Question

For the given digital circuit, write the truth table and identify the logic gate it represents.

• A. OR-Gate
• B. NOR-Gate
• C. NAND-Gate
• D. AND-Gate

Answer 1

Answer: (D)

AND-Gate

To solve the circuits with truth table only, three truth tables will be required ($C,D,Y$). Hence, it is useful to solve it with boolean algebra.

From the attached diagram,

$C=\overline{A+A}$

$⟹C=\overline{A}$

Similarly, $D=\overline{B}$

$Y=\overline{C+D}$

$Y=\overline{\overline{A}+\overline{B}}$

Using De-Morgan's law, $Y=AB$ which is AND gate.

Following is the truth table for the above:

A	B	C	D	Y
0	0	1	1	0
0	1	1	0	0
1	1	0	0	1
1	0	0	1	0