Plnitive / The Demultiplexer

The more widely used Data distributor, known as Demultiplexer, or "Demux" for short, works in stark contrast to the Multiplyer we saw in previous training.

Demultiplexer receives a single input data line and then switches to any of the individual output lines at once. Demultiplexer converts a serial data signal at the input to parallel data on the output lines, as shown below.

1×4 Channel Demultiplexer

Demultiplexer
1×4 Channel Demultiplexer
Demultiplexer
Truth table

For this Demultiplexer from 1 to 4 above, the Boolean expression, outputs from A to D, and data selection lines are given as a, b:

Demultiplexer
Boolean Expression

Demultiplexer's function is to pass a common row of data input from A to D to any of the 4 output data rows in our example above. As with the multiplexer, individual solid state switches are selected with the binary input Address code on the output selection pins "a" and "b", as shown.

Demultiplexer Output Line Selection

Demultiplexer
Demultiplexer Output Line Selection

As with the previous Multiplexer circuit, it is possible to change more outputs that give 1-to-2n data line output by adding more Address line input.

Some standard demultiplexer ICs also have an additional "enable output" pin that disables or blocks the transmission of input to the selected output. Some also have latches placed on their outputs to maintain the level of output logic after the address entries have been changed. However, in standard decoder type circuits, address input will determine which single data output will have the same value as the data entry, and all other data outputs will have a logic value of "0".

The application of the above Boolean expression using individual logic gates will require the use of six separate doors consisting of and not gates, as shown.

4 Channel Demultiplexer Using Logic Gates

Demultiplexer
4 Channel Demultiplexer Using Logic Gates

Demultiplexer Symbol

Demultiplexer
Demultiplexer Symbol