Capacitor grounded between 2 resistors
This is a low-pass filter.

The only place I've ever seen this used is as the loop filter on a 4046 PLL circuit, in Don Lancaster's "CMOS Cookbook".  I don't remember how much analysis he included.

You need to show the rest of the circuit, the driver to the left and the receiver to the right.  If you have a pure voltage source on the left, and a pure open on the right, it'll behave one way.  If you have a short to ground on the right, it'll behave differently.