New concepts for the design of carry lookahead adders

Several new concepts for the design of carry lookahead adders (CLA), using dynamic logic, are introduced. Using an enhanced multiple output domino logic (EMODL), sums of several consecutive bits can be built in one tree, with a single carry-in. Based on this result, the fully carry chain, which contains carries for all bit positions and is required by conventional CLA algorithms, can be reduced to a sparse carry chain which contains carries for only a few bit positions. Conventional bit level generates and propagates are not necessary for the new architecture, and thus the preliminary stage, required by any existing CLA adder and generating bit level generates and propagates for all bit positions, can be eliminated. Using an example of a 32-bit adder, it is shown that only four carries, i.e., c/sub 4/, c/sub 8/, c/sub 12/, and c/sub 16/, are sufficient for generating all sums in the last stage.<<ETX>>