Comparison of Different Design Approaches:Comparison of All Different Design Approaches.

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Comparison of All Different Design Approaches

As discussed so far, we have a very wide spectrum of different design approaches, from full-custom design approaches to the design approaches with off-the-shelf packages, as illustrated in Table 49.1. Digital systems can be designed by combining them. Depending upon different criteria imposed by different design motivations, such as speed, power consumption, size, design time, ease of changes, and reliability, designers can use the following approaches:

1. Custom-design full- and semi-custom approaches

2. Off-the-shelf discrete components and off-the-shelf IC packages, along with memory packages

3. Off-the-shelf microcomputers along with off-the-shelf IC packages

The full-custom design approaches give us the highest performance and reliability or the smallest chip size, although they are most time-consuming. (Even in the case of microcomputers, the full- custom designed microcomputers have better performance and smaller size than off-the-shelf micro- computers, by being tailored to the users’ specific needs.) This is one end of the wide spectrum of different design approaches. At the other end, the off-the-shelf microcomputers give us a design approach where the development time is shortest, by programming rather than by chip design (including logic design), and the design changes are the easiest. The off-the-shelf discrete components and off-the-shelf IC packages give us logic networks tailored to specific needs with less programming than the off-the-shelf microcomputers.

Custom design approaches, in particular the full-custom design approaches, are the most economical for very high production volumes (on the order of a few hundred thousand) but the least economical for low production volumes.

When the production volume is low, the off-the-shelf discrete components and off-the-shelf IC packages give us the most economical approaches for simple tasks, but the off-the-shelf microcomputers are more economical for complex tasks, although performance is usually sacrificed.

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