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Dual channel ADC wrapping

Discussion in 'Analog & Mixed-Signal Design' started by zegichk, Mar 21, 2017.

  1. zegichk

    Thread Starter New Member

    Mar 21, 2017
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    Hi, I am using a dual channel ADC to sample quadrature RF receiver. I write the data though SPI to my PC and process it there afterwards. I have my test setup as following. In the first measurement feeding channel 1 with a sine wave and channel 2 is open. In the second measurement I feed channel 2 with a sine and channel 1 is open. What I see is that channel 1 is always good, e.g., I can very clearly see the sine wave I feed in, but on the second channel I see the sine wave wrapped, .e.g, there are jump in the amplitude. I can still recognize the signal to be sine wave but I cannot explain to myself those jumps (wraps) . Do you have any ideas or suggestions why this wrapping would occur?
     
  2. ScottWang

    Moderator

    Aug 23, 2012
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    1,047
    Could you post the schematic and take some pictures of waveform?
    Files resolution as 800x600 .gif or jpg.
     
  3. zegichk

    Thread Starter New Member

    Mar 21, 2017
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    Hi Scott, hereby is the output I get from the ADC. It clearly is a sine wave but you can see that it is clearly wrapped, which I cannot explain myself.
    screen1.jpg
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    6,777
    1,047
    Schematic?
    If looks like you have had mixed with the square wave as digital signal.

    screen1_20170321-01.gif
     
  5. MrChips

    Moderator

    Oct 2, 2009
    19,146
    6,152
    It also looks like code wrap for negative values.
    What is the part number of the ADC?
    How is the ADC interfaced? What processor is used to interface with the ADC?
    Can you post program code used to read the ADC?
     
  6. zegichk

    Thread Starter New Member

    Mar 21, 2017
    4
    0
    I do not have the schematic at hand right away. I will post later... Do you propose it is mixing with the conversion start signal somehow? then why would it be only on the first channel? When I apply the same signal to the second channel I get a nice sine wave as in your image. I am also suspecting that the ADC could be reading one bit less, e.g., the conversion select switches off too early?
     
  7. zegichk

    Thread Starter New Member

    Mar 21, 2017
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    I was suspecting that too but I measured the DC offset I use to bias the signal so that it does not fall below zero and it is high enough. I use Max1377 ADC converter.
     
    Last edited: Mar 21, 2017
  8. MrChips

    Moderator

    Oct 2, 2009
    19,146
    6,152
    Are you using SINGLE OUTPUT or DUAL OUTPUT mode?
    Sounds like there is a problem with your serial interface.
    You will have to show a circuit schematic and program code.
     
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