multiplexor

Multiplexor, or multiplexer, is a digital switch that selects one of several input signals and forwards that input to a single output line according to a set of select signals. The device effectively concentrates multiple data paths into one, enabling shared use of a resource such as a data bus.

Architecture: An n-to-1 multiplexer has n data inputs, k select lines, where n ≤ 2^k; most designs use n = 2^k. The output equals the selected input D_i, where i is encoded by the select lines. A common implementation uses a chain of AND gates that gate each input with a unique select code, followed by an OR gate to combine the results.

Analog multiplexers exist for continuous signals and use switches (transmission gates) controlled by select signals. Examples include digital, such as 2-to-1, 4-to-1, 8-to-1, and larger; analog families include 74HC4051 (8-channel multiplexor) and CD4051.

Demultiplexer vs multiplexor: a demultiplexer performs the inverse operation, taking one input and routing it to one of several outputs, while a multiplexor selects one of many inputs to pass through.

Applications: data routing on buses in microprocessors, time-division multiplexing in telecommunications, memory addressing reduction, function selection in ALUs, digital signal processing, and analog signal routing in audio/video circuits.

Limitations: added latency (propagation delay) and word- or bit-width constraints; drive requirements and fan-out on select lines; power consumption.