Using Momentum RF
3
Chapter 3 introduces how to analyze a layout using Momentum RF. By the end of this
lesson, you will be able to:

Open up a Layout of an RFIC launch

Enable Momentum RF Mode

Precompute Substrate and Mesh, if necessary

Perform a Momentum RF Simulation

Display the S-parameter results

Setup and display the current visualization
Note
At this point, some of the basic ADS operations should be familiar. For example, detailed
steps in presenting plots have been covered in the previous chapters. Primarily, only the
steps that are new or different from previous exercises will be explained in detail.
If needed, refer to the previous chapters for a more detailed explanation of:
Chapter 1 – overview of the Momentum process
Chapter 2 – detailed discussion of copying projects
Starting from schematics
Defining ports, Setting Mesh parameters, simulation
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Chapter 3 – Using Momentum RF
Lab: RFIC Launch
RFIC Launch Analysis in Momentum RF
This lab focuses on a typical design problem. A launch may be used for testing purposes. It
may be important to know how much energy is coupled between the ports. For example, a
high gain RFIC amplifier circuit without sufficient isolation may become an inadvertent
oscillator instead! In this chapter we will concentrate on how to set up and analyze a
structure such as this in Momentum RF and show the S-parameter and current visualization
results.
Port 1
In the structure above the ports represent where we might want to feed signals or bias into
or take signals out of the RFIC. All ports are terminated with 50 ohms by default, but each
port can have any real or imaginary impedance applied to it. For example a bias line might
be a low impedance with some series inductance while a test port may be a very high
impedance.
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Chapter 3 – Using Momentum RF
Lab: RFIC Launch
Opening the layout:
1. It is assumed that ADS is running and the Momentum project mom_class_prj is already
opened. If this is not the case start ADS and load the mom_class_prj from the
users\defaults directory.
2. Open a new layout window by clicking the layout icon
on the Main ADS
window or choose the Window > Layout menu command in the schematic window.
3. In the layout window choose File > Open Design… and select RFIC.dsn. There is no
schematic for this structure.
4. As a first step we will look at how regular Momentum would mesh this structure. The
substrate should have already been calculated so we’ll go directly to the meshing setup
window. Momentum>Mesh>Setup…
5. In the mesh setup window select a Mesh Frequency of 1 GHz, 30 Cells per Wavelength
and enable Edge Mesh. Leave 0 for the Edge Mesh width to have the program choose
the optimal width. When done press OK to close this dialog box.
6.
Select Momentum>Mesh>Precompute… and press OK to use the 1GHz frequency for
meshing. There will be some warnings about parallel lines; they can be ignored here.
The Meshed topology should then show up.
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Chapter 3 – Using Momentum RF
Lab: RFIC Launch
7. The layout shows a large number of rectangles and triangles are required to mesh this
structure (986 in all). In this example conductor fill has been turned off (outline only) to
make the display of the mesh easier to see.
8. Select Momentum>Mesh>Summary… to show a listing of the meshing statistics. It is
the number of unknown currents that will primarily determine the simulation time.
Mesh Info:
--------Rectangular cells
:
302
Triangular cells
:
688
Via cells
:
0
Unknown currents
:
1313
9. We will not be doing a regular Momentum simulation, as it would take about an hour on
your computers. Clear the mesh with Momemtum>Mesh>Clear .
10. Select Momentum>Enable RF Mode.
11. Select Momentum RF>Mesh>Precompute… to generate the mesh using the same set
of parameters as with the previous mesh shown above.
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Chapter 3 – Using Momentum RF
Lab: RFIC Launch
12. The mesh shown above contains approximately 58 polygons. These polygons were
created by combining the rectangles and triangles shown on the previous page.
13. Perform a simulation Momentum RF>Simulation>S-parameters…
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Chapter 3 – Using Momentum RF
Lab: RFIC Launch
14. After changing the parameters on the Simulation Control dialog box, press the simulate
button.
15. After the simulation is complete open a data display window. From the layout window
select Window>New Data Display or press
the icon on the Main or
Schematic window.
16. Change the default dataset on the data display window to RFIC_a. This will allow the
display of the adaptive frequencies generated by the Momentum RF Adaptive frequency
sweep.
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Chapter 3 – Using Momentum RF
Lab: RFIC Launch
17. To display the current distribution on the circuit select Momentum RF>PostProcessing>Visualization. The default display is of the object. To display the current
select Current>Set Port Solution Weights… Select the 1 GHz and 1 volt on Port 1 and
press OK. Then select Current>Plot Currents…
18. To make the display more interesting you can try several things:

Move the slider bar up and down to see the current caused by different phases of
voltage on port 1.

Click on Display Properties and select Animate and press OK.

Change the maximum value, in red, from 2.1211 to 0.01. This will allow us to see the
weakly coupled signals easier.
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Chapter 3 – Using Momentum RF
Lab: RFIC Launch
Port 1
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