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TLV320AIC3204: Mixing balanced (differential) and unbalanced inputs

Joe454
Intellectual 580 points
Part Number: TLV320AIC3204


If possible, I'd like to mix the differential and single-ended inputs to the ADC, but how do we maintain balance not knowing if a source is plugged into the unbalanced input?

When the unbalanced input is plugged in, it all works fine, but if there's nothing plugged into the unbalanced input, the presence of the CM on the negative input of the ADC throws off the balance of the differential input.

We could add a jack detection to programmatically change the CM (or just not mix) but I didn't know if there was something more clever that could be done.

  • 0
    TI__Mastermind 23030 points

    I am sorry i could not understand fully your query?. Would it be possible to draw it on a piece of paper?

    The common mode, is given to set the dc voltage to the ADC to the center of the  ADC range. Both pins should get this DC Level  .An AC coupled signal adds and subtracts from this level

     What eactly do you mean when you refer to the balance of differential input ?

  • 0 in reply to Sanjay Dixit
    Intellectual 580 points

    Thanks for responding.

    I have left and right balanced inputs, coupled to the ADC with 20k programmatically. (Really the MICPGA input + and -)

    I also have an unbalanced input (IN3) coupled to the ADC with 20k, and CM (also 20k) as required.

    I would like to mix them all together, if possible. (For each L,R channel)

    However, when I have nothing plugged into the IN3 input, the CM is still present on the MICPGA- input. This creates a small offset on that signal that disrupts the balanced signal. If I present the same input to MICPGA+ and -, I should get zero, but because of this small offset from the CM being applied, I don't get zero. The differential signal input is disturbed and no longer cancels to zero.

    Of course, if I (via software) disconnect the CM from MICPGA-, it works fine. I was hoping there was a way to make it "just work" without having to change a setting based on plug state.


    Does that clarify things?  I could draw it out if I had to I suppose.

  • 0 in reply to Joe454
    TI__Mastermind 29755 points

    Hi Joe,

    Yes you can mix them as the diagram shown in datasheet.

    So you have the SE in IN3 and where is the balanced connected to? Are all your input ports capacitively coupled including your SE ports? 

    Regards,

    Peter

  • 0 in reply to pdjuandi
    Intellectual 580 points

    Everything is capacitively coupled properly (1u).  The balanced inputs are fed to IN1_L and IN1_R, and the other channel is IN2_L and IN2_R. 

  • 0 in reply to Joe454
    TI__Mastermind 29755 points

    Hi Joe,

    Can you provide drawing of your setup to be sure?