Layout Components for EMDS

Layout Components are user-defined components that you can create from a layout page in ADS. The component that can be inserted in a schematic page just like any other component, and represents the (parametric) layout from the layout page. The symbol representing this component in schematic can either be a black box or a layout look-alike symbol.

Once the Layout Component is defined, you as a user can use it in one of the following ways.
You can directly include the Layout Component in the schematic. When doing a circuit simulation from the schematic environment, the EMDS for ADS EM solver will be called automatically during the circuit simulation (EM/Ckt co-simulation) to generate a EMDS for ADS model on the fly. The user-defined layout parameters and the most relevant EMDS for ADS simulation parameters can be set from the schematic page. With the co -optimization feature you can also determine an optimized value for your Layout Component without returning to layout. The layout components have a built-in database mechanism that keeps track of previously calculated EMDS for ADS simulation results, that is, once the EMDS for ADS simulation is done for a certain layout component, no new EM simulations are required, unless there is a change in the parameters for this component.

Layout Components and Circuit Co-simulation

The Electromagnetic-Circuit co-simulation feature enables you to combine EM (EMDS for ADS) and circuit simulations from the schematic. From a layout in Advanced Design System, you can create and insert a (parametric) layout component in a schematic. The symbol representing this component in a schematic can either be a black box or a layout look-alike symbol.

You can set the layout and EMDS for ADS simulation parameters such as model type and mesh density from the schematic. When a circuit simulation is done in a schematic that includes a layout component, the EMDS for ADS simulation engine is automatically called as part of the circuit simulation process. The co-optimization feature enables you optimize your component during this simulation. For more information on co-optimization, refer to Co-optimization with Parameterized Layout Components

Layout components have a built-in database mechanism that keeps track of previously calculated EMDS for ADS simulation results. Once the EMDS for ADS simulation is completed for a certain layout component, no new EM simulations are required unless there is a change in the component parameters.

Note When a Layout Component is simulated during an EM/Circuit co-simulation session, a work layout design < name >work is created (where < _name > is the name of the layout component) with an instance of the layout component inserted. The work design is then sent to EMDS for ADS for EM simulation. The simulation results are stored back into the model database associated with the original layout component. This work design is only used temporarily and can be ignored. It is not automatically deleted after the simulation.

Setting up a Layout

There are two basic ways to create a layout. Use the one that best complements your own design methodology and suits your design needs:

• Layout synchronized from a schematic
• Directly drawn or imported layout

Once you have a layout, you will need to prepare it for a EMDS for ADS simulation using the following steps before you create a layout component:

1. Set up the substrate and layer mapping
2. Use Port Type Mapping to insert ports and set the port types
   You can also specify mesh settings and frequency plans if you haven't done so in the schematic window.

Note Only single (calibrated) and internal (uncalibrated) ports are supported with the layout components. Other port types will be mapped to single or internal port types during component creation. More information on port mapping is given in Port Type Mapping.

Adding Layout Parameters

Layout components with layout parameters enable you to sweep, tune, or optimize geometrical (shape) variations of planar layout objects. This includes:

• Typical dimensions such as lengths, widths, gaps, spacing, or diameters
• Interdependent layout modifications such as length and width varying simultaneously
• Unconventional layout modifications such as varying port locations

Note There is a limit of 100 layout parameters per component.

There are two ways to create a parameterized layout:

• Using nominal/perturbed designs
• Using subnetwork parameters

Only the latter is supported by EMDS layout components.

Using Existing Layout Components

A parameterized layout can be set up using a combination of several built-in microstrip components. Use the Layout Component Parameter dialog box ( EMDS > Component > Parameters ) to specify subnetwork parameters for the layout component.

Once a subnetwork parameter is defined, it can be used to set the parameters values of one or more component instances used in the layout.

In this example, the subnetwork parameter L1 is used to set parameter value L of the MLIN instance.

Note Only the top-level design parameters can be used to set the lower level instance parameters. The use of any other variable is prohibited.

Creating a Layout Component

Use the Create Layout Component dialog box ( EMDS > Component > Create/Update ) to specify the appropriate settings for creating a layout component.

Note The Add Reference Pin checkbox enables you to turn on or off the addition of an extra reference pin during layout component creation. This "extra" pin is used by EMDS for ADS to provide a reference voltage for all other pins in the layout and enables you to model ground effects (e.g., ground bounce, imperfect ground connections, etc.). The Add Reference Pin option is only available for the layout look-alike symbol selection. When selecting black box this option is unavailable (grayed out), however because black box uses standard symbols, a reference pin will appear in all schematic black box representations. This can cause problems if you are creating a structure with finite ground planes and wish to use them in the schematic. In this case, the layout look-alike component with Add Reference Pin disabled is a better choice. This option should also be disabled and the layout look-alike component used for components intended for use with the Schematic > Generate/Update command. The presence of this extra pin can cause an error during design synchronization.

Once the setup is complete, click OK to create the layout component. This layout component will have the same name as the layout design. The following actions are performed automatically:

• The technology data is saved. For more information on technology data, refer to Technology Files.
• A component symbol is created
• The component definition is updated
• The model database is initialized

An information dialog box will be displayed to confirm that the creation or update was completed successfully.

Note You need to update a layout component whenever a change is made to any layout attribute such as the parameters, ports, and the shape. You also need to reinsert or swap existing instances of the component in a schematic using Edit > Component > Swap Components.

Selecting a Symbol

You can choose between two schematic symbol types:

1. A layout look-alike symbol for which the symbol shape is a scaled copy of the layout shape.

1. A black box symbol with a generic rectangular shape.

Scaling the layout look-alike symbol can be set in three different ways:

• Setting the minimal pin-pin distance in schematic units.
  One schematic unit corresponds with the size of most standard two port components such as resistors, capacitors, and inductors. Setting the minimal pin-pin distance to one schematic unit (1 inch) ensures that a component with a given symbol size will fit between two pins.

• Setting the maximum pin-pin distance in schematic units.

The following figure illustrates the scaling when the maximal pin-pin distance is set to be equal to one schematic unit (1 inch).

• Mapping the layout unit dimensions to the schematic unit dimensions (recommended when combining different components in the same schematic page).

When you combine different layout components on a single schematic, a fixed, absolute scaling factor is the most appropriate choice to ensure that the relative sizes of the layout components are preserved.

Model Parameter Defaults

Each time a new layout component instance is inserted on a schematic page, the model parameter values specified during the layout component creation are applied as the initial settings for the instance. These parameters are a subset of the EMDS for ADS simulation control options in the Layout environment.

You can specify the following model parameters.

• Model Type set the EM Simulator to be used to Momentum MW, Momentum, or EMDS
• Substrate specify the substrate description ( *.slm ) using the browse button
• Lowest Frequency lowest frequency to be used during the EMDS for ADS model generation for the adaptive frequency sweep algorithm
• Highest Frequency highest frequency to be used during the EMDS for ADS model generation for the adaptive frequency sweep algorithm

  Note If the circuit simulation requires frequency points outside the specified range, this is done through extrapolation.

Model Database Settings

When running a circuit simulation, EMDS for ADS is invoked to generate a model for the layout component. This model is stored in the layout component's model database. During the creation or update of a layout component, you have the option of deleting all previous models for this component.

• Delete previous database toggle deletes all previously calculated models for this component.

Primitive and Hierarchical Components

Parameters Type	Component Type	Artwork Type
None	Primitive	AEL Macro
Subnetwork	Hierarchical	Synchronized
Nominal/Perturbed	Primitive	AEL Macro

Layout Component File Structure

The layout component is made up of a group of files that combine to define the component. Manually modifying or deleting one or more of these files may corrupt the component definition resulting in unexpected behavior.

Technology Files

During the layout component Create/Update process, four technology related files are created or modified. Three of these files define the substrate technology:

1. <substrate>_layout.lay layout (or mask) layers definition file
2. <substrate>_layout.prf layout preferences file
3. <substrate>.slm substrate definition file

The names for these files are derived from the substrate name that was chosen. The default name is the layout design name.

The fourth file is the schematic layers definition file < schematic.lay >. This file is loaded whenever a new schematic window is opened and it specifies the drawing layers for the schematic. In the case of a layout look-alike symbol, additional layers are appended to this file to draw the schematic symbol for the layout component. They can be recognized by their ` _lay ' postfix. Keep in mind that a schematic window that is already open does not dynamically update its layers definition. You will need to manually load the modified schematic.lay file.

Model Database Files

The EMDS for ADS model database is stored under the mom_dsn/<comp> directory where < comp > is the design name of the component. A model.ndx file keeps track of the models that are stored in the database.
Models are stored in a two level hierarchy. The top level differentiates entries (models) based on the model parameter settings. The bottom level differentiates entries (model samples) based on the layout parameter settings.

Two models are considered to be the same if the following model parameter settings are identical:

• Model type (ModelType)
• Simulation control (SimControl)
• Lowest model frequency (LowFreq)
• Highest model frequency (HighFreq)

For a given model, one or more (in the case of a parameterized component) samples can be generated and added to the database.

The models already available for a component can be viewed by choosing EMDS > Component > Model Database . This will open the layout Component Model Database dialog box.

In this example one model is available in the model database. By selecting the model, the parameter values for which the model is generated become visible in the Description box

Using Layout Components in a Schematic

The layout components created in the layout window can be inserted in a schematic, either by selecting the component using the library browser (select Insert > Component > Component Library ) or by typing the name of the component in the component name entry field. The layout ports become schematic pins that can be connected to other components.

Specifying Layout Component Instance Parameters

Double click a layout component in the schematic to display the Layout Component dialog box. This dialog box has three tabs that enable you to set the parameters and their display for the layout component instance.

Model Parameters

Model Type Selection

The Model Type selection list offers the following choices:

• Momentum MW S-parameter model generated by Momentum in MW mode
• Momentum RF S-parameter model generated by Momentum in RF mode
• EMDS S-parameter model generated by EMDS for ADS
• File Based S-parameter model available in a Dataset, CITI or Touchstone file or model given by an ADS netlist file
• Subnetwork (for hierarchical components only) the component will be netlisted based on the subnetwork topology in the schematic page of the component design and use the built-in models

EMDS for ADS Simulation Control Settings

The first three options enable you to change the settings of the most important EMDS for ADS Simulation Control parameters.

• Schematic - schematic settings overwrite the ones found in the corresponding layout design from where the component was created. Only a subset of all EMDS for ADS Control parameters can be accessed and an adaptive frequency sweep (AFS) will be performed by EMDS for ADS. For more information on adaptive frequency sampling refer to, About Adaptive Frequency Sampling.

Model Database Settings

All generated models are automatically stored in the layout component model database. When performing an optimization, select the Reuse Model and Interpolate Model options to minimize the number of EM simulations.

• Reuse Model the database will be inspected, if the model for the specified parameters is available, it will be reused. When this option is not selected a new EMDS for ADS simulation is launched without inspecting the database first.

Click the Select button to display the Select Model dialog box that lists the currently available models.

• Interpolate Model switch interpolation on or off. When this option is selected a linear interpolation scheme is used. The circuit simulator only invokes EMDS for ADS for an EM simulation if the requested model sample can not be obtained by interpolation between neighbor model samples. Neighbor model samples must be within a normalized distance (L1 measure) smaller than one from the requested sample. The normalization of the distance is with respect to the interpolation delta values specified in the Set Interpolation Options dialog box.

Click the Options button to display the Set Interpolation Options dialog box, which shows the interpolation type and the interpolation grid setting for each parameter for the current model parameter settings. You can change the interpolation grid values or reset them to their defaults (automatically calculated based on the highest model frequency and the mesh density) by clicking the Defaults button.

For more information about the model database and its model interpolation refer to Model Database Flow During Simulation.

Layout Parameters

The Parameters tab enables you to set the layout parameters (nominal/perturbed or subnetwork) similar to any other component in ADS.

Click the Optimization Setup button to specify an optimization setup for the selected parameter.

Display Parameters

The Display tab allows you to individually select which parameters will be visible on the schematic.

Port Type Mapping

Only single (calibrated) and internal (uncalibrated) ports are supported with layout components. The following examples illustrate how simulations with differential, ground reference, and common mode ports can be set up in the schematic in a way that is equivalent to the simulations in the layout.

Differential Ports

Ports 1,3 and 2,4 are differential port combinations. EMDS for ADS calculates a four-by-four S parameter result. This can then be converted to a differential excitation using the following illustration of a setup for S-parameter ports.

Common Mode Ports

Ports 1,3 and 2,4 are Common Mode port combinations. To obtain Common Mode results, use the setup illustrated in the following schematic.

Optimization and Tuning

During a tuning session, models cannot be generated on the fly. Consequently, tuning of parameters that influence a layout component is only possible when the requested layout component model samples are already part of the database or if the database can provide interpolated results.

If the database cannot return a valid model, tuning will fail and issue an error message indicating that the model database is incomplete. In other words, tuning is only possible within specific ranges that are covered by a sufficient number of samples.

Model Database Flow During Simulation

The following illustration shows how the model database handles a request for a model sample for a given layout component. Multiple requests may be generated during an analysis even when only one instance of the component is present. This is the case when layout component parameters are swept, optimized, or tuned.

A first model request will propagate to the Reuse Model? point. If the Reuse Model option is off, EMDS for ADS will be invoked to (re)calculate the model.

If the Reuse Model option is on, the model database will verify if the requested sample is already part of the database. If this is the case, the existing model will be reused.
If the model sample is not available yet, the component instance's Interpolate Model option will be checked. If this option is off, EMDS for ADS will be invoked to calculate a new model. The following warning message will be issued to the status window:

The model for the Layout Component is not found in the Database, a new model is generated for the requested parameter values.

If the Interpolate Model option is on, the model database will try to locate neighbor samples. Samples are considered to be neighbor samples if they are within the interpolation delta distance (L1 measured), which can be viewed and specified in the Set Interpolation Options dialog box. If no neighbor sample is found, EMDS for ADS will be invoked to calculate a new model. A warning message, which is the same as the one above, will be issued to the status window. In the case of a tuning session, the following error message will be sent to the status window.

Model Database for <instanceName> is not complete for tuning. Simulate the Layout Component first to complete the Model Database.

If at least one sample is found in the neighborhood, the database will try to interpolate in the database. If sufficient samples are not available, they will be added automatically based on the interpolation deltas that were specified (or their default settings). The number of additional samples is kept as low as possible to save computation time. When this happens, the following message is shown in the status window:

There are not enough samples available to allow interpolation, a new sample is generated and added to the Model Database.

Co-optimization with Parameterized Layout Components

The co-optimization feature enables you to optimize parameterized layout components in the schematic as part of a co-simulation. This section provides an exercise illustrating how to set up, perform and view the results of co-optimization.

Copying an Example Project

Start by copying an ADS EMDS for ADS example project into your local directory.

1. From the Main window, choose File > Copy Project...
2. In the Copy Project dialog From Project section, choose Example Directory.
3. Select Browse....
4. In the drop down menu, choose Momentum > Microwave select Coupled_line_filter_prj and click OK to select project.
5. In the To Project section, select a location for the project to be copied to.
6. Activate Copy Project Hierarchy and Open Project After Copy then, click OK. This opens the project and saves it to the new location.

Editing the Component

This section describes how to prepare and parameterize a component for co-optimization.

1. When the project opens, dismiss the README window.
2. Select the Coupled_line_filter layout window.
3. Next, choose EMDS > Component > Parameters. This opens the EMDS for ADS Component Parameters dialog.
4. In the Create/Edit Parameter section, type L1 for the parameter name and. choose Subnetwork for the parameter type. The set the Default Value at 300 um.
   
5. Click Add then select OK.
6. In the Layout window double click on Microstrip Line TL6 to select it. This opens a new dialog.
   
7. Select Parameter L in the MLIN column and set Line Length L to L1 in the Parameter Entry Mode column.
   
8. Click OK to dismiss this dialog.

Creating the Parameterized Component

This section describes how to create the parameterized component.

1. In the Layout window, select EMDS > Component > Create/Update . This opens the Create Layout Component dialog.
   
2. In the Symbol section of this dialog, choose layout look-alike and enable Add reference pin .
3. In the Model section, ensure the Model Type is set to EMDS , set the frequency range from 25 GHz to 50 GHz and deselect Edge Mesh .
4. Click OK to create the parameterized component.
5. This brings up two new dialogs, select OK in the message window advising you the component was successfully created and select No in the Add simulation to Model Database dialog.
   

Adding and Using the Component in a Schematic

This section describes how to add and use the parameterized layout component in the schematic.

1. Open a new Schematic window. Insert the newly created component by opening the library browser and selecting Sub-networks > Coupled_line_filter_prj * > *Coupled_line_filter component. Place the layout component in the Schematic window.
   
2. Add 2 S-parameter ports and 3 grounds to the schematic as shown in the following illustration.
   
3. Add an S-parameter simulation block to the schematic. Set the Start frequency to 25 GHz , the Stop frequency to 50 GHz and the Step-size to 0.1 GHz .
   
4. Click OK .

Optimization Setup for a Parameterized Layout Component in the Schematic

This section discusses setup required to the optimize a parameterized layout component during schematic simulation.

1. Double click the Coupled_line_filter component. This brings up the EMDS for ADS Component dialog.
2. Choose the Parameters tab, then select the Optimization Setup... , to bring up the Optimization dialog.
   
3. In this dialog, set Optimization Status to Enabled , set the Minimum Value to 200 um and the Maximum Value to 400 um .
4. Click OK .
5. Add a Goal and an Optimization block to the schematic.
6. For the Goal block set:
   • Expr = "dB(S11)"
   • SimInstanceName = "SP1"
   • Max = -10
   • Weight = 1 **
   • RangeVar[1] = "freq"
   • RangeMin[1] = 39 GHz
   • RangeMax[1] = 42 GHz
7. In the Optimization block set the Optimization Type to Minimax .
   
8. Save the schematic design as " filter_opt ". Choose File > Save Design As...
   
9. From the Schematic window, choose Simulate > Simulate to start the simulation.
10. After 9 iterations the optimized value of 207.039e-6 is shown in the status window.

Using and Viewing the Results of Co-optimization

This sections shows how to use the results obtained from a co-optimization.

1. Select Edit > Component > Deactivate/Activate. Click the Goal and Optimization blocks to deactivate them.
2. Double click the Coupled_line_filter component to bring up the EMDS for ADS Component dialog.
3. Choose the Parameters tab then select the Optimization Setup... button.
4. Set the Optimization Status to Disabled and select OK .
5. Set the parameter value of L1 to 207 um. This is the optimized value.
   
6. Save this schematic design as " filter2 ". Choose File > Save Design As....
7. Choose Simulate > Simulate from the toolbar to start the simulation. If the simulation runs successfully, a Data Display window will open.
8. Insert a rectangular plot in the Data Display with the data set dB(S11).
   

The plot shows an optimized value for S11 < -10dB. This is within the range of the optimized goal that was previously set.

Limitations when Using Layout Components

There are some limitations on the components that are available from the layout palettes:

• Do not use substrate components that might appear on layout component palettes. You must use the dialog box under EMDS > Substrates > Create/Modify to create or edit substrate definitions.

• Lumped elements cannot be included in a layout that is to be simulated by EMDS for ADS.

• Components from the Microstrip palette can be used, with limitations:
  • The substrate name (e.g., Subst = MSub1) is not used in EMDS for ADS. Substrate definitions must be loaded from the EMDS > Substrates menu.
  • Any electrical properties, if defined, are not used. For example, the parameters CPUA, RsT, and RsB in MFTC are ignored.

• For most of the components in Layout, only the geometry is transferred to EMDS for ADS. Any electrical properties must be defined from the EMDS for ADS menus.

• Components from the Printed Circuit Board or Waveguide palette cannot be used in a layout that will be simulated using EMDS for ADS.

• Stripline and suspended substrates components can be used, but the substrate name parameters for these components will be ignored.

• A maximum of 100 layout parameters can be used per component.