| 摘要 |
<p>A carry lookahead adder (100) having a reduced internal block fanout which is achieved efficiently in terms of the silicon area needed to implement the carry lookahead adder (100). The carry lookahead adder (100) of the present invention is characterized by a modified binary tree structure having carry generate/propagate signal operators (21, 31, 35, 41, 44, 48, 51, 23, 25, 33, 37, 42, 46, 75, 76, 77, 78, 79, 80, 81, 82, 51-54, 83-86, 55, 57, 59, 63, 56, 58, 61, 64) located in such a manner that the maximum internal block fanout is equal to (adder width)/8 for adders having a width of at least 16 bits. For adders having a width of less than 16 bits, the internal block fanout is 2. The routing complexity is increased in order to implement redundant overlapping carry generate/propagate operations which, in turn, decreases the internal block fanout of the adder. However, increases in routing complexity can be accomplished within the minimum X-by-Y area of each stage of the adder. Therefore, the overall performance of the carry lookahead adder (100) of the present invention can be optimized while meeting minimum area requirements. <IMAGE></p> |
