4-Bit Carry Lookahead Adder
High-performance ALUs rely on parallel carry computation to break the linear delay dependency of ripple architectures. The carry lookahead adder computes all intermediate carry signals simultaneously using propagate and generate terms, drastically reducing the critical path depth in wide datapaths.
Implement a 4-bit carry lookahead adder. The circuit must add two 4-bit inputs A and B alongside a carry-in Cin to produce a 4-bit sum S and a carry-out Cout. To achieve the required gate-level performance, you must compute the generate G and propagate P signals for each bit, and use them to evaluate all internal carry bits in parallel.
| A | B | Cin | S | Cout | |-----|-----|-------|-----|--------| | 0 | 0 | 0 | 0 | 0 | | 5 | 3 | 0 | 8 | 0 | | 15 | 1 | 0 | 0 | 1 | | 10 | 5 | 1 | 0 | 1 | | 15 | 15 | 1 | 15 | 1 |
Constraints
- Implement combinational logic only.
- Do not use high-level adder macros or built-in arithmetic blocks.
- Limit the critical path to a maximum of 5 gate levels from any input to
CoutorS. - Compute intermediate carries directly from
Cin,P, andGwithout chaining them sequentially.
Topics
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