What is Electromagnetic Theory ? What is Electromagnetism?

The electromagnetic theory is a united theory of electromagnetism established by James Clerk Maxwell. This theory primarily discusses the relationships between electric field and magnetic field based from previous observations and experiments related to electricity, magnetism and optics combined.

Electromagnetism, science of charge and of the forces and fields associated with charge. Electricity and magnetism are two aspects of electromagnetism.

Electromagnetism is a branch of physics which involves the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually exhibits electromagnetic fields, such as electric fields, magnetic fields, and light

What is the need of Digital Signal Processing?

Real world signal is analog. Digitized signal can approximate real world analog signal to a limited degree. Limited in terms of time resolution or accuracy. Digital signal processing is needed to improve the digital representation of the real world signal. Improvement can come in the form of accuracy, interpretation, transformation, or compression.

Many of these processing has an equivalent form in analog domain - ex. filtering. However, digital signal processing can typically be implemented cheaper, faster, and with more consistent result. 

Digital signal processing has a wide variety of applications, including:

Ø  Audio and video compression (the quality depends on the sampling rate chosen - higher sampling rate = higher quality. The file size can be compressed by applying source coding, such as Huffman coding.)

Ø  Audio signal processing (example: applying a low pass or bandpass filter to reduce external noise from an audio recording)

Ø  Image processing (example: using FFT, filtering and inverse FFT in order to remove noise from an image)

Ø  Medical applications (example: applying a histogram equalization to enhance an x-ray image)

Explain Gibbs Phenomenan in context of fourier series.

Gibb's Phenomenon

We can approximate a signal having a Fourier Series expansion by taking a finite number of terms of the expansion.

i.e:  is an approximation to the periodic signal x(t).

 is also called a Partial Sum. We would obviously expect that as the number of terms taken is increased, this summation would become a better and better approximation to x(t), i.e  would approach x(t) uniformly.

Indeed this happens in regions of continuity of the original signal. However, at the points of discontinuity in the original signal, an interesting phenomenon is observed. The partial sum oscillates near the point of discontinuity. We might expect these oscillations to decrease as the number of terms taken is increased. But surprisingly, as the number of terms taken is increased, although these oscillations get closer and closer to the point of discontinuity, their amplitude does not decrease to zero, but tends to a non zero limit. This phenomenon is known as the Gibb's Phenomenon, after the mathematician who accounted for these oscillations.

The illustration below shows the various Fourier approximations of a periodic square wave.

Mathematically, this means if the periodic signal has discontinuities, its Fourier Series does not converge uniformly.

What do mean by digital electronics ? Explain advantage of digital circuit over analog circuit ?

Digital electronics are those electronics systems that use a digital signal instead of an analog signal. Digital electronics are the most common representation of Boolean algebra and are the basis of all digital circuits for computers, mobile phones, and numerous other consumer products.

The most common fundamental unit of digital electronics is the logic gate. By combining numerous logic gates (from tens to hundreds of thousands) more complex systems can be created. The complex system of digital electronics is collectively referred to as a digital circuit.

The usual advantages of digital circuits when compared to analog circuits are:

• Digital systems interface well with computers and are easy to control with software. It is often possible to add new features to a digital system without changing hardware, and to do this remotely, just by uploading new software. Design errors or bugs can be worked-around with a software upgrade, after the product is in customer hands.

• Information storage can be much easier in digital systems than in analog ones. In particular, the great noise-immunity of digital systems makes it possible to store data and retrieve it later without degradation. In an analog system, aging and wear and tear will degrade the information in storage, but in a digital system, as long as the wear and tear is below a certain level, the information can be recovered perfectly.

What is Electronics ?

Electronics means study of flow of electrons in electrical circuits. The word Electronics comes from electron mechanics which means learning the way how an electron behaves under different conditions of externally applied fields. 

IRE - The Institution of Radio Engineers has given a definition of electronics as "that field of science and engineering, which deals with electron devices and their utilization." 

What do you mean by autocorrelation ?

Autocorrelation, also known as serial correlation, is the correlation of a signal with itself at different points in time. Informally, it is the similarity between observations as a function of the time lag between them. It is a mathematical tool for finding repeating patterns, such as the presence of a periodic signal.

Why crystalline continuity is required for a semiconductor pn junction?

If a block of P-type semiconductor is placed in contact with a block of N-type semiconductor in Figure below(a), the result is of no value. We have two conductive blocks in contact with each other, showing no unique properties. The problem is two separate and distinct crystal bodies. The number of electrons is balanced by the number of protons in both blocks. Thus, neither block has any net charge.

However, a single semiconductor crystal manufactured with P-type material at one end and N-type material at the other in Figure below (b) has some unique properties. The P-type material has positive majority charge carriers, holes, which are free to move about the crystal lattice. The N-type material has mobile negative majority carriers, electrons. Near the junction, the N-type material electrons diffuse across the junction, combining with holes in P-type material. The region of the P-type material near the junction takes on a net negative charge because of the electrons attracted. Since electrons departed the N-type region, it takes on a localized positive charge. The thin layer of the crystal lattice between these charges has been depleted of majority carriers, thus, is known as the depletion region. It becomes non conductive intrinsic semiconductor material. In effect, we have nearly an insulator separating the conductive P and N doped regions.

(a) Blocks of P and N semiconductor in contact have no exploitable properties. (b) Single crystal doped with P and N type impurities develops a potential barrier.

This separation of charges at the PN junction constitutes a potential barrier. This potential barrier must be overcome by an external voltage source to make the junction conduct. The formation of the junction and potential barrier happens during the manufacturing process. The magnitude of the potential barrier is a function of the materials used in manufacturing. Silicon PN junctions have a higher potential barrier than germanium junctions.