A comparison of two fast binary adder configurations

Abstract

Conditional sum and binary lookahead carry are two methods for performing fast binary addition. These methods are quite different, but the adders have a common feature that makes them interesting to compare. Both adders have the carry generating logic implemented as a binary tree, which grows in depth as log(sub 2) n,n equals the number of bits in the adder. The delay in the carry paths also grows in proportion to log(sub 2) n. This paper shows that the Transmission-Gate Conditional-Sum adder and the binary lookahead carry adder have the same speed of addition, but that the conditional sum adder requires only 46 percent of the area.