Increasing interest by traditional systems houses in the design of custom and semi-custom integrated circuits (LSI and VLSI) provided the impetus for the development of a lower cost interactive graphics system (/GS) for VLSI design, design verification, and the efficient generation of optical pattern generation and electron beam control files.
While extremely attractive, but expensive, IGS units are available from such manufacturers as Applicon and Calma for use in very large design groups, it was felt that a lower cost system incorporating the latest in design aids was needed for smaller or geographically dispersed design operations. This paper describes the implementation of one such system, and examines the various implementation options which must be examined by any group which might wish to build or acquire such a capability. computer-aided design, integrated circuits, system implementation just as there is no one 'best' circuit technology, there is no best design methodology or CAD toolset for LSI and VLSI design.
Designers quickly learn that there are four basic design methodologies of current interest. Listed in increasing order of layout complexity, they are: gate arrays (uncommitted logic arrays), standard cells, symbolic layout, and hand crafted.
Despite the resurgence of interest in older design automation (DA) techniques (as exemplified by the work 1-3 at Cal Tech and other universities with 'silicon compilers'), our studies show a continuing requirement for interactive graphics tools to support VLSI design. As examples, consider the requirements to design memory cells, as well as the cells (gates, standard cells, compiler units, etc) used by DA programs. In addition, there is the requirement to generate manually interconnections for manually prepared layouts or to edit and complete DA generated layouts.
However, all of these design technologies can, and should, be treated as variations on a basic hierarchical (structured) design methodology. In fact, the hierarchical layout should be the last step in a continuing structured design procedure 4 . This, in turn, requires that the CAD systems in use be DMT Corporation, Nashua, NH, USA organized for manipulation of hierarchically related design files.