Integrated Circuit(IC)

Digital Circuits are constructed with Integrated circuit. An integrated circuit abbrevivated as IC.A silicon semiconductor crystal informally called as a chip,containing the electronic components for the digital gates. The various gates are connected on the chip to form the IC. The chip is mounted in a ceramic container,connection are welded from the chip to external pins to form the IC. The number of pins may range from 14 on a small IC package to several hundred package.Each IC has a numeric designation printed on the surface of package for identification. Each vendor publishes a data book that contains the description and all the necessary information about IC’s .These books are often available in vendor’s website.

Level of Integration: As the technology of IC has improved,the number of gates that can be put on single silicon chip has increased considerably. The differentiation between those chips that have a few internal gates and those having thousands  to millions of gates is made by customary refrence to a package as been a simple,medium , large or very large scale Integration device.

Small Scale Integrated (SSI):Devices contains several independent gates in a single package . The inputs and outputs of gates are connected directly to the pins in the package. The number of gates is usually less than 10 and is limited by the number of pins available in the IC.

Medium Scale Integrated (MSI): Devices have complexity of approximately ten to 100 gates in a single package. They usually perform specific elementary digital functions are similar to function blocks.

Large Scale Integrated (LSI) : Devices contains between 100 and few 1000 gates in a single package . They include digital systems such as small processors, small memory and programmable modules.

Very Large scale Integrated (VLSI):  Devices contains several 1 thousands to 10 million in a single package .Example:complex processor or micro processor and digital signal processing chip. Because of their small size and low cost,VLSI devices have revolutionized computer system design technology,giving designer the capabilities to create complex structure that preveisouly weren’t economical to manufacture.

Digital Logic Families (DLF): Digital Integrated circuits are classified not only by their logical operation,but also by the specific circuit technology to which they belong to.The circuit technology is referred to as the digital logic families . Each such family has its own basic electronic circuit upon which more  complex digital circuits and functions are developed. The primitive circuit in each technology are typically NAND,NOR,AND and NOT gates. The electronic components used in the construction of the basic circuit gave the name to the technology. Many different logic families of IC have been introduced commercially.

Historically,the following have been the most important.

RTL = Resistor Transistor Logic

DTL = Diode Transistor Logic

TTL = Transistor Transisitor Logic

ECL = Emitter Coupled Logic

MOS = Metal Oxide Semiconductor

CMOS = Complementary Metal Oxide Semiconductor.

BiCMOS  = Bipolar Complementary Metal Oxide Semiconductor.

GaAs = Gallium Arsenide

RTL and DTL were the earliest logic family and are now obsolete. TTL is a widely used logic family that has been available for decades but is declining rapidly used. ECL has an advantage in system requiring high speed operation,but is being rapidly overtaken by CMOS. MOS is suitable for circuits that need high component density , CMOS is preferable in systems requiring no power consumption. In fact,low power consumption is so essential to prevent large complex dense devices from overheating that CMOS is now the dominant technology by CMOS which combinations . CMOS with a bit of TTL is used selectively incase . GaAs is used very selectively incase .GaAs is used very selectively for very high speed circuit.