An Automated Approach to Generating Leaf Cells for a Macro Cell Configuration


IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E76-A   No.8   pp.1334-1342
Publication Date: 1993/08/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: PAPER
Category: Computer Aided Design (CAD)
VLSI design,  computer aided design,  macro cell,  

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This paper describes a new automated approach to generating the patterns of CMOS leaf cells from transistor-level connectivity data. This method can generate CMOS leaf cells that are configurable to a macro cell satisfying user-specified constraints. The user-specified constraints include the aspect ratio and port positions of the macro cell. We propose a top-down method for converting the macro cell level constratints to leaf cell level ones. Using this method, a variety of customized macro cells can be designed in a short turn-around time. The method consists of four processes--diffusion sharing, initial placement, placement improvement and routing--which culminate in the automatic generation of symbolic representations. Using a compactor, those symbolic representations can be converted to physical patterns which are gathered into a macro cell by a macro generator. We define various objective functions to improve unit pair placement. We also introduce five ways to optimize leaf cell area: 1) multi-row division, 2) gate division 3) rotation, 4) power line and diffusion overlapping and 5) reconstruction of hierarchical structure. The proposed approach has been applied to various kinds of CMOS leaf cells. Experimental results show that the generated cells have almost the same areas as those generated by conventional bottom-up approaches in leaf and macro cell layouts. This approach offers a further advantage in that the various-sized macro cells required by layout disigners can also be generated.