Digital Electronics - Combinational Logic Circuits - Discussion

The output of NOT gate will be the complement of the input. The operation of AND gate is product of the output of NOT gate. The operation of OR gate is addition of two inputs.

1ST AND GATE O/P IS - A`.B`
2ND AND GATE O/P IS - A.B
OR GATE O/P IS - (A`B`)+(AB) = AB + A`B`.

Why not option B is correct? Because a'b'=[ab]'.

@Aakash, a'b'=[ab]' is not correct.

~A and ~B means that to get a high output you would need logic 0 for both A and B. Where as ~(AB) means that any combination of logic values for A and B will yield a high output except both being logic 1.

Just make the truth tables and you will see:

AB|~A|~B|~A~B AB|~(AB)
00 | 1 | 1 | 1 00 | 1
01 | 1 | 0 | 0 01 | 1
10 | 0 | 1 | 0 10 | 1
11 | 0 | 0 | 0 11 | 0

Option D is correct answer because (A) AND Gate !(B) OR Gate.

Opinion B is not correct answer because !(AB).

Not option B, because A'B' = [A + B]'