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DDC114: Noise issue in Test mode

Cyril GAIROARD
Prodigy 30 points
Part Number: DDC114

Hi,

I am currently working with a DDC114 with a custom board.

I get the following value in TEST mode in RANGE 7 on channel 1. When i read the datasheet, on range 7 with 0pF detector the noise shall be 3.7 RMS noise (PPM FSR).

At 3 sigma it should translate into 11.1  peak to peak (PPM FSR). Now with 2^20 FSR x 11.1ppm = 11.64 count noise peak to peak.

I get about 20-25 on my custom board (this the graphic below).


Could you confirm that my calculation is good and that i have an issue on my board? 

Thanks in advance, Cyril.

  • 0
    TI__Mastermind 49176 points

    Hi Cyril,

    I am currently looking at your issue and will get back to you shortly.

  • 0
    TI__Mastermind 49176 points

    Hi Cyril,

    20-25 counts peak-to-peak noise (~3.7 ppm of FSR RMS noise) seems to be valid for the range setting 7 with 0pF detector.

    Noise amplitude in a histogram representation exhibits a Gaussian (normal) distribution centered around the mean.

    Depending on how much coverage of the noise you want, you can choose the ratio of peak-to-peak to RMS (also referred to as the Crest factor).

    Typically crest factor is 6.6 (+/- 3.3 sigma) or 6 (+/- 3 sigma) depending on whether you would like 99.7 or 99.9% coverage.