ece137a notes set 1
TRANSCRIPT
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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
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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
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Terminal Characteristics: NPN bipolar transistor
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Coulomb)10(6022.1chargeelectron
retemperatuabsolute
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Ib
Ie
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Terminal Characteristics: PNP bipolar transistor
reversed.simplyarepolaritiesvoltage
anddirectionscurrent,ansistorbipolar trPNPFor the
Vbc
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Ic
Ib
Ie
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Voltage Polarities and Notation
normally.operatedisrtransistothewhenPOSITIVE
areuestheir valsodefinedareriablescurrent vaandvoltageDC
possible,wheneverFurther,a voltage.definingleany variabwith
associateddiagramcircuittheonsigns-anddrawingbyvoltages
ofpolaritythedefiningrecommendIInstead,correct.polaritieskeeptodifficultoftenisitnotation,textbookstandardtheisthisAlthough
.toleadsThis
andwhereright,
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Vbe
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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
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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
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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
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Common-base current gain (
junction).base-collectorbiased-(reverse0forcing
positive,madeisvoltagecollectorThe
%cb
C
V
V
Vcb
IcIb
+Vc
IE
(
(&
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or
1
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gaincurrentbase-Common
BC
BC
BC
C
E
C
II
II
II
I
I
I
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Typical values of DC current gain
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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
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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
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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
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ET
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ETbe
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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
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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
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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
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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
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class notes, ECE137A, rodwell, University of California, Santa Barbara, copyrighted page 17
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
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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
-Va linear regionVcb>0
saturation regionVcb
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Modes of operation: Saturation
amplifieranasusedrtransistotheofswing
voltagemaximumtheonlimitoneisSaturation
switch.voltage-lowawantwely whendeliberateusedSometimes
biasedforwardjunction BC
biasedforwardjunction BE
Saturated
Ic
Vce
increasingIb
-Va linear regionVcb>0
saturation regionVcb
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class notes, ECE137A, rodwell, University of California, Santa Barbara, copyrighted page 20
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
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DC model for bias analysis
stages.similarandpull-pushin
currentsbiasforandmirrorscurrent
fornecessaryisiprelationsh2ndthe
accurate)(more)/ln(
(quick)
eitherUse
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AC small signal model
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AC small-signal model
biasc
AbiasCE
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AbiasCE
biasc
Vce
c
Vce
c
ce
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bembbemcCb
Vbe
b
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