• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 30 subscribers
  • Views 2142 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

PCM1754 Noise Problem

Seong Jong Lee
Prodigy 30 points
Other Parts Discussed in Thread: PCM1754

hi,

I'm using PCM-1754 DAC. I selected the part refered to that the SNR and THD+N of PCM1754 is 106dB. But, when we incorporated the PCM-1754 into our board, the output white noise is over -75dBm (i. e. SNR never be more than 80dB).

I really wonder that waht cause that problem. please let me know the reason.

For more understanding, I attache my schematics regarding PCM-1754 and output LPF.

I think your immediate response will be very helpful for me. 

  • 0
    TI__Guru**** 189399 points

    Hi, Seong Jong,

    Sorry that you are having trouble with our device. There are many reasons why this may be occurring.

    Things you may want to look at:

    - noisy power supply

    - noise picked up from a system ground loop

    - ground noise picked up thru ground plane

    I am not sure which is more likely, so please check these and let us know what you find.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 30 points

    Hi, Dapkus,

    Thanks for your immediate response and advice.

    Recently, I received e-mail from TI Korea regading my problem, but the suggestion in the mail is a method to reduce out-band (over 20kHz) noise. My problem is related to the in-band (300~3000Hz) noise. Within 300~3000Hz, PCM1754 output noise is seriously higher than other CODEC's (AD1938 from Analog Device) output. 

    If there is some problem on our board's GND, the outputs of other CODECs should have same problem with PCM1754 output, but other CODECs output don't have the noise problem (They have -90~95dBm noise level).

    Firstly, I reviewed our schematic to check whether our circuit is designed per TI reference circuit and I think that our circuit is designed per your recommendation. So, I bought another LOT and mounted it to our board, but the situation is same.

    I don't know what make the higher noise, although SNR specification in your datasheet is 106dB.

    If you have some advice or recommendations, please let me know.

    Thanks.

    S. J. Lee

  • 0 in reply to Seong Jong Lee
    TI__Guru**** 189399 points

    Hi, SJ,

    JY is going to contact you directly.

    -d2