1.

What should be done to obtain an OR gate from a NAND gate?(a) We need only 3 NAND gates(b) We need two NOT gates obtained from NAND gates and one NAND gate(c) We need 3 NOT gates obtained from NAND gates and 3 NAND gates(d) We need 2 NAND gates and 4 AND gates obtained from NAND gates.I have been asked this question during a job interview.I need to ask this question from Digital Electronics and Logic Gates topic in chapter Semiconductor Electronics : Materials, Devices and Simple Circuits of Physics – Class 12

Answer»

Right choice is (b) We need two NOT gates OBTAINED from NAND gates and one NAND gate

The EXPLANATION: We need OR gate (Y = A + B) from NAND gate (Y = not (A.B))

Y = not (not (A.B))

Y = not (not (A)) + not (not (B))[USING the Boolean identify ➔ not (A.B) = not (A) + not (B)]

So, Y = A + B[Since not (not (A)) = A and not (not (B)) = B]

THEREFORE, to OBTAIN an OR gate from a NAND gate, we need two NOT gates obtained from NAND gates and one NAND gate.



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