Introduction to RF Design Fundamentals

Introduction to RF Design0,000,01
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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
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sin(x) sin(2x)
Period = 1/freq
V=Sin(ωt+ɸ)
Period = 1/freq

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

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
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What Does a Simple Transmitter Look Like?
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Multiplexer
Signal
Processing
Modulation
Frequency
Change Filter
Power
Amplifier

What Does a Simple Receiver Look Like?
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Filter
Frequency
Change
Demodulation
Signal
Processing
Demux
LNA
Antenna

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

Amplifier Outputs
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Mixer
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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

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
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Analog Modulated Waveforms
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Digitally Modulated Waveforms
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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
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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
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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
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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
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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
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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
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Putting it all together
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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

Introduction to RF Design Fundamentals

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Introduction to RF Design Fundamentals