Electronics-I Lecture 26

# Electronics-I Lecture 26 - BiasingtheBJT VBB=VCC[R2(R1 R2...

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Lecture 26 Electronics I 1 Bias using a single Power supply V BB  = V CC  [R 2 /(R 1  + R 2 )] R B  = R 1 R 2 /(R 1 + R 2 ) V BB  = I B R B  + V BE  +   I R E I E  = (V BB  – V BE )/[R +R B /( β +1)] To make I E  insensitive to  temperature, we design circuit to  satisfy    V BB  >> V BE To make I E  insensitive to  β  , we  design circuit to satisfy  R E  >> R B /( β +1) Biasing the BJT

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Lecture 26 Electronics I 2 Biasing the BJT I E  = (V BB  – V BE ) /[R +R B /( β +1)] I E  insensitive to temperature       if   V BB  >> V BE Limit on V BB As V BB  increases  I C R + V CB  (or V CE )   decreases I C R should be large to allow for large  signal swing before cut-off and high  gain (voltage gain = – I C R C  /V T ) V CB  (or V CE ) should be large to allow   large signal swing before saturation conflicting requirements Design rule V BB   1/3V CC V CB  (or V CE  1/3V
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