A Review: O-ALU An Optimization-Enhanced Low Power ALU Design using Clock Gating and Power Gating

Abstract

The rapid growth of portable, embedded, and IoT systems has made power efficiency a primary design constraint for Arithmetic Logic Units (ALUs), FPGA platforms, and RISC-V based processors. This review critically examines recent low-power design techniques reported between 2020 and 2025, covering clock gating, data gating, power gating, architectural optimization, and emerging device-level solutions. The surveyed literature shows that clock- and activity-aware gating methods, such as hybrid clock gating and signal-based gating, can achieve dynamic power reductions in the range of 45–66% while maintaining acceptable performance. FPGA-based implementations further demonstrate that clock gating, pipelining, and bio-inspired transition suppression can lower power consumption by up to 40%, though often at the cost of increased area and timing overhead. Technology-level innovations, including GDI logic, reversible logic, ternary logic, and sub-threshold operation, provide additional improvements in power-delay and energy-delay products, but their practical adoption is limited by design and verification complexity. At the system level, power-gated SRAM-FPGAs, FSM partitioning, and RISC-V based power management units enable substantial leakage and runtime power reduction, particularly for battery-constrained applications. Overall, the review indicates that hybrid strategies combining ALU-level gating, architectural power management, and system-level control offer the most balanced trade-off between power efficiency, performance, and scalability in modern digital systems.

Introduction

The text presents a comprehensive review of energy-efficient design techniques for digital systems, focusing on ALUs, FPGAs, and RISC-V processor architectures used in embedded systems, IoT devices, and high-performance computing. As technology scales, managing dynamic and leakage power has become increasingly challenging, making low-power design a critical objective.

The review examines widely adopted techniques such as clock gating, power gating, Dynamic Voltage Threshold (DVT), data gating, and multi-Vdd methods, which reduce switching activity and leakage during idle periods. Among these, clock gating and activity-aware control emerge as the most effective strategies, achieving power reductions of 45–66% in many ALU and processor implementations, though often at the cost of increased control logic complexity.

FPGAs are highlighted as flexible platforms for low-power optimization through pipelining, logic restructuring, parallelism, and distributed clock gating. Advanced circuit-level approaches—including GDI, FinFET, reversible logic, QCA, and ternary logic—further improve power-delay and energy efficiency, particularly in nanoscale designs. However, these methods introduce challenges related to layout complexity, verification, and scalability.

The review also covers low-power ALU designs (8-bit, 16-bit, and 32-bit) and RISC-V architectures, where techniques such as PMUs, voltage scaling, data gating, fault tolerance (TMR), encryption accelerators, and sub-threshold operation enable energy-efficient, reliable, and secure computing for edge and IoT applications.

Overall, the analysis highlights the trade-offs between power savings, performance, area, and design complexity, concluding that hybrid and activity-aware power management strategies offer the most practical balance for modern energy-efficient and scalable digital systems.

Conclusion

This review has presented a comprehensive analysis of low-power design methodologies applied to Arithmetic Logic Units (ALUs), FPGA-based systems, and RISC-V processor architectures. The surveyed research primarily focused on power-saving techniques such as data gating, clock gating, power gating, and Dynamic Threshold Voltage (DVT) scaling to reduce both dynamic and leakage power consumption. A wide range of strategies—including Hybrid Clock Gating (HCG), distributed and signal-based clock gating, and multi-Vdd schemes—have been explored to achieve energy-efficient operation while maintaining acceptable performance levels. These techniques have been validated across technology nodes ranging from 180 nm to 20 nm using industry-standard design tools such as Xilinx Vivado, Cadence Virtuoso, and ModelSim. FPGA-based implementations have played a significant role in advancing low-power design through architectural optimizations such as parallelism, pipelining, and High-Level Synthesis (HLS). Experimental results reported in the literature demonstrate power reductions ranging from approximately 24% to more than 66%, confirming the effectiveness of gating and hybrid optimization methods. However, these benefits are often accompanied by increased design complexity, higher control overhead, synchronization challenges, and additional area requirements due to the inclusion of monitoring and control logic. Despite these limitations, the reviewed architectures have proven highly suitable for embedded systems, Internet of Things (IoT) applications, and high-speed digital systems, where energy efficiency and performance are critical design requirements. In parallel, significant advancements have been achieved in low-power RISC-V processor designs, where energy optimization has been coupled with enhanced reliability and security. The integration of Power Management Units (PMUs), fault-tolerant techniques such as Triple Modular Redundancy (TMR), hybrid encryption accelerators, and intelligent data gating has enabled dynamic power control while maintaining robust system performance. Furthermore, innovations at the device and logic levels—such as FinFET-based ALUs, reversible logic designs, Quantum Dot Cellular Automata (QCA), and ternary logic—have contributed to substantial improvements in power-delay product for nanoscale technologies. FPGA and CMOS implementations have also demonstrated notable gains in power efficiency, area utilization, and fault resilience, particularly in aerospace and IoT-oriented systems. In summary, the reviewed studies clearly indicate that while existing low-power techniques are effective in significantly reducing energy consumption, achieving an optimal balance among power savings, scalability, performance, and design simplicity remains an open challenge. Future low-power computing architectures must therefore emphasize unified, reconfigurable, and fault-tolerant design approaches that can adapt to varying workloads and technology constraints while minimizing control complexity and verification overhead.

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Copyright

Copyright © 2026 Shivraj Singh Lodhi, Hariom Yadav, Rajendra Patel . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.