Lecture #23

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# Lecture #23 - PowerPoint PPT Presentation

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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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

Lecture #23

EE130 Lecture 23, Slide 1

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

Circuit Configurations

Output Characteristics for Common-Emitter Configuration

EE130 Lecture 23, Slide 3

Modes of Operation

Common-emitter output characteristics

(ICvs.VCE)

EE130 Lecture 23, Slide 4

*or not strongly forward biased

BJT Electrostatics
• Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctions

EE130 Lecture 23, Slide 5

Electrostatic potential, V(x)

Electric field, e(x)

Charge density, r(x)

EE130 Lecture 23, Slide 6

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

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

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

Performance parameters:
• Emitter efficiency
• Base transport factor
• Common base d.c. current gain
• Common emitter d.c. current gain

EE130 Lecture 23, Slide 10

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

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

Diffusion equation:

Boundary Conditions:

Emitter Region Formulation

EE130 Lecture 23, Slide 13

Diffusion equation:

Boundary Conditions:

Base Region Formulation

EE130 Lecture 23, Slide 14

Diffusion equation:

Boundary Conditions:

Collector Region Formulation

EE130 Lecture 23, Slide 15