1. Spring 2007EE130 Lecture 23, Slide 1 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

2. Spring 2007EE130 Lecture 23, Slide 2 The base current consists of majority carriers supplied for 1.Recombination of injected minority carriers in the base 2.Injection of carriers into the emitter 3.Reverse saturation current in collector junction Reduces | I B | 4.Recombination in the base-emitter depletion region Base Current Components (Active Bias) EMITTER BASE COLLECTOR p-type n-typep-type

3. Spring 2007EE130 Lecture 23, Slide 3 Circuit Configurations Output Characteristics for Common-Emitter Configuration

4. Spring 2007EE130 Lecture 23, Slide 4 Modes of Operation Common-emitter output characteristics (I C vs. V CE ) ModeEmitter JunctionCollector Junction CUTOFFreverse bias Forward ACTIVEforward biasreverse bias* Reverse ACTIVEreverse bias*forward bias SATURATIONforward bias *or not strongly forward biased

5. Spring 2007EE130 Lecture 23, Slide 5 BJT Electrostatics Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctions

6. Spring 2007EE130 Lecture 23, Slide 6 Electrostatic potential, V(x) Electric field,  (x) Charge density,  (x)

7. Spring 2007EE130 Lecture 23, Slide 7 BJT Performance Parameters (PNP) Emitter Efficiency: –Decrease (5) relative to (1+2) to increase efficiency Base Transport Factor: –Decrease (1) relative to (2) to increase transport factor Common-Base d.c. Current Gain:

8. Spring 2007EE130 Lecture 23, Slide 8 Collector Current (PNP) 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 I CB0 is the collector current which flows when I E = 0 Common-Emitter d.c. Current Gain:

9. Spring 2007EE130 Lecture 23, Slide 9 Summary: BJT Fundamentals Notation & conventions: Electrostatics: –Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctions I E = I B + I C pnp BJTnpn BJT

10. Spring 2007EE130 Lecture 23, Slide 10 Performance parameters: –Emitter efficiency –Base transport factor –Common base d.c. current gain –Common emitter d.c. current gain

11. Spring 2007EE130 Lecture 23, Slide 11 Notation (PNP BJT) N E = N AE D E = D N  E =  n L E = L N n E0 = n p0 = n i 2 /N E N B = N DB D B = D P  B =  p L B = L P p B0 = p n0 = n i 2 /N B N C = N AC D C = D N  C =  n L C = L N n C0 = n p0 = n i 2 /N C

12. Spring 2007EE130 Lecture 23, Slide 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

13. Spring 2007EE130 Lecture 23, Slide 13 Emitter Region Formulation Diffusion equation: Boundary Conditions:

14. Spring 2007EE130 Lecture 23, Slide 14 Base Region Formulation Diffusion equation: Boundary Conditions:

15. Spring 2007EE130 Lecture 23, Slide 15 Collector Region Formulation Diffusion equation: Boundary Conditions: