A fanout buffer is the most basic type of clocking circuit. It is used to split the input signal into multiple identical output signals that are sent to various devices within the system that all use the same frequency. Buffer circuits can be made using PLL or Non-PLL based circuitry, depending on whether the system needs to minimize the propagation delay between the source signal and output. The red arrow in this PLL Fanout diagram represents the feedback loop in the PLL design.

