Computer Aids for VLSI Design
Steven M. Rubin
Copyright © 1994

Chapter 1: The Characteristics of Digital Electronic Design

Section 6 of 6

1.6 Summary

This chapter has described the VLSI design process and the characteristics of such design as a foundation for understanding CAD systems. Hierarchy is a major consideration in design because it is difficult to specify properly. In addition, there are many aspects of hierarchical design that place heavy demands on CAD systems. The use of differing views is important in all design. These views should be handled uniformly so that structure can be related to behavior. Coupled with this are the problems of conversion and correspondence between views. An important characteristic, specific to circuit design, is connectivity, which is related to the notion of nets. Not only are connected nets important in circuitry, but connected constraints help make the design process more flexible. Finally, the basically two-dimensional nature of circuits is another characteristic that should be recognized as important to VLSI design. An understanding of these issues sets the stage for the computer-aided design tools described in this book.


  1. Name some two-and-one-half-dimensional design environments other than VLSI.
  2. What is the most important reason for the use of hierarchy: (a) to save space in memory, (b) to allow humans to design circuits more effectively, (c) to enable multiperson projects, (d) to speed display by drawing bounding boxes.
  3. Design a scheme for view correspondence when the two corresponding hierarchies are different.
  4. How does a net differ from a wire?
  5. Describe a situation in which a cell definition would be different from the cell's hierarchical contents.
  6. What is the meaning of the term "computer-aided engineering"? How did it arise?
  7. List some attributes of mechanical design that are not found in VLSI design.


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