Integrated circuits | Readstall

Integrated circuits

13-02-19 Mounika Mayakuntla 0 comment

Integrated circuits:

                   Digital circuits are constructed with integrated circuits. An integrated circuit (IC) is a small silicon semi conductor crystal, called a chip, containing the electronic components for the digital gates. 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 by thin gold wires to external pins to form the integrated circuit. The number of pins may range from 14 in a small IC package to 100 or more in a larger package. Each IC has a numeric designation printed on the surface of the package for identification.

Decoder: As the technology of IC’s has improved, the number of gates that can be put in a single chip has increased considerably. The differentiation between those chips that have a few internal gates and those having hundreds or thousands of gates is made by a customary reference to a package as being either a small medium or large scale integration device.

Small Scale Integration (SSI): 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 in the package is usually less than 10 and is limited by the number of pins available in the IC.

Medium Scale Integration (MSI): MSI devices have a complexity of approximately 10 to 200 gates in a single package. They usually perform specific elementary digital functions such as decoders, adders and registers.

Large Scale Integration (LSI): LSI devices contain between 200 and a few thousand gates in a single package. They include digital systems, such as processors, memory chips and programmable modules

Very Large Scale Integration (VLSI): VLSI devices contain thousands of gates within a single package. Examples are large memory arrays and complex micro computer chips. Because of their small size and low cost, VLSI devices are revolutionized the computer system design technology, giving designers the capability to create structures that previously were not economical.

          Digital integrated circuits are classified not only by their logic 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 functions are developed. The basic circuit in each technology is either a NAND, a NOR, or an Inverter gate. Many different logic families of IC’s 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 widespread logic family that has been in operation for many years and is considered as standard. ECL has an advantage in systems requiring high speed operation.MOS is suitable for circuits that need high component density, and CMOS is preferable in systems requiring low power consumption.

          Because of their many advantages, IC’s are used exclusively to provide various digital components needed in the design of computer systems. To understand the organization and design of digital computers it is very important to be familiar with the various components encountered in IC.



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