Question

Design a 2x1 mux and then use as many of them as needed to make a bigger mux which can be used to compare two 2-bit binary numbers.

Answer 1

The multiplexer or MUX is a digital switch, also called as data selector. It is a combinational circuit with more than one input line, one output line and more than one select line. It allows the binary information from several input lines or sources and depending on the set of select lines , particular input line , is routed onto a single output line.

2-to-1 Multiplexer

A 2-to-1 multiplexer consists of two inputs D0 and D1, one select input S and one output Y. Depends on the select signal, the output is connected to either of the inputs. Since there are two input signals only two ways are possible to connect the inputs to the outputs, so one select is needed to do these operations.

If the select line is low, then the output will be switched to D0 input, whereas if select line is high, then the output will be switched to D1 input. The figure below shows the block diagram of a 2-to-1 multiplexer which connects two 1-bit inputs to a common destination.

The truth table of the 2-to-1 multiplexer is shown below.

From the truth table the Boolean expression of the output is given as

Bigger MUX using 2:1 MUX which can be used to compare two 2-bit binary numbers.