The input signal at B1 is a square waveform. The signal source is a function generator (50 Ohm impedance). The voltage waveform is shown with "Visual Analog" for different frequencies.
500 kHz 1Vpp (without offset)
1MHz 1Vpp (without offset)
4 MHz 1V pp (without offset)
(a) I assume that the ADC blocked only a DC component (and frequencies up to 100 KHz by 1uF or 5 pF capacitor) . This should not result in the effect. I only expect a form according to the Gibbs phenomenon.
(b) It looks like a charge - or discharge process.
How could I avoid this effect?