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PGA2311: Zero-Crossing Detection

Hao Wang14
Expert 4415 points
Part Number: PGA2311

Hi Team,

PGA2311 has zero-crossing detection function for noise-free level transitions. Does it mean that PGA2311 automatically changes between the specific gain setting with lowest output noise when there is no input signal and the user's setting gain when there is input signal? If my understanding is not correct, could you please help explain the function details? Thanks!

Best Regards!

Hao

  • 0
    TI__Guru 54576 points

    Hi Hao,

    When the Zero-Crossing detection function is enabled, (ZCEN pin 1 set high), after the user programs a gain change, the PGA2311 will wait until the input signal crosses zero volts to minimize any noise or transient signal that is generated at the PGA output while changing the gain.   Essentially, after the user issues a gain change by programming the 16-bit frame into the serial port of the PGA2311, the PGA2311 will wait until the input signal crosses zero prior executing the gain change.  Changing the gain of the PGA2311 when the input is close to zero volts minimizes any transients at the PGA2311 output, since there is only a very small or zero input voltage signal present when the gain change occurs.

    As explained in the datasheet, the new gain setting is not implemented until either a positive slope zero crossing is detected, or until a time-out period of 16 ms has elapsed. When the 16-ms time-out occurs, the new gain setting takes effect with no attempt to minimize audible artifacts.  In other words, if a non-zero signal is still present at the PGA2311 inputs after the 16-ms timeout elapses, a transient/noise signal at the output will appear when the PGA2311 switches gains, as the output level will change as a function of the programmed gain and input signal present. 

    Thank you and Best Regards,

    Luis

  • 0 in reply to Luis Chioye
    TI__Expert 4415 points

    Hi Luis,

    Thanks for the detailed explanation. So when the gain setting is implemented, PGA2311 cannot suppressed the input transitions any more. Does it mean that the zero-crossing detection function is only used for noise-free level transitions at the very beginning such as the power up before the gain is changed?

    Thanks and Best Regards!

    Hao

  • 0 in reply to Hao Wang14
    TI__Guru 54576 points

    Hi Hao,

    This function is not related to device power-up.  The PGA2311 is an audio volume control, and the zero-crossing detect function will attempt to execute any gain changes when the input signal crosses zero volts to minimize noise artifacts at the output.

    When the zero-crossing detection is enabled, the PGA2311 will delay the gain change until the input signal crosses zero volts to minimize any noise artifact at the PGA2311 output. If the device does not detect an input zero crossing at the input after the 16-ms delay elapses, it will then execute the gain change regardless. 

    See example below.  The PGA2311 has an input sinusoidal audio signal applied at its input.  If the zero-crossover function is enabled, it executes the gain changes at the zero crossing of the input signal, avoiding noise artifacts.

    Thank you and Regards

     Luis