my customer.

    Best regards.

  • 0 in reply to Taichi Noda
    Expert 1350 points

    Hi,all

    I don't receive yet an answer that I want.

    Is my question is confusing?

    Please teach me an answer.

    Best regards.

  • 0 in reply to Taichi Noda
    TI__Guru 57366 points

    Hello Taichi-san,

    In the case of setting VREF =  24 mV from external source, your differential input range would be your common-mode +/- 24 mV. As long as your input signal fits in this range,  the ADS1298 will be able to make the analog-to-digital conversion. Depending whether you use dual supplies or single supplies (i.e. 5 V and GND or +/- 2.5 V), the common-mode voltage is chosen to ensure that your inputs are within the power supply range.

    How large are your input signals now? Is there a reason you wish to attenuate them before the ADC?

    Please refer to this other post for added explanation of ADC input voltage range: http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/p/309671/1088275.aspx#1088275

    Regards,

  • 0 in reply to Ryan Andrews
    Expert 1350 points

    Hello Mr.Ryan ,

    Thank you for quick reply.

    I undestood that  settable Vref input range is under power supply,that I can input 24mV to Vref input.

    In respect of an amplitude of input wave and the reason of  attenuating them,

    I  asked them to my customer a while ago.

    Best Regards.