Consider the two cascaded 2-to-1 multiplexers as shown in the figure The…

2016

Consider the two cascaded 2-to-1 multiplexers as shown in the figure

The minimal sum of products form of the output \(X\) is

  1. A.

    \(\overline{P} \ \overline {Q}+PQR\)

  2. B.

    \(\overline{P} \ {Q}+QR\)

  3. C.

    \(PQ +\overline{P} \ \overline{Q}R\)

  4. D.

    \(\overline{Q} \ \overline{R} + PQR\)

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Correct answer: D

Key insight: analyze what each multiplexer outputs depending on its select line.

  • Left MUX (select = P): selects between 0 (when P = 0) and R (when P = 1). So its output is P·R.

  • Right MUX (select = Q): when Q = 0 it outputs ¬R; when Q = 1 it outputs the left MUX output (PR).

  • Combine the two cases: X = ¬Q·¬R + Q·(P·R) = ¬Q·¬R + P·Q·R. This is already the minimal sum-of-products form.

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