Studying Electronics … the Sooriya’s way 🙂
2.9 inteGrated CirCuits
An integrated circuit (IC) is fabricated on a die of a silicon semiconductor crystal, called a chip, containing the electronic components for constructing digital gates. The complex chemical and physical processes used to form a semiconductor circuit are not a subject of this book. The various gates are interconnected inside the chip to form the required circuit. The chip is mounted in a ceramic or plastic container, and connections are welded to external pins to form the integrated circuit. The number of pins may range from 14 on a small IC package to several thousands on a larger package. Each IC has a numeric designation printed on the surface of the package for identification. Vendors provide data books, catalogs, and Internet websites that contain descriptions and infor- mation about the ICs they manufacture.
90 Chapter 2 boolean algebra and Logic Gates
Levels of Integration
Digital ICs are often categorized according to the complexity of their circuits, as mea- sured by the number of logic gates in a single package. The differentiation between those chips that have a few internal gates and those having hundreds of thousands of gates is made by customary reference to a package as being either a small-, medium-, large-, very large-scale, or ultra large-scale integration device.
Small-scale integration (SSI) devices contain several independent gates in a single package. The inputs and outputs of the gates are connected directly to the pins in the package. The number of gates is usually fewer than 10 and is limited by the number of pins available in the IC.
Medium-scale integration (MSI) devices have a complexity of approximately 10 to 1,000 gates in a single package.They usually perform specific elementary digital opera- tions. MSI digital functions are introduced in Chapter 4 as decoders, adders, and multi- plexers and in Chapter 6 as registers and counters.
Large-scale integration (LSI) devices contain thousands of gates in a single package. They include digital systems such as processors, memory chips, and programmable logic devices. Some LSI components are presented in Chapter 7.
Very large-scale integration (VLSI) and Ultra large-scale integration (ULSI) devices now contain millions of gates within a single package, with ULSI circuits having over one-million transistors. Examples are large memory arrays and complex microcomputer chips. Because of their small size and low cost, VLSI devices have revolutionized the computer system design technology, giving the designer the capability to create struc- tures that were previously uneconomical to build.
Digital Logic Families
Digital integrated circuits are classified not only by their complexity or logical operation, but also by the specific circuit technology to which they belong. The circuit technology is referred to as a digital logic family. Each logic family has its own basic electronic circuit upon which more complex digital circuits and components are developed. The basic circuit in each technology is a NAND, NOR, or inverter gate. The electronic components employed in the construction of the basic circuit are usually used to name the technol- ogy. Many different logic families of digital integrated circuits have been introduced commercially. The following are the most popular:
TTL transistor–transistor logic;ECL emitter-coupled logic;MOS metal–oxide semiconductor;CMOS complementary metal–oxide semiconductor.
TTL is a logic family that has been in use for 50 years and is considered to be stan- dard. ECL has an advantage in systems requiring high-speed operation. MOS is suit- able for circuits that need high component density, and CMOS is preferable in systems requiring low power consumption, such as digital cameras, personal media players, and
section 2.9 integrated Circuits 91