let's consider this pass transistor logic:
Let's assume that the MOSFET is always active (CK = high for a N-MOSFET). Now, immagine that at the beginning Vin = 10V and Vx = 0: the capacitance Cx will be charged and at the end we will get Vx = 10V.
Now suppose that Vin becomes 1V: the capacitance will discharge itself until it reaches the value 1V. But, which is the resistance to which it discharges itself? If I look to the previous circuit I see, since the transistor is ON, simply a voltage source equal to 1V in parallel with a capacitor which is precharged to 10V.
Is it the internal resistance of the voltage source connected to Vin, the internal resistance of the transistor etc?