Virtual Grid Symbolic Layout

Free form or "stick" type symbolic layout provides a means of simplifying the design of IC subcircuits. To successfully utilize this style of layout, a complete design approach and the necessary tools to support this methodology are required. In particular, one of the requirements of such a design method is the ability to "compact" the loosely specified topology to create a set of valid mask data. This paper presents a new compaction strategy which uses the concept of a virtual grid. The compaction algorithm using the virtual grid is both simple and fast, an attribute which allows the designer to conveniently interact with the algorithm to optimize a layout. In addition to the compaction algorithm, methods used to create large building blocks will be described. The work described here is part of a complete symbolic layout system called MULGA which is written in the C programming language and resides on the UNIX operating system.