Gate-level equivalence using DeMorgan’s laws An AND gate with inversion “bubbles” on each input is functionally equivalent to which single gate?

Difficulty: Easy

Correct Answer: NOR

Explanation:


Introduction / Context:
Schematic “bubbles” indicate logical inversion. Recognizing bubble-pushing patterns and applying DeMorgan’s theorems enables quick translation between gate symbols and their equivalent logic functions, which is crucial in reading or redrawing schematics.



Given Data / Assumptions:

  • Gate: AND with inverted inputs (bubbles on each input).
  • No bubble on the output.
  • Standard Boolean notation: complement shown with a prime (’).


Concept / Approach:
The function of an AND gate with complemented inputs is Y = A’ · B’. DeMorgan’s theorem states that (A + B)’ = A’ · B’. Therefore, A’ · B’ equals (A + B)’. The latter is precisely the definition of a NOR gate.



Step-by-Step Solution:
Write the AND-with-bubbles expression: Y = A’ · B’.Apply DeMorgan: A’ · B’ = (A + B)’.Recognize that Y = (A + B)’ is a 2-input NOR function.Hence, the composite symbol performs as a NOR gate.


Verification / Alternative check:
Construct a truth table for A’ · B’ and compare with NOR(A, B); they match for all input combinations.



Why Other Options Are Wrong:
NOT: a unary operation; our function depends on two inputs.OR: would be Y = A + B (no inversion).NAND: corresponds to (A · B)’ which is different from (A + B)’.


Common Pitfalls:
Forgetting that bubbles invert signals and that DeMorgan converts between AND-of-complements and complement-of-OR.



Final Answer:
NOR

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