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AIC3104 Output Noise

Denis
Intellectual 505 points
Other Parts Discussed in Thread: TLV320AIC3104, CC8520

I need some assistance in reducing the TLV320AIC3104 when the line outputs are turned on.  It sounds like white noise. Here's the configuration, I have a master and slave unit which operate using the CC8520 Pure Path Wireless SOIC. The master has a differential mic input on the MIC1R channel of a AIC3104 and the slave's AIC3104 is configured such that the received signal is outputted onto both the left and right line outs differentially. When the slave first powers up, the outputs are nice and quite, but when the master pairs, the outputs turn on and the noise is heard. Even after turning off my master, the noise is still heard, even though I power down the line outputs going from active to low-power on the CC8520 (although this may not be occurring since it seems the outputs are still active with no signal.)

Unused inputs to the AIC3104 are floating. Do I need to capacitively couple them to ground even though the inputs are not powered?

The mic gain on the master is set to 20dB. Only a highpass filter is used with a cut off at 1Hz.

The output gain on the slave is set to 0dB gain on both left and right DACs, and 9dB gain on both the left and right line outs. I don't have a filter set at this time in the slave.

Any recommendations?

Thanx,

Denis

  • 0
    TI__Mastermind 28585 points

    There should not be much noise at the output of the AIC3104 if it is configured correctly. You might want to double check the DAC path you are using. L1/R1 will be a good choice. Are you seeing the noise directly at the output of the AIC3104 or is there an amplifier? 

     

    If you can provide a schematic and register settings, I will take a look.

  • 0 in reply to Converter Apps
    Prodigy 130 points

    Hi,

    We have the problem with our codec tlv320aic3104...I'm already using L1/R1...

    I think the problem comes from DAC when it power up.

    Is there any reserved register we can configure to enable auto mute DAC like aic32XX ?

     

     

    Thank you

  • 0 in reply to ivan mercier
    TI__Mastermind 28585 points

    No, the DAC would need to be muted manually. 

  • 0 in reply to Converter Apps
    Prodigy 130 points

    So the only way to cut this noise, is to mute manually after playing!?

    But the noise will be still here during playing...

    How can you get a SNR of 102-dBA with this codec?

     

    Thanks a lot

  • 0 in reply to ivan mercier
    TI__Mastermind 28585 points

    Hi Ivan,

     

    The specs in the data sheet can easily be reproduced with our EVM and an appropriate tester such as the Audio Precision. If you are not getting this performance, I would suggest that there is something going on in your system or with your test setup. i would be happy to help you. i would need:

    1. full system schematics. The small section above doesn't show enough to provide any clues.

    2. Register settings

    3. External Clock frequencies

    4. Picture of the noise (Frequency domain is best)

    5. test setup with input signal, where the output is tested etc...

    Unfortunately, there are many ways to run into system level problems with audio. Sometimes small things can lead to big problems. Everything from grounding to power supplies must be checked...

     

  • 0 in reply to Converter Apps
    Intellectual 505 points

    Ivan,

    A couple of things you may want to try:

    1) Isolate your Analog and Digial grounds paying close attention to which grounds are considered analog (AVSS1, AVSS2, DRVSS(driver output so you may want to isolate this from the other analogs to keep large currents from circulating) and which grounds are considered digital (DVSS) in the 3104.

    2) Apply a simple single order low pass filter on the output of the 3104. A 100 ohm resistor and a 10nF capacitor combination. This helps to take out the switching noise from the DAC.

    Hope this helps.

  • 0 in reply to Denis
    TI__Mastermind 28585 points

    Very good point on the output filter. This is especially true if the output is being measured at the output of an amplifier. Noise that is out of the audio band can cause problems with class d amps for instance.

     

    Here is a good app note on the effects of out-of-band noise on CODECs:

     

    http://www.ti.com/lit/an/slaa313/slaa313.pdf

  • 0 in reply to Denis
    Prodigy 130 points

    OK well,

    we've found the noise source.

    It comes from codec configuration:

    Regarding my HW setup, HPRCOM should be configured as external feedback with HPLCOM as constant VCM output instead of differential of HPROUT. (R38).

     

    Thanks for your answers.