1.6 Summary

1.6 Summary

In this chapter we have looked at the difference between full-custom ASICs, semi-custom ASICs, and programmable ASICs. Table 1.3 summarizes their different features. ASICs use a library of predesigned and precharacterized logic cells. In fact, we could define an ASIC as a design style that uses a cell library rather than in terms of what an ASIC is or what an ASIC does.

TABLE 1.3 Types of ASIC.

ASIC type

Family member

Custom mask layers

Custom logic cells

Full-custom

Analog/digital

All

Some

Semicustom

Cell-based (CBIC)

All

None

 

Masked gate array (MGA)

Some

None

Programmable

Field-programmable gate array (FPGA)

None

None

 

Programmable logic device (PLD)

None

None

You can think of ICs like pizza. A full-custom pizza is built from scratch. You can customize all the layers of a CBIC pizza, but from a predefined selection, and it takes a while to cook. An MGA pizza uses precooked crusts with fixed sizes and you choose only from a few different standard types on a menu. This makes MGA pizza a little faster to cook and a little cheaper. An FPGA is rather like a frozen pizza—you buy it at the supermarket in a limited selection of sizes and types, but you can put it in the microwave at home and it will be ready in a few minutes.

In each chapter we shall indicate the key concepts. In this chapter they are

  • The difference between full-custom and semicustom ASICs
  • The difference between standard-cell, gate-array, and programmable ASICs
  • The ASIC design flow
  • Design economics including part cost, NRE, and breakeven volume
  • The contents and use of an ASIC cell library

Next, in Chapter 2, we shall take a closer look at the semicustom ASICs that were introduced in this chapter.

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