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The output waveform of the given logical circuit for the following inputs A and B as shown below, is [Figure: A and B each go into a NAND gate with tied inputs; the outputs feed a NAND gate giving Y. Inputs: A is 1 from t₁ to t₃ and from t₅ to t₆, 0 otherwise. B is 1 from t₂ to t₄ and after t₆, 0 otherwise. Options: (a) 1 until t₂, 0 from t₂ to t₃, 1 after; (b) 1 until t₁, 0, 1 from t₄ to t₅, 0 after; (c) 0 until t₁, 1 from t₁ to t₄, 0 from t₄ to t₅, 1 after t₅; (d) a single pulse from t₁ to t₃.]
Asked in JEE Main 30th Jan 1st Shift 2023 · Waveforms, switches and diode gates
- (1) 1 until t₂, 0 from t₂ to t₃, 1 after
- (2) Pulses only before t₁ and between t₄ and t₅
- (3) 0 until t₁, 1 to t₄, 0 to t₅, 1 after
- (4) A single pulse from t₁ to t₃
Answer: (3) 0 until t₁, 1 to t₄, 0 to t₅, 1 after
Step-by-step solution
Tied NANDs give A,B, and the last NAND gives Y=A+B.
Before t₁ both are 0: Y=0. From t₁ to t₄ at least one is 1: Y=1.
From t₄ to t₅ both are 0: Y=0. After t₅ at least one is 1: Y=1.
Why the other options are wrong
- (1) Not the OR of the inputs.
- (2) This is NOR of the inputs.
- (4) This is just A over part of the time.
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