Design and FPGA Implementation of a 4-Bit ALU Using Reversible Logic Gates

Abstract

Reversible computing offers a promising approach to mitigate the power dissipation challenges inherent in conventional digital systems. In this work, we present the design and analysis of a novel 4-bit reversible Arithmetic Logic Unit (ALU) that leverages reversible logic gates—including Fredkin, Feynman, Universal Reversible Gate (URG), and Thapliyal-Srinivas Gate (TSG)—to perform a suite of fundamental arithmetic and logical operations. The ALU is architected to execute operations such as binary addition, subtraction, logical AND, OR, and NOT under a unified reversible computing framework, thereby ensuring a one-one mapping between inputs and outputs and minimizing energy loss due to information erasure. To validate the design, the complete system was modeled using MATLAB Simulink and further synthesized to VHDL code, with implementation on a BASYS-3 FPGA featuring a Xilinx ARTIX-7 device. Comprehensive simulation results demonstrate the circuit’s functional correctness and favorable performance in terms of resource utilization and power consumption. The study also includes performance analysis highlighting the low usage of Look-Up Tables (LUTs) and flip-flops and identifies potential avenues for further optimization, including reductions in quantum cost and propagation delay. The proposed reversible ALU underscores the practicality of energy-efficient, reversible logic in real-world VLSI and quantum-aware architectures, thus opening new possibilities for sustainable computing technology.

Introduction

The article discusses the design and analysis of a reversible 4-bit Arithmetic Logic Unit (ALU) aimed at improving energy efficiency in digital computing by minimizing information loss during operations. Reversible computing, which avoids energy dissipation from data erasure, is proposed as a solution to the energy bottlenecks in traditional systems.

The ALU performs basic arithmetic and logical functions (addition, subtraction, AND, OR, NOT) using reversible logic gates such as Fredkin, Feynman, Universal Reversible Gate (URG), and Thapliyal-Srinivas Gate (TSG). These gates ensure reversibility, reduce quantum cost, and minimize garbage outputs.

The text also covers reversible combinational modules (e.g., multiplexers, adders/subtractors) and sequential modules (e.g., SR latch, D latch, T flip-flop, and a 4-bit up/down counter) critical for timing and control in computation.

The reversible ALU is implemented and simulated in MATLAB Simulink and VHDL, then synthesized on a Xilinx ARTIX-7 FPGA board. Results demonstrate correct functionality and practical feasibility, suggesting reversible logic’s potential for energy-efficient and low-power VLSI and quantum computing systems.

Conclusion

From this process of designing an ALU consisting of reversible logic gates, we have known the capability of design environment in VLSI domain to enhance the chip performance many-folds. We conclude that our designed ALU can be essential component in a novel reversible computer architecture and it holds the virtue to be optimized in terms of power consumption, propagation delay, quantum cost and area. The proposed ALU can also serve in day-to-day applications if incorporated with conventional computer architectures to optimize speed of calculation. This research is an attempt to understand and experimentally cater the advancements and capacity of reversible logic in modern-day applications. The re-configurability of FPGA made this research possible. We have understood that mainly three paths of advancements exist for proposed ALU design, which can be stated as: 1) Power-reduction and Optimization is one of the important paradigm one can look into for enhancing the performance of proposed ALU design. This will also help to steer through Landauer’s principle to reduce power consumption and make it viable for commercial usage. 2) Insertion of more operations like shifting, multiplication and more would make this ALU design more acceptable in recent computer architectures. While modified the design, complexity will increase but balance has to be maintained between compactness and ALU functionalities. 3) Lowering the Quantum Cost is a key advancement which can be done in proposed ALU design as it will not only reduce the area consumed but also reduce complexity in terms of time and space simultaneously.

References

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Copyright

Copyright © 2025 Yug Milind Thosar, Param Patel, Sunil 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.