Design and Verification of High Speed and Energy Efficient Carry Skip Adder

Dasari Siva Kumari, Yarram Uma Maheswari, Sannikanti Kishore Babu


In this paper, we present a carry skip adder (CSKA) structure that has a higher speed yet lower energy consumption compared with the conventional one. The speed enhancement is achieved by applying concatenation and incrementation schemes to improve the efficiency of the conventional CSKA (Conv-CSKA) structure. In addition, instead of utilizing multiplexer logic, the proposed structure makes use of AND-OR-Invert (AOI) and OR-AND-Invert (OAI) compound gates for the skip logic. As the number of transistors is reduced to half by using AOI/OAI logic when compare to MUX, Power reduction is achieved without compromising the speed making it suitable for wide range of low-power applications. The structure may be realized with both fixed stage size and variable stage size styles, wherein the latter further improves the speed and energy parameters of the adder.  The hybrid variable latency structure, which lowers the power consumption without considerably impacting the speed, is presented. This extension utilizes a modified parallel structure for increasing the slack time, and hence, enabling further voltage reduction. The proposed structures are assessed by comparing their speed, power, and energy parameters with those of other adders using a 45-nm static CMOS technology for a wide range of supply voltages. In addition, the power–delay product was the lowest among the structures considered in this paper, while its energy–delay product was almost the same as that of the Kogge–


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