Design of high-performance CMOS priority encoders and incrementer/decrementers using multilevel lookahead and multilevel folding techniques

Lookahead signals to form the multilevel folding architecture for priority-encoding-based designs was used to improve the performance to the order of O(log N). Analysis showed that both the multilevel lookahead and the multilevel folding techniques could be easily merged and implemented in the dynamic CMOS circuits. For the 256-bit priority encoder, the new design adopting all the proposed techniques can achieve nearly ten times performance while spending nearly half the power consumption as compared to the conventional design, utilizing only a simple lookahead structure. For the 64-bit incrementer/decrementer, the new design adopting all the proposed techniques requires less than one-third delay time as compared to a high-speed carry-select adder (CSA)-based incrementer/decrementer. The power consumption evaluated at the maximum operating frequency and the transistor count of the new incrementer/decrementer are also reduced to 67% and 35%, respectively, as compared to the CSA-based design. The measurement results indicate that the proposed 256-bit priority encoder and the proposed 64-bit incrementer/decrementer can operate up to 116 and 139 MHz, respectively, when they are designed based on a 0.6-μm CMOS technology.