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Thread: ADC noise different for each group.

  1. #1
    New Member New Member NickyKremers is on a distinguished road
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    Feb 2017

    ADC noise different for each group.

    Dear all,

    I'm using the XMC 4800-F100x2048 chip on a custom build circuit board. And Dave 4.3.2 with the DAVE CE apps. For the ADC results I'm using J-scope to see actual values of the variables.

    For our application we need to convert 4 analog signals (Later even more). Preferably we need the conversion of the ADC signals simultaniously at a frequency of 20kHz. But more important is that the converted values are equal when applied with same input signal.

    So i tried the ADC_MEASUREMENT_ADV app and the ADC_MEASUREMENT app. I've noticed that the ADC conversion introduces a noise signal on top of the actual converted signal. This is the case for both apps. I'm using the same input signal for all the 4 analog inputs.
    I'm using pins 14.0, 14.2, 14.4 15.8. (15.8 not available on group 0)

    Click image for larger version

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    What I have seen is that the noise level is depending on the adc group set in the resource list. When I'm using 4 times the same group the noise level is the same for all four groups. But when I use different groups the noise level between all the converted values is different.
    That is why I think it has something to do with the adc conversion inside the chip and not with using the Dave apps.

    When I want to use the ADC_MEASUREMENT_ADV app and use the sync conversion with three slaves then all inputs need to be at different groups and same chanel, so this wont work for me because of the difference in noise. And when I want the noise level to be the same for all four inputs I'm not free to choose the pins I want to use.

    Filtering the signal won't work because the noise is on top of the signal and averaging the signal still keeps a difference between the inputs.

    Hopefully I've explained the problem clearly. I've atached a test application that I've used.

    Is there any solution for this problem?

    Thanks for your help.

    Kind regards Nicky

  2. #2
    New Member New Member
    Infineon Employee
    Infineon Employee
    Eric is on a distinguished road
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    Mar 2013
    Hi NickyKremers,

    You can use the same Trigger input for all groups.
    I changed your trigger to HW PWM input and sync only the clk.
    (no channel snyc!)
    Project attached.

    Or you use the sync. Conversion with channel snyc (checkbox "sync master") function and select CH0 or CH1 for the master.
    With the Alisas function of the ADC you can reach any PIN of the ADC slaves.

    When you use only one group and 4 channels they will be sampled one after each other.
    A change/noise in the measured signal will be visible.

    I hope this will help!
    The views expressed here are my personal opinions, have not been reviewed or authorized by Infineon and do not necessarily represent the views of Infineon.

  3. #3
    New Member New Member NickyKremers is on a distinguished road
    Join Date
    Feb 2017
    Hi Eric,

    Thanks for your fast response. I will give it a try today and let you know if it works.

    Kind regards,

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