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In which of the following adder circuits, the carry look ripple delay is eliminated?

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carry look ripple delay is eliminated in Carry-look-ahead adder as carry is already provided before the operation starts .

carry is calculated as follows:-

Substituting C1 into C2, then C2 into C3, then C3 into ​​​​​​​C4 yields the following expanded equations:

Here G (carry generator) is equal to

P(propagate) as follows

all the carry are calculated using the above formula and provided to input as mentioned in a diagram. Thus ripple delay is eliminated.

Option D; as in CLA the carry is generated in parallel. Hence no concept of ripple carry.

Please refer to the carry equation
Where $Gi$ is the generator Function and $Pi$ is the propagation function.
$Gi$ = $AiBi$ (Ai,Bi are Bit pairs of the two n bit numbers)
$Pi$ = $Ai+Bi$ or $Ai ⊕ Bi$
Follow CLA for further clarification.
by
option (d) is correct.

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