The document discusses the carry lookahead adder, which reduces carry propagation time in multi-bit addition. It does this through generating all carry outputs after just 2 gate delays, as opposed to the standard n gate delays of a ripple carry adder. Specifically, it mentions that a carry lookahead adder uses full adders with half adders to generate carries, and shows the logic diagram for a 4-bit adder with carry lookahead. The summary provided defines the carry lookahead adder and notes that its main advantage is improved speed over standard adders, though it has more complex circuits for larger bit sizes.

1. Carry Lookahead Adder

2. Full adder with two half adders

3. Full adder with two half adders

4. Full adder with two half adders
2 gate levels

5. Four-bit binary parallel adder

6. Four-bit binary parallel adder
From C0 to C4: 8 gate levels
For n-bit adder, 2n gate levels from input carry to output carry

7. Carry output of each stage

8. Logic diagram of carry lookahead generator
All output carries are generated after a delay of
2 gate levels.

9. 4-bit adder with carry lookahead

10. Summary
• A carry lookahead adder (CLA) is a type of adder used in digital logic
to reduce carry propagation time.
• Advantage:
• Improves speed by reducing the amount of time required to determine the
carry bits
• Disadvantage:
• Complex circuits for carry outputs over more than 4-bits