Decoder

Decoder :
It is a combinational circuit that convert binary information from N input lines to a maximum of 2N unique output lines.
The block diagram of deocder can be drawn as:

For example, consider 3x8 decoder circuit as below:

Truth table for above 3x8 decoder:

x y z D0 D1 D2 D3 D4 D5 D6 D7
0 0 0 1 0 0 0 0 0 0 0
0 0 1 0 1 0 0 0 0 0 0
0 1 0 0 0 1 0 0 0 0 0
0 1 1 0 0 0 1 0 0 0 0
1 0 0 0 0 0 0 1 0 0 0
1 0 1 0 0 0 0 0 1 0 0
1 1 0 0 0 0 0 0 0 1 0
1 1 1 0 0 0 0 0 0 0 1

Tips:-  A decoder provides the 2N minterm of n variables. Since any boolean function can be expressed in sum of minterms canonical form,one can use a decoder to generate the minterms and an external OR gate to form the sum.
 

 

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