Approximate Recursive Multipliers Using Low Power Building Blocks

Approximate computing, frequently used in error tolerant applications, aims to achieve higher circuit performances by allowing the possibility of inaccurate results, rather than guaranteeing a correct outcome. Many contributions target the binary multiplier aiming to minimize the complexity of this common yet power-hungry circuit. Approximate recursive multipliers are low-power designs that exploit approximate building blocks to scale up to their final size. In this paper, we present two novel 4x4 approximate multipliers obtained by carry manipulation. They are used to compose 8x8 designs with different error-precision trade-off. The final circuits exhibit a competitive behavior in terms of error while reducing the power dissipation when compared to state-of-the-art proposals. The proposed multipliers and state-of-the-art designs found in the literature, have been synthesized targeting a 14nm FinFET technology to determine the electrical characteristics. Compared with an exact 8×8 multiplier, the least dissipative design proposed in this paper reduces power consumption and silicon area by 46%, and minimum delay by 21%. It also consumes 14% less power than the least power-hungry recursive circuit found in the literature, while offering 81% higher accuracy. Ιmage processing applications and a convolutional neural network are shown to demonstrate the effectiveness of the proposed multipliers.