Study On Detailed Placement Algorithms In VLSI

Placement is a key in VLSI physical design. Placement generally consists of two major stages:global placement and detailed placement. Legalization is throughout the whole placement problem. In the past few years, there have been a lot of researches in the area of global placement. Many effective global placement algorithms have emerged. In comparison, not much attention has been paid to the legalization and detailed placement problems.Based on the existing flow of the conventional placement algorithm, this paper proposed a complete legalization and detailed placement algorithm dealing with the standard-cell and mixed-size circuits. In the legalization algorithm of mixed-mode circuits, it was improved in constructing the constraint graphs by depth first search to deal with the significant memory consumption. Besides, we adopted a fast legalization algorithm with minimal movement in the legalization of standard-cell circuits. We formed a detailed placement algorithm of the cell swapping based on the optimal region and cell flipping based on the bin structure. It could improve the objective function-half perimeter wirelength (HPWL).Finally, we had done lots of experiments using ibm benchmark circuits. From the experimental results, the legalization algorithm can remove the overlaps between objects in the circuit of two modes, and the detailed placement algorithm can also improve the quality of the placement effectively.