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Clock noise in PCM4202

Daniel Vazquez1
Prodigy 60 points
Other Parts Discussed in Thread: PCM4202

Hi,

We have designed a board with one ADC(PCM4202) and DAC, both are working at 96KHz of fsample and MCLK of 24.576 MHz (256fs), but each one working with different clock, I mean, they are not synchronous each other. In these conditions the DAC's clock leak to ADC input because we can see very noise in ADC spectrum. What are the points more sensitive in the PCM4202 to this clock?

We have tested to make to work the ADC and DAC with the same clock (synchronized each other) and we don’t found this problem. In our application, these clocks have to working in asynchronous mode. Thanks.

  • 0
    TI__Guru**** 189399 points

    Hi, Daniel,

    I am sorry that you are having trouble with your design.

    Do you have a plot showing the noise?

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 60 points

    Hi Don Dapkus,

    Yes, i'll show plots for both cases (with clocks synchronized and unsynchronized):

    Spectrum when clocks are synchronous each other:

    And when the clocks are not synchronous each other:

    In both cases ADC is without signal at input (Idle).

     

  • 0 in reply to Daniel Vazquez1
    TI__Mastermind 27920 points

    Hi Daniel,

    This noise could be due to a couple factors, there could be leakage into the ground by the clock which should be mitigated by the decoupling caps fro the PCM4202 depending on the PCB layout, these caps need to be as close to the PCM4202 as possible, but separation your digital and analog ground could also help. Next would be to look at the input pins for the PCM4202 which would be the most sensitive to this clock noise, make sure they are separated from any switchers for power. Much of these issues are rooted in the PCB layout.

    Justin