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TLV320AIC3256 - high noise level detected at line & headset output

Peck
Prodigy 230 points
Other Parts Discussed in Thread: TLV320AIC3256EVM-U

Hi,

We perform the following audio loopback test:

1) apply a 1k sine wave into the analog input using a function generation

2) loopback the analog input to the headset output (measure with oscilloscope)

2) set page 1 - reg 16 & 17 to 0x0 (0dB) - HPL & HPR driver gain

3) about 50mVpp of high frequency noise (370KHz) was detected on the output.

4) as the HPL & HPR driver gain increase, the output noise is higher.

Is there any digital filtering we could do in the register of the codec?

 

  • 0
    Prodigy 230 points

    Hi,

    We tried to isolate the noise source by disable the analog input.

    It seems that the noise come from the headset output and not from the analog input.

    Attached is the screen capture of the output noise when the analog input is disable but the HPL & HPR driver gain is set to 0dB.

    Our observation:

    - increasing the analog input does not increase this noise level.

    - increase the HPL & HPR driver gain will increase the noise level.

    Thanks & best regards.

    Peck

     

  • 0 in reply to Peck
    TI__Mastermind 46195 points

    Peck,

    Try the following:

    1. Mute DAC output (p0_r64_d3-2).
      1. If noise is still there, then probably there is some system noise coupling into HPVDD or CPVDD. Try using a cleaner supply.
    2. If noise is removed when muting DAC, then probably there may be something wrong with the register settings.

    Try to match the settings found on the TLV320AIC3256EVM-U Control Software example configurations. It helps to match the register settings of your system to the ones in the software as much as possible for debugging.

    Try using the lineouts instead of the headphone outs since these are less prone to issues (no charge pump, easier to configure).

    Some noise above the audible range is normal in a sigma delta converter. But in your screenshot, it looks like some spikes are there which do not seem normal.

    Check this app note http://www.ti.com/lit/pdf/slaa404 which includes many configuration settings for the AIC3254. It is register compatible with AIC3256, except that it does not a ground centered headphone amp. But if you use the lineouts, the registers are all the same.

    Regards,

    J-