The Design of an Asynchronous Carry-Lookahead Adder Based on Data Characteristics

Yijun Liu and Steve Furber

Abstract

Addition is the most important operation in data processing and its speed has a significant impact on the overall performance of digital circuits. Therefore, many techniques have been proposed for fast adder design. An asynchronous ripple-carry adder is claimed to use a simple circuit implementation to gain a fast average performance as long as the worst cases input patterns rarely happen. However, based on the input vectors from a number of benchmarks, we observe that the worst cases are not exceptional but commonly exist. A simple carry-lookahead scheme is proposed in the paper to speed up the worst-case delay of a ripple-carry adder. The experiment result shows the proposed adder is about 25% faster than an asynchronous ripple-carry adder with only small area and power overheads.

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