How can Propagation delay be avoided in a parallel adder?

The parallel adder which we use in the digital circuits ,the carry output of each full adder stage is connected to the carry input of the next higher order stage.therefore,the sum and carry outputs of any stage cannot be produced until the input carry occurs;

This leads to a time delay in the addition process.This delay is known as carry propagation delay.

to the second question the propagation delay can be avoided in the binary parallel adder with the help of look ahead carry generator

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