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Explanation: Kogge-Stone Adder Design

The Kogge-Stone Adder is a type of parallel prefix adder that efficiently computes binary addition by reducing the propagation delay typically associated with ripple-carry adders. Its design is based on a prefix tree structure, allowing multiple stages to compute carry signals concurrently, which significantly reduces delay.

Key Components

  1. Generate Signal: Determines whether a bit position generates a carry, regardless of any carry from the lower bits.
    Gen[i] = A[i] & B[i]
    If both A and B have a value of 1 at a specific bit position, this bit will generate a carry for sure.

  2. Propagate Signal: Determines whether a bit position propagates an incoming carry to the next higher bit.
    Pro[i] = A[i] ^ B[i]
    If either A or B at this bit position is 1, then it will propagate a carry from the previous bit to the next.

  3. Prefix Tree Structure: Carries are computed through multiple layers, where each layer combines previous generate and propagate signals, allowing the carry to reach the highest bit in log₂(N) stages (for N-bit addition). Each layer covers an exponentially larger range, ultimately ensuring every bit has the correct carry value.

    For each layer, k takes values 1, 2, 4, ..., 2^m:

    • Gen[i] = Gen[i] ∣ (Pro[i] & Gen[i - k])
      This indicates whether Gen[i] should be set to 1 due to carry propagation from bit i - k.
    • Pro[i] = Pro[i] & Pro[i - k]
      This indicates whether the carry at bit i - k can propagate to bit i.
  4. Final Sum Calculation: The sum for each bit is calculated as:
    S[i] = Pro[i] ^ C[i-1]
    where C[i-1] is the carry from the previous stage.

The result is a highly efficient adder with a fast carry propagation path, which enables binary addition with minimal delay.

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