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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]
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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.
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
-Va linear regionVcb>0
saturation regionVcb<0
Vce,sat
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
Modes of operation: Saturation
Ic
Vce
increasingIb
-Va linear regionVcb>0
saturation regionVcb<0
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
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
ECE137A class notes, UCSB, Mark Rodwell, copyright 2019
Template slide
template math 1+1=2