Introduction to RF Design

0,000,01

0,020,03

0,04

0,05

0,06

0,07

0,08

0,09

0,10

0,110,12 0,13

0,14

0,15

0,16

0,17

0,18

0,19

0,20

0,21

0,22

0,23

0,24

0,25

0,26

0,27

0,28

0,29

0,30

0,31

0,32

0,33

0,34

0,35

0,360,370,38

0,39

0,40

0,41

0,42

0,43

0,44

0,45

0,46

0,470,48

0,49

0-1

0

-20

-30

-40

-50

-60

-70

-80-90

-100

-110

-120

-130

-140

-150

-160-170

±180170

160

150

140

130

120

110

10090

80

70

60

50

40

30

20

10

0,1

0,1

0,2

0,2

0,3

0,4

0,6

0,7

0,8

0,9

1,21,4

1,61,8

3

4

50

1

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1 1,2

1,4

1,6

1,8

2 3 4 5 10 20

0,8

0,6

0,4

0,20,5

1

2

5

10

20

20

10

5

4

3

2

1,8

1,61,4

1,210,9

0,8

0,7

0,6

0,5

0,4

0,3

0

Information Processing Transmitter

Transmission Medium

Receiver Information Processing

Information Destination

Information Source

01.04.2014 3

Simplified Communications System Block Diagram

Information Processing Transmitter

Transmission Medium

Receiver Information Processing

Information Destination

Information Source

01.04.2014 4

What is different about a wireless system? Focus on the Transmission medium

Simple Analog Signals in Time Domain

01.04.2014 5

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10 12 14 16

sin(x) sin(2x)

Period = 1/freq

V=Sin(ωt+ɸ)

Period = 1/freq

RF Spectrum

01.04.2014 6

RF Spectrum

01.04.2014 7

Key difference RF vs Simple Analog • Size relative to wavelength Analog Phase of Signal much greater than

physical geometries RF Phase of Signal close to physical

geometries (KEY Here) Optical Phase of Signals much smaller

than physical geometries • Voltage and current change • Typically talk in Power • Order of magnitude of signals used log

scale) • Connections typically cause degradation i.e.

reflections • High quality cables, connections, and

components are critical to performance especially at higher frequencies

01.04.2014 8

9

Reflections and interference

Impedance Change

RF Link

01.04.2014 10

Design Considerations

o Link budget? o How big a signal do I need to

transmit? o How good a receiver or LNA do I

need? o What kind of antenna do I need?

o Where from to? o What does environment look like?

o Weather o Obstacles o Direct Line of Sight o Spectrum

o What am I sending o Real-time o How fast o How much data o Am I moving, stationary, how fast

o Physical limitations o Size o Weight o Power

01.04.2014 11

Key background

dB (comparing large numbers easily) Add rather than multiply Ratio not absolute

Simple Matrix algebra Key Software Spreadsheet analysis Matlab Labview Python

01.04.2014 12

What Does a Simple Transmitter Look Like?

01.04.2014 13

Multiplexer Signal Processing Modulation

Frequency Change

Filter

Power Amplifier

What Does a Simple Receiver Look Like?

01.04.2014 14

Filter

Frequency Change

Demodulation Signal Processing Demux

LNA

Antenna

Superheterodyne Receiver

01.04.2014 15

Antenna ı converts electrical power into radio

waves, and vice versa ı Intercepts electromagnetic wave from

air to produce tiny voltage ı Isotropic antenna send energy equally

in all directions ı Gain or directivity tells how much an

antenna transmits in one direction relative to isotropic

ı Antenna pattern

01.04.2014 16

Filter

01.04.2014 17

IN BAND 3 dB Bandwidth 1 dB Bandwidth Insertion Loss (Max, Min Avg.) Ripple Phase Response

Out of Band Ultimate Rejection 40 dB Bandwidth Rejection at ? Where do the signals go?

Amplifier

SMALL kTB Noise Floor Noise Figure Dynamic Range

01.04.2014 18

Large ı P1dB Compression ı OIP3 ı ACPR ı Harmonics ı Spurious ı Dynamic Range

Amplifier Outputs

01.04.2014 19

Mixer

01.04.2014 20

Noisy Output ı Sum ı Difference ı RF, LO ı Harmonics ı Integer Multiples ı Reflections ı ALL Integer Multiples ı All Signals

Noisy Output ı Lo ı Reflections ı All Signals

Intput ı Signal ı Difference ı RF, LO

Mixer Outputs

01.04.2014 21

Modulator / Demodulator • Carrier wave carrier(time) = (carrier amplitude)*sin(carrier frequency*time + phase shift)

• Typically modulation involved adding information to any of these parameters

• Phase • Frequency • Amplitude

• Common modulation formats are analog or digital • For analog modulation signals are continuously variation to the carrier wave • For digital modulation signals different states exist which represent sequences

of bits

01.04.2014 22

Analog Modulated Waveforms

01.04.2014 23

Digitally Modulated Waveforms

01.04.2014 24

QPSK

Signal Processing • Typically used in receivers • Gives the receiver the ability to be “adaptable” • The bandwidth or filter characteristics can be tailored to current conditions • Maintains signal levels and optimal use of the channel • Transmission channel changes dramatically due to conditions and motion

“equalization” • Modern cellular systems assign different channels specific to immediate needs

01.04.2014 25

Test and Verification Key Components

• Design is complete • Review is complete • Prototype has been built • Verification that system

meets specification • Design Verification

• Spectrum Analyzer • Signal Generator • Vector Network Analyzer • Power Meter

01.04.2014 26

Spectrum Analyzer • Basic measurement device required if looking at complex signals or where

multiple signals are used. • Basic measurement is frequency vs power • Typically two main types swept tuned and FFT • Modern version have many new capabilities for measuring including:

• Noise Figure • Group Delay • Phase Noise • Basic Modulation Analysis • Complex Modulation Analysis for:

• Mobile Wireless • Wireless LAN • Bluetooth • Satellite Communications • RADAR

01.04.2014 27

Signal Generator • Basic measurement device required to generate simple

and complex input signal • Basic use is a Sin wave at different power levels

and frequencies • Two main types analog and vector • Modern version have many new capabilities for

generating complex signals including: • AM, FM, PM • Arbitrary signals generated mathematically • Frequency hopping signals • Complex Modulation Signals including:

• Mobile Wireless • Wireless LAN • Bluetooth • Satellite Communications • RADAR

01.04.2014 28

Vector Network Analyzer • More complex measurement device used to

stimulate and measure amplitude and phase response of high frequency devices. • Basic use is stimulate a device such as an

amplifier with a Sin wave and measure the amplitude and phase response

• Modern version have many new capabilities for measuring more complex devices such as:

• Mixers or converters • Multiport devices up to 48 ports

01.04.2014 29

Power Meter • Most basic measurement device

• Measures power level coming out of devices • Typically two types

• Diode Based – higher dynamic range, fast • Thermistor Based – most accurate but lower

dynamic range • Gives no information as to frequency content • Newer power meters typically include sensor

with PC software based measurement unit • Can use in conjunction with a signal generator

to get basic frequency response of devices • Modern versions have ability to measure pulsed

or bursed signals

01.04.2014 30

Putting it all together

01.04.2014 31

Conclusion

• This is intended to be the first in a series of courses on the process of RF system design.

• RF system design is a complex process beginning with a detailed understanding of many things such as: • Operating environment • Size, weight, power • What information to be sent • One-way or two way • Stationary or moving • Target Cost • Available spectrum or frequency

• After a system is conceptualized, it is typically simulated • Finally a prototype needs to be built and its performance validated

01.04.2014 32

References

01.04.2014 33