characterization and compensation of non-linear effects in … · 2017. 3. 24. · summary ılinear...

Dr. Florian Ramian

Characterization and Compensation of Non-Linear

Effects in Components

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

Introduction

ı What is a non-linear device?

16.03.2017 A&D Symposium 3

DUT

Agenda







Equalizer


ı Summary


Characterization of Non-Linear Devices

Characterization Parametersı Distortion: AM/AM,

AM/PM

ı Gain

ı Compression


Characterization of Non-Linear Devices

CW Stimulusı Measurement of amplitude dependent effects sweep input amplitude

ı Level swept CW signal


Measurement Instruments

ı VNA

ı Signal Generator / Signal Analyzer


CW Measurement


Modulated Measurements

DistortionCW distortion

measurement

describes DUT

behavior, but

does not indicate

whether the DUT

will distort the

modulated signal

significantly


Stimulus: Ramp

AM/AM is a line as expected

Line Width: Memory Effect

Stimulus: Modulated signal

AM/AM is a “cloud”


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



Gain Measurementı Measurement on a modulated signal is equivalent to multiple gain measurements across

the input power range



Principle


VSG

(play

waveform)

VSA

(capture RF

signal)RF connection

Data / Control Connection (LAN)

DSP

Reference

signal (Ref)

Measured signal

(Meas)

DUT

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)


All Characterization Results from a Single Measurement


ACLR

Distortion

Numeric

Results,

modulation

accuracy:

• EVM

• I/Q

Imbalance

• …


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


Agenda







Equalizer


ı Summary


Compensation of Linear and Non-Linear Effects

ı Frequency response

ı Non-linear effects


Compensation of Frequency Response

Equalizerı Frequency response can be compensated by a filter, often referred to as “equalizer”

ı Flattened magnitude / phase vs. frequency


Equalizer

Compensation of Non-Linearities



DPD

EVM

ACLR

Model Based DPD

Characterization of DUT


Apply (inverse) model to signal, i.e. in the

TX chipset

DUT

DUT

TX Chipset

𝑧−1 𝑛BB

Inverse

Waveform Based DPD

DPD on Individual Samples


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

Waveform Based DPD

Iterative Approach

Measure

Compensate each individual

sample

Upload new WV to SigGen


DUT

Agenda







Equalizer


ı Summary


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


characterization and compensation of non-linear effects in … · 2017. 3. 24. · summary ılinear...

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