Karnaugh map (K-map) fundamentals: Which statement best describes what a Karnaugh map is and how it relates to the truth table?

Difficulty: Easy

Correct Answer: It is simply a rearranged truth table.

Explanation:


Introduction / Context:
A Karnaugh map (K-map) is a visual method for simplifying Boolean expressions and designing logic with minimal gates. It retains the exact information of a truth table but organizes it spatially so that adjacent cells differ by only one variable (Gray code ordering). This makes it easy to spot groups of 1s (or 0s) and derive simplified sum-of-products or product-of-sums forms.


Given Data / Assumptions:

  • We are dealing with combinational logic functions of typically up to 4–6 variables for practical hand simplification.
  • Grouping on a K-map follows powers of two (1, 2, 4, 8, ...).
  • Gray code labeling ensures adjacency reflects a single-bit change.


Concept / Approach:
The K-map is nothing more than a truth table rearranged in two dimensions to expose adjacency. Every cell corresponds to one minterm (or maxterm) of the original function. By grouping adjacent 1s into largest possible rectangles, we factor out variables that do not change within the group, yielding a minimized Boolean expression that implements with fewer gates or literals.


Step-by-Step Solution:

Start from the truth table and place each output value into the K-map cell addressed by its input combination (Gray-coded axes).Identify adjacent 1s and form groups of size 2^n (wrap-around adjacency is allowed).Translate each group into a product term (for SOP) by including only variables that remain constant over the group.Combine all product terms to get the simplified expression.


Verification / Alternative check:
Cross-verify by expanding the simplified expression back into minterms and confirming it yields the same truth table as the original function. Karnaugh and algebraic minimization give identical results when done correctly.


Why Other Options Are Wrong:

  • Eliminates the need for NAND/NOR: K-maps do not dictate gate families; they only simplify logic expressions.
  • Variable complements can be eliminated: Complements may remain; K-maps do not inherently remove inversion.
  • Replace Boolean rules: K-maps complement algebra; they do not replace the underlying Boolean laws.


Common Pitfalls:
Forgetting Gray code ordering, missing wrap-around adjacency, or making non-power-of-two groups. Also, confusing don't-care conditions with zeros can lead to suboptimal or incorrect simplifications.


Final Answer:
It is simply a rearranged truth table.

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