Question

Limiting factor on the speed of a parallel adder is:

A. Input delay
B. Carry propagation delay
C. Input propagation delay
D. Output delay

Answer 1

The speed of a parallel adder is primarily limited by the carry propagation delay, which is the time it takes for a carry to ripple through the adder from one end to the other.

Step-by-step explanation:

The limiting factor on the speed of a parallel adder is B. Carry propagation delay. In the context of digital circuits, when performing an addition operation, each bit of the sum can be calculated simultaneously except for the carry-out from one bit position to the next. This can create a delay because each carry must be calculated from the previous one, effectively creating a chain reaction that takes time to complete. This delay is intrinsic to the design of simple ripple-carry adders, and it limits the speed at which the overall addition operation can be performed. To mitigate the carry propagation delay, more complex adder designs such as carry-lookahead adders and carry-save adders are used, which are designed to calculate the carry bits in a more efficient manner.