Logic Design for Array-Based Circuits
Copyright © 1996, 2001, 2002 Donnamaie E. White
Last Edit July 22, 2001
The initial version of any design is almost guarenteed not to be the best solution. It is always possible to improve on an existing design, hardware or software, just as it is always possible to edit a manuscript. The trick is in knowing when to start and stop the process, also known as the endless loop.
Design optimization should be performed once an initial version of the design has been drafted at the block-diagram level. The design should be reviewed for optimization under the constraints of the established design objectives. It should also be reviewed for optimization using the particular characteristics of the technology and array series selected.
A second design optimization review should be performed once the macro conversion has been accomplished. The first step in this process is another review of the chosen macro library. Familiarity with the macros available will be invaluable in contributing to an optimized final design. The process is shown in Figure 4-1.
It has been shown that familiarity with the macro library is even more important than previous design experience! Something many designers argue with until faced with a case in point.
After reviewing the steps required to solve the simple case study example, it should be obvious that the selection of macros to solve a circuit implementation is much more complex than simply selecting the macros that appear to solve the equation. Timing, cell utilization and power dissipation are integrated elements that must be considered in parallel during the design process.
Design automation tools are moving in the direction of design synthesis and design review-for-criteria. Example systems are the NCR ViSys Design Advisor available on the Mentor Graphics and VCR-supported CAE workstations. A future expansion to that system is the NCR design synthesis tool. Design synthesis tools will become more prevalent over the next few years. They should be considered as a tool to assist the designer, not to replace the designer. [This was written in 1991-4 so there are presumably more systems available. Check the current literature for other references.]