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PCM4204: 2pcs cascaded acquisition of noise

user5883945
Expert 1886 points
Part Number: PCM4204
Other Parts Discussed in Thread: PCM1690

Tool/software:

Dear,

Customer uses 2pcs PCM4204 cascaded to achieve 8-channel ADC audio acquisition. During recording, there is a probability of sustained noise of around -45db, which can be restored after resetting the IC.

They conducted the following investigation (the problem is that white noise of -45dB is added to each channel, as shown in the recording file below, which appears probabilistically)
1. The CPU provides SCKI, LRCK, BCK, and connects SDOUT1 of PCM4204 to DIN1 of PCM1690, indicating the presence of noise probability.
2. Modify SCKI from 24.576MHz to 12.288MHz (LRCK is 48kHz, BLK is 12.288MHz, i.e. BCK=256fs), and noise probability exists.
3. The CPU resets PCM4204 during operation, with a reset time of 10ms, and there is a probability of noise.
4. Reducing the period_2 and buffer_2 of the CPU increases the probability of occurrence.
5. Connecting to the CPU through telnet may also result in noise.
Overall, we confirm that this noise is generated by PCM4204, but since SCKI, LRCK, and BCK are provided by the CPU, we suspect that the timing of SCKI, LRCK, and BCK from the CPU may have affected PCM4204.

sheet-PCM4204.pdf

SCH

Noise recording file

 IIS waveform:
Channel 1: MCLK
Channel 2: BCK
Channel 3: LRCK
Channel 4: SDOUT1

  • 0
    TI__Intellectual 2655 points

    Hello,

    A couple comments/questions about the setup here:

    • Are you trying to use TDM or I2S audio format? Your schematic indicates TDM, but the scope shots and hardware pin selection show I2S. 

     - From the schematic: FMT2 : FMT1 : FMT0=1 : 0 : 0 音频格式：TDM with One BCK Delay for Start of Frame

     - However, this pin selection is for 24-bit I2S if I understand correctly (FMT2=0,FMT1=0,FMT0=1). This would make sense given your scope.

    • Where are you measuring the noise? 

    - On SDOUT or the output pins of PCM1690? We mentioned over email if it was possible to do an FFT of the digital data output SDOUT1.

    My last comment is the SDOUT to DIN connection, as it may be helpful to provide the PCM1690 part of the schematic as well. I am confused why both PCM4204s have the same labels on the SDOUT (indicating a connection). The PCM1690 would have a separate DIN pin for each SDOUT.

    Best,

    Garret