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4-Bit Carry Look-ahead Adder In parallel adders, carry output of each full adder is given as a carry input to the next higher-order state. Hence, these adders it is not possible to produce carry and sum outputs of any state unless a carry input is available for that state.

## What is 4-bit ripple carry adder?

Ripple carry adder is a combinational logic circuit used for the purpose of adding two n-bit binary numbers. 4-bit ripple carry adder is used for adding two 4-bit binary numbers. N-bit ripple carry adder is used for adding two N-bit binary numbers.

A carry-look ahead adder or CLA is a type of adder which is used in digital logic to decrease the carry propagation time. It improves the speed. It calculates one or more carry bits before the sum, this reduces the wait time to calculate the result of the bits which have a larger value.

A carry-Lookahead adder is a fast parallel adder as it reduces the propagation delay by more complex hardware, hence it is costlier. In this design, the carry logic over fixed groups of bits of the adder is reduced to two-level logic, which is nothing but a transformation of the ripple carry design.

A carry-lookahead adder (CLA) or fast adder is a type of electronics adder used in digital logic. The carry-lookahead adder calculates one or more carry bits before the sum, which reduces the wait time to calculate the result of the larger-value bits of the adder.

Disadvantages of Carry Look Ahead Adder- It involves complex hardware. It is costlier since it involves complex hardware. It gets more complicated as the number of bits increases.

6. What is one disadvantage of the ripple-carry adder? Explanation: The main disadvantage in using this type of adders is that the time delay increases as for each adder to add the carry should be generated in the previous adder, and for that to add the carry from the one before is required.

By combining four 4-bit CLAs, a 16-bit adder can be created but additional logic is needed in the form of an LCU. The LCU then generates the carry input for each CLA.

What are carry generate combinations?

Explanation: If the input is either 0, 0, 0 or 0, 0, 1 then the output will be 0 (i.e. independent of input) and if the input is either 1, 1, 0 or 1, 1, 1 then the output is 1 (i.e independent of input). Such situation is known as carry generate combinations.

## What is carry in full adder?

Full Adder is the adder which adds three inputs and produces two outputs. The first two inputs are A and B and the third input is an input carry as C-IN. The output carry is designated as C-OUT and the normal output is designated as S which is SUM.

4-Bit Carry Look-ahead Adder In parallel adders, carry output of each full adder is given as a carry input to the next higher-order state. Hence, these adders it is not possible to produce carry and sum outputs of any state unless a carry input is available for that state.