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ADS1298: Background noise is over riding the original ECG signal

Part Number: ADS1298

we are using ADS 1298  8-Channel 24-bit ADC With Integrated ECG Front End. when we power up device approximate  30 sec output will come exactly then noise will add all channels as per my observation when power up  VCAP3 voltage level approximately 3V is there after that constantly decreasing voltage level when  level draping  the 2.82V or less than that then  noise is over riding  original ECG signal. 

Please replay as early as possible

thanks and regards 

Chandrashekara 

  • Hello Chandrashekara,

    Thanks for your post!

    Can you provide a schematic and waveforms showing the issue?
  •  Hi Alexander,

    here attached schematic, Supply 3.3V , VREFP  =  2.4V, 

      

    and here i attached before noise all 12 Channel ECG signal  

    after background noise 

    Thanks and Regards

    Chandrashekara

  • Hi Chandrashekara,

    VCAP3 should be AVDD + 1.9V. When there is an issue with the VCAP voltage it usually means there is an issue with your power supplies or the device is dead. Since you are able to get data for 30s before seeing issues I do not think the device is dead.

    Can you verify your power up sequence is as recommended in the datasheet and probe your supplies to ensure that they are clean without noise?

    Take a look at the other VCAP voltages during your startup routine to see if they ever reach the below values:

    VCAP1: AVSS + 1.2V
    VCAP2: (AVDD+AVSS)/2
    VCAP3: AVDD + 1.9V
  • Hi Alex,

    We replaced the ADC but still we are getting the noise problem.
    VCAP3 voltage level approximately 3.7V is coming at power up condition after that constantly decreasing once it crosses the 2.82V, noise is over riding the original ECG signal. We have checked by replacing the battery with clean power supply.

    VCAP1 = AVSS + 1.2V and VCAP2 = (AVDD+AVSS)/2 is correct.

    Let us know the reasons for the noise and ideas to rectify it.


    Best Regards
    Chandrashekara

  • Hello Chandrashekara,

    Can you verify your power up sequence is as recommended in the datasheet?