A low-power carry cut-back approximate adder with fixed-point implementation and floating-point precision

Abstract

This paper introduces an approximate adder architecture based on a digital quasi-feedback technique called Carry Cut-Back in which high-significance stages can cut the carry propagation chain at lower-significance positions. This lightweight approach prevents activation of the critical path, improving energy efficiency while guaranteeing low worst-case relative error. It offers a degree of freedom which allows to dissociate precision and dynamic range in fixed-point implementation. A design methodology is presented along with results and a comparative study. For a worst-case accuracy of 98 %, energy savings up to 44 % and power-delay-area reductions up to 62 % are demonstrated compared to low-power conventional designs.

Combining structural and timing errors in overclocked inexact speculative adders

“…Yet, some of these designs still exhibits decent overall accuracy such as ISA (16,2,1,6). This latter relegates to the second place ISA (16,7,0,8), which has a more accurate architecture but is found less resilient to aggressive overclocking. Understanding this variability in timing-error robustness as well as the difference of threshold between structural and timing errors could be highly beneficial to low-power and time-constrained circuit design.…”

Cassis: Characterization with Adaptive Sample- Size Inferential Statistics Applied to Inexact Circuits

“…Approximations in circuits have been introduced in different manners such as overclocking [1] at circuit level or computation skipping [2] at algorithmic level. The logic structure of original exact operators can also be modified into an inexact version [3]- [7]. Inexact operators generate errors with varied amplitude and error rate.…”

A Fast and Fuzzy Functional Simulator of Inexact Arithmetic Operators for Approximate Computing Systems

“…Inexact operators are obtained by making a functional approximation. The boolean function of inexact operators is slightly modified to reduce the logic complexity and/or length of critical paths [9], [4], [17]. The main interest of inexact operators compared , .…”

“…Inexact operators have been developed to overcome the performance limitations of exact arithmetic operators. Many inexact adders have been proposed ( [9], [4], [17]) and their performances are compared in [8]. The comparison between adders is done in terms of normalized mean error distance (NMED), ER, and mean relative error distance (MRED).…”