Introduction to EM Simulation Microwave Office Training.

Introduction to EM Simulation

Microwave Office Training

EM Simulation

• EM simulation setup has changed in 7.5.– EM uses drawing layers.

• Case 1: Draw and Simulate a Structure in the EM Environment.

• Case 2: Using a Layout Created in the EM Environment in normal layout.

• Case 3: Importing DXF and GDSII Layouts Into EM.• Case 4: Extracting layout from the Schematic Layout.

The EM Environment

Step 1: Open up the project 4Layer_PCB_Start.emp.

This is the EM Socket. Projects go in here.

To create a project - RC on EM Structures.

The various EM simulators - we are using EMSight.

EM Enclosure Settings

The Enclosure menu controls many of the important features of EM:

• X and Y box dimensions, and grid size.

•Bulk material properties.

•Dielectric Layer Setup.

•The conducting line properties - layer, conductivity, and thickness.

•EM Layer Mapping (Used when working with schematic layout and artwork cells.

Note: Later we will be seeing the Stackup Element for extraction.

It is almost the same as the Enclosure

(with some extra features).

EM Enclosure Settings - 2

Sets the x and y dimensions of the enclosing box. The height (z) we set later.

Sets the grid in the x and y directions. You want the box size a whole number of cells.

Enclosure

Grid Size Tips

• Lines should be 3 to 5 cells wide.– Edge couplers might require more.

• Box size - Don’t have the wall too close to nearest metal ... two substrate heights away is good.

• Make sure gaps / spacing in filters is an integer number of cells.

• If possible - start on a simple problem you know the answer to - simple bend, open line, 2 coupled lines,...– Gives you an idea how many cells to use.

• Double your number of cells and see if your answer changes a lot.

Note: 1000 unknowns - runs in 30 seconds/frequency.

Solution time grows as N3...10,000 unknowns - 30,000 seconds/frequency.

Number of Unknowns.

EM Enclosure Settings - 3Material Definitions

Adding Dielectrics

Conductor Properties

Used for Surface Impedances

New in 7.5 - Preset values remember materials you added before.

EM Enclosure Settings - 4

Dielectric Layers

Materials can be picked from the list of Dielectrics.

Draw scale used for 3D visibility.

New in 7.5 - Place the mouse on a layer to see its properties.

Can set the top and bottom Boundary Conditions.

EM Enclosure Settings - 5Materials

Sets the conducting lines properties:

• The thickness of the line.

• What it’s made of (from list of Conductors in Material Definitions).

Note: Etch Angle and Roughness are reserved for future use.

New in 7.5: Perfect Conductor will always exist - made out of material definition - Perfect Conductor.

EM Enclosure Settings - 2EM Layer Mapping

This controls how drawing layers are mapped to EM layers. We’ll worry about it later.

New in 7.5: This mapping is in the Enclosure Options.

Drawing in the EM Environment

To draw in EM:

•Select an EM Layer.

•Select Material.

•Select Conductor or Via.

Extent is how many layers down the via extends.

New in 7.5: The stackup display shows you the layer you are on.

Drawing in the EM Environment - 2

Step 2: Draw a line - 60 mils wide - layer 3 to layer 4 connected by a via (50X60mils).

Use material - c - as the conductor.

Draw Tools

New in 7.5: There is not any separate button for vias.

Drawing in the EM Environment - 33D View

The 3D view shows the structure to be simulated.

New in 7.5: Always check the 3D view - it will only show what is being included in the simulation.

Drawing in the EM Environment - 4Adding Edge Ports

Step 3: Add an edge port to each of the lines.

• Select the line.

•Select the edge port icon, and click at the end of the line.

•Double click the edge port and use the drag handles to select the deembedding length.

EM Structure Layout

Ports

You can double click on a port and change its impedance. Also can change how much power goes into it.

Note: This only affects current and antenna pattern viewing. S parameters are not changed.

There are 3 kinds of ports:

• Edge Ports - Like network analyzer hooking up at edges of structure.

•Via Port - One port to top or bottom of box (ground). Like 1 point probe.

•Internal Port - Across gap - like 2 point probe.

Tip: Be careful! Where is ground for an internal port?

There are 3 Webinars in KB on this - EM Simulation: A Look Under the Hood: 1, 2, 3.

Drawing in the EM Environment - 5

Properties of an EM Shape

RC on any shape - Properties.

You can change a shape’s material and EM layer.

Note: The Mesh Options Tab controls how finely a shape is meshed. You normally don’t change this - unless you want to override default automesh settings.

You can see the shape properties in the Lower left corner of the UI.

Drawing in the EM Environment - 6

Showing Only Active Layer

New in 7.5: There are various new viewing options for understanding layers.

RC in the stackup display - Hide Shapes on Non-active Layers.

In this example - only layer 3 conductors and vias will be visible.

Tip: You can use the mouse wheel to go through the layers.

EM Simulation Options

RC to set solver options.

RC on project to get individual project options.

Some global options under: Options > EM Options.

EM Options for an EM Structure

This tab is simulator specific.

EM Simulation Options - 2

Frequency Control

Project frequencies can be overridden locally.

You can set the meshing frequency if you wish.

Tip: Often you want fewer EM frequencies because of long simulation times.

EM Simulation Options - 3

Advanced Frequency Sweep

AFS - simulates over frequency band with (hopefully) fewer frequencies and (hopefully) more accuracy than just set, discrete frequencies.

EM Simulation Options - 4

AFS adds frequency points up to the maximum - until convergence is reached.

You can specify a band besides the default if you want.

Note: When AFS is finished, the frequency points displayed in graphing will be the original points in the frequency tab... So - you might want to set at a high number.

EM and Normal Layout

• Schematic Layout and Artwork Cells use Drawing layers that have already been named.

• The EM Mapping file is used to give drawing layers material properties (conductivity and thickness) and layer position.

• There are a number of scenarios where this is needed:– Importing Artwork cells to EM for simulation.

– Using an EM layout in schematic layout.

– Extracting a circuit’s schematic layout to EM layout.

Using an EM Layout in Schematic Layout

When we created our EM project - what drawing layers did it use?

Remember - If you can see it, it’s a drawing layer!

Answer - it autogenerated these drawing layers.

Note: All autogenerated EM layers begin in +.

So long as we are only in EM - this is fine.

But - what happens if we use this layout in the schematic layout?

Using an EM Layout in Schematic Layout - 2

Step 4: Create a new schematic - EM_as_Sub-circuit.

- Add the EM Structure as a sub-circuit.

Schematic View

Layout View

It draws on the error layer.

The problem is the schematic layout has no idea where to put the auto-generated layers.

Using an EM Layout in Schematic Layout - 3

The secret is to understand the EM mapping file. It lives in the LPF file.All layouts - schematic layout, artwork cells, EM projects ... have an LPF file. All LPF files have an EM mapping file - it tells the materials and line position in the stackup for each drawing layer.

EM Mapping file for EM project - start.

These 3 layers have material and EM layer position.

Note: Layer number is top of dielectric layer.

Using an EM Layout in Schematic Layout - 4

Default LPF for project.

The schematic layout uses the default project LPF, and its EM Mapping.

This is why it doesn’t know what to do with the autogenerated layers...

They aren’t even defined in the schematic layout LPF.

Using an EM Layout in Schematic Layout - 5

To fix the problem -

• The EM project’s LPF was generated from the project LPF - then the autogenerated layers were added.

•We fix the project LPF - so that any EM project we create will have the right mapping.

Step 5: Modify 4LayerPCB.lpf.

Modified default LPF. Note: A common mistake is to misspell the material name.

Using an EM Layout in Schematic Layout - 6

Step 6: Update the dependent LPFs (i.e. the EM projects created).

RC on the LPF in Layer Setup - and Update.

You can select the Dependent LPFs to update.

Using an EM Layout in Schematic Layout - 7

Schematic Layout

The EM auto generated layers have disappeared.

They aren’t needed. For example, it knows if you want a conductor on em layer 3, you are on drawing layer met2.

Note: Any new EM projects will also have this mapping - as they are generated from the default project LPF.

Options for Viewing Layers

There are a variety of viewing options.

RC in the drawing layers pane.

Options for viewing:

•Shapes on unmapped layers.

•Shapes on mapped layers.

•Shapes on missing layers.

I’ve uncloaked all unmapped layers. An X indicates unmapped.

Tip: The 3D EM view only shows mapped layers. Good way to see what is really simulating.

Multiple EM Mapping Files

You can have multiple EM Mapping Files. You can create these for the project LPF, or for EM Mapping File for a given project.

Different EM Mappings

Examples:

• Switch between lossy lines and perfect conductors.

•In MMIC - might not want to map to EM all metal layers.

Different LPF files.

Importing DXF and GDSII into EM

External World

• GDSII Libraries

•DXF Libraries

Artwork Cell Layout

EM Layout

Looks for Model Layers by same name - or creates them.

Step 7: Import mypad.dxf.

Method 1:

• Copy and paste the drawing layers.

• Select the shapes and change the layers.

Method 2:

• Change the EM Mapping file - so can repeatedly use the mapping in the future.

Method 1: Import and Change the Layers

Step 8: Copy the EM project - start. Rename the copy to Via_Sim.

- Delete the structures.

Tip: One way to make many EM projects with same settings - is to copy an empty EM project.

Step 9: Copy and paste the artwork cell - New_DXF_Cell into the EM Project.

- You can use Ctrl - C, Ctrl - V.

Method 1: Import and Change the Layers - 2

It’s placed on the Error layer.

You can fix it by selecting the properties of each element ...

and moving it to the right drawing layer.

Step 10: Set the shapes on TopMetal to met1... the shape on Pad to EMLayer 2, Via.

Settings for TopMetal Settings for Pad

Method 1: Import and Change the Layers - 3

To finish it up - you would change the box size, and extend the line and add a port.

Method 2: Update the EM Mapping in the LPF File

Step 11: Create a new EM Mapping - call it PadMap.

Step 12: Setup the mapping or Pad and TopMetal.

Note: We could have just modified the Default Mapping - but this gives us practice with multiple EM Mappings.

Method 2: Update the EM Mapping in the LPF File - 2

Step 13: Copy the EM Project - start - rename it to Pad_with_Mapping.

- Delete the shapes.

Step 14: Update Dependent LPF’s - select only +Pad_with_Mapping.

Method 2: Update the EM Mapping in the LPF File - 3

You have the EM Mappings from the LPF in the EM project. Select PadMap - and you can now import the shapes.

EM Extraction

Extraction sends selected PCells and other shapes to the EM Socket.

Advantages

• Drawing carried out by the PCells.

• As schematic layout changes - can keep sending new layout to EM simulator easily.

• Ports, and deembedding lines are automatically included.

• S parameter results are automatically brought back into the schematic and re-simulated.

Disadvantages

• Almost too easy! Never see the EM layout.

• Box can be too small, wrong layers, boundary conditions...

•Can get off mesh.

EM Extraction - 2

Step 15: Open up the project double_stub.emp.

EM Extraction - 3

Make sure the layout is connected. Simulation Results.

EM Extraction -4

To extract the circuit to EM we need two elements.

The Extraction Element

Elements > Simulation Control

Elements > Substrates

The Stackup Element

Controls

• Size of enclosure and mesh

•Simulator Type

•What elements are extracted.

Controls

• Layers, Materials, ...

•It’s essentially the same as Enclosure with extra feature of Line Type extractions.

EM Extraction - 5

Step 16: Add the Extraction block to the schematic and configure it.

EM_Doc - The EM Project created.

Name - The extraction group name.

Extension - The box will be this much bigger than nearest conductor.

Note: Put in “ “.

EM Extraction - 6

Step 17: Configure the Stackup block.

EM Extraction - 7

Note: When you change the mapping file - you will get a warning ... next slide.

EM Extraction - 8

Line Type Mapping - This can be used as an alternative to EM mapping - when you setting up what EM Layer and Material for a Line Type to use.

Note: It is normally used with iNets.

EM Extraction - 8

The project LPF - will be changed to the new EM Mapping file. Be careful before you do this.

Tip: Make a new EM mapping file - before you do this - so you don’t overwrite the original.

EM Extraction - 9

Step 18: Select all the elements.

- RC on properties - enable all of them for extraction under Model Options.

Don’t use quotes!

EM Extraction - 10

Selecting the Extract block shows the elements are enabled for extraction.

EM Extraction - 11

Step 19: RC on the schematic icon and Add Extraction.

The EM project is created.

Tip: It’s always a good idea to check things over the first time you extract. Look at the 3D, etc.

EM Extraction - 12

Step 20: Enable AFS for the EM Project.

Simulate - and look at the results in the graph. Note the S parameters are automatically updated.

EM Extraction - 13

Note: After simulating the EM:

• I froze the traces: Ctrl - F.

•Went to the schematic and disabled the Extraction Block.

•Resimulated. There is a large difference in filter response.

Viewing the Mesh

The mesh is viewed in the 3D view as an annotation.

Note: It doesn’t need to simulate to see the mesh.

Viewing Currents

Currents can be viewed as a 3D annotation.Note: You cannot view currents with AFS turned on.

I disabled AFS, and simulated at 1 point - 20 GHz.

Viewing Currents - 2

You can animate it - cycles through phase.

EM 3D Layout Toolbar.