Download F6 Basic Amplifier stages I

Contents: Basic Amplifier Stages I
In this lecture we will discuss:
- Where is amplification needed
- Large and small signal transistor models
- Basic one stage amplifiers
Reading instructions: 173-182, 199-201
Modern Electronics: F6 Basic Amplifier Stages I
1
Introduction
- Digital domain: Data processing and memories
Clock-frequencies up to a few GHz
- Analog domain: Communication
Wide range of frequencies dependent on application
Bluetooth, WiFi, GSM, 4G...
Sync ˈn go
Streaming
HDMI
Modern Electronics: F6 Basic Amplifier Stages I
2
Introduction
The frequency spectrum is allocated to different bands
mm-wave
region
30-300 GHz
Modern Electronics: F6 Basic Amplifier Stages I
3
Introduction
To transmit a signal we modulate (change) frequency, amplitude, and/or
phase of a carrier signal
Modern Electronics: F6 Basic Amplifier Stages I
4
Introduction
When the signal is transmitted between devices it is attenuated
Free space path loss at 4 m
Distance d
Wave length l
FSPL  (
4d
l
)2
The signal is also distorted by reflections, users in the same frequency band,
and noise
Amplification is needed!
Modern Electronics: F6 Basic Amplifier Stages I
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Introduction
A typical transmitter contains a power amplifier as the final stage before
the signal is delivered to the antenna
It should be optimized to give as high amplification as possible, given
constraints on linearity and power consumption
Digital block
Mixer
Power
Amplifier
Oscillator
Modern Electronics: F6 Basic Amplifier Stages I
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Introduction
- A typical receiver contains a low noise amplifier as the first stage after the
receiving antenna
- It should be optimized to give high gain at acceptable noise level
Digital block
Mixer
Low noise
Amplifier
Oscillator
Modern Electronics: F6 Basic Amplifier Stages I
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Amplifiers
-Amplification is the process of increasing the magnitude of a signal (current,
voltage, or power)
-To accomplish this we need active devices with gain i.e transistors
-The energy needed to amplify the analog small-signal is available by biasing the
transistor in the active region
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Introduction
Circuits may either be fabricated in III-V technology (MMICs: Millimeter-wave
integrated circuits) or in Si technology (RF-CMOS)
Material
Device Type
Benefits
Limitations
III-V (GaAs, InP)
HBT, HEMT
Speed, Performance,
Insulating substrate
Limited integration
level
Si, SiGe
CMOS, HBT,
Bi-CMOS
Cost
Complexity
Performance
Source
Chicago
Inst. Tech.
Source Wikipedia
Modern Electronics: F6 Basic Amplifier Stages I
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Transistor models
- Large signal and linearization
DIOUT
DVIN
- Taylor expansion
iOUT  f (vIN ), vIN  VIN  vin
iOUT (t )  I OUT  iout (t )  f (VIN ) 
f (VIN )
vin   n
vIN
Modern Electronics: F6 Basic Amplifier Stages I
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Circuit elements
- Voltage source
- Current source
i
i
vg
v
i
ig
v
i
vg
v
v
-ig
Modern Electronics: F6 Basic Amplifier Stages I
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Circuit elements
- Voltage source
- Current source
i
i
vg
v
i
ig
v
i
vg
v
v
-ig
Modern Electronics: F6 Basic Amplifier Stages I
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Circuit elements
- Open circuit
- Short circuit
i
i
v
- Resistance
v
i
v
i
v
i
v
Modern Electronics: F6 Basic Amplifier Stages I
R
Slope
=???
v
13
Circuit elements
- Open circuit
- Short circuit
i
i
v
- Resistance
v
i
v
i
v
i
v
Modern Electronics: F6 Basic Amplifier Stages I
R
Slope
G=1/R
v
14
Transistor models
- Large signal and small signal model
G
D
VGS
ID
S
Modern Electronics: F6 Basic Amplifier Stages I
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Common source amplifier
- Most common type of transistor stage
- Used as a voltage or transconductance amplifier
VDD
RD
vIN
vOUT
Modern Electronics: F6 Basic Amplifier Stages I
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Common source amplifier
Key Metricts: input resistance, transconductance, and output resistance
i
Gm  o
vi
,
v0  0
v
Ri  i
ii
,
v0  0
v
Ro  o
io
Digital block Mixer
Low noise
Amplifier
vi  0
Oscillator
VDD
RD
vi
vi
gmvin
ro
RD
vo
vO
Modern Electronics: F6 Basic Amplifier Stages I
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Common source amplifier
Calculation of key metrics:
ii
gmvin
vi
Ri 
Ro 
vi
ii
vo
io

v0 0
 RD ro
vi 0
io
ro
RD
vo
Open circuit voltage gain:
vo
rR
 gm o D
vi
ro  RD
Using KCL:
g m vi 
vo
v
 o 0
ro
RD
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Variation I: Source degeneration
- Improves linearity
- Increased output resistance
- Degrades gain, parasitic source resistance
VDD
RD
vIN
vOUT
RS
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Variation II: Common emitter amplifier
- Bipolar transistors are used for high gain
VCC
RC
vIN
vOUT
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Biasing
-Proper biasing important
-Clipping gives distortion
Modern Electronics: F6 Basic Amplifier Stages I
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