Low-complexity QCA universal shift register design using multiplexer and D flip-flop based on electronic correlations

Quantum-dot cellular automata (QCA) represent an alternative technology for implementing various computations and high-performance, low-power consumption digital circuits at nanoscale. Meanwhile, an universal shift register (USR) with guaranteed free position shift and parallel input and transfer of the stored bit value of the register is an essential element in the design of the circuit. Therefore, we propose an USR circuit based on QCA (QUSR) which can be configured by combining the shift register with a multiplexer (Mux) to select the function of the register. In this study, we propose a 2-to-1 Mux based on the electronic correlations between the cells, and then extend this to a 4-to-1 Mux. We also propose a new D flip-flop, and design a shift register by connecting these. Finally, we propose a QUSR with an extremely optimized area and latency, by connecting four 4-to-1 Muxes and a four-bit shift register. The proposed QUSR is highly efficient, in terms of the space, time complexity and energy dissipation. All proposed structures are simulated by QCADesigner to demonstrate the clarity of the motion and efficiency. We also measured and compared the energy dissipation in three tunneling levels by QCAPro.