Gate identification from behavior: A signal is inhibited by applying a LOW to one input, yet the output remains HIGH. Which logic gate matches this description?
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AAND
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BNAND
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CNOR
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DOR
Answer
Correct Answer: NAND
Explanation
Introduction / Context:Recognizing a gate from its qualitative behavior is a key digital logic skill. The description says a LOW on any input inhibits the signal but produces a HIGH output regardless of the other inputs. This strongly hints at the inversion of an AND function, which is the NAND gate.
Given Data / Assumptions:
- At least two-input logic gate.
- Driving one input LOW forces the output to a known state.
- Observed output is HIGH when any single input is LOW.
Concept / Approach:The NAND truth function is Y = NOT(A * B * …). For NAND, the output is LOW only when all inputs are HIGH. If any input is LOW, the product A * B * … equals 0, so NOT(0) = 1 → output HIGH. Hence a LOW on an input 'inhibits' the low-output condition and produces HIGH, matching the description.
Step-by-Step Solution:
For NAND: if any input = 0 → product = 0 → output = 1.Therefore a LOW input guarantees a HIGH output (signal inhibited).Only when all inputs are 1 is the output 0.Verification / Alternative check:Compare to AND: any LOW makes output LOW (contradicts the statement). Compare to OR: any HIGH makes HIGH (doesn’t mention LOW causing HIGH). Compare to NOR: any HIGH causes LOW (opposite behavior). Thus only NAND fits.
Why Other Options Are Wrong:
- AND: Any LOW → output LOW, not HIGH.
- NOR: Any HIGH → output LOW, opposite behavior.
- OR: Any HIGH → output HIGH; the described trigger is a LOW input.
Common Pitfalls:Confusing NAND with NOR; remember NAND inverts AND (only all HIGH gives LOW), while NOR inverts OR (any HIGH gives LOW).
Final Answer:NAND