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ADS1292ECG-FE: I only use 2 electrode (ADS1292) for 1-Lead ECG without RLD,In this case， how to realize the function of lead off?

leo chen
Prodigy 235 points
Part Number: ADS1292ECG-FE

Dear TI experts:

               I have a project that I need use  ADS1292 for 1-LEAD ECG application.   I only use 2 electrode to measure 1-Lead ECG without  RLD  .In this case，These electrode inputs must be AC-coupled,so how to realize the function of lead off? THX

  • 0
    Prodigy 235 points

    Dear TI experts:

           One more question,  In this case，CMR is only 66dB,   How to improve this indicator，thx

  • 0 in reply to leo chen
    TI__Guru 66176 points

    Hi Leo,

    Thanks for your post.

    This question is very common for single-lead ECG applications. The electrode inputs are generally AC-coupled and biased on the ECG system circuit board. Please read through some of the related threads in our forum as well as the ADS129x BIOFAQ page.

    CMRR can be improved by utilizing the RLD feedback loop as well as by reducing the tolerances of input signal chain components. This works to match the impedance seen by each electrode input and reduces common-mode to differential signal conversion.

    Best regards,

  • 0 in reply to Ryan Andrews
    Prodigy 235 points

    hi，Ryan

          Thx for your reply,

         I had used RLD feedback loop,but CMRR is only 66dB,can you help me ?I had try R30 or R31,but the result is the same ~66dB.

  • 0 in reply to Ryan Andrews
    Prodigy 235 points

    hi，ryan

         I have read the ADS129x BIOFAQ page before，but  I didn't find an effective way

  • 0 in reply to leo chen
    TI__Guru 66176 points

    Hi Leo,

    Are you sensing the common-mode signal at the PGA outputs? This is done using the RLD_SENS register.

    Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 235 points

    hi,ryan

        My test mode is based on your recommendation，The registers have been set as required, but the CMRR  has not improved！

       Can u tell What is the typical value of the CMRR when the RLD works,Just like my project, R31 is welded，R30 is NC.THX

  • 0 in reply to leo chen
    TI__Guru 66176 points

    Hi Leo,

    CMRR performance is highly dependent on the entire signal chain. As you are only using two electrodes, it's very possible for the common-mode noise to convert to differential noise before the AC-coupling capacitors. The 22-M pull-up resistors can only help to suppress the remaining common-mode noise after the AC-coupling capacitors, but this technique cannot reduce the noise that has already become differential.

    Improving CMRR requires accurately matching the input impedances in both (+) and (-) signal paths. This impedance includes the electrode contact impedance as well as PCB traces and passive component tolerances.

    Best regards,