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Integrated Circuits A collection of one or more gates fabricated on a single silicon chip is called an integrated circuit(IC).Large ICs with tens of millions of transistors may be half an inch or more on a side, while small ICs may be less than one-tenth of an inch on a side.39687
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Regardless of its size, an IC is initially part of a much larger, circular wafer, up to ten inches in diameter, containing dozens to hundreds of replicas of the same IC. All of the IC chips on the wafer are fabricated at the same time, like pizzas that are eventually sold by the slice, except in this case, each piece(IC chip)is called a die. After the wafer is fabricated, the dice are tested in place on the wafer and defective ones are marked. Then the wafer is sliced up to produce the inpidual dice, and the marked ones are discarded.(Compare with the pizza-maker who sells all the pieces, even the ones without enough pepperoni!)Each unmarked die is mounted in a package, its pads are connected to the package pins, and the packaged IC is subjected to a final test and is shipped to a customer.
Some people use the term “IC” to refer to a silicon die. Some use “chip” to refer to the same thing. Still others use “IC” or “chip” to refer to the combination of a silicon die and its package. Digital designers tend to use the two terms interchangeably, and they really don’t care what they’re talking about. They don’t require a precise definition, since they’re only looking at the functional and electrical behavior of these things. In the balance of this text, we’ll use the term IC to refer to a packaged die.
In the early days of integrated circuits, ICs were classified by size—small, medium, or large—according to how many gates they contained. The simplest type of commercially available ICs are still called small-scale integration(SSI),and contain the equivalent of 1 to 20 gates. SSI ICs typically contain a handful of gates or flip-flops, the basic building blocks of digital design.
The SSI ICs that you’re likely to encounter in an educational lab come in a 14-pin dual in-line-pin(DIP) package. As shown in Figure 1-4(a),the spacing between pins in a column is 0.1 inch and the spacing between columns is 0.3 inch. Larger DIP packages accommodate functions with more pins, as shown in (b) and (c). A pin diagram, shows the assignment of device signals to package pins, or pinout. Figure 1-5 shows the pin diagrams for a few common SSI ICs. Such diagrams are used only for mechanical reference, when a designer needs to determine the pin numbers for a particular IC. In the schematic diagram for a digital circuit , pin diagrams are not used. Instead the various gates are grouped functionally, as we’ll show in Section 5.1.
Although SSI ICs are still sometimes used as “glue” to tie together larger-scale elements in complex systems, they have been largely supplanted by programmable logic devices, which we’ll study in Sections 5.3 and 8.3.
The next larger commercially available ICs are called medium-scale integration(MSI), and contain the equivalent of about 20 to 200 gates.An MSI IC typically contains a functional building block, such as a decoder, register, or counter. In Chapter 5 and 8, we’ll place a strong emphasis on these building blocks. Even though the use of disrete MSI ICs is declining, the equivalent building blocks are used extensively in the design of larger ICs.
Large-scale integration(LSI) ICs are bigger still, containing the equivalent of 200 to 200000 gates or more. LSI parts include small memories, microprocessors, programmable logic devices, and customized devices.
The piding line between LSI and very large-scale integration(VLSI) is fuzzy, and tends to be stated in terms of transistor count rather than gate count. Any IC with over 1000000 transistors is definitely VLSI, and that includes most microprocessors and memories nowadays, as well as larger programmable logic devices and customized devices. In 1999, the VLSI ICs as large as 50 million transistors were being designed[19].