question_answer

                In the following circuit, the output Y for all possible inputs A and B is expressed by the truth table:                                                                                                                                                                                                                

A)                                 A             B             Y                                 0              0              0                                 0              1              0                                 1              0              0                                 1              1              1

B)                                            A             B             Y                                 0              0              1                                 0              0              1                                 1              0              1                                 1              1              0

C)                                 A             B             Y                                 0              0              1                                 0              1              0                                                              1              0              0                                 1              1              0

D)                                 A             B             Y                                 0              0              0                                 0              1              1                                 1              1              1

Correct Answer: D

Solution :

                Key Idea: Gates-I and II are NOR gates. We can simplify the gate circuit as                                 Here, gates-I and II are NOR gates. The output \[(\overline{A+B})\] of gate-I will be appeared as input of gate-II. The final output is                 \[Y=\overline{\overline{A+B}}\,=A+B\]                 This is he Boolean expression of OR gate whose truth table is given below:

A	B	Y
0	0	0
0	1	1
1	0	1
1	1	1