Integrated Circuits and Symbol

September - 9 - 2009

An Introduction to IC – Integrated Circuits

555 timer IC

The integrated circuit was introduced in 1958. It has been called the most significant technological development of twentieth century. It has radically altered the world of electronics. The profound effect of these micro-electronic ‘giants’ was first felt in the computer and digital field. First-generation electronic computers employed vacuum tubes. Vacuum tubes were replaced by transistors, cheaper in cost, smaller in size, less power consuming and reliable, in second generation computers. Third generation computers used digital ICs, largely reducing computer size and increasing computer reliability and speed. Integrated circuits have further reduced product dimensions and cost, while ensuring even greater reliability.

As the state of the art advanced, specially designed ICs were used in linear circuits in communications, military, and industrial applications. ICs and large scale ICs have changed the design of electronic devices from the use of only discrete components to hybrid solid-state devices which mix discrete components with ICs.

Discrete circuits:

we have discussed so far in previous blog posts, consisted of separately manufactured components, such as resistors, inductors, capacitors, diodes, transistors, etc., joined by wires or plated conductors on printed boards. Such circuits have two main drawbacks. Firstly, they occupy a large space. This is because of involvement of large number of components in a large electronic circuit such as a TV circuit or a computer circuit. Secondly, there is problem of reliability, as hundreds of components are to be soldered. To overcome these drawbacks of space conservation and reliability, engineers started a drive for miniaturized circuits. This led to the development of integrated circuits in 1958.

Integrated circuit is not just a mere efficient transistor or several transistors inside a small case. It is a complete electronic circuit consisting of both the active and passive components (including their interconnections) fabricated on an extremely tiny single chip of silicon. The active components are those which are capable of producing gains, such as, transistors, FETs. Passive components are diodes, resistors, capacitors etc. An IC is so small in size that we normally require a microscope to see the connections between the components. The processes employed in fabrication of IC chips are basically the same as employed in the fabrication of discrete transistors, diodes etc. However, in IC technology, all the circuit elements (transistors, diodes, resistors, capacitors etc.) including their interconnections are fabricated at a time. Rather a batch of identical chips is fabricated at a time. This is the reason that such IC chips have identical characteristics.

IC SYMBOL

IC Symbol

In general there is no standard symbol for ICs. Normally, ICs are represented by either a triangle or a rectangle with numbered terminals, as illustrated in figure. Internal circuit is not shown by the IC symbol.