Question:

Identify the correct output signal \( Y \) in the given combination of gates for the given inputs \( A \) and \( B \) shown in the figure. 
 

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De-Morgan’s Theorem is a useful tool to simplify Boolean expressions: \( \overline{A \cdot B} = \overline{A} + \overline{B} \) and \( \overline{A + B} = \overline{A} \cdot \overline{B} \).
Updated On: May 20, 2025
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The Correct Option is D

Approach Solution - 1

Step 1: {Understanding the Logic Circuit} 
The given circuit consists of: - NOT gates applied to inputs \( A \) and \( B \). - AND gate processing the inverted signals. 
Step 2: {Deriving the Boolean Expression} 
The circuit implements: \[ Y = \overline{A} \cdot \overline{B} \] Applying De-Morgan’s theorem: \[ Y = \overline{(A + B)} \] 
Step 3: {Comparing with Output Waveforms} 
Analyzing the truth table, we match the waveform and determine that the correct output is given by waveform 4. Thus, the correct answer is (D). 
 

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Approach Solution -2

Step 1: Understanding the Logic Circuit
The given circuit contains two inputs, \( A \) and \( B \). Each of these inputs is first passed through a NOT gate, producing the inverted signals \( \overline{A} \) and \( \overline{B} \). These inverted outputs are then fed into an AND gate.

Step 2: Deriving the Boolean Expression
The output of the AND gate with inverted inputs is: \[ Y = \overline{A} \cdot \overline{B} \] We can now apply De Morgan’s Theorem to this expression: \[ \overline{A} \cdot \overline{B} = \overline{A + B} \] So, the final expression becomes: \[ Y = \overline{(A + B)} \] This is the standard Boolean expression for a NOR gate.

Step 3: Comparing with Output Waveforms / Logic Behavior
Let’s interpret the behavior of the output from the expression \( Y = \overline{(A + B)} \). This logic gate produces a high output (1) only when both inputs are 0. If either \( A \), \( B \), or both are 1, the output becomes 0.

Here is the truth table for verification:

ABA + BY = &overline;(A + B)
0001
0110
1010
1110

Conclusion:
The circuit's output logic matches that of a NOR gate. Hence, the logic operation performed by the circuit is: \[ \boxed{Y = \overline{A + B}} \Rightarrow \text{NOR gate} \]

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