A spanning tree carry lookahead adder | IEEE Journals & Magazine | IEEE Xplore

A spanning tree carry lookahead adder


Abstract:

The design of the 56-b significant adder used in the Advanced Micro Devices Am29050 microprocessor is described. Originally implemented in a 1- mu m design role CMOS proc...Show More

Abstract:

The design of the 56-b significant adder used in the Advanced Micro Devices Am29050 microprocessor is described. Originally implemented in a 1- mu m design role CMOS process, it evaluates 56-b sums in well under 4 ns. The adder employs a novel method for combining carries which does not require the back propagation associated with carry lookahead, and is not limited to radix-2 trees, as is the binary lookahead carry tree of R.P. Brent and H.T. Kung (1982). The adder also utilizes a hybrid carry lookahead-carry select structure which reduces the number of carriers that need to be derived in the carry lookahead tree. This approach produces a circuit well suited for CMOS implementation because of its balanced load distribution and regular layout.<>
Published in: IEEE Transactions on Computers ( Volume: 41, Issue: 8, August 1992)
Page(s): 931 - 939
Date of Publication: 06 August 2002

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