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Lecture #23

QUIZ #3 Results (undergraduate scores only, N = 39) Mean = 22.1; Median = 22; Std. Dev. = 1.995 High = 25; Low = 18 OUTLINE The Bipolar Junction Transistor Fundamentals Ideal Transistor Analysis Reading: Chapter 10, 11.1. Lecture #23. Base Current Components (Active Bias).

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Lecture #23

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  1. QUIZ #3 Results (undergraduate scores only, N = 39) Mean = 22.1; Median = 22; Std. Dev. = 1.995 High = 25; Low = 18 OUTLINE The Bipolar Junction Transistor Fundamentals Ideal Transistor Analysis Reading: Chapter 10, 11.1 Lecture #23 EE130 Lecture 23, Slide 1

  2. Base Current Components (Active Bias) The base current consists of majority carriers supplied for • Recombination of injected minority carriers in the base • Injection of carriers into the emitter • Reverse saturation current in collector junction • Reduces | IB | • Recombination in the base-emitter depletion region EMITTER COLLECTOR BASE n-type p-type p-type EE130 Lecture 23, Slide 2

  3. Circuit Configurations Output Characteristics for Common-Emitter Configuration EE130 Lecture 23, Slide 3

  4. Modes of Operation Common-emitter output characteristics (ICvs.VCE) EE130 Lecture 23, Slide 4 *or not strongly forward biased

  5. BJT Electrostatics • Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctions EE130 Lecture 23, Slide 5

  6. Electrostatic potential, V(x) Electric field, e(x) Charge density, r(x) EE130 Lecture 23, Slide 6

  7. Emitter Efficiency: Decrease (5) relative to (1+2) to increase efficiency BJT Performance Parameters (PNP) • Base Transport Factor: • Decrease (1) relative to (2) to increase transport factor • Common-Base d.c. Current Gain: EE130 Lecture 23, Slide 7

  8. The collector current is comprised of Holes injected from emitter, which do not recombine in the base  (2) Reverse saturation current of collector junction  (3) where ICB0 is the collector current which flows when IE = 0 Collector Current (PNP) • Common-Emitter d.c. Current Gain: EE130 Lecture 23, Slide 8

  9. Summary: BJT Fundamentals IE = IB + IC • Notation & conventions: • Electrostatics: • Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctions pnp BJT npn BJT EE130 Lecture 23, Slide 9

  10. Performance parameters: • Emitter efficiency • Base transport factor • Common base d.c. current gain • Common emitter d.c. current gain EE130 Lecture 23, Slide 10

  11. Notation (PNP BJT) NE = NAE DE = DN tE = tn LE = LN nE0 = np0 = ni2/NE NB = NDB DB = DP tB = tp LB = LP pB0 = pn0 = ni2/NB NC = NAC DC = DN tC = tn LC = LN nC0 = np0 = ni2/NC EE130 Lecture 23, Slide 11

  12. Ideal Transistor Analysis • Solve the minority-carrier diffusion equation in each quasi-neutral region to obtain excess minority-carrier profiles • different set of boundary conditions for each region • Evaluate minority-carrier diffusion currents at edges of depletion regions • Add hole & electron components together  terminal currents EE130 Lecture 23, Slide 12

  13. Diffusion equation: Boundary Conditions: Emitter Region Formulation EE130 Lecture 23, Slide 13

  14. Diffusion equation: Boundary Conditions: Base Region Formulation EE130 Lecture 23, Slide 14

  15. Diffusion equation: Boundary Conditions: Collector Region Formulation EE130 Lecture 23, Slide 15

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