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TLV320AIC3104 Eval Board I2S with DC offset

Leonid Ayzenshtat
Intellectual 275 points


Hello,

I am using the Line1 input.

My signal has audio as well as a 50mV DC offset.

I need to digitize the audio along with the 50mV of DC. I know that I2S can carry DC data.

I have tried to bypass the AC coupling capacitors on the Eval board but that does not really solve the problem.

What would be the best way to get this to work.

thanks;
Leo

  • 0
    TI__Guru**** 189401 points

    Hi, Leo,

    I am going to move your post to the Audio Converters forum.

    -d2

  • 0
    TI__Mastermind 28585 points

    Hi Leo,

    The AIC3104 will measure the AC as well as the DC signal (assuming of course that you are DC coupled). The AIC3104 has a fixed internal DC input bias of around 1.35V. So at DC = 1.35 you will be at the zero crossing level. As an audio converter, the DC bias is not particularly accurate and will have some level of fixed offset from the target 1.35V. So depending on the level of accuracy you require, you might need to do some level of calibration in your system. 

  • 0 in reply to Converter Apps
    Intellectual 275 points

    So do I just connect a function generator directly to the input?

    Do I need to do a source impedance transformation? OpAmp buffer?

    What is the easiest way to overwrite the 1.35V dc?

    Does it matter if my input on the codec is setup for differential or single ended?

  • 0 in reply to Leonid Ayzenshtat
    TI__Mastermind 28585 points

    Hi Leo,

    From a DC standpoint, you would have to consider the input range to be from 0.35V to 2.35V, with 1.35 V being zero output level. If you connect directly to a signal generator that is ground referenced, with no signal you would already be beyond the negative full scale of the input (the output would saturate at max negative code). It would be necessary to create a 1.35V offset externally to get centered on the input range. Most signal generators allow you to add an offset. If not, you would need to add a summing junction or some other level shifter externally to add in 1.35V

    If you are differential, then you will reject most of the DC that is common to the inputs but you still need to keep the inputs within the common mode input range of the device which will be about the same as the input range (0.35V to 2.35V). The CMRR is typically around 60 dB.

  • 0 in reply to Converter Apps
    Intellectual 275 points

    Hello,

    Thank you for the response. But you did not really answer any of my question.

    1. So do I just connect a function generator directly to the input?

    2. Do I need to do a source impedance transformation? OpAmp buffer?

    3. What is the easiest way to overwrite the 1.35V dc?

    4. Does it matter if my input on the codec is setup for differential or single ended?

    Can you please answer the 4 questions above in full detail.

    Thanks;

    Leo