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7/22/2019 Chapter 6 BJT
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Neamen Microelectronics Chapter 6-114 February 2012 McGraw-Hill
Microelectronics
Circuit Analysis and Design
Donald A. Neamen
Chapter 6
Basic BJT Amplifiers
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Neamen Microelectronics Chapter 6-214 February 2012 McGraw-Hill
In this chapter, we will:
Understand the concept of an analog signal and
the principle of a linear amplifier. Investigate how a transistor circuit can amplify a
small, time-varying input signal.Discuss and compare the three basic transistor
amplifier configurations.
Analyze the common-emitter amplifier. Understand the ac load line & determine the
maximum symmetrical swing of the output.Analyze the emitter-follower amplifier.
Analyze the common-base amplifier. Analyze multitransistor or multistage amplifiers. Understand the concept of signal power gain in an
amplifier circuit.
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Neamen Microelectronics Chapter 6-314 February 2012 McGraw-Hill
Common Emitterwith Time-Varying Input
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Neamen Microelectronics Chapter 6-414 February 2012 McGraw-Hill
IBVersus VBECharacteristic
bB
T
beBQB iI
V
vIi )1(
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Neamen Microelectronics Chapter 6-514 February 2012 McGraw-Hill
ac Equivalent Circuitfor Common Emitter
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Neamen Microelectronics Chapter 6-614 February 2012 McGraw-Hill
Small-Signal Hybrid pModel for npn BJT
p
p
rg
I
Vr
V
Ig
m
CQ
T
T
CQ
m
Phasor signals are shown in parentheses.
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Neamen Microelectronics Chapter 6-714 February 2012 McGraw-Hill
Small-Signal Equivalent Circuit UsingCommon-Emitter Current Gain
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Neamen Microelectronics Chapter 6-814 February 2012 McGraw-Hill
Small-Signal Equivalent Circuit for
npn Common Emitter circuit
))((B
CmvRr
rRgA
p
p
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Neamen Microelectronics Chapter 6-914 February 2012 McGraw-Hill
Problem-Solving Technique:BJT AC Analysis
1. Analyze circuit with only dc sources to find Qpoint.
2. Replace each element in circuit with small-signal model, including the hybrid pmodel forthe transistor.
3. Analyze the small-signal equivalent circuit
after setting dc source components to zero.
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Neamen Microelectronics Chapter 6-1014 February 2012 McGraw-Hill
Transformation of Elements
Element DC Model AC Model
Resistor R R
Capacitor Open C
Inductor Short L
Diode +Vg, rf rd= VT/ID
Independent Constant
Voltage Source
+ VS - Short
Independent ConstantCurrent Source
IS Open
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Neamen Microelectronics Chapter 6-1114 February 2012 McGraw-Hill
Hybrid p Model for npn with Early Effect
CQ
Ao
IVr
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Neamen Microelectronics Chapter 6-1214 February 2012 McGraw-Hill
Hybrid p Model for pnp with Early Effect
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Neamen Microelectronics Chapter 6-1314 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-1414 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-1514 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-1614 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-1714 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-1814 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-2014 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-2114 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-2214 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-2314 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-2414 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-2514 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-2614 February 2012 McGraw-Hill
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Neamen Microelectronics Chapter 6-2714 February 2012 McGraw-Hill
Expanded Hybrid pModel for npn
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Neamen Microelectronics Chapter 6-2814 February 2012 McGraw-Hill
h-Parameter Model for npn
p
fe
bie
h
rrrh
o
oe
re
rrh
r
rh
11
p
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Neamen Microelectronics Chapter 6-2914 February 2012 McGraw-Hill
T-Model of an npn BJT
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Neamen Microelectronics Chapter 6-3014 February 2012 McGraw-Hill
4 Equivalent 2-port Networks
Voltage Amplifier
Current Amplifier
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Neamen Microelectronics Chapter 6-3114 February 2012 McGraw-Hill
4 Equivalent 2-port Networks
TransconductanceAmplifier
Transresistance
Amplifier
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Neamen Microelectronics Chapter 6-3214 February 2012 McGraw-Hill
Common Emitter with Voltage-DividerBias and a Coupling Capacitor
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Neamen Microelectronics Chapter 6-3314 February 2012 McGraw-Hill
Small-Signal Equivalent Circuit Coupling Capacitor Assumed a Short
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Neamen Microelectronics Chapter 6-3414 February 2012 McGraw-Hill
npn Common Emitterwith Emitter Resistor
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Neamen Microelectronics Chapter 6-3514 February 2012 McGraw-Hill
Small-Signal Equivalent Circuit:Common Emitter with RE
)()1(
)1(
21
Si
i
E
C
v
ibi
Eib
RR
R
Rr
RA
RRRR
RrR
p
p
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Neamen Microelectronics Chapter 6-3614 February 2012 McGraw-Hill
REand Emitter Bypass Capacitor
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Neamen Microelectronics Chapter 6-3714 February 2012 McGraw-Hill
Problem-Solving Technique:Maximum Symmetrical Swing
1. Write dc load line equation that relates ICQand VCEQ.
2. Write ac load line equations that relates icand vce
3. In general, ic= ICQIC(min), where IC(min)is zero or other minimum collector current.
4. In general, vce= VCEQVCE(min), whereVCE(min) is some specified minimum
collector-emitter voltage.
5. Combine above 4 equations to find optimumICQ and VCEQ.
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Neamen Microelectronics Chapter 6-3814 February 2012 McGraw-Hill
Common-Collectoror Emitter-Follower Amplifier
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Neamen Microelectronics Chapter 6-3914 February 2012 McGraw-Hill
Small-Signal Equivalent Circuit:Emitter Follower
)())(1(
))(1(
))(1(
21
Si
i
Eo
Eo
v
ibi
Eoib
RR
R
Rrr
RrA
RRRR
RrrR
p
p
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Neamen Microelectronics Chapter 6-4014 February 2012 McGraw-Hill
Output Resistance:Emitter Follower
oEo rRrRp
1
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Neamen Microelectronics Chapter 6-4114 February 2012 McGraw-Hill
Common-Base Amplifier
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Neamen Microelectronics Chapter 6-4214 February 2012 McGraw-Hill
Small-Signal Equivalent Circuit:Common Base
]1
)[(
)(
E
LC
Cmi
LCmv
Rr
RR
RgA
RRgA
p
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Neamen Microelectronics Chapter 6-4314 February 2012 McGraw-Hill
Input Resistance:Common Base
Rie= rp/(1+)
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Neamen Microelectronics Chapter 6-4414 February 2012 McGraw-Hill
Output Resistance:Common Base
RO = RC
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Neamen Microelectronics Chapter 6-4514 February 2012 McGraw-Hill
Common Emitter Cascade Amplifier
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Neamen Microelectronics Chapter 6-4614 February 2012 McGraw-Hill
Small-Signal Equivalent Circuit:Cascade Amplifier
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Neamen Microelectronics Chapter 6-4714 February 2012 McGraw-Hill
Darlington Pair
21
iA
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Neamen Microelectronics Chapter 6-4814 February 2012 McGraw-Hill
Cascode Amplifier
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Small-Signal Equivalent Circuit:Cascode Amplifier
)(1 LCmv RRgA