AN-2560: Creating Amplifier2 Models in Keysight ADS Using Genesys and SystemVue Sys-Parameter Models

INTRODUCTION

Keysight Sys-Parameters are nonlinear table-based behavioral models that work in Keysight Genesys and SystemVue. Noise, distortion, and compression can be simulated using these models, in addition to the traditional S-parameter simulations (small-signal gain, return loss, and reverse isolation). Analog Devices, Inc., maintains an extensive library of Sys-Parameters for its RF amplifiers and mixers. Although these models work in the Keysight Genesys and SystemVue simulation platforms, they do not directly work in the popular Keysight RF circuit simulator, advanced design system (ADS).

Amplifier2 (AMP2) and Mixer2 (MIX2) models are nonlinear RF amplifier and mixer models that are native to ADS. These models have similar structures and capabilities to Sys-Parameter models.

This application note describes a step by step approach to creating an AMP2 model using a Sys-Parameter dataset and an S-parameter dataset. For users who do not have access to Sys-Parameter datasets, a separate process for creating AMP2 models is described in the Building Amplifier2 Models for Users That Do Not Have Access to Keysight Genesys and SystemVue section.

SYS-PARAMETER VS. AMPLIFIER2 MODELS

SYS-PARAMETER MODELS

Figure 1 shows the structure of a typical Sys-Parameter model. It consists of a table of data in .csv format that includes gain, return loss, reverse isolation, noise figure, 1 dB compression, and third-order intercept vs. frequency.

Figure 1. Accessing Sys-Parameter Data from Keysight Genesys or SystemVue

Sys-Parameter models can be used to simulate frequency response, compression, noise, and third-order intermodulation distortion (IMD3), along with system level simulations such as adjacent channel power ratio (ACPR) and error vector magnitude (EVM) (see Figure 2).

Figure 2. Typical Sys-Parameter Simulations in Keysight Genesys

The dataset in this model can be easily accessed from Genesys or from SystemVue by right-clicking the Sys-Parameter library part and then clicking Spreadsheet (see Figure 1) to open the .csv file in Excel. For users who do not have access to Keysight Genesys or SystemVue, these data can be extracted from ADIsimRF (see the Building Amplifier2 Models for Users That Do Not Have Access to Keysight Genesys and SystemVue section).

AMPLIFIER2 MODELS

AMP2 models are native to Keysight ADS, and provide similar functionality to Sys-Parameter models.

Figure 3 shows an ADS schematic that includes an AMP2 model. The AMP2 model dataset consists of frequency variant gain, along with noise figure (NF), third-order intercept (TOI), reverse isolation (RISO), and output 1 dB compression (GainCompPower).

Figure 3. A Keysight ADS Schematic that Includes an Amplifier2 Model

In Figure 3, the AMP2 model data are contained in a data access component. Data access components are structures that allow frequency variant data tables to be associated with an AMP2 model and other behavioral models available in ADS. In this case, Data Access Component 1 (DAC1) is used to point to an .mdf file containing gain, output third-order intercept (OIP3), output 1 dB compression (OP1dB), RISO, and NF data.

A step by step procedure for creating AMP2 models using SysParameter datasets is described in the Creating an Amplifier2 Model That Includes Gain, Reverse Isolation, Noise, Distortion, and Compression section and the Creating an Amplifier2 Model That Includes Noise and Distortion Data, Along with a Full S-Parameter Dataset section. Two different AMP2 models are created. These differ in complexity. The first AMP2 model is simpler consisting of gain, OIP3, OP1dB, RISO, and noise, and assumes an ideal 50 Ω input and output return losses. The second model includes the complete S-parameter dataset along with OIP3, OP1dB, and noise.

CREATING AN AMPLIFIER2 MODEL THAT INCLUDES GAIN, REVERSE ISOLATION, NOISE, DISTORTION, AND COMPRESSION

The following are the three steps involved in creating the AMP2 model:

Create an .mdf file containing gain, RISO, OIP3, OP1dB, and NF data, and associate it with the AMP2 model using a data access component.
Create a variable (VAR) block that connects the .mdf file to the AMP2 model.
Create associations inside the AMP2 model that point to the appropriate data in the data access component and VAR block.

CREATING AN .MDF FILE

The first step is to retrieve the Sys-Parameter data from Genesys or SystemVue (an alternative procedure for creating this file using data from ADIsimRF is described in the Building Amplifier2 Models for Users That Do Not Have Access to Keysight Genesys and SystemVue section for ADS users who do not have access to Keysight Genesys or SystemVue).

Starting in Genesys or SystemVue,

Click View > Part Selector (Ctrl + Shift + A) to open the Part Selector window.
Use the drop down box to locate the Analog Devices Sys-Parameter library, which is called AnalogDevicesInc Sys-Parameters (see Figure 4).
Scroll to the device of interest, right-click the Sys-Parameter file, and click Spreadsheet (see Figure 4) to open the .csv file in Excel (see Figure 5)

Figure 4. Locating a Sys-Parameter File in Keysight Genesys

Figure 5. A Typical Sys-Parameter Dataset

The following changes must be made to the Sys-Parameter dataset so that it can be reformatted into an .mdf file:

In Cell A2, insert BEGIN data (case sensitive).
Remove the G, H, I, and J columns (removes S11 and S22 data), leaving only six columns of data (frequency, gain, noise figure, OP1dB, RISO, and OIP3).
In Row 4,

Change Freq to %Freq_In(real)
Change Gain to Gain(real)
Change Noise Figure to NF(real)
Change OP1dB to OP1dB(real)
Change RISO to RISO(real)
Change OIP3 to OIP3(real)

In Row 5, change (MHz) to !(Hz).
Convert the frequency data in Column A from MHz to Hz, that is, multiply the existing data by 1,000,000.
In the row immediately after the last data point, add END (case sensitive) in the first column.

The updated dataset now looks similar to Figure 6.
Save the file in a text (MS-DOS) format (that is .txt extension).
Locate the file and change the extension from .txt to .mdf (case sensitive).
Move this file to a location where you plan to store the AMP2 models.

Figure 6. Structure of a Typical .mdf File, Viewed in Excel

ASSOCIATING THE .MDF FILE WITH THE AMPLIFIER2 MODEL

After the .mdf file has been created, it must be associated with an AMP2 model via a data access component.

To do this, open an existing Keysight ADS workspace that contains an AMP2 model with a data access component. An example is shown in Figure 7. A template workspace is available from Analog Devices on request.

Figure 7. Associating an .mdf File with a DAC1 Data Access Component

Double click DAC1 to open the window shown in Figure 8.

Figure 8. Data Access Component Settings

In this window, make the following changes:

Click Browse to navigate to the location of the .mdf file and select it.
Ensure that the File Type drop down is set to Generic MDIF.
In the Independent Variable tab, set Name and Value to “Freq_In” and Freq_In, respectively. If these variables are not present, select Add to add them (see Figure 9).
In the Interpolation tab,

Set Interpolation Method to Linear or 0.
Set Interpolation Domain to Rectangular.
Set Extrapolation Method to Constant Extrapolation.

Figure 9. Setting Independent Variables in Data Access Component 1

Figure 10. Setting Independent Variables in Data Access Component 1

ADDING A VAR BLOCK

Next, add a VAR block by clicking the VAR icon at the top of the schematic window and use File Based entry mode to extract the desired parameters from the DAC1 instance (see Figure 11). The required equations for adding a VAR block, as shown under Select Parameter (see Figure 11) are as follows:

AmpNF=file{DAC1, "NF"}
AmpGain=file{DAC1, "Gain"}
AmpRISO=file{DAC1, "RISO"}
AmpOP1dB=file{DAC1, "OP1dB"}
AmpOIP3=file{DAC1, "OIP3"}

Figure 11. Adding File-Based Equations to Extract the Desired Parameters from the DAC1 Instance

CHECKING THE PARAMETER ASSIGNMENTS IN THE AMPLIFIER2 MODEL

The next step is to check that all of the parameter assignments inside the AMP2 model are correct. To do this, double click the AMP2 model (see Figure 12).

Figure 12. Parameter Assignment for the AMP2 Model

The specific equations for checking parameter assignments are as follows:

S21=dbpolar(AmpGain,0)
S12=dbpolar(AmpRISO,0)
NF=AmpNF dB
TOI=AmpOIP3
GainCompPower=AmpOP1dB
Psat=AmpOP1dB+2

Assuming ideal input and output impedances, set the input and output return losses to infinity.

S11=polar(0,0)
S22=polar(0,180)

SETTING UP A BASIC SIMULATION TO VERIFY OPERATION OF AMPLIFIER2 MODEL

Double click HARMONIC BALANCE shown in Figure 7 to open the harmonic balance simulation controller (see Figure 13). In the Freq tab, set the Frequency to Freq_In. On the Noise tab, ensure that Noise is enabled. Ensure that Frequency is set to Freq_In, and that Input Frequency is set to Noisefreq to allow the harmonic balance simulator to simulate noise figure.

Figure 13. Harmonic Balance Simulation Setup

Double click PARAMETER SWEEP (see Figure 7) to open the Parameter Sweep window shown in Figure 14. In the Sweep tab, set Start, Stop, and Step-size to Fstart, Fstop, and Fstep, respectively (the actual values for these are set in the VAR1 block).

In the Simulations tab, set Simulation 1 to HB1 (see Figure 15).

Figure 15. Parameter Sweep, Simulations Tab

Double click LSSP (see Figure 7) to open the Large-Signal S-Parameters window shown in Figure 16. Frequency is equal to Freq_In in the Freq tab. In the Ports tab (see Figure 17), set Port 1 and Port 2 to Freq_In.

Figure 16. Large Signal S-Parameter Controller, Freq Tab

Figure 17. Large Signal S-Parameter Controller, Ports Tab

Next, run a simulation, which yields the results shown in Figure 18.

Figure 18. Typical Results of a Harmonic Balance Simulation of an Amplifier2 Model

CREATING AN AMPLIFIER2 MODEL THAT INCLUDES NOISE AND DISTORTION DATA, ALONG WITH A FULL S-PARAMETER DATASET

The process of creating an AMP2 model that includes S-parameter data is very similar to the previously described process (see the Creating an Amplifier2 Model That Includes Gain, Reverse Isolation, Noise, Distortion, and Compression section) but has a few extra steps. The process is summarized as follows:

Create an .mdf file containing OIP3, OP1dB, and NF data, and associate it with the AMP2 model using a data access component (DAC1).
Associate the S-parameter file of the RF amplifier with the AMP2 model using a second data access component (DAC2).
Create a VAR block that connects the .mdf file to the AMP2 model.
Create associations inside the AMP2 model that point to the appropriate data in the data access components.

CREATING AN .MDF FILE

The process of creating the .mdf file is very similar to the process already described in the Creating an Amplifier2 Model That Includes Gain, Reverse Isolation, Noise, Distortion, and Compression section. However, in this case, the gain and RISO are also removed (these data come from the S-parameter file).

Make the following changes to the S-parameter dataset so that it can be reformatted into an .mdf file:

In Cell A2, insert BEGIN data (case sensitive).
Remove the B, E, G, I, and J columns, leaving only four columns of data (frequency, noise figure, OP1dB, and OIP3).
In Row 4,

Change Freq to %Freq_In(real)
Change Noise Figure to NF(real)
Change OP1dB to OP1dB(real)
Change OIP3 to OIP3(real)

In Row 5, change (MHz) to !(Hz).
Convert the frequency data in Column A from MHz to Hz, that is, multiply the existing data by 1,000,000.
In the row immediately after the last data point, add END (case sensitive) in the first column.

The updated dataset now looks similar to Figure 19.
Save the file in a text (MS-DOS) format (that is .txt extension).
Locate the file and change the extension from .txt to .mdf (case sensitive).
Move this file to a location where you plan to store the AMP2 models.

Figure 19. Structure of a Typical .mdf File, Containing Noise Figure, OP1dB, and OIP3 Data

ASSOCIATING THE .MDF FILE WITH THE AMPLIFIER2 MODEL

Once the .mdf file containing NF, OP1dB, and OIP3 data vs. frequency has been created, it must be associated with an AMP2 model via DAC1. This process is similar to what was described in the Associating the .mdf File with the Amplifier2 Model section.

Open an existing Keysight ADS workspace that contains an AMP2 model with two data access components (see Figure 20). A template workspace is available from Analog Devices on request.

Figure 20. Associating the .mdf File with the DAC1 Data Access Component

Double click the DAC1 component and make the same changes that are described for Figure 8, Figure 9, and Figure 10.

ADDING A VAR BLOCK

Next, add a VAR block by clicking the VAR icon at the top of the schematic window and use File Based entry mode to extract the desired parameters from the DAC1 instance (see Figure 21).

The required equations for adding a VAR block, as shown under Select Parameter (see Figure 21) are as follows:

AmpNF=file{DAC1, "NF"}
AmpOP1dB=file{DAC1, "OP1dB"}
AmpOIP3=file{DAC1, "OIP3"}

Figure 21. Adding File-Based Equations to Extract the Desired Parameters from the DAC1 Instance

ASSOCIATING THE S-PARAMETER FILE WITH THE AMPLIFIER2 MODEL

The next step is to associate the S-parameter file of the device with the second data access component, DAC2. First, locate the S-parameter file. The AnalogDevicesInc Sys-Parameter library also contains S-parameter files for each device. The default install location for the Sys-Parameter and the S-parameter files is as follows:

C:\Users\jdoe\AppData\Local\Keysight\Genesys2018\Data\AnalogDevicesInc Sys-Parameters_data

For ADS users who do not have access to Keysight Genesys or SystemVue, the S-parameter file of the device can be downloaded at www.analog.com.

Move the S-parameter file to the same location where the .mdf file is located.

In the ADS schematic, double click DAC2. Click Browse to navigate to the location of the S-parameter file and select it (see Figure 22). Click Apply and OK.

Figure 22. Associating the S-Parameter File with the DAC2 Data Access Component

Returning to the schematic, DAC1 and DAC2 are now associated with the .mdf file and the S-parameter file, respectively (see Figure 23).

Figure 23. Schematic with Correctly Associated DAC1 and DAC2 Components

CHECKING THE PARAMETER ASSIGNMENTS IN THE AMPLIFIER2 MODEL

The next step is to check that all of the parameter assignments inside the AMP2 model are correct. To do this, double click the AMP2 model (see Figure 24).

Figure 24. Parameter Assignment for the AMP2 Model

There are a total of seven associations that refer to the location of S11, S21, S12, S22, NF, OIP3, and OP1dB data. For example, the first line, S21=file{DAC2, “S[2,1]”}, indicates that the S21 data is to be found in the S21 column of the file that is associated with DAC2 (that is, the S-parameter file). Similarly, TOI=AmpOIP3 points to the VAR block, which in turn points to the DAC1 component (that is the .mdf file). All of these associations can be set by the drop down boxes on the right side

BUILDING AMPLIFIER2 MODELS FOR USERS THAT DO NOT HAVE ACCESS TO KEYSIGHT GENESYS AND SYSTEMVUE

The procedures described in this application note rely on the user having access to Keysight Genesys or SystemVue. However, even without access to these tools, ADS users can still construct AMP2 models. The S-parameter data for all of Analog Devices RF amplifiers can be downloaded from analog.com. Gain, NF, IP3, and P1dB data can be exported from ADIsimRF. To export data from ADIsimRF, use the following procedure.

If necessary, download and install ADIsimRF from analog.com. In ADIsimRF, load the device (see Figure 25). Click the Plots tab and perform a frequency sweep (see Figure 26). Adjust the step size until the trace starts granulating as shown in Figure 26 (the granulation optimizes the size of the dataset). Then click on the Excel icon to export the data into Excel, which converts the data into a format that can be used to make an .mdf file (see the Creating an .mdf File section).