A layout style that enables either an automatic layout synthesizer or a layout designer to take full advantage of the second metal layer available from today's technology is proposed. The style not only facilitates power/ground diffusion overlapping but also simplifies the intracell routing problem by having power/ground in the middle and routing in the upper and the lower constraint-free regions. An automatic leaf cell layout synthesizer, called THEDA.P, that is based on the proposed style has been implement. Using the same transistor placement algorithm, THEDA.P outperforms a synthesizer based on T. Uehara and W.M. van Cleemput's (1981) approach by almost 20% in layout compactness across a wide range of small-scale integrated circuits. THEDA.P has been used to build a standard cell library that was previously handcrafted. Results from designing two modules show that THEDA.P's layout quality is very competitive.>

We propose a new layout style that enables an automatic layout synthesizer to take full advantage of the second metal layer available from today's technology.our style not only facilitates power/grotmd-diffttsion overlapping but also sirnplities the intra-cell routing problem.We have implemented an automatic layout synthesizer, called THEDA.P (Tsing Hua Electronic Design Automation), based on the proposed style.Using the same transistor placement algorithm, THEDA.P outperforms a synthesizer based on [Ueh8 1]'s style by almost 20% in layout mmpacmess across a wide range of SS1 circuits.THEDA.P has been used to build a standard cell library that was previously handcrafted.Results from designing two ASIC modules show that THEDA.P's layout quality is very competitive.

An automatic layout generation system, called LiB, for the small-scale integrated (SSI) cells used in CMOS VLSI design, is presented. LiB takes a transistor-level circuit schematic in SPICE format and outputs a mask layout in CIF. The layout style is a modification of that proposed by T. Uehara, and W. M. van Cleemput (IEEE Trans. Comput., vol.C-30, no.5, p.305-12, 1981). An optimal transistor chaining algorithm has been developed to derive a transistor placement with a minimum number of diffusion separations. To meet the cell height constraint, large transistors are folded into multiple columns algorithmically. The whole cell is divided into five routing regions. Two are on the diffusion island and the others are rectilinear-shaped routing channels. A graph-theoretic method for selecting nets (subnets) for routing on the diffusion island is proposed. A global routing algorithm has been developed to assign the remaining nets to the three rectilinear channels. For the detailed routing SILK, a simulated evolution router, is employed. LiB can be used as a cell library builder or as a subsystem of a random logic module generator. Users can alternate LiB's layout using a symbolic editor.>

We present an automatic layout generation system, called LiB, for the library cells used in CMOS ASIC design. LiB takes a transistor-level circuit schematic in SPICE format and outputs a symbolic layout. Our layout style is similar to that proposed by Uehara and van Cleemput in [17]. We propose several heuristic algorithms to solve the transistor-clustering, -pairing, -chaining, -folding, the chain placement, the routing, and the net assignment problems, respectively. Experimental results are presented to show the capability of LiB.

A fast algorithm is produced for the optimal transistor chaining problem in CMOS functional cell layout based on T. Uehara and W.M. van Cleemput's layout style (IEEE Trans. Comput., vol. C-30, p.305-12, May 1981). The algorithm takes a transistor-level circuit schematic and outputs a minimum set of chains. Possible diffusion abutments between the transistor pairs are modeled as a bipartite graph. A depth-first search algorithm is used to search for the optimal chaining. Theorems on the number of branches needed to be explored at each node of the search tree are derived. A theoretical lower bound on the size of the chain set is derived. This bound enables pruning the search tree efficiently. The algorithm has been implemented and tested. It is able to find optimal solutions almost instantly for all the cases available to use from the literature.>