Propagation delay

• An electromagnetic wave travelling through a medium has a propagation delay determined by the speed of light in that particular medium, or ca. 1 nanosecond per in a vacuum. • An electric signal travelling through a wire has an propagation delay of ca. 1 nanosecond per . See also radio propagation, velocity factor, signal velocity and mechanical wave. == Electronics ==

of a NOT gate has an overall gate delay of 3 logic gates from the inputs A and B to the carry output Cout shown in red. Logic gates can have a gate delay ranging from picoseconds to more than 10 nanoseconds, depending on the technology being used. • Increases in output load capacitance, often from placing increased fan-out loads on a wire, will also increase propagation delay. All of these factors influence each other through an RC time constant: any increase in load capacitance increases C, heat-induced resistance the R factor, and supply threshold voltage increases will affect whether more than one time constants are required to reach the threshold. If the output of a logic gate is connected to a long trace or used to drive many other gates (high fanout) the propagation delay increases substantially. == Networking ==

In computer networks, propagation delay is the amount of time it takes for the head of the signal to travel from the sender to the receiver. It can be computed as the ratio between the link length and the propagation speed over the specific medium. Propagation delay is equal to d / s where d is the distance and s is the wave propagation speed. In wireless communication, s=c, i.e. the speed of light. In copper wire, the speed s generally ranges from .59c to .77c. This delay is the major obstacle in the development of high-speed computers and is called the interconnect bottleneck in IC systems. == See also ==