Mixed-cell-height Placement with Minimum-Implant-Area and Drain-to-Drain Abutment Constraints

In modern circuits, mixed-cell-height standard cells have been prevailing to meet various requirements and achieve better trade-offs among timing, power, and routability. Besides, the constraints of the minimum-implant-area (MIA) and drain-to-drain-abutment (DDA) arise as emerging challenges at advanced technology nodes. In this paper, we present an algorithm to address the mixed-cell-height placement problem with MIA and DDA constraints in three major stages: (1) post-global placement, (2) legalization, and (3) detailed placement. In the post-global stage, we first align mixed-cell-height standard cells to the desired rows by conjugate gradient method with dynamic step size and then reorder them by the shortest path algorithm to distribute the source nodes evenly. In the legalization stage, we propose a two-step combination algorithm to cluster cells and repack the clusters to minimize the wirelength, after which we presented a queue based method to address the inter-row MIA violations. In the detailed placement, an MIA-aware DDA reduction algorithm is adopted after multi-region partitioning to eliminate DDA violations without introducing MIA violations. Experimental results show that our algorithm can resolve all MIA and almost all DDA violations with a 13% reduction in displacement, a 4% reduction in HPWL, and 25% less runtime compared with the state-of-the-art work.