VLSI design has reached the point at which most circuits are too complex to be specified completely by hand. Although computers can be used to record layout, thus making design easier, they can also be programmed to take an active role by doing synthesis or analysis. Synthesis tools generate circuitry automatically and analysis tools attempt to verify existing circuitry that has been designed by hand. This chapter covers synthesis tools and the next two chapters are devoted to analysis tools.
There is nothing magical about synthesis tools; in fact many of them are simple applications of machine iteration. When design is done manually, it is easy to see areas of high repetition and regularity that lend themselves to automation. It is the combination of many of these techniques that begins to make computers appear intelligent in circuit design. Ultimately, it would be valuable to have a single synthesis tool that produces a complete layout from a high-level description of a circuit. This is the goal of today's silicon compilers, which are collections of simpler tools. However, since silicon compilers have not yet advanced to the stage at which they can replace all other tools, it is important for a design system to provide the individual synthesis tools so that they can be used selectively.
This chapter will illustrate a number of synthesis tools for VLSI design. These techniques are all based on the premise that a circuit consists of cells and their interconnection. Some tools generate and manipulate the contents of cells (PLA generators, gate-array generators, gate-matrix generators, compacters); some tools work with the layout external to cells (routers, placement systems, pad-frame generators); and some tools work with the interrelation of the cells and their environment (aligners, pitch matchers). Of course, there are silicon compilers that combine these techniques to produce cells and complete systems, ready for fabrication. Finally, there are synthesis tools that help to convert completed layout into suitable form for manufacturing (compensation, mask-graphics generators). These are just some of the tools that should be provided by a good design system.
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