Multiplexers

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 Multiplexer (MUX)


 MUX is a Combinational Logic Circuit with more than one input line, one output line and more than one select line

 It accepts the binary information from several input lines or sources and depending on the set of select lines, a particular input line is routed onto a single output line.

 Multiplexer acts as a multiple-input and single-output switch

It has only one output and  2n inputs

It identified as digital Switch


Types of Multiplexers

1) 2 X 1 MUX                        

 2) 4 X 1 MUX       

3) 8 X 1 MUX 

 

1)   2 X 1 MUX  

A 2-to-1 multiplexer consists of two inputs D0 and D1, one select input S and one output Y.

 Depending on the select signal, the output is connected to either of the inputs. Since there are two input signals, only two ways are possible to connect the inputs to the outputs, so one select is needed to do these operations.

If the select line is low, then the output will be switched to D0 input, whereas if select line is high, then the output will be switched to D1 input. The figure below shows the block diagram of a 2-to-1 multiplexer which connects two 1-bit inputs to a common destination.


Truth Table

Input Lines  => 2            

Selection Lines => n = 1 

 

 


S

A0

A1

Y

0

0

X

0

0

1

X

1

1

X

0

0

1

X

1

1


Y = SA0 + SA1 

The logic circuit of 2-to-1 multiplexer can be implemented using logic gates . It consists of two AND gates, one NOT gate and one OR gate. When the select line, S=0, the output of the lower AND gate is zero, but the output of upper AND gate is A0. Thus, the output generated by the OR gate is equal to A0.


Logic Circuit






 Simulate Circuit

since Selection input(S) is 0, the 0th input will be the output. So as you can see the O is become as 1. 

 since Selection input(S) is 1, the 1st input will be the output. So as you can see the O is become as 0. 






2) 4 x 1 MUX

 Input Lines  => 2n = 4 

Selection Lines => n = 2 



Truth Table

One of these 4 inputs will be connected to the output based on the combination of inputs present at these two selection lines.

Selection Lines

Output

S1

S0

Y

0

0

A0

0

1

A1

1

0

A2

1

1

A3



   Y = S1 S0 A0 + S1 S0 A1 + S1 S0 A2 + S1 S0 A3 

Create Circuit and Simulate








                                                               3) 8 x 1 MUX

Create Circuit and Simulate







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