In
electronicsElectronics is a branch of science and technology that deals with the controlled flow of electrons. The ability to control electron flow is usually applied to information handling or device control. Electronics is distinct from electrical science and technology, which deals with the generation,...
, a
multiplexer or
mux (occasionally the terms
muldex or
muldem are also found for a combination multiplexer-demultiplexer) is a device that performs
multiplexingThe multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
; it selects one of many analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2
n inputs has n select lines, which are used to select which input line to send to the output.
An electronic multiplexer makes it possible for several signals to share one device or resource, for example one A/D converter or one communication line, instead of having one device per input signal.
On the other end, a demultiplexer (or
demux) is a device taking a single input signal and selecting one of many data-output-lines, which is connected to the single input. A multiplexer is often used with a complementary demultiplexer on the receiving end.
An electronic multiplexer can be considered as a multiple-input, single-output switch, and a demultiplexer as a single-input, multiple-output switch. The schematic symbol for a multiplexer is an
isosceles trapezoidAn isosceles trapezoid is a quadrilateral with a line of symmetry bisecting one pair of opposite sides, making it automatically a trapezoid. Two opposite sides are parallel, the two other sides are of equal length. The diagonals are of equal length. An isosceles trapezoid's base angles are...
with the longer parallel side containing the input pins and the short parallel side containing the output pin. The schematic on the right shows a 2-to-1 multiplexer on the left and an equivalent switch on the right. The wire connects the desired input to the output.
In telecommunications, a multiplexer is a device that combines several input information signals into one output signal, which carries several communication channels, by means of some
multiplex techniqueThe multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
. A
demultiplexer is in this context a device taking a single input signal that carries many channels and separates those over multiple output signals.
In telecommunications and
signal processingSignal processing is an area of electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time to perform useful operations on those signals...
, an analog time division multiplexer (TDM) may take several samples of separate analogue signals and combine them into one
pulse amplitude modulated-Overview:Pulse-amplitude modulation, acronym PAM, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses....
(PAM) wide-band analogue signal. Alternatively, a digital TDM multiplexer may combine a limited number of constant bit rate digital data streams into one data stream of a higher data rate, by forming data frames consisting of one timeslot per channel.
In telecommunications, computer networks and
digital videoDigital video is a type of video recording system that works by using a digital rather than an analog video signal.The terms camera, video camera, and camcorder are used interchangeably in this article.- History :...
, a statistical multiplexer may combine several variable bit rate data streams into one constant bandwidth signal, for example by means of packet mode communication. An
inverse multiplexerAn inverse multiplexer allows a data stream to be broken into multiple lower data rate communication links...
may utilize several communication channels for transferring one signal.
Cost savings
One use for multiplexers is cost savings by connecting a multiplexer and a
demultiplexer (or
demux) together over a single channel (by connecting the multiplexer's single output to the demultiplexer's single input).
The image to the right demonstrates this.
In this case, the cost of implementing separate channels for each data source is more expensive than the cost and inconvenience of providing the multiplexing/demultiplexing functions.
In a physical
analogyAnalogy is a cognitive process of transferring information from a particular subject to another particular subject , and a linguistic expression corresponding to such a process...
, consider the merging behaviour of commuters crossing a narrow bridge; vehicles will take turns using the few available lanes. Upon reaching the end of the bridge they will separate into separate routes to their destinations.
At the receiving end of the data link a complementary
demultiplexer is normally required to break single data stream back down into the original streams.
In some cases, the far end system may have more functionality than a simple demultiplexer and so, whilst the demultiplexing still exists logically, it may never actually happen physically.
This would be typical where a multiplexer serves a number of IP network users and then feeds directly into a
routerA router is a networking device whose software and hardware are usually tailored to the tasks of routing and forwarding information. For example, on the Internet, information is directed to various paths by routers....
which immediately reads the content of the entire link into its routing processor and then does the demultiplexing in memory from where it will be converted directly into IP packets.
Often, a multiplexer and demultiplexer are combined together into a single piece of equipment, which is usually referred to simply as a "multiplexer". Both pieces of equipment are needed at both ends of a transmission link because most communications systems transmit in
both directionsA duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions...
.
A real world example is the creation of
telemetryTelemetry is a technology that allows remote measurement and reporting of information. The word is derived from Greek roots tele = remote, and metron = measure. Systems that need external instructions and data to operate require the counterpart of telemetry, telecommand.Although the term commonly...
for transmission from the computer/instrumentation system of a satellite, space craft or other remote vehicle to a ground-based system.
In analog circuit design, a multiplexer is a special type of analog switch that connects one signal selected from several inputs to a single output.
Digital multiplexers
In
digital circuitDigital electronics are systems that represent signals as discrete levels, rather than as a continuous range. In most cases the number of states is two, and these states are represented by two voltage levels: one near to zero volts and one at a higher level depending on the supply voltage in use...
design, the selector wires are of digital value. In the case of a 2-to-1 multiplexer, a logic value of 0 would connect to the output while a logic value of 1 would connect to the output.
In larger multiplexers, the number of selector pins is equal to where is the number of inputs.
For example, 9 to 16 inputs would require no fewer than 4 selector pins and 17 to 32 inputs would require no fewer than 5 selector pins.
The binary value expressed on these selector pins determines the selected input pin.
A 2-to-1 multiplexer has a boolean equation where and are the two inputs, is the selector input, and is the output:
Which can be expressed as a
truth tableA truth table is a mathematical table used in logic—specifically in connection with Boolean algebra, boolean functions, and propositional calculus—to compute the functional values of logical expressions on each of their functional arguments, that is, on each combination of values taken by their...
:
| |
|
|
|
| 0 |
1 |
1 |
1 |
| 1 |
0 |
1 |
| 0 |
1 |
0 |
| 0 |
0 |
0 |
| 1 |
1 |
1 |
1 |
| 1 |
0 |
0 |
| 0 |
1 |
1 |
| 0 |
0 |
0 |
This truth table shows that when then but when then . A straightforward realization of this 2-to-1 multiplexer would need 2 AND gates, an OR gate, and a NOT gate.
Larger multiplexers are also common and, as stated above, requires selector pins for inputs. Other common sizes are 4-to-1, 8-to-1, and 16-to-1. Since digital logic uses binary values, powers of 2 are used (4, 8, 16) to maximally control a number of inputs for the given number of selector inputs.
The boolean equation for a 4-to-1 multiplexer is:
Two realizations for creating a 4-to-1 multiplexer are shown below:
| |
 |
These are two realizations of a 4-to-1 multiplexer:
- one realized from a decoder
A decoder is a device which does the reverse of an encoder, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode....
, AND gateThe AND gate is a digital logic gate that implements logical conjunction - it behaves according to the truth table to the right. A HIGH output results only if both the inputs to the AND gate are HIGH . If neither or only one input to the AND gate is HIGH, a LOW output results...
s, and an OR gatePRASADThe OR gate is a digital logic gate that implements logical disjunction - it behaves according to the truth table to the right. A HIGH output results if one or both the inputs to the gate are HIGH . If neither input is HIGH, a LOW output results...
- one realized from 3-state buffers and AND gates (the AND gates are acting as the decoder)
Note that the subscripts on the inputs indicate the decimal value of the binary control inputs at which that input is let through.
|
|
Chaining multiplexers
Larger multiplexers can be constructed by using smaller multiplexers by chaining them together. For example, an 8-to-1 multiplexer can be made with two 4-to-1 and one 2-to-1 multiplexers. The two 4-to-1 multiplexer outputs are fed into the 2-to-1 with the selector pins on the 4-to-1's put in parallel giving a total number of selector inputs to 3, which is equivalent to an 8-to-1.
List of ICs which provide multiplexing
The
7400 seriesThe 7400 series of Transistor-transistor logic integrated circuits are historically important as the first widespread family of TTL integrated circuit logic . It was used to build the mini and mainframe computers of the 1960s and 1970s...
has several ICs that contain multiplexer(s):
| S.No. | IC No. | Function | Output State |
|---|
| 1 |
74157 |
Quad 2:1 mux. |
Output same as input given |
| 2 |
74158 |
Quad 2:1 mux. |
Output is inverted input |
| 3 |
74153 |
Dual 4:1 mux. |
Output same as input |
| 4 |
74352 |
Dual 4:1 mux. |
Output is inverted input |
| 5 |
74151A |
8:1 mux. |
Both outputs available (i.e., complementary outputs) |
| 6 |
74151 |
8:1 mux. |
Output is inverted input |
| 7 |
74150 |
16:1 mux. |
Output is inverted input |
Digital demultiplexers
Demultiplexers take one data input and a number of selection inputs, and they have several outputs.
They forward the data input to one of the outputs depending on the values of the selection inputs.
Demultiplexers are sometimes convenient for designing general purpose logic, because if the demultiplexer's input is always true, the demultiplexer acts as a
decoderA decoder is a device which does the reverse of an encoder, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode....
.
This means that any function of the selection bits can be constructed by logically OR-ing the correct set of outputs.
List of ICs which provide demultiplexing
The
7400 seriesThe 7400 series of Transistor-transistor logic integrated circuits are historically important as the first widespread family of TTL integrated circuit logic . It was used to build the mini and mainframe computers of the 1960s and 1970s...
has several ICs that contain demultiplexer(s):
| S.No. | IC No. | Function | Output State |
|---|
| 1 |
74139 |
Dual 1:4 demux. |
Output is inverted input |
| 3 |
74156 |
Dual 1:4 demux. |
Output is open collector Open collector is a type of output on many integrated circuits . Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized on a pin of the IC. The emitter of the transistor is connected...
|
| 4 |
74138 |
1:8 demux. |
Output is inverted input |
| 5 |
74154 |
1:16 demux. |
Output is inverted input |
| 6 |
74159 |
1:16 demux. |
Output is open collector and same as input |
See also
- Barrel shifter
A barrel shifter is a digital circuit that can shift a data word by a specified number of bits in one clock cycle. It can be implemented as a sequence of multiplexers , and in such an implementation the output of one mux. is connected to the input of the next mux. in a way that depends on the shift...
- MDM
MDM may stand for:* machine debug manager* Market-dominant minority, a term coined by Amy Chua in her book World on Fire* Marszałkowska Dzielnica Mieszkaniowa, a neighbourhood in Warsaw with socialist realism architecture...
- Inverse multiplexer
An inverse multiplexer allows a data stream to be broken into multiple lower data rate communication links...
- Statistical multiplexer
- Digital subscriber line access multiplexer
A Digital Subscriber Line Access Multiplexer allows telephone lines to make faster connections to the Internet. It is a network device, located in the telephone exchanges of the service providers, that connects multiple customer Digital Subscriber Lines to a high-speed Internet backbone line...
(DSLAM)
- Rule 184
Rule 184 is a one-dimensional binary cellular automaton rule, notable for solving the majority problem as well as for its ability to simultaneously describe several, seemingly quite different, particle systems:...
, a cellular automatonA cellular automaton is a discrete model studied in computability theory, mathematics, physics, theoretical biology and microstructure modeling. It consists of a regular grid of cells, each in one of a finite number of states, such as "On" and "Off". The grid can be in any finite number of...
in which each cell acts as a multiplexer for the values from the two adjacent cells
- Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
- Code-division multiplexing
- Frequency-division multiplexing
Frequency-division multiplexing is a form of signal multiplexing which involves assigning non-overlapping frequency ranges to different signals or to each "user" of a medium.-Non telephone:...
- Time-division multiplexing
Time-division multiplexing is a type of digital or analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several...
- Wavelength-division multiplexing
In fiber-optic communications, wavelength-division multiplexing is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths of laser light to carry different signals. This allows for a multiplication in capacity, in addition to...
- Statistical multiplexing
Statistical multiplexing is a type of communication link sharing, very similar to dynamic bandwidth allocation . In statistical multiplexing, a communication channel is divided into an arbitrary number of variable bit-rate digital channels or data streams. The link sharing is adapted to the...