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PCM4220 noise increases after changing sampling rate

[FAE] Andrew Wang
Genius 10685 points
Other Parts Discussed in Thread: PCM4220

Hi Team,

My customer Advantech is working on a Sound/Vibration DAQ, they are using PCM4220, it's closed to RTM (2015 Q2). Currently they are seeing a strange problem. Here is how to duplicate the issue.

0.Turn on the power and initialize register.

1. Apply voltage to input

2. Use Normal mode 54KS/s and run for a while to capture enough data, then we can obtain a RMS noise value

3. Change to Quad Speed Mode 216 kS/s and run for a while

4. Change back to Normal Mode 54 kS/s and run for a while to capture enough data, this time the RMS noise is different. The noise increase 2~3x than in step.2.

 5. problem can be resloved by RESET the device. 

What can be the root cause? Is that due to digital filter remains historical data of 216KS/s?

Many thanks for help.

 P.S. The project block diagram is attached.

For Advantech Vibration DAQ (2014_Sep Update).pptx

  • 0
    TI__Mastermind 27980 points
    Hi Andrew,

    Yes the part should be held in reset while the pull ups and pull downs are changed as this is an older part. Taking the part back to reset will ensure that the part is able to start from a cleared state to the desired state. Its possible that the OSR is sticking with the higher sampling rate which could cause a rise in noise at a lower sampling rate.

    Justin