Multiplexer

A multiplexer, or MUX, is a combinational digital or analog circuit that selects one of several input signals and forwards the chosen input to a single output line. Selection is controlled by a set of select signals. The number of inputs is typically a power of two, and the number of select lines equals log2(number of inputs).

Digital multiplexers are common in digital logic design. A k-to-1 multiplexer has 2^k inputs and k select lines. For example, a 4-to-1 MUX has four data inputs and two select lines. The output equals the input corresponding to the binary value on the select lines. Additional enable control may be provided, allowing the output to be forced to a known state when disabled.

Analog multiplexers route one of several analog signals through to a common output, using analog switches such as transistors. They are used for selecting sensor signals, routing audio, and other signal routing tasks where preserving signal integrity is important. Common devices include integrated circuits labeled as MUX/DEMUX with various channel counts (e.g., 8-channel, 16-channel).

Applications of multiplexers include data routing in buses, time-division multiplexing where multiple signals share a line in different time slots, and memory addressing to select data from registers. They help reduce wiring complexity and the number of data paths in digital systems, while maintaining fast, controlled signal selection.

A demultiplexer performs the inverse operation, taking a single input and routing it to one of several outputs. Many devices implement both functions or combine them in a single MUX/DEMUX block to support flexible signal routing.