What is a multiplexer?

A multiplexer, also commonly known as a mux, is a device that selects which of the digital or analogue input signals will be passed to the output of the device.  Multiplexers typically have either 2, 4, 8 or 16 inputs, select pins and a single output. A multiplexer is therefore a switch for multiple inputs and a single output.

Multiplexers are advantageous because they increase the amount of data that can be sent across a single channel. Multiplexors are commonly used in communication systems, computer memories and telephone networks.

2-to-1 Multiplexor

A 2-to-1 multiplexor is shown in the schematic. If the select pin (S) is set to 0 (0 voltage) then the first channel (channel A) will be passed to the output. If the select pin (S) is set to 1 (positive voltage) then the second channel (channel B) will be passed to the output.

4-to-1 Multiplexor

A 4-to-1 multiplexor is shown in the schematic. Two select pins are required to multiplex 4 input channels.

The following table shows which input channel will be pass to the output, when different select pin combinations are implemented.

S0 S1 Output
0 0 Channel A
0 1 Channel B
1 0 Channel C
1 1 Channel D

 

8-to-1 and 16-to-1 multiplexor

Multiplexors with more than 4 inputs, work on a similar principle to 4-to-1 multiplexor, except additional select pins are also requires. 3 select pins are required to multiplex 8 input signals and 4 select pins are required to multiplex 16 input signals.