RC circuit intuition
If you connect a fixed voltage at the input, current will flow through the capacitor and then through the resistor, with a resulting voltage drop across the resistor, which is also your output voltage.  But the capacitor is charging, and as it does, it opposes the input voltage, so the current decreases.  This shows up as a decreasing voltage across the output resistor.

And you are the guy with your hand on the voltage control at the input. And you see the output decreasing, so you turn the voltage up, so that your applied voltage is larger than that charge across the capacitor.  More current flows, the voltage at the output goes up again.  But then the capacitor charges some more.  So you raise the input voltage some more...

There's a balance between the output voltage wanting to fall off, and you continuously raising the input voltage to try to keep the output  where it is.   And you, continuously raising the input voltage...that's the ramp. 

Big capacitor? It charges slowly, and you don't have to "chase it" by raising the input so fast.  Big resistor? Less current flow and thus less through the capacitor (from their point of view they are in series) and again the cap doesn't charge so fast.   For smaller value parts, the reverse will be true.