Combination Circuits

Multiplexers

It is a combinational circuit which selects one of the 2n input lines and transmits the information from that line to the output line. The selection of the input line depends upon the ‘n’ input selection lines. It is also called data selector and is also referred to by only MUX.

Smallest MUX we have is 2 to 1 mux which has 2 input lines, 1 output line and 1 selection line. We also have 4 to 1, 8 to 1 mux and so on

Q- Implement the 2 to 1 MUX

Ans: Here we have 2 input, 1 selection pin and 1 output pin and truth table is

 SEL(s)    Y

0              D0

1              D1

So the equation for MUX can be written as

Y = s’D0 + sD1

which can be implemented using gates as follow:

For a 4 to 1 MUX we have total of 6 inputs (4 input lines and 2 selection lines). So we’ll have 64 combinations. The block representation and the truth table is as:

 a              b             Output (Y)

0              0              D0

1              0              D1

0              1              D2

1              1              D3

So the equation for MUX can be written as

Y = a’b’D0 + a’bD1 + ab’D2 + abD3 which can be implemented

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