Importance of electronics

Electronics

" The branch of applied physics, which deals with principles and ways by which the flows of electrons is controlled, is called “Electronics”.  
It is done by using electric circuits containg diode, transistors and other semiconductor devices. In everyday life we use electronic devices like radio, T.V, cassette players, the various automatic machines, all of these work on the basic principles of electronics. Electronic devices are fitted in satellites, which produce electromagnetic waves, which carry message for the controlling stations on Earth. The E-mail and Internet facilities are also due to electronics. It seems impossible to meet the requirements of present modern life. In future the person without knowledge of computer would be considered as illiterate. 
 The two.main branches of electronics are 
 (1) Analogue
 (2) Digital

Analogue quantites

The analogue quantities are those whose value either remain constant or vary continuously. For example the variation of atmospheric temperatures with time . This shows that temperature variation with time is continuous. There is no abrupt change in it. So we can say that atmospheric temperature is an analogue quantity with respect to time. Similarly, pressure, distance covered by a moving car etc are all analogue physical quantities.

Analogue quantities

The section of electronic, which is concerned with circuits processing analogue quantities like current, voltage etc; is called analogue electronics.

 Analogue voltage signal

The microphone converts sound energy into continuously varing voltage. It is called analogue voltage signal. This signal is applied to an electric amplifier, which is also analogue electronic circuit, which amplifies the signal with out changing its shape, which operates the loud speaker. The computer operates by counting the digits. The voltage signal required to operate a computer is not continuously varying signals. But its has only two values maximum or minimum. 
The electrons which is based on such voltage signals is called “digital electronics”. 
The shape of analogue and digital voltage . 

 Uses 

 Digital electronics is being used in every modem electronic device like modern telephone system, radar system, naval and other military controlling systems, modem cameras, control system of operation of industrial machines, medical equipment etc. All things we perceive by our sense in our daily life are all analogue quantities. 
These cannot be processed by digital electronic circuits. This difficultly is resolved and circuit has been designed which converts analogue signal into digital signal in the form of digits. This is called analogue to digital converter (ADC). 
 The signal obtained from ADC is processed by digital electronic circuit and its output is also in digital form. This digital output voltage signal is ‘again’ converted by the help of another circuit known as “digital to analogue converter circuit” (DAC). 
As finally we get analogue signal so it can be sensed readily by us. Analogue Watch Digital Watch The above explanation shows that electronic systems used in these days consists of both analogue and digital type circuits.

Daily life devices

The digital devices used in our daily life are Computer T.V. Digital camera Mobile phone Security system And the device based on analogue voltage signals are Refrigerators Electric fans Electric iron . Electric lamps Radio receiver. There are three types of material objects, regarding their electrical, properties.

Conductors: 

 The substances through which electric current /heat can pass easily, are called conductors. For example copper, iron, brass, steel, gold are good conductors; and electric current heat'can pass through these easily. Our body is also'a good conductor. Earth is also a big conductor. 
All the conductors contain free electrons, which have free movement, so current can easily flow through the conductors. 

Insulators. 

 The substances through which electric current cannot pass are called insulators. These do not have free electrons.
 For example, glass, plastic ,mica, rubber etc. The electrons, in these substances, are bound tightly to their respective nuclei, so these are unable to move freely inside these substances. And no current can flow through them. 

Semiconducters 

The elements whose ability to conduct electric current through them lies midway between insulator and conductors.
 More famous semi-conductors are Germinium and silicon- 

 Behavior of Semi-conductors ~ 

The semiconductor to elements belong to 4th group. Hence each atom of these has four valence electrons. In the figure below we see the cross section of crystal of Germinium or Silicon from front side. This figure shows the arrangement of atoms inside this crystal. . 
 There are four atoms, which have covalent bonds with same single atom. So that the sharing atom has eight electrons in its outermost orbit. No electron is allowed to leave this orbit. This is due to the formation of covalent bonds as shown is above figure. 
When all the electrons are bound in the stable outer orbits then no free electrons is available to make electric current to pass through them. Hence pure semiconductor crystal (at low temperature) has no free electron, and it behaves like insulator.
 This behaviour of semiconductor is at temperature near zero Kelvin. makes free electron available for IS conduction of current. This proves that when a co-valent bond breaks then a ' “free electron” and a “hole” is created. It is called electron hole pair Due to both of these (electrons, hole) the electric current can start in the semi-conductor. 
This shows that at room temperature the crystal of Germinium or silicon becomes a semi-conductor (which was behaving like insulator at temperature near zero Kelvin). The number of free electrons plus the number of holes in a semi-conductor is much small, as compared with free electrons inside conductors. 
The number of holes or free electrons is zero at temperature near OK.

 Intrinsic Semi-Conductor:

 The semi-conductor crystal, which can equal number of holes and free electrons is called intrinsic semi-conductor. 

Doping: 

' The mixing of an impurity of, 3rd, or of 4th group element, in an intrinsic semiconductor to increase its conductivity is called doping. . Due to doping the semiconductor does not remain pure. And it is called extra intrinsic semiconductor. Doping is made while a single crystal of silicon or germinium is being grown.
 Doping increases drastically the property of conducting current in semiconductors. 

Types of intrinsic semiconductors 

There are two types of extra intrinsic semiconductors. 
One is called, N- type and the other is called P-type semiconductor crystal .
P-types semiconductor crystal
P-types semiconductor crystal contains “holes” as majority charge carriers and electrons as minority charge carriers.
 N-type semiconductor crystal 
  N-type semiconductor crystal contains “free electrons” as majority charge carriers and holes as minority charge carries. If doping in semiconductor is made of an element belonging to 3rd group of element, such as aluminium (A) iridium (Ir), Boron (B) or germinium (Ga) while preparing single crystal of germinium or silicon, then number of holes in such a crystal is much greater than number of free electrons. And “holes” are supposed to carry positive charge, due to which a crystal doped with an impurity from 3rd group of elements, in called P-type semiconductor crystal. The atom of impurity of 3,d group has three valence electrons. It can complete three covalent bonds, whereas fourth sharing bond remains uncompleted in the structure of crystal. 

This gives extra “hole”. Hence every impurity atom gives one extra hole to give majority of hole in such a crystal. N-type 

Semiconductor: 

 During the development of a single crystal if impurity of an element of 5th group is- addedj then we get N-type semiconductor crystal. In this case each impurity atom has five valence electrons. So it can be complete four co-valent bonds while its 5th valence electron remains free.
 Due to this reason the crystal is called N-type semiconductor crystal. It is majority of negative charge carriers (electron) and has minority charge carriers as “holes”.
 . P-types semiconductor crystal contains “holes” as majority charge carriers and electrons as minority charge carriers. 
 N-type semiconductor crystal contains “free electrons” as majority charge carriers and holes as minority charge carries. P-type semiconductor crystal.
 Doping in semiconductor is made of an element belonging to 3rd group of element, such as aluminium (A) iridium (Ir), Boron or germinium (Ga) while preparing single crystal of germinium or silicon, then number of holes in such a crystal is much greater than number of free electrons. And “holes” are supposed to carry positive charge, due to which a crystal doped with an impurity from 3K group of elements, in called . P-type semiconductor crystal The atom of impurity of 3,d group has three valence electrons. It can complete three covalent bonds, whereas fourth sharing bond remains uncompleted in the structure of crystal. This gives extra “hole”. Hence every impurity atom gives one extra hole.to give majority of hole in such a crystal. N-type Semiconductor: During the development of a single crystal if impurity of an element of 5th group is- added; then we get N-type semiconductor crystal. In this case each impurity atom has five valence electrons. So it can be complete four co-valent bonds while its 5th valence electron remains free. Due to this reason the crystal is called N-type semiconductor crystal. It is majority of negative charge carriers and has minority charge carriers as“holes”. It the doping element is antimony, then each atom of it surrounded by four germinium or silicon atoms, to four co-valent bonds. Its 5th valence electron remains free. Hence impurity atom provides' one free electron. Due to this free elements become in majority, as compared with free electron. Why is the potentiol
  P-N Junction 
If crystal of germinium silicon is developed in such a way a pari made P-type and the remaining part of it is made N-type, then sepan plane between these two is called P-N junction. On one side of P-N junction there are free electrons in majority (N-type side) and on the other side “holes” are in majority (P-type side). The'
free electrons  N-type side are more mobile as compared  “holes” Just after the PN—junction is formed some of free electrons of  N type side diffuse into the P-type region of P-N junction.
 These car negative charge along with them. The electrons set themselves, in tl holes, near the junction. Due to this a negative charge layer is produced, i P-type side, near the junction. Because each impurity atom of P-type sid becomes negative ion. 
This negative ion does not move from its place, a atoms have fixed seats inside the crystal. Due to diffusion of electrons from N-type side to P-type side, each impurity atom of  N-type side becomes   ion. It is due to loss of one The P-type side connection in called anode and N-type side connection is called cathode. 
When there is no electric potential difference between two terminals of semiconductor diode, then no current passes through it. It is due to the presence of potential barrier automatically developed across P-N junction. Forward Biased Diode: - If a semiconductor is provided an electric potential difference so that its P- type side is at higher and at N-type side is at lower potential, then it is said to be in “forward bias”.

 It this case majority charge carriers of both side of semiconductor diode move across P-N junction. Due to which considerably large amount of current flows. And P-N junction act like low resistance. 

Conditions for Forward Bias Connection 

Conditios for forward bias connection of semiconductor
The following are two conditions for the forward bias connection of semiconductor diode. The P-type side connection must be at higher potential and its N-type side must be at low potential. The applied voltage must be greater than the value of potential bamer. 
So that charge carries overcome the potential barrier to have continuous flow through P-N junction. A specified maximum value of current can be passed through semiconductor diode. If current exceeds this specific value then it is heated up and is likely to be damaged. To prevent it from damaging, a suitable resistance is connected in series with the semiconductor diode . 
When a diode is forward biased then width of its depletion region is decreased. 
This means that there is small number of positive and negative ions present in this region. So height of potential barrier is small. Therefore, large amount of current flows through the junction. This is shown is the figure below. 
Dotted line shows the depletion region for un-biascd diode and solid line shows the depletion region when the diode is in forward bias. Reverse Biased Diode If the anode or P-type side of a diode is at low potential and the N-type side or cathode is at high potential, then diode is said to be in reverse bias.