A 4-bit carry lookahead adder, which adds two 4-bit numbers, is designed using…

Given:

- 4-bit carry lookahead adder (CLA)

- Inputs available in both complemented and uncomplemented forms

- Gate delay = 1 time unit

- Carry network uses 2-level AND-OR logic

Propagation delay calculation:

1. Generation of Propagate (Pi) and Generate (Gi):

Pi = Ai XOR Bi

Gi = Ai AND Bi

XOR = 2 gates → 2 time units

AND = 1 gate → 1 time unit

Since both are done in parallel, Pi/Gi delay = 2 time units.

2. Carry Lookahead Logic (two-level AND-OR):

Ci+1 = Gi + Pi*Gi-1 + Pi*Pi-1*Gi-2 + ...

This takes 2 more gate delays (one AND level + one OR level)

So carry delay = 2 time units.

3. Sum calculation:

Si = Pi XOR Ci

Another XOR = 2 gate delays

Total worst-case delay:

= Pi/Gi computation (2)

+ Carry lookahead (2)

+ Sum operation (2)

= 6 time units

Final Answer: 6 time units.