Ripple Carry Adder

Question

Comments

@gabbar 3.23 * 10^6 @Prabhanjan_1

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i have used pipeline concrpt over here:

for first addition it needs = (169+32) * 8 ns

after that each addition needs only (169+32)ns

by using this i got 4975117 ... whts wrong with this

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@monty please check the answer once again is it 5.23*10^6???

Answer 1

So we care about only the carry generated by FA because these act as inputs to the other FA.

So computing time for Carry C1,C2,C3,C4,C5,C6,C7.

we get 18+27+23+32+18+23+27 = 168 ns

So for last FA B2 we get compute sum also S8 = 23ns

seconds per addition = 168+23=191ns

additions per second  = 1 / seconds per addition. 

                                    = 1 / 191ns = 5.23*10^6 

Comments

we take max(carry, sum)=(200,191)=200

So, answer 5 X 10⁶

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For last FA that is at leftmost end we compute sum value S8.

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we need addition

So, it needs sum and also carry bit.

So, max(sum, carry) will take place in addition calculation

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Just think like this to get S8 we need all  carries c1...c7 and S8 delay ........ that is how i thought

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@Prabhanjan_1 

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but why they have computed 3 sums only ??

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how we are calculating sum and carry generation from above can any one explain plz

Answer 2

It is (1÷310ns) = 3.23* 10^6.

Because S7 bit of sum takes 310ns to get generated.
FA_C2 adder receives its input-carry bit C6 after 141ns and this adder takes 169 ns to generate S7. In this way we get S7 bit after (141 + 169 = 310 ns).

Actually here we get S7 bit (at 310 ns) after S8(at 191 ns). Therefore complete output is generated after 310 ns.

Comments

 @monty this is very nice ques,plz help me this ques is from which source u found?