. I NTEGRATED C IRCUITS The conventional method of making circuits is to choose components like diodes, transistor, R , L , C etc., and connect them by soldering wires in the desired manner. Inspite of the miniaturisation introduced by the discovery of transistors, such circuits were still bulky. Apart from this, such circuits were less reliable and less shock proof.
The concept of fabricating an entire circuit (consisting of many passive components like R and C and active devices like diode and transistor) on a small single block (or chip) of a semiconductor has revolutionised the electronics technology. Such a circuit is known as Integrated Circuit (IC) . The most widely used technology is the Monolithic Integrated Circuit. The word Input Output A B Y (b) monolithic is a combination of two greek words, monos means single and lithos means stone.
This, in effect, means that the entire circuit is formed on a single silicon crystal (or chip ). The chip dimensions are as small as 1mm × 1mm or it could even be smaller. Figure . shows a chip in its protective plastic case, partly removed to reveal the connections coming out from the ‘chip’ to the pins that enable it to make external connections.
Depending on nature of input signals, IC’s can be grouped in two categories: (a) linear or analogue IC’s and (b) digital IC’s. The linear IC’s process analogue signals which change smoothly and continuously over a range of values between a maximum and a minimum. The output is more or less directly proportional to the input, i.e., it varies linearly with the input. One of the most useful linear IC’s is the operational amplifier.
The digital IC’s process signals that have only two values. They contain circuits such as logic gates. Depending upon the level of integration (i.e., the number of circuit components or logic gates), the ICs are termed as Small Scale Integration, SSI (logic gates < ); Medium Scale Integration, MSI (logic gates < ); Large Scale Integration, LSI (logic gates < ); and Very Large Scale Integration, VLSI (logic gates > ). The technology of fabrication is very involved but large scale industrial production has made them very inexpensive.
FIGURE . The casing and connection of a ‘chip’.