Following is a refresher on the XNOR gates.

Figure 1 XNOR gate

Alternate equation for an XNOR gate is :

O = (A)bar * (B)bar + A * B

This can be derived using Kmaps as following.

 Figure 2. Kmap for XNOR gate.

We know that the equation for a 2:1 MUX is of following form :

Out = S * A + (S)bar * B.

We need to turn this of the form

O = (A)bar * (B)bar + A * B

It seems easy enough to achieve this. In the 2:1 MUX equation, if we tie (A)bar in place of B, we get

Out = S * A + (S)bar * (A)bar

This is the equation of XNOR gate for inputs S and A.

Figure 3 XNOR using 2:1 MUX

Do you think we are done with 2:1 MUX series now ? There is still some more devices that we can make. Will continue in next post.

-SS