This can also be called the transmission delay, flight time or time of flight for the signal. Propagation delay is present in data networks as well, as it takes time for the signals to travel from the point of transmission to the receiver. Therefore, the propagation delay is an important factor in high-speed circuit design and is a limiting factor of the processing speed, or hertz, that a processor can run at. Inconsistent propagation delay in an IC can cause data errors or race conditions on a chip. Modern ICs can have billions of total gates and operate at incredible speed.
Each gate must stabilize before the next one in the sequence can be read, so the total time for each gate in the longest possible output sequence is added together to form the total delay. Propagation delay is small, in a human scale, often measured in nanoseconds or picoseconds. But the specifics can vary greatly depending on the exact type used. The propagation delay will also depend on the logic family used, either transistor-transistor logic or complementary metal-oxide semiconductor. Temperature can also affect the material. The speed that the charge can move is roughly 100,000 m/s to 200,000 m/s depending on the semiconductor material used. This is due, in part, to the time it takes for an electrical charge to move through a semiconductor and for the individual gates to stabilize at the correct output. It can also be called gate delay and is more related to the amount of time it takes for the individual components, called logic gates, to change than the time for the signal to move from one point to another.
In this context, propagation delay is defined as the amount of time required after an input signal is applied and has stabilized to the input of a circuit to the time that the output of the circuit has stabilized to the correct output signal. Therefore, they hear the thunder after they see the flash of lightning due to the much longer propagation delay of sound than light.Įlectrical engineers need to take propagation delay into account when creating integrated circuits (ICs). Sound travels much slower in air, at only about 343 meters per second (m/s) or 1 mile in 4.7 seconds. The flash from the lightning travels incredibly quickly, at the speed of light of about 300,000 kilometers per second (km/s) or 186,000 miles a second. This is true for all signals from small to great and distances from short to vast.Īn everyday example of propagation delay is the difference between when people can see a strike of lightning flash and when they hear the thunder. Since nothing can travel faster than light and light has a finite speed, there will always be some delay as a signal moves from source to destination. The fundamental limit on propagation delay is the speed of light (c). Propagation delay is of primary interest in electronic circuit design and computer networking, although all signals will inherently experience some form of propagation delay. Propagation delay is the amount of time required for a signal to be received after it has been sent it is caused by the time it takes for the signal to travel through a medium.