Question

For the following combination of logic gates, when all the three inputs are first high and then low, the output \(Y\) will respectively be

• A. \(1, 0\)
• B. \(0, 0\)
• C. \(1, 1\)
• D. \(0, 1\)

Hint:

Always evaluate logic gate questions stepwise by identifying each gate and applying the truth table one stage at a time.

Answer 1

The Correct Option is D

Step 1: Identify the logic gates.
From the diagram, the first gate is an OR gate taking inputs \(A, B, C\). The output of this OR gate is then fed into a NAND gate (AND gate followed by NOT).

Step 2: Case 1 — All inputs are HIGH (A = B = C = 1).
OR gate output = \(1 \lor 1 \lor 1 = 1\).
This output is applied to the NAND gate input.
NAND gate output = \(\overline{1} = 0\).

Step 3: Case 2 — All inputs are LOW (A = B = C = 0).
OR gate output = \(0 \lor 0 \lor 0 = 0\).
This output is applied to the NAND gate input.
NAND gate output = \(\overline{0} = 1\).

Step 4: Conclusion.
When inputs are first HIGH, output is \(0\), and when inputs are LOW, output is \(1\).