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Which of the following circuits has the same output as that of the given circuit? [Figure: A and B drive two AND gates. Upper AND: A and B (B through a NOT gate). Lower AND: A and B. Both outputs feed a NOR gate giving Y. Options: (a) an AND gate with inputs A, B; (b) a NAND gate with both inputs tied to A; (c) an AND gate with inputs A, B followed by a NOT gate; (d) a NAND gate with both inputs tied to B.]
Asked in JEE Main 28th Jan 1st Shift 2025 · Gate combinations and truth tables
- (1) AND gate with inputs A, B
- (2) NAND gate with both inputs tied to A
- (3) AND gate followed by NOT (NAND of A, B)
- (4) NAND gate with both inputs tied to B
Answer: (2) NAND gate with both inputs tied to A
Step-by-step solution
Upper AND: AB. Lower AND: AB.
NOR: Y=AB+AB=A(B+B)=A
A NAND gate with both inputs tied to A also gives A.
Why the other options are wrong
- (1) The output is 1 when A=0 whatever B is, which AND cannot give.
- (3) NAND of A and B is 1 for A=1,B=0, but the circuit gives 0 there.
- (4) The output does not depend on B at all.
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