• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 515 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

PCM1754 noise

PCM1754: Unsatbel out of band noise

Mochi
Genius 4175 points
Part Number: PCM1754


Hello,

Our customer is trying to replace the DAC to PCM1754.

During their ES sample evaluation, they found unstable noise floor level at more than 20KHz non audible band.

It seems “Delta Sigma modulator” create noise shaping characteristics, but some reason, high frequency noise floor is changed by I2S clock ON/OFF synchronization internal DAC.

Anyway, we knew PCM1754 is little bit old design primitive 106dB DAC and all of audio DAC performance is specified under 20KHz with AES filter, even High-Reso Fs=192KHz source.

Do you say this DAC behavior is not out of specification?

Is it possible to explain what is root cause of this noise floor changing by PCM1754 DS modulator re-synchronization?

Our customer wants to know at least this mechanism.

 

Attached FFT data is taken at Fs=48KHz, SCK=256Fs with 1st order LPF.

 

Regards,

Mochizuki

  • 0
    TI__Guru 55043 points

    Hi Mochizuki-san,

    The out-of-band noise starts to increase on this device at 50%×fS.  The behavior of the noise beyond 50%×fS is dependent on the devices digital-filter and the input data.  

    I will continue to review this case and update you tomorrow.

    Thanks,
    Paul

  • 0 in reply to Paul_Frost
    Genius 4175 points

    Hi Paul,

     

    Per our conversation on the phone, we could understand this behavior is not only our ES product environment but it comes from PCM1754 characteristics itself.

    And on usual application circuit Out of Band Noise is reduced by DAC post LPF.

     

    Regards,

    Mochizuki