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ADS1298R: ADS1298R CMRR improve

Ravi Chaudhari1
Prodigy 50 points
Part Number: ADS1298R

Hi,

We are looking at CMRR improving by using Input Multiplexer (Rerouting The Right Leg Drive Signal)(As mention in the datasheet (9.3.1.7 ECG-Specific Functions)),.

When we referencing the "Improving Common-Mode Rejection Using the Right-Leg Drive Amplifier -Application report" document, that have mention section 5 (the effect of Led-off detection in RLD section) have one suggestion to connect a switch between the PGA output common-mode averaging point and the inverting input terminal of the RLD amplifier to configure this scenario. Here I attached this page image.

As per a datasheet PGA output common-mode averaging point is an internal point inside the chip and RLD inviting point has a pin connection on PCB. The block diagram show PGA output and RLD inverting input have a common connection. Here also the attached block diagram image.

We have the following questions, kindly provide an appropriate solution.

Where can connect a switch?
IF we connect a switch between the below mention image(in between RLDINV pin and 1Mohm resistor). is it work?
The switch is helping to verify Lead- off detect while on/off condition. am I right?
If we are using the input multiplexer technique to improving CMRR that Is it affecting patient leakage and defibrillation?

Regards,

  • 0
    TI__Genius 11550 points

    Hi Ravi,

    Thanks for the post. We will look into this and get back to you. 

    Thanks

    -TC

  • 0 in reply to TCT
    Prodigy 50 points

    Hi, 

    any update...

    We are eagerly awaiting a response. 

    Regards,

    Ravi Chaudhari

  • 0 in reply to Ravi Chaudhari1
    TI__Genius 11550 points

    Hi Ravi,

    Apologized for the late response to your questions. 

    Both the diagrams that you show is not the solution to ensure the working of the RLD feedback loop during leadoff condition using the internal RLD amplifier. The idea is whenever the system detects a leadoff condition; the system should disconnect the common-mode sensing from the RLD feedback path by opening the RLD_SENSP and RLD_SENSN switches of that particular channel. Doing this will help to ensure that the RLD feedback loop will provide the correct bias potential to the patient’s body.

    Thanks

    -TC