A layout-aware physical design method for constructing feasible QCA circuits
M. Bubna, Sudip Kumar Roy, Naresh Shenoy, Subhra Mazumdar · 2008
Quantum-dot Cellular Automata (QCA) is an emerging computing paradigm, in which logical operations as well as signal transmission occurs due to Coulombic charge interaction between neighbouring QCA cells, moderated by a 4-phase QCA clock potential. Thermodynamic constraints like the number of QCA cells in a clocking zone must be obeyed to obtain a logically correct and feasible QCA circuit. These constraints depend on various design factors like total wirelength in a circuit, height of a clocking zone etc. which are not available until actual circuit layout is obtained. In this paper, the various design automation problems assosciated with obtaining a feasible QCA layout are addressed. The layout generation problem is formulated as embedding the netlist digraph in an orthogonal grid, which provides an abstraction of the actual physical layout to be obtained. Novel graph theoretic algorithms are proposed to perform placement and global routing and various design parameters like clock rate, wasted area and total wirelength are used to estimate the quality of the layout obtained. Also, planarization methods are used to remove all wire crossings, which are expensive to fabricate. The methods applied on a large number of MCNC'93 and ISCAS'89 benchmarks show good results.