The subject electronics deals with the techniques leading to manipulation of electron flow. It involves study of active components such as diodes, transistors, Vacuum tubes e.t.c. which can control the flow of electron through them. By controlling the currents these devices along with passive components amplification of weak signals can be achieved, logical operations can be performed, long distance communication, Signal processing, Information processing is made possible.

The field of electronics started with vacuum tubes which work on the principle of thermionic emission. A diode made of vacuum tube contains two electrodes anode and cathode enclosed in a sealed container with vacuum. When the bulb’s filament is heated red-hot and anode is made more positive than the hot filament, a direct current flows through the vacuum to the cathode (Conventional current flow will be in the direction opposite to the direction of flow of electrons). As the current only flows in one direction i.e. from anode to cathode, it makes rectification possible. The introduction of a third electrode, a grid between the filament and the plate allows the device to be used as an electronic amplifier. A voltage applied to the grid controls the current flowing from the filament to the plate.

Then the devices fabricated through semiconductor technology replaced the vacuum tubes in every frontier after the invention of transistor by William Shockley, John Bardeen and Walter Brattain in 1947. The field of micro electronics emerged after the concept of integrated technology is invented by Jack St. Clair Kilby in 1958. Microelectronics refers to integrated circuit technology capable of producing circuits that contains millions of components in a small piece of silicon.

The IC shown in the figure is INTEL i5 processor with approximately 382 million transistors in a area of 81 mm2

Except for some high power and high frequency application such as in micro wave frequencies, solid state devices replaced vacuum tubes.In electronics we will be dealing mainly with low voltage, low current signals, low power applications except for power amplifiers which are optimized to handle high powers and at low and RF frequency range. Signals we will be dealing will be of mainly two types a) analog signals and b) digital signals. Analog signals can have any signal amplitudes but digital signal can have only two levels high or low. Accordingly the electronic circuits used for low voltage and low current application are divided into two types

a) Analog electronics: Analog electronics will be dealing with analog signals whose amplitude levels are a continuum. Most of the analog circuits will be dealing with amplification, rectification, Wave shaping of AC signals. Negative feedback is introduced for improving the stability in amplifiers. By providing positive feedback in the circuits containing transistors, the output can be made to oscillate at a particular frequency dependent on the passive elements in the circuit such as in multivibrators, oscillators. These are used in timing and control circuits for synchronization of processes. The active filters (filters using active devices) also find a lot of application in the field of communications. Using basic amplifier circuits made from transistors as a building block a compound amplifier is designed known as operational amplifiers has superior characteristics compared to individual amplifier stages. The circuits made of Opamps are capable of analog computation along with amplification; wave shaping e.t.c.

Bipolar junction transistor (BJT) technology is dominating in analog circuit design due to its high gain bandwidth product.

b) Digital electronics: Digital electronics deals with logic and switching circuits with basic building blocks made from transistor operated at extremes of input output characteristics. These circuits satisfy Boolean algebra and deals with only two levels high, low. Computers, embedded systems, PLC’s e.t.c all are made from digital circuits. Manipulation and processing of data and computation can be done efficiently by digital circuits. Even the digital circuits are finding its way in the field of communication as digital signals are more efficient in handling noise.  The basic building blocks of digital communication Analog to Digital Converters and Digital to Analog Converters involve analog circuit design along with digital circuitry.  Digital electronics re again divided into two types a) one with memory known as sequential circuits and the b) one without memory combinational circuits. Some of the basic building blocks of digital electronics are Logic gates, Adders, Flip-flops, Counters, Registers, Multiplexers, Schmitt triggers e.t.c.

There are large number of logic families each with its different design philosophy,  pros and cons but CMOS technology (which is a combination of n-MOSFET and p-MOSFET) is dominant in digital circuit design due to its high fan in and fan out, noise immunity and less power dissipation. 

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