Audio Amplifier

B.E. PROJECT REPORT

EDA (12817)

Prepared by

Salman Khaliq Bajwa (3746)Hassam Haq ( )

Waqar Khokhar( )

AdvisorAsstt. Professor, Amir Hasan Khan

College of Engineering

PAF-Karachi Institute of Economics & Technology

Karachi

DEDICATION

This report is dedicated to

My Parents, Teachers & Friends,

Whose love, affection and support helped me in bringing my work to this level of

accomplishments; I am also thankful to them for their unconditional support and encouragement

to pursue my interests, even when the interest went beyond the boundaries of field and scope.

Without their support and kindness this work would not have been possible.

ACKNOWLEDEMENT

Praise to Allah the most beneficent and the most merciful

We are grateful to our project advisor Mr. Amir Hasan Khan, for enlightening us with his

precious knowledge and vast experience to benefit us in the future. We also like to thank to our

teachers and lab assistants for their assistance and support.

We would also thank with all gratitude and depth of our hearts to our parents who helped us

not only financially but with integrity too and support us in all our hardships. Finally our sincere

thanks to our institute PAF-KIET, College of Engineering, for providing us the opportunity to

gave us the strength to undertake this research.

Special thanks to all our fellows and friends who lend us a hand throughout this project.

We pray this effort may prove to be the beginning of new era, a era in which Science and

Technology may make great progress in Pakistan and Pakistan may become a part of the

developed nations.

Thank you.

Objective:

The main objective of this is to understand the working of amplifiers.

Purpose:

The purpose of this project is to understand the need and working of amplifiers.

Description:

Before we go into the depth of our project, we first need to understand what is an amplifier

and why do we need it?

An amplifier is a device for increasing the power of a signal by use of an external energy source.

In an electronic amplifier, the input "signal" is usually a voltage or a current. Other types exist; a

fluidic amplifier increases the power of signals represented as flow of as or liquid, for example.

Amplifiers may be classified in a variety of ways depending on their application, the frequency

range they cover, or the active devices used. Ideally an amplifier increases the power of a signal

without otherwise altering it; practical amplifiers have finite distortion and noise which they

invariably add to the signal.

The quality of an amplifier can be characterized by a number of specifications, listed below.

1. Gain

The gain of an amplifier is the ratio of output to input power or amplitude, and is usually

measured in decibels. (When measured in decibels it is logarithmically related to the power

ratio: G(dB)=10 log(Pout /(Pin)). RF amplifiers are often specified in terms of the maximum power

gain obtainable, while the voltage gain of audio amplifiers and instrumentation amplifiers will

be more often specified (since the amplifier's input impedance will often be much higher than

the source impedance, and the load impedance higher than the amplifier's output impedance).

For example, an audio amplifier with a gain given as 20 dB will have a voltage gain of ten (but a

power gain of 100 would only occur in the event the input and output impedances were

identical).

If two equivalent amplifiers are being compared, the amplifier with higher gain settings would

be more sensitive as it would take less input signal to produce a given amount of power.

2. Bandwidth

The bandwidth of an amplifier is the range of frequencies for which the amplifier gives

"satisfactory performance". The definition of "satisfactory performance" may be different for

different applications. However, a common and well-accepted metric is the half power points

(i.e. frequency where the power goes down by half its peak value) on the output vs. frequency

curve. Therefore bandwidth can be defined as the difference between the lower and upper half

power points. This is therefore also known as the −3 dB bandwidth. Bandwidths (otherwise

called "frequency responses") for other response tolerances are sometimes quoted (−1 dB, −6

dB etc.) or "plus or minus 1dB" (roughly the sound level difference people usually can detect).

3. Efficiency

Efficiency is a measure of how much of the power source is usefully applied to the amplifier's

output. Class A amplifiers are very inefficient, in the range of 10–20% with a max efficiency of

25% for direct coupling of the output. Inductive coupling of the output can raise their efficiency

to a maximum of 50%.

Drain efficiency is the ratio of output RF power to input DC power when primary input DC

power has been fed to the drain of an FET. Based on this definition, the drain efficiency cannot

exceed 25% for a class A amplifier that is supplied drain bias current through resistors (because

RF signal has its zero level at about 50% of the input DC). Manufacturers specify much higher

drain efficiencies, and designers are able to obtain higher efficiencies by providing current to

the drain of the transistor through an inductor or a transformer winding. In this case the RF

zero level is near the DC rail and will swing both above and below the rail during operation.

While the voltage level is above the DC rail current is supplied by the inductor.

4. Linearity

An ideal amplifier would be a totally linear device, but real amplifiers are only linear within

limits.

When the signal drive to the amplifier is increased, the output also increases until a point is

reached where some part of the amplifier becomes saturated and cannot produce any more

output; this is called clipping, and results in distortion.

In most amplifiers a reduction in gain takes place before hard clipping occurs; the result is a

compression effect, which (if the amplifier is an audio amplifier) sounds much less unpleasant to

the ear. For these amplifiers, the 1 dB compression point is defined as the input power (or

output power) where the gain is 1 dB less than the small signal gain. Sometimes this

nonlinearity is deliberately designed in to reduce the audible unpleasantness of hard clipping

under overload.

Ill effects of nonlinearity can be reduced with negative feedback.

5. Noise

This is a measure of how much noise is introduced in the amplification process. Noise is an

undesirable but inevitable product of the electronic devices and components; also, much noise

results from intentional economies of manufacture and design time. The metric for noise

performance of a circuit is noise figure or noise factor. Noise figure is a comparison between

the output signal to noise ratio and the thermal noise of the input signal.

6. Slew rate

Slew rate is the maximum rate of change of the output, usually quoted in volts per second (or

microsecond). Many amplifiers are ultimately slew rate limited (typically by the impedance of a

drive current having to overcome capacitive effects at some point in the circuit), which

sometimes limits the full power bandwidth to frequencies well below the amplifier's small-

signal frequency response.

7. Stability

Stability is an issue in all amplifiers with feedback, whether that feedback is added intentionally

or results unintentionally. It is especially an issue when applied over multiple amplifying stages.

Stability is a major concern in RF and microwave amplifiers. The degree of an amplifier's

stability can be quantified by a so-called stability factor. There are several different stability

factors, such as the Stern stability factor and the Linvil stability factor, which specify a condition

that must be met for the absolute stability of an amplifier in terms of its two-port parameters.

Audio Amplifier:

An audio amplifier is an electronic amplifier that amplifies low-power audio signals (signals

composed primarily of frequencies between 20 - 20 000 Hz, the human range of hearing) to a

level suitable for driving loudspeakers and is the final stage in a typical audio playback chain.

Circuit:

Schematic: