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ADS1292R: ADS1292R Using RLD. Could the IN1 be used as the RLD signal source?

yuhang Yang
Intellectual 550 points
Part Number: ADS1292R

Hi everyone,

    I'm using the ADS1292R now. I noticed that the IN1 should be applied as the respiration signal input, and the IN2 still can detect the ECG.

    I want to use the RLD when acquiring the ECG. In the datasheet, I found an example that the RLD signal could generated from channel 1 and routed to the N-side of channel 2. 

    So I want to make sure if the IN1 could still be used as the RLD signal source while acquiring ECG, even though the IN1 is applied to the respiration?

Thanks a lot,

Yuhang.

  • 0
    TI__Mastermind 49431 points

    Hi Yuhang,

    I think there is a little confusion about the routing options here. 

    IN1 cannot sense ECG and respiration at the same time.

    You can use IN1 to derive the RLD signal while being used for either ECG or respiration, which will then be output by the normal RLD pins. 

    In the event that your RLD electrode falls off, you can route the RLD signal through IN1 to keep the patient biased. When using this configuration, channel 1 will not be able to acquire ECG or respiration, as it is busy routing the RLD signal.

  • 0 in reply to Alexander Smith
    Intellectual 550 points

    Hi Alex,

        Thanks for your help.

        I use the IN1 for respiration and IN2 for ECG. I still have some questions.

        1. If the IN1 be applied for respiration like this:

        could it still be used for ECG? 

        2. In this situation, when I acquire ECG with IN2, could I route the RLD signal through IN1 (which has been applied for respiration, but not being used)?

        3. If the answer is no, does that mean the only way I can get the RLD signal when aquiring ECG through IN2 is to use RLD electrode? 

    Thanks a lot.

  • 0 in reply to Alexander Smith
    Intellectual 550 points

    Hi Alex,

    In the datasheet, it said the capacitor of PGA1 should be 47nF if respiration and channel 1 be used:

    But in the MultiParameter BioSignal Monitor Design Guide, the capacitor of PGA1 you're using is 4.7nF:

    So, I want to ask which value should I set to the capacitor of PGA1?

    Thanks.

  • 0
    TI__Guru 60866 points

    Hello Yuhang,

    How many electrodes are you using in your application?

    You cannot output the RLD signal through IN1N because the signal path on IN1N is AC-coupled in your schematic. The RLD signal requires a DC-coupled signal path to set the common-mode voltage on the body.

    It sounds like you are trying to measure one channel at a time (respiration or ECG) and route the RLDOUT signal through a pin on the other channel. The RLD output is not typically connected to the INxP or INxN pins under normal operating conditions. Instead, the RLD output is usually connected to a separate, dedicated electrode. Channel 1 and Channel 2 are intended to measure respiration and ECG simultaneously. The output of Channel 2 (i.e. the ECG channel) can be used to sense the common-mode signal and feed it to the inverting input of the RLD amplifier for common-mode noise cancellation.

    Best regards,