multiplexers

A multiplexer, or MUX, is a digital or analog device that selects one of several input signals and forwards the chosen input to a single output line. The selection is controlled by a set of select lines. Multiplexers are used to share a single data path among many signals, enabling efficient routing of information in circuits and communication systems.

An N-to-1 multiplexer has N data inputs (D0 through D(N−1)) and log2(N) select lines. The output Y equals the input Dk where k is the binary value on the select lines. Common examples include 2-to-1, 4-to-1, and 8-to-1 multiplexers. For instance, a 4-to-1 MUX uses two select lines to choose among D0, D1, D2, and D3.

Digital multiplexers are implemented as combinational logic and are widely available as integrated circuits, sometimes with an enable or strobe input to force a defined output when disabled. Analog multiplexers use transmission gates or MOS switches to pass analog signals, with attention to on-resistance, signal integrity, and bandwidth. Some designs also provide an active-low or active-high enable for additional control.

Applications include data routing in CPUs and microcontrollers, bus sharing, and implementing time-division multiplexing in communications. They also serve as building blocks in programmable logic and signal selection within larger circuits. Design considerations include propagation delay, fan-in/fan-out, noise, power consumption, and, for analog MUXes, on-resistance and charge injection.

Related devices include demultiplexers, which perform the inverse operation, and crossbar switches, which route multiple inputs to multiple outputs. Multiplexers are fundamental components in digital design and appear in a wide range of integrated circuits and systems.