Designing Dynamic Carry Skip Adders: Analysis and Comparison

Addition represents an important operation that significantly impacts the performance of almost every data processing system. Due to their importance and popularity, addition algorithms and their corresponding circuit implementations have consistently received attention in research circles, over the years. One of the most popular implementations for long adders is the Carry Skip Adder. In this paper, we present the design space exploration for a variety of Carry Skip Adder implementations. More specifically, the paper focuses on the implementation of these adders using traditional as well as novel dynamic circuit design styles. 8-16-32-64-bit adders were implemented using traditional domino, footless domino, and data driven dynamic logic (D3L) in ST Microelectronics 45nm 1V CMOS process. In order to further exploit the advantages of the domino and D3L approaches, a new hybrid methodology combining both strategies was implemented and presented in this work. The adders were analyzed for energy-delay trade-offs at different process corners. They were also examined for their sensitivity to process and supply voltage variations. Comparative simulation results reveal that the full D3L adder ensures a better energy-delay product over all process corners (down to 34% and 25% lower than the domino and hybrid implementations, respectively, at the typical corner), while showing at the same time similar performance in terms of process and supply voltage variability as compared to the other considered Carry Skip Adder configurations.