Lec-11/logic/multiplixers

Multiplexers
A multiplexer is one of the important combinational circuits and has a wide range of applications, the term multiplex means “many into one”. Multiplexers transmit large numbers of information channels to a smaller number of channels. A digital multiplexer is a combinational circuit that selects binary information from one of the many input channels and transmits to a single output line. That is why the multiplxers are also called data selectors. The selection of the particular input channel is controlled by a set of select inputs.

A digital multiplexer of 2n input channels can be controlled by n numbers of select lines and an input line is selected according to the bit combinations of select lines.
A 4-to-1 line multiplexer is defined as the multiplexer consisting of four input channels and information of one of the channels can be selected and transmitted to an output line according to the select inputs combinations. Selection of one of the four input channels is possible by two selection inputs. Figure 1 illustrates the truth table, input channels I0, I1, I2, and I3 are selected by the combinations of select inputs S1 and S0.
The circuit diagram is shown in Figure 2, to demonstrate the operation, let us consider that select input combination S1S0 is 01. The AND gate associated with I1 will have two of inputs equal to logic 1 and a third input is connected to I1. Therefore, output of this AND gate is according to the information provided by channel I1. The other three AND gates have logic 0 to at least one of their inputs which makes their outputs to logic 0. Hence, OR output (Y) is equal to the data provided by the channel I1. Thus, information from I1 is available at Y.