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ADS1298R: Connection with only 2 unipolar electrodes

Damien_Effi
Intellectual 555 points
Part Number: ADS1298R
Other Parts Discussed in Thread: , ADS1298ECGFE-PDK

Dear TI team,

I am designing an ECG medical device. Our customer wants to use the ADS1298R but with only 2 unipolar electrodes and I have question about connection:

When only 2 electrodes are used, how connect RLDREF, RLDOUT and RLDINV?

Can you have a look on the schematic and let me know your remarks.

Schema.pdf

Regards,

Damien

  • 0
    TI__Guru 66446 points
    Hello Damien,

    Thank you for your post!

    RLDREF, RLDOUT, and RLDINV can all be left floating if unused. Internally, you can power down the RLD amplifier and disconnect the PGA outputs from the inverting RLD amplifier input via register settings.

    With the 2-electrode configuration, your input signals to CH2 will need to be AC-coupled as well. You can connect these inputs to the right side of the 100 nF capacitors and set the common-mode to mid-supply with a resistor divider as you did for CH1.

    Best Regards,
  • 0 in reply to Ryan Andrews
    Intellectual 555 points

    Hello Ryan,

    Thanks a lot for your quick reply.

    OK, so I will left floating RLDREF, RLD OUT and RLDNIV.

    About the 2 electrodes configuration, I will add this:

    But, when you look at the ADS1298R ECG FE reference schematic, ther is neither AC coupled neither common mode on CH2.

    Can you clarify this?

    Thanks

    Regards,

    Damien

  • 0 in reply to Damien_Effi
    TI__Guru 66446 points
    Hi Damien,

    Your picture did not attach correctly. Please try to upload it again.

    The ADS1298RECGFE-PDK assumes you are using the RLD to bias the DC-coupled inputs.

    Check out our training portal for some useful videos on ECG signal chain. This may be helpful to explain the different signal chain requirements. One of the sections details the difference between AC coupled and DC coupled inputs.

    training.ti.com/how-measure-ecg-guide-signals-system-blocks-and-solutions

    Best Regards,
  • 0 in reply to Damien_Effi
    Intellectual 555 points

    Hello Ryan,

    Can you have a look on the schematic and let me know your remark?

    I have an other question:

    As we are using only 2 unipolar electrodes, how I must connect the RLDREF, RLDOUT and RLDINV pins?

    Thanks

    Regards,

    Damien

  • 0 in reply to Ryan Andrews
    Intellectual 555 points

    Hello Ryan,

    Can you check the schematic I attached and can you also reply to my questions?

    Thanks

    Regards,

    Damien

  • 0 in reply to Damien_Effi
    TI__Guru 66446 points

    Hi Damien,

    A few comments on the schematic:

    1. You can remove the two 2.2-nF capacitors in the Channel 2 signal path. C24 and C26 already AC couple the signals.
    2. Low-pass filters are still generally recommended on the ECG channels for anti-aliasing. The ADS1298ECGFE-PDK as some examples.
    3. The remaining unused analog inputs should be tied to AVDD. Please see the Pin
      Configuration and Functions section of the data sheet.
    4. You should consider adding a single 10-uF capacitor on AVDD and DVDD somewhere in the vicinity of the ADC. The smaller 100-nF caps are good to place next to each individual power supply pin, but the larger 10-uF caps provide bulk decoupling for the supply.

    Best Regards,