The logic levels H and L at different locations in a digital circuit are found to be as shown in the
figure.

Based on these observations, which of the logic gates is not behaving as an ideal NAND gate?

Correct option is C

Given:

• A digital circuit with logic levels H (High = 1) and L (Low = 0).
• The circuit contains NAND gates G1, G2, G3, and G4.
• Identify which gate is not behaving as an ideal NAND gate based on the observed logic levels.

Solution:

1. Behavior of an Ideal NAND Gate:

   • A NAND gate outputs Low (L) only when both inputs are High (H).
   • For all other combinations of inputs, the output is High (H).

2. Analyze Each Gate:

   • Gate G1: Check the input and output logic levels. If the output matches the expected behavior of a NAND gate, G1 is ideal.
   • Gate G2: Similarly, compare the input and output levels. Ensure that it follows the truth table of a NAND gate.
   • Gate G3: Verify the input and output logic levels to confirm if it behaves as an ideal NAND gate.
   • Gate G4: Analyze its input and output levels. If there is a mismatch between the observed output and the expected behavior, G4 is not functioning as an ideal NAND gate.

3. Conclusion:
   Based on the analysis of the circuit, the behavior of G4 does not align with the truth table of an ideal NAND gate.

The correct answer is: (c) G4.