A nano-scale n-bit ripple carry adder using an optimized XOR gate and quantum-dots technology with diminished cells and power dissipation

Abstract

In the nano-scale era, quantum-dot cellular automata (QCA) technology has become an appealing substitute for transistor-based technologies. QCA will be the preferred technology for developing the next generation of digital systems. On the other hand, the full-adder and ripple carry adder (RCA) are the crucial building blocks of complex circuits, the most used structures in digital operations systems, and a practical part of the most well-known complex circuits in QCA technology. In addition, this technology was used to design the full adder for several procedures, like multiplication, subtraction, and division. For this reason, the full adder is generally investigated as a central unit and microprocessor in developing QCA technology. Furthermore, most previous QCA-based adder structures have suffered from some drawbacks, such as a high number of cells, high energy consumption, the high number of gates, and the placement of inputs and outputs in a closed loop; hence, the implementation of an efficient adder with only one gate and a low number of cells, such as exclusive-OR (XOR) gate, can solve all previous problems. Therefore, in this paper, a significantly improved structure of 3-input XOR is suggested based on the promising QCA technology. In addition, a QCA clocking mechanism and explicit cell interaction form the foundation of the proposed QCA-based XOR gate configuration. This gate can be easily converted into an adder circuit while containing a small number of cells and being extremely compressed. The suggested QCA-based XOR design is focused on optimizing a single-bit adder using cellular interaction. The suggested single-bit adder contains 14 cells. Based on this adder, several different RCAs, such as 4, 8, 16, and 32-bit, are designed. The comparison of the proposed single-bit adder to the best coplanar and multi-layer ones shows a 51.72% and 36.36% reduction of cells, respectively. In addition, all suggested designs are verified through simulation using QCADesigner and QCAPro. Finally, many physical validations are provided to approve the functionality of the suggested XOR design.