em techniques (momentum)rfmw.em.keysight.com/flash/eesof/ads_2012_layout... · audience: engineers...

ADS 2012 EM Basics (v2 April 2013)

© Copyright Agilent Technologies 2013

LAB EXERCISE 3B

EM Techniques (Momentum)

Topics: EM options for meshing and the preprocessor, and using EM to simulate an inductor and use the model in schematic.

Audience: Engineers who have a basic working knowledge of ADS 2011, have completed the prerequisite course, or who require EM training.

Prerequisites: Completion of the course, Workspaces and Simulation Tools or equivalent experience, including basic circuit design concepts.

Objectives: Be able to specify different meshes, current models, create a look-alike symbol for use in schematic, visualize current, and use many other features and settings in EM.

Lab 3B: EM Techniques

Copyright 2013 Agilent Technologies

2

Table of Contents: Lab 3B

1. Workspace and Schematic for DemoKit Inductor 3

2. Generate the Layout and Insert Ports 4

3. EM Setup: Mesh Control 5

4. EM Setup: Preprocessor Healing and Arc Resolution 6

5. Mesh Control – RF Mode 7

6. EM Setup: Current Models for Via and Thick Metal 8

7. Substrate Modification: Thick Metal 8

8. Ports: Area/Edge Pins 11

9. EM Setup: Frequency Plan 12

10. EM Setup: Output Plan – Dataset Names 12

11. EM Setup: Model / Symbol 13

12. EM Simulation 13

13. Hierarchy: Symbol and emModel in Schematic 15

14. Visualize the 3D Surface Currents 18

15. Optional: FEM Example 20



3

This lab exercise will compare a schematic inductor model to an EM model. You will also see how closely spaced lines can affect the design.

1. Workspace and Schematic for DemoKit Inductor

a. Create a new workspace and name it: My_EM_Inductor_wrk.

.

b. Create a new schematic and name it: IND_test.

c. Then insert the S-Params templates as shown here: Insert >Templates and then scroll down and select the ads_templates_S_Params and click OK.

d. From the demoKit_Non_Linear palette, insert and connect the inductor, DEMO_IND, and Tech Include component shown here.



4

e. In the schematic window, change the nturns value = 4. Also, change the simulation Stop frequency to 20 GHz as shown here.

f. Save the design and then click the Simulate command. When the simulation is finished, look at the results that will automatically appear in the data display from the template. Notice the inductor, at 3.91nH, has about 15 dB of loss near 20 GHz. This is the nominal value.

g. Save the schematic and data display.

Now that you have the circuit simulator results, it’s time to simulate the same inductor using Momentum – but with some modifications that represent connection and manufacturing concerns for either board or MMIC designs.

2. Generate the Layout and Insert Ports

a. In the schematic window, use the command: Layout > Generate/Update Layout. Click OK to the messages that pop up.

b. When the layout opens, insert pins, P1 and P2, as shown here. You can change the arrow size using the command: Edit > Component > Pin/Ground Size (use 30 or 40).



5

c. Click on the 3D EM Preview icon and an error message will appear reminding you there is no EM Setup. Click OK to close this message.

Notice that your Main window Folder View also has no EM Setup which is required for 3D viewing. Therefore, click on the EM icon in layout

3. EM Setup: Mesh Control

a. Click on the EM Setup icon – the setup dialog should appear with no yellow caution signs because the pins were automatically recognized as ports – click OK if a message dialog pops up.

b. In the EM Setup, select the Options icon and click on the Mesh tab.

c. In the Mesh > Global tab, set the Mesh Frequency = 20 GHz and set the Mesh Density = 100 Cells/Wavelength as shown here. Also, turn ON Edge Mesh as shown here. In some cases, you can increase the default density to ensure more accuracy, including the Edge Mesh which guarantees calculations for current bunching along the edges, especially for closely spaced lines. But simulation time will also increase.

d. Click the Save icon to save the mesh settings.



6

4. EM Setup: Preprocessor Healing and Arc Resolution

a. Click on the Preprocessor tab and look at the settings. The default is checked to Heal the Layout – this is recommended and will help in the meshing process.

b. Click: Show Visual Aid near the top of the tab.

Notice the picture that appears – this shows what the layout Preprocessor will do with the settings you make.

c. Look at the section for Simplify the Layout – this is ON by default. Notice the arc resolution is set to 45 degrees. For circles or arcs in your layout, this controls how they are simplified for a more uniform mesh. In some cases, you may want to decrease the value from 45 degrees if those arcs or circles must be maintained for the desired solution.

For this lab exercise, you can leave the defaults, but remember these tabs in the Options, in case you need them for your designs.

d. Close the Visual Aid when you are satisfied that you understand how the Preprocessor works.



7

5. Mesh Control – RF Mode

a. In the EM Setup, click the EM top level icon and then set the Simulator to Momentum RF.

b. At the bottom of the EM Setup you will see the Generate field. Use the arrow button to select Mesh (as shown here) and click: Go.

c. Immediately, you will see the Job dialog appear with messages. Click OK to any dialogs that pop up after reading the information.

d. Look at the Job window – it shows all the information about the mesh. It also indicates the layout is electrically small. Look at mesh and zoom in to see the fine edge mesh that was created. This is how you can control what the mesh will be before simulation and you can make adjustments.

e. Close the Job window.

f. Use the layout menu command: EM > Clear Momentum Mesh and it will be removed from the layout. Then use: EM > Show Most Recent > Momentum Mesh to restore it - this is how you control the mesh.



8

NOTE on RF Mode – Because the layout is electrically small, the faster RF Mode can be used and the results will be accurate. Next, you will set thick metal in the EM Setup and Substrate.

6. EM Setup: Current Models for Via and Thick Metal

a. In the EM Setup, click on the Options icon – then click the Physical Model tab as shown.

b. Notice that you can set specific layers or globally set the type of current models for either vias or thick conductors. Your Thick Conductor and Via should be set to 3D-distributed as shown here. Leave all the other settings in their defaults.

c. Click the Copy as button and then type in the name: my_options - this will save your options and you can use them for other simulations.

7. Substrate Modification: Thick Metal

a. In the EM Setup, click on the Substrate icon – then click the Open button.

b. When the substrate editor opens, notice that the substrate is READ ONLY. Click on the M2 (metal winding) and you see the conductor settings are grayed-out. This is typical for a PDK.



9

c. In the demo substrate, click File > Save As. When the dialog appears, type in the name my_demo and click OK to save it in your library.

d. In the open demo substrate, click File > Open and then select your library (My_EM_Inductor_lib) and your saved substrate and click OK. After your saved substrate opens, close the demo substrate.

e. In Click on the M2 metal bar as shown here – M2 is the metal for the inductor winding. Then click the button to: Expand the substrate. Leave the other settings as they are. This effectively makes the substrate 1 micron thicker (1.12 microns) with 1 micron of thick metal extruding upward as shown here.



10

f. Next you will change the M2 material from PERFCET_CONDUCTOR to Gold. However, Gold was not available in the Read-Only DemoKit substrate you copied, so now you can add it from the database.

To do this, click on the M2 metal bar, then click the box with three dots […] Edit Materials. When the Material Definitions dialog appears, click the button Add From Database. Then select Gold and click OK. Now you can select Gold for M2. Finally, Save your substrate and Close it.

At this point, the inductor has the following EM setup: the simulator will be Momentum RF, the Mesh is set to a denser pattern than the default, the substrate and EM setup have thick metal, and 3D current models. Only a few steps remain to get the EM solution for the inductor.



11

8. Ports: Area/Edge Pins

a. In the layout, zoom in and select the P1 port arrow. Then use the icon (shown here) or the command: Edit > Move > Move and Disconnect – then move the port arrow over to the right.

b. Set M2 as the entry layer and draw a small rectangle inside the input to the inductor: approximately 3 x 2.5 microns as shown here – change or turn off the Grid snap if necessary. Then insert the pin again.

c. Select the rectangle and use the command: Edit > Edge/Area Pin. When the dialog appears, select Pin Number 1 and click OK. The rectangle should become blue (like a connected pin color). This means that the connection point for the solution could be anywhere on the rectangle. Then Save the layout.

NOTE: Edge pins can also be created with a polyline.



12

9. EM Setup: Frequency Plan

a. In the EM Setup, click the Frequency Plan icon.

b. Change the frequency plan to sweep from 1 GHz to 20 GHz as shown here. This is the same range as the circuit simulation.

c. Save the EM Setup again.

10. EM Setup: Output Plan – Dataset Names

a. Click on the Output Plan icon.

b. In the dialog, click the Edit button for the Dataset. Then uncheck the box to Use cell name and type in the name: IND_20GHz - use the same Data Display (cell name) and click OK.

c. Notice the name has changed – this is how you can name the dataset specifically instead of the cell name. Also in the Output Plan, uncheck the box to: Open data display when simulation completes. You already have a data display with the results of the circuit simulation so you will be plotting the Momentum RF dataset results on that plot for comparison.

d. Click OK when finished.



13

11. EM Setup: Model / Symbol

a. In the EM Setup, go to the Model/Symbol. In the EM Model field, check the box to Create EM Model when simulation is launched, as shown here.

b. In the Symbol field, check the box to Create Symbol when simulation is launched.

c. Leave all other settings alone as shown here and Save the EM setup.

12. EM Simulation

a. Review the EM Setup and check your layout one more time. Then Save and Close the EM Setup.

b. If all the settings are correct, set the Generate field to S-Parameters at the bottom and click the Simulate button or click the EM icon in layout – the simulation process will begin.



14

c. Click OK to any pop-up message dialogs and watch the information in the Job window. Notice the WARNING for P1 – it is an area pin/port now and so it is not calibrated like P2 which is excited along the entire edge– this is OK because the P1 connection is more realistic with this type of port.

d. Close the Job window.

e. When the simulation is finished, look at the Main window. It now shows all the icons from the EM setup and analysis. Notice that a new symbol and emModel appear.



15

f. Open (double-click) the emModel and look at the contents. The emModel is created from the emSetup and the simulation results.

You can use an emModel in an ADS schematic like an S-parameter file – it will be represented by the symbol (look-alike) that was also generated.

Notice that you can edit an emModel – this is really editing the emSetup which generates the model. Think of the emModel like a sub-circuit generated by the EM simulator.

Close it when finished.

g. Open (double-click the icon) the symbol and you will see the look-alike component as shown here. This symbol looks like your inductor layout and it can represent the schematic component model or the emModel from Momentum.

Close it when finished.

13. Hierarchy: Symbol and emModel in Schematic

a. In the Main window, open your existing schematic.

b. Delete the DemoKit inductor as shown here.



16

c. From the Main window, drop and drag the symbol into the schematic – then rotate it (CTRL+R) and connect it as shown here.

d. In schematic, use the command: Simulate > Simulation Settings and uncheck the Dataset box to Use cell name. Then type in the name: my_symbol. Click Apply.

e. Click the Simulate button and notice that an error message pops-up. This is due to the symbol not having a view to simulate. In other words, the look-alike symbol is just a symbol and does not point to a model. Click OK to close it.

f. In schematic, select the inductor symbol. Then click on the icon (show here) to Choose View for Simulation. Notice that you need to select a model to simulate.



17

g. In the dialog, click on the emModel and notice that the symbol now indicates which model it represents: emModel.

h. Click OK to close the dialog.

NOTE: The standard Hierarchy policy will simulate in the order shown here. Therefore, if you do not choose which view to simulate it will always simulate in this order unless no view is associated with the symbol. This is not a step – just a note showing how to view the Hierarchy Policy:

i. Click the Simulate button again (Simulation Setup). When finished, plot the S21 data for my_symbol (dataset) in your existing Data Display on the Forward Transmission plot. You can also add the S21 trace from the Momentum RF simulation. Notice that they are the same – but the DemoKit model is a little different.

Now, you have a slightly more accurate model than before because it includes thick metal and the loss associated with the material Gold.

j. Save and close the Data Display and schematic. Close the Simulation Setup and all other windows except the Main and layout windows.



18

14. Visualize the 3D Surface Currents

Now you can visualize the currents in your inducotor.

a. In the layout window from which you ran the Momentum simulation, click on the Visualization icon shown here.

In a moment, you will see the inductor in the Visualization window – notice the shading which represents current intensity.

b. Use the Visualization icons and your mouse and/or mouse wheel to zoom

in and examine the structure. Note the Port 1 area pin/port connection and the thick metal as shown here. This is an accurate 3D representation of the layout and the specific enhancements you created.



19

c. Now it is time to try using all of the features in the Visualization window to better understand how current moves through the inductor. Here are some suggestions – look at the left bottom of the window for Properties, Solution Setup, and Plot Properties.

Properties: Turn Mesh Visible On / Off Vis – turn On / Off for each

Solution Setup: Port 1 and 1 GHz.

Plot Properties: Enable each one with animation as desired.

Notice how the arrows show the surface current density, direction, and magnitude changing with phase.

d. Try different settings: changing the Options to set the Maximum scale to 100 A/m. Or use Options > Lighting to toggle the external lighting off.

e. Close Visualization and other windows when finished.



20

Note: some examples of EM/circuit co-simulation are included with ADS in the /examples/Momentum/emcktcosim directory. Now you know how to use the Momentum simulator to solve all the issues described in the video. You should now be able to use Momentum with confidence. The final step is Optional and shows an FEM example. 15. Optional: FEM Example

a. From the Main window, use Open > Example icon and select the FEM folder and then select QFN_Designer_wrk.7zads - and click Open. Follow the unarchive wizard prompts, use the defaults, and you will finish with the workspace shown here.

NOTE: FEM solves layouts that are finite in the X-Y planes – not infinite like Momentum.

b. Examine the cells: layout, setup and substrate – examine the ReadMe.

c. Try copying the design to another layout and add the symmetry plane. Also, try adding layers to the substrate. Then solve the layout using the FEM simulator. Or, try different things – refer to the Help if necessary.

NOTE: There is a YouTube video that you can watch to guide you through using FEM with ADS 2011 or 2012:

http://www.youtube.com/watch?v=Sc2b9BNElo4

END of LAB EXERCISE

em techniques (momentum)rfmw.em.keysight.com/flash/eesof/ads_2012_layout... · audience: engineers...

Documents