Multiplexer And Demultiplexer

Multiplexer

• It is a combinational logic circuit that takes 2^n (2 power n) Input Signals with “n” selection lines (also called control signals) and gives only one Output signal.
• It has multiple inputs and a single output.
• The output signal is called multiplexed signal.
• The selection of a particular input line is controlled by a set of selection lines. Those are also called Control Inputs.
• In short form, the multiplexer is called “MUX”.
• It is multiple input and single output device.
• Parallel to Serial conversion will happen here.
• The Operation principle is many to one.
• Examples: — 2 to 1 MUX, 4 to 1 MUX,.. 2^n to 1 MUX.(where n= number of selection lines)
• Multiplexers can handle two types of data. That data are analog and digital.
• The multiplexer has multiple designs like 2-to-1, 4-to-1, 8-to-1 multiplexer.
• In general, a 2 n-to-1-line multiplexer is constructed from an n -to-2 n decoder by adding 2n input lines to it, one to each AND gate. The outputs of the AND gates are applied to a single OR gate.
• The size of a multiplexer is specified by the number 2n
  of its data input lines and the single output line.
• Here we will discuss 2-to-1, 4-to-1 multiplexer.

Types of Multiplexer

1. 2-to-1 Multiplexer

The logic of 2-to-1 Multiplexer(Truth Table): -

• If S=0 then I0 will be output, S=1 then I1 is output.

2. 4-to-1 Multiplexer

• The AND gates and inverters in the multiplexer resemble a decoder circuit, and indeed, they decode the selection input lines.

The logic of 4-to-1 Multiplexer(Truth Table): -

• There are many more multiplexers like 8-to-1,16-to-1 etc.

Multiplexing Processes

• It is mainly separated by dividing data into Digital Signals and Analog Signals.
• In Digital input Signals type the multiplexing process is “Time Division Multiplexing(TDM)”. It is subdivided into synchronous and asynchronous.
• In the Analog input Signals type, the multiplexing processes are “Frequency Division Multiplexing” and “Wavelength Division Multiplexing”.

Time Division Multiplexing

• In this process, the data signals will be transmitted over a common communication channel at different time slots.
• In this process, overall time will be divided into fixed-length time slots. Each user will be given a specific time interval to transmit the data. In that time they can use the full bandwidth of the channel.
• It is used in Telephone Networks.

Frequency Division Multiplexing

• It is a multiplexing process that divides the available bandwidth into multiple sub-bands in which the signal will be carried.
• The sub-bands are separated by guard bands.
• Guard band acts as a gap between two subbands to eliminate interference. It will have a small frequency range.
• It is an Analog multiplexing technique.
• It allows sharing a single copper line or fiber line among multiple input signals.
• It is used in radio broadcasting, TV networks, etc.

Wavelength Division Multiplexing

• In this technique, we combine light signals and transmit them through the channel.
• In fiber optics communication wavelength division multiplexing process multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light.

Advantages

• It allows multiple connections over one fiber thus reducing fiber plant requirement.
• This can provide fiber redundancy.
• Provides managed fiber service.

Applications of Multiplexer

Demultiplexer

• It is opposite to Multiplexer. A combinational circuit that takes a single input line and gives multiple output lines.
• In short form, it is called “Demux”.
• Serial to Parallel conversion will happen here.
• The operation principle is one to many.
• It also has selection lines that are used to decide the output.
• One input signal with “n” selection lines gives 2^n output signals.(n=1,2,3..)
• Types are like 1-to-2, 1-to-4, 1-to-8 etc.

Demultiplexer examples

• Below you can see the demultiplexer containing single input and gives multiple outputs.

1-to-4 Demultiplexer

TRUTH TABLE

Application of Demultiplexer

Conclusion

Both multiplexers and demultiplexers are required in the communication system because of its bidirectional nature. These two devices perform the exact opposite operations of each other. A major difference between multiplexer and demultiplexer is based on their input and output lines, i.e., a multiplexer has many input lines and one output line, whereas a demultiplexer has one input line and many output lines.

Authors :

Aadarsh Dontul (12220007)

Vedant Bhagwan (12220256)

Rohan Boge (12220065)

Nisarg Doshi (12220169)