lec23 - count more noise susceptibility I B ~10 I X...

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EE 3113 INTRODUCTION TO RF CIRCUIT DESIGN Lecture Notes for A-term 2003 LECTURE 23 Prof. R. Ludwig Department of Electrical and Computer Engineering Worcester Polytechnic Institute Worcester, MA 01609 copyright © 2003, R. Ludwig Copyright, 1998 © R. Ludwig
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EE3113_L23 2 Biasing networks Biasing networks are needed to set appropriate operating conditions for active devices There are two types: Passive biasing (or self-biasing) – resistive networks – drawback: poor temperature stability Active biasing – additional active components (thermally coupled) – drawback: complexity, added power consumption
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EE3113_L23 3 Passive biasing V CC R 1 RFC R 2 I B I 1 RF OUT RF IN I C RFC C B C B Simple two element biasing blocking capacitors C B and RFCs to isolate RF path Very sensitive to collector current variations
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EE3113_L23 4 Passive biasing V CC R 1 RFC R 2 I B RF OUT RF IN I C RFC R 3 R 4 I X V X C B C B Voltage divider to stabilize V BE Freedom to choose suitable voltage and current settings (V x , I x ) Higher component
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Unformatted text preview: count, more noise susceptibility I B ~10% I X EE3113_L23 5 Active biasing V CC RFC R C 1 RF OUT RF IN RFC V C 1 Q 2 Q 1 I 1 I B 1 I B 1 I C 2 R B 1 R B 2 R E 1 R C 2 I C 1 C B C B • Base current of RF BJT (Q 2 ) is provided by low-frequency BJT Q 1 • Excellent temperature stability (shared heat sink) • high component count, more complex layout EE3113_L23 6 Active biasing in common base V CC RFC R C 1 RF OUT RF IN RFC V C 1 Q 2 Q 1 I 1 I B 1 I B 1 I C 2 R B 1 R B 2 R E 1 R C 2 I C 1 C B C B RFC V CC RFC R C 1 RFC Q 2 Q 1 R B 1 R B 2 R E 1 R C 2 C B C B RFC V CC RFC R C 1 RF OUT RF IN RFC Q 2 Q 1 R B 1 R B 2 R E 1 R C 2 C B C B RFC DC path RF path EE3113_L23 7 FET biasing V D V G C B RFC C B RFC RF OUT RF IN V D V S C B C B RFC RF OUT RF IN RFC RFC V D R S C B C B RFC RF OUT RF IN RFC Bi-polar power supply Uni-polar power supply V G <0 and V D >0...
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