Amplifier

Amplifier:

Fig:Amplifier

An electronic amplifier, amplifier, or (informally) amp is an electronic device that increases the power of a signal.
It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude. In this sense, an amplifier modulates the output of the power supply to make the output signal stronger than the input signal. An amplifier is effectively the opposite of an attenuator: while an amplifier provides gain, an attenuator provides loss.
The four basic types of electronic amplifiers are voltage amplifiers, current amplifiers, transconductance amplifiers, and transresistance amplifiers. A further distinction is whether the output is a linear or nonlinear representation of the input. Amplifiers can also be categorized by their physical placement in the signal chain.

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Bipolar Transistor

Fig:Bipolar transisitor

 Bipolar Transisitor:-
A bipolar transistor is a semiconductor device commonly used for amplification. The device can amplify analog or digital signals. It can also switch DC or function as an oscillator. Physically, a bipolar transistor amplifies current, but it can be connected in circuits designed to amplify voltage or power.

How Bipolar Transisitors work?

figure(2)

The way a transistor works can be described with reference to fig 2 which shows the basic doping of a junction transistor and Fig 4.2 the method of operation of the device.
The operation of the transistor is very dependent on the degree of doping of the various parts of the semiconductor crystal. The N type emitter is very heavily doped to provide many free electrons as majority charge carriers. The lightly doped P type base region is extremely thin, and the N type collector is very heavily doped to give it a low resistivity apart from a layer of less heavily doped material near to the base region. This change in the resistivity of the collector close to the base, ensures that a large potential is present within the collector material close to the base.

Importance of Bipolar Transisitor

1. The transistor is the key active component in practically all modern electronics.
2. Many consider it to be one of the greatest inventions of the 20th century. Its importance in today's society rests on its ability to be mass-produced using a highly automated process (semi-conductor device fabrication) that achieves astonishingly low per-transistor costs.
3. Although several companies each produce over a billion individually packaged (known as discrete ) transistors every year, the vast majority of transistors are now produced in integrated circuits (often shortened to IC, microchips or simply chips), along with diodes, resistors, capacitors and other electronic components, to produce complete electronic circuits
4. A logic gate consists of up to about twenty transistors whereas an advanced microprocessor, as of 2009, can use as many as 3 billion transistors (MOSFETs).
5. The transistor's low cost, flexibility, and reliability have made it a ubiquitous device. Transistorized mechatronic circuits have replaced electromechanical devices in controlling appliances and machinery.
6. It is often easier and cheaper to use a standard microcontroller and write a computer program to carry out a control function than to design an equivalent mechanical control function.

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Diode

Diode

1.Diode

Fig:-Diode

The semi-conductor device formed simply by joining on n-type and p-type material together is called diode.

Ideal Diode

 It is a two terminal device having the circuit symbol as shown in fig(a) and i-v characteristics curve as shown in figure(b).

Biasing of diode

No Biasing applied(V_D=0v)

In absence of an applied bias, the net flow of electron or holes(charges) in one direction is zero.

Hence, no current flow if no biasing voltage is applied.

VD=0

Reverse Biasing(V_D<0v)

Due to reverse biasing the width of depletation region is increased resulting the majority carrirer flow to zero.

The number of minority carriers, however entering the region will not change, resulting in minority-carrier flow vectors of the same magnitude indicated in Figure below with no applied voltage.

The current that exist under reverse-bias condition is called the reverse saturation current and is represented by I_S.

Forward biasing

A forward bias condition is established by appying the positive potential p-type material and the negative potential to n-type material as shown in the figure.

The application of forward bias vol tage reduces the width of depletation region and hence enhances the flow of majority charge carriers. And the result is increase in forward current. As the applird bias increases in magnitude,the depletion region will continue to decrease until a flood of electrons can pass through the junction, resulting in exponential rise in current in forward-bias region.

Diode Models

Ideal Diode Model

The ideal model of a diode is a simple switch. When diode is forward biased it acts like a closed(ON) switch and when it is reversed biased it acts as open(OFF) switch.

VF=Forward bias voltage

VR=Reverse bias voltage

IF=Forward bias current

IR=reverse bias current

Practical Diode Model

Practically we need to overcome the barrier potential by application of forward bias voltage.

Hence practical model adds the barrier potential to the ideal diode model.

When the diode is forward-biased, it is equivalent to a closed switch in series with a small equivalent voltage source equal to barrier potential(0.7v for silicon and 0.3v for germanium) with positive side towards the anode. When the diode is reverse-biased, it is equivalent to open switch.

Complete Diode Model

The complete diode model consist of the barrier potential, the small forward dynamic resistance(r_d') and the large reverse resistance(r_R').The reverse resistance is taken into account because it provides path for the reverse current which is included in this model.

When the diode is forward biased, it acts as closed switch in series with the barrier potential voltage and the small forward dynamic resistance((r_d').

When the diode is reverse-biased, it acts as open switch in parallel with the large internal resistance((r_R').

I-V characteristics curve of a diode

 

Fig:-I-V characteristics of diode

The general characteristics of semi-conductor diode can be defined by the shuckley's equation for forward and reverse biased regions.

I_D=I_s(e^VD/nVT-1)

I_D ~I_se^V_D^/nV_T------------------------------------------------------------------------------------------(1)

Where, I_D=current in diode

                I_s-reverse saturation current

                V_D=applied forward-bias viltage

                V_T=KT/q, is thermal voltage

                K=Boltzmann's constant=1.38*10^-23

                T=Absolute Temperature in Kelvin

                q=magnitude of electronic charge=1.6*10^-19

               

                1<=n(eta)<=2depending a wide variety of factors.

Differntiating equation(1), we have

r_d(dynamic resistance of diode)=v_d/i_d=nV_T/I_D

I_D1 =I_se^V_D1^/nV_T

I_D2 =I_se^V_D2^/nV_T

I_D2/I_D1=e^V_D2^-V_D1^/nV_T

Taking natural log on both the sides, we get

V_D2-V_D1/nV_T=In(I_D2/I_D1)

V_D2-V_D1=nV_TIn(I_D2/I_D1)

Zener Diodes

Fig-:Zener diode

The Zener diode is a silicon p-n junction device that differs from rectifier diodes because it is designed for operation in the reverse-breakdown region.If a Zener diode is forward biased, it operates as a rectifier diode.

There are two types of breakdown in zener diode:

(i)Zener breakdown

Fig:-I-V characteristics Zener diode

 It occurs in a zener diodes at low reverse voltages.A zener diode is very heavily doped to reduce breakdown voltage. This causes a very thin depletation region.As a result, an intense electric field exist within the depletation region.Near zener breakdown voltage(V_Z),the field is intense enough to pull electrons from their valance bonds and create current.This phenomenon is called breakdown.

(ii)Avalanche  Breakdown

The multiplication of conduction electrons due to knocking of valence electrons by free minority electrons under the action of reverse bias voltage is called Avalanche Breakdown.

Breakdown characteristics

As the reverse voltage V_R is increased the reverse current I_R remains extremly small upto the knee of the curve. Current at this point of curve is Zener Knee current I_ZK.From this point zener breakdown start and current rises rapidly upto I_ZM, Zener maximum current. The Zener breakdown voltage(V_Z) remains essentially constant altough it increases slightly as the zener current I_Z increases.

Zener Regulation

The ability to keep the reverse voltage across its terminals essentially constant is the key feature of zener diode, which enables for its property of voltage regulation.

A zener diode operating in breakdown region acts as voltage regulator over a specified range of reverse-current values(I_ZK to I_ZM).

Below knee current I_ZK voltage regulation is lost and above I_ZM(zener maximum current) diode may be damaged due to excessive power dissipation.

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Electronic Devices Importance

Importance of Electronic Device

The electronic devices are most important things to do work fast and makes easy to do job efficiently.
Its going on basic needs for a todays world.

Nowadays many people cannot be separates from electronic devices. They believe it can help them to finish their work. It’s true because by using electronic devices it will make us easier to do our job. For instance computer. If we use computer in working like make a report, send an email, and finding sources it will be easier beside we do not need use computer. It is because we do not need to write it manually, if we make a report or an email, we just type it in the computer and it will be faster than we write it manually. We also do not need to find sources that we need from magazine or newspaper, because now we have an internet connection in computer. By using an internet we can find many things that we need in a snap, so it will not waste our time. Internet is very useful for our life and it also happen for university student, for it gives us many advantages but there are also some disadvantages of internet.

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