Demultiplexer

combinatorial-logic

Definition

Demultiplexer

A demultiplexer (DMX) is a combinatorial logic circuit is the inverse of a multiplexer. It is a combinatorial logic circuit that takes a single input signal and routes it to one of many output lines based on the values of control or selection signals.

Example

The following example shows a 1-to-4 demultiplexer which has enable input $e$, two selection lines $S_0,S_1$ and four outputs $o_0,o_1,o_2,o_3$.

As the table below shows, similar to the multiplexer, the demultiplexer chooses its output $o_i$ based on the decimal number representation of the binary word $i=(S_1{S}_2{)}_2$ and sets $o_i=e$ (the enable signal.)

However, in contrast to the multiplexer, the demultiplexer also receives an enable signal $e$ which, when set to $e=0$, all $o_i$ are zero regardless of the selection line values.

$S_1$	$S_0$	$e$	$o_3$	$o_2$	$o_1$	$o_0$
$X$	$X$	$X$	0	0	0	0
$0$	$0$	$1$	0	0	0	1
$0$	$1$	$1$	0	0	1	0
$1$	$0$	$1$	0	1	0	0
$1$	$1$	$1$	1	0	0	0

Example: If $S_1=1$ and $S_0=1$, then the demultiplexer selects $o_3=e$ since the binary word $(S_1{S}_0)$ is equal to $(11{)}_2$, which is equal to $(3{)}_{10}$ in the decimal system.