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ADS1298 Not installed components

Zubair Lutfullah
Intellectual 295 points
Other Parts Discussed in Thread: ADS1298

Hello

I have read the design note regarding the Not installed components.

http://e2e.ti.com/support/data_converters/precision_data_converters/w/design_notes/1152.aspx

Can you please refer components for the capacitor, resistors as well?

Is there any other purpose other than a fixed offset and a DC block?

Regards

Zubair

  • 0
    TI__Mastermind 43915 points

    Hi Zubair,

    The caps as you mentioned are DC blocking caps a lot of time used during respiratory measurements on channel one. When the DC blocking cap is installed, you will need weak pull up and down resistors to keep the input within operating range. Generally we recommend large (>1Mohm) resistors for the pull up and down resistors.

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    Intellectual 295 points

    Thank-you Tony.

    ECG Spectrum starts at 0.05Hz. And onwards.


    I was wondering what capacitor would not interfere in that range onwards. And still block DC.

    Regards

    Zubair

  • 0 in reply to Zubair Lutfullah
    Intellectual 295 points

    I noticed I can simply test using C100 and C99. They are installed in the path. 2200pf. Interesting. I believe that is somewhat related to the respiratory path.

    Regards

    Zubair

  • 0 in reply to Zubair Lutfullah
    TI__Mastermind 43915 points

    Hi Zubair,

    Give this post a read -

    http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/162315.aspx#597370

    You are going to need a big cap to HPF at 0.5Hz in order to still pass the full ECG bandwidth. This is why we kept the cap uninstalled. The Majority of ECG applications will not include a DC blocking cap unless the electrode DC offset + ADC gain exceeds the input range. The ADS1298, being a very low noise converter optimized for ECG, does not need high gain to reproduce the ECG signal and is why AC coupling the inputs is not required. 

    Regards,

    Tony Calabria