Propagation delay
Encyclopedia
Propagation delay is a technical term that can have a different meaning depending on the context. It can relate to networking
, electronics
or physics
. In general it is the length of time taken for the quantity of interest to reach its destination.
s, propagation delay is the amount of time it takes for the head of the signal to travel from the sender to the receiver over a medium.
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.
, digital circuit
s and digital electronics, the propagation delay, or gate delay, is the length of time starting from when the input to a logic gate
becomes stable and valid, to the time that the output of that logic gate is stable and valid. Often this refers to the time required for the output to reach from 10% to 90% of its final output level when the input changes. Reducing gate delays in digital circuit
s allows them to process data at a faster rate and improve overall performance.
The difference in propagation delays of logic elements is the major contributor to glitch
es in asynchronous circuit
s as a result of race condition
s.
The principle of logical effort utilizes propagation delays to compare designs implementing the same logical statement.
Propagation delay increases with operating temperature
, marginal supply voltage as well as an increased output load capacitance. The latter is the largest contributor to the increase of propagation delay. 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.
Wires have an approximate propagation delay of 1 ns for every 6 in of length. Logic gates can have propagation delays ranging from more than 10 ns down to the picosecond range, depending on the technology being used.
, particularly in the electromagnetism
field, the propagation delay is the length of time it takes for a signal to travel to its destination. For example, in the case of an electric signal, it is the time taken for the signal to travel through a wire. See also, velocity of propagation
.
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
, electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
or physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
. In general it is the length of time taken for the quantity of interest to reach its destination.
Networking
In computer networkComputer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
s, propagation delay is the amount of time it takes for the head of the signal to travel from the sender to the receiver over a medium.
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
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
. 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
Interconnect bottleneck
The interconnect bottleneck, the point at which integrated circuits reach their capacity, is expected sometime around 2010.Improved performance of computer systems has been achieved, in large part, by downscaling the IC minimum feature size. This allows the basic IC building block, the transistor,...
in IC systems.
Electronics
In electronicsElectronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
, digital circuit
Digital circuit
Digital electronics represent signals by discrete bands of analog levels, rather than by a continuous range. All levels within a band represent the same signal state...
s and digital electronics, the propagation delay, or gate delay, is the length of time starting from when the input to a logic gate
Logic gate
A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
becomes stable and valid, to the time that the output of that logic gate is stable and valid. Often this refers to the time required for the output to reach from 10% to 90% of its final output level when the input changes. Reducing gate delays in digital circuit
Digital circuit
Digital electronics represent signals by discrete bands of analog levels, rather than by a continuous range. All levels within a band represent the same signal state...
s allows them to process data at a faster rate and improve overall performance.
The difference in propagation delays of logic elements is the major contributor to glitch
Glitch
A glitch is a short-lived fault in a system. It is often used to describe a transient fault that corrects itself, and is therefore difficult to troubleshoot...
es in asynchronous circuit
Asynchronous circuit
An asynchronous circuit is a circuit in which the parts are largely autonomous. They are not governed by a clock circuit or global clock signal, but instead need only wait for the signals that indicate completion of instructions and operations. These signals are specified by simple data transfer...
s as a result of race condition
Race condition
A race condition or race hazard is a flaw in an electronic system or process whereby the output or result of the process is unexpectedly and critically dependent on the sequence or timing of other events...
s.
The principle of logical effort utilizes propagation delays to compare designs implementing the same logical statement.
Propagation delay increases with operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
, marginal supply voltage as well as an increased output load capacitance. The latter is the largest contributor to the increase of propagation delay. If the output of a logic gate is connected to a long trace or used to drive many other gates (high fanout
Fanout
In digital electronics, the fan-out of a logic gate output is the number of gate inputs to which it is connected.In most designs, logic gates are connected together to form more complex circuits. While no more than one logic gate output is connected to any single input, it is common for one output...
) the propagation delay increases substantially.
Wires have an approximate propagation delay of 1 ns for every 6 in of length. Logic gates can have propagation delays ranging from more than 10 ns down to the picosecond range, depending on the technology being used.
Physics
In physicsPhysics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, particularly in the electromagnetism
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
field, the propagation delay is the length of time it takes for a signal to travel to its destination. For example, in the case of an electric signal, it is the time taken for the signal to travel through a wire. See also, velocity of propagation
Velocity of propagation
The velocity factor , also called wave propagation speed or velocity of propagation , of a transmission medium is the speed at which a wavefront passes through the medium, relative to the...
.
See also
- Delay calculationDelay calculationDelay calculation is the term used in integrated circuit design for the calculation of the gate delay of a single logic gate and the wires attached to it. By contrast, static timing analysis computes the delays of entire paths, using delay calculation to determine the delay of each gate and...
- Contamination delayContamination delayIn digital circuits, the contamination delay is the minimum amount of time needed for the output of an electronic component's output to match input presented to it. If there is insufficient delay from the output of one flip-flop to the input of the next, the input may change before the hold time...
- Transmission delayTransmission delayIn a network based on packet switching, transmission delay is the amount of time required to push all of the packet's bits into the wire. In other words, this is the delay caused by the data-rate of the link....
- Latency (engineering)Latency (engineering)Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...