Demultiplexers

A demultiplexer(DEMUX) performs the reverse operation of a multiplexer. It takes input from one line and distributes it to a given number of output lines. It is also known as adata distributor. A demultiplexer with 2n output lines should have n data-selector lines.

1:4 Demultiplexer

A 1:4 demultiplexer takes input from one line and distributes it to 4 output lines. It has 2 data selector lines.

1x4 demultiplexer block diagram

The operation of a 1:4 demultiplexer is described in the truth table.

Data SelectorOutputs
S1S0Y3Y2Y1Y0
00I000
010I00
1000I0
11000I

The logical expression can be derived from the truth table.

Y_3=S_1S_0I
Y_2=S_1\overline{S_0}I
Y_1=\overline{S_1}S_0I
Y_0=\overline{S_1}\overline{S_0}I

It can be implemented using the following circuit.

1x4 demultiplexer circuit

The data input lines go to all of the AND gates. The two data-selector lines enable only one gate at a time based on its value.

if S1=0 and S0=0 then the data input is distributed to the Y3 output line and the value of all other output lines will be 0.

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