Adder arithmetic units

Adders are a universal component of nearly every computing system, whether traditional or modern. Even the most fundamental machine, which performs no arithmetic, requires an adder to calculate address offsets and branch instructions. Adders are also generally less complex than other arithmetic units found in system. This chapter introduces four different adders: a ripple-carry adder, a carry-look-ahead adder, a carry-select adder, and a conditional-sum adder. The traditional CMOS circuits for each of the adders are described, and the performance and area of these designs are each analyzed. The adders vary in terms of their complexity. The simplest design is the ripple-carry adder, and the most complex design is the carry-look-ahead adder. In general, as the complexity of the adder increases, the speed and performance improve.