Approximate Ripple Carry and Carry Lookahead Adders - A Comparative Analysis
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Approximate ripple carry adders (RCAs) and carry lookahead adders (CLAs) are presented which are compared with accurate RCAs and CLAs for performing a 32-bit addition. The accurate and approximate RCAs and CLAs are implemented using a 32/28nm CMOS process. Approximations ranging from 4- to 20-bits are considered for the less significant adder bit positions. The simulation results show that approximate RCAs report reductions in the power-delay product (PDP) ranging from 19.5 from 4- to 20-bits. Also, approximate CLAs report reductions in PDP ranging from 16.7 4- to 20-bits. On average, for the approximation sizes considered, it is observed that approximate CLAs achieve a 46.5 approximate RCAs. Hence, approximate CLAs are preferable over approximate RCAs for the low power implementation of approximate computer arithmetic.
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