Distorted measurement ADC

[JR2963]

Hi,

on STM32F303 I use ADC with DMA (12 bit), I measure signals on 3 channels + Vrefin.

The input signal is pure sine wave 50 Hz (I can see it on scope). But when I measure it with ADC, so there is distored sine wave, I tried to change SAMPLING TIME, and also Sampling frequency. It changed, but this is the best result what I have got, but still distored. Is there any chance how to solve that problem?

There is no saturation, there is reserve in amplitude

[waclawek.jan]

Where is the 1.65V coming from, and how does that look like on the oscilloscope?

JW

[waclawek.jan]

Also, don't you try to use the ADC in differential mode? If so, have you read the Errata?

JW

[JR2963]

I am sorry, now I can see on the scope the signa is not pure wave.I hadn't really seen the distortion before!

There is 50% amplitude:

[JR2963]

I am sorry, now I can see on the scope the signa is not pure wave.I hadn't really seen the distortion before!

Anyway the 1.65 is from OPAMP, but now when the input signal is distored...

I do not understan that, it is 230 Volts throught the isolation transformer directly to the voltage divider...