an introduction to rf design, live presentation at eelive 2014
DESCRIPTION
Wireless communications is a hot topic in technology today, driven by technologies like Wireless Networking, Cellular Telephony, Wireless Connectivity and Satellite Communications among others. Traditionally, wireless and RF communications has been one of the last bastions of analog engineering. With the advent of low cost digital, high speed integrated circuits, this too has become part of the digital domain. Although information transmitted today is largely digital high frequency signals whether digital or analog always behave like analog signals so having fundamental knowledge of this high frequency behavior is key.TRANSCRIPT
Introduction to RF Design
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Information Processing Transmitter
Transmission Medium
Receiver Information Processing
Information Destination
Information Source
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Simplified Communications System Block Diagram
Information Processing Transmitter
Transmission Medium
Receiver Information Processing
Information Destination
Information Source
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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
RF Spectrum
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RF Spectrum
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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
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Reflections and interference
Impedance Change
RF Link
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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
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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
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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
Mixer Outputs
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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
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References
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