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ECE340ELECTRONICS I
BIPOLAR JUNCTION TRANSISTOR
BIPOLAR JUNCTION TRANSISTOR
• THREE TERMINAL DEVICE
• CONSISTS OF TWO PN JUNCTIONS
• CURRENT AMPLIFIER
NPN BJT PHYSICAL STRUCTURE
E B C
n+
n-
p
base
emitter
collector
PNP BJT PHYSICAL STRUCTURE
E B C
n
p
p
base
emitter
collector
TWO PN JUNCTION DEVICE
P TYPE N TYPE P TYPE
EMITTER BASE COLLECTOR
ACTUAL SCALED DIMENSIONS
P
N
P
EMITTER BASE COLLECTOR
MODES OF OPERATION
• CUTOFF
• ACTIVE OR LINEAR
• SATURATION
PNP CUTOFF MODE OF OPERATION
- VEB ++ VBC -
REVERSE-BIASED REVERSE-BIASED
EMITTER COLLECTOR
BASE
IE=0IC=0
IB=0
PNP ACTIVE MODE OF OPERATION
+ VEB - + VBC -
FORWARD-BIASED REVERSE-BIASED
EMITTER COLLECTOR
BASE
IE IC
IB
PNP SATURATION MODE OF OPERATION
+ VEB - - VBC +
FORWARD-BIASED FORWARD-BIASED
EMITTER COLLECTOR
BASE
IE IC
IB0
NPN CUTOFF MODE OF OPERATION
+ VBE -- VCB +
REVERSE-BIASED REVERSE-BIASED
EMITTER COLLECTOR
BASE
IE=0IC=0
IB=0
NPN ACTIVE MODE OF OPERATION
- VBE + - VCB +
FORWARD-BIASED REVERSE-BIASED
EMITTER COLLECTOR
BASE
IE IC
IB
NPN SATURATION MODE OF OPERATION
- VBE + +VCB -
FORWARD-BIASED FORWARD-BIASED
EMITTER COLLECTOR
BASE
IE IC
IB0
BJT CURRENTS
BCE
BCE
III
III
0
CURRENT RATIOS
11
1B
EBBEBCE
E
C
B
C
I
IIIIIII
I
I
I
I
COLLECTOR CURRENT CHARACTERISTICS
T
BE
T
BE
T
BE
Vv
BB
inEC
BB
inESC
Vv
SCCV
v
SCC
eWN
nDqAI
WN
nDqAI
eIIeII
22
1
BASE CURRENT CHARACTERISTICS
T
BE
T
BE
T
BE
Vv
BB
inEB
BB
inESB
Vv
SBBV
v
SBB
eWN
nDqAI
WN
nDqAI
eIIeII
22
1
EMITTER CURRENT CHARACTERISTICS
T
BE
T
BE
T
BE
Vv
BB
inEE
BB
inESE
Vv
SEEV
v
SEE
eWN
nDqAI
WN
nDqAI
eIIeII
22
1
BJT CURRENT SUMMARY
T
BE
T
BE
T
BE
T
BE
VV
SCEV
VSC
E
VV
SCB
VV
SCC
eIIeI
I
eI
I
eII
1
LARGE SIGNAL MODELS
• T MODEL
• HYBRID PI MODEL
T MODEL
C
B
E
BC II
T
BEV
V
SEE eII VBE
+
-
E
B
C
EC II
T
EBV
V
SEE eII VEB
+
-
NPN PNP
IBIB
IE
IE
PNP HYBRID PI MODEL
VEB
E
CB
IE
IBIC
ISCexp(VEB/VT)
PNP
NPN HYBRID PI MODEL
ISCexp(VBE/VT)NPN
B
VBE
C
E
BJT SYMBOLS
NPN PNP
COLLECTOR CURRENT CHARACTERISTICS
iC
vBE
VBE
COLLECTOR CURRENT CHARACTERISTICS
V_VCE
0V 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 4.5V 5.0V... IC(Q1)
0A
2mA
4mA
6mA
8mA
10mA
iB
iB=80A
iB=60AiC {
VCE=2V
DC AND AC CURRENT GAIN
uA
mA
i
i
uA
mA
I
I
ACB
CAC
DCBQ
CQDC
20
2
80
7
SMALL SIGNAL PARAMETERS
• BASE RESISTANCE
• EMITTER RESISTANCE
• COLLECTOR RESISTANCE
• TRANSCONDUCTANCE
BASE RESISTANCE
T
beBb
VV
SCB
T
beVV
SCB
T
beVv
Vv
VV
SCB
VvV
SCB
V
vIieII
V
veIi
V
ve
eeIieIi
T
BE
T
BE
T
be
T
be
T
BE
T
beBE
11
INCREMENTAL BASE RESISTANCE
C
TCB
B
T
be
b
T
beBb
VV
SCB
I
Vr
II
I
Vr
v
ir
V
vIieII T
BE
1
TOTAL BASE RESISTANCE
• INCLUDES BASE SPREADING RESISTANCE MODELING PHYSICAL STRUCTURE
• rx ~ 50Ω TO 100Ω
• BASE SPREADING RESISTANCE SMALL COMPARED TO INCREMENTAL BASE RESISTANCE
• NORMALLY OMITTED
INCREMENTAL EMITTER RESISTANCE
• TYPICALLY VERY SMALL
• SIGNIFICANT PARAMETER IN COMMON BASE AMPLIFIERS
INCREMENTAL EMITTER RESISTANCE ANALYSIS
T
beEe
T
beEE
T
beVV
SCE
Vv
VV
SCE
VvV
SCE
V
vIi
V
vIi
V
ve
Ii
eeI
ieI
i
T
BE
T
be
T
BE
T
beBE
11
INCREMENTAL EMITTER RESISTANCE DEFINITION
E
Te
be
ee
T
beEe
I
Vr
v
ir
V
vIi
1
EARLY EFFECT
• DEFINES FINITE OUTPUT RESISTANCE AT THE COLLECTOR TERMINAL
• COLLECTOR CURRENT LINES IN ACTIVE REGION OF OPERATION ARE NOT FLAT
• CONSEQUENCE OF SIGNIFICANT CONTRIBUTION OF COLLECTOR-BASE VOLTAGE - VCB
COLLECTOR OUTPUT RESISTANCE
C
AO
A
C
CE
C
A
CECC
A
CEVv
SCC
I
Vr
V
I
v
i
V
vIi
V
veIi T
BE
11
TRANSCONDUCTANCE
T
beCc
T
beCC
T
beVV
SCC
Vv
VV
SCCV
vV
SCC
V
vIi
V
vIi
V
veIi
eeIieIi
T
BE
T
be
T
BE
T
beBE
11
TRANSCONDUCTANCE DEFINITION
T
Cm
be
cm
T
beCc
V
Ig
v
ig
V
vIi
TOTAL CURRENTS
bee
VV
SCE
bemV
V
SCC
bex
VV
SCB
vr
eI
i
vgeIi
vrr
eI
i
T
BE
T
BE
T
BE
1
1
SMALL SIGNAL MODEL
rπ ro
b
e
c
+
vπ
-
gmvπ
