in this chapter, we will: microelectronics circuit analysis and...
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10/15/2013
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Neamen Microelectronics, 4e Chapter 4-1McGraw-Hill
Microelectronics Circuit Analysis and Design
Donald A. Neamen
Chapter 4
Basic FET Amplifiers
Neamen Microelectronics, 4e Chapter 4-2McGraw-Hill
In this chapter, we will:
� Investigate a single-transistor circuit that can amplify a small, time-varying input signal
� Develop small-signal models that are used in the analysis of linear amplifiers.
� Discuss and compare the three basic transistor amplifier configurations.
� Analyze the common-source amplifier.
� Analyze the source-follower amplifier.
� Analyze the common-gate amplifier.
� Analyze multitransistor or multistage amplifiers.
Neamen Microelectronics, 4e Chapter 4-3McGraw-Hill
NMOS Common-Source Circuit
Neamen Microelectronics, 4e Chapter 4-4McGraw-Hill
NMOS Common-Source Circuit
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Neamen Microelectronics, 4e Chapter 4-5McGraw-Hill
NMOS Common-Source Circuit
Neamen Microelectronics, 4e Chapter 4-6McGraw-Hill
NMOS Common-Source Circuit
Neamen Microelectronics, 4e Chapter 4-7McGraw-Hill
NMOS CS Circuit
Neamen Microelectronics, 4e Chapter 4-8McGraw-Hill
Simple NMOS Small-Signal Equivalent Circuit
phasor components in parentheses
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Neamen Microelectronics, 4e Chapter 4-9McGraw-Hill
Simple NMOS Small-Signal Equivalent Circuit
112
1
][])([
)(
−−
−
∂
∂
≅−=
=
DQTNGSQno
v
i
o
IVVKr
rDS
D
λλ
Recall the slope in the MOSFET characteristic curve!
The effect is that of drain to source resistance r.
Neamen Microelectronics, 4e Chapter 4-10McGraw-Hill
NMOS Transistor Small-Signal Parameters
� Values depends on Q-point
112
1
][])([
)(
2)(2
−−
−
∂
∂
∂
∂
≅−=
=
=−=
==
DQTNGSQno
v
i
o
DQnTNGSQnm
gs
d
v
i
m
IVVKr
r
IKVVKg
v
ig
DS
D
GS
D
λλ
Neamen Microelectronics, 4e Chapter 4-11McGraw-Hill
NMOS Common-Source Circuit
AC Small-signal
)( Domiov RrgVVA −==
Neamen Microelectronics, 4e Chapter 4-12McGraw-Hill
Problem-Solving Technique:MOSFET AC Analysis
1. Analyze circuit with only the dc sources to find quiescent solution. Transistor must be biased in saturation region for linear amplifier.
2. Replace elements with small-signal model.
3. Analyze small-signal equivalent circuit, setting dc sources to zero, to produce the circuit to the time-varying input signals only.
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Neamen Microelectronics, 4e Chapter 4-13McGraw-Hill
Common-Source Configuration
DC analysis:
Coupling capacitor is assumed
to be open.
AC analysis:
Coupling capacitor is assumed
to be a short. DC voltage
supply is set to zero volts.
Neamen Microelectronics, 4e Chapter 4-14McGraw-Hill
Small-Signal Equivalent Circuit
))((Sii
iDomiov
RR
RRrgVVA
+−==
Neamen Microelectronics, 4e Chapter 4-15McGraw-Hill
DC Load Line
Q-point near the middle
of the saturation region
for maximum symmetrical
output voltage swing,.
Small AC input signal for
output response to be
linear.
Neamen Microelectronics, 4e Chapter 4-16McGraw-Hill
Common-Source Amplifier with Source Resistor
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Neamen Microelectronics, 4e Chapter 4-17McGraw-Hill
Small-Signal Equivalent Circuitfor Common-Source with Source Resistor
Sm
Dmv
Rg
RgA
+
−=
1
Neamen Microelectronics, 4e Chapter 4-18McGraw-Hill
Common-Source Amplifier with Bypass Capacitor
Small-signal equivalent circuit
Neamen Microelectronics, 4e Chapter 4-19McGraw-Hill
NMOS Source-Follower or Common Drain Amplifier
Neamen Microelectronics, 4e Chapter 4-20McGraw-Hill
Small-Signal Equivalent Circuit for Source Follower
)(1
Sii
i
oS
m
oS
vRR
R
rRg
rRA
++
=
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Neamen Microelectronics, 4e Chapter 4-21McGraw-Hill
Determining Output ImpedanceNMOS Source Follower
oS
m
O rRg
R1
=
Neamen Microelectronics, 4e Chapter 4-22McGraw-Hill
Common-Gate Circuit
Neamen Microelectronics, 4e Chapter 4-23McGraw-Hill
Small-Signal Equivalent Circuitfor Common Gate
Sim
LDm
vRg
RRgA
+=
1
)()
1)((
Sim
Sim
LD
D
i
Oi
Rg
Rg
RR
R
I
IA
++==
Neamen Microelectronics, 4e Chapter 4-24McGraw-Hill
Comparison of 3 Basic Amplifiers
Configuration Voltage Gain
Current Gain
Input Resistance
Output Resistance
Common Source Av > 1
__RTH
Moderate to high
Source Follower Av ≈ 1
__RTH Low
Common Gate Av > 1 Ai ≈ 1 Low
Moderate to high
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Neamen Microelectronics, 4e Chapter 4-25McGraw-Hill
NMOS Amplifier with Enhancement Load Device
Neamen Microelectronics, 4e Chapter 4-26McGraw-Hill
CMOS Common-Source Amplifier
Neamen Microelectronics, 4e Chapter 4-27McGraw-Hill
Small-Signal Equivalent Circuit for CMOS Common Source
)( oponmnv rrgA −=
Neamen Microelectronics, 4e Chapter 4-28McGraw-Hill
CMOS Common Gate
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Neamen Microelectronics, 4e Chapter 4-29McGraw-Hill
Cascade Circuit
Neamen Microelectronics, 4e Chapter 4-30McGraw-Hill
Small-Signal Equivalent Circuit for Cascade Circuit
Neamen Microelectronics, 4e Chapter 4-31McGraw-Hill
PMOS Common-Source Circuit
)( Domiov RrgVVA −==
Neamen Microelectronics, 4e Chapter 4-32McGraw-Hill
PMOS Common-Source Circuit
)( Domiov RrgVVA −==