clasification of amplifiers

7/30/2019 Clasification of Amplifiers

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CLASSIFICATIONOF AMPLIFIERS

BY G.PREETHI

ECE-B

11P61A0464


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CONTENTS Amplifier Classification of Amplifiers Class A amplifier, its characteristics . Class B amplifier, its characteristics . Class AB amplifier, its characteristics . Class D amplifier, its characteristics . Class G & H amplifiers .


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AMPLIFIER An Amplifier is a device for increasing

the power of a signal by use of anexternal energy source.

Amplifiers may be classified in a varietyof ways depending on the applications ,frequency range, etc.


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Practical amplifiers have finitedistortion and noise which theyinvariably add to signal.

Electronic amplifiers are used in radio& television transmitters and receivers,micro computer and guitar and otherinstrument amplifiers .


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example


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CLASS A AMPLIFIER

An amplifier is said to beclass A amplifier if the Q

point and the input signal areselected such that the outputsignal is obtained for a full

input cycle, so this is themost linear of all the classes.


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For this , position of the Q point isapproximately at the mid point of theload line.

For all the values of the input signal,the transistor remains in the activeregion and never enters into cut-off orsaturation region.


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These class A amplifiers run hot , asthe transistor in power amplifier are onand running at full power all the time.

Class A amplifier is the most inefficientof all power amplifier designs .

There are many factors for theinefficiency.


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FACTORS FORINEFFICINECY For every watt of output power , they

usually waste at least 4-5 watts as heat .

They are usually large and heavy.

They run very hot, needs lot of ventilation.

All this is due to amplifier constantlyoperating at full power.


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DISADVANTAGES

They are most accurate of allamplifiers available but at significant

cost to manufacture, because of tighttolerances and additional componentsfor cooling and heat regulation.


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AMPLIFIER In this amplifier , the positive and negativevalue of the signal are dealt with bydifferent parts of circuit.

The input signal has to be a lot larger, itneeds to be stepped up in a gain voltage ,so that signals will allow the outputtransistors to operate more efficiently.


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There have to be at least two outputdevices with this type of amplifier

This output stage employs two output

devices , so that each side amplifieseach half of the waveform.

Each output device is on for completelyone half of complete signal cycle.


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These amplifier run cooler than class Aamplifier, but the sound quality is notpure , as there is a lot of cross overdistortion.

This type of amplifier design, or topology,gives us the term PUSH-PULL, as onedevice pushes the signal, the other pullsthe signal.


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AMPLIFIER Class AB operation has some of the

best advantages of both class A andclass B built in.

In fact many class AB amplifier operatein class A at lower output levels, againgiving the best of both worlds.


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The output bias is set so that currentflows in specific output devices for morethan half cycle but less than the entirecycle.

There is enough current flowing througheach device to keep it in operating so theyrespond instantly to input voltagedemands.


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There are many implementations ofclass AB design .

A benefit is that the inherent non

linearity of class B designs is almosteliminated, while avoiding the heat-generating and wasteful inefficienciesof class A design.


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They are better termed switchingamplifiers because here the outputdevices are rapidly switched on and off

at least twice for each cycle. Depending on the switching frequency

they may be switched on or off millionsof times a second.


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Class D operation is theoretically 100%efficient , but in practice , they are closerto 80-90%.

Class D amplifier uses fixed frequency

signal having pulses that vary in widthbased on input signal amplitude.

The efficiency gain is at the cost of highfidelity.


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clasification of amplifiers

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