demultiplex

Demultiplexing is the process of separating a single combined signal into its original component signals. A demultiplexer (often abbreviated as demux) takes one input line carrying time-division multiplexed or frequency-division multiplexed data and routes it to the correct output line based on control signals called select lines. This reverses the work done by a multiplexer on the transmitting end and is essential in any communication or data system where multiple signals share one physical channel.

In digital electronics, an integrated circuit demultiplexer typically has one input, multiple outputs, and a set of address or select pins. A 1-to-8 demux, for example, has 3 select lines (since 2 to the power of 3 equals 8) that determine which of the 8 output lines receives the input signal at any given moment. The select lines usually carry binary values: if you apply binary 101 to the select pins, the input connects to output 5. The switching happens at nanosecond timescales in modern logic chips.

Analog and digital domains

In time-division multiplexing (TDM) systems, such as older telephone switching or serial data busses, demultiplexing recovers sequential samples or bytes. In frequency-division multiplexing (FDM), demultiplexing uses filters or frequency selectors to separate signals that occupy different bands within the same physical channel, common in radio and cable television. The two methods demand different hardware: TDM demuxes are usually digital logic circuits, while FDM demuxes rely on tuned filters, resonant circuits, or software-defined techniques in modern systems.

Timing is the critical failure point in demultiplexing. If the select signals at the transmitter and receiver are not synchronized, or if clock skew causes jitter, data arrives at the wrong output or becomes corrupted. Industrial systems use clock recovery circuits or dedicated synchronization lines to maintain phase alignment. Any mismatch between the multiplexing rate and the demultiplexing rate introduces bit errors or dropped samples.

Demultiplexing appears throughout industrial control and communication networks. In programmable logic controllers (PLCs), demuxes route sensor inputs from a shared analog-to-digital converter to different memory registers. In fieldbus protocols and industrial Ethernet, demultiplexing separates traffic destined for different devices or functions on a shared medium. The term itself mirrors the structure of its counterpart: multiplex combines, demultiplex separates.