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PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
C
C H
H A
A P
P T E
E R
9
Transistor Fundamentals
McGraw-Hill
1
GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.1 Controlled-source models of
linear amplifier transistor operation
ro
+
i in
ri
i in
ro
v in
ri
vin
+
_
_
(a) Current-controlled current source
(b) Voltage-controlled voltage source
ro
+
v in
ri
v in
ro
i in
ri
iin
+
_
_
(c) Voltage-controlled current source
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(d) Current-controlled voltage source
2
GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.2 Models of ideal transistor
switches
iin
ri
iin
0
iin
ri
iin
0
v in
0
Current-controlled switch
+
vin
_
+
ri
vin
0
v in
ri
_
Voltage-controlled switch
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GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.4 Bipolar junction transistors
Collector
Collector
C
C
C
p
Base
n
n B
B
Base
p+
pB
B
n+
E
E
Emitter Circuit symbols
pnp transistor
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C
4
GIORGIO RIZZONI
E
E
Emitter Circuit symbols
npn transistor
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.10 Determination of the operation
region of a BJT
RC
1k
C
RB
40 k
B
V3
V CC
V
BB
4V
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E
V1
RE
500
12 V
V2
5
GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.12 A simplified bias circuit for a BJT
amplifier
By appropriate choice of I BB , R C
and V CC , the desired Q point may
be selected.
IC
C
B
+
IB
V CE
+
I BB
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RC
VBE
_
_
VCC
E
6
GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.13 Load-line analysis of a simplified
BJT amplifier
50 m
45 m
40 m
35 m
30 m
25 m
20 m
15 m
10 m
5m
0
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I B = 250 A
I B = 200 A
Q
I B = 150 A
I B = 100 A
IB = 50 A
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Collector-emitter voltage, V
7
GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.15 Circuit illustrating the
amplification effect in a BJT
IC
IB
V
VB
BE
IC
C
+
IB
VCE
+
RB
+
_~
+
+
R
+
C
VCE
B
+
VBE
–
–
E
V CC
VBB
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8
GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.16 Amplification of sinusoidal
oscillations in a BJT
I C (mA)
50
I B = 230 A
190 A
28.6
150 A
Q
22
15.3
0
110 A
75 A
0
5
10
t
15
VCE (V)
t
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GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.20 Practical BJT self-bias DC circuit
IC
R1
RC
IB
R2
+
VBE
–
+
VCE
–
IE
VCC
RE
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GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.21 DC self-bias circuit represented
in equivalent-circuit form
IC
R1
IB
+
VBE _
VCC R 2
RE
+ R
C
VCE
_
IE VCC
IC
IB
RB
VBB
(a)
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+
VBE _
RE
+ R
C
VCE
_
I EVCC
(b)
11
GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.22 npn BJT large-signal model
C
Cutoff state conditions:
V BE V
B
IB = 0
IC = ICEO
VCE 0
C
I CEO
IB = 0
E
Active state conditions:
VBE = V
B
IB 0
IC = I B
VCE V
IC
IB
+
V
–
E
C
IC
Saturated state conditions:
VBE = V
B
IB 0
IC
IB
VCE = Vsat
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+
Vsat
–
IB
+
V
–
E
12
GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.30(a) An n-channel MOSFET is normally
off in the absence of an external electric field
D
G
Gate
iD
Source
+
VDS +_ VDD
_
n+
Drain
p
n+
Bulk (substrate)
+ V
_ DD
S
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GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.30(d) If the drain and gate supply voltages are both varied a
family of curves (shown in Figure 9.31(b)) can be generated, illustrating the
MOSFET cutoff, ohmic, saturation, and breakdown regions
iD
D
VGG
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+
_
G
+
+
V DS
_
VGS
_
+
_
V DD
S
14
GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.32 n-channel enhancement MOSFET
circuit and drain characteristic for Example 9.8
iD (mA)
v GS = 2.8 V
100
80
2.6 V
Q
60
2.4 V
2.2 V
40
2.0 V
20
0
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0
2
4
6
8
1.8 V V
GG
1.6 V
1.4 V
10 v DS (V)
15
GIORGIO RIZZONI
D
G
+
v GS
–
iD
+
v DS
–
S
RD
VON
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.40(a) When the gate-source voltage is lower than Vp, no current flows. This is the cutoff region
Gate
Source
Drain
p
Channel
n
p
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GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.40(b) For small values of drain-source voltage, depletion regions form around the gate
sections. As the gate voltage is increased, the depletion regions widen, and the channel width
(i.e., the resistance) is controlled by the gate-source voltage. This is the ohmic region of the
JFET
Gate
Source
Drain
p
n Channel
p
depletion
regions
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GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.40(c) As the drain-source voltage is increased, the depletion
regions further widen near the drain end, eventually pinching off the
channel. This corresponds to the saturation region
Gate
Source
Drain
p
n Channel
p
Pinched-off
channel
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GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000
PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING
THIRD EDITION
Figure 9.41 JFET characteristic curves
4m
0V
3m
– 0.5 V
2m
– 1.0 V
2m
– 1.5 V
800 u
0
0
– 2.0 V
– 2.5 V
VGS = – 3 V
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0
Drain-source voltage, V
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GIORGIO RIZZONI
© The McGraw-Hill Companies, Inc. 2000