Combination Circuits

Q: Implement Full Adder using DECODER

Q- Implement the Full adder using 3 to 8 decoder.

Ans: equation for sum S = ab’c’ + a’b’c + a’bc’ + abc = Σ(1,2,4,7)

C = ab + ac + bc = ab(c + c’) + ac (b + b’) + bc (a + a’) = abc + abc’ + abc + ab’c + abc + a’bc

= abc +a’bc +ab’c+abc’= Σ (3, 5, 6, 7)

So we can implement it from decoder using OR gates as follow:

One can obtain larger decoder circuit from given decoder circuit as shown on next page.

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