121B_1_EE121B_Slide04 - BJT2

121B_1_EE121B_Slide04 - BJT2 - EE 121B Principles of...

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Slide 4-1 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui EE 121B Principles of Semiconductor Device Design Bipolar Junction Transistors - II Professor Chi On Chui Electrical Engineering Department University of California, Los Angeles Email: chui@ee.ucla.edu Slide 4-2 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui Outline BJT Biasing Modes and Circuit Configurations Ebers-Moll Model
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Slide 4-3 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui BJT (NPN) Regions of Operation Under Bias V BC V BE Saturation Forward Active Cutoff Reverse Active p n p n n p p n p n n p p n p n n p p n p n n p C (n) B (p) E (n) C (n) B (p) E (n) C (n) B (p) E (n) C (n) B (p) E (n) Slide 4-4 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui C (n) B (p) E (n) BJT (NPN) Band Diagrams Under Various Bias V BC V BE Saturation Forward Active Cutoff Reverse Active C (n) B (p) E (n) C (n) B (p) E (n) C (n) B (p) E (n)
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Slide 4-5 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui Measurement of IV Characteristics n p n I E I C I B V BE V CB + - + - Common Base n p I E I C I B V CE V BE + - + - Common Emitter V CE I B I C + - V BE + - I E I B I C V BE - + I E + - V CB Slide 4-6 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui -0.5 0 0.5 1 1.5 2 2.5 00 . 511 . 522 . 5 Vce (Volts) Ic (mA) Ib = 10 μA Ib = 8 μA I C -V CE or Common Emitter Characteristic Our previous analysis already took I CB 0 into account () () () = = 1 exp 1 exp coth csch 2 1 kT qV C kT qV C y n y n L D Aq I I BE BC E C n n En E What is β of this BJT? Why isn’t I C constant with V CE ? V CE I B I C + - V BE + - I E = 1 exp 1 exp 4 3 kT qV C kT qV C I BE BC C + = 1 exp 1 exp 5 kT qV kT qV C I BE BC B
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Slide 4-7 © 2006 Marko Sokolich All Rights Reserved EE 121B – Chi On Chui -0.5 0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5 Vce (Volts) Ic (mA) Ib = 10 μA Ib = 8 μA I C -V CE or Common Emitter Characteristic Maintaining constant I B as V CE is reduced eventually leads to the BC junction being forward biased.
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121B_1_EE121B_Slide04 - BJT2 - EE 121B Principles of...

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