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NCERT Class XII Chapter
Semiconductor Electronics
Questions With Solutions

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Question : 17 of 19
Marks: +1, -0
You are given two circuits as shown in figure which consist of NAND gates. Identify the logic operation carried out by the two circuits.
Solution:  
(a) Let us find Boolean expression for given logic circuit
so, output Y = AB⋅AB−––––––––––––−\overset{-}{ AB \cdot \overset{-}{AB}^{{––––––––––––}} } = AB––––––––––\overset{––––––}{ \overset{––––}{ \mathrm{AB} } } = AB
hence logic circuit operates as AND gate.
(b) By De-Morgan’s theorem
(A−B−)−\left( \overset{-}{A} \overset{-}{B} \right)^{-} = A−−+B−−){\overset{-}{A}}^{-} + {\overset{-}{B}}^{-} ) = A + B
so, the given logic circuit acts as OR gate.
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