Quantum-dot cellular automata (QCA), which is a candidate technology to replace CMOS technology, promises extra low-power, extremely dense and high-speed structures at a nano scale. In this paper, a novel 3-input XOR gate structure is proposed based on half distance and cell interaction. Accordingly, a lowcomplexity and high-speed QCA one-bit full adder is designed by employing the proposed 3-input QCA XOR gate. Then a new 4-bit QCA Ripple Carry Adder (RCA) is proposed based on the proposed 3-input QCA XOR gate. The proposed designs are simulated using the both coherence and bi-stable simulation engines of QCADesigner version 2.0.3. Our simulation results indicate the efficiency and robustness of the proposed designs. The simulation results show 50% area improvement for the proposed 3-input XOR gate, 76% and 50% improvements in terms of cell count and latency, respectively for the proposed robust QCA full-adder, 58% and 52% improvements in terms of latency and cost, respectively for 4-bit QCA RCA compared to the previous designs.
