Approximate computing is an emerging paradigm to improve power and
performance efficiency for error-resilient application. Recent approximate
adders have significantly extended the design space of accuracy-power
configurable approximate adders, and find optimal designs by exploring the
design space. In this paper, a new energy-efficient heterogeneous block-based
approximate adder (HBBA) is proposed; which is a generic/configurable model
that can be transformed to a particular adder by defining some configurations.
An HBBA, in general, is composed of heterogeneous sub-adders, where each
sub-adder can have a different configuration. A set of configurations of all
the sub-adders in an HBBA defines its configuration. The block-based adders are
approximated through inexact logic configuration and truncated carry chains.
HBBA increases design space providing additional design points that fall on the
Pareto-front and offer better power-accuracy trade-off compared to other
configurations. Furthermore, to avoid Mont-Carlo simulations, we propose an
analytical modelling technique to evaluate the probability of error and
Probability Mass Function (PMF) of error value. Moreover, the estimation method
estimates delay, area and power of heterogeneous block-based approximate
adders. Thus, based on the analytical model and estimation method, the optimal
configuration under a given error constraint can be selected from the whole
design space of the proposed adder model by exhaustive search. The simulation
results show that our HBBA provides improved accuracy in terms of error metrics
compared to some state-of-the-art approximate adders. HBBA with 32 bits length
serves about 15% reduction in area and up to 17% reduction in energy compared
to state-of-the-art approximate adders.Comment: Submitted to the IEEE-TCAD journal, 16 pages, 16 figure