Question

Fast-look-ahead carry circuits found in most 4-bit full-adder circuits which ___________

(a) Determine sign and magnitude

(b) Reduce propagation delay

(c) Add a 1 to complemented inputs

(d) Increase ripple delay

I had been asked this question by my school principal while I was bunking the class.

My question is based upon 4-Bit Parallel Adder/Subtractor topic in section Arithmetic Circuits of Digital Circuits

Answer 1

Right option is (b) Reduce propagation delay

To explain I would say: A carry-lookahead adder (CLA) is a type of adder used in digital logic. A carry-lookahead adder improves speed by reducing the amount of time required to determine carry bits. It reduces the propagation delay by making the hardware more complex. The ripple carry design is converted in such a way that carry over a group of bits of the adder becomes 2-level logic.