Which type of adder is designed to overcome the propagation delay issues in…

The correct option is B: Carry-Lookahead Adder

Detailed Solution:

1. The Problem: Ripple-Carry Adder (RCA)

In a Ripple-Carry Adder, the addition process behaves like a row of falling dominoes. Each individual Full Adder stage must wait for the carry bit (Cin) to be calculated and passed down by the previous stage before it can compute its own sum and output carry (Cout)

For an n-bit adder, the time delay grows linearly (O(n)). This creates a massive performance bottleneck (propagation delay) as the bit-width increases (e.g., in 32-bit or 64-bit systems).

2. The Solution: Carry-Lookahead Adder (CLA)

A Carry-Lookahead Adder is specifically designed to eliminate this waiting dependency. Instead of waiting for the carry to ripple sequentially from stage to stage, it uses an independent internal logic circuit to calculate all carry bits simultaneously in parallel.

It achieves this by examining the input bits (A and B) at the very beginning and breaking the carry logic down into two simple parallel concepts for every bit position:

• Carry Generate (Gi ): Gi = A i . Bi (This stage creates a carry out on its own).

• Carry Propagate (Pi ): Pi = Ai ⊕ Bi (This stage will pass an incoming carry along to the next stage).

Because all Giand Pi signals are calculated at the exact same moment from the primary inputs, the central lookahead generator can predict and produce the exact carries for every stage without any ripple delay. This reduces the propagation delay dramatically to near-constant time (O(log n)), making the circuit exponentially faster.