Question

Following diagram performs the logic function of

• A. OR gate
• B. AND gate
• C. XOR gate
• D. NAND gate

Answer 1

Answer: (B)

For our convenience, the output of first NAND gate is chosen as X as shown,

Output is first NAND gate.
$X=\overline{A\cdot B}$
Using De-Morgan's theorem,
$\overline{A.B}=\bar{A}+\bar{B}$
So $X=\bar{A}+\bar{B}$
Now, output of $2nd$ NAND gate,
$Y=\bar{X}=\overline{\bar{A}+\bar{B}}$
again$\overline{\bar{A}+\bar{B}}=\overline{\bar{A}}\cdot \overline{\bar{B}}=A\cdot B$ $(\because \overline{\bar{A}}=A)$
Hence, $Y=A\cdot B$
This is the logic function of AND aate.