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ADS1298: ADS1298 signal reference

jack jackson52
Prodigy 200 points

Part Number: ADS1298
Other Parts Discussed in Thread: INA128

Dear All,

I would like to use the ads1298 to collect the EMG, but I have no idea how to provide a reference signal for my application.

Using INA128 I can connect the ref pin to the ref electrode. How is it done with the ADS1298?

What is the RLDIN and how can I used it? Is it my reference pin?

On page 99, I notice that pins RLDxxx are used. How does it work?

Best wishes,

  • 0
    TI__Guru 61352 points
    Hello Jack,

    Welcome to the forum and thanks for your post!

    There is an internal reference on the device and it is possible to connect an external reference to VREFP. I recommend you take a look at Figure 31 & 32 in the datasheet.

    RLDIN is part of the right leg drive circuit which is used for biasing the patient in order to remove the common mode noise. This is not your reference pin. Section 9.3.1.7.6 of the datasheet explains this function.

    Additionally, my colleague put this great set of training videos together which will greatly increase your understanding of these types of systems.
    training.ti.com/how-measure-ecg-introduction-what-ecg
  • 0 in reply to Alexander Smith
    Prodigy 200 points
    Thank you for your answer!


    Fig. 31 and 32 show the ref signal for ADC (internal.external). I asked for the reference signal for my EMG signal as we have it in INA128.
    I though that RLDIN is only for RLD, but I wanted to ask anyway.
    The movies are great for students.

    I guess, I found an answer here: e2e.ti.com/.../521787

    However, I would like to sum it up. Is it true:
    in the ina128, we can use a reference electrode and here, current flow from a patien to the ampifier and set the reference level.
    in the ads1298, we use the RLDOUT pin and apply a common-mode voltage on a patient, which should actively reduce the common-mode voltage and bring the inputs level to the range of supply?
  • 0 in reply to jack jackson52
    TI__Guru 61352 points
    Hello Jack,

    I see now, my apologies - I didn't understand your terminology in the original post. Thank you for using the search!

    You are correct. RLDOUT will be used to apply the common-mode voltage on the patient which will greatly improve the noise rejection - mostly from the mains (50/60Hz). RLDOUT can be set internally to either mid supply or derived from the input channels of your choosing by changing the MUX settings (Figure 43.). Additionally RLDOUT can be supplied from an external source although this is not very common.

    Once again, sorry for missing the original question! Please let us know if you have any additional questions.
  • 0 in reply to Alexander Smith
    Prodigy 200 points

    Hallo Alexander,

    thank you for you answer! That solved my problem!
    btw. there is no need to appologize :)

    Have a nice day!