Ece137a Notes Set 1

8/10/2019 Ece137a Notes Set 1

1/23

class notes, ECE137A, rodwell, University of California, Santa Barbara, copyrighted page 1

ECE137A Notes Set 1:Bipolar Transistors Characteristics

Mark Rodwell

University of California, Santa Barbara

[email protected]


2/23


Why study bipolar transistors ?

sheets.dataforneededisninformatiolimitedonlythatsuchare

iticscharacterstheirandavailable,widelyarebjtsdiscreteQualityMOSFETs.

usingprojectslabrysatisfactodesigntodifficultverythereforeisItn.informatio

designlimitedverygivesheetsdatatheavailable,aretheyasInsofarprojects.lab

for theneededformdiscretetheinobtaintodifficultveryalsoaremosfetsQuality

ICs.ionscommunicatopticalandfrequency

radioinwidelyusedand,convertersdigital-analogresolutionhighfasterinused

stillhoweverarestransistorBipolarICs.analogof95%probablyandICs,digitalindominant99.999%beingcommon,moremuchnowareMOSFETs


3/23


Terminal Characteristics: NPN bipolar transistor

! "

Coulomb)10(6022.1chargeelectron

retemperatuabsolute

inJoule/Kelv)10(38.1constantsBoltzmann'voltage"thermal"thecalledis

re)temperatu(roomKelvin300atmV8.25/

where/

1

biased)reversejunctionbase(collector0for

19

23

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#

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q

T

kV

qkTV

II

eII

V

T

T

Eb

VV

esE

cb

Tbe

&

Vbe

Vcb

Ic

Ib

Ie


4/23


Terminal Characteristics: PNP bipolar transistor

reversed.simplyarepolaritiesvoltage

anddirectionscurrent,ansistorbipolar trPNPFor the

Vbc

Veb

Ic

Ib

Ie

! "

/

1

then),0(

biasedreverseisjunctionbasecollectortheifAgain,

/

&Eb

VV

esE

bc

II

eII

V

Teb

$

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%


5/23class notes, ECE137A, rodwell, University of California, Santa Barbara, copyrighted page 5

Voltage Polarities and Notation

normally.operatedisrtransistothewhenPOSITIVE

areuestheir valsodefinedareriablescurrent vaandvoltageDC

possible,wheneverFurther,a voltage.definingleany variabwith

associateddiagramcircuittheonsigns-anddrawingbyvoltages

ofpolaritythedefiningrecommendIInstead,correct.polaritieskeeptodifficultoftenisitnotation,textbookstandardtheisthisAlthough

.toleadsThis

andwhereright,

thetonotationetaught thbeenhavemayYou

'

#$

#$#$

ebbe

beebebbe

VV

VVVVVV

Vbe

Vcb

Vbe

Vbc



Polarities of voltages: NPN and PNP

PN tofrommove

negative,beingElectrons,

diode.biased-forwarda

inNtoPfromflowscurrent

Franklin)(BenalConvention

tly.significanconducts

diodebaised-forwardA

side.-Nthethan

positivemoreisside-Pthe

ifbiasedforwardisdiodeA

Vbe

Vcb

Ic

Ib

Ie

Vbc

Veb

Ic

Ib

Ie

N P N

Ib

Ie Ic

N P

Idiode

Vdiode

Vbe Vcb

P N P

Ib

IeIc

Veb Vbc



Polarities of voltages: NPN and PNP

Vbe

Vcb

Ic

Ib

Ie

Vbc

Veb

Ic

Ib

Ie

N P N

Ib

Ie Ic

N P

Idiode

Vdiode

Vbe Vcb

P N P

Ib

IeIc

Veb Vbc

.directionscurrentand

polaritiesltagecorrect vothe

determinecanwerule,By this

biased.-reverseis

junctioncollector-basetheand

biased,-forwardis

junctionemitter-basethe

BJToperating-normallyaIn



Common-emitter current gain & or HFE

junction).base-collectorbiased-(reverse0forcing

positive,lysufficientmadeisvoltagecollectorThe

%cb

C

V

V

Vcb Ic

Ib

+Vc

FEB

C HI

I$$&

gaincurrentemitter-Common



Common-base current gain (

junction).base-collectorbiased-(reverse0forcing

positive,madeisvoltagecollectorThe

%cb

C

V

V

Vcb

IcIb

+Vc

IE

(

(&

&

&(

(

#$

'$)

'$'$*

1

or

1

1)/(

/

gaincurrentbase-Common

BC

BC

BC

C

E

C

II

II

II

I

I

I



Typical values of DC current gain

998.095.020020

rstransisto...)microwave,(power,dSpecialize

997.095.030050

:projectslabinusedBJTs2N3906-2N3904Jellybean

0.998-799.0500300:circuitssimilarand

convertersdigital-AnaloginusedBJTspurpose-General

endously.vary tremcanThis

#+,#+

#+,#+

+,#+

(&

(&

(&



Common-base DC characteristics

Vbe

Ic

+Vcb

IE

A

measuredagainandandvariedagain

new value,atochangedtheniscurrentemitterThe

measured.arevoltage

emitter-basetheandcurrentcollectorThevaried.is

andapplied,iscurrentemitterofvaluefixedA

BECCB

BE

C

CBE

VIV

V

I

VI



Common-base DC characteristics

Vcb

Ic

Ie=5 mA

Ic=5 mA

Ie=10 mA

Ic=10 mA

~0.5 Volts

base-collectorbreakdown voltage

Vbr,cbo

Vbe

Ic

+Vcb

IE

A

very slightvariation of Vbe

with Vcb

Ic

Vbe

exponentialI-V curve



Base-emitter voltage

Vbe

Ic

+Vcb

IE

A

-0.005

0

0.005

0.01

0.015

0.02

-0.2 0 0.2 0.4 0.6 0.8

emittercurrent,amps

Vbe, volts

devices.vintage-2000forvolts0.9-0.8

lab,theinusedBJTsvintage-s60'for

volts0.7-0.6ofrangetheintypicallyis

ionapproximatrough

iprelationshactualln1ln

,

,

onbe

onbebe

ES

ET

ES

ETbe

V

VV

IIV

IIVV

-$

-../

0112

3+..

/

0112

3'$

10-12

10-10

10-8

10-6

10-4

0.01

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

current

,amps

Vbe, volts


14/23


Common-base curves measured on a microwave BJT

-20

0

20

40

60

-1 0 1 2 3 4

Ic

,mA

Vcb

, Volts

Ie= 55 mA

Ie= 45 mA

Ie= 35 mA

breakdown

-5

0

5

10

15

20

0 0.2 0.4 0.6 0.8 1

Ic,mA

Vbe, Volts

Vbe

Ic

+Vcb

IE

A


15/23


PNP Transistor: common-base DC characteristicsIc

Ie=5 mA

Ic=5 mA

Ie=10 mA

Ic=10 mA

~0.5 Volts

base-collectorbreakdown voltageVbr,cbo

Vcb

Veb

Ic

Vbc

IE A

currents.ofdirectionscorrecttheandvoltagesofpolarities

correctheremember ttoispointimportantmostThe

ly.infrequentthemusewepractice,Intexts.instandardaresticscharacteriPNPofPlots


16/23


Common-Emitter DC characteristics

V100-50typicallyistage,Early volthe,

~/curvetheofslopeThe

effect.EarlythecalledisThis

voltage.collectorwithofvariationsomealsoisThere

region,lineartheIn

A

ACE

C

CEC

c

bc

V

VV

IdVdI

I

II

'

4+&Ic

Ib

+Vce

Ic

Vce

increasingIb

-Va linear regionVcb>0

saturation regionVcb


17/23


Common-emitter curves measured on a microwave BJT

0

5

10

15

20

0 0.5 1 1.5 2 2.5

Ic,mA

VCE, V

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 1 2 3 4 5 6 7 8

Ic,mA

VCE, V

Above curvesare for150,300,450,600,750 uA base current

M d f ti Li A ti


18/23


Modes of operation: Linear Active

N

P

Ib

Ie

Ic

Vbe

Vcb

N

biasedreversejunction BC

biasedforwardjunction BE

ionamplificatlinearforoperationofmodeNormal

:ModeActiveLinear

operation

ofmodes4usgivenscombinatio4Thebiased.-reverse

orforwardbecanEachjunctions.PN2hasBJTThe

Ic

Vce

increasingIb




19/23


Modes of operation: Saturation

amplifieranasusedrtransistotheofswing

voltagemaximumtheonlimitoneisSaturation

switch.voltage-lowawantwely whendeliberateusedSometimes

biasedforwardjunction BC

biasedforwardjunction BE

Saturated

Ic

Vce

increasingIb




20/23


Modes of operation: Cutoff

gain.currentlowverybut withmode,active

forwardthetosimilarlyoperatesr thentransistoThebiased.

forwardisjunctionBCtheandbiasedreverseisjunction

BEthewhichinmode,activereverseaalsoisThere

amplifier.anasusedrtransistotheofswing

voltagemaximumtheonlimitsecondaisCutoff

off.isrtransistoThe

zero.nearbellcurrent wiemitterthethenbiased)forward(barelysmalltooisltageemitter vo-basetheIf

biasedreversejunction BC

on.junctionturntobiasedforward

lysufficientnotorbiased,reversejunction BE

offCut

DC d l f bi l i


21/23


DC model for bias analysis

stages.similarandpull-pushin

currentsbiasforandmirrorscurrent

fornecessaryisiprelationsh2ndthe

accurate)(more)/ln(

(quick)

eitherUse

)(

ESETbe

onbebe

IIVV

VV

$

$

&(Ib)

B

E

C

Ib


22/23

AC small signal model


23/23


AC small-signal model

biasc

AbiasCE

ce

AbiasCE

biasc

Vce

c

Vce

c

ce

ce

bembbemcCb

Vbe

b

be

be

I

VV

R

VV

I

V

I

V

I

R

RR

VgIVgIII

V

IR

RR

be

be

ce

,

,

,

,

constant

constant

1

0

constant

1

:fromEstimate

sheetdataafromortracer-curveafromfindBest to

)(

:orfindNow

/soand/But

)(

:orfindNow

'

$,

'$

55

5

5

*

$$$

55

*

#

#

&&

6

&(Ib)B

E

C

IbgmVbe

Rce

or R0

Rbe

or R6

Vbe

or

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Ece137a Notes Set 1