Rohde&Schwarz SMW-K540, SMW-K541, SMW-K546 User Manual

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R&S®SMW-K540, R&S®SMW-K541, R&S®SMW-K546

Envelope Tracking, AM/AM, AM/PM Predistortion, Digital Doherty User Manual

(;Úí62)

1176950602 Version 23

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This document describes the following software options:

●

R&S®SMW-K540 Envelope Tracking (1413.7215.xx)

●

R&S®SMW-K541 AM/AM, AM/PM Predistortion (1413.7267.xx)

●

R&S®SMW-K546 Digital Doherty (1414.6487-xx)

This manual describes firmware version FW 5.00.044.xx and later of the R&S®SMW200A.

© 2021 Rohde & Schwarz GmbH & Co. KG Mühldorfstr. 15, 81671 München, Germany Phone: +49 89 41 29 - 0 Email: info@rohde-schwarz.com Internet: www.rohde-schwarz.com Subject to change – data without tolerance limits is not binding. R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG. Trade names are trademarks of the owners.

1176.9506.02 | Version 23 | R&S®SMW-K540, R&S®SMW-K541, R&S®SMW-K546

The following abbreviations are used throughout this manual: R&S®SMW200A is abbreviated as R&S SMW; the license types 02/03/07/11/13/16/12 are abbreviated as xx.

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R&S®SMW-K540, R&S®SMW-K541, R&S®SMW-K546

1 Welcome to the R&S SMW-K54x options.............................................5

1.1 Accessing the required settings..................................................................................6

1.2 What's new.....................................................................................................................7

1.3 Documentation overview..............................................................................................7

1.3.1 Getting started manual....................................................................................................7

1.3.2 User manuals and help................................................................................................... 7

1.3.3 Tutorials...........................................................................................................................7

1.3.4 Service manual............................................................................................................... 8

1.3.5 Instrument security procedures.......................................................................................8

1.3.6 Printed safety instructions............................................................................................... 8

1.3.7 Data sheets and brochures............................................................................................. 8

Contents

1.3.8 Release notes and open source acknowledgment (OSA).............................................. 8

1.3.9 Application notes, application cards, white papers, etc...................................................8

1.4 Scope............................................................................................................................. 9

1.5 Notes on screenshots...................................................................................................9

2 Generation of envelope tracking signals...........................................10

2.1 Required options.........................................................................................................10

2.2 About the envelope tracking......................................................................................10

2.2.1 Envelope voltage adaptation modes............................................................................. 11

2.2.2

2.2.3 Envelope shaping and shaping methods...................................................................... 12

Signal parameters for testing according to the eTrak® specification.............................12

2.3 General RF envelope settings....................................................................................21

2.4 Envelope settings....................................................................................................... 29

2.5 Shaping settings......................................................................................................... 31

2.6 Edit I/Q envelope shape settings...............................................................................40

2.7 Polynomial coefficients settings............................................................................... 42

3 Applying digital predistortion............................................................. 45

3.1 Required options.........................................................................................................45

3.2 About digital predistortion......................................................................................... 45

3.2.1 Defining the power level of the generated signal.......................................................... 46

3.2.2 Defining the correction values.......................................................................................47

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3.2.3 Finding out the correction values.................................................................................. 50

3.3 Digital predistortions AM/AM and AM/PM settings..................................................51

3.3.1 General settings............................................................................................................ 52

3.3.2 Predistortion settings.....................................................................................................55

3.3.3 Edit predistortion table settings..................................................................................... 59

3.3.4 Polynomial coefficients settings.................................................................................... 62

3.3.5 Normalized data settings...............................................................................................65

3.4 Compensating non-linear RF effects........................................................................ 67

4 Testing Doherty power amplifiers...................................................... 69

4.1 Required options.........................................................................................................69

4.2 About the digital Doherty power amplifiers..............................................................69

4.2.1 RF phase alignment...................................................................................................... 70

Contents

4.2.2 Defining the correction values.......................................................................................71

4.3 Digital Doherty settings..............................................................................................72

4.3.1 General settings............................................................................................................ 73

4.3.2 Shaping settings and settings for classic Doherty shaping........................................... 76

4.3.3 Edit shaping table settings............................................................................................ 77

4.3.4 Polynomial coefficients settings.................................................................................... 78

4.3.5 Normalized data settings...............................................................................................79

5 How to generate a control signal for power amplifier envelope

tracking tests........................................................................................80

6 How to apply a DPD to improve the efficiency of RF PAs................84

7 Remote-control commands.................................................................89

7.1 SOURce:IQ:OUTPut subsystem................................................................................ 90

7.2 SOURce:IQ:OUTPut:ENVelope commands.............................................................. 92

7.3 SOURce:IQ:DPD subsystem.................................................................................... 107

7.4 SOURce:IQ:DPD and SOURce:IQ:DOHerty subsystem.........................................114

7.5 SOURce:IQ:DOHerty subsystem............................................................................. 123

List of commands.............................................................................. 131

Index....................................................................................................135

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1 Welcome to the R&S SMW-K54x options

The R&S SMW-K540 is a software option that allows you to generate an envelope tracking signal, that follows the envelope variation of the RF signal.

R&S SMW-K540 key features

●

Baseband signal, RF signal, and envelope signal generation out of one instrument

●

Envelope signal derived directly and in real time from the baseband signal

●

Fully synchronous envelope and RF signal with optional delay compensation for time alignment of the envelope signal

●

Simultaneous output of envelope and inverted envelope signal

●

Flexible envelope shaping based on different algorithms incl. a build-in table shaping editor

●

Import/export interface for files describing shaping functions

●

Real-time display of the characteristics of the envelope signal

Welcome to the R&S SMW-K54x options

The R&S SMW-K541 is a software option that adds functionality to define and apply AM/AM and AM/PM predistortions.

R&S SMW-K541 key features

●

Applying user-defined AM/AM and AM/PM digital predistortions directly on the digital baseband signal

●

Digital predistortions are applied directly and in real time to the baseband signal, i.e. to any Digital Standard signal or with ARB waveforms

●

Separate or superimposed AM/AM or AM/PM predistortion also with variable order in the processing flow

●

Flexible shaping of the predistortion functions based on a polynomial function and a build-in table editor

●

Import/export interface for files describing the predistortion functions, i.e. load of AM/AM and AM/PM tables directly from characterization software

●

Real-time display of the correction functions

●

In instruments equipped with the option R&S SMW-K540, digitally predistorted baseband signal, RF signal, and envelope signal generation out of one instrument

The R&S SMW-K546 is a software option that assists development and testing of Doherty amplifiers by digitally splitting one input signal into two components for carrier and peaking amplifiers.

R&S SMW-K546 key features

●

RF signals for two power amplifiers (PA) generated out of one instrument

●

Ensured constant phase delta between the two RF signals

●

Applying user-defined, input power dependent power and phase functions directly and in real time on the digital baseband signal

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●

Flexible shaping of the power and phase based on a polynomial function and a built-in table editor

●

Import/export interface for files describing the power and phase functions, i.e. load of shaping tables directly from characterization software

●

Real-time display of the power and phase correction values

●

In instruments equipped with the option R&S SMW-K541, superimposing digital predistortion and digital Dohtery

This user manual contains a description of the functionality that the application provides, including remote control operation.

All functions not discussed in this manual are the same as in the base unit and are described in the R&S SMW user manual. The latest version is available at:

www.rohde-schwarz.com/manual/SMW200A

Installation

You can find detailed installation instructions in the delivery of the option or in the R&S SMW service manual.

Welcome to the R&S SMW-K54x options

Accessing the required settings

1.1 Accessing the required settings

To open the dialog with Envelope Tracking settings

1. In the block diagram of the R&S SMW, select the "I/Q OUT" connector to unfold the "I/Q Analog" block.

A dialog box opens that displays the provided general settings.

2. Select "I/Q Analog > I/Q Analog Outputs > General".

3. Select "RF Envelope > On".

To open the dialog with DPD settings

► In the block diagram of the R&S SMW, select "I/Q Mod > Digital Predistortion >

AM/AM AM/PM".

A dialog box opens that displays the provided settings.

The signal generation is not started immediately. To start signal generation with the default settings, select "State > On".

To open the dialog with Digital Doherty settings

► In the block diagram of the R&S SMW, select "I/Q Mod > Digital Predistortion >

Digital Doherty".

A dialog box opens that displays the provided settings.

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1.2 What's new

This manual describes firmware version FW 5.00.044.xx and later of the R&S®SMW200A.

Compared to the previous version there are editorial changes only.

1.3 Documentation overview

This section provides an overview of the R&S SMW user documentation. Unless specified otherwise, you find the documents on the R&S SMW product page at:

www.rohde-schwarz.com/manual/smw200a

1.3.1 Getting started manual

Welcome to the R&S SMW-K54x options

Documentation overview

Introduces the R&S SMW and describes how to set up and start working with the product. Includes basic operations, typical measurement examples, and general information, e.g. safety instructions, etc. A printed version is delivered with the instrument.

1.3.2 User manuals and help

Separate manuals for the base unit and the software options are provided for download:

●

Base unit manual Contains the description of all instrument modes and functions. It also provides an introduction to remote control, a complete description of the remote control commands with programming examples, and information on maintenance, instrument interfaces and error messages. Includes the contents of the getting started manual.

●

Software option manual Contains the description of the specific functions of an option. Basic information on operating the R&S SMW is not included.

The contents of the user manuals are available as help in the R&S SMW. The help offers quick, context-sensitive access to the complete information for the base unit and the software options.

All user manuals are also available for download or for immediate display on the Internet.

1.3.3 Tutorials

The R&S SMW provides interactive examples and demonstrations on operating the instrument in form of tutorials. A set of tutorials is available directly on the instrument.

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1.3.4 Service manual

Describes the performance test for checking compliance with rated specifications, firmware update, troubleshooting, adjustments, installing options and maintenance.

The service manual is available for registered users on the global Rohde & Schwarz information system (GLORIS):

https://gloris.rohde-schwarz.com

1.3.5 Instrument security procedures

Deals with security issues when working with the R&S SMW in secure areas. It is available for download on the Internet.

1.3.6 Printed safety instructions

Provides safety information in many languages. The printed document is delivered with the product.

Welcome to the R&S SMW-K54x options

Documentation overview

1.3.7 Data sheets and brochures

The data sheet contains the technical specifications of the R&S SMW. It also lists the options and their order numbers and optional accessories.

The brochure provides an overview of the instrument and deals with the specific characteristics.

See www.rohde-schwarz.com/brochure-datasheet/smw200a

1.3.8 Release notes and open source acknowledgment (OSA)

The release notes list new features, improvements and known issues of the current firmware version, and describe the firmware installation.

The open-source acknowledgment document provides verbatim license texts of the used open source software.

See www.rohde-schwarz.com/firmware/smw200a

1.3.9 Application notes, application cards, white papers, etc.

These documents deal with special applications or background information on particular topics.

See www.rohde-schwarz.com/application/smw200a and www.rohde-schwarz.com/

manual/smw200a

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1.4 Scope

Tasks (in manual or remote operation) that are also performed in the base unit in the same way are not described here.

In particular, it includes:

●

Managing settings and data lists, like saving and loading settings, creating and accessing data lists, or accessing files in a particular directory.

●

Information on regular trigger, marker and clock signals and filter settings, if appropriate.

●

General instrument configuration, such as checking the system configuration, configuring networks and remote operation

●

Using the common status registers

For a description of such tasks, see the R&S SMW user manual.

Welcome to the R&S SMW-K54x options

Notes on screenshots

1.5 Notes on screenshots

When describing the functions of the product, we use sample screenshots. These screenshots are meant to illustrate as many as possible of the provided functions and possible interdependencies between parameters. The shown values may not represent realistic usage scenarios.

The screenshots usually show a fully equipped product, that is: with all options installed. Thus, some functions shown in the screenshots may not be available in your particular product configuration.

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2 Generation of envelope tracking signals

Envelope tracking (ET) is a method used by modern power amplifiers (PA) to improve their efficiency, especially when amplifying RF signals with a high peak to average power (PAPR). An envelope tracking detector "tracks" the power variations in the input signal of the PA. The PA then varies synchronously to this variation the supply voltage vcc at its end amplifying stage.

This section introduces the concept of the envelope tracking functionality and the way it is implemented in the R&S SMW.

Refer to Chapter 5, "How to generate a control signal for power amplifier envelope

tracking tests", on page 80 for step-by-step instruction on how to use the provided

function.

2.1 Required options

Generation of envelope tracking signals

About the envelope tracking

The equipment layout for generation and output of envelope tracking signal includes:

●

Option Standard or wideband Baseband Generator (R&S SMW-B10/-B9) Option Baseband Main Module, one/two I/Q paths to RF (R&S SMW-B13/B13T) or Wideband baseband main module (R&S SMW-B13XT) Incl. output the baseband signal at the single ended outputs

●

Option Differential Analog I/Q Outputs (R&S SMW-K16) per signal path

●

Option Envelope Tracking (R&S SMW-K540) per signal path If R&S SMW-B13XT is installed, the option can be installed once, in path A

●

Optional option AM/AM AM/PM Predistortion (R&S SMW-K541) per signal path

For more information, see data sheet.

2.2 About the envelope tracking

The R&S SMW allows you to generate an envelope tracking signal, that follows the envelope variation of the RF signal.

Principle of the envelope tracking

The Figure 2-1 shows a simplified test setup for testing of a PA with an envelope tracking. This illustration is intended to explain the principle in general, not all connections and required equipment are considered.

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I BAR OUT

(Rear Panel)

Figure 2-1: Simplified test setup for power amplifier envelope tracking tests

The R&S SMW in this setup is configured to generate both, an RF signal with complex modulation scheme and an envelope signal, that follows the envelope variation of this RF signal. A suitable test signal is, for example, an EUTRA/LTE DL signal.

Generation of envelope tracking signals

About the envelope tracking

RF Signal

I OUT

(Rear Panel)

out

RF A

Envelope Signal (E)

Inverted Envelope Signal (Ē)

PEP

Modulator

out

The R&S SMW generates the envelope signal directly from the baseband signal. The envelope signal is a voltage signal, with voltage level V

the RF signal (√[I(t)2+Q(t)2]) of the corresponding path. If you do not apply a shaping function, the envelope signal linear dependent follows the variation of the RF signal's envelope.

The envelope signal is output at the I out and I Bar out rear panel connectors. This envelope signal is then further fed to an external DC modulator.

The PA receives the RF input signal and the dynamically adapted supply voltage vcc. Ideally, the PA gain stays constant.

Suitable baseband signal to observe the effect of the envelope tracking settings

To simplify the explanation in the following sections, we use a simple ramp function as a baseband signal modulated on the RF carrier.

Other suitable baseband signals are signals with relative constant envelope. You find a choice of predefined signals in the "Baseband > Custom Digital Mod > Set according to standard" dialog. With the default settings in this dialog, you can observe the generated envelope signal and the effects of enabled shaping.

2.2.1 Envelope voltage adaptation modes

proportional to the power of

out

In the R&S SMW, you define the voltage of the generated envelope signal using one of the following modes:

●

Auto Power/Normilized Envelope Voltage Adaptation:

In this mode, you define the desired input characteristics of the power amplifier. Based on these values and depending on the crest factor of the generated signal,

the R&S SMW calculates: – The voltage on the I out/I Bar out connectors (V

Min/Max) and a bias (Bias),

out

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– The RMS level of the RF signal The auto voltage adaptation mode is a suitable choice, if you have knowledge on

the power amplifier components and characteristics. Common PA characteristics are the supply voltage Vcc, the input power PEPin required for working in the linear

range and the gain characteristics of the external DC modulator. You find the required values in the documentation of your power amplifier, for example in its data sheet.

●

Manual Envelope Voltage Adaptation:

In this mode, you can also define the operating range of the power amplifier based on a pre-gain and a post-gain range. Based on these values, the instrument calculates the supply voltage Vcc.

All modes support envelope shaping.

Generation of envelope tracking signals

About the envelope tracking

2.2.2

Signal parameters for testing according to the eTrak

In the R&S SMW, you can select one of the predefined eTrak® interface types so that the generated signal is conformed with the MIPI®Alliance specification "Analog Reference Interface for Envelope Tracking Specification".

Table 2-1: Default parameters per eTrak® Interface Type

Parameter 1.2 Vpp 1.5 Vpp 2 Vpp

I/Q output Type Differential Differential Differential

Bias 500 mV 600 mV 900 mV

Vpp Max 1.2 V 1.5 V 2 V

Bipolar Input On On On

2.2.3 Envelope shaping and shaping methods

Envelope shaping is a method that uses functions to describe the relationship between supply voltage and RF input power. An envelope shaping function is a trade-off between effectivity and improved linearity of the PA.

specification

In the R&S SMW, you can select the way you define the shaping function. You can choose between:

●

2 predefined simple linear functions (see Chapter 2.2.3.1, "About the linear functions", on page 13)

●

3 detroughing functions with a configurable factor (see Chapter 2.2.3.2, "About the detroughing function", on page 14)

●

A polynomial function with up to 10 polynomial coefficients (see Chapter 2.2.3.3, "About the polynomial function", on page 14)

●

A shaping function defined as a shaping table (see Chapter 2.2.3.4, "About the shaping table", on page 15)

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●

To set the correction values in raw format with a single remote control command (see Chapter 2.2.3.5, "Shaping function in raw data format", on page 16)

The linear, the detroughing and the polynomial shaping functions are mathematical expressions that are described as function of the variable x, see Table 2-2.

Table 2-2: Definition of the variable x depending on the envelope voltage adaptation mode

"Envelope Voltage Adaptation" x

Generation of envelope tracking signals

About the envelope tracking

Auto Power x = Vin - V

Auto Normalized x = Vin/V

Manual x = V

The mathematical expressions and further information on the shaping functions are provided in the corresponding sections.

See also Chapter 2.2.3.6, "Converting shaping functions and understanding the dis-

played values", on page 16.

● About the linear functions........................................................................................13

● About the detroughing function............................................................................... 14

● About the polynomial function.................................................................................14

● About the shaping table.......................................................................................... 15

● Shaping function in raw data format........................................................................16

● Converting shaping functions and understanding the displayed values................. 16

2.2.3.1 About the linear functions

The linear shaping can be used for less demanding applications, simple analysis, and the first interactions by designing the optimum envelope shape. Because the shaping gain of the linear function is 0 dB, in "Envelope Voltage Adaptation > Manual" mode this function is suitable for determining the "Pre-/Post-Gain" values (see Example "Cal-

culating the current VCC in "Manual" mode" on page 20).

in, min

x ≥ 0

in,max

Env/VEnv,max

Provided are two linear functions, where each of them depends on the "Envelope Voltage Adaptation" mode:

●

Linear (Voltage) – f(x) = x in "Auto Normalized/Manual" – f(x) = b*x + V

●

Linear (Power) –

f(x) = x2 in "Auto Normalized/Manual"

–

f(x) = b*x2 + V

in "Auto Power"

cc,min

in "Auto Power"

cc,min

Where:

●

The variable x depends on the "Envelope Voltage Adaptation" mode, see

Table 2-2.

●

The constant b is calculated as: b = (V

cc,max

- V

cc,min

)/(V

in,max

- V

in,min

)

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See also Chapter 2.2.3.6, "Converting shaping functions and understanding the dis-

played values", on page 16.

2.2.3.2 About the detroughing function

Detroughing functions are well-defined mathematical functions that prevent that the supply voltage Vcc drops down to zero or falls under specified limits. That is, they pre-

vent that the signal is clipped.

Provided are the following functions:

●

f(x) = x + d*e

●

f(x) = 1 - (1 - d)*cos(x*pi/2)

●

f(x) = d + (1 - d)*x

-x/d

Where:

●

x is a variable, that depends on the "Envelope Voltage Adaptation" mode, see

Table 2-2

●

a is the Exponent (a).

●

d is the Detroughing Factor (d), that limits the supply voltage Vcc in the low-power region and controls the shaping.

The detroughing factor (d) can be set manually or derived from the selected V value. In the latter case, it is calculated as follows:

d = V

cc,min/Vcc,max

See Couple Detroughing Factor with Vcc. A "Detroughing Factor = 0" defines a linear function.

Generation of envelope tracking signals

About the envelope tracking

See also Chapter 2.2.3.6, "Converting shaping functions and understanding the dis-

played values", on page 16.

2.2.3.3 About the polynomial function

The polynomial function is an analytical method to describe a shaping function. The polynomial function is defined as follows:

f(x) = a0 + ∑(an*xn), where n ≤10 and:

●

Depending on the "Envelope Voltage Adaptation" mode, f(x) is: – f(x) = Vcc(x) in "Auto Power"

– f(x) = Vcc/V

●

The polynomial order n, the polynomial constant a0, and polynomial coefficients a

(x) in "Auto Normalized/Manual"

cc,max

to an are user-definable, see Chapter 2.7, "Polynomial coefficients settings", on page 42

●

x depends on the "Envelope Voltage Adaptation" mode, see Table 2-2

The default polynomial function with n = 1, a0 = 0 and a0 = 1 describes a linear function.

2.2.3.4 About the shaping table

Generation of envelope tracking signals

About the envelope tracking

The envelope shaping table is a widely used method to define the shaping function. This kind of definition is suitable if you have knowledge on or aim to achieve an exact relation between supply voltage and RF input power. For example, with suitable settings, the shaping table can precisely describe the transition region of the PA.

You can receive information on suitable envelope shaping values form the power amplifier manufacturer.

In the R&S SMW, there are two ways to define a shaping table function:

●

Externally

Create a shaping table file as a CSV file with Microsoft Excel, with a Notepad or a similar tool. Save it with the predefined extension, transfer it to and load it into the instrument. See also "File format of the shaping table file" on page 15.

●

Internally

Use the built-in editor table editor, see Chapter 2.6, "Edit I/Q envelope shape set-

tings", on page 40.

File format of the shaping table file

The shaping table files are files with predefined extension and simple file format, see

Table 2-3.

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Table 2-3: Shaping table files: format and extensions

"Envelope Voltage Adaptation" File extension Header (optional)

Generation of envelope tracking signals

About the envelope tracking

Auto Power

Auto Normalized/Manual

*.iq_lutpv # Rohde & Schwarz - IQ Output

*.iq_lut # Rohde & Schwarz - IQ Output

The header is optional. The file content is list of up to 4000 comma-separated value pairs; a new line indicator separates the pairs.

Example: Shaping table file content (*.iq_lut file)

# Rohde & Schwarz - IQ Output Envelope Shaping Table

# Vin/Vmax,Vcc/Vmax

0.3,0.4

0.35,0.45

0.56,0.55

0.4,0.5

0.6,0.65

0,0.135

2.2.3.5 Shaping function in raw data format

Envelope Shaping Table

# Power[dBm],Vcc[V]

Envelope Shaping Table

# Vin/Vmax,Vcc/Vmax

The shaping values are defined directly, with a single remote control command. You define up to 4000 comma-separated value pairs, describing the Vin/Vmax,Vcc/Vmax or Power[dBm],Vcc[V].

Example:

SOURce1:OUTPut:ANALog:ENVelope:SHAPing:PV:FILE:DATA 0,0, 0.1,0.2, 1,1

See:

●

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE:DATA

on page 104

●

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:PV:FILE: DATA on page 104

●

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE:NEW

on page 104

●

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:PV:FILE:NEW

on page 104

2.2.3.6 Converting shaping functions and understanding the displayed values

If an envelope function is defined, the "Shaping" dialog displays the diagram of the resulting envelope shape.

See for example Figure 2-7.

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Several parameters influence the displayed information:

●

The selected "Envelope Voltage Adaptation" determines whether the x-axis uses normalized or linear values

●

The selected "Graphic Configuration > Scale" sets the x-axis units

●

The selected VccMin/Max and PEPinMin/Max values set the borders of the clipping areas

●

The selected "Shaping" function and the parameters influence the envelope shape.

The illustration on Figure 2-2 shows how these parameters influence a linear shaping function.

Generation of envelope tracking signals

About the envelope tracking

Figure 2-2: Understanding the displayed values ("Shaping > Linear (Voltage)")

Shaded area = Area where the signal is clipped and the envelope signal is held constant 1a, 1b, 2a, 2b = V

Shaping = Linear (Voltage) 3a = Linear function (dashed line) in "Auto Power" mode, if V

3b = Linear function in "Auto Power" mode, if V 4a = Linear function (dashed line) in "Auto Normalized" mode, if V 4b = Linear function in "Auto Normalized" mode, if V V

VccNorm = Vcc in "Auto Normalized" mode VccPow

VccPow

cc,min/Vcc,max

= Operating point

= Vcc in "Auto Power" mode and V = Vcc in "Auto Power" mode and V

and PEPinMin/Max values that set the borders of the clipping areas

= 0 V

cc,min

> 0 V

cc,min

= 0 V

cc,min

> 0 V

cc,min

= 0 V

cc,min

> 0 V

cc,min

For information on the provided shaping functions and their formulas, see:

●

Chapter 2.2.3.1, "About the linear functions", on page 13

●

Chapter 2.2.3.2, "About the detroughing function", on page 14

●

Chapter 2.2.3.3, "About the polynomial function", on page 14

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Generation of envelope tracking signals

The group of examples in this section uses the same linear shaping function to explain the representation in the different voltage adaptation modes. The example explains the displayed values and how they are calculated and converted. The same principle applies for the other shaping methods.

Common settings

●

"Envelope Voltage Adaptation > Auto Power"

●

Vcc Max = 1 V

●

PEPinMin = -30 dBm corresponds to V

●

PEPinMax = 0 dBm corresponds to V

●

Pin = -15 dBm corresponds Vin = 0.04 V

●

PEP = -3.4 dB

●

"Shaping > Linear (Voltage)"

"Graphic Scale > Power" "Graphic Scale > Voltage"

= 0.0071 V

in,min

= 0.2236 V

in,max

About the envelope tracking

Example: Calculating the current VccPow0 ("Auto Power" mode, Vcc Min = 0 V)

Configuration as described in Common settings and:

●

= 0 V

cc,min

●

f (x) = b*x + V

cc,min

(see Chapter 2.2.3.1, "About the linear functions", on page 13)

VccPow0 = [(V

cc,max

- V

cc,min

)/(V

in,max

- V

)] * (Vin - V

in,min

) + V

cc,min

VccPow0 = [(1 - 0)/(0.2236 - 0.0071)]*(0.04 - 0.0071) + 0

VccPow0 = 0.151 V

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Example: Calculating the current VccPow1 ("Auto Power" mode, Vcc Min > 0 V)

Configuration as described in Common settings and:

●

= 200 mV

cc,min

VccPow1 = [(V

cc,max

- V

cc,min

)/(V

in,max

- V

VccPow1 = [(1 - 0.2)/(0.2236 - 0.0071)]*(0.04 - 0.0071) + 0.2

VccPow1 = 0.321 V

Generation of envelope tracking signals

About the envelope tracking

)] * (Vin - V

in,min

) + V

cc,min

Example: Calculating the current VccNorm ("Auto Normalized" mode)

Configuration as described in Common settings and:

●

"Envelope Voltage Adaptation > Auto Normalized"

●

The x-axis shows the normalized values Vin/V

in,max

; The operating point with Vin = 0.04 V corresponds to Vin/V

●

f (x) = x, i.e. VccNorm = Vin/V

= 0.04 / 0.2236 = 0.178

in.max

in,max

VccNorm = 0.178 V

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Generation of envelope tracking signals

About the envelope tracking

If the V

●

If 0 < Vin/V

●

If Vin/V

For the previous example, if V

value is changed (V

cc,min

≤ V

in,max

> V

in,max

cc,min

> 0 V), then the following applies:

cc,min

, the signal is clipped and VccNorm = V

cc,min

, then VccNorm = Vin/V

= 200 mV, that VccNorm = V

cc,min

in,max

cc,min

= 0.2 V.

Example: Calculating the current VCC in "Manual" mode

In "Envelope Voltage Adaptation > Manual" mode, set the parameter "Pre-Gain = PEP = - 3.4 dB".

The displayed shaping function resembles the shaping function in "Auto Normalized" mode; the same formulas apply, too.

You can also query the VCC values for any specified x in the supported voltage adaptation mode and units.

See [:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:VALue? on page 101.

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Additional information

The described principle applies for any shaping function.

Only if linear shaping is used, the VCCNorm can also be directly converted to VCCPow according to the following formula:

Pow

(x) = [f

Norm

(x) - V

in,min/Vin,max

]*[(V

cc,max

Generation of envelope tracking signals

General RF envelope settings

- V

cc,min

)/(1 - V

in,min/Vin,max

)]

For example, if f

(x) = VCCNorm = 0.178 V, f

Norm

VccPow0 = [0.178 - 0.0071/0.2236]*[(1 - 0)/(1 - 0.0071/0.2236)]

VccPow0 = 0.151 V

2.3 General RF envelope settings

Access:

1. In the block diagram, select the "I/Q OUT" connector to unfold the "I/Q Analog" block.

2. Select "I/Q Analog > I/Q Analog Settings > General".

3. Select "RF Envelope > On".

(x) = VccPow0 is:

Pow

Figure 2-3: RF Envelope Settings (Example)

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1 = Termination and input impedance of the circuit board 2 = Voltage level measured at the circuit board 3 = Signal characteristics of the DC Modulator 4 = Signal characteristics at the inputs of the PA (see the documentation of the PA, for example its data

sheet)

The remote commands required to define these settings are described in Chap-

ter 7.2, "SOURce:IQ:OUTPut:ENVelope commands", on page 92.

Settings:

State..............................................................................................................................22

Set to Default................................................................................................................ 22

Save/Recall...................................................................................................................23

RF Envelope................................................................................................................. 23

Envelope Voltage Adaptation........................................................................................23

eTrak® Interface Type....................................................................................................24

I/Q Output Type.............................................................................................................24

Envelope Voltage Reference.........................................................................................24

Min/Max...................................................................................................................25

out

Bias............................................................................................................................... 25

DC Modulator characteristics........................................................................................25

└ EMF................................................................................................................ 26

└ Rin................................................................................................................... 26

└ Termination..................................................................................................... 26

└ Bipolar Input....................................................................................................26

└ VppMax............................................................................................................ 27

└ Gain................................................................................................................ 27

└ VccOffset..........................................................................................................27

PA characteristics..........................................................................................................28

└ VccMin/Max......................................................................................................28

└ Power Offset................................................................................................... 29

└ PEPinMin/Max................................................................................................. 29

Generation of envelope tracking signals

General RF envelope settings

State

Enables/disables the analog I/Q output. Note: By default, these output connectors are deactivated. Remote command:

[:SOURce<hw>]:IQ:OUTPut:ANALog:STATe on page 90

Set to Default

Calls the default settings. The values of the main parameters are listed in the following table.

Parameter Value

"State" Not affected by the "Set to Default"

"RF Envelope" Off

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Parameter Value

Generation of envelope tracking signals

General RF envelope settings

"I/Q Output Type"

"I/Q Level Vp (EMF)" 1 V

"Bias (EMF)" 0 mV

Depends on "System Configuration > External RF and I/Q > Preset behavior: Keep connections to external instruments":

●

"Off": Single Ended

●

"On": Not affected by the "Set to Default"

Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:PRESet on page 90

Save/Recall

Accesses the "Save/Recall" dialog, that is the standard instrument function for saving and recalling the complete dialog-related settings in a file. The provided navigation possibilities in the dialog are self-explanatory.

The settings are saved in a file with predefined extension. You can define the filename and the directory, in that you want to save the file.

See also, chapter "File and Data Management" in the R&S SMW user manual. Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:CATalog? on page 91 [:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:STORe on page 91 [:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:LOAD on page 91 [:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:DELete on page 91

RF Envelope

Option: R&S SMW-B9 - enabled in "System Config > Mode = Standard". Option: R&S SMW-B10 - enabled in "System Config > Mode = Standard/Advanced". Enables the output of a control signal that follows the RF envelope. This control signal

is provided for power amplifiers envelope tracking testing. The signal is output at the I out and I Bar out connectors.

See Chapter 5, "How to generate a control signal for power amplifier envelope tracking

tests", on page 80

Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:STATe on page 95

Envelope Voltage Adaptation

Defines the way you configure the voltage of the envelope tracking generator (see

Chapter 2.2.1, "Envelope voltage adaptation modes", on page 11).

"Auto Normalized"

Generation based on the physical characteristics of the power amplifier; the power values are normalized based on the selected PEPin

Max value.

This mode enables you to use the complete range of a selected detroughing function. See also Shaping settings and compare the values on the X axis on the graphical display.

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Generation of envelope tracking signals

General RF envelope settings

"Auto Power"

Generation based on the physical characteristics of the power amplifier, where the input power of the PA "PEPin" is defined with its min

and max values.

"Manual"

Generation, in that the operating range of the amplifier is defined based on a pre-gain and a post-gain range.

Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:ADAPtion on page 95

eTrak® Interface Type

Selects one of the predefined interface types or allows user-defined settings. See Chapter 2.2.2, "Signal parameters for testing according to the eTrak® specifica-

tion", on page 12.

Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:ETRak on page 96

I/Q Output Type

Selects the type of output signal. The provided parameters in the "I/Q Analog Outputs" dialog depend on the selected

output mode.

●

"Single-Ended"

If "RF Envelope > Off" Single-ended output at the I/Q connectors. Option: R&S SMW-B9: the signal from "I/Q Analog B" is output at the I Bar connectors.

●

If "RF Envelope > On" The envelope signal E is output at the I connectors.

You can define a bias between the output signal and ground.

"Differential"

Option: R&S SMW-B10 and R&S SMW-K16 Or R&S SMW-B9 and R&S SMW-K17.

●

If "RF Envelope > Off" The analog I/Q signal components are output at the I/Q and I/Q Bar connectors. Option: R&S SMW-B9: the differential signal output can be activated in "I/Q Analog A" block only. Single-ended and differential signals cannot be output simultaneously.

●

If "RF Envelope > On" The inverted envelope signal Ē is output at the I Bar connectors.

Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:TYPE on page 92

Envelope Voltage Reference

Defines whether the envelope voltage V

is set directly or it is estimated from the

out

selected supply voltage Vcc. Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VREF on page 96

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R&S®SMW-K540, R&S®SMW-K541, R&S®SMW-K546

Min/Max

out

Displays the minimum and maximum values of the peak-to-peak voltage V on the interface between the circuit board and the DC modulator.

For "Envelope Voltage Reference" , sets the value of this parameter. To measure the V

●

Use a suitable probe, i.e. use a differential probe if a "Wire to Wire" termination is

voltage:

out

used and a single ended probe otherwise

●

Measure at the circuit board after the termination impedance Rin.

Generation of envelope tracking signals

General RF envelope settings

voltage

out

Estimated "V

Min/Max" values are calculated based on the selected supply voltage

out

VccMin/Max, enabled Gain and VccOffset in the DC modulator.

Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VOUT:MIN on page 97 [:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VOUT:MAX on page 97

Bias

Sets a DC voltage, superimposed upon the envelope signal E and the inverted envelope signal E Bar.

Use this parameter to define the operating point of a DUT.

"I/Q Output Type" Termination "Bias" defines

"Single Ended" - The bias between the envelope signal E and ground

"Differential" "To Ground" Superimposed DC voltage, where "Bias" is related to

the selected Rin.

2.4 Envelope settings

Access:

1. Enable the generation of envelope tracking signal. See Chapter 2.3, "General RF envelope settings", on page 21.

2. Select "I/Q Analog Settings > Envelope Settings".

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1 = Enabled Digital Predistortion 2 =

3a, 3b = (for "Envelope Voltage Adaptation > Manual") Pre-Gain/Post-Gain 4 = Shaping state and shaping function; gray background color = deactivated shaping 5 = Enabled Envelope to RF Delay 6 = Indicates the output connectors, depending on the I/Q Output Type

Envelope detector, √[I(t)2+Q(t)2]; indication changes, depending on the Envelope Voltage

Adaptation

Generation of envelope tracking signals

Envelope settings

The dialog displays an interactive overview diagram of the ET processing chain. The diagram displays information on shaping state, incl. current shaping method and setting, like gains or delay.

Tip: Hotspots for quick access. The displayed blocks are hotspots. Select one of them to access the related function.

The remote commands required to define these settings are described in Chapter 7.2,

"SOURce:IQ:OUTPut:ENVelope commands", on page 92.

Settings:

Envelope to RF Delay................................................................................................... 30

Calculate Envelope from Predistorted Signal................................................................31

Envelope to RF Delay

Sets the time delay of the generated envelope signal relative to the corresponding RF signal. A positive value means that the envelope signal delays relative to the RF signal and vice versa.

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Generation of envelope tracking signals

Shaping settings

Figure 2-6: Effect of enabled positive RF delay

1 = RF signal 2a, 2b = Envelope signal E and inverted envelope signal E BAR

Use this parameter to compensate possible timing delays caused by connected cables and align the input signals at the PA to prevent unwanted effects, like memory effects or decreased linearity.

Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:DELay on page 96

Calculate Envelope from Predistorted Signal

Option: R&S SMW-K541 Enables the calculation of the envelope signal from the original baseband signal or

from the AM/AM and/or AM/FM predistorted signal. See also Chapter 3, "Applying digital predistortion", on page 45. Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:FDPD on page 97

2.5 Shaping settings

Access:

1. Enable the generation of envelope tracking signal.

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See Chapter 2.3, "General RF envelope settings", on page 21.

2. Enable "Envelope Voltage Adaptation > Auto Power/Normalized".

3. Select "I/Q Analog Outputs > Shaping".

Generation of envelope tracking signals

Shaping settings

Figure 2-7: Understanding the displayed information ("Envelope Voltage Adaptation > Auto

1a, 1b = Indicates the values of VccMin/Max 2a = Values smaller than PEPinMin are clipped 2b = Values greater than PEPinMax are clipped 3 = Operating point; corresponds to the RF RMS power level

3a = Current RF RMS power level; an enabled "RF Level > Level Offset" is considered 3b = Current V

4 = Crest factor of the generated signal 5a, 5b = The values correspond to the PEP of the generated RF signal and the VCC; shaded area indi-

6 = Current envelope shape, defined by the detroughing function and detroughing factor

Power", "Shaping > Detroughing")

cates the calculated Pre-Gain

The settings allow the configuration of the shape of the RF envelope signal. The instrument applies the settings and calculates the shaping function. A diagram visualizes the resulting envelope shape, as function of the selected supply voltage V

and PEPin value limits, the calculated pre-gain and the estimated operating point of the PA.

2.6 Edit I/Q envelope shape settings

The envelope shaping table is a method to define the shaping function.

Access:

1. Enable the generation of envelope tracking signal. See Chapter 2.3, "General RF envelope settings", on page 21.

2. Select "Envelope Voltage Adaptation > Manual".

3. Select "Shaping Settings > Shaping > From Table".

4. Select "Shaping Table > New"

5. Enter the "File Name", e.g. MyLUT The "Envelope Shaping File" dialog closes.

The "Shaping > Shaping Table" confirms that the newly created file is assigned.

6. Select "Shaping Table > MyLUT > Edit"

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7. Define the value pairs "Vin/Vmax" and "Vcc/Vmax". The order is uncritical.

Figure 2-12: Shaping table in "Envelope Voltage Adaptation > Manual" mode

Generation of envelope tracking signals

Edit I/Q envelope shape settings

8. Select "Save". The instrument loads the configured values automatically and displays the shaping

function.

9. Select "Shaping Settings > Interpolation > Linear (Voltage)".

The display confirms the used interpolation.

The remote commands required to define these settings are described in Chapter 7.2,

"SOURce:IQ:OUTPut:ENVelope commands", on page 92.

Settings:

Vin/Vmax, Vcc/Vmax/Power (dBm), Vcc (V).................................................................41

Fill Table Automatically..................................................................................................41

Goto, Edit, Save As, Save.............................................................................................42

Vin/Vmax, Vcc/Vmax/Power (dBm), Vcc (V)

Sets the normalized values of the value pairs. "Vin/Vmax, Vcc/Vmax"

Value pairs in "Envelope Voltage Adaptation > Manual/Auto Normalized" mode.

"Power(dBm), Vcc(V)"

Value pairs in "Envelope Voltage Adaptation > Auto Power" mode.

Remote command: n.a.

Fill Table Automatically

Standard function for filling a table automatically with user-defined values.

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"From / Range"

Defines the start line and number of the rows to be filled.

"Select Column to Fill"

Selects the respective value, including the unit.

"Start / End Value"

Default values corresponding to the selected column. "Increment" "Fill"

Determines the step size.

Fills the table.

Fill both columns and then save the list. Otherwise the entries are

lost.

Generation of envelope tracking signals

Polynomial coefficients settings

Goto, Edit, Save As, Save

Standard functions for editing of data lists. Changed and unsaved values are displayed on a yellow background. Remote command:

n.a.

2.7 Polynomial coefficients settings

Access:

1. Enable the generation of envelope tracking signal.

See Chapter 2.3, "General RF envelope settings", on page 21.

2. Select "Envelope Voltage Adaptation > Auto Normalized".

3. Select "Shaping Settings > Shaping > Polynomial".

4. Select "Polynomial Coefficients".

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Figure 2-13: Polynomial Coefficients: Understanding the displayed information

The polynomial function is an analytical method to describe a shaping function. With the provided settings, you can define a polynomial function with up to 10 order to describe the envelope shape.

Generation of envelope tracking signals

Polynomial coefficients settings

5. Select "Polynomial Order = 2" (n = 2).

6. Set the constant a0 and the polynomial coefficients a1 and a2.

7. Select "Apply".

The instrument loads the configured values and displays the shaping function.

8. To store the defined shaping function:

a) Select "Save/Recall Polynomial" b) Navigate throughout the file system and enter a "File Name", e.g. MyPolyno-

mial_2thOrder

c) Select "OK".

9. Select "Polynomial Coefficients > OK" to close the dialog.

The remote commands required to define these settings are described in Chapter 7.2,

"SOURce:IQ:OUTPut:ENVelope commands", on page 92.

Settings:

Save/Recall Polynomial................................................................................................ 43

Polynomial Order.......................................................................................................... 44

Polynomial constant and coefficients............................................................................44

Apply, OK...................................................................................................................... 44

Save/Recall Polynomial

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The settings are saved in a file with predefined extension. You can define the filename and the directory, in that you want to save the file.

See also, chapter "File and Data Management" in the R&S SMW user manual. The polynomial files are files with extension *.iq_poly, see "File format of the poly-

nomial function file" on page 15.

Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:COEFficients: CATalog? on page 105 [:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:COEFficients: STORe on page 105 [:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:COEFficients: LOAD on page 105

Polynomial Order

Defines the polynomial order n, that is the number of polynomial coefficients (see

Chapter 2.2.3.3, "About the polynomial function", on page 14).

To confirm the settings, select "Apply". Remote command:

See [:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:

COEFficients on page 104.

Generation of envelope tracking signals

Polynomial coefficients settings

Polynomial constant and coefficients

Sets the polynomial constant a0 and the polynomial coefficients a1 to an. The polynomial constant and coefficients influence the envelope shape.

Remote command:

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:COEFficients

on page 104

Apply, OK

Triggers the instrument to adopt the selected function. Use "OK" to apply the setting and exits the dialog. Remote command:

See [:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:

COEFficients on page 104

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3 Applying digital predistortion

Digital predistortion (DPD) is a method to improve the efficiency of RF power amplifiers. In the R&S SMW, the generated digital signal can be deliberately AM/AM and AM/PM predistorted.

3.1 Required options

The equipment layout for digital predistortion includes:

●

Option standard or wideband baseband generator (R&S SMW-B10/-B9) Option baseband main module, one/two I/Q paths to RF (R&S SMW-B13/B13T) or wideband baseband main module (R&S SMW-B13XT)

●

Option frequency (e.g. R&S SMW-B1003/-B2003)

●

Option AM/AM AM/PM predistortion (R&S SMW-K541) per signal path; Where each signal path must be equipped with baseband generator, main module and frequency option

●

Optional option envelope tracking (R&S SMW-K540) per signal path

Applying digital predistortion

About digital predistortion

3.2 About digital predistortion

Power amplifiers are an essential part of any telecommunication systems. While amplifying the transmitted signal, power amplifiers sometimes also distort this signal and change its amplitude and/or phase characteristics. Such distortions result in undesired effects like spectrum regrowth, harmonic generation, intermodulation (IM) products, or increased bit error rate.

The principle of the digital predistortion

To compensate for the distortions caused by the transmission system, the signal is deliberately digitally predistorted. Digital predistortion (DPD) is a method to apply wanted and well-defined predistortion on the transmitted signal. When this signal is amplified, the resulting signal features the identical characteristics, as the initial signal before the predistortion.

signal

a b c

DPD

out

Figure 3-1: Illustration of predistortion principle

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DPD = Digital predistortion PA = Power amplifier a = Predistortion function b = Characteristic of the power amplifier, for example the non-linear input power vs. output power

(AM/AM) function

c = Ideal linearized characteristic of the amplified signal

Digital predistortion models

When testing power amplifiers, it is important to measure and analyze signal distortions.

Of several known models, this implementation focuses on the following two types of distortion:

●

The AM/AM (amplitude-to-amplitude) distortion and

●

The AM/PM (amplitude-to-phase) distortion.

An AM/AM representation is a standard method that shows the signal power level at the input of the DUT against the power level at the output of the DUT. The default unit for both axes is dBm but the AM/AM representation can also be normalized.

Applying digital predistortion

About digital predistortion

An AM/PM curve shows the phase difference in degrees (y-axis) for every input power level (x-axis).

With option R&S SMW-K541, you can define both, an AM/AM and an AM/PM predistortion and apply them separately or superimposed on each other on the generated digital baseband signal.

If your instrument is equipped with the option R&S SMW-K540, you can also apply predistortions on the generated envelope signal.

Refer to Chapter 2, "Generation of envelope tracking signals", on page 10 for more information.

3.2.1 Defining the power level of the generated signal

You can define the level of the generated signal in one of the following ways:

●

"Level Reference > Before DPD"

In this mode, the "Level" parameter in the status bar of the instrument defines the signal level before the DPD is applied. Signal with selected level is pre-distorted and depending on the selected AM/AM and AM/PM functions, attenuated or boosted. See Table 3-1.

●

"Level Reference > After DPD"

In this mode, you define the resulting signal level. Based on this value and depending on current predistortion function, the R&S SMW calculates the level of the signal to be pre-distorted. The level calculation requires several interaction cycles; the number of iterations is a trade-off between level accuracy and speed. See "To perform manual iterations to achieve a desired resulting signal level after

the DPD" on page 86 for explanation of how the interactions are performed.

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Table 3-1: Difference between the level reference modes

"Level Reference > Before DPD" "Level Reference > After DPD"

Applying digital predistortion

About digital predistortion

1: "LevelIN = Level = -15 dBm", i.e. signal level before DPD

2: "PEPIN = PEP -3.43 dBm", i.e. PEP of the signal before DPD

3: "Level

4: "PEP

= -15.42 dBm", resulting signal level after DPD

OUT

= -3.68 dBm", resulting PEP of the signal after DPD

OUT

3.2.2 Defining the correction values

In the R&S SMW, you can select the way you define the predistortion function and choose between:

●

A polynomial function with up to 10 polynomial coefficients (see Chapter 3.2.2.1, "Polynomial function", on page 47)

●

A predistortion function defined as a look-up table (see Chapter 3.2.2.2, "Shaping table", on page 48)

●

A normalized data (see Chapter 3.2.2.3, "Normalized data", on page 49)

●

To set the correction values in raw format with a single remote control command (see Chapter 3.2.2.4, "Predistortion function in raw data format", on page 50).

1: "Level

2: "PEP DPD

3: "LevelIN = -15.43 dBm", calculated signal level before DPD

4: "PEPIN = -3.86 dBm", calculated of the signal before DPD

5: allowed maximum level error 6: maximum number of iterations used to achieve the required

level error

= Level = -15 dBm", i.e. signal level after DPD

OUT

= PEP = -3.57 dBm", i.e. PEP of the signal after

OUT

3.2.2.1 Polynomial function

The polynomial function is an analytical method to describe a predistortion function. When using the polynomial function, you do not define the correction values (ΔPower and ΔPhase) directly as it is in the look-up table. You describe the predistortion function and the R&S SMW derives the correction values out of it.

See Chapter 3.3.4, "Polynomial coefficients settings", on page 62.

This implementation uses a polynomial with complex coefficients defined as follows:

(x) = ∑[(an+j*bn)*xn],

DPD

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Where:

●

n = "Polynomial Order" ≤ 10

●

x = Pin/PinMax

●

an and bn are user-defined coefficients, defined as Cartesian (polar) or cylindrical coordinates.

In Cartesian coordinates system, the coefficients bn are expressed in degrees.

The R&S SMW calculates the AM/AM and AM/PM predistortion functions as follows:

●

AM/AM(x) = abs[P

●

AM/PM(x) = tan-1{Im[P

DPD

(x)]

DPD

(x)]/Re[P

A dedicated graphical display visualizes the resulting functions, see Figure 3-4.

The R&S SMW calculates the correction values (ΔAM/AM and ΔAM/PM functions) as follows:

●

ΔAM/AM(x) = AM/AM(x) - x = abs[P

●

ΔAM/PM(x) = AM/PM(x) = tan-1{Im[P

DPD

(x)]}

(x)] -x

(x)]/Re[P

DPD

Applying digital predistortion

About digital predistortion

(x)]}

DPD

A dedicated graphical display visualizes the calculated correction functions, see Fig-

ure 3-5 and compare with Figure 3-4.

File format of the polynomial file

The file contains an optional header # Rohde & Schwarz - Digital

Predistortion Polynomial Coefficients # a0,b0, a1,b1, a2,b2, ...

and a list of comma-separated coefficient value pairs, stored in Cartesian coordinates.

For values above the selected Input Range (PEPin) From/To, the predistortion function assumes a linear ratio of the input to output power.

Example: Polynomial function file content

# Rohde & Schwarz - Digital Predistortion Polynomial Coefficients

# a0,b0, a1,b1, a2,b2, ...

0,0,-0.25,0.2,0.6,-0.3,0.3,0.3,0.5,-0.4

3.2.2.2 Shaping table

In the R&S SMW, there are two ways to define the predistortion function in form of a shaping table:

●

Externally

Create a correction table file as a CSV file with Microsoft Excel, with a Notepad or a similar tool. Save the file with the predefined extension, transfer and load it into the instrument. See also "File format of the correction table file" on page 49.

●

Internally

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Use the built-in editor table editor, see Chapter 3.3.3, "Edit predistortion table set-

tings", on page 59.

File format of the correction table file

The correction table files are files with predefined extension and simple file format, see

Table 3-2.

Table 3-2: Shaping table files: format and extensions

Predistortion model File extension Header (optional)

Applying digital predistortion

About digital predistortion

AM/AM

AM/PM

The header is optional. The file content is a list of up to 4000 comma-separated value pairs, describing the delta values for amplitude or phase related to the absolute input power Pin. A new line indicator separates the pairs.

For values above the selected Input Range (PEPin) From/To, the predistortion function assumes a linear ratio of the input to output power.

Example: Shaping table file content (*.dpd_magn file)

# Rohde & Schwarz - Digital AM/AM Predistortion Table

Pin[dBm],deltaPower[dBm]

-30,0.5

3,-0.01

3.2.2.3 Normalized data

In the R&S SMW, there are two ways to define the predistortion function as normalized data:

●

Externally

We recommend that you calculate the normalized correction data by a connected R&S®FSW equipped with R&S®FSW-K18 power amplifier and envelope tracking measurements option. You can also create the correction table file as a CSV file with Microsoft Excel, with a Notepad or a similar tool. Save the file with the predefined extension, transfer and load it into the instrument. See also "File format of the correction table file" on page 49.

●

Internally

Use the built-in editor table editor, see Chapter 3.3.3, "Edit predistortion table set-

tings", on page 59.

*.dpd_magn # Rohde & Schwarz - Digital AM/AM

Predistortion Table Pin[dBm],deltaPower[dB]

*.dpd_phase # Rohde & Schwarz - Digital AM/PM

Predistortion Table Pin[dBm],deltaPhase[deg]x

File format of the normalized data

The normalized data files are files with predefined extension *.dpd_norm and simple file format, see "File format of the normalized data" on page 49.

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The file contains an optional header # Rohde & Schwarz - Digital Predistortion Normalized Table Data # PinMax [dBm] # number of points # Vin/Vmax, deltaV/V, deltaPhase [deg], the values of the Pin

the number of the subsequent points and a list of comma-separated groups of three values.

Example: Normalized data file content

# Rohde & Schwarz - Digital Predistortion Normalized Table Data

# PinMax [dBm]

# number of points

# Vin/Vmax, deltaV/V, deltaPhase [deg]

4096

0,0,0

0.0002442,-0.00018246,0.28052

0.0004884,-0.00036487,0.28041

0.0007326,-0.00054723,0.2803

0.0009768,-0.00072954,0.28019

0.001221,-0.00091181,0.28008

0.0014652,-0.001094,0.27996

...

Applying digital predistortion

About digital predistortion

Max

3.2.2.4 Predistortion function in raw data format

The predistortion values are defined directly, with a single remote control command:

●

Define up to 4000 comma-separated value pairs, describing the absolute input power Pin and the delta values for amplitude or phase (ΔPower and ΔPhase).

Example:

SOURce1:IQ:DPD:SHAPing:TABLe:AMAM:FILE:DATA -30.4,-5.2,

-25.1,-4.5, -18.5,-2.5, -10.5,-1

See: – [:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMAM:FILE:DATA

on page 117

– [:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMPM:FILE:DATA

on page 117 – [:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMAM:FILE:NEW on page 117 – [:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMPM:FILE:NEW on page 117

●

Define the absolute maximum input power Pin points, and the normalized values Vin/Vmax, ΔV/V, ΔPhase [deg] as binary data.

See [:SOURce<hw>]:IQ:DPD:SHAPing:NORMalized:DATA on page 120.

3.2.3 Finding out the correction values

, the number of subsequent

max

If you know the properties of the used power amplifier, you can calculate suitable correction values.

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We assume that the characteristics of a power amplifier have been measured and that the left graphic in the following table shows the AM/AM curve of this amplifier.

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

Defining correction coefficients for an AM/AM predistortion (example)

a = ideal characteristic; if the amplifier did not distort the signal, the normalized magnitude would be a line

b = measured AM/AM curve; the normalized magnitude varies as a function of input power

The required correction coefficient ΔPower is the difference between the ideal and the real normalized amplitude for one particular input power. To compensate for the nonlinearity and the deviation from the ideal line: select a negative correction value (-Δ) for any input power where the real normalized amplitude is greater than the ideal one (1). Logically, a positive correction value (+Δ) compensates for (i.e. boost) an amplitude that is smaller than the ideal one (2).

Resulting AM/AM predistortion function (example)

a = ideal characteristic b = measured AM/AM curve c = resulting AM/AM predistortion function, i.e. correction values

curve d = ideal predistorted signal

Ideally, a signal predistorted with a suitable function (c) and then amplified by the particular PA would have a linear characteristic (a).

In the practice, however, you do not calculate the correction coefficients manually but they are calculated automatically. A suitable solution is the R&S®FS-K130PC software or the R&S®FSW-K18 power amplifier and envelope tracking measurements option, see Chapter 6, "How to apply a DPD to improve the efficiency of RF PAs", on page 84.

3.3 Digital predistortions AM/AM and AM/PM settings

You can add digital predistortion to the generated baseband signal and thus compensate an amplitude and a phase distortion of the DUT, for example of the tested power amplifier.

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Access:

► Select "I/Q Mod > Digital Predistortion > AM/AM AM/PM".

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

The dialog covers the settings for digital predistortion, like select and enabling an AM/AM and/or AM/PM predistortion, select the way the predistortion function is defined and specify the correction values.

The remote commands required to define these settings are described in Chapter 7.3,

"SOURce:IQ:DPD subsystem", on page 107.

Settings:

3.3.1 General settings

State..............................................................................................................................52

Set to Default................................................................................................................ 53

Save/Recall...................................................................................................................53

AM/AM First.................................................................................................................. 53

Level Reference............................................................................................................53

Maximum Output Level Error........................................................................................ 54

Maximum Number of Iterations.....................................................................................54

Achieved Output Level Error.........................................................................................54

Input/Output PEP, Level and Crest Factor.................................................................... 54

AM/AM and AM/PM State............................................................................................. 54

State

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Remote command:

[:SOURce<hw>]:IQ:DPD:STATe on page 109

Set to Default

Calls the default settings. The values of the main parameters are listed in the following table.

Parameter Value

"State" Not affected by the "Set to Default"

"Level Reference" Before DPD

"AM/AM First" Off

"AM/PM, AM/AM" Off

Remote command:

[:SOURce<hw>]:IQ:DPD:PRESet on page 110

Save/Recall

The settings are saved in a file with predefined extension. You can define the filename and the directory, in that you want to save the file.

See also, chapter "File and Data Management" in the R&S SMW user manual.

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

Remote command:

[:SOURce<hw>]:IQ:DPD:SETTing:CATalog? on page 110 [:SOURce<hw>]:IQ:DPD:SETTing:STORe on page 110 [:SOURce<hw>]:IQ:DPD:SETTing:LOAD on page 110 [:SOURce]:IQ:DPD:SETTing:DELete on page 110

AM/AM First

Toggles the order the AM/AM and AM/PM predistortions are applied. Remote command:

[:SOURce<hw>]:IQ:DPD:AMFirst on page 111

Level Reference

Switches between dynamic and static adaptation of the range the selected DPD is applied on.

"Before DPD/After DPD"

Selects dynamic range calculation and defines whether the selected "Level" value corresponds to the signal level before or after the predistortion, see Chapter 3.2.1, "Defining the power level of the gener-

ated signal", on page 46.

Option: R&S SMW-K546 If in the same path "I/Q Mod > Digital Predistortion > Digital Doherty > General > State > On", the value is set to "Level Reference = Before DPD" and cannot be changed.

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Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

"Static DPD"

Remote command:

[:SOURce<hw>]:IQ:DPD:LREFerence on page 111

Maximum Output Level Error

For "Level Reference > After DPD", sets the allowed maximum error, see Chap-

ter 3.2.1, "Defining the power level of the generated signal", on page 46.

Remote command:

[:SOURce<hw>]:IQ:DPD:OUTPut:ERRor:MAX on page 112

Maximum Number of Iterations

For "Level Reference > After DPD", sets the maximum number of performed iterations to achieving the required Maximum Output Level Error.

See also Chapter 3.2.1, "Defining the power level of the generated signal", on page 46. Remote command:

[:SOURce<hw>]:IQ:DPD:OUTPut:ERRor:MAX on page 112

Achieved Output Level Error

Displays the resulting level error, see Chapter 3.2.1, "Defining the power level of the

generated signal", on page 46.

Remote command:

[:SOURce<hw>]:IQ:DPD:OUTPut:ERRor? on page 111

Selects static (constant) range limits. To adjust the range, use the parameter Pre-Gain.

Input/Output PEP, Level and Crest Factor

Displays the calculated values the before and after the DPD. See "To perform manual iterations to achieve a desired resulting signal level after the

DPD" on page 86.

A value of -1000 indicates that the calculation is impossible or there are no measurements results available.

Remote command:

[:SOURce<hw>]:IQ:DPD:INPut:PEP? on page 113 [:SOURce<hw>]:IQ:DPD:INPut:LEVel? on page 113 [:SOURce<hw>]:IQ:DPD:INPut:CFACtor? on page 113 [:SOURce<hw>]:IQ:DPD:OUTPut:PEP? on page 113 [:SOURce<hw>]:IQ:DPD:OUTPut:LEVel? on page 113 [:SOURce<hw>]:IQ:DPD:OUTPut:CFACtor? on page 113

AM/AM and AM/PM State

Enables/disables the AM/AM and AM/PM digital predistortion. If both predistortions are enabled simultaneously, the instrument applies the AM/AM

predistortion first and compensates the phase error of the PA afterwards. Compare the displayed signal processing chain. Remote command:

[:SOURce<hw>]:IQ:DPD:AMAM:STATe on page 111 [:SOURce<hw>]:IQ:DPD:AMPM:STATe on page 111

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3.3.2 Predistortion settings

Access:

1. Select "I/Q Mod > Digital Predistortion > AM/AM AM/PM > Predistortion Settings".

2. Select a shaping function, for example the shaping file form Example "Shaping

table file content (*.dpd_magn file)" on page 49.

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

Figure 3-2: Predistortion Settings > From Table: Understanding the displayed information

1a = Normalized value of the current RF RMS power level 2a = Normalized value of the current PEP of the generated RF signal 1b, 2b = Correction values White dashed line = Ideal zero correction function; no correction is necessary Yellow curve = Predistortion function 3a, 3b = Input Range (PEPin) From/To

4 = Positive correction coefficients to compensate values below the ideal ones 5 = Values greater than the PEPin Max are ignored

Settings:

Shaping.........................................................................................................................56

Interpolation.................................................................................................................. 56

Invert Correction Values................................................................................................56

Input Range (PEPin) From/To........................................................................................57

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Pre-Gain........................................................................................................................57

Shaping Table............................................................................................................... 58

Polynomial Coefficients.................................................................................................59

Normalized Data........................................................................................................... 59

Graphic Configuration................................................................................................... 59

└ Scale...............................................................................................................59

└ AM/AM and AM/PM Diagrams........................................................................59

Shaping

Selects the method to define the correction coefficients. "From Table"

As value pairs in form of a shaping table. Select "AM/AM or AM/PM Shaping Table" to access the settings, see

Chapter 3.3.3, "Edit predistortion table settings", on page 59.

Select "Power Table" or "Phase Table" to to access the settings.

"Polynomial"

By a polynomial with configurable order and coefficients. Select "Polynomial Coefficients" to access the settings, see Chap-

ter 3.3.4, "Polynomial coefficients settings", on page 62.

"Normalized"

As a normalized data. Select "Normalized Data" to access the settings, see Chapter 3.3.5,

"Normalized data settings", on page 65.

"Classic Doherty"

Option: R&S SMW-K546 Selects a shaping function defined by the "Power" coefficient.

Remote command:

[:SOURce<hw>]:IQ:DPD:SHAPing:MODE on page 113 [:SOURce<hw>]:IQ:DOHerty:SHAPing:MODE on page 129

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

Interpolation

For "Shaping > From Table/Normalized", enables a linear interpolation between limited number of defined value pairs in the table, to prevent abrupt changes.

Table 3-3: Effect of parameter Interpolation

"Interpolation > Off" "Interpolation > Linear (Power)"

Remote command:

[:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:INTerp on page 118 [:SOURce<hw>]:IQ:DOHerty:SHAPing:TABLe:INTerp on page 118

Invert Correction Values

Inverts the defined correction values.

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Applies the exact invert predistortion coefficients without changing the defined predistortion table.

This function is also useful to toggle between predistortions with corrections related to the input power and to the output power.

Table 3-4: Effect of parameter Invert correction values

"Invert correction values > Off" "Invert correction values > On"

Remote command:

[:SOURce<hw>]:IQ:DPD:SHAPing[:TABLe]:INVert on page 118 [:SOURce<hw>]:IQ:DOHerty:SHAPing[:TABLe]:INVert on page 118

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

Input Range (PEPin) From/To

Defines the minimum and maximum input power PEPin. If you apply digital predistortion on signals used for power amplifier tests with envelope

tracking, set the PEPinMax value to the maximum value of the input power PEPin Max, as required by the power amplifier (PA).

Remote command:

[:SOURce<hw>]:IQ:DPD:PIN:MIN on page 116 [:SOURce<hw>]:IQ:DPD:PIN:MAX on page 116 [:SOURce<hw>]:IQ:DOHerty:PIN:MIN on page 116 [:SOURce<hw>]:IQ:DOHerty:PIN:MAX on page 116

Pre-Gain

For "General > Level Reference > Static DPD", sets a pre-gain (i.e. an attenuation) to define the range the DPD is applied in. The pre-gain can be used to define and test only a specific (required) part of the operating range.

For "General > Level Reference > Before/After DPD", the range is limited by the current PEP of the signal.

See Figure 3-2.

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1 = Pre-gain limits the effective range of the shaping function 2 = Values above this limit are ignored

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

Remote command:

[:SOURce<hw>]:IQ:DPD:GAIN:PRE on page 113

Shaping Table

Accesses the standard "Predistortion Select" dialog with functions to define a new shaping table file, select, or edit an existing one.

The shaping table files are files with predefined extension and file format, see "File for-

mat of the correction table file" on page 49.

You can create a shaping table externally or internally. "Select" "New" "Edit"

Selects and loads an existing file. Creates a file. Access a standard built-in table editor, see Chapter 3.3.3, "Edit pre-

distortion table settings", on page 59.

Remote command: For AM/AM distortions:

[:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMAM:FILE:CATalog? on page 116 [:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMAM:FILE[:SELect] on page 117

For AM/PM distortions:

[:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMPM:FILE:CATalog? on page 116 [:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMPM:FILE[:SELect] on page 117

For power:

[:SOURce<hw>]:IQ:DOHerty:SHAPing:TABLe:AMAM:FILE:CATalog?

on page 116

[:SOURce<hw>]:IQ:DOHerty:SHAPing:TABLe:AMAM:FILE[:SELect]

on page 117 For phase:

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[:SOURce<hw>]:IQ:DOHerty:SHAPing:TABLe:AMPM:FILE:CATalog?

on page 116

[:SOURce<hw>]:IQ:DOHerty:SHAPing:TABLe:AMPM:FILE[:SELect]

on page 117

Polynomial Coefficients

For "Shaping > Polynomial", accesses a dialog to describe the predistortion function as a polynomial function, see Chapter 3.3.4, "Polynomial coefficients settings", on page 62.

Normalized Data

For "Shaping > Normalized", accesses a dialog to describe the predistortion function as a normalized data, see Chapter 3.3.5, "Normalized data settings", on page 65.

Graphic Configuration

Comprises setting to configure the graphical display.

Scale ← Graphic Configuration

Determines the unit of the x-axis, "Voltage" or "Power". Remote command:

[:SOURce<hw>]:IQ:DPD:SCALe on page 116 [:SOURce<hw>]:IQ:DOHerty:SCALe on page 116

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

AM/AM and AM/PM Diagrams ← Graphic Configuration

Visualize the resulting correction functions, as function of the selected PEPin value limits.

See Figure 3-2. Remote command:

[:SOURce<hw>]:IQ:DPD:AMAM:VALue:LEVel? on page 121 [:SOURce<hw>]:IQ:DPD:AMAM:VALue:PEP? on page 122 [:SOURce<hw>]:IQ:DPD:AMAM:VALue? on page 122 [:SOURce<hw>]:IQ:DPD:AMPM:VALue:LEVel? on page 121 [:SOURce<hw>]:IQ:DPD:AMPM:VALue:PEP? on page 122 [:SOURce<hw>]:IQ:DPD:AMPM:VALue? on page 122 [:SOURce<hw>]:IQ:DOHerty:AMAM:VALue:LEVel? on page 121 [:SOURce<hw>]:IQ:DOHerty:AMAM:VALue:PEP? on page 122 [:SOURce<hw>]:IQ:DOHerty:AMAM:VALue? on page 122 [:SOURce<hw>]:IQ:DOHerty:AMPM:VALue:LEVel? on page 121 [:SOURce<hw>]:IQ:DOHerty:AMPM:VALue:PEP? on page 122 [:SOURce<hw>]:IQ:DOHerty:AMPM:VALue? on page 122

3.3.3 Edit predistortion table settings

The predistortion table is an internal editor where you define the correction values, ΔPower and ΔPhase, in form of a look-up table.

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Access:

1. Select "I/Q Mod > Digital Predistortion > AM/AM AM/PM > Predistortion Settings".

2. Select "Shaping > From Table".

3. Select "AM/AM > Shaping Table > Predistortion AM/AM Shaping File > New"

4. Enter the "File Name", e.g. My_DPD_AM-AM The "Predistortion AM/AM Shaping File" dialog closes.

The "Shaping Table > My_DPD_AM-AM" confirms that the newly created file is assigned.

5. Select "Shaping Table > Predistortion AM/AM Shaping File > Edit"

6. Define the value pairs "Pin/dBm" and "ΔPower/dB". The order is uncritical.

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

Figure 3-3: Example of an AM-AM predistortion table values

7. Select "Save". The instrument loads the configured values automatically and displays the function

of the delta correction values.

8. Select "Predistortion Settings > Interpolation > Linear".

The display confirms the used interpolation.

Settings:

Pin (dBm), Delta Power (dB)/Pin (dBm), Delta Phase (deg).........................................60

Fill Table Automatically..................................................................................................61

Goto, Edit, Save As, Save.............................................................................................61

Pin (dBm), Delta Power (dB)/Pin (dBm), Delta Phase (deg)

Sets the correction value pairs.

ΔPower"

"Pin,

Value pairs for the AM/AM predistortion

"Pin, ΔPhase"

Value pairs for the AM/PM predistortion

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Remote command: See [:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMAM:FILE[:SELect] on page 117 and [:SOURce<hw>]:IQ:DPD:SHAPing:TABLe:AMPM:FILE[:SELect] on page 117 See [:SOURce<hw>]:IQ:DOHerty:SHAPing:TABLe:AMAM:FILE[:SELect] on page 117 and [:SOURce<hw>]:IQ:DOHerty:SHAPing:TABLe:AMPM:FILE[:SELect] on page 117

Fill Table Automatically

Standard function for filling a table automatically with user-defined values.

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

"From / Range"

Defines the start line and number of the rows to be filled.

"Select Column to Fill"

Selects the respective value, including the unit.

"Start / End Value"

Default values corresponding to the selected column. "Increment" "Fill"

Goto, Edit, Save As, Save

Standard functions for editing of data lists. Changed and unsaved values are displayed on a yellow background. Remote command:

n.a.

Determines the step size.

Fills the table.

Fill both columns and then save the list. Otherwise the entries are

lost.

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3.3.4 Polynomial coefficients settings

Alternatively to the look-up table, you can define the predistortion functions as a polynomial function. The R&S SMW calculates the AM/AM and AM/PM predistortion functions and the required correction coefficients out of the defined polynomial.

To access the polynomial coefficients setting and define a higher-order polynomial

1. Select "I/Q Mod > Digital Predistortion > AM/AM AM/PM > Predistortion Settings".

2. Select "Shaping > Polynomial".

3. Select "AM/PM > Polynomial Coefficients".

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

Figure 3-4: Polynomial Coefficients: Understanding the displayed information

n = Polynomial order a0, b0, ... = Polynomial coefficients 1 = Ideal AM/AM function (the normalized amplitude is a line) 2 = Resulting AM/AM predistortion function, calculated as AM/AM(x) = abs[P

3 = Ideal AM/PM function (constant phase at 0 degrees) 4 =

Resulting AM/PM predistortion function, calculated as AM/PM(x) = tan-1{Im[P Re[P

(x)]}

DPD

(x)]

With the provided settings, you can define a polynomial function with up to 10 order to describe the predistortion function. The graphical display updates on-the-fly and visualizes the resulting AM/AM and AM/PM functions.

4. Select "Polynomial Order = 4" (n = 4).

5. Set the polynomial coefficients a0 to b4.

Use, for example, the values shown on Figure 3-4.

DPD

(x)]/

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6. Select "Apply".

The instrument loads the configured values, calculates the correction values, and displays the predistortion functions.

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

Figure 3-5: Predistortion Settings > Polynomial: Understanding the displayed information

1a = Current RF RMS power level 2a = Current PEP of the generated RF signal 1b, 2b = Correction values White dashed line = Ideal zero function; no correction is necessary AM/AM yellow curve = AM/AM correction values, calculated as ΔAM/AM(x) = AM/AM(x) - x AM/PM yellow curve = AM/PM correction values, calculated as ΔAM/PM(x) = AM/PM(x) 3a, 3b = X-axis scale, calculated from the Input Range (PEPin) From/To

4 = Negative correction coefficients 5 = Values greater than the PEPin Max are ignored

7. To store the defined predistortion function:

a) Select "Save/Recall Polynomial" b) Navigate throughout the file system and enter a "File Name", e.g. MyPolyno-

mial_4thOrder

c) Select "OK".

8. Select "Polynomial Coefficients > OK" to close the dialog.

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Settings:

Save/Recall Polynomial................................................................................................ 64

System Coordinates......................................................................................................64

Polynomial Order.......................................................................................................... 64

Apply, OK...................................................................................................................... 65

Polynomial coefficients..................................................................................................65

Save/Recall Polynomial

The settings are saved in a file with predefined extension. You can define the filename and the directory, in that you want to save the file.

See also, chapter "File and Data Management" in the R&S SMW user manual. The polynomial files are files with extension *.dpd_poly, see "File format of the poly-

nomial file" on page 48. The polynomial function is stored in Cartesian format.

Remote command:

[:SOURce<hw>]:IQ:DPD:SHAPing:POLYnomial:COEFficients:CATalog?

on page 119

[:SOURce<hw>]:IQ:DPD:SHAPing:POLYnomial:COEFficients:LOAD

on page 119

[:SOURce<hw>]:IQ:DPD:SHAPing:POLYnomial:COEFficients:STORe

on page 119

[:SOURce<hw>]:IQ:DOHerty:SHAPing:POLYnomial:COEFficients: CATalog? on page 119 [:SOURce<hw>]:IQ:DOHerty:SHAPing:POLYnomial:COEFficients:LOAD

on page 119

[:SOURce<hw>]:IQ:DOHerty:SHAPing:POLYnomial:COEFficients:STORe

on page 119

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

System Coordinates

Defines whether the polynomial function is defined in Cylindrical (Polar) or in Cartesian coordinates.

Remote command: n.a.

Polynomial Order

Defines the polynomial order n, that is the number of polynomial coefficients (see

Chapter 3.2.2.1, "Polynomial function", on page 47).

The polynomial order defines the degree, complexity, and the number of terms in the polynomial function.

Remote command: See [:SOURce<hw>]:IQ:DPD:SHAPing:POLYnomial:COEFficients on page 118. See [:SOURce<hw>]:IQ:DOHerty:SHAPing:POLYnomial:COEFficients on page 118.

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Apply, OK

Triggers the instrument to adopt the selected function. Use "OK" to apply the setting and exits the dialog. Remote command:

[:SOURce<hw>]:IQ:DPD:SHAPing:POLYnomial:COEFficients on page 118 [:SOURce<hw>]:IQ:DOHerty:SHAPing:POLYnomial:COEFficients

on page 118

Polynomial coefficients

Sets the polynomial coefficients a0 to an and b0 to bn. In "System Coordinates > Cylindrical", the polynomial coefficients b0 to bn are

expressed in degrees. The polynomial coefficients influence the shape of the predistortion function, see Fig-

ure 3-4 for an illustration of a polynomial function.

Select "Apply" to confirm the settings. Remote command:

See "Apply, OK" on page 65.

Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

3.3.5 Normalized data settings

The normalized data table is an internal editor where you define the correction values, Vin/Vmax, ΔV/V and ΔPhase, in form of a table.

To access the internal editor

1. Select "I/Q Mod > Digital Predistortion > AM/AM AM/PM > Predistortion Settings".

2. Select "Shaping > Normalized Data".

3. Select "Normalized Data".

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Applying digital predistortion

Digital predistortions AM/AM and AM/PM settings

4. Enter the Pin

max

Note: Enter the correction values in the required order. The value range of the subsequent correction values adjusts automatically.

5. To store the setting in a file, select "Save/Recall Normalized Data > Save".

Enter a "File Name", e.g. My_DPD_Normalized.

Settings:

Save/Recall Normalized Data....................................................................................... 66

............................................................................................................................ 67

Max

Vin/Vmax, Delta V/V, Delta Phase (deg).......................................................................67

Apply, OK...................................................................................................................... 67

Save/Recall Normalized Data

The settings are saved in a file with predefined extension. You can define the filename and the directory, in that you want to save the file.

See also, chapter "File and Data Management" in the R&S SMW user manual. The normalized data files are files with extension *.dpd_norm, see "File format of the

normalized data" on page 49.

Remote command:

[:SOURce<hw>]:IQ:DPD:SHAPing:NORMalized:DATA:CATalog? on page 121 [:SOURce<hw>]:IQ:DPD:SHAPing:NORMalized:DATA:LOAD on page 121 [:SOURce<hw>]:IQ:DPD:SHAPing:NORMalized:DATA:STORe on page 121 [:SOURce<hw>]:IQ:DOHerty:SHAPing:NORMalized:DATA:CATalog?

on page 121

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[:SOURce<hw>]:IQ:DOHerty:SHAPing:NORMalized:DATA:LOAD on page 121 [:SOURce<hw>]:IQ:DOHerty:SHAPing:NORMalized:DATA:STORe on page 121

Max

Sets the value of the maximum input power level. Pin

corresponds to a normalized input power of 1, that is the max. allowed value on

max

the x-axis. Select "Apply" to confirm the settings. Remote command:

n.a.

Vin/Vmax, Delta V/V, Delta Phase (deg)

Sets the correction as a group of three values. Select "Apply" to confirm the settings. Remote command:

See "Apply, OK" on page 67.

Applying digital predistortion

Compensating non-linear RF effects

Apply, OK

Triggers the instrument to adopt the normalized data. Use "OK" to apply the setting and exits the dialog. Remote command:

[:SOURce<hw>]:IQ:DPD:SHAPing:NORMalized:DATA on page 120 [:SOURce<hw>]:IQ:DOHerty:SHAPing:NORMalized:DATA on page 120

3.4 Compensating non-linear RF effects

The R&S SMW provides a built-in function for compensating of its own non-linear RF effects caused by the amplifiers. If the function is enabled, the instrument uses the digital predistortion function and applies automatically calculated AM/AM predistortion values to the generated baseband signal.

The RF linearization and the "Digital Predistortions, AM/AM and AM/PM" cannot be used simultaneously; activating the "Linearize RF" parameter disables the "Digital Predistortions, AM/AM and AM/PM" settings.

To access the required settings:

1. Select "I/Q Mod > I/Q Modulator > General > Linearize RF".

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2. Select "Adjust Linearization Current Frequency".

The R&S SMW calculates the required correction values for the selected RF and the current generated signal.

Applying digital predistortion

Compensating non-linear RF effects

Settings:

Linearize RF

Option: R&S SMW-K541 Enables an automatic AM/AM predistortion of the non-linear RF chain. During RF linearization, disables "Digital Predistortions AM/AM and AM/PM" settings. Remote command:

[:SOURce<hw>]:IQ:DPD:LRF:STATe on page 113

Adjust Linearization Current Frequency

Calculates the correction data for the currently selected frequency. During RF linearization, disables "Digital Predistortions AM/AM and AM/PM" settings. Remote command:

[:SOURce<hw>]:IQ:DPD:LRF:ADJust? on page 114

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4 Testing Doherty power amplifiers

Power amplifiers are an essential part of any telecommunication systems and the Doherty power amplifiers (PA) in particular are widely used in wireless base stations. A typical digitally assisted Doherty amplifier uses two parallel working PAs, one for the carrier amplification and the second one for the peaking amplification. Hence, testing of these dual-input digital Doherty amplifiers requires two synchronous control signals, one for each of the build-in PAs.

In the R&S SMW, you can generate the required two baseband signals and two RF signal that act as control signals out of the same instrument.

4.1 Required options

The equipment layout for generating signals for testing Doherty amplifiers includes:

●

Option standard or wideband baseband generator (R&S SMW-B10/-B9) Option baseband main module, two I/Q paths to RF (R&S SMW-B13T) or wideband baseband main module (R&S SMW-B13XT)

●

Option frequency (e.g. R&S SMW-B1003 and R&S SMW-B2003)

●

Option Phase coherence (R&S SMW-B90)

●

2x Option AM/AM AM/PM predistortion (R&S SMW-K541)

●

Option Digital Doherty (R&S SMW-K546)

Testing Doherty power amplifiers

About the digital Doherty power amplifiers

4.2 About the digital Doherty power amplifiers

The Digital Doherty option assists you by the development of Doherty amplifiers by digitally splitting one input signal into components for carrier and peaking amplifiers.

The Figure 4-1 shows a simplified test setup for testing of Doherty amplifiers. This illustration is intended to explain the principle in general, not all connections and required equipment are considered.

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Figure 4-1: Simplified test setup for testing dual-input digital Doherty power amplifiers

Testing Doherty power amplifiers

About the digital Doherty power amplifiers

RF RF

= corresponds to the unmodified input signal

in, carrier

= derived from the control signal for the carrier amplifier by modifying it with power and phase val-

in, peaking

ues

The input (baseband) signal is output unmodified at the RF A output and is intended for the carrier amplifier. The signal for the peaking amplifier is output at the RF B output. You modify this signal by applying a power and phase relative to the signal at the RF A. To split optimally the signal components for the amplifier, the power and phase values are adjusted as a function of the input power.

If the Digital Doherty is activated, the R&S SMW works in constant phase mode, so that the phases of the signal at the RF outputs are kept aligned.

A suitable input test signal is, for example, a continuous wave (CW) signal or your test signal loaded as a waveform in the ARB generator. The control signals are output at the RF A/RF B connectors and fed to the inputs of the Doherty power amplifiers.

Additionally to defining the power and phase values, you can also apply digital predistortion (DPD). If activated ("I/Q Mod > Digital Predistortion > AM/AM AM/PM > State > On"), digital predistortion is applied before the Digital Doherty. With other words, the input signal is predistorted before the signal components are derived.

4.2.1 RF phase alignment

To ensure efficient operation of the amplifier, the R&S SMW uses internal algorithm to keep the phase alignment between the RF signals whenever the Digital Doherty is activated ("Digital Doherty > State > On").

The phases of the RF signals are influenced by several parameters, that can be divided into two groups:

●

Phase parameters within the "Digital Doherty" dialog You can, for example: – Use the phase offset parameter ("Digital Doherty" > Phase Offset) to calibrate

the overall phase of the signal.

– Apply phase delta correction values ("Digital Doherty" > "Phase Delta > State")

for phase compensation based on the input level.

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●

Phase-related parameters outside the "Digital Doherty" dialog

Tips for best results

Modifying one of the parameters within the "Digital Doherty" dialog ensures RF signals with aligned phases.

This behavior cannot be guaranteed for parameters outside the "Digital Doherty" dialog.

For details, see "Tips for best results" on page 71.

Table 4-1: Do and Do not

Testing Doherty power amplifiers

About the digital Doherty power amplifiers

Which parameter of the output RF signals do you want to change?

RF frequency "Status bar > A/B > Frequency" "I/Q Stream Mapper > Frequency Offset"

RF level "Status bar > A/B > Level" "Digital Doherty" > Dig Att

Used baseband signal Different waveforms in the two paths Load the same waveform the ARB genera-

Do not use Use instead

(adds frequency offset and thus shifts the signal digitally in the frequency domain)

(attenuates the signal digitally and thus changes the level of the output signal)

tor "Baseband > ARB > Load Waveform"

Do not modify the baseband signal while "Digital Doherty" is activated

Always configure the baseband signal first Configure and activate the "Digital Doh-

erty"

4.2.2 Defining the correction values

In the R&S SMW, you can select the way you define the correction function and choose between:

●

A polynomial function with up to 10 polynomial coefficients (see Chapter 3.2.2.1, "Polynomial function", on page 47)

●

A shaping function defined as a look-up table (seeChapter 3.2.2.2, "Shaping table", on page 48 )

●

A normalized data (see Chapter 3.2.2.3, "Normalized data", on page 49)

●

The parameters of classical Doherty amplifier See "Power Breakpoint" on page 77.

Because the first three methods follow the same concept as the methods used by the DPD functionality, these methods and the corresponding settings are described together.

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4.3 Digital Doherty settings

In the following, we assume that you are familiar with the DPD functionality because the DPD option is a prerequisite for the digital Doherty functionalities.

For background information on the DPD principles and description of the provided settings, see Chapter 3, "Applying digital predistortion", on page 45.

Access:

► Select "I/Q Mod > Digital Predistortion > Digital Doherty".

Testing Doherty power amplifiers

Digital Doherty settings

Figure 4-2: Digital Doherty: Understanding the displayed information

1 = "Frequency A = Frequency B" so that both RF outputs use the same frequency 2a, 2b = "PEP" and "Level" values in path A, calculated based on the current baseband signal 3a, 3b = "PEP" and "Level" values in path B at the I/Q outputs; shaping ("Power Spilt" and "Phase

Delta") and DPD are considered

4, 4a,4b= If "Couple Dig Att = Off", you can set different attenuation values "Dig Att" in path A and B; in

this example, a "Dig Att = 10 dB" is applied on the second path. The indication "Lev Att" on the "Status bar" confirms the coupling.

5 = Adds a phase offset for compensating for phase differences between the signals or for intro-

ducing a phase between them deliberately; resembles the value of the parameter "I/Q Mod B > Digital Impairments > Phase Offset"

6 = You can enable "Power Spilt" and "Phase Delta" shaping according to the selected shaping

function

The dialog covers the settings for digital Doherty, like defining the level settings, enabling power and phase corrections, select the way these correction functions are defined and specifying the correction values.

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Interdepended settings

If digital Doherty is enabled ("State > On"), the following configurations and settings are set automatically:

●

The signal at the RF outputs is at the same frequency, i.e. "Status bar > Frequency A = Frequency B".

●

To ensure phase alignment between the two control signals: – The local oscillators of both paths are locked, i.e. "RF > LO Coupling > Mode >

A internal & A -> B Coupled". You recognize this state by the LO indication on the Block diagram.

– The phase difference between the two RF signals is looked; i.e. "RF > Level >

RF Level > Settings Characteristics = Continuous-Phase".

●

The level of the RF signals can be changed ("Status bar > Level") but the allowed level range is selected so that the continuous phase condition is ensured.

●

The displayed "PEP" and "Level" values ("Status bar > PEP/Level") are calculated based on the current baseband signal.

●

The signals at the RF outputs are generated from the same stream and if DPD is not enabled, from the same baseband signal. The signal at the second RF output (RF B) is, if enabled, predistorted by user-defined power and/or phase corrections. Thus, the signal from the "Baseband A" and the corresponding stream A is automatically routed to both RF outputs, i.e. "Block diagram > I/Q Stream Mapper > Stream A > RF A/RF B". You recognize this state by Steam A indication at each of the RF A and RF B outputs.

Testing Doherty power amplifiers

Digital Doherty settings

Because the provided configurations and settings are similar to the DPD settings, they are described together. The same apples also for the remote control commands.

This section describes only the settings that are dedicated to the digital Doherty option. For description of all other settings, see Chapter 3.3, "Digital predistortions

AM/AM and AM/PM settings", on page 51.

The remote commands required to define the settings are described in:

●

Chapter 7.5, "SOURce:IQ:DOHerty subsystem", on page 123

●

Chapter 7.4, "SOURce:IQ:DPD and SOURce:IQ:DOHerty subsystem",

on page 114.

4.3.1 General settings

Access:

► Select "I/Q Mod > Digital Predistortion > Digital Doherty".

See Figure 4-2.

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State..............................................................................................................................74

Set to Default................................................................................................................ 74

Save/Recall...................................................................................................................74

PEP, Level.................................................................................................................... 75

Dig Att........................................................................................................................... 75

Couple Dig Att...............................................................................................................75

Phase Offset..................................................................................................................75

Power and Phase State................................................................................................ 76

State

Option: R&S SMW-B9 - enabled in "System Config > Mode = Standard". Option: R&S SMW-B10 - enabled in "System Config > Mode = Standard/Advanced". Enables/disables the generation of control signals for testing Doherty amplifiers. If digital Doherty is enabled ("State > On"), some configurations and settings are set

automatically, see "Interdepended settings" on page 73. Remote command:

[:SOURce]:IQ:DOHerty:STATe on page 125

Testing Doherty power amplifiers

Digital Doherty settings

Set to Default

Calls the default settings. The values of the main parameters are listed in the following table.

Parameter Value

"State" Not affected by the "Set to Default"

"Couple Dig. Att." Off

"Power" Off

"Phase" Off

"Dig. Att.", "Phase Offset", "PEP", "Level" As set in other dialogs

Not affected by the "Set to Default"

Remote command:

[:SOURce]:IQ:DOHerty:SETTing:PRESet on page 126

Save/Recall

The settings are saved in a file with predefined extension. You can define the filename and the directory, in that you want to save the file.

See also, chapter "File and Data Management" in the R&S SMW user manual. Remote command:

[:SOURce]:IQ:DOHerty:SETTing:CATalog? on page 126 [:SOURce]:IQ:DOHerty:SETTing:STORe on page 126 [:SOURce]:IQ:DOHerty:SETTing:LOAD on page 126 [:SOURce]:IQ:DOHerty:SETTing:DELete on page 127

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PEP, Level

Indicated are the PEP and level values per signal path, where:

●

The values for I/Q A are derived from the baseband signal and correspond to the values at the I/Q output and RF A output and are displayed in the "Status bar".

●

The values for I/Q B after the shaping functions are the values at the I/Q output and are also displayed and set in the Status bar. The values for I/Q B before the shaping are calculated automatically depending on the baseband signal and the DPD and considering the "Power" and "Phase" shaping functions so that the resulting PEP and Level at the I/Q B are as set in the Sta-

tus bar. See also Figure 4-2. "---.--"

Indicates that the values are in calculation.

Remote command: I/Q A and I/Q B:

[:SOURce<hw>]:IQ:DOHerty:OUTPut:PEP? on page 129 [:SOURce<hw>]:IQ:DOHerty:OUTPut:LEVel? on page 129

I/Q B:

[:SOURce<hw>]:IQ:DOHerty:INPut:PEP? on page 128 [:SOURce<hw>]:IQ:DOHerty:INPut:LEVel? on page 128

Calculation status: see [:SOURce]:IQ:DOHerty:MEASurement[:STATe]? on page 130

Testing Doherty power amplifiers

Digital Doherty settings

Dig Att

Applies additional digital attenuation to the signal. The value resembles the value set with the parameter "Block diagram > RF > Level >

RF Level > Digital Attenuation". If Couple Dig Att > "Off", you can set th values for both outputs separately. Remote command:

[:SOURce<hw>]:IQ:DOHerty:POWer:ATTenuation on page 128

Couple Dig Att

Enable this parameter to couple the "Dig Att" values for both signals; the difference between the values is, however, maintained.

Example:

For "I/Q if "I/Q

A > Dig Att = 30 dB", "I/Q

DPD

A > Dig Att = 40 dB" than "I/Q

DPD

B > Dig Att = 20 dB" and "Couple Dig Att = On",

DPD

B > Dig Att" is set to 30 dB.

DPD

Remote command:

[:SOURce]:IQ:DOHerty:POWer:ATTenuation:COUPling[:STATe]

on page 127

Phase Offset

Adds a phase offset for compensating for phase differences between the signals or for introducing a phase dealy between them deliberately.

The value resembles the value set with the parameter "I/Q Mod B > Digital Impairments > Phase Offset".

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Remote command:

[:SOURce<hw>]:IQ:DOHerty:PHASe:OFFSet on page 127

Power and Phase State

Enables/disables the power and phase corrections. If both shaping functions are enabled simultaneously, the instrument applies the power

correction values first and compensates the phase error of the PA afterwards. Compare the displayed signal processing chain. Remote command:

[:SOURce<hw>]:IQ:DOHerty:SHAPing:POWer:STATe on page 128 [:SOURce<hw>]:IQ:DOHerty:SHAPing:PHASe:STATe on page 128

4.3.2 Shaping settings and settings for classic Doherty shaping

Access:

Testing Doherty power amplifiers

Digital Doherty settings

1. Select "I/Q Mod > Digital Predistortion > Digital Doherty > Shaping".

2. Select a shaping function, for example select "Shaping > Classic Doherty".

The dialog covers the shaping settings, like select the way the shaping function is

defined and specify the correction values.

This section lists only the settings dedicated to digital Doherty. For description of all

other settings, see Chapter 3.3.2, "Predistortion settings", on page 55.

Settings:

Power Breakpoint..........................................................................................................77

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Power Breakpoint

Sets the power breakpoint value required for the calculation of the correction function if classic Doherty shaping is used.

Remote command:

[:SOURce<hw>]:IQ:DOHerty:SHAPing:POWer:BREakpoint on page 129

4.3.3 Edit shaping table settings

The shaping table is an internal editor where you define the correction values, ΔPower and ΔPhase, in form of a look-up table.

Access:

1. Select "I/Q Mod > Digital Predistortion > Digital Doherty > Shaping".

2. Select "Shaping > From Table".

3. Select "Power Table > New"

Testing Doherty power amplifiers

Digital Doherty settings

4. Enter the "File Name", e.g. My_Power

The "Doherty Power Table" dialog closes.

The "Shaping > Power Table > My_Power" confirms that the newly created file is

assigned.

5. Select "Power Table > File > Edit"

6. Define the value pairs "Pin/dBm" and "ΔPower/dB". The order is uncritical.

Figure 4-3: Example of a Power Table values

7. Select "Save".

The instrument loads the configured values automatically and displays the function

of the delta correction values.

8. Select "Shaping > Interpolation > Linear (Power)".

The display confirms the used interpolation.

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For settings description, see Chapter 3.3.3, "Edit predistortion table settings",

on page 59.

4.3.4 Polynomial coefficients settings

Alternatively to the look-up table, you can define the correction functions as a polynomial function. The R&S SMW calculates the power and phase correction functions and the required correction coefficients out of the defined polynomial.

To access the polynomial coefficients setting and define a higher-order polynomial

1. Select "I/Q Mod > Digital Predistortion > Digital Doherty > Shaping".

2. Select "Shaping > Polynomial".

3. Select "Polynomial Coefficients"

See Figure 3-4.

With the provided settings, you can define a polynomial function with up to 10

order to describe the shaping function.

The graphical display updates on-the-fly and visualizes the resulting functions.

Testing Doherty power amplifiers

Digital Doherty settings

4. Select "Polynomial Order = 4" (n = 4).

5. Set the polynomial coefficients a0 to b4.

6. Select "On Edit, Auto Update Shaping > On"

The instrument loads the configured values, calculates the correction values, and

displays the shaping functions.

See Figure 3-5.

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7. To store the defined shaping function:

a) Select "Polynomial Coefficients > Save/Recall Polynomial"

b) Navigate throughout the file system and enter a "File Name", e.g. MyPolyno-

mial_4thOrder

c) Select "OK".

8. Select "Polynomial Coefficients > OK" to close the dialog.

For settings description, see Chapter 3.3.4, "Polynomial coefficients settings",

on page 62.

Dedicated settings:

On Edit, Auto Update Shaping......................................................................................79

On Edit, Auto Update Shaping

If enabled, the any setting change is applied on-the-fly. The "Apply" and "OK" functions are disabled.

Testing Doherty power amplifiers

Digital Doherty settings

4.3.5 Normalized data settings

The normalized data table is an internal editor where you define the correction values, Vin/Vmax, ΔV/V and ΔPhase, in form of a table.

To access the internal editor

1. Select "I/Q Mod > Digital Predistortion > Digital Doherty > Shaping".

2. Select "Shaping > Normalized Data".

3. Select "Normalized Data".

See "To access the internal editor" on page 65.

4. Enter the Pin

Note: Enter the correction values in the required order. The value range of the sub-

sequent correction values adjusts automatically.

5. To store the setting in a file, select "Save/Recall Normalized Data > Save".

Enter a "File Name", e.g. My_Normalized.

For settings description, see Chapter 3.3.5, "Normalized data settings",

on page 65.

max

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5 How to generate a control signal for power

amplifier envelope tracking tests

Refer to Figure 2-1 for an example of a simplified test setup for power amplifier testing with envelope tracking. The illustration is intended to explain the principle in general, not all connections and required equipment are considered.

The R&S SMW in this setup is configured to generate an LTE RF signal with complex modulation scheme and high peak to average power (PAPR), and the required envelope signal. A polynomial shaping function is defined.

The PA receives the RF input signal and the dynamically adapted supply voltage. Ideally, the gain of the PA should stay constant.

Required are the following values:

●

Characteristics of the power amplifier: supply voltage VCC, the input power PEP

●

Characteristics of the external DC modulator: gain, peak-to-peak voltage VPP, input

impedance R

How to generate a control signal for power

amplifier envelope tracking tests

To configure the R&S SMW to generate the RF and RF envelope signal

1. Enable the R&S SMW to generate an EUTRA/LTE FDD DL signal.

Select "Baseband > EUTRA/LTE" and enable for example:

a) Select "Link Direction > Downlink"

b) Select "Test Model > E-TM1_1--5MHZ"

c) Enable "State > On"

2. Set "Frequency = 2.143 GHz" and "Level = -15 dB"

3. In the block diagram, select "I/Q Out > I/Q Analog > I/Q Analog Outputs > General"

and perform the following:

a) Select "RF Envelope > On".

b) Select "Envelope Voltage Adaptation > Auto Power"

c) Select "I/Q Output Type > Differential"

d) Configure the settings as shown on Figure 2-3.

e) Select "I/Q Analog Outputs > Envelope Settings" and set for example "Enve-

lope to RF Delay = 10 ps" f) Select "I/Q Analog Outputs > Shaping > Shape > Detroughing". g)

Set "Detroughing Function = 1: f(x) = x + d*e h) Set "Detroughing Factor (d) > Coupled with Vcc = On". i) Select "Graphic Configuration > Scale > Power".

(-x/d)

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How to generate a control signal for power

amplifier envelope tracking tests

1a, 1b = VCCmin = 0.5 V, VCCmax = 2.5 V 2a, 2b = Pinmin = -30 dBm, Pinmax = 0 dBm 3 = RF Level = -15 dBm (operating point)

3a, 3b = Current VCC = 0.612 V (operating point) 4 = Crest factor = 11.6 dB

5a = PEP = -3.4 dBm; current Pinmax limit 5b = Current VCC limit

4. Select "I/Q Analog Output > State > On"

5. Enable "RF > State > On".

6. Trigger the signal generation

7. Select "I/Q Out > I/Q Analog > I/Q Analog Outputs > General", enable "Power Offset = 1 dB" and compare the operating point.

The level display value in the status bar of the instrument shows "Level = -14 dBm" and confirms that a "Level Offset = Power Offset = 1 dB" is enabled.

The instrument generates and outputs:

● An RF signal with the specified level and level offset

● An RF envelope signal that follows the power changes of the RF signal. The envelope signal E is output at the I Out connector; the inverted envelope sig-

nal E BAR at the I Bar Out. The voltage of this envelope signal is automatically adjusted so that the supply voltage stays within the specified limits.

To observe the impact of baseband signal and its crest factor on the generated envelope signal, try out the following:

● Select "Baseband > Off" and compare the displayed envelope shape, in partic-

ular the shaded area.

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● Select "Baseband > On", enable "Baseband > EUTRA/LTE > Filter/Clipping/

ARB... > Clipping > State > On" and select "Clipping Level = 75%"

Possible extensions

Consider to extend the test setup as follows:

●

To apply digital predistortion (DPD) on the baseband signal and compare the behavior of the power amplifier (DUT) See Chapter 6, "How to apply a DPD to improve the efficiency of RF PAs", on page 84.

●

To perform RF analysis, use the R&S®FSW

●

To measure and evaluate the AM/AM and AM/PM distortions, use the R&S®FSWK18 Power Amplifier and Envelope Tracking Measurements.

●

To observe the characteristics of the generated signal, use an oscilloscope, for example R&S®RTO

How to optimize the signal to improve the linearity and efficiency of the power amplifier

How to generate a control signal for power

amplifier envelope tracking tests

Refer to Figure 5-1 for an example of a simplified test setup for power amplifier testing with envelope tracking and digital predistortion. The illustration is intended to explain the principle in general, not all connections and required equipment are considered.

FSW, equipped with R&S

R&S

SMW200A

R&S

LAN

I BAR OUT

(Rear Panel)

RF Signal

RF A

I OUT

(Rear Panel)

out

Envelope Signal (E)

Inverted Envelope Signal (ē)

AM/AM and AM/PM coefficients

Modulator

out

Figure 5-1: Simplified test setup for power amplifier envelope tracking tests with DPD

FSW-K18

LAN

INPUT

Use the following general guidelines:

Provide the output signal of the DUT to the R&S®FSW and measure the signal. Suitable RF measurements are the ACLR and EVM characteristics of the signal.

2. In the R&S SMW, select "I/Q Analog Outputs > Envelope Settings" and vary the "Envelope to RF Delay" to minimize the ACLR and EVM measured with the R&S®FSW.

3. Change the shaping method and shaping function and measure the power amplifier characteristics.

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Did its linearity and efficiency improved?

Use the R&S®FSW-K18 to evaluate the signal, calculate suitable predistortion values, and store the AM/AM and AM/PM tables.

5. Transfer the predistortion functions to R&S SMW and load them (select "I/Q Mod > AM/AM AM/PM > Predistortion Settings"). See Chapter 6, "How to apply a DPD to improve the efficiency of RF PAs", on page 84.

In the R&S®FSW, measure the power amplifier characteristics.

Did its linearity improved?

How to generate a control signal for power

amplifier envelope tracking tests

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6 How to apply a DPD to improve the effi-

ciency of RF PAs

Refer to Figure 6-1 for an example of a simplified test setup for power amplifier testing with envelope tracking and digital predistortion. The illustration is intended to explain the principle in general, not all the connections and required equipment are considered.

How to apply a DPD to improve the efficiency

of RF PAs

FSW, equipped with R&S

R&S

SMW200A

R&S

RF Signal

RF A

LAN

Figure 6-1: Simplified test setup for power amplifier envelope tracking tests with DPD

I BAR OUT

(Rear Panel)

I OUT

(Rear Panel)

out

Envelope Signal (E)

Inverted Envelope Signal (ē)

AM/AM and AM/PM coefficients

Modulator

out

LAN

A real test setup comprises of the following equipment:

●

R&S SMW to generate the RF signal, and to calculate and apply the DPD. In test setups for envelope tracking tests, the R&S SMW also generates the envelope tracking signal.

●

R&S®FSW equipped with R&S®FSW-K18 Power Amplifier and Envelope Tracking Measurements to:

– Measure and analyze the AM/AM and AM/PM predistortion – Calculate the AM/AM and AM/PM correction tables – Store and export the correction tables

●

DUT, that is the power amplifier.

●

Optional, R&S®RTO to monitor the generated envelope signal.

FSW-K18

INPUT

General steps for tests to improve the efficiency of RF power amplifiers

Consider the following general steps:

1. Enable the R&S SMW to generate a baseband signal. A suitable baseband signal is a simple ramp function or, to minimize memory effects, a signal with small bandwidth.

2. Compare the input waveform to the output of the power amplifier and determine how the amplifier is distorting the signal.

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The normalized AM/AM and AM/PM curves show the variation of the magnitude and phase over the variation of the input power and thus provide a suitable representation and good basis for analysis.

3. A simple straightforward method to retrieve the DPD correction values is to "invert" the curves, see Chapter 3.2.3, "Finding out the correction values", on page 50. Use the R&S®FSW-K18 to retrieve the AM/AM and AM/PM correction values automatically.

4. Use the retrieved correction values and define the predistortion functions.

5. Enable the AM/AM and AM/PM predistortion and predistort the original baseband signal. See "To configure the R&S SMW to predistort the baseband signal" on page 85

6. Measure the behavior of the power amplifier, for example perform EVM and ACP measurements or evaluate the AM/AM and AM/PM curves.

Does the output signal of the DUT have a better performance with regards to ACP and/or EVM?

How to apply a DPD to improve the efficiency

of RF PAs

To configure the R&S SMW to predistort the baseband signal

1. Enable the R&S SMW to generate an EUTRA/LTE FDD DL signal.

2. Set "Frequency = 2.143 GHz" and "Level = -15 dB".

3. In the block diagram, select "I/Q Mod > Digital Predistortion > AM/AM, AM/PM", and perform the following:

a) Select "Digital Predistortion AM/AM, AM/PM > Predistortion Settings" and

enable "Shaping > From Table".

b) Select "AM/AM Table > New", enter a file name, and select "AM/AM Table >

Edit".

c) Enter the correction values and select "Save".

See the example on Figure 3-3. d) Adjust the AM/PM correction values in the same way. e) Select "Interpolation > Liner (Power)". f) Select "Digital Predistortion AM/AM, AM/PM > General". g) Select "Maximum Input Power PEPIN Max > 3 dBm".

h) Select "AM/AM State > On", "AM/PM State > On" and "Predistortion State >

On". i) Select "Level Reference > After DPD", "Maximum Output Level Error = 0.1 dB"

and "Maximum Number of Iterations = 3".

4. Enable "RF > State > On".

5. Trigger the signal generation

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To perform manual iterations to achieve a desired resulting signal level after the DPD

To explain the iteration principle, we assume that the R&S SMW has been configured as described in "To configure the R&S SMW to predistort the baseband signal" on page 85 and the DPD uses an AM/AM predistortion function as shown on Fig-

ure 6-2.

To achieve a signal level of -15 dB after the DPD, perform the following steps and obey the rule:

Vary the "Level" with small steps. Always start with small value and increase the "Level" at the subsequent iterations.

1. Select "Digital Predistortion AM/AM, AM/PM > General > Level reference > Before DPD".

How to apply a DPD to improve the efficiency

of RF PAs

2. Calculate the Δ

Figure 6-2: Manual iterations on an example AM/AM predistortion function ("Input Range PEPin =

P_1

-17 dBm to -12 dBm"): Step#1

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How to apply a DPD to improve the efficiency

of RF PAs

1 = current operating point: PIN = Level 2 = first iteration with Level a = Δ

P_1

b = difference between the correction values at the current and the new operating points

● Level

● Δ

P_1

= Level = -15 dBm

IN_1

= -15.42 dBm

OUT_1

= Level - Level

3. Set the "Level" = Level + Δ

IN_2

OUT_1

P_1

The diagram displays the achieved output values; Level

4. Calculate the Δ

P_2

= -15 dBm

IN_1

= -15 + 15.42 = 0.42 dBm

= -15.45 dBm.

= - 15.02 dBm.

OUT_2

Figure 6-3: Manual iterations on an example AM/AM predistortion function ("Input Range PEPin =

1 = initial operating point: PIN = Level 2 = current operating point: PIN = Level 3 = second iteration with Level a = Δ

P_2

b = difference between the correction values at the current and the new operating points

● Level

● Δ

5. Set "Level" = Level + Δ

The diagram confirms the achieved output value; Level

-17 dBm to -12 dBm"): Step#2

= - 15.55

IN_2

= -15.02 dBm

OUT_2

= Level - Level

P_2

= -15 dBm

IN_1

= -15.45 dBm

IN_2

IN_3

= -15 + 15.02 = - 0.02 dBm

OUT_2

= -15.43 dBm

P_2

= - 15 dBm.

OUT_3

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6. Compare the operating point on the AM/AM functions.

How to apply a DPD to improve the efficiency

of RF PAs

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7 Remote-control commands

The following commands are required to perform signal generation in a remote environment. We assume that the R&S SMW has already been set up for remote operation in a network as described in the R&S SMW user manual. Knowledge about the remote control operation and the SCPI command syntax is assumed.

Conventions used in SCPI command descriptions

For a description of the conventions used in the remote command descriptions, see section "Remote Control Commands" in the R&S SMW user manual.

Common suffixes

The following common suffixes are used in remote commands:

Suffix Value range Description

Remote-control commands

SOURce<hw>

Value ranges and *RST values

The values ranges and the *RST values correspond to the values of standard baseband instrument (R&S SMW-B10).

Programming examples

The corresponding sections of the same title provide simple programming examples for the R&S SMW. The purpose of the examples is to present all commands for a given task. In real applications, one would rather reduce the examples to an appropriate subset of commands.

The programming examples have been tested with a software tool which provides an environment for the development and execution of remote tests. To keep the examples as simple as possible, only the "clean" SCPI syntax elements are reported. Non-executable command lines (e.g. comments) start with two // characters.

At the beginning of the most remote control program, an instrument (p) reset is recommended to set the R&S SMW to a definite state. The commands *RST and SYSTem:PRESet are equivalent for this purpose. *CLS also resets the status registers and clears the output buffer.

In all the examples, we assume that a remote PC is connected to the instrument, the remote PC and the instrument are switched on, a connection between them is established. We also assume that the security setting "System Config > Setup > Security > SCPI over LAN" is enabled.

[1] to 4 Available baseband signals

The following commands specific to the R&S SMW-K540/-K541 options are described here:

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● SOURce:IQ:OUTPut subsystem.............................................................................90

● SOURce:IQ:OUTPut:ENVelope commands............................................................92

● SOURce:IQ:DPD subsystem................................................................................ 107

● SOURce:IQ:DPD and SOURce:IQ:DOHerty subsystem.......................................114

● SOURce:IQ:DOHerty subsystem..........................................................................123

7.1 SOURce:IQ:OUTPut subsystem

This section describes the commands of the output of an analog I/Q signal.

[:SOURce<hw>]:IQ:OUTPut:ANALog:STATe.......................................................................90

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:PRESet...................................................................90

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:CATalog?................................................... 91

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:STORe......................................................91

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:LOAD........................................................91

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:DELete......................................................91

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:TYPE......................................................................92

Remote-control commands

SOURce:IQ:OUTPut subsystem

[:SOURce<hw>]:IQ:OUTPut:ANALog:STATe <State>

Activates the specified analog I/Q output.

Note: By default, the output connectors [I/Q Out x] are deactivated.

Suffix:

:SOURce<hw>

1|2 Selects the [I/Q Out] connectors

Parameters:

<State> 1 | ON | 0 | OFF

*RST: 0

Example:

SOURce:IQ:OUTPut:ANALog:STATe ON

Activates the output of the analog I/Q signal on the [I/Q Out 1] connectors.

Manual operation: See "State" on page 22

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:PRESet

Sets the default settings (*RST values specified for the commands).

Not affected are:

●

The state set with the command [:SOURce<hw>]:IQ:OUTPut:ANALog:STATe.

●

If SCONfiguration:EXTernal:PBEHaviour 1, the I/Q ouptput type set with the command [:SOURce<hw>]:IQ:OUTPut[:ANALog]:TYPE.

Example:

SOURce1:IQ:OUTPut:ANALog:PRESet

Usage: Event

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Manual operation: See "Set to Default" on page 22

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:CATalog?

Queries the files with I/Q output settings in the default directory. Listed are files with the file extension *.iqout.

Return values:

<Catalog> string

Usage: Query only

Manual operation: See "Save/Recall" on page 23

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:STORe <Filename>

Stores the current settings into the selected file; the file extension (*.iqout) is assigned automatically.

Setting parameters:

<Filename> "<filename>"

Filename or complete file path

Remote-control commands

SOURce:IQ:OUTPut subsystem

Usage: Setting only

Manual operation: See "Save/Recall" on page 23

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:LOAD <Filename>

Loads the selected file from the default or the specified directory. Loaded are files with extension *.iqout.

Setting parameters:

<Filename> "<filename>"

Filename or complete file path

Usage: Setting only

Manual operation: See "Save/Recall" on page 23

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:SETTing:DELete <Filename>

Deletes the selected file from the default or specified directory. Deleted are files with the file extension *.iqout.

Setting parameters:

<Filename> "<filename>"

Filename or complete file path

Usage: Setting only

Manual operation: See "Save/Recall" on page 23

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[:SOURce<hw>]:IQ:OUTPut[:ANALog]:TYPE <Type>

Sets the type of the analog signal.

Remote-control commands

SOURce:IQ:OUTPut:ENVelope commands

Example:

SOURce1:IQ:OUTPup:ANALog:TYPE DIFFerential

Options: DIFFerential requires R&S SMW-K16

Manual operation: See "I/Q Output Type" on page 24

7.2 SOURce:IQ:OUTPut:ENVelope commands

The following remote control commands require software option R&S SMW-K540.

Example: Generating an RF envelope signal and defining the shaping function

*RST

// enable LTE signal

SOURce1:BB:EUTRa:SETTing:TMOD:DL "E-TM1_1__5MHz"

SOURce1:BB:EUTRa:STATe 1

// define the RF level and frequency

SOURce1:FREQuency:CW 2143000000

SOURce1:POWer:LEVel:IMMediate:AMPLitude -15

SOURce1:POWer:LEVel:IMMediate:OFFSet 0.5

SOURce1:CORRection:VALue?

// Response: 1

// enable RF envelope generation and define the settings

SOURce1:IQ:OUTPut:ANALog:ENVelope:STATe 1

SOURce1:IQ:OUTPut:ANALog:ENVelope:ADAPtion AUTO

SOURce1:IQ:OUTPut:ANALog:TYPE DIFF

SOURce1:IQ:OUTPut:ANALog:ENVelope:ETRak USER

SOURce1:IQ:OUTPut:ANALog:ENVelope:VREF VCC

SOURce1:IQ:OUTPut:ANALog:ENVelope:POWer:OFFSet?

// Response: 1.5

SOURce1:IQ:OUTPut:ANALog:ENVelope:VPP:MAX 4

SOURce1:IQ:OUTPut:ANALog:ENVelope:GAIN 0

SOURce1:IQ:OUTPut:ANALog:ENVelope:EMF:STATe 1

SOURce1:IQ:OUTPut:ANALog:ENVelope:RIN 50

SOURce1:IQ:OUTPut:ANALog:ENVelope:TERMination GROund

SOURce1:IQ:OUTPut:ANALog:ENVelope:BINPut 1

SOURce1:IQ:OUTPut:ANALog:ENVelope:VCC:OFFSet 2

SOURce1:IQ:OUTPut:ANALog:ENVelope:VCC:MIN 0.5

SOURce1:IQ:OUTPut:ANALog:ENVelope:VCC:MAX 2.5

SOURce1:IQ:OUTPut:ANALog:ENVelope:BIAS 0

SOURce1:IQ:OUTPut:ANALog:ENVelope:OFFSet -2

SOURce1:IQ:OUTPut:ANALog:ENVelope:VOUT:MAX?

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// Response: 0.5

SOURce1:IQ:OUTPut:ANALog:ENVelope:VOUT:MIN?

// Response: -1.5

SOURce1:IQ:OUTPut:ANALog:ENVelope:PIN:MIN -30

SOURce1:IQ:OUTPut:ANALog:ENVelope:PIN:MAX 0

SOURce1:IQ:OUTPut:ANALog:ENVelope:DELay 0.00000000001

SOURce1:IQ:OUTPut:ANALog:ENVelope:FDPD OFF

// enable envelope shaping

// SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:MODE DETR

// SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:DETRoughing:FUNCtion F3

// SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:DETRoughing:COUPling OFF

// SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:DETRoughing:FACtor 0.225

// SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:DETRoughing:PEXPonent 1

// quering the oprating point level, current PEP and levels

// SOURce1:IQ:OUTPut:ANALog:ENVelope:ADAPtion?

// Response: Auto

// SOURce1:IQ:OUTPut:ANALog:ENVelope:VCC:VALue:LEVel?

// Response: 0.927

// SOURce1:IQ:OUTPut:ANALog:ENVelope:VCC:VALue:PEP?

// Response: 1.922

// SOURce1:IQ:OUTPut:ANALog:ENVelope:VCC:VALue? 1,NORM,VOLT

// Response: 2.5

// SOURce1:IQ:OUTPut:ANALog:ENVelope:VCC:VALue? 0,NORM,VOLT

// Response: 0.563

// SOURce1:IQ:OUTPut:ANALog:ENVelope:PIN:MAX?

// Response: 0

// SOURce1:IQ:OUTPut:ANALog:ENVelope:PIN:MIN?

// response: -30

// SOURce1:IQ:OUTPut:ANALog:ENVelope:VCC:VALue? 0,DBM,POW

// Response: 2.5

// SOURce1:IQ:OUTPut:ANALog:ENVelope:VCC:VALue? -30,DBM,POW

// Response: 0.563

Remote-control commands

SOURce:IQ:OUTPut:ENVelope commands

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:MODE TABL

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:PV:FILE:CATalog?

// Response: myLUT_pv

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:PV:FILE:SELect "/var/user/myLUT_pv.iq_lutpv"

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:INTerp LIN

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:SCALe POWer

// change the envelope shaping mode

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:MODE POLY

// query files with polynomial functions in the default user directory

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:COEFficients:CATalog?

// Response: env_poly_evm,myPoly

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:COEFficients:LOAD "myPoly"

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:COEFficients?

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// Response: 0.135,0.82

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:COEFficients 0.135,0.83

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:COEFficients:STORe "/var/user/myPoly.iq_poly"

// enable the outputs

SOURce1:IQ:OUTPut:ANALog:STATe 1

OUTPut1:STATe 1

// store the settings

MMEMory:CDIRectory "/var/user/setups"

SOURce1:IQ:OUTPut:ANALog:SETTings:CATalog?

// Response: etrak_v1-2

SOURce1:IQ:OUTPut:ANALog:SETTings:STORe "my_ET"

SOURce1:IQ:OUTPut:ANALog:PREset

// change the envelope voltage adaptation mode

SOURce1:IQ:OUTPut:ANALog:ENVelope:ADAPtion MAN

SOURce1:IQ:OUTPut:LEVel 4

Remote-control commands

SOURce:IQ:OUTPut:ENVelope commands

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:GAIN:PRE -3

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:GAIN:POST 2.5

// change the envelope shaping mode

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:MODE TABL

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:FILE:CATalog?

// Response: myLUT_vv

SOURce1:IQ:OUTPut:ANALog:ENVelope:SHAPing:FILE:SELect "/var/user/myLUT_vv.iq_lut"

// set the shaping values in raw format

// SOURce1:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE:DATA 0,0, 0.1,0.2, 1,1

// SOURce1:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE:CATalog?

// Response: myLUT_vv

// set the shaping values and store them into a file

// SOURce1:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE:NEW "LUT_vv_raw", 0,0, 0.1,0.2, 1,1.5

// SOURce1:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE:CATalog?

// Response: myLUT_vv, LUT_vv_raw

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:STATe......................................................95

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:ADAPtion.................................................95

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:ETRak.....................................................96

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VREF...................................................... 96

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:DELay..................................................... 96

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:FDPD......................................................97

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VOUT:MIN............................................... 97

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VOUT:MAX.............................................. 97

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:BIAS........................................................97

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:OFFSet....................................................98

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VPP[:MAX]...............................................98

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:EMF[:STATe]............................................ 98

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:RIN......................................................... 98

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[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:TERMination............................................ 99

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:BINPut.....................................................99

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:GAIN.......................................................99

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:OFFSet..........................................100

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:MIN............................................... 100

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:MAX..............................................100

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:VALue:PEP?...................................100

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:VALue:LEVel?.................................100

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:VALue?..........................................101

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:PIN:MIN.................................................101

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:PIN:MAX................................................102

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:POWer:OFFSet?.................................... 102

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:MODE.....................................102

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:SCALe.....................................103

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:GAIN:PRE............................... 103

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:GAIN:POST............................. 103

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE:CATalog?......................... 103

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:PV:FILE:CATalog?.................... 103

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE[:SELect]...........................103

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:PV:FILE[:SELect]......................103

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE:DATA............................... 104

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:PV:FILE:DATA..........................104

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:FILE:NEW................................104

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:PV:FILE:NEW...........................104

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:INTerp..................................... 104

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:COEFficients............................104

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:COEFficients:CATalog?............. 105

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:COEFficients:STORe................105

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:COEFficients:LOAD..................105

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:DETRoughing:FUNCtion........... 106

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:DETRoughing:COUPling........... 106

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:DETRoughing:FACTor...............106

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:SHAPing:DETRoughing:PEXPonent.........106

Remote-control commands

SOURce:IQ:OUTPut:ENVelope commands

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:STATe <State>

Enables the output of a control signal that follows the RF envelope.

Parameters:

<State> 1 | ON | 0 | OFF

*RST: 0

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "RF Envelope" on page 23

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:ADAPtion <AdaptionMode>

Defines the envelope voltage adaption mode.

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Parameters:

<AdaptionMode> AUTO | MANual | POWer

AUTO = Auto Normalized, POWer = Auto Power, MANual = Manual

*RST: AUTO

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "Envelope Voltage Adaptation" on page 23

Remote-control commands

SOURce:IQ:OUTPut:ENVelope commands

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:ETRak

Selects one of the predefined interface types or allows user-defined settings.

See Table 2-1.

Parameters:

<ETrakIfcType> USER | ET1V2 | ET1V5 | ET2V0

*RST: USER

Example:

Manual operation:

SOURce1:IQ:OUTPut:ANALog:ENVelope:ETRak ET2V0

See "eTrak® Interface Type" on page 24

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VREF <VoltageReferenc>

Defines whether the envelope voltage V

is set directly or it is estimated from the

out

selected supply voltage Vcc.

Parameters:

<VoltageReferenc> VCC | VOUT

*RST: VCC

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "Envelope Voltage Reference" on page 24

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:DELay <Delay>

Enables a time delay of the generated envelope signal relative to the corresponding RF signal.

Parameters:

<Delay> float

Range: -500E-9 to 500E-9 Increment: 1E-12 *RST: 0

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

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Manual operation: See " Envelope to RF Delay" on page 30

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:FDPD <CalcFromDpdStat>

Enables calculation of the envelope from predistorted signal.

Parameters:

<CalcFromDpdStat> 1 | ON | 0 | OFF

*RST: 0

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Options: R&S SMW-K540/K541

Manual operation: See "Calculate Envelope from Predistorted Signal" on page 31

Remote-control commands

SOURce:IQ:OUTPut:ENVelope commands

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VOUT:MIN

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VOUT:MAX <VoutMax> Queries the minimum and maximum values of the estimated envelope output voltage

out

Parameters:

<VoutMax> float

Range: 0.04 to 8 Increment: 1E-3 *RST: 1

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "V

Min/Max" on page 25

out

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:BIAS <Bias>

Sets a bias.

Parameters:

<Bias> float

Range: -3.390V to 3.990V (R&S SMW-B10) / -0.2V to 2.5V

(R&S SMW-B9) Increment: 1E-4 *RST: 0 Default unit: V

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92.

Manual operation: See "Bias" on page 25

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[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:OFFSet <Offset>

Sets an offset between the envelope and the inverted envelope signal.

Parameters:

<Offset> float

Range: (-4+Vp/2+V

B10) / -2V to 2V (R&S SMW-B9) Increment: 1E-4 *RST: 0 Default unit: V

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92.

Remote-control commands

SOURce:IQ:OUTPut:ENVelope commands

/2),V to (4-Vp/2-V

bias

/2),V (R&S SMW-

bias

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VPP[:MAX]

Set the maximum value of the driving voltage Vpp of the used external DC modulator.

Parameters:

<VppMax> float

Range: 0.02V to 8V (R&S SMW-B10) / 0.04V to 4V

(R&S SMW-B9) Increment: 1E-3 *RST: 1 Default unit: V

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92.

Manual operation: See "VppMax" on page 27

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:EMF[:STATe] <EmfState>

Defines whether the EMF or the voltage value is used.

Parameters:

<EmfState> 1 | ON | 0 | OFF

*RST: 1

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "EMF" on page 26

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:RIN <InputResistance>

Sets the input impedance Rin of the used external DC modulator.

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Parameters:

<InputResistance> float

Range: 50|100 to 1E6 Increment: 0.1 *RST: 50

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "Rin" on page 26

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:TERMination <Termination>

Sets how the inputs of the DC modulator are terminated.

Parameters:

<Termination> GROund | WIRE

*RST: GROund

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Remote-control commands

SOURce:IQ:OUTPut:ENVelope commands

Manual operation: See "Termination" on page 26

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:BINPut <BipolarInput>

Enables the generation of a bipolar signal.

Parameters:

<BipolarInput> 1 | ON | 0 | OFF

*RST: 0

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "Bipolar Input" on page 26

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:GAIN <Gain>

Sets the gain of the used external DC modulator.

Parameters:

<Gain> float

Range: -50 to 50 Increment: 0.01 *RST: 0

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "Gain" on page 27

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[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:OFFSet <VccOffset>

Applies a voltage offset on the supply voltage Vcc.

Parameters:

<VccOffset> float

Range: 0 to 30 Increment: 1E-3 *RST: 0 Default unit: mV

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "VccOffset" on page 27

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:MIN <VccMin> [:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:MAX <VccMax>

Sets the maximum value of the supply voltage Vcc.

Remote-control commands

SOURce:IQ:OUTPut:ENVelope commands

Parameters:

<VccMax> float

Range: 0.04 to 8 Increment: 0.001 *RST: 1

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Manual operation: See "VccMin/Max" on page 28

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:VALue:PEP?

Queries the Vcc value of the current PEP of the generated RF signal.

Return values:

<VccForCrtPep> float

Range: 0 to 38 Increment: 1E-3 *RST: 0

Example: See Example "Generating an RF envelope signal and defining

the shaping function" on page 92

Usage: Query only

Manual operation: See "Diagram" on page 40

[:SOURce<hw>]:IQ:OUTPut[:ANALog]:ENVelope:VCC:VALue:LEVel?

Queries the Vcc value of the current RMS power level (operating point).

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Rohde&Schwarz SMW-K540, SMW-K541, SMW-K546 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Contents

1 Welcome to the R&S SMW-K54x options

1.1 Accessing the required settings

1.2 What's new

1.3 Documentation overview

1.3.1 Getting started manual

1.3.2 User manuals and help

1.3.3 Tutorials

1.3.4 Service manual

1.3.5 Instrument security procedures

1.3.6 Printed safety instructions

1.3.7 Data sheets and brochures

1.3.8 Release notes and open source acknowledgment (OSA)

1.3.9 Application notes, application cards, white papers, etc.

1.4 Scope

1.5 Notes on screenshots

2 Generation of envelope tracking signals

2.1 Required options

2.2 About the envelope tracking

2.2.1 Envelope voltage adaptation modes

2.2.3 Envelope shaping and shaping methods

2.2.3.1 About the linear functions

2.2.3.2 About the detroughing function

2.2.3.3 About the polynomial function

2.2.3.4 About the shaping table

2.2.3.5 Shaping function in raw data format

2.2.3.6 Converting shaping functions and understanding the displayed values

2.3 General RF envelope settings

2.4 Envelope settings

2.5 Shaping settings

2.6 Edit I/Q envelope shape settings

2.7 Polynomial coefficients settings

3 Applying digital predistortion

3.1 Required options

3.2 About digital predistortion

3.2.1 Defining the power level of the generated signal

3.2.2 Defining the correction values

3.2.2.1 Polynomial function

3.2.2.2 Shaping table

3.2.2.3 Normalized data

3.2.2.4 Predistortion function in raw data format

3.2.3 Finding out the correction values

3.3 Digital predistortions AM/AM and AM/PM settings

3.3.1 General settings

3.3.2 Predistortion settings

3.3.3 Edit predistortion table settings

3.3.4 Polynomial coefficients settings

3.3.5 Normalized data settings

3.4 Compensating non-linear RF effects

4 Testing Doherty power amplifiers

4.1 Required options

4.2 About the digital Doherty power amplifiers

4.2.1 RF phase alignment

4.2.2 Defining the correction values

4.3 Digital Doherty settings

4.3.1 General settings

4.3.2 Shaping settings and settings for classic Doherty shaping

4.3.3 Edit shaping table settings

4.3.4 Polynomial coefficients settings

4.3.5 Normalized data settings

7 Remote-control commands

7.1 SOURce:IQ:OUTPut subsystem

7.2 SOURce:IQ:OUTPut:ENVelope commands