A HIGH SPEED DYNAMIC RIPPLE CARRY ADDER

Abstract

Adder, which is one of the basic building blocks of a processor affect the performance of the processor. There are many adder architectures each of them have their own advantage. Ripple Carry Adder (RCA) architecture occupies the minimum area among the other architectures with lesser power dissipation. RCA experiences more delay due to its carry propagation in critical path; apart from the delay it also experiences glitches. Constant delay (CD) logic solves both the delay problems and glitch related problems. CD logic, due to its pre-evaluated characteristics delivers high speed but due its bulkier nature it is used only in the critical path. In this paper two new techniques are presented which modifies the conventional timing block (requires ten transistors) in CD logic and two new timing blocks one with eight transistors and other with nine transistors are developed. The CD logic with the two new timing block is used in critical path of RCA to achieve higher speed performance with lesser area compared to conventional CD logic. The CD logic with 9-transistor timing block achieves 70% and 39% delay reduction compared to Static and Domino logics. It also achieves 21% and 5% reduction in power dissipation and delay. The 8-transistor version also achieves reduction of delay by 65% and 29% compared to Static and dynamic logic. The two versions of timing blocks have their own advantages where 9-transistor version provides high speed and 8- transistor version provides lesser power dissipation. Simulations are carried out in 130 nm at 1V power supply using mentor graphics tools.