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PCM1789: SNR and THD over high issue

Henry Wang3
Genius 3065 points
Part Number: PCM1789
Other Parts Discussed in Thread: PCM1798

Tool/software:

Hi Sir,

My customer tested the audio DAC performance of PCM1798, they got some test results over high for SNR and THD.
Could you please help to review the scheamtics to advise some comments to fix those issues? Thanks!

Schematics:

DV PCM1789.pdf

SNR test result:

THD test result:

  • 0
    TI__Mastermind 21490 points

    Hi Henry,

    One of our DAC experts will update this thread shortly

  • 0
    TI__Mastermind 25640 points

    Hello Henry,

    The THD and SNR are very off and considering they  have other components on the board such as ADC they  should  measure the THD and SNR at the output of the DAC just  before sending it for filtering and DIFF to SE conversion. They  might have a lot of noise coupled through GNDs,  but first they  need to make sure the huge degradation is in the DAC itself and not after the amplifiers connected to the DAC

    Also they have to make sure the signal going to DAC (from the source) is clean,

    And finally I recommend to use a simpler schematic at the output of the DAC, Below is one possible recommendation that can save components and a cleaner path. I close the thread for now but let me know if they have any question. 

    Any issue with the ADC, you need to open a new thread as I am not much familiar with ADC side.

    Regards,

    Arash