BJT characteristics ece137A - UCSB€¦ · b C c m be b m be be V b be be I V V R V V I V I V I R R R I I I g V I g V V I R R R be be ce,,,, constant constant 1 0 constant 1 Estimate

ECE137A class notes, UCSB, Mark Rodwell, copyright 2019

ECE137A Notes Set 1:

Bipolar Transistor Characteristics

Mark Rodwell, Doluca Family Chair, ECE DepartmentUniversity of California, Santa [email protected]


Why study bipolar transistors ?

MOSFETs are now much more common, being completely dominant in digital

ICs, and probably 99.5% of analog ICs. Bipolar transistors are however still

used in high-performance instruments, and in some radio-frequency and

optical communications ICs.

But, quality mosfets are very difficult to obtain in the discrete form needed for the

lab projects. Insofar as they are available, the data sheets give very limited design

information. It is therefore very difficult to design satisfactory lab projects using

MOSFETs. Quality discrete bjts are widely available, and their charactersitics

are such that only limited information is needed from the data sheets.

Given that the lab design projects are a key part of this class, we therefore study

both MOSFETs and BJTs.


Terminal Characteristics: NPN bipolar transistor

Coulomb )10(6022.1charge electron

re temperatuabsolute

inJoule/Kelv )10(38.1constant sBoltzmann'

voltage"thermal" thecalled is

re) temperatu(room Kelvin300at mV 8.25/

where

/

1

biased) reverse junction base (collector

0for

19

23

/

q

T

k

V

qkTV

II

eII

V

T

T

Eb

VV

esE

cb

Tbe

Vbe

Vcb

Ic

Ib

Ie


Terminal Characteristics: PNP bipolar transistor

reversed.simply are polarities voltage

and directionscurrent ,ansistor bipolar tr PNPFor the

Vbc

Veb

Ic

Ib

Ie

/

1

then),0(

biased reverse is junction basecollector theif Again,

/

Eb

VV

esE

bc

II

eII

V

Teb


Voltage Polarities and Notation

normally. operated isr transisto the whenPOSITIVE

are ues their valso defined are riablescurrent va and voltageDC

possible, whenever Further,a voltage. defining leany variab with

associated diagramcircuit theon signs - and drawingby voltages

ofpolarity thedefining recommend I Instead, correct. polarities keep

todifficult often isit notation, textbook standard theis thisAlthough

. toleads This

and whereright,

the tonotation e taught thbeen havemay You

ebbe

beebebbe

VV

VVVVVV

Vbe

Vcb

Vbe

Vbc

ebV


Polarities of voltages: NPN and PNP

PN to from move

negative, being Electrons,

diode. biased-forwarda

inN to Pfrom flowscurrent

Franklin)(Ben alConvention

tly.significan conducts

diode baised-forward A

side.-N thethan

positive more is side- Pthe

if biased forward is diode A

Vbe

Vcb

Ic

Ib

Ie

Vbc

Veb

Ic

Ib

Ie

N P N

Ib

IeIc

N P

Idiode

Vdiode

Vbe Vcb

P N P

Ib

IeIc

Veb Vbc


Polarities of voltages: NPN and PNP

.directionscurrent and

polarities ltagecorrect vo the

determine can werule, By this

biased.-reverse is

junctioncollector -base theand

biased,-forward is

junctionemitter -base the

BJToperating-normallya In

Vbe

Vcb

Ic

Ib

Ie

Vbc

Veb

Ic

Ib

Ie

N P N

Ib

IeIc

N P

Idiode

Vdiode

Vbe Vcb

P N P

Ib

IeIc

Veb Vbc


Common-emitter current gain or HFE

junction). base-collector biased-(reverse 0 forcing

positive,ly sufficient made is voltagecollector The

cb

C

V

V

VcbIc

Ib

+Vc

FE

B

C HI

I

gaincurrent emitter -Common


Common-base current gain a

junction). base-collector biased-(reverse 0 forcing

positive, made is voltagecollector The

cb

C

V

V

a

a

a

a

1 or

1

1)/(

/

gaincurrent base-Common

BC

BC

BC

C

E

C

II

II

II

I

I

I

Vcb

IcIb

+Vc

IE


Typical values of DC current gain

998.095.020020

rs transisto...) microwave, (power, dSpecialize

997.095.030050

:projects lab in used BJTs2N3906-2N3904 Jellybean

0.998-799.0500300 :circuitssimilar and

converters digital-Analog in used BJTspurpose-General

endously. vary tremcan This

a

a

a


Common-base DC characteristics

measured again and and variedagain

new value,a tochanged theniscurrent emitter The

measured. are voltage

emitter-base theand current collector The varied.is

and applied, is current emitter of valuefixed A

BECCB

BE

C

CBE

VIV

V

I

VI

Vbe

Ic

+Vcb

IE

A


Common-base DC characteristics

Vbe

Ic

+Vcb

IE

A

Vcb

Ic

Ie=5 mA

Ic=5 mA

Ie=10 mA

Ic=10 mA

~0.5 Volts

base-collectorbreakdown voltageVbr,cbo

very slightvariation of Vbewith 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

em

itte

r curr

en

t, a

mp

s

Vbe, volts

devices. vintage-2000for volts0.9-0.8

lab, thein used BJTsvintage-s60'for

volts0.7-0.6 of range thein typicallyis

ionapproximat rough

iprelationsh actual ln 1ln

,

,

onbe

onbebe

ES

E

T

ES

E

Tbe

V

VV

I

IV

I

IVV

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

cu

rren

t, a

mps

Vbe, volts


Common-base curves measured on a microwave BJT

Vbe

Ic

+Vcb

IE

A

-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, m

A

Vbe, Volts


PNP Transistor: common-base DC characteristics

Veb

Ic

Vbc

IE A

Ic

Ie=5 mA

Ic=5 mA

Ie=10 mA

Ic=10 mA

~0.5 Volts

base-collectorbreakdown voltageVbr,cbo

Vcb

currents. of directionscorrect theand voltagesof polarities

correct heremember t toispoint important most The

ly.infrequent themuse wepractice, In

texts.in standard are sticscharacteri PNPof Plots


Common-Emitter DC characteristics

V 100-50 typicallyis tage, Early vol the,

~/ curve theof slope The

effect. Early thecalled is This

voltage.collector with of variationsome also is There

region,linear theIn

A

ACE

C

CEC

c

bc

V

VV

IdVdI

I

II

Ic

Ib

+Vce

Ic

Vce

increasingIb

-Va linear regionVcb>0

saturation regionVcb<0

Vce,sat


Common-emitter curves measured on a microwave BJT

0

5

10

15

20

0 0.5 1 1.5 2 2.5

Ic, m

A

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, m

AVCE, V

Left curves are for 150,300,450,600,750 uA base current


Modes of operation: Linear Active

biased reverse junction BC

biased forward junction BE

ionamplificatlinear for operation of mode Normal

: ModeActiveLinear

operation

of modes 4 us give nscombinatio 4 The biased.-reverse

or forward be can Eachjunctions. PN 2 has BJTThe

N

P

Ib

Ie

Ic

Vbe

Vcb

N

Vbe

Vcb

Ic

Ib

Ie

Ic

Vce

increasingIb



Vce,sat


Modes of operation: Saturation

Ic

Vce

increasingIb



Vce,sat

amplifier an as usedr transisto theof swing

voltagemaximum theonlimit one is Saturation

switch. voltage-lowa

want wely whendeliberate used Sometimes

biased forward junction BC

biased forward junction BE

Saturated

Vbe

Vcb


Modes of operation: Cutoff

gain.current low very but with mode, active

forward thetosimilarly operates r then transistoThe biased.

forward is junction BC theand biased reverse is junction

BE the whichin mode, active reversea also is There

amplifier. an as usedr transisto theof swing

voltagemaximum theonlimit seconda is Cutoff

off. isr transistoThe

zero.near be llcurrent wiemitter the thenbiased)

forward(barely small toois ltageemitter vo-base theIf

biased reverse junction BC

on. junction turn tobiased forward

lysufficientnot or biased, reverse junction BE

offCut


DC model for bias analysis

stages.similar and pull-push in

currents biasfor and mirrorscurrent

fornecessary is iprelationsh 2nd the

accurate) (more )/ln(

(quick)

either Use

)(

ESETbe

onbebe

IIVV

VV

(Ib)

B

E

C

Ib


AC small-signal model

re. temperaturoomat /26/

"resistanceemitter signal small" the defined have weNote

/1//

hence

)1(but

: findFirst

constan t

//

constan t

EETe

e

eeTCm

T

C

Vbe

c

VV

ES

VV

ESc

Vbe

c

m

bbem

m

ImVIVr

r

rrVIg

V

I

V

I

eIeII

V

Ig

Ivg

g

ce

TbeTbe

ce

a

aa

(Ib)B

E

C

IbgmVbe

Rce

or R0

Rbe

or R

Vbe

or


AC small-signal model

biasc

AbiasCE

ce

AbiasCE

biasc

Vce

c

Vce

c

ce

ce

bembbemcCb

Vbe

b

be

be

I

VVR

VV

I

V

I

V

IR

RR

VgIVgIII

V

IR

RR

be

be

ce

,

,

,

,

constan t

constan t

1

0

constan t

1

:from Estimate

sheetdata a fromor tracer -curvea from find Best to

)(

:or findNow

/ so and /But

)(

:or findNow

(Ib)

B

E

C

IbgmVbe

Rce

or R0

Rbe

or R

Vbe

or


Template slide

template math 1+1=2

Documents

BJT characteristics ece137A - UCSB€¦ · b C c m be b m be be V b be be I V V R V V I V I V I R R R I I I g V I g V V I R R R be be ce,,,, constant constant 1 0 constant 1 Estimate