Multiplexer, we can simply say that a circuit which can deliver single output from multiple inputs. It can often refer as data selector or mux. The inputs to this circuit may be Analog or Digital. It is very useful in sending large amount of data over a network with decrease in bandwidth and time. A single pole multi-positioned switch is a plain example of a multiplexer which is not having an electronic circuit or components. But for high speed switching, automatically selecting electronic multiplexers are implemented. Multiplexers that are built from transistors and relays are employed for analog applications. In digital applications, standard logic gates are used to build it. They are also termed as digital multiplexer.
This circuit selects one of the inputs with the help of control signals and delivers that particular input into a single line as output.
Therefore, it is also termed as data selector. The figure below shows the pin diagram of multiplexer.
4 to 1 Multiplexer
For understanding the multiplexer further, we are selecting a 4-to-1 Multiplexer. There are many others like 2-to-1, 8-to-1, 16-to-1 multiplexers etc. In this multiplexer, the details are the following:
As the name indicates, there are 4 input bits. They are D0, D1, D2 and D3.
The number of output is one and is referred as Y.
- Control Bits
Two control bits are used here, A and B. This will decide which input bit should have to be selected. The output clearly depends on this control bits.
If the condition AB = 00, the top most AND gate is enabled (shown in figure above). At this time, all the other three AND gates are in disabled condition. So, input bit D0 is selected and transmitted as output. Thus, Y = D0.
If the condition AB = 11, every other AND gates are disabled excluding the bottom most AND gate. So, input bit D3 is selected and transmitted as output. Thus, Y = D3.
The examples of multiplexers are IC 74153, IC 45352 (4-to-1 multiplexers), IC 74150 (16-to-1 multiplexer)
Applications of Multiplexer
Multiplexers are implemented in several fields where there is a necessity of transmitting large amount of data with use of single line.
In computer, the huge quantity of memory is implemented by means of multiplexers. It also has advantage of reduction in number of copper lines which are used for the connection of memory to other parts in the computer.
Multiplexer is implemented in this system to increase efficiency. Using a single transmission line, various types of data (video, audio etc) are transmitted at the same instant.
Here, the multiple audio signals are brought into a single line and transmitted with the implementation of multiplexer. By this method, the numerous audio signals are made isolated and ultimately the recipient will receive the required audio signals.
Computer System of a Satellite Transmission
Multiplexers are implemented for the data signals to be transmitted from space craft or computer system of satellite to the earth by means of GPS.