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I have some questions about capacitor and the circuit shown below:

enter image description here

The original signal including noise is shown below:

enter image description here

There are three waveforms shown in one picture.

The top one, middle one, and last one is connected to 4.7µF, 0.1µF, and 100µF respectively. Why is the top one smoother than middle one? Why is the last one out of shape and attenuated? If I change GND to 2.5V, is it able to filter out the noise? If I can filter out the noise only with capacitor, why using RC?

enter image description here

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    \$\begingroup\$ Your source/load ratio of impedance defines this slope change. \$\endgroup\$
    – D.A.S.
    Commented Dec 27, 2019 at 17:42
  • \$\begingroup\$ For the same reason you use a clutch on a car as opposed to revving up and crashing the gears without a clutch. \$\endgroup\$
    – Andy aka
    Commented Dec 27, 2019 at 17:52
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    \$\begingroup\$ Obviously your source is not ideal. Is it a buffered signal generator with 2.5V DC bias? Every part has some resistance. Even your source and the capacitor. It is the nonlinear ratio that causes distortion. \$\endgroup\$
    – D.A.S.
    Commented Dec 27, 2019 at 17:52

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Your distortion is due to source unable to drive as much current for positive waves.
But I will not guess your source.

All capacitors uses electrodes and the surface area and chemical bond determines the effective series resistance , which can load AC waveforms which changes the slope of the voltage and the peak amplitude.

Usually that's a good thing but it all depends on the driving current-limited source-resistance ratio to load capacitive impedance and it's internal ESR.

schematic

simulate this circuit – Schematic created using CircuitLab

Although I could guess why out positive wave slope reduces with higher resistance, let's see here how Vpp and Ipp changes at some arbitrary low frequency and fixed series resistance.

enter image description here

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