Integrated circuits (IC) now became a vital part in modern electronics era. Integrated circuit means that all the components are integrated on a same chip. These are commonly used in computers, home appliances, communication, and control systems, where they permit miniaturization and superior performance and not possible with discrete components. IC’s are now being used in all type of electronic equipment because of the long, trouble free service they provide. In addition, they are economical because they are mass produced.
CLASSIFICATION OF ICs
ICs are basically classified according to their mode of operation, Digital or Linear.
Digital ICs are complete functioning logic networks that are equivalent to basic transistor logic circuits. They are used to form such circuits as gates, counters, multiplexers, demultiplexers, shift registers, and others. Since a digital ic is a complete pre-design package, it usually requires nothing more than a power supply, input, and output.
Digital circuits are primarily concerned with only two levels of voltage (or current), HIGH and LOW. Therefore, accurate control of operating region characteristics is not required in digital circuits, unlike in Linear circuits. For this reason, digital circuits are easy to design and are produced in large quantities as low cost devices.
Linear ICs are equivalent of discrete transistor networks, such as amplifiers, filters, frequency multipliers, and modulators, that often require additional external components for satisfactory operations. For example, external resistors are necessary to control the voltage gain and frequency response of an op amp. In linear circuits the output electrical signals vary in proportion to the input signals applied or the physical quantities they represent. Since the electrical signals are analogous to the physical quantities, linear circuits are also referred as analog circuits.
Of all presently available linear ICs, the majority are operational amplifiers. With suitable external components, the op amp is used in amplifiers, active filters, integrators, differentiators, and in countless other applications. A wide variety of special purpose linear ICs are available for use in comparators, voltage regulators, digital-interface circuits, and in radio frequency and power amplifiers.
In addition to the op amp and special purpose linear ICs, components arrays are also available in IC form. Such arrays may consist of groups of isolated transistors, diodes, and resistors as well as for darlington pairs or individual stages such as differential and cascade amplifiers.
Op amps are further classified into two groups: General Purpose and Special Purpose. General purpose op amps may be used for a variety of applications, such as integrator, differentiator, summing amplifier, and others…
TYPES OF INTEGRATED CIRCUITS
Integrated circuits may be classified as either Monolithic or Hybrid. Most linear ICs are produced by the monolithic process in that all transistors and passive elements are fabricated on a single piece of semiconductor material, usually silicon. Monolithic is a greek based word means that “ONE STONE”
In monolithic ICs all component (active and passive) are formed simultaneously by a diffusion process. Then a metallization process is used in inter connecting these components to form the desired circuits. Electrical isolation between the components in monolithic ICs can be achieved by any one of the three isolation techniques: Di-electric, Beam-Lead, PN junction. However, the PN junction isolation is most economical and is, therefore, commonly used.
The monolithic process makes low cost mass production of ICs possible. Also, monolithic ICs exhibit good thermal stability because all the components are integrated on the same chip very close to each other.
However, the large values of resistors and capacitance that are required in some linear circuits cannot be formed using the monolithic process. Moreover there is no method available to fabricate transformers or to for large values of inductors in integrated circuit form. However, if these components are required In a given application, external discrete components can be used with the IC.
In Hybrid ICs, passive components and the interconnections between them are formed on an insulating substrate. The substrate is used as a chassis for the integrated components. Active components such as transistors and diodes, as well as monolithic integrated circuits, are then connected to form a complete circuit. For this reason, low-volume production is best suited for Hybrid IC technology.
Hybrid ICs are further classified as Thin film or Thick film, depending on the method used to form the resistors, capacitors and related interconnections on the substrate. When the suitable material is evaporated on a substrate, forming resistors, capacitors and interconnections, a thin film Hybrid IC is obtained. On the other hand, in a thick film Hybrid Ic the Resistors, capacitors are formed on the substrate by SILK SCREENING.