Multiplexers and Demultiplexers Introduction
There are many applications where many devices or systems need to access a common transmission media.
Let us consider our cable TV system, in which multiple TV channels are received at home via a shared transmission media. Similarly, in computer networking, many computers need to access a common printer or other shared hardware.
In Smart instrumentation, a PC or microcontroller can acquire data gathered from many sensors through a single ADC. Our telephone exchanges utilize these multiplexers and demultiplexers extensively.
Multiplexers and demultiplexers are normally used for sharing resources. Multiplexers route the data from many sources to one destination and demultiplexers redistribute data back from one source to many destinations. In this module you will learn about the basic architecture of multiplexers and demultiplexers along with real life applications.
Principles of Multiplexing and Demultiplexing
Let us now begin with principles of multiplexing and demultiplexing. Let us consider a system with n-inputs. Multiplexing means sharing. It means many to one. A multiplexer (MUX) is a device that allows digital information from several inputs to be routed on to a single line for transmission.
The multiplexed data is transmitted over a single line to a common destination. Demultiplexer accepts this data and redistributes it to the n outputs.
Data select lines are used in many into one operation of multiplexer and one to many operation of demultiplexer. In short, multiplexers and demultiplexers are combinational circuits designed to provide sharing of resources. The keyword is sharing.
Multiplexer
Multiplexer means many to one. A multiplexer (MUX) is a combinational circuit which is often used when the information from many sources must be transmitted over long distances and it is less expensive to multiplex data onto a single wire for transmission.
A multiplexer can be considered as the semiconductor equivalent of a multi-position switch. It is a combinational logic circuit which has many input lines and a single output line. The basic operation is controlled by a selector line that routes one of many input signals to the output.
Multiplexers are also called a DATA Selector or router because it accepts several data inputs and allows only one of them to get through to the output at a time.
The basic multiplexer has n input lines and single output line. It also has m – select or control lines. The relation between number of select lines and number of data inputs are 2^m = n As the multiplexer selects one out of many, it is often called a 2^m to 1 line converter.
Applications of multiplexers
Multiplexer or data selectors are combinational circuits which transfer data from many sources to output under the control of data select lines.
Multiplexer has many applications right from data routing, time division multiplexing, function generator to parallel to serial converter etc. A single multiplexer can replace several logic gates ICs, saving PCB area, interconnections, design efforts and cost.
A list of popular applications is given below.
- Data routing
- Data bussing
- Switch setting comparator
- Multiplexer as a function generator
- Parallel to serial converter
- Cable TV signal distribution
- Telephone network
- Sharing printer /resources
Demultiplexer
Demultiplexer has a single input and n output lines. Demultiplexer can be visualized as reverse multi-position switch.
Demultiplex means one into many. A demultiplexer reverses the multiplexing operation. In other words, the demultiplexer takes one data input source and selectively distributes it to 1 of N output channels just like a multi-position switch. It also has ‘m’ select lines for selecting the desired output for the input data as shown in fig. 10. The mathematical relation between select lines and ‘n’ output are: 2^m = n
A demultiplexer takes data from one input line and distributes over a 2^m output line, hence it is often referred to as a 1 to 2m line converter. There are four basic types of demultiplexers: 1 to 2 demultiplexer, 1 to 4 demultiplexer, 1 to 8 demultiplexer and 1 to 16 demultiplexer as shown in fig. 11. Number of select lines decides this classification
Applications of Demultiplexers
Digital demultiplexers are combinational devices controlled by a selector address that routes input data to one of many outputs of the demultiplexers. These can be used in following applications.
- Data demultiplexing
- Clock demultiplexing
- Memory addressing
- Four phase clock generator
- Function generation using DEMUX
- Switch encoding
- Serial to parallel converter
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