Electronics-I Lecture 27

Electronics-I Lecture 27 - feedbackresistor VCC=IERC IBRB...

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Lecture 27 Electronics I 1 Biasing using Collector-to-Base  feedback resistor Biasing for CE amplifiers V CC  = I E R C  + I B R B  + V BE   I E  insensitive to  β  if  R C  >> R B /( β +1) R B  determines the  allowable swing at C V CB  = I B R =   R B I E /   ( β +1) 1 R R V V I B C BE CC E + β + - =
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Lecture 27 Electronics I 2 Biasing using a current source R E  is replaced by a  constant current source I is independent of values  β   and R B R B  can be increased to  provide high input resistance Bias stability is not affected
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Lecture 27 Electronics I 3 Biasing using a current source Q 1  & Q 2  are matched pairs Q 1  connected as a diode Assuming high  β  neglecting  base currents I REF   = [V CC  – V BE  – (– V EE )]/R Identical transistors have same  V BE   so I = I REF Current I remains constant if  Q2 remains in active region Possible if collector voltage                  V > – V EE  + V BE Also known as Current Mirror
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