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Demultiplexer

Demultiplexer is in fact a circuit which can distribute or deliver multiple outputs from a single input. It can often refer as data distributor or demux. It can perform as single input many output switch. The output lines of demultiplexer are ‘n’ in number, select line number is ‘m’ and n = 2m. The control signal or select input code decides the output line which the input has to be transmitted. The demux can also perform as binary to decimal decoder. For this, the data input line should be at logic 1 level and the binary input is given to the select input lines. The corresponding line will give the output. In the designing of multiple combinational circuits, this circuit is really useful.

Since, the need of package count is least for demultiplexer. The function of this circuit is the reverse of the multiplexer.reverse of the multiplexer The pin diagram of demultiplexer is in figure below. demultiplexer

1 to 4 Demultiplexer

Now, we can select a 1 to 4 Demultiplexer. There are many other types like 1-to-2, 1-to-8, 1-to-16 demultiplexers etc. The details of this type are the following:
  • Input
    1 input bit is present. Here it is Data D.
  • Outputs
    The number of outputs is four. They are Y0, Y1, Y2 and Y3.
  • Control Bits
    Two control bits are used here. They are A and B. The input data bit is send to the data bit of the output lines depending on the value of the select input or control bit.

If the condition AB = 01; the second AND gate from the top is enabled (shown in figure above). At this moment, all the other three AND gates are in disabled condition. So, input bit Data D is delivered to the output. Thus, Y1 = Data.
When the input is set as 0, Y1 will be low that is 0 and when input is 1 (high), Y1 will be 1(high). Thus, we can say that the Y1 value will directly depend on input D. The other three outputs are 0 (low state).
If the condition AB = 10, every other AND gates are disabled excluding the second AND gate from the bottom. So, input bit D is sent to Y2 output. Thus, Y2 = Data D.
Truth Table

Data D
Control
Input
Outputs
-
A
B
Y0
Y1
Y2
Y3
1
0
0
1
0
0
0
1
0
1
0
1
0
0
1
1
0
0
0
1
0
1
1
1
0
0
0
1
The examples of multiplexers are IC 74155 (4-to-1 multiplexer), IC 74154 (16-to-1 multiplexer which has 4 control bits, 1 input bit and the outputs are 16 bits)

Applications of Demultiplexer

Demultiplexers are implemented in several fields where there is a necessity of connecting single source to several destinations.

Communication System of Demultiplexer

Generally the communication system includes transmission and reception of the signals. For these purposes, the multiplexer in the transmitting end and the demultiplexer in the receiving end have to work simultaneously. Transmission is done with the implementation of multiplexer. The output of the multiplexer; which is the single output and it is given as the input of the demultiplexer. The demultiplexer in the receiver will change this given input to the original signals.

Arithmetic and Logic Unit (ALU) of Demultiplexer

With the implementation of demultiplexer, the output of the ALU can keep in storage units or multiple registers. Here, the ALU output is given to the demultiplexer as its input. The outputs of the demultiplexer are given to the multiple registers where the data is stored.

Serial to Parallel Converter of Demultiplexer

This converter can give (recreate) the parallel data from the received serial data. Here, the input serial data is set as the input of demultiplexer. This is done at regular intervals. At the control input of demultiplexer, a counter is attached. The data signal is directed to the demultiplexer output with the help of this counter. After every bit of data signals is stored, the demultiplexer output can be extracted. It can be read out in parallel.



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