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Computer Science

A combinational logic circuit with three inputs P,Q,R produces 1 if and only if an odd number of 0's are inputs.

  1. Draw a truth table.
  2. Derive a canonical SOP expression for the above truth table.
  3. Find the complement of the above derived expression using De-Morgan's theorem and verify whether it is equivalent to its POS expression or not.

Boolean Algebra

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Answer

Truth Table

PQROutputMin
Terms
Max
Terms
0001P'Q'R'
0010P+Q+R'
0100P+Q'+R
0111P'QR
1000P'+Q+R
1011PQ'R
1101PQR'
1110P'+Q'+R'

SOP expression = P'Q'R' + P'QR + PQ'R + PQR'

POS expression = (P+Q+R').(P+Q'+R).(P'+Q+R).(P'+Q'+R')

Complement of P'Q'R' + P'QR + PQ'R + PQR'
= [P'Q'R' + P'QR + PQ'R + PQR']'
= (P'Q'R')'.(P'QR)'.(PQ'R)'.(PQR')'
= (P''+Q''+R'').(P''+Q'+R').(P'+Q''+R').(P'+Q'+R'')
= (P+Q+R).(P+Q'+R').(P'+Q+R').(P'+Q'+R)

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