Fast Ripple-Carry Adders in Standard-Cell CMOS VLSI

Abstract

This paper presents a number of new high-radix ripple-carry adder designs based on Ling's addition technique and a recently-published expansion thereof. The proposed adders all have one inverting CMOS cell per stage along the carry-in to carry-out critical path and, at 16-b word lengths, the fastest of them matches the speed of a 16-b prefix adder for only 63% of the area. These adders will be of use in VLSI circuits implementing modern wireless DSP algorithms and in Floating-Point Unit exponent logic, both of which typically use short word length arithmetic.