ADC Noise

[gviereck]

We use a STM32F7xx microcontroller with LQFP144 case
Part of the ADC Pins are on the 1-36 pin side.
Unfortunately this is also the side where the Quartz (Pins  OSC_IN and OUT, PC14-OSC32_IN, PC15-OSC32_OUT) and the RMII_CLK are mapped.
This leads to additional noise (app. 10 LSB with peak regions at 500 Hz compared to 5 LSB  noise on other similar filtered sensor signals)  on the pins 36 (ADC123_IN2) and 37 (ADC123_IN3) despite anti-aliasing filter.
Unfortunately we could not find any other pin available on ADC1 and ADC2.
Is this a well known problem that oscillators may disturb ADC's of STM32Fxxx microcontrollers?

[gviereck]

We have changed the ADC-channels. The 2 ADC channels too close to the RMII clock: one is no longer used and we found an available ADC-pin further away, the other one is used for a signal that is less sensitive to noise (motor turn pulse).
The noise is reduced. All the ADC channels dedicated to the position sensors show now app. the same level of noise.