Title: Approximate Ripple Carry and Carry Lookahead Adders - A Comparative Analysis,
Abstract: 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% to 82% than the accurate RCA for approximation sizes varying
from 4- to 20-bits. Also, approximate CLAs report reductions in PDP ranging
from 16.7% to 74.2% than the accurate CLA for approximation sizes varying from
4- to 20-bits. On average, for the approximation sizes considered, it is
observed that approximate CLAs achieve a 46.5% reduction in PDP compared to the
approximate RCAs. Hence, approximate CLAs are preferable over approximate RCAs
for the low power implementation of approximate computer arithmetic.