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Understanding of the Single ended to 'balanced' converter

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  • Understanding of the Single ended to 'balanced' converter

    Hi everyone,

    I need help with understanding the schematic used in the course before feeding our single ended biased signal to the ADC differential inputs.

    Click image for larger version

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    VCOM is the biasing voltage.

    I understood that r306 and C307 form a low pass filter, but why not connecting the cap to GND ? I believe it has to do with the "balanced" conversion, we want the same common mode voltage on both lines I think, but it's still obscur to me.

    Can you please help me understanding that circuit? I searched online but did not find responses.
    And, what if we did not used that circuit, and directly connected the biased voltage to -IN, and the biased signal to +in of the ADC ?

    Thank you very much.

  • #2
    R306 and C307 alone are not a low pass filter.
    You can consider R307 at as being in series with R306 for that filter and then the question is how low impedance is Vcom?
    If you want a more direct low pass filter, C307 need to be connected to Gnd.
    As it is now, when ADC_IN+ goes up, so does ADC_IN-, until R307 can lower it back to Vcom.

    This also is not a differential signal as ADC_IN- is almost constant at Vcom. Transients on ADC_IN+ are the same polarity on ADC_IN- due to C307 as mentioned before.


    • #3
      To understand that subject I'll need more explanation, can you maybe redirect me to ressources on that subject ? I searched but did not find enough explanation on that, I am a still a beginner regarding analog stuff, I need to learn more.


      • #4
        "...that subject..." I assume you mean the RC filter?
        Well, you would need to start there ("RC filter") together with the basic circuit elements resistors and capacitors in this case.