Digital Predistortion

This block controls the DPD processing for the IQ waveform. You can turn on digital predistortion or set it Thr (through) by clicking the Closed

toggle button on the block.

The Digital Predistortion block supports two DPD modes. Each mode has a unique set of parameters.

Extract and Apply: First, the PA model is extracted using the algorithm and parameters set in this block and PA output signal from the Signal Analyzer. Then the waveform is pre-distorted based on the extracted model to compensate for the non-linearity introduced by the PA.
Apply Only: The waveform is directly pre-distorted with the user input LUT of PA input versus PA output in terms of amplitude and phase or the Memory Polynomial or Volterra Series Coefficient File.

Extract and Apply Mode

Export DPD Model Button

Click this button to export the DPD model into a .csv file.This button is only visible when the DPD Mode is set to Extract and Apply.

If the PA Model Type is Look-up Table, the exported .csv file has three rows, which are AM In (V), AM Out (V), and PM Out (deg) respectively. The exported coefficients of the DPD model can be applied to the IQ data when DPD Mode is set to Apply IQ LUT.
If the PA Model Type is Memory Polynomial or Volterra Series, the exported .csv file has one row which is the coefficient of the polynomial that is used for DPD modeling.The exported data can not be applied to the IQ data through N7614B Signal Studio for Power Amplifier Test.

Export Pre-distorted Waveform Button

Click this button to export the pre-distorted waveform to a file. The waveform is encrypted and can be played on a signal generator with the related licenses. Note that no file will be exported if the current Mode is Real-time or the Digital Predistortion block is set to off.

Digital Predistortion Setting Table

1. General	2. Model Settings	3. Details
DPD Mode Frequency Offset Compensation	Number of Iteration PA Model Type Model Identification Algorithm Memory Order Nonlinear Order Odd Orders Only Cross Term Order LUT Type LUT Size AM/AM Polynomial Order AM/PM Polynomial Order	1. Function Command 2. Input Variables Normalized DPD Input Normalized PA Input Captured Signal Generator Power Loss In Loss Out 3. Output Variables DPD Output

1. General

2. Model Settings

3. Details

MATLAB Script

DPD Mode

Frequency Offset Compensation

Number of Iteration

PA Model Type

Model Identification Algorithm

AM/AM Polynomial Order

AM/PM Polynomial Order

1. Function

2. Input Variables

Signal Generator Power

Loss In

Loss Out

3. Output Variables

DPD Output

1. General

DPD Mode

Choice: Extract and Apply | Apply Only

Default: Extract and Apply

Double-click or use the drop-down menu to set the DPD mode.

Frequency Offset Compensation

Choice: On | Off

Default: Off

Coupling: Disables Burst Shape and Mask in Waveform block

This parameter activates carrier frequency offset compensation. It should be used when one of the 10 MHz reference is not connected.

When you use an AXIe AWG configuration without PSG, the DUT accepts the I/Q signal from M8190A. The I/Q modulation, up-conversion and PA are integrated together. If there is no 10 MHz external reference on the DUT, the RF signal may have a carrier frequency offset when the signal analyzer captures the I/Q data. So frequency offset compensation should be used.

Before playing a waveform, extract DPD model or apply DPD, a training signal will be sent first, and the signal will be captured. The frequency offset will be estimated based on the captured signal.

2. Model Extraction

Number of Iteration

Range: 1 to 1000

Default: 1

Enter the iteration number for the DPD process.

PA Model Type

Choice: Memory Polynomial | Volterra Series | Look-up Table | User-defined MATLAB Script

Default: Look-up Table

Double-click or use the drop-down menu to select the PA model extraction algorithm to be used. Memory Polynomial is a simplified version of Volterra Series. Look-up Table is suitable for memoryless PA component.

When PA Model Type is set to User-defined MATLAB Script (supported only under ARB and Extract and Apply modes), the N7614B software interacts with MATLAB to execute the DPD algorithm defined in the MATLAB script. The N7614B software also controls the instruments to run the whole test flow.

If User-defined MATLAB Script is selected, Signal Studio and Preloaded become invalid selections for Waveform Type.

For more detailed information, refer to DPD Concept.

Model Identification Algorithm

Choice: LSE using QR | LSE using SVD

Default: LSE using QR

Coupling: Available only when the DPD Mode is set to Extract and Apply and the PA Model Type is set to Memory Polynomial or Volterra Series.

Double-click or use the drop-down menu to specify the model identification algorithm.

Memory Order

Range: 0 to 20

Default: 1

Coupling: Available only when the DPD Mode is set to Extract and Apply and the PA Model Type is set to Memory Polynomial or Volterra Series.

Set the memory depth of the DPD model.

Nonlinear Order

Range: 1 to 20

Default: 5

Coupling: Available only when the DPD Mode is set to Extract and Apply and the PA Model Type is set to Memory Polynomial or Volterra Series.

Set the nonlinear order of the DPD model.

Cross Term Order

Range: 0 to 10

Default: 0

Coupling: Available only when the DPD Mode is set to Extract and Apply and the PA Model Type is set to Volterra Series.

Set the order of the cross terms in the Volterra Series algorithm.

Odd Orders Only

Choice: On | Off

Default: Off

Coupling: Available only when the DPD Mode is set to Extract and Apply and the PA Model Type is set to Memory Polynomial or Volterra Series.

Double-click or use the drop-down menu to specify whether to use only the odd orders of the nonlinear terms or not.

LUT Type

Choice: Normalized | Absolute

Default: Normalized

Coupling: Available only when the PA Model Type is set to Look-up Table.

Set the type of values in the AM/AM, AM/PM in the look-up table.

LUT Size

Range: 1 to 3000

Default: 128

Coupling: Available only when the DPD Mode is set to Extract and Apply and the PA Model Type is set to Look-up Table.

Set the size of the look-up table. The amplitude range of the PA input signal is divided into equal parts with the number of LUT Size. And each segment is an entry for look-up table.

AM/AM Polynomial Order

Range: 1 to 12

Default: 5

Coupling: Available only when the DPD Mode is set to Extract and Apply and the PA Model Type is set to Look-up Table.

Enter the order for the polynomial approximation of the AM/AM curve.

AM/PM Polynomial Order

Range: 1 to 12

Default: 5

Coupling: Available only when the DPD Mode is set to Extract and Apply and the PA Model Type is set to Look-up Table.

Enter the order for the polynomial approximation of the AM/PM curve.

3. Details (MATLAB Script)

1. Function

Command

Set the MATLAB script command line. The software will invoke this function via MATLAB API. Assume the script file is under MATLAB working path. The function name (e.g. dpd) should be the same with the MATLAB function name, the input variable name (e.g. dpdIn, dutIn, capture) and output variable name (eg. dpdOut) should match the software settings under Digital Predistortion block.

2. Input Variables

Normalized DPD Input

Default: dpdIn

Set the variable name for normalized DPD input waveform. The waveform is the baseband I/Q waveform without DPD. The waveform is normalized to 1 with its peak magnitude. User’s MATLAB script will apply the extracted DPD model on the DPD input waveform and get the predistorted baseband waveform. For the first iteration, the Normalized DPD input waveform should be the same as the Normalized PA Input.

Normalized PA Input

Default: dutIn

Set the variable name for normalized PA Input waveform. User will use Normalized PA Input waveform and Captured waveform to extract the PA model. If user need absolute PA input waveform, user should calculate the waveform based on Normalized PA Input, Signal Generator Power, and Loss In.

Captured

Default: captured

Set the variable name for captured waveform. User will use Normalized PA Input waveform and Captured waveform to extract the PA model. If user need absolute PA output waveform, user should calculate the waveform based on Captured and Loss Out.

Signal Generator Power

Default: sgPower

Set the variable name for Signal Generator power. The variable value will be the Amplitude value under RF Signal Generator block and it will be written into MATLAB workspace.

Loss In

Default: lossIn

Set the variable name for loss in. The variable value Loss In value under PA block and it will be written into MATLAB workspace.

Loss Out

Default: lossOut

Set the variable name for loss out. The variable value Loss Out value under PA block and it will be written into MATLAB workspace.

3. Output Variables

DPD Output

Default: dpdOut

Set the variable name for predistorted waveform.

Apply Only Mode

Export Pre-distorted Waveform Button

1. General	2. Model Settings	3. Details
DPD Mode Frequency Offset Compensation Show Results (w/o DPD)	PA Model Type LUT Type LUT Apply Mode Coefficient File	Add Remove Open Save Apply

1. General

2. Model Settings

3. Details

DPD Mode

Frequency Offset Compensation

Show Results (w/o DPD)

1. General

DPD Mode

Choice: Extract and Apply | Apply Only

Default: Extract and Apply

Double-click or use the drop-down menu to set the DPD mode.

Frequency Offset Compensation

Choice: On | Off

Default: Off

Coupling: Disables Burst Shape and Mask in Waveform block

This parameter activates carrier frequency offset compensation. It should be used when one of the 10 MHz reference is not connected.

Before playing a waveform, extract DPD model or apply DPD, a training signal will be sent first, and the signal will be captured. The frequency offset will be estimated based on the captured signal.

Show Results (w/o DPD)

Choice: On | Off

Default: On

Coupling: Available only when DPD Mode is set to Apply IQ LUT and Measurement Enabled in the Measurement view settings is set to On.

Double-click or use the drop-down menu to choose whether to make AM-AM, AM-PM,and ACP measurements without applying DPD, for comparison.

If this parameter is set to On, in the measurement view, AM-AM, AM-PM, ACP windows will display two measurement traces, with DPD and without DPD.

If this parameter is set to Off, in the measurement view, AM-AM, AM-PM, ACP windows will display only one measurement trace, with DPD.

2. Model Settings

PA Model Type

Choice: Memory Polynomial | Volterra Series | Look-up Table

Default: Look-up Table

For more detailed information, refer to DPD Concept.

LUT Type

Choice: Normalized | Absolute

Default: Normalized

Coupling: Available only when the PA Model Type is set to Look-up Table.

Set the type of values in the AM/AM, AM/PM in the look-up table.

LUT Apply Mode

Choice: AM/AM, then AM/PM | AM/PM, then AM/AM | AM/AM Only | AM/PM Only

Default: AM/AM, then AM/PM

Coupling: Available only when the PA Model Type is set to Memory Polynomial or Volterra Series.

Set the method to apply the LUT table. Refer to Digital Pre-distortion Concept for more details.

Coefficient File

Coupling: Available only when the PA Model Type is set to Memory Polynomial or Volterra Series.

Choose the coefficient file for memory polynomial or Volterra series DPD models.

3. Details

This area is used to configure the IQ LUT. There are five buttons on the top: Add, Remove, Open, Save, and Apply. In the middle, there is a list of LUTs, and at the bottom shows the details of the selected LUT.

Add

Click this button to add a new LUT. The new table is added to the end of the list.

Remove

To remove a LUT, select the table name in the list, then click this button.

Open

Click this button to import a LUT.

Save

Click this button to save the table as .csv file.

Apply

Click this button to apply the selected table.