Design of an Efficient N × N Butterfly Switching Network in Quantum-Dot Cellular Automata (QCA)

Abstract

Quantum-dot cellular automata (QCA) is a rapidly growing nanotechnology very well suited for designing ultra-dense, low-power, and high-performance digital circuits. In parallel computing, the multistage interconnection network (MIN) provides maximum bandwidth to the components and minimum latency access to the memory modules. Much research has been conducted on CMOS-based MINs for parallel computing. However, the QCA-based switching network is still underexplored. This article proposes a QCA architecture of a new single-layer butterfly switching network (BSN). To achieve this, we design an efficient 2 × 2 switching element (SE), using a modified majority ( $\mathcal{M}{_{[x,y]}}$ ) gate that is fully utilized (i.e., no fixed logic like “0” and “1” at the inputs). The use of a fully utilized majority gate over a partially utilized majority (PUM) one makes the proposed SE more cost-efficient and versatile, and therefore it is used as the building block for designing the switching network. In addition, we deploy the SE to realize 4 × 4 and 8 × 8 BSNs. We also show how the design can be extended for an N × N BSN. All the proposed circuits have been modeled and verified by QCADesigner. QCAPro is used for estimating the average switching and leakage energy dissipation of the proposed circuits. The results show considerable enhancement in terms of cell count, device area, and latency, and thereby outperform all reported prior designs.