unexpected waveform in Examples/OPAMP/OPAMP_PGA/ in G4 package

[HDaji.1]

I try to learn how to use OPAMP by testing the example code Examples/OPAMP/OPAMP_PGA/.

The MCU board is Nucleo-G431RB.

This is the case of OPAMP_PGA_GAIN_2_OR_MINUS_1: blue line is output by DAC and red is by OPAMP.

My 1st question: why the amplified signal is distorted. Isn't it supposed to be another sine wave?

This is the case of OPAMP_PGA_GAIN_4_OR_MINUS_3.

My 2nd question: the amplitudes of the amplified signal seem not matching the gain.

Once the gain >= 8, the amplified signal becomes almost straight line. I also wonder why.

I want to modify the example code: I want to route the OPAMP output internally to a ADC channel. What steps I need to do?

[HDaji.1]

Dear @Igor Cesko​ 

I have another question:

The above pic shows the signals captured from DAC and OPAMP output pins: blue is DAC; red OPAMP.

What puzzles me is their amplitudes: DAC output is from -40mv to 40mv; while OPAMP output is -0.8v to 0.8v. The gain is 20 times, but for OPAMP PGA setting is

  hopamp3.Init.PgaGain = OPAMP_PGA_GAIN_2_OR_MINUS_1;

[HDaji.1]

@Igor Cesko​ sorry, my fault. The two probes themselves have 2 different gains: x1 & x10, so now everything makes sense.

Thx.

[Michal Dudka]

Check your measurments. Looks like you have wrong osciloscope probe configuration in you SW (10x vs 1x).