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TLV320AIC3106: ADC PGA Signal Bypass with AGC enabled issue

Miguel S
Intellectual 830 points
Part Number: TLV320AIC3106


Hi all,

I am enabling the bypass path from microphone PGA to Headphone Output.

The AGC + Noise Gate is enabled for the microphone.

I am seeing that, when the mic signal is above the noise threshold, everything is working as expected; AGC sets a gain to reach the target level and the output of PGA is fed to the headphones output.

But, when the mic signal is below the noise threshold, the signal fed to the headphones is the noise captured by the microphone with a high gain applied, so the noise can be clearly heard.  In that situation, the digital signal after the ADC does not have such noise.

So, it seems that the noise gate is applied to the signal sent to the ADC but not to the signal sent to the 'ADC PGA Bypass Path'.  Can you please confirm this? Is the 'ADC PGA Bypass Path' expected to be enabled with AGC disabled?

Thanks,

  Miguel

  • 0
    TI__Mastermind 22950 points

    Hello Miguel,

    How are you quantifying no noise on DOUT?

    To answer your question regarding the ADC PGA bypass, no the bypass path is not expected to be enabled when the AGC is disabled. 

    Regards,

    Aaron 

  • 0 in reply to Aaron Estrada
    Intellectual 830 points

    Hello Aaron, thanks for your answer.

    The codec is connected to a microprocessor, and I am saving the digital samples present on DOUT.

    I have seen than the noise present on the 'ADC PGA Bypass Path' is affected by the 'Maximum PGA Gain Applicable'.  If I reduce this parameter, the noise level is also reduced (in the case there is none speaking through the mic).  So, my guess is that the noise gate is not applied to the signal sent to 'ADC PGA Bypass Path'.  Can you please confirm this, please?

    Best Regards,

      Miguel

  • 0 in reply to Miguel S
    TI__Mastermind 30220 points

    Hi Miguel, 

    The noise gate functionality is handled digitally while the gain portion of the AGC is analog.  So it would be impossible for the noise gate to appear on the analog bypass path. 

    When using the AGC and noise gate along with with the Analog bypass path,  this would result in exactly what you are describing.  

    best regards,

    -Steve Wilson

  • 0 in reply to Steve-Wilson
    Intellectual 830 points

    Hi Steve,

    Everything is clear to me now.  Thanks a lot.

    Regards,

      Miguel