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ADS1291: ADS1291 problem

en-chao liu
Prodigy 40 points
Part Number: ADS1291


  1. When 1P and 1N (3PIN, 4PIN) of the ADS1291 add series resistances and identification instrument input 5mV sine wave, the value of sine waves obtained from the ECG acquisition will seriously exceed the amplitude.If a small DC component is added to the sine wave of the identification instrument, the sine wave will appear normal; However,adding a DC component directly to the circuit will not work. What is the cause of this?

b. When 1P and 1N (3PIN, 4PIN) of the ADS1291 have capacitances and resistances in series,the value of sine waves is 5 mV and normal,which is read from the identification instrument.However, when collecting or shorting between R and L leads, there is a small protrusion on the ECG line,as shown below. Could you please tell me how to solve the problem of one second fluctuation of capacitance? And what is the reason for this?

I am also in accordance with the recommended figure to debug, the same phenomenon, PCB line is no problem

  • 0
    TI__Guru 67206 points
    Hi En-Chao,

    Thanks for your post and welcome to our forum!

    Remember that each input signal should be centered around the same mid-supply common mode voltage. Right now, you show a 10k pull-up resistor to RLDOUT on IN1N. What is the common-mode of IN1P?

    Best Regards,
  • 0
    TI__Guru 56522 points
    Hello En-Chao,

    Thanks for your post and welcome to the forums!

    1) What do you mean by seriously exceed the amplitude? Do you mean that the wave is larger than the input sine wave that was applied? Are you measuring this at the input pins of the ADC or the output? What are the gain settings on these channels?

    Since these channels are measured deferentially, the common DC component will be canceled out.

    2) When you say collecting, do you mean reading data? It looks like an inductor is charging and discharging. Perhaps shorting these leads or the introduction of the components are causing the current to lag the voltage resulting in an inductance.
  • 0 in reply to Ryan Andrews
    Prodigy 40 points
    I should use your ADS1291 recommended circuit, It's still a problem . The gain is not set。
  • 0 in reply to Alexander Smith
    Prodigy 40 points
    Hello Alexander Smith:
    1) What do you mean by seriously exceed the amplitude? Do you mean that the wave is larger than the input sine wave that was applied? Are you measuring this at the input pins of the ADC or the output? What are the gain settings on these channels?
    identification instrument input 5mV sine wave（ input），the ECG acquisition will seriously exceed the amplitude（DISPALY）,I didn't set gain Settings。

    2) When you say collecting, do you mean reading data? It looks like an inductor is charging and discharging. Perhaps shorting these leads or the introduction of the components are causing the current to lag the voltage resulting in an inductance.
    Excuse me,My circuit should be resistance or capacitance？What can I do?
    Best regards,
  • 0 in reply to en-chao liu
    TI__Guru 56522 points

    Hello En-Chao,

    Did Ryan's answer solve the common mode problem?
    Are you having trouble configuring the gain settings of the device?

    I don't fully understand the issue that you are having. Can you please explain in further detail?
    Is this voltage going to the 1P and 1N (3PIN, 4PIN) of the device? What is the magnitude?
    Are the input pin limitations being exceeded due to the common mode issue?

  • 0 in reply to Alexander Smith
    Prodigy 40 points

    Hello Alexander Smith:

    1.Did Ryan's answer solve the common mode problem?

         RLDOUT  connection   to 1 p, 1N pin is not connected,I also don't connection to RLDOUT, The same phenomenon.


    2.Are you having trouble configuring the gain settings of the device?

         I can.but, I didn't set gain Settings.

    I don't fully understand the issue that you are having. Can you please explain in further detail?
    Is this voltage going to the 1P and 1N (3PIN, 4PIN) of the device? What is the magnitude?
    Are the input pin limitations being exceeded due to the common mode issue?

    Look at the picture


    display:


    I set  sine wave 0.3mV, no problem.

    There's no problem in the other waves ，There is sine wave wrong