Diffusion sharing across cell boundaries in cell based design

A layout design often contains regular, repeatable or iterative structures, and datapath is an example of such a design-style. Designers take advantage of regularity by using library cells for density and productivity improvements, This study is aimed at studying the impact on overall density due to diffusion sharing across cell boundaries. Often the library cell area is optimized without comparing the global impact on the assembled design. We compare two methods of designing cells, a practically used one and an intuitively desired one. We show that the intuitive method is not always feasible and that a hybrid method of designing a cell is optimal. Studies on real examples have shown the gains to be made in density by diffusion sharing across cell boundaries. We also present situations in which the diffusion sharing causes a loss of overall density. The conclusion is a set of guidelines on when to use diffusion sharing among the library cells