a) AC coupling is a method of inputting a video signal to a circuit to remove any DC offset, or the overall voltage level that the video signal “rides” on. One way to find the signal is to remove the DC offset by AC coupling, and then do DC restoration to add a known DC offset (one that we selected). Another reason AC coupling is important is that it can remove harmful DC offsets. b) A connection that removes the constant voltage (DC component) on which the signal (AC component) is riding.

Implemented by passing the signal through a capacitor.