UNIVERSAL COLLEGE OF ENGG. AND TECH.

BIPOLAR JUNCTIONBIPOLAR JUNCTION TRANSISTORS TRANSISTORS

EE314

The transistor was probably the most important invention of the 20th Century, and the story behind the invention is one of clashing egos and top secret research. 

First - BJTs

Reference:Bell Labs MuseumB. G. Streetman & S. Banerjee ‘Solid State Electronic Devices’, Prentice Hall 1999.

Point-Contact Transistor – first transistor ever made

First Bipolar Junction TransistorsW. Shockley invented the p-n junction transistorThe physically relevant region is moved to the bulk of the material

Understanding of BJT

force – voltage/currentwater flow – current - amplification

Basic models of BJT

Diode

Diode

Diode

Diode

npn transistor

pnp transistor

Basic models of BJT

BJTs – Basic ConfigurationsFluid Flow AnalogyDifference between FET (field effect transistor) and BJTTechnology of BJTs

pnp BJT npn BJT

BJTs – Practical Aspects

Heat sink

BJTs – Testing

BJTs – Testing

RECALL P-N JUNCTION

P NWVappl > 0

-+

N PWVappl < 0

-+

Forward bias, + on P, - on N (Shrink W, Vbi)

Allow holes to jump over barrier into N region as minority carriers

Reverse bias, + on N, - on P (Expand W, Vbi)

Remove holes and electrons awayfrom depletion region

I

V

I

V

BIPOLAR JUNCTION TRANSISTORS: BASICS

+

- +

-

IE IBIC

IE = IB + IC ………(KCL)

VEC = VEB + VBC ……… (KVL)

BJT CONFIGURATIONS

EC

E 6

63

GAIN CONFIG

BIPOLAR JUNCTION TRANSISTORS: BASICS

EC

E 6

63

Bias Mode E-B Junction C-B Junction

Saturation Forward Forward

Active Forward Reverse

Inverted Reverse Forward

Cutoff Reverse Reverse

BJT FABRICATION

EC

E 6

63

PNP TRANSISTOR AMPLIFIER ACTION

EC

E 6

63

IN (small)

OUT (large)

Clearly this works in common emitterconfiguration

COMMON BASE DC CURRENT GAIN - PNP

Common Base – Active Bias mode:

EC

E 6

63

IC = DCIE + ICB0

ICp = TIEp = TIE

IC = TIE + ICn

DC = T

COMMON EMITTER DC CURRENT GAIN - PNP

Common Emitter – Active Bias mode:

EC

E 6

63

IE = DCIB + ICE0

DC = DC /(1-DC)

IE

IBIC

IC = DCIE + ICB0

= DC(IC + IB) + ICB0

IC = DCIB + ICB0

1-DC

GAIN !!

COMMON EMITTER DC CURRENT GAIN - PNP

EC

E 6

63

T

Tdc

1

Thin base will make T 1Highly doped P region will make 1

THAN

K YO

U