| Scope and method of study. Quantum-Dot Cellular Automata (QCA) is one of the most emerging technologies. It has been introduced as a possible alternative to CMOS (Complementary Metal Oxide Semiconductor). The main objective of this thesis work is to apply CMOS based asynchronous methodology to QCA paradigm. The concept of QCA clocking is quite different from that of CMOS clocking. In the QCA, the clock is used as a control signal in stead of a data signal. Inherited characteristics of QCA, such as the way to hold state, the way to synchronize data flows, and the way to power QCA cells make the design of QCA circuits quite different from VLSI. This also introduces a variety of new challenges to the design and the greatest challenges are due to the fact that the overall timing of a QCA circuit is mainly dependent on its layout. In order to eliminates "Layout=Timing" constraint from QCA circuits, delay-insensitive data encoding scheme such as NCL(Null Convention Logic) are applied to the QCA paradigm. Proposed QCA-based NCL full adder illustrates how NCL prevents timing constraint from QCA circuits.; Findings and conclusions. Basically, "Layout=Timing" constraint forces synchronous QCA circuits to waste many buffers for synchronization purpose. Applying NCL to QCA eliminates the "Layout=Timing" problem as well as the delay buffers from QCA circuits. The NCL provides numerous advantages such as easier floorplanning, increased circuit density, decreased QCA cell count, and reduced circuit complexity. Especially, NCL is more suitable for a large scale circuit design. |
