A Piecewise-Linear Approximation-based Energy-Efficient Error-Optimized Unsigned Square Rooter for Accuracy-Critical Applications

Abstract

Approximate computing improves energy efficiency in error-resilient applications, but square root units remain challenging due to the trade-off between hardware cost and computational accuracy. This paper presents an energy-efficient, error-optimized, piecewise-linear approximation-based unsigned square rooter (EOSQR) for 2n-bit inputs that achieves high accuracy with low hardware complexity, using only simple arithmetic and shift operations. The EOSQR design is implemented in Verilog-HDL and evaluated on a 16-bit benchmark synthesized on an Artix-7 FPGA. Compared to representative state-of-the-art approximate square rooters, EOSQR achieves the lowest error among accuracy-critical designs while delivering 61.91 percent resource savings, 77.54 percent power savings, and 53.11 percent latency reduction relative to a precise restoring array-based square rooter. To enable holistic evaluation, a Composite Efficiency Metric (CEM) is introduced to jointly capture accuracy and energy efficiency. EOSQR is further validated across representative image-processing workloads, including Sobel edge detection, K-means colour quantization, and K-nearest-neighbour (KNN) classification. Experimental results demonstrate that EOSQR achieves high computational accuracy with a superior CEM-based accuracy-hardware efficiency trade-off while maintaining visual quality and classification performance, making it well-suited for real-time edge-embedded systems.