Multiplexors

Multiplexors, more commonly called multiplexers or muxes, are digital logic devices that select one of several input signals and forward the chosen input to a single output line. The selection is controlled by a set of select lines that encode the index of the input to be routed. An n-to-1 multiplexer has n data inputs and m select lines, where n = 2^m. The output reflects the input corresponding to the binary value on the select lines. Some designs include an enable input that can gate the output or place it in a high-impedance state, which is useful when multiple devices share a bus.

Multiplexers can be implemented with basic logic gates (AND and OR) or with transmission gates in CMOS technology. Larger multiplexers can be built by cascading smaller units, such as forming a 4-to-1 multiplexer from two 2-to-1 units. Analog multiplexers exist for continuous signals and often feature specified on-resistance characteristics; common families include CMOS-based analog muxes.

Applications of multiplexers include data routing in digital circuits, shared-bus architectures, and conditional data paths in processors. They are used to select data sources for peripherals, implement memory address decoding, and support time-division multiplexing schemes as part of broader system designs. In a typical system, a demultiplexer serves as the inverse function, taking a single input and routing it to one of several outputs, often in conjunction with a multiplexer to implement complex data paths.