ch13 - Chapter 13 Output Stages and Power Amplifiers 13.1...

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Chapter 13 Output Stages and Power Amplifiers 13.1 General Considerations 13.2 Emitter Follower as Power Amplifier 13.3 Push-Pull Stage 13.4 Improved Push-Pull Stage 13.5 Large-Signal Considerations 13.6 Short Circuit Protection 13.7 Heat Dissipation 13.8 Efficiency 13.9 Power Amplifier Classes 1
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Why Power Amplifiers? Drive a load with high power. Cell phone needs 1W of power at the antenna. Audio system needs tens to hundreds Watts of power. Ordinary Voltage/Current amplifiers are not equipped for such applications 2 CH 13 Output Stages and Power Amplifiers
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Chapter Outline 3 CH 13 Output Stages and Power Amplifiers
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Power Amplifier Characteristics Experiences small load resistance. Delivers large current levels. Requires large voltage swings. Draws a large amount of power from supply. Dissipates a large amount of power, therefore gets “hot”. 4 CH 13 Output Stages and Power Amplifiers
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Power Amplifier Performance Metrics Linearity Power Efficiency Voltage Rating 5 CH 13 Output Stages and Power Amplifiers
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Emitter Follower Large-Signal Behavior I As V in increases V out also follows and Q 1 provides more current. 6 CH 13 Output Stages and Power Amplifiers
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Emitter Follower Large-Signal Behavior II However as V in decreases, V out also decreases, shutting off Q 1 and resulting in a constant V out . 7 CH 13 Output Stages and Power Amplifiers
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Example: Emitter Follower 1 1 ln 0.5 211 out in T out L S in out V V V I V R I V V V mV - + = = ≈ - ( 29 1 1 1 1 1 ln 0.01 390 C in T C L S C in I V V I I R I I I V mV = + - 8 CH 13 Output Stages and Power Amplifiers
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As Vin decreases the output waveform will be clipped, introducing nonlinearity in I/O characteristics. 9
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This note was uploaded on 04/05/2010 for the course EE EE taught by Professor Ee during the Spring '10 term at Korea Advanced Institute of Science and Technology.

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ch13 - Chapter 13 Output Stages and Power Amplifiers 13.1...

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