CALVIN ENGR 332 - Chapter 9 (29 pages)

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Chapter 9



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Chapter 9

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Lecture Notes


Pages:
29
School:
Calvin College
Course:
Engr 332 - ANALOG CIRCUITS AND SYSTEMS DESIGN

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Chapter 9 Output Stages And Power Amplifiers Low Output Resistance no loss of gain Small Signal Not applicable Total Harmonic Distortion fraction of Efficiency Temperature Requirements Fig 9 1 Collector current waveforms for transistors operating in a class A b class B c class AB and d class C amplifier stages Class A Transfer Characteristics IE1 I iL The bias current I must ve greater the largest negative current value Otherwise Q cutts off The transfer characyteristic of the emitter follower for this figure is vO v I v BE1 Where vBE1 depends on the emitter current iE1 and thus on the load current iL If we neglect the relative small changes in vBE1 60mV for every factot of 10 change in iE the transfer curve results Fig 9 2 An emitter follower Q1 biased with a constant current I supplied by transistor Q2 Fig 9 3 Transfer characteristic of the emitter follower in Fig 9 2 This linear characteristic is obtained by neglecting the change in vBE1 with iL The maximum positive output is determined by the saturation of Q1 In the negative direction the limit of the linear region is determined either by Q1 turning off or by Q2 saturating depending on the values of I and RL Class A Transfer Characteristics From figure 9 3 we can see that v omax VCC VCE1sat In the negative direction the limite of the linear region is determined either by Q1 turning off v Omin I RL or by Q2 saturating v Omin VCC VCE2sat Depending on the values of I and RL The absolutely lowest output voltage is that given by the previous equation and is achieved provided that the bias current I is greater than the magnitude of the corresponding load current I VCC VCE2sat RL Class A Transfer Characteristics Exercises D9 1 and D9 2 Class A Signal Waveforms 1 vo t 2 vcE1 t 0 1 0 5 10 1 0 0 t 1 1 0 10 t 2 ic1 t 5 pD1 t 0 5 0 5 t 10 0 0 5 t 10 Class A Power Dissipation P VCC I Largest Power Dissipation When vo 0 Q1 must be able to withsatnd a continuous dissipation of VCC I The power dissipation of Q1 depends on the



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