For a decoder, If the input is a N bit binary number, then the output will be one the lines of the 2^N output lines.

So, for a 2-bit binary input, there will be 2^2 output lines and only one of the output lines will be active according to the binary combination of the inputs. This type of decoder is known as 2 to 4 decoder.

A

B

Q0

Q1

Q2

Q4

0

0

1

0

0

0

0

1

0

1

0

0

1

0

0

0

1

1

1

0

0

0

1

Consider a 8:1 multiplexer that takes 8 two-bit inputs (T8 to T1), three-bit control signal (S) and has an output (Out). This Type of multiplexer is known as a 8 to 1 multiplexer. The truth table is given below:

S2

S1

S0

OUT

0

0

0

T1

0

0

1

T2

0

1

0

T3

0

1

1

T4

1

0

0

T5

1

0

1

T6

1

1

0

T7

1

1

1

T8

A decoder is a combinational circuit. It has n input and to a maximum m = 2n outputs. Decoder is identical to a demultiplexer without any data input. It performs operations which are exactly opposite to those of an encoder.

*formed using simulator.

Encoder, Decoder, Convertor, Full Adder using Decoder

Realization of 4:2 bit Encoder Circuit using Basic Logic Gates