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ADC SPURS STM32H743

VIvan.1
Associate II

Hi! I use embendded ADC1 channel 3 in STM32H743VIT6 for sampling data. Input in differential mode. For improve SNR i added capacitor 47pF parallel to diff input pins see fig1. 0693W000001smNPQAY.gif

Also this capacitor required by AN5354

0693W000001smOIQAY.jpg

This led to decrease noise floor level, but its produces many spurs see fig below.

0693W000001smPkQAI.png

If i remove this capacitor (47pF) spectr became look very good see

0693W000001smQ4QAI.png

Please help me to understand how this capacitor impact to input driver and produce nonlinear products?

Thanks a lot!

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