Question

Identify which logic gate OR, AND and NOT is represented by the circuits in the line boxes 1, 2 and 3. Give the truth table for the entire circuit for all possible values of A and B.

Answer 1

In dotted line box 1 is a NOT gate

Explanation. Its circuits is as shown in Fig.1

Here $y=\overline{A.A}=\overline{A}+\overline{A}=\overline{A}=NO{T}^{\prime }{A}^{\prime }$

In dotted line box 2 is an OR gate.

Explanation. Its circuit is as shown in Fig.2

Here, $y=\overline{\overline{A}+\overline{B}}=A+B=AORB$

(From De-Morgan's Theorem)

In dotted line box 3 is AND gate.

Explanation. Its circuit is as shown in Fig.3

Here, $y=\overline{\overline{(A.B)}.\overline{(A.B)}}=A.B+A.B=2(A.B)=A.B=AANDB$