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PCM2906C noise spaced 1kHz apart

Anand Joseph
Prodigy 10 points

Hi, I was interested in using the PCM290XC series of USB audio convertors for a project of mine. I primarily need the ADC interface with the DAC having little to no use for my project. I have noticed that while the ADC noise (when there is no signal input) is less than -89dB, the noise itself  has peaks spaced 1kHz apart. In other words, there are spectral peaks at 0Hz, 1kHz, 2kHz, 3kHz and so on. While this is not an issue when the input signal level is sufficiently high, it does become a problem  when the signal is low and amplified in software. The noise is pretty visible at frequencies above 4kHz. The following image is the FFT magnitude spectrum after amplification/scaling by 50dB:


Has anyone else faced this problem and if so have they found a way to reduce this noise?

  • 0
    TI__Genius 16270 points

    Anand,

    Because the USB runs the 12MHz clock at 1kHz interval, this noise can occur during recording.  One thing to do is to ensure the current flow between the USB controller and USB transceiver of the PCM290xC is minimized in the signal and GND path between the analog source and the analog input of the PCM290xC.  Second, connect all the GND pins to each other under the PCM290xC.  If the problem persists, common mode choke coils on the data lines and power lines may help to reduce common mode noise and reduce clock disturbance, improving performance.