An electronic multiplexer can be considered as a multiple-input, single-output switch, and a demultiplexer as a single-input, multiple-output switch.

2 X 1 Multiplexer:

In digital circuit design, the selector wires are of digital value. In the case of a 2-to-1 multiplexer, a logic value of 0 would connect I0 (input A) to the output while a logic value of 1 would connect I1 (input B) to the output. In larger multiplexers, the number of selector pins is equal to log₂n where n is the number of inputs.

A 2-to-1 multiplexer has a boolean equation where A and B are the two inputs, S is the selector input, and Z is the output:

Z = ( A . S') + (B . S)

Truth Table

4 X 1 Multiplexer:

Larger multiplexers are also common and requires ceil(log₂n) selector pins for n inputs. Other common sizes are 4-to-1, 8-to-1, and 16-to-1. Since digital logic uses binary values, powers of 2 are used (4, 8, 16) to maximally control a number of inputs for the given number of selector inputs.

Truth Table