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Amplifier

Amplifier

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Audio amplifier prj Audio amplifier prj Document Transcript

  • Audio Amplifier B.E. PROJECT REPORT EDA (12817) Prepared by Salman Khaliq Bajwa (3746) Hassam Haq ( ) Waqar Khokhar( ) Advisor Asstt. Professor, Amir Hasan Khan College of EngineeringPAF-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 ofaccomplishments; 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 mercifulWe are grateful to our project advisor Mr. Amir Hasan Khan, for enlightening us with hisprecious knowledge and vast experience to benefit us in the future. We also like to thank to ourteachers 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 usnot only financially but with integrity too and support us in all our hardships. Finally our sincerethanks to our institute PAF-KIET, College of Engineering, for providing us the opportunity togave 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 andTechnology may make great progress in Pakistan and Pakistan may become a part of thedeveloped 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 amplifierand 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; afluidic 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 frequencyrange they cover, or the active devices used. Ideally an amplifier increases the power of a signalwithout otherwise altering it; practical amplifiers have finite distortion and noise which theyinvariably add to the signal.The quality of an amplifier can be characterized by a number of specifications, listed below.1. GainThe gain of an amplifier is the ratio of output to input power or amplitude, and is usuallymeasured in decibels. (When measured in decibels it is logarithmically related to the powerratio: G(dB)=10 log(Pout /(Pin)). RF amplifiers are often specified in terms of the maximum powergain obtainable, while the voltage gain of audio amplifiers and instrumentation amplifiers willbe more often specified (since the amplifiers input impedance will often be much higher thanthe source impedance, and the load impedance higher than the amplifiers output impedance).For example, an audio amplifier with a gain given as 20 dB will have a voltage gain of ten (but apower gain of 100 would only occur in the event the input and output impedances wereidentical).
  • If two equivalent amplifiers are being compared, the amplifier with higher gain settings wouldbe more sensitive as it would take less input signal to produce a given amount of power.2. BandwidthThe bandwidth of an amplifier is the range of frequencies for which the amplifier gives"satisfactory performance". The definition of "satisfactory performance" may be different fordifferent 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. frequencycurve. Therefore bandwidth can be defined as the difference between the lower and upper halfpower points. This is therefore also known as the −3 dB bandwidth. Bandwidths (otherwisecalled "frequency responses") for other response tolerances are sometimes quoted (−1 dB, −6dB etc.) or "plus or minus 1dB" (roughly the sound level difference people usually can detect).3. EfficiencyEfficiency is a measure of how much of the power source is usefully applied to the amplifiersoutput. Class A amplifiers are very inefficient, in the range of 10–20% with a max efficiency of25% for direct coupling of the output. Inductive coupling of the output can raise their efficiencyto a maximum of 50%.Drain efficiency is the ratio of output RF power to input DC power when primary input DCpower has been fed to the drain of an FET. Based on this definition, the drain efficiency cannotexceed 25% for a class A amplifier that is supplied drain bias current through resistors (becauseRF signal has its zero level at about 50% of the input DC). Manufacturers specify much higherdrain efficiencies, and designers are able to obtain higher efficiencies by providing current tothe drain of the transistor through an inductor or a transformer winding. In this case the RFzero 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 withinlimits.When the signal drive to the amplifier is increased, the output also increases until a point isreached where some part of the amplifier becomes saturated and cannot produce any moreoutput; this is called clipping, and results in distortion.In most amplifiers a reduction in gain takes place before hard clipping occurs; the result is acompression effect, which (if the amplifier is an audio amplifier) sounds much less unpleasantto the ear. For these amplifiers, the 1 dB compression point is defined as the input power (oroutput power) where the gain is 1 dB less than the small signal gain. Sometimes thisnonlinearity is deliberately designed in to reduce the audible unpleasantness of hard clippingunder overload.Ill effects of nonlinearity can be reduced with negative feedback.5. NoiseThis is a measure of how much noise is introduced in the amplification process. Noise is anundesirable but inevitable product of the electronic devices and components; also, much noiseresults from intentional economies of manufacture and design time. The metric for noiseperformance of a circuit is noise figure or noise factor. Noise figure is a comparison betweenthe output signal to noise ratio and the thermal noise of the input signal.6. Slew rateSlew rate is the maximum rate of change of the output, usually quoted in volts per second (ormicrosecond). Many amplifiers are ultimately slew rate limited (typically by the impedance of adrive current having to overcome capacitive effects at some point in the circuit), whichsometimes limits the full power bandwidth to frequencies well below the amplifiers small-signal frequency response.7. Stability
  • Stability is an issue in all amplifiers with feedback, whether that feedback is added intentionallyor 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 amplifiersstability can be quantified by a so-called stability factor. There are several different stabilityfactors, such as the Stern stability factor and the Linvil stability factor, which specify a conditionthat 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 (signalscomposed primarily of frequencies between 20 - 20 000 Hz, the human range of hearing) to alevel suitable for driving loudspeakers and is the final stage in a typical audio playback chain.Circuit:
  • Schematic: