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ContentsClamp Diodes and the EF-VAS.184The Benefits of the EF-VAS..184The Cascode VAS...............185How the Cascode VAS Works.187A Brief History of the Cascode VAS...188The Benefits of the Cascode VAS.....188The VAS Buffer.............189VAS Distortion Due to Output Stage Loading.191Some More VAS Variations......194VAS Operating Conditions........195VAS Current Limiting.........196The Class-AB VAS and Further Developments.197Manipulating Open-loop Bandwidth.197Conclusions..........199References ......200Chapter 8 The Push-pull Voltage-Amplifier Stage..201The Push-pull VAS............202Single Input Stages with a Push-pull VAS...202The Hitachi Push-pull VAS.......202The Hitachi Push-pull VAS:Heating and Drift.205The Hitachi Circuit:AC Gain............205The Hitachi push-pull VAS:distortion......206The Hitachi Push-pull VAS:Asymmetrical Clipping.207The Lender Push-pull VAS................207The Lender Push-pull VAS:Heating and Drift.209Single Input Stages with a One-input Push-pull VAS..210The Series Input Stage Push-pull VAS..........213Single-input Push-pull VAS Circuits:Conclusions......215The Double Input Stage Push-pull Simple VAS..........216The Double Input Stage Push-pull Simple VAS:Open-loop Gain..217The Double Input Stage Push-pull Simple VAS:Distortion.219The Double Input Stage Push-pull Simple VAS:NoiseThe Double Input Stage Push-pull Simple VAS:PSRR.221A Brief History of the Double Input Stage Push-pull VAS..221The Double Input Stage Push-pull EF-VAS...........222The Double Input Stage Push-pull EF-VAS:Open-loop Gain..223The Double Input Stage Push-pull EF-VAS:Distortion......223The Double Input Stage Push-pull EF-VAS:Slew-rate....224ContentsXVThe Double Input Stage with Mirrors and Push-pull Simple VAS.....224The Double Input Stage Push-pull VAS:Conclusions....226A More Advanced Push-pull VAS.227The Folded-cascode VAS.......The Push-pull VAS:Final ConclusionsReferences ..........229Chapter 9 The Output Stage.....231.232The Distortions of the Output............234Harmonic Generation by Crossover Distortion.234Comparing Output Stages..........235The Emitter-follower Output ..........235Multiple Output Devices:EF Output..237.237Multiple Output Devices:CFP Output.239Output Stages with Gain ..............241Quasi-complementary Outputs........243Triple-based Output Configurations.245Triple EF Output Stages.....249Quadruple Output Stages....250Series Output Stages ......251Selecting an Output Stage.253Output Stage Conclusions.253.254Chapter 10 Output Stage Distortions......Output Stage Distortions and their Mechanisms.256Large-signal Distortion (Distortion 3a)..........256The Load-Invariant Concept......259The LSN Mechanism........259LSN with Doubled Output Devices....260LSN with Better Output Devices...260LSN with Feedforward Diodes....262LSN with Triple Output StagesLoads below42...·.263Better 8 Performance.....264A Practical Load-Invariant Design.264xviContentsMore on Multiple Output Devices.266Load Invariance:Summary..269Crossover Distortion(Distortion 3b)....269Output Stage Quiescent Conditions...An Experiment on Crossover Distortion.277Vq as the Critical Quiescent Parameter.279Switching Distortion(Distortion 3c).......280Thermal Distortion............281Thermal Distortion in a Power Amp IC.....282Closing the Loop:Distortion in Complete Amplifiers.283.286.287Distortion Four:VAS Loading Distortion...288Distortion Five:Rail Decoupling Distortion.288Distortion Six:Induction Distortion ......290Distortion Seven:NFB Takeoff Point Distortion.295Distortion Eight:Capacitor Distortion......297Distortion Nine:Magnetic Distortion .....300Distortion Ten:Input Current Distortion....302Distortion Eleven:Premature Overload Protection.302Design Example:a 50 W Class-B Amplifier.....302References ....308Chapter 12 Closely Observed Amplifiers:Design ExamplesAmplifier 1:EF-VAS,CFP Output Stage,Miller Compensation......310Amplifier 2:Simple VAS,CFP Output Stage,Miller Compensation.316Amplifier 3:EF-VAS,CFP Output Stage,Inclusive Compensation...319Amplifier 4:EF-VAS,CFP Output Stage,Miller Compensation....323Amplifier 5:EF-VAS,CFP Output Stage,Inclusive Compensation..323Conclusions.....326References ............326Chapter 13 Compensation and StabilityCompensation and Stability.....328Dominant Pole Compensation..329Maximal Negative Feedback..329ContentsDominant Pole Miller Compensation.......331Dominant Pole Miller Compensation at High Gains.331Dominant Pole Shunt Compensation........333Output-inclusive Compensation............334The Problems of Output Inclusion..........334Input-inclusive Compensation................334Stable Output-inclusive Compensation:The History..336Stable Output-inclusive Compensation:Implementation..336Experimenting with Output-inclusive Compensation..340Ultra-low Distortion Performance Comparisons.....341.341Factors Affecting the Two-pole Loop-gain Response.....343Effect of Two-pole Compensation on the Closed-loop Gain..345Eliminating the Two-pole Midband Loop-gain Peak.....347Two-pole Compensation and PSRR................348Two-pole Compensation:Summary .........348Combining Two-pole and Output-inclusive Compensation.348.349Stability and VAS-collector-to-ground Capacitance.349.349Nested Differentiating Feedback Loops..........351.353Chapter 14 Output Networks and Load Effects..355Output Networks..................356Amplifier Output Impedance .....356Minimising Amplifier Output Impedance.357.358Output Inductors......................358Designing the Output Inductor:Single-layer Coils.364Designing the Output Inductor:Multi-layer Coils.366Crosstalk in Amplifier Output Inductors .......367Coil Crosstalk Conclusions........369Coil Placement Issues..............370Cable Impedance Effects............370Reactive Loads and Speaker Simulation.371.373Modelling Real Loudspeaker Loading.373Loudspeaker Loads and Output Stages..375