# Multiplexer and Demultiplexer – Electronics Circuits

In large-scale digital systems, one line is necessary to hold one, two or many digital signals; and, of course, at the same time, one signal is located on one line. Therefore, what’s needed could be a device which would permit us to select a signal; and, the signal we have a tendency to would likely be placed on a typical line, such a circuit is stated to as multiplexer. The function of the multiplexer is to pick the i/p of any n input lines and feed that to at least one output line. The function of the demultiplexer is, inverse to the operation of the multiplexer. The short form of  multiplexer and demultiplexer are Mux and Demux. Some multiplexers perform both multiplexing and demultiplexing operations. The main function of the MUX is that it combines i/p signals, permits information compression, and shares one transmission.. This article gives an overview of multiplexer and demultiplexer.

## Multiplexer

A Multiplexer or Mux is a device that has many inputs and a single output. The selected line decides which i/p is connected to the o/p, and also increases the amount of data that can be sent over an n/w within a certain time. A multiplexer is also called as a data selector. The best example of non-electronic circuit of the multiplexer is a single-pole, multi-position switch, which is generally used in many electronics circuits. The main purpose of mux is to perform high speed switching and is constructed by a basic electronic components. These are accomplished by handling both analog and digital applications. In analog applications, these are made up of transistor switches and relays, whereas in digital applications, these are made up of logic gates. When the mux is used in digital applications, it is called as a digital multiplexer.

### 4-to-1 Multiplexer

The 4X1 multiplexer comprises 4-input bits, 1- output bit, and 2- control bits. The four input bits are namely 0, D1, D2 and D3, respectively; only one of the input bit is transmitted to the output. The o/p ‘q’ depends on the value of control input AB. The control bit AB decides which of the i/p data bit should transmit the output. The following figure shows the 4X1 multiplexer circuit diagram using AND gates. For example, when the control bits AB =00, then the higher AND gate are allowed while remaining AND gates are restricted. Thus, data input D0 is transmitted to the output ‘q”

If the control input is changed to 11, then all gates are restricted except the bottom AND gate. In this case, D3 is transmitted to the output and q=D0. If the control input is changed to AB =11, all gates are disabled except the bottom AND gate. In this case, D3 is transmitted to the output and q = D3.The best example of 4X1 multiplexer is IC 74153. In this IC, the o/p is same as the i/p. Another example of 4X1 multiplexer is IC 45352. In this IC, the o/p is the compliment of the i/p

#### Applications of Multiplexers

A Multiplexer is used in various applications wherein multiple data can be transmitted using a single line.

Communication System – A Multiplexer is used in communication systems, which has a transmission system and also a communication network. A Multiplexer is used to increase the efficiency of the communication system by allowing the transmission of data, such as audio & video data from different channels via cables and single lines.

Computer Memory – A Multiplexer is used in computer memory to keep up a vast amount of memory in the computers, and also to decrease the number of copper lines necessary to connect the memory to other parts of the computer.

Telephone Network – A multiplexer is used in telephone networks to integrate the multiple audio signals on a single line of transmission.

Transmission from the Computer System of a Satellite:

A Multiplexer is used to transmit the data signals from the computer system of a satellite to the ground system by using a GSM communication.

## De-Multiplexer

A demultiplexer is a device, that has one input and multiple output lines which is used to send a signal to one of the various devices. The most prominent distinction between a multiplexer and demultiplexer is that a multiplexer takes two or a lot of signals and encodes them on a wire, whereas a demultiplexer reverses what the multiplexer does.

### 1-4 De-multiplexers

The 1-to-4 demultiplexer comprises 1- input bit, 4-output bits and – control bits. The 1X4 demultiplexer circuit diagram is shown below.

The i/p bit is considered as Data D. This data bit is transmitted to the data bit of the o/p lines, which depends on the AB value and the control i/p.

When the control i/p AB = 01, the upper second AND gate is permitted while the remaining AND gates are restricted. Thus, only data bit D is transmitted to the output and Y1 = Data.

If the data bit D is low, the output Y1 is low. IF data bit D is high, the output Y1 is high. The value of the output Y1 depends upon the value of data bit D, the remaining outputs are in a low state.

If the control input changes to AB = 10,then  all the gates are restricted except the third AND gate from the top. Then, data bit D is transmitted only to the output Y2; and, Y2 = Data. . The best example of 1X4 demultiplexer is IC 74155.

#### Applications of Demultiplexer

Demultiplexers are used to connect a single source to multiple destinations. These applications include the following:

Communication System – Multiplexer and Demultiplexer both are used in communication systems to carry out the process of data transmission. A De-multiplexer receives the output signals from the multiplexer; and, at the receiver end, it converts them back to the original form.

Arithmetic Logic Unit – The output of the arithmetic logic unit is fed as an input to the De-multiplexer, and the o/p of the demultiplexer is connected to a multiple registers. The output of the ALU can be stored in multiple registers.

Serial to Parallel Converter – The serial to parallel converter is used to reform parallel data. In this method, serial data are given as an input to the De-multiplexer at a regular interval, and a counter is attached to the demultiplexer at the control i/p to sense the data signal at the demultiplexer’s o/p. When all data signals are stored, the output of the demultiplexer can be read out in parallel.

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1. M iqbal says:

1. Tarun Agarwal says:

Hi M iqbal
Thank you so much for your feedback.

2. Gulrez says:

Best notes on multiplexer

1. Tarun Agarwal says:

Hi Gulrez