principles of radio transmitters and receivers 1
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Principles of radio transmittersand receivers
Dr Ding JiaXinEngineer of Radio Monitoring Division
State Radio Monitoring Center
[email protected]+8610-68312933
Radio Monitoring and Spectrum Management Training
(China,23-31,May,2005)
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Contents:
1. Introduction
2. Basic concepts
3. Radio transceiver architectures4. Amplifiers
5. Mixers
6. Oscillators7. Modulation and Demodulation
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Contents:
1. Introduction
2. Basic concepts
3. Radio transceiver architectures4. Amplifiers
5. Mixers
6. Oscillators7. Modulation and Demodulation
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What are radio transceivers?
Radio transmitters:
electrical signals => radio waves
Radio receivers:
radio waves => electrical signals
Radio transceivers
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Typical radio transceivers:
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Basic framework
RF
Section
Baseband
Section
antenna
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What is an RF signal
Analog signal
Its spectrum is not centered around
zero frequency
f0 f1
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RF section is the design
bottleneck
Noise
Power Linearity
Gain
Frequency
Supply voltage
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Summary:
Radio transceivers functions
RF and Baseband
RF signal
RF section is bottleneck
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Contents:
1. Introduction
2. Basic concepts
3. Radio transceiver architectures4. Amplifiers
5. Mixers
6. Oscillators7. Modulation and Demodulation
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Basic concepts
Memoryless system
Time-invariant system
Linear system
Harmonics
Gain compression
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Basic concepts (cont.)
Desensitization & Blocking
Intermodulation
Noise figure
Sensitivity
Dynamic range
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A memoryless system:
Its output does not depend on the
past values of its input.
Memoryless
system
)()( txty )(tx
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A time-invariant system:
If
then
)()( tytx
Time-invariant
system
)( tx )(y t
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A linear system:
If
then
)()( 11 tytx
)()( 22 tytx
Linear
system)(b 2 tx
)(a 1 tx )()(a 21 tbyty
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A memoryless, time-invariant,
nonlinear system:
The output signal can include frequencycomponents that do not exist in the input
signal
Investigativesystem
)(tx )()()()(3
3
2
21
txtxtxty
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Effects of nonlinearity
Harmonics
Gain compression
Desensitization and Blocking
Intermodulation
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Harmonics:
If
then
system)(tx )()()()(
3
3
2
21 txtxtxty
tfAtx 12cos)(
tfA
ftA
tfA
AA
ty 1
3
31
2
21
3
31
2
2 6cos4
4cos2
2cos)4
3(
2)(
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Harmonics:
System y(t)x(t)
ff1
x(t)
0
ff1
y(t)
0 2f1 3f1
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Gain compression:
As the signal amplitude increases,
the gain begins to vary
The output is a compressive function
of the input
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1-dB compression point:
20logAin
20logAout
1dB
A1-dB
A measure of the maximum input range
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Desensitization & Blocking:
Systems with compressivecharacteristics process a weak desired
signal with a strong interferer
The weak signal may experience avanishing small gain
If the gain drops to zero, the signal isblocked
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Blocking signals:
Refers to interferers that desensitize acircuit even if the gain does not fall to
zero
Many receivers must be able to
withstand blocking signals 60 to 70 dBgreater than the wanted signal
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Intermodulation (IM)
When two signals with differentfrequencies are applied to a nonlinear
system, the output in general exhibitssome components that are notharmonics of the input frequencies
ff1 f2ff1 f2 2f1-f2 2f2-f1
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IM is a troublesome effect
Particular interest are the third-orderIM products at 2f1-f2 and 2f2-f1
Interferers Desired
Channel
ff1 f2 ff1 f22f1-f2 2f2-f1
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Third intercept point (I P3) :
20logA
K=1
K=3
IIP3
OIP3
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The relationship of 1-dB
compression point and IIP3:
The input level at 1-dB compressionpoint is less 10 dB than IIP3
BA
A
IP
B
d6.93
d1
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Noise Figure (NF)
Noise factor= SNRin/SNRout
Noise figure=10lg(Noise factor)
The noise figure of a noiseless system is
equal to 0 dB
The typical NF of receiver is less than
12 dB
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Sensitivity:
The minimum signal level that the
system can detect with acceptable
performance
a function of the bandwidth
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Dynamic Range (DR):
The ratio of the maximum input levelthat the system can tolerate to the
minimum input level that the systemprovides a reasonable signal quality
The definition is quantified in differentapplications differently
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Summary
The concepts of memoryless,
Time-invariance, linearity
Effects of nonlinearity
Harmonics
Gain compression
Desensitization and Blocking
Intermodulation
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Summary (cont.):
NF 12 dB
IIP3 17 dBm
DR 100 dB AIIP3 A1-dB+10dB
Blocking level: 60~70 dB
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Contents:
1. Introduction
2. Basic concepts
3. Radio transceiver architectures4. Amplifiers
5. Mixers
6. Oscillators7. Modulation and Demodulation
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Radio transceiver architectures:
General considerations
Radio receiver architectures
Radio transmitter architectures
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Radio transceiver architectures:
General considerations
Radio receiver architectures
Radio transmitter architectures
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Radio receiver block diagram:
BPFRF IF
Amplifier
Antenna
LNA
LO
BPF
Mixer
BPF: Band-Pass Filter
LNA: Low-Noise AmplifierLO : Local Oscillator
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Radio transmitter block diagram:
BPFIF RF
HPA
Antenna
Amplifier
LO
Mixer
BPF: Band-Pass Filter
HPA: High-Power Amplifier
LO : Local Oscillator
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Band & Channel:
fReceive
band
Desired
channel
f
BPF
LNA
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Band selection
Channel selection
front-end BPF only select the band ofinterest , postponing channel selectionto some other point in the receiver
Band selection & Channel selection:
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Radio transceiver architectures:
General considerations
Radio receiver architectures
Radio transmitter architectures
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Radio receiver architectures:
Superheterodyne architecture
Direct-conversion architecture
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Superheterodyne architecture:
BPF1 BPF2
Mixer
tfV RFRF 2cos
tfV LOLO 2cos
LNA IF amplifier
RF IF
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Basic blockings:
BPF1: band selection
BPF2: channel selection
Mixer: down conversion mixing
fIF=fLO - fRF
LNA: providing enough gain
IF amplifier: amplify IF signal
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The advantages of
superheterodyne architecture: fIF
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Problem of image:
Mixer is not a ideal multiplier
Mixer is a nonlinearity device
Image frequency
Desired channel
Image
f
f
fRF fim
fLO
fIF fIF
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Problem of image (cont.):
BPF
tfLO2cos
mixer
ffIF
Desired channel
Image
f
f
fRF fim
fLO
fIF fIF
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Image-reject filter:
ff1 fim
2fIF
Image reject
filter
Image
reject filter
LNA
tfLO2cos
mixer
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The choice of IF:
fIF higher, sensitivity better
fIF lower , selectivity better
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A question:
Why the RF spectrum is not simply
translated to the baseband in the firstdownconversion
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Direct-conversion (zero-IF)
architecture:LPF
f
mixer
f LNA 0f1
tf12cos
LPF
LNA
tf12cos
LPF
(a)
tf1
2sin
(b)
Baseband
I
BasebandQ
LPF: Low-Pass Filter
LNA: Low-Noise Amplifier
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The advantages of
direct-conversion architecture:
fIF = 0 , no image-reject filter is required
Be easily realized by integrated circuit
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The disadvantages of
direct-conversion architecture:
DC offsets
LO leakage Flicker noise
I/Q mismatch
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Radio transceiver architectures:
General considerations
Radio receiver architectures
Radio transmitter architectures
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Radio transmitter architectures:
Direct-conversion architecture
Two-step architecture
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Direct-conversion architecture:
Matching
Network
Power
amplifier
Baseband
I
Baseband
Q
tfc2cos
tfc2sin
antenna
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Direct-conversion architecture
(cont.):
Modulation and upconversion in the
same circuit Matching network
Baseband signal is strong
The noise of the mixers is not critical
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The disadvantage of
Direct-conversion architecture: LO pulling
Power
amplifier
I
Q
LO BPF
ffLO
LO: Local Oscillator
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Two-step architectures:
Baseband
I
Baseband
Q
tf12sin
tf12cos BPF BPF
ff1+f2
tf22cos
Power
amplifier
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Summary:
Basic blocks of transceivers
antenna
filter mixer
oscillator
amplifier
Band & Channel
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Summary (cont.):
Superheterodyne receiver
Image frequency
Direct-conversion receiver
Direct-conversion transmitter
LO pulling
Two-step transmitter
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Contents:
1. Introduction
2. Basic concepts
3. Radio transceiver architectures4. Amplifiers
5. Mixers
6. Oscillators7. Modulation and Demodulation
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Function of amplifiers:
Make signals bigger
Small signal in Big signal out
Amplifier
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Classification of amplifiers:
High-Power Amplifiers (HPA)
Low-Noise Amplifiers (LNA)
Other special amplifiers
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Position of HPA:
BPFIF RF
HPA
Antenna
Amplifier
LO
Mixer
BPF: Band-Pass Filter
HPA: High-Power Amplifier
LO : Local Oscillator
radio transmitter architecture
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Function of HPA:
Delivering RF power to antenna
efficiently
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HPA characteristics:
Output power
Efficiency Power-Added Efficiency (PAE)
dc
inPAE
P
PPPAE
out
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Position of LNA:
BPFRF IF
Amplifier
Antenna
LNA
LO
BPF
Mixer
BPF: Band-Pass Filter
LNA: Low-Noise Amplifier
LO : Local Oscillator
radio receiver architecture
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LNA characteristics:
Enough gain
As little noise as possible
Large dynamic range
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Typical LNA characteristics:
NF 2dB
IIP3 -10dBm
Gain 15dB
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Other special amplifier:
Variable Gain Amplifier (VGA)
Small signal in Big signal out
VGA
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Summary:
High-Power Amplifiers (HPA)
Low-Noise Amplifiers (LNA)
Other special amplifiers VGA
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Contents:
1. Introduction
2. Basic concepts
3. Radio transceiver architectures4. Amplifiers
5. Mixers
6. Oscillators7. Modulation and Demodulation
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Functions of mixers:
Frequency translation
Up-conversion
Down-conversion
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Position of mixer:
BPFRF IF
Amplifier
Antenna
LNA
LO
BPF
Mixer
BPF: Band-Pass Filter
LNA: Low-Noise AmplifierLO : Local Oscillator
radio receiver architecture
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Mixers fundamentals:
The core of all mixers is a multiplicationof two signals in the time domain
tfftffAB
tfBtfA )(2cos)(2cos2
)2cos)(2cos( 212121
fRF
fLO
fIF
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Implementation of mixers
VRF
VLO
S1
VIF
RL
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Passive mixers:
Not providing any gain
A higher linearity and speed
Application in microwave andbase station circuits
VRF VIF
RL
VLO
M1
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Active mixers:
Providing some gain
Be widely used in RF systems
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Conversion gain:
The ratio of the voltage of the IF signal tothe voltage of the RF signal
Approximately 10 dB
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Noise figure of mixer:
Single-sideband noise figure (SSB NF)
Double-sideband noise figure (DSB NF)
SSB NF = DSB NF + 3 dB
SSB NF : 10 ~15 dB
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Port-to-port isolation:
To minimize interaction among the RF,IF,and LO ports
The required isolation levels greatlydepend on the environment in which the
mixer is utilized
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Summary:
Frequency translation
The core of all mixers is a multiplicationof two signals in the time domain
Implementation of mixer
Passive / Active mixer
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Summary (cont.):
Typical mixer characteristics:
SSB NF 10-15dB
IIP3 5dBmGain 10dB
Port-to-port isolation 10-20dB
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Summary:
1. Introduction
2. Basic concepts
3. Radio transceiver architectures4. Amplifiers
5. Mixers
6. Oscillators7. Modulation and Demodulation
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Question and Answer
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LUNCH TIME