principles of radio transmitters and receivers 1

8/22/2019 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


5. Mixers



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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


5. Mixers



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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


5. Mixers



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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


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 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 transmitter architectures:


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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(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


5. Mixers



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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


HPA: High-Power Amplifier


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


LNA: Low-Noise Amplifier


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


5. Mixers



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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


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


5. Mixers



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Question and Answer


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LUNCH TIME

principles of radio transmitters and receivers 1

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