All circuits require a complete current loop to function. In the case of a single ended circuit, the signal is sent over a single trace to the receiver and the current return path is usually carried via a printed circuit board (PCB) ground plane that is common to many other circuits in the system. One disadvantage of this scheme is that any noise that exists on the ground plane will affect all of the circuits connected to it. In contrast, differential signals use two wires or PCB traces. The second wire or trace provides the return path for the current, and the signal on this wire (the complement) has a 180 degree phase shift relative to the true signal. Unlike single ended signaling, the return path is dedicated to that circuit. Ideally, to minimize noise coupling, there is no common return path with other circuits. A ground plane is still included in the differential diagram shown here because other circuits in the integrated circuit, such as band gap bias circuits or power regulators, still connect to the common ground. Typically only the inputs and outputs and their associated circuits, such as pre-drivers and gain stages, are connected differentially. Note that if the differential signals are not perfectly balanced, some portion of the output driver current will flow through the common ground plane.