121B_1_EE121B_Slide06 - BJT4

121B_1_EE121B_Slide06 - BJT4 - EE 121B Principles of...

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Slide 6-1 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui EE 121B Principles of Semiconductor Device Design Bipolar Junction Transistors - IV Professor Chi On Chui Electrical Engineering Department University of California, Los Angeles Email: [email protected] Slide 6-2 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui Outline BJT Small Signal Equivalent Circuits Charge Control Analysis Base transit time Diffusion capacitance AC intrinsic small signal models Frequency Response Cutoff frequency Junction capacitance Switching
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Slide 6-3 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui Simple BJT Models Small Signal Model of Common Base Configuration Model only valid for slowly varying small signal + - + - V in V out i in i out R in g m V in R L V BE R L V CB + - v s n x’=0 x’=W’ Neutral Base = 1 ) 0 ( 0 kT eV p E BE e n n n ( ) s BE v V n + ( ) s BE v V n + - v out Slide 6-4 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui Common Base Small Signal Model V BE R L V CB + - v s I E I C () kT V q I y n L D qA I BE E E n n E ~ exp coth 0 kT V q I y n L D qA I BE C E n n C ~ exp csch 0 BE E BE E in kT V q kT q I V d dI r = = = ~ exp ~ 1 0 BE C BE C m kT V q kT q I V d dI g = = = ~ exp ~ 0 + - + - v in v out i in i out r in g m v in R L s BE BE v V V ~ ~ +
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Slide 6-5 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui Common Base Small Signal Model Now that we have basic input and output elements we can calculate voltage and power gain of a common base amplifier + - + - v in v out i in i out V T /I E R L T L C in L in T C in L out in out V R I v R v V I v R i v v = = = = in T C v V I T L E o o in in out out V R I v i v i α = = Voltage Gain Power Gain E T E r V I 1 Slide 6-6 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui Simple BJT Models: CE input resistance Small Signal Model of Common Emitter Configuration + - + - v in v out i in i out r in g m v in R L V CC V CE I B I C + - V BE + - R L () BE E o E o BE B in kT V q kT q I I V d dI r = = = = ~ exp 1 1 ~ 1 0 E o T in I V r = = 1 In a good transistor the CE mode has much higher input resistance than the CB mode BE C m V d dI g = = ~ The transconductance is the same
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Slide 6-7 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui Simple BJT Models: Voltage and Power Gain + - + - v in v out i in i out R L in T C v V I () o E r α 1 ( ) L m in L in m in L out in out R g v R v g v R i v v = = = ( ) L m in L m in in in out out R g i R g i v i v i β = = Voltage Gain Power Gain = = = E o T T E o in in in m in out I V V I r v v g i i 1 Current Gain Slide 6-8 © 2006 Marko Sokolich
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This note was uploaded on 11/11/2010 for the course EE 121b taught by Professor Bjt-gamma during the Winter '08 term at UCLA.

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121B_1_EE121B_Slide06 - BJT4 - EE 121B Principles of...

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