Vol. Digital Circuits
Chapter 9 Combinational Logic Functions


A multiplexer, abbreviated mux, is a device that has multiple inputs and one output.

The schematic symbol for multiplexers is


The truth table for a 2-to-1 multiplexer is


I1 I0 A D
0 0 0 0
0 0 1 0
0 1 0 0
0 1 1 1
1 0 0 1
1 0 1 0
1 1 0 1
1 1 1 1


Using a 1-to-2 decoder as part of the circuit, we can express this circuit easily.


using a 1 to 2 decoder as part of the circuit diagram


using a 1 to 2 decoder as part of the circuit diagram



Multiplexers can also be expanded with the same naming conventions as demultiplexers. A 4-to-1 multiplexer circuit is


4 to 1 multiplexer circuit


That is the formal definition of a multiplexer. Informally, there are a lot of confusions. Both demultiplexers and multiplexers have similar names, abbreviations, schematic symbols and circuits, so confusion is easy. The term multiplexer, and the abbreviation mux are often used to also mean a demultiplexer, or a multiplexer and a demultiplexer working together. So when you hear about a multiplexer, it may mean something quite different.


  • RediDad August 02, 2020

    I couldn’t quite understand Multiplexers by reading this. Can you give a little bit detail to it?

    Like. Reply
    • RK37 August 11, 2020
      Here are some additional resources that you might find helpful: https://www.allaboutcircuits.com/technical-articles/implementing-multiplexers-with-pass-transistor-logic/ https://www.allaboutcircuits.com/worksheets/multiplexers-and-demultiplexers/ https://forum.allaboutcircuits.com/threads/how-multiplexer-truth-table-works.111483/
      Like. Reply