Integrated Circuit Chip – Classification, Advantages, Disadvantages

Integrated circuit Chip is a tiny device that controls electric signals in such electronic equipment as computers and television sets. Many integrated circuits contain thousands of electronic parts on a paper-thin chip of silicon. These parts include capacitors, diodes, resistors and transistors. The silicon chip may measure less than 4 millimetres square. An integrated circuit does many of the tasks performed by a conventional circuit, which consists of separate parts connected together. Integrated circuits are much smaller than conventional circuits, cost less to build and operate and work faster and more reliably. Scientists developed integrated circuits during the early 1960‘s for guided missiles and satellites. These circuits enabled them to design more advanced computers that could be built with conventional circuits. The idea for integrated circuits came from the English radar engineer W.A. Dummer in 1952. In 1959 Robert N. Noyce (US) and Jack Kilby (US) were awarded patents for such devices.

In electronic circuits usually the discrete components namely transistors, diodes, resistors, capacitors etc. are soldered by means of wires or by printed boards. But the reliability of the circuit can be enhanced if soldering is eliminated. In integrated circuits the components are fabricated in a single crystal chip of silicon (usually called a chip) and are interconnected at the time of manufacturing. The chip has a cross section of only (1/8) cm x(1/8) cm. Depending upon the number of components fabricated in an IC chip integrated circuits are classified as

(1) Small scale integration (SSI) which contains less than a dozen of logic gates,

(2) Medium-scale integrations (MSI) containing more than 12 but less than 100 gates

(3) Large scale integration (LSI) containing more than 100 and less than 1000 gates and

(4) Very large scale integration (VLSI) containing more than 1000 gates.

The chip is enclosed in a packing whose size is not much bigger than a transistor. There are pins for external connection.

Advantages of IC Chips

1. Low cost

2. Small size

3. High reliability

4. Improved performance

Limitations of IC Chips

(i) If any component of IC goes out of order, the whole IC has to be replaced by a new IC.

(ii) Inductors and transformers cannot be fabricated in an IC. It is usually connected externally.

(iii) High value capacitors cannot be fabricated in an IC. It is also connected externally.

(iv) It is not possible to produce high power ICs (greater than 10 W).

Types of Integrated Circuit Chips

Four basic types of construction are employed in the manufacture of integrated circuits. They are:

(i) monolithic (ii) thin film (iii) thick film (iv) hybrid

Monolithic ICs provides the benefits of embed all the components in a single rigid structure which can be batch fabricated, such that hundreds of identical circuits is made all together on a silicon wafer. On the other hand, hybrid circuits offer excellent isolation between components and allow the use of more precise resistors and capacitors. In addition, hybrid circuits are less expensive to make in small numbers.

Analog Integrated Circuits

An analog IC can carry out amplification or other linear operations on signals. Hence it is also known as linear IC. An analog IC deals with continuously varying quantities such as temperature, pressure. Examples of analog circuits are simple amplifiers, operational amplifiers etc.

Digital Integrated Circuits

Digital IC can carry out circuit function with discrete quantities (integer or fractional number). In digital IC information is represented by binary digits, bits. A bit may assume either one of two values: 0 or 1. It is based on a mathematical system that uses only two digits and is called a binary system as against decimal system which we are familiar.

Digital ICs involve logic and memory, for applications in computers, calculators, microprocessors etc. By far the greatest volume of ICs has been in the digital field, since large numbers of such circuits are required. Since digital circuits generally require only "on-off" operation of a transistor, the design requirements for digital ICs are often less stringent than for analog circuits.

Initially the digital IC chip was containing one logic gate per chip. However, later, it became possible to fabricate several similar gates on a single chip at very little additional cost. The next step, therefore, was to obtain the lowest cost per gate by forming as many gates as possible on one chip. The increasing complexity, coupled with the variety of logic circuit types, generated the need for definition of complexity levels. The different levels of integration of IC chips are defined as below:

■ SSI (Small-Scale-Integration): The number of logic gates on a chip is less than 10.

■ MSI (Medium-Scale-Integration): The number of logic gates on a chip is from 10 to 100.

■ LSI (Large-Scale-Integration): The number of logic gates on a chip is from 100 to 10,000.

■ VLSI (Very-Large-Scale-Integration): The number of gates on a chip is more than 10,000.

The above definitions are not unique. Particularly, the definition of VLSI is not definite. There is a constant development in the IC technology causing the packing density to grow higher and higher.