Consider the minterm list form of a Boolean function 𝐹 given below. 𝐹(𝑃,𝑄,…

2018

Consider the minterm list form of a Boolean function 𝐹 given below.

𝐹(𝑃,𝑄, 𝑅, 𝑆) = βˆ‘π‘š(0, 2, 5, 7, 9, 11) + 𝑑(3, 8, 10, 12, 14)

Here, π‘š denotes a minterm and 𝑑 denotes a don’t care term. The number of essential prime implicants of the function 𝐹 is ______.

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Correct answer: 3

Answer: 3 essential prime implicants.

Work through:

  • Combine minterms and don’t-cares to form the one-set: 0, 2, 3, 5, 7, 8, 9, 10, 11, 12, 14

  • Identify prime implicants (groups of adjacent ones/don’t-cares):

    • P AND NOT Q (P Q'): covers indices 8, 9, 10, 11 β€” therefore covers minterms 9 and 11.

    • NOT Q AND NOT S (Q' S'): covers indices 0, 2, 8, 10 β€” therefore covers minterms 0 and 2.

    • NOT P AND Q AND S (P' Q S): covers indices 5 and 7 β€” therefore covers minterms 5 and 7.

  • Check essentiality: each minterm is covered by exactly one of the listed prime implicants:

    • Minterms 0 and 2 are covered only by NOT Q AND NOT S (Q' S').

    • Minterms 9 and 11 are covered only by P AND NOT Q (P Q').

    • Minterms 5 and 7 are covered only by NOT P AND Q AND S (P' Q S).

Since each of the three prime implicants uniquely covers (at least) one minterm, all three are essential. Therefore the number of essential prime implicants is 3.

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