WHAT IS A MULTIPLEXER?

 MULTIPLEXER

we are going to see more complex combinational logic circuits or combinational devices which are the multiplexer and demultiplexer. These devices are can be found as integrated circuits (ICs) and are widely used in the field of telecommunication like in multiplexing.

WHAT IS A MULTIPLEXER?

A multiplexer also called data selector is a device that selects one of many input signals and forwards the selected input to the output. A multiplexer of 2ⁿ inputs has n select bits, which are used to select which input line to send to the output.  See figure 1.

An electronic multiplexer makes it possible for several signals to share one device or resource like one communication line instead of having one device per input signal. An example can be in a cyber where many computers are connected to the same printer, another example is an mp3 player, laptop, digital cable TV connected to a single surrounding sound system through a Mux.

 

2 DATA INPUT MULTIPLEXER

A two 2 to 1-line multiplexer have; 2 inputs, 1 select input and 1 output. 4 data inputs, 2 select input and 1 output.

 

An example is the 74LS157 quad 1-of-2 data selector IC, shown in figure below 

  

TRUTH TABLE OF A 2 TO 1 LINE MULTIPLEXER

 Below is the truth table of a 2 to 1 line data selector

 

Boolean expression of the output of a 2 to 1 multiplexer

This expression is obtained from the truth table above

 

Logic circuit of a 2 to 1 line Multiplexer

Hence, using the boolean expression above, we obtain the logic circuit below

   4 TO 1 LINE MULTIPLEXER

A 4-data multiplexer have; 4 data inputs, 2 select input and 1 output.

4 data input multiplexer                  

Example: using the figure above we are going to implement a 4 data multiplexer

TRUTH TABLE OF A 4 TO 1 LINE MULTIPLEXER

 Below is the truth table of a 4 to 1 line data selector

The Boolean expression of the output from the truth table is given by

Hence, from the Boolean expression we obtain the logic circuit below

Implementation of a 4-data input multiplexer.

8 DATA INPUT MULTIPLEXER

An 8-line to 1-line multiplexer has 8 data inputs, 3 select input and 1 output. This is shown in figure below. An example of an 8 data multiplexer IC is the 74151 shown in fig below with its pin configuration.

Truth table of an 8 data input multiplexer

The corresponding Truth table of the 8 data input multiplexer is given below

From the truth table above, the Boolean expression of the 8 data input multiplexer is given below

Logic circuit of an 8 data input multiplexer

Hence, we obtain the logic circuit below

Implementation of an 8 data multiplexer.