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Chptr 1 - Basic BJT Amplifier(II)

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Basic BJT Amplifier
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  ANALOG ELECTRONIC CIRCUITS 1 EKT 204 Basic BJT Amplifiers (Part 2) 1   The basic common-emitter circuit used in previous analysis causes a serious defect  :  If BJT with V BE =0.7 V is used, I B =9.5 μA & I C =0.95 mA  But, if new BJT with V BE =0.6 V is used, I B =26 μA & BJT goes into saturation; which is not acceptable   Previous circuit is not practical  So, the emitter resistor  is included: Q-point is stabilized against variations in β, as will the voltage gain, A V  Assumptions  C C  acts as a short circuit  Early voltage = ∞ ==> r  o  neglected due to open circuit Basic Common-Emitter Amplifier 2  Common-Emitter Amplifier with Emitter Resistor CE amplifier with emitter resistor Small-signal equivalent circuit (with current gain parameter, β ) inside transistor 3  Common-Emitter Amplifier with Emitter Resistor  ac output voltage  Input voltage loop  Input resistance, R ib  Input resistance to amplifier, R i  Voltage divider equation of V in to V s Remember  : Assume V A  is infinite ,    r  o  is neglected    C bo  R I V         E bbbin  R I  I r  I V            E binib  Rr  I V  R        1 ibi  R R R R 21   sS iiin  V  R R RV       4
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