AMR-MUL: An Approximate Maximally Redundant Signed Digit Multiplier

TL;DR

This paper introduces AMR-MUL, an energy-efficient approximate signed digit multiplier that balances speed, power, and accuracy through a novel reduction cell design and a branch-and-bound optimization algorithm.

Contribution

It proposes a new approximate multiplier design with optimized reduction cells and a systematic exploration algorithm for improved energy efficiency and controlled accuracy loss.

Findings

7x reduction in energy consumption

1.6% accuracy loss

Effective design for high-speed, low-power multiplication

Abstract

In this paper, we present an energy-efficient, yet high-speed approximate maximally redundant signed digit (MRSD) multiplier (called AMR-MUL) based on a parallel structure. For the reduction stage, we suggest several approximate Full-Adder (FA) reduction cells with average positive and negative errors obtained by simplifying the structure of an exact FA cell. The optimum selection of these cells for each partial product reduction stage provides the lowest possible error, turning this task into a design space exploration problem. We also provide a branch-and-bound design space exploration algorithm to find the optimal assignment of reduction cells based on a predefined constraint (i.e., the width of the approximate part) by the user. The effectiveness of the proposed (Radix-16) multiplier design is assessed under different digit counts and approximate border column. The results show that the energy consumption of the MRSD multiplier is reduced by 7x at the cost of a 1.6% accuracy loss.