characterization and compensation of non-linear effects in … · 2017. 3. 24. · summary ılinear...
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Dr. Florian Ramian
Characterization and Compensation of Non-Linear
Effects in Components
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Agenda
ı Introduction: What Is a Non-Linear Device
ı Characterization of Non-Linear Devices
Characterization Parameters
Traditional CW level swept measurement
Modulated Measurement
ı Compensation of Linear and Non-Linear Effects
Equalizer
Digital Predistortion (DPD)
ı Summary
A&D Symposium 216.03.2017
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Introduction
ı What is a non-linear device?
16.03.2017 A&D Symposium 3
DUT
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Agenda
ı Introduction: What Is a Non-Linear Device
ı Characterization of Non-Linear Devices
Characterization Parameters
Traditional CW level swept measurement
Modulated Measurement
ı Compensation of Linear and Non-Linear Effects
Equalizer
Digital Predistortion (DPD)
ı Summary
A&D Symposium 416.03.2017
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Characterization of Non-Linear Devices
Characterization Parametersı Distortion: AM/AM,
AM/PM
ı Gain
ı Compression
16.03.2017 A&D Symposium 5
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Characterization of Non-Linear Devices
CW Stimulusı Measurement of amplitude dependent effects sweep input amplitude
ı Level swept CW signal
16.03.2017 A&D Symposium 6
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Measurement Instruments
ı VNA
ı Signal Generator / Signal Analyzer
16.03.2017 A&D Symposium 7
CW Measurement
Modulated Measurement
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Modulated Measurements
DistortionCW distortion
measurement
describes DUT
behavior, but
does not indicate
whether the DUT
will distort the
modulated signal
significantly
16.03.2017 A&D Symposium 8
Stimulus: Ramp
AM/AM is a line as expected
Line Width: Memory Effect
Stimulus: Modulated signal
AM/AM is a “cloud”
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Modulated Measurements
Gain Measurementı Gain at specified frequency / level can be precisely measured with CW
Gain @ 2 GHz / 0 dBm input level: 17.9 dB
ı But: a real word signal looks like this
16.03.2017 A&D Symposium 9
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Modulated Measurements
Gain Measurementı Measurement on a modulated signal is equivalent to multiple gain measurements across
the input power range
16.03.2017 A&D Symposium 10
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Modulated Measurements
Principle
16.03.2017 A&D Symposium 11
VSG
(play
waveform)
VSA
(capture RF
signal)RF connection
Data / Control Connection (LAN)
DSP
Reference
signal (Ref)
Measured signal
(Meas)
DUT
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Measurement Principle (DSP)
A&D Symposium 12
DSP
Reference
signal (Ref)
Measured
signal (Meas)
Sync
Synchronized
Meas signal
Compare
Gain,
Distortion,
EVM, …
16.03.2017
Reference
signal (Ref)
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Modulated Measurements
All Characterization Results from a Single Measurement
16.03.2017 A&D Symposium 13
ACLR
Distortion
Numeric
Results,
modulation
accuracy:
• EVM
• I/Q
Imbalance
• …
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Modulated Measurements
Modulation Accuracyı EVM Measurement based on a sample-by-
sample comparison
ı Depending on oversampling and distortion
of DUT, EVM may differ from demodulation
EVM measurements
16.03.2017 A&D Symposium 14
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Agenda
ı Introduction: What Is a Non-Linear Device
ı Characterization of Non-Linear Devices
Characterization Parameters
Traditional CW level swept measurement
Modulated Measurement
ı Compensation of Linear and Non-Linear Effects
Equalizer
Digital Predistortion (DPD)
ı Summary
A&D Symposium 1516.03.2017
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Compensation of Linear and Non-Linear Effects
ı Frequency response
ı Non-linear effects
16.03.2017 A&D Symposium 16
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Compensation of Frequency Response
Equalizerı Frequency response can be compensated by a filter, often referred to as “equalizer”
ı Flattened magnitude / phase vs. frequency
16.03.2017 A&D Symposium 17
Equalizer
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Compensation of Non-Linearities
Digital Predistortion (DPD)
16.03.2017 A&D Symposium 18
DPD
EVM
ACLR
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Model Based DPD
Characterization of DUT
16.03.2017 A&D Symposium 19
Apply (inverse) model to signal, i.e. in the
TX chipset
DUT
DUT
TX Chipset
𝑧−1 𝑛BB
Inverse
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Waveform Based DPD
DPD on Individual Samples
16.03.2017 A&D Symposium 20
ı Each sample is predistorted to a
new value
ı Since each sample is individually
predistorted, any memory effect
can be compensated
samples of equal level may have
different predistorted levels
compensation is limited to
measured bandwidth
Original Signal
Measured Signal
Predistorted Signal
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Waveform Based DPD
Iterative Approach
Measure
Compensate each individual
sample
Upload new WV to SigGen
16.03.2017 A&D Symposium 21
DUT
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Agenda
ı Introduction: What Is a Non-Linear Device
ı Characterization of Non-Linear Devices
Characterization Parameters
Traditional CW level swept measurement
Modulated Measurement
ı Compensation of Linear and Non-Linear Effects
Equalizer
Digital Predistortion (DPD)
ı Summary
A&D Symposium 2216.03.2017
![Page 23: Characterization and Compensation of Non-Linear Effects in … · 2017. 3. 24. · Summary ıLinear and non-linear effects contribute significantly to signal quality ıNon-linear](https://reader035.vdocuments.us/reader035/viewer/2022071505/61262c390661ae63a362f8ad/html5/thumbnails/23.jpg)
Summary
ı Linear and non-linear effects contribute significantly to signal quality
ı Non-linear effects may vary significantly, depending on the stimulus (input signal)
ı Characterization of these effects is vital to understand limitations to system design
ı With effects understood, compensation methods can be contemplated
ı R&S FSW-K18 Amplifier Measurement Personality characterizes signal and evaluated
different compensation methods
16.03.2017 A&D Symposium 23